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Article

Disentangling and Closing the Nutrient-Based Potato Yield Gap Using Integrated Nutrient Management Under Temperate Environments of Sub-Saharan Africa

by
Jabulani Ntuli
1,*,
Nomali Ziphorah Ngobese
2,
Lucky Sithole
3 and
Sandile Hadebe
1
1
Department of Plant Production, Soil Science and Agricultural Engineering, University of Limpopo, Private Bag Box X1106, Sovenga 0727, South Africa
2
Unit for Environmental Sciences and Management, Faculty of Natural and Agricultural Sciences, Potchefstroom Campus, North-West University, Potchefstroom 2520, South Africa
3
Department of Agriculture and Rural Development, Pietermaritzburg 3245, South Africa
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(7), 835; https://doi.org/10.3390/horticulturae11070835
Submission received: 2 June 2025 / Revised: 27 June 2025 / Accepted: 13 July 2025 / Published: 15 July 2025
(This article belongs to the Section Protected Culture)
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Abstract

Closing the nutrient-based potato yield gap in sub-Saharan Africa (SSA) remains a major challenge due to low fertilizer use, degraded soils, and rising temperatures that exacerbate nutrient losses. Field experiments were conducted over two growing seasons to investigate the causes of the potato nutrient-based yield gap and develop an integrated nutrient management (INM) strategy aimed at narrowing this gap. Integrated nutrient management factors included three fertilizer application rates [no fertilizer (control), 50%, and 100% of recommended fertilizer application rates], two soil cover levels (grass mulch applied and absent), and four potato cultivars (Mondial, Sababa, Panamera, and Tyson). The study identified a substantial yield gap of 42–45 t/ha, largely driven by insufficient fertilizer application and poor nutrient retention. Integrating full recommended fertilizer rate, mulching, and Panamera closed up to 84% of this gap, achieving a yield of 43 t/ha. Notably, reduced fertilizer application combined with mulching and Panamera maintained high yields (35–41 t/ha), indicating that resource-efficient practices can sustain productivity. These findings underscore the importance of coupling judicious fertilizer use with nutrient loss-mitigating and nutrient uptake-enhancing strategies. Further research is needed to address the residual yield gap and assess the economic feasibility of INM adoption under potato farming conditions in SSA.

Graphical Abstract

1. Introduction

Food security remains a central concern in developing regions such as sub-Saharan Africa (SSA) where agricultural productivity is chronically low. This challenge is highlighted in Sustainable Development Goal (SDG) 2, which prioritizes the eradication of hunger and the achievement of food security as critical drivers of sustainable socioeconomic development, particularly in low-income economies [1,2]. In SSA, agricultural yields consistently fall below their attainable potential, making the closure of yield gaps a pressing strategy for ensuring a stable food supply and improving regional food security [3]. Potatoes (Solanum tuberosum L.) are a vital staple crop in SSA, yet yields remain far below the global average of 20.1 t/ha, with regional outputs often ranging between 6 and 10 t/ha [4,5,6]. Several interlinked factors contribute to this persistent potato yield gap in SSA, including low fertilizer use, poor nutrient management, climate and weather constraints, and widespread soil degradation [7,8,9]. These factors exacerbate nutrient-related yield limitations through increased losses, poor uptake, and reduced soil fertility, ultimately widening the overall yield gap. While these constraints are widely acknowledged, there remains a lack of evidence-based studies that systematically identify, quantify, and disentangle the individual contributions of nutrient-related yield gaps in potato production systems.
Among the contributing factors, chronic mismanagement and underutilization of soil nutrients emerge as the dominant and most pressing drivers of the region’s yield disparity [10]. Fertilizer use in SSA is among the lowest globally, largely constrained by high costs, poor infrastructure, and limited farmer access to appropriate and quality inputs [11,12]. Average fertilizer application rates in SSA are estimated to be as low as 13–20 kg/ha, significantly below the global average of approximately 135 kg/ha [13,14]. While inorganic fertilizers are essential for boosting crop productivity, their use in SSA is often ineffective due to suboptimal application rates, poor matching with soil nutrient profiles, and degradation of soil health [15,16]. Simply increasing fertilizer input without addressing these underlying agronomic and environmental factors can exacerbate nutrient imbalances, increase losses through leaching and volatilization, and, ultimately, contribute to soil degradation and unsustainable production [16].
In many regions of SSA, climatic trends over recent decades show a marked increase in the frequency of warm days and nights, the duration of heatwaves, and overall maximum temperatures compared to the last three decades of the twentieth century [17,18]. Summer temperatures in many SSA areas regularly exceed 30 °C, intensifying soil nutrient losses, particularly through ammonia volatilization and reducing soil moisture availability [19,20]. These combined effects significantly contribute to the widening nutrient-related yield gap in potato production and exacerbate regional food insecurity [21]. Therefore, any strategy aimed at narrowing the potato yield gap in SSA must also address the environmental conditions that aggravate nutrient losses, particularly those induced by elevated temperatures. To put this into perspective, temperature increases from 20 °C to 30 °C lead to a 1.4 to 1.8-fold rise in cumulative ammonia volatilization losses in marginal soils [22]. Such temperature-driven nutrient losses not only diminish soil fertility but also impair nutrient uptake efficiency, further constraining productivity under heat-stressed conditions.
Approximately 65% of agricultural land in SSA is classified as degraded, limiting its ability to retain and supply essential nutrients for crop production and further constraining the region’s capacity to support high-yielding crops like potatoes [23,24]. Potato cultivation, which requires intensive tillage for planting and ridge formation, often exacerbates soil degradation by disrupting soil structure and accelerating organic matter loss. Moreover, excessive reliance on inorganic fertilizers can degrade soil health over time by disturbing nutrient cycling and microbial balance [25]. These challenges highlight the need for a more sustainable approach to fertilizer use that integrates complementary nutrient management strategies to narrow the potato nutrient yield gap in SSA [26]. This is in line with the fourth proposed principle of conservation agriculture (CA), which promotes the appropriate use of fertilizers to enhance crop productivity [27]. The fourth principle, often framed as integrated nutrient management (INM) [28,29], emphasizes the importance of using fertilizers strategically and appropriately to optimize crop yields while minimizing environmental impacts. Lal [28] argued that the fourth principle should be rephrased to “improving soil fertility through integrated nutrient management for healthy soils and productive crops.” This is in line with Sommer et al. [30] who also criticized the lack of holistic nutrient management in the initially proposed principle by Vanlauwe et al. [27], where Sommer and co-authors argued that to increase soil and crop productivity, particularly in SSA where agricultural soils are highly degraded and yield gaps are notoriously high, both nutrient management and judicious application of fertilizers would be needed. Incorporating CA practices such as judicious inorganic fertilizer application, soil surface cover, and strategic cultivar selection into an INM framework could, therefore, offer a viable pathway to reduce nutrient losses, enhance nutrient uptake, and sustainably intensify potato production. Against this backdrop, the current study aims to experimentally investigate the underlying causes of the potato nutrient-based yield gap in SSA and to develop INM strategies to effectively narrow this gap under high-temperature and nutrient-limited conditions. Through this analysis, we performed a component-level assessment to quantify the contributions of individual nutrient-based practices to the overall potato yield gap. Based on these insights, we propose INM strategies tailored to close the identified nutrient-related yield gaps and contribute to the ongoing discourse on the fourth proposed principle of CA.

2. Materials and Methods

2.1. Study Site Description

Field trials were conducted during the 2022/23 and 2023/24 summer potato growing season at the University of Limpopo Sykerfuil experimental farm (23°50′2.98 S, 29°41′31.11 E; 1242 m.a.s.l). Climate data were sourced from a nearby weather station located 100 m from the experimental site (Figure 1). Soils were classified as Kimberley soil (according to the Soil Classification Working Group) [31] with a sandy clay loam texture, containing 67% sand content within a 1 m soil profile, which is a testament to the coarse-structured nature of potato-producing fields in the region. The average soil pH of the experimental area is 7.0, providing a neutral soil environment where most essential nutrients are adequately available, making it a suitable reference point for nutrient-related studies. The experimental site is characterized by shallow soils, with a restrictive layer occurring at approximately 0.8 m depth.

2.2. Plant Material

Four potato cultivars (Mondial, Tyson, Panamera, and Sababa) that differ in their maturity time and agroecological adaptability were used in this study (Table 1). Third-generation potato tuber seeds were obtained from Wesgrow® located in Christiana, South Africa (27.9021° S, 25.1625° E) and planted at the middle age (3–6 sprouts) physiological sprouting stage [32]. Mondial is a well-established medium-late maturing cultivar (110–115 days) and is cultivated by 55% of potato growers in South Africa [33,34]. This cultivar is sensitive to high soil temperatures and fluctuations in fertilizer application [35]. Tyson is a medium-maturing cultivar (105–110 days) that has been bred for hot, dry conditions due to excellent drought and dehydration stress tolerance, which is associated with the downregulation of the CPB80 gene in its leaves [35,36,37]. The idea of using cultivars with varying degrees of drought and heat tolerance was to observe whether these traits could provide a yield advantage under hot conditions in sub-tropical regions. To test whether differences in maturity time lend a nutrient uptake advantage, cultivars with different maturity times to medium maturing cultivars were added to the study. Panamera is a late-maturing cultivar (115–120 days) [33], characterized by a low nitrogen (N) requirement (less than 120 kg N/ha), although it lacks documented adaptation to hot and dry environments. On the other hand, Sababa was used as an early-maturing cultivar (100–105 days) with no known adaptation to hot and dry conditions [32].

2.3. Experimental Factors, Design, Layout, and Procedure

Field experiments employed a 3 × 2 × 4 factorial arrangement, laid out as a split-split plot in a randomized complete block design that was replicated three times. Three fertilizer application rates [no fertilizer (control), 50% of the recommended fertilizer application rates, and 100% of the recommended fertilizer application rates] were the main blocking factors separated by 10 m pathways to limit lateral nutrient flow and nutrient cross-contamination between blocks. One hundred percent of the recommended fertilizer application rates were based on the FERTASA guidelines [38] to meet the crop’s nutrient needs and represented scenarios where soil was saturated with inorganic fertilizers and cases where growers can afford the expensive costs of fertilizer application. Fifty percent of the recommended fertilizer application rates represented a reduction in inorganic fertilizer application, where growers may also apply fertilizers sparingly due to affordability constraints or lack of soil testing before planting. Furthermore, the control represented a situation where growers rely on existing soil nutrients for potato production, mainly due to financial constraints. The amount of nitrogen (N), phosphorus (P), and potassium (K) fertilizers applied during the first and second growing seasons, together with soil test results, are reflected in Table 2. Nitrogen application rate was based on potential yield without consideration of existing N levels. This meant that full N requirements were added over and above existing soil nutrients, leading to potential N oversaturation in soils. Fallow land was cultivated in the first season, whereas land cultivated with potatoes from the first season was used for the second season. This may explain relatively higher N, P, and K levels during the first season compared to the second season, leading to higher nutrient levels in the control during the first season compared to the second season (Table 2). Soil cover was designated as a sub-blocking factor with blocks that had grass/lucerne mulch applied and absent. Pathways of 5 m between mulching blocks to limit the accrual of mulching benefits to non-mulched blocks. A total of 100% of the soil surface was covered with grass/lucerne mulch a week after crop emergence, with a rate of 6000 kg/ha of mulch application. Each sub-block consisted of four potato cultivars (Mondial, Sababa, Panamera, and Tyson), which served as a third experimental factor. Cultivars were planted in four rows, with the outer two rows serving as boundary rows and the inner two rows serving as experimental rows. Inter-row and intra-row spacing were set at 0.9 m and 0.3 m, respectively, resulting in a planting density of 37,037 plants per hectare. The total experimental area covered 1393.8 m2, comprising 72 experimental units, each measuring 3 m in length and 2.7 m in width.

2.4. Agronomic Practices

A 1 m deep soil profile pit was excavated within the experimental unit to characterize the soil and collect samples for classification and fertility assessment. Soil classification followed the guidelines of the Soil Classification Working Group [31] using the HM-519 Munsell Soil Color Chart for horizon differentiation. Prior to planting, soil fertility samples were collected using a grid sampling method designed to ensure spatial representation across the experimental plot. Nine (9) sampling points were established across the experimental unit, and soil samples were collected using a soil auger. At each point, separate samples were taken from the Orthic A (0–0.3 m) and Red Apedal B (0.3–0.8 m) horizons, which represent the effective rooting depth of potato plants. This resulted in a total of eighteen (18) soil samples for the experimental area. Mechanical land preparation was conducted using a moldboard plough and disc plough to loosen the soil. Fertilizer application rates of N, K, and P were calculated using the recommended application rates that were based on the FERTASA guidelines [38] and the study site soil physicochemical analysis results from Cedara College of Agriculture. The P:K ratio was used to select a fertilizer containing an NPK ratio of 2:3:2 (22) + Zn. Balance for P procedure was used to determine the amount of fertilizer mixture to apply to reach the yield target of 50 t/ha. The target yield of 50 t/ha was used as the basis for determining N fertilizer requirements. This value reflects the attainable yield of potatoes under optimal agronomic conditions, including adequate nutrient supply, effective irrigation, proper pest and disease management, and favorable climatic conditions. The selected target aligns with documented potential yields reported in both developed and developing production systems [39,40,41]. As such, it provides a practical and evidence-based benchmark for estimating nutrient requirements and assessing yield gaps under the nutrient-limited and high-temperature conditions typical of SSA. To supply the deficit N, urea (46% N) was added alongside NPK compound fertilizer to achieve the desired yield. Plants have specific growth stages where they require different nutrients in varying amounts. Therefore, split fertilizer was applied to match the timing of nutrient availability with the plant’s needs more closely, thereby increasing nutrient uptake efficiency and reducing nutrient leaching in sandy soils. Potato plants mainly rely on the seed tubers for nutrients up to tuber initiation, where an additional supply of N before tuber initiation can suppress tuberization [42]. As a result, the first half of the split fertilizer was applied soon after tuber initiation. Potato N and K uptake is the highest during the bulking stage [43,44]. Therefore, the second half of the split fertilizer was applied during the tuber bulking stage using the banding application method. Lucerne grass mulch was spread evenly to cover the entire plot area in mulch treatment plots at 6000 kg/ha when 90% of the potato seedlings had emerged (approximately 25–30 DAP). Irrigation was conducted based on the available soil moisture and 80% field capacity. To determine the amount of soil moisture during the growing season, two access tubes per sub-plot were carefully installed into the soil following planting. PR 2/4 soil moisture probe connected to a calibrated HH2 moisture meter (Delta-T Devices Ltd., London, UK) was used to read out and store the corresponding soil moisture content from the access tubes. The difference between 80% field capacity and the measured soil water content was calculated to determine how much irrigation water to apply in order to reach 80% field capacity using a sprinkler irrigation system. Field capacity values were obtained from a SPAW (Soil–Plant–Air–Water) computer model. The SPAW model uses minimum input values of soil texture, organic matter, salinity, and bulk density to provide soil hydrological properties such as wilting point, field capacity, saturation point, and saturated hydraulic conductivity [45]. During the late stages of tuber bulking, the potato plants typically experience reduced water demand. This is because tuber growth slows down as the tubers reach maturity and begin to accumulate starch and dry matter. Therefore, irrigation was withdrawn at late tuber bulking as indicated by the end of flowering. Regular field scouting was conducted to monitor pest and disease incidence. Upon detection of aphid infestation, Efekto Malasol (Agro-Serve (Pty) Ltd., Kempton Park, South Africa) was applied as a control measure.

2.5. Data Collection

2.5.1. Phenological Development

As part of data collection, the days to physiological maturity were recorded by observing when 90% of the plants in the experimental rows exhibited senescence of the haulms, a clear indicator of crop maturity. This stage was identified by the visible yellowing and drying of the leaves and stems, signaling the end of the plant’s active growth period.

2.5.2. Crop Growth and Yield

The automatic color threshold (ACT) image analysis tool, Canopeo (Mathworks, Inc., Natick, MA, USA), was used to measure fractional green canopy cover (FGCC), which estimates crop canopy development. To ensure accurate FGCC measurements and avoid overestimation, the smartphone camera was positioned approximately 0.5 m above the canopy [46]. In addition, ten (10) plants per experimental factor in each replicate were harvested in the experimental rows at physiological maturity for subsequent data collection. Fresh shoots were collected and oven-dried at 65 °C for 48 h to determine dry shoot biomass using an electronic balance. Fresh tubers were weighed to determine tuber yield per plant and expressed in tons per hectare (t/ha), offering a comprehensive evaluation of both crop development and yield performance. Yield gaps (t/ha) were quantified as the difference between the potential yield and the baseline yield observed under different nutrient application rates and INM strategies.

2.6. Data Analysis

All the collected data were subjected to analysis of variance (ANOVA) using GenStat@ version 21 (VSN, International, Hemel Hempstead, UK). Means were separated using the least significant difference (LSD) at 5% level of significance. Multiple mean comparisons were conducted using the Bonferroni test. Data collected from the two growing seasons (2022/23 and 2023/24) were analyzed separately to account for inter-seasonal variability in environmental conditions and treatment responses.

3. Results and Discussion

3.1. Integrated Nutrient Management as the Fourth Principle of Conservation Agriculture

Conservation agriculture aims to sustainably enhance productivity while maintaining environmental integrity [47]. The findings of this study demonstrate that INM can play a pivotal role in meeting this dual objective (Table 3). The integration of the full recommended fertilizer application rates with soil surface cover and a late-maturing cultivar significantly boosted productivity, with yield gains of 35 t/ha and 38 t/ha above the baseline yields (8 t/ha and 5 t/ha) recorded during the 2022/23 and 2023/24 growing seasons, respectively raising total yields to 43 t/ha in both seasons. A large portion of this high productivity emerged from full recommended fertilizer application rates. While high yields are central to the productivity pillar of CA [47], the environmental costs associated with blanket N recommendations are considerable. Therefore, applying full recommended fertilizer rates can lead to excessive N inputs associated with poor soil fertility, nutrient leaching, runoff, eutrophication, and increased greenhouse gas emissions [48,49]. Furthermore, the economic viability of full-rate fertilizer application remains a major constraint for resource-limited farmers in SSA [50], limiting the adoption of such input-intensive INM strategies.
Importantly, this study also shows that reducing inorganic fertilizer application to 50% of the recommended rate, when combined with soil surface cover and a late-maturing cultivar, can maintain high yield levels. This INM strategy produced total yield gains of 33 t/ha and 30 t/ha in 2022/23 and 2023/24, respectively, resulting in final yields of 41 t/ha and 35 t/ha, only marginally lower than those achieved under full fertilization. In addition to maintaining high yields, this reduced-input strategy enhances nutrient use efficiency, lowers environmental risk, supports long-term soil health, and improves profitability by minimizing input costs. These findings support the application of INM as a fourth principle of CA, particularly in line with the proposition by Lal [29], which emphasizes the role of INM in enhancing soil fertility. Moreover, this strategy also aligns with Vanlauwe et al. [27], who advocate for the judicious use of fertilizers to sustainably intensify farming systems. Therefore, INM, particularly when optimized through reduced inorganic fertilizer application rates, mulching, and strategic cultivar selection, can be considered a core pillar for achieving higher productivity and profitability, while simultaneously enhancing soil health and promoting environmental sustainability.

3.2. Applying Fertilisers Is a Crucial Bedrock of Integrated Management Strategy Under Marginal Environments

Fertilizer application emerged as the most influential component among the INM practices in maximizing potato yields (Figure 2). The application of the full recommended fertilizer rate resulted in yield increases of 21 t/ha and 24 t/ha in the 2022/23 and 2023/24 seasons, respectively, relative to the nutrient-deprived baseline. These findings reinforce the need to increase fertilizer use in SSA to address low crop productivity. However, blanket fertilizer recommendations, particularly for N, follow a “one-size-fits-all” approach that often fails to consider local soil fertility levels, crop nutrient demands, or the economic realities of resource-constrained farmers [15,51]. Such recommendations can lead to suboptimal fertilizer use efficiency, environmental degradation, and limited adoption due to affordability barriers. As a result, many resource-constrained farmers are forced to apply nutrient inputs below optimal levels. Interestingly, reducing fertilizer application to half the recommended rate still resulted in substantial yield gains of 14 t/ha and 16 t/ha during the 2022/23 and 2023/24 seasons, respectively. This suggests that moderate fertilizer use, when integrated with complementary nutrient management practices to minimize losses, could offer a practical and more accessible alternative for improving nutrient use efficiency and crop performance under resource-limited conditions. The consistently low yields of 8 t/ha and 5 t/ha recorded in control plots (no fertilizer applied) across both seasons highlight the extent of nutrient deficiency in SSA potato fields, where average yields commonly range between 6 and 10 t/ha [5]. In contrast, fertilized treatments yielded between 21 and 29 t/ha, surpassing the global average of 20.1 t/ha [6]. These results underscore the substantial yield gap in SSA and the potential to close it through targeted and efficient fertilizer strategies.

3.3. Incorporating Mulches Reduces Soil Nutrient Losses, Conferring a Potato Yield Advantage

In addition to increasing fertilizer use, the inclusion of soil surface cover proved to be a key factor in enhancing potato yield (Figure 2), particularly under the high-temperature conditions of SSA, where daytime temperatures can exceed 36 °C [52]. Such thermal conditions exacerbate nutrient losses, especially through volatilization and evaporation, thereby reducing nutrient availability and crop productivity [53]. The integration of soil surface cover, applied as mulch, significantly improved yields across all fertilizer application rates. In the 2022/23 season, yields increased to 16, 38, and 36 t/ha under 0, 50, and 100% of the recommended nutrient rates, respectively. Similarly, in the 2023/24 season, yields reached 9, 32, and 36 t/ha across the same fertilizer treatments. The most notable yield gains attributed to mulching occurred under the 50% fertilizer rate, where mulch contributed 16 t/ha and 11 t/ha of additional yield in the 2022/23 and 2023/24 seasons, respectively. These results highlight the synergistic effect of soil cover in improving nutrient use efficiency in low-input systems by conserving soil moisture, moderating soil temperatures, and reducing N losses. The more pronounced benefit of mulching under reduced fertilizer rates than under full application rates suggests that soil surface cover offers diminishing marginal returns when nutrient supply is already high; however, it becomes especially valuable in resource-constrained systems where maximizing the efficiency of limited inputs is critical. This has important implications for resource-constrained farmers who cannot afford high fertilizer inputs. By integrating soil surface cover with reduced fertilizer application, these farmers can maximize nutrient use efficiency, minimize nutrient losses (e.g., volatilization and leaching), and sustain yield improvements with lower input costs. The substantial yield increase resulting from inorganic fertilizer application and soil cover highlights the critical role of fertilizers in agricultural productivity. This underscores the necessity of incorporating judicious fertilizer use within the INM strategies as the fourth principle of CA to maintain soil fertility and improve crop yields in nutrient-limited environments.

3.4. Increasing Cultivar Season Length Renders a Fertiliser Uptake Advantage Under Integrated Nutrient Management

Incorporating a late-maturing cultivar as a strategy to enhance nutrient uptake significantly improved potato yields (Figure 2), doubling the global average yield to 41 and 43 t/ha under reduced and full fertilizer application with mulch, respectively, in the first growing season. Even in nutrient-deprived fields, integrating a late-maturing cultivar with soil surface cover resulted in a yield of 24 t/ha, surpassing the global average potato yield. These findings suggest that integrating a late-maturing cultivar with soil surface cover has the potential to elevate yields in SSA to match or even exceed global yield levels. In the second growing season, the inclusion of a late-maturing cultivar within the INM approach contributed an additional yield gain of 3 t/ha and 7 t/ha under the reduced and full recommended fertilizer application rates, respectively, raising total yields to 35 t/ha and 43 t/ha. The yield-enhancing effect of late-maturing cultivars can be attributed to their prolonged nutrient uptake period (Table 1), which enables sustained growth and resource utilization. Additionally, these cultivars exhibit a robust and prolonged canopy cover, which enhances photosynthetic capacity by capturing more solar radiation over an extended period. This increased photosynthetic activity translates into greater starch accumulation and improved dry matter partitioning into tubers, ultimately contributing to higher yields. These results underscore the importance of strategic cultivar selection in nutrient-limited environments, particularly when integrated with fertilizer application and soil surface cover. Fertilizers remain a key component of this system as they provide essential nutrients that support the extended growth duration of late-maturing cultivars. Thus, optimizing fertilizer use in combination with late-maturing cultivars and soil surface cover offers a viable strategy for closing the potato yield gap in SSA, improving resource use efficiency, and achieving sustainable intensification in potato production.

3.5. Effectiveness of Integrated Nutrient Management in Bridging the Nutrient-Driven Potato Yield Gap in Sub-Saharan Africa

Under conditions where water supply, plant population, and pest and disease control were optimized, the study revealed a substantial yield gap of 42–45 t/ha in potato production (Figure 3). This gap was primarily attributed to inadequate fertilizer application and poor nutrient management. The yield gap reflects the difference between yields (5–8 t/ha) obtained under typical smallholder scenarios in SSA (characterized by low input use) and the potential yield (50 t/ha) achievable through optimal management practices in the absence of limiting stresses such as water, nutrients, pests and diseases [14,54]. Application of the full recommended fertilizer rates significantly closed the nutrient-limited yield gap by 50–53%, indicating that more than half of the 42–45 t/ha yield gap was attributable to insufficient fertilizer application. This finding supports growing consensus among research, development, and donor communities regarding the urgent need to improve smallholder access to mineral fertilizers as a strategy to enhance crop productivity and address food and nutrition insecurity across SSA [51,55]. Despite this recognized need, fertilizer use in SSA remains critically low, typically ranging from 37 to 40 kg/ha, well below the recommended 100–200 kg/ha required for optimal crop production [56]. Several barriers contribute to this limited adoption of fertilizers, including high fertilizer costs, limited access to credit, poor market linkages, and variable returns on investment due to suboptimal agronomic management [15,57]. Even in areas where fertilizer subsidies have temporarily increased usage, yield responses have been inconsistent [15]. This is partly due to the persistence of outdated, blanket fertilizer recommendations, particularly N, that often lead to nutrient imbalances, especially excessive N application, resulting in low nitrogen use efficiency (NUE) [51,56]. Such imbalances not only reduce yield potential but also degrade soil fertility over time, particularly when nutrient application is not complemented by practices that maintain soil health.
Although the application of full fertilizer recommendations significantly narrowed the nutrient-limited yield gap, a residual yield gap of approximately 21 t/ha persisted, attributable to nutrient loss or use inefficiency. This portion of the yield gap arises when nutrients, though applied, are not fully taken up or effectively utilized by the crop due to losses through various pathways, such as leaching, runoff, soil erosion, denitrification, volatilization, or residual build-up in the soil post-harvest [48,49,53,58]. These findings highlight that while inorganic fertilizer application is essential for yield improvement, its standalone use often leads to diminished returns unless nutrient losses are concurrently minimized [51,55]. We then emphasize that fertilizer application alone is insufficient; it must be integrated with complementary nutrient management practices to reduce losses and enhance nutrient use efficiency, supporting the fourth CA principle proposed by Lal [29], which centers on improving soil fertility through INM. The use of soil surface cover was shown to reduce this nutrient loss yield gap by 33% under full fertilizer application rates, indicating its effectiveness in conserving nutrients. Mulching contributes to improved nutrient use efficiency by reducing soil evaporation and volatilization, maintaining moisture in the root zone, moderating topsoil temperature, restricting erosion, and decreasing nutrient leaching; all of which collectively enhance nutrient availability and uptake [6,59,60,61]. These results support the integration of mulching into fertilizer-based management systems as a practical strategy to improve nutrient retention and close the use efficiency or nutrient loss yield gap. However, a comprehensive cost-benefit analysis is needed to determine the profitability of integrating mulching, which, despite its agronomic benefits, may pose additional costs to resource-constrained farmers.
Despite the benefits of mulching in reducing nutrient losses, it does not completely eliminate them, as evidenced by a remaining nutrient uptake yield gap of approximately 14 t/ha even after mulch application. A significant portion of fertilizer applied during the season often remains in the soil post-harvesting [62] and may subsequently be lost to the environment, especially as organic mulch gradually decomposes, and its protective effect diminishes over time. Cultivars with enhanced nutrient uptake traits, particularly late-maturing genotypes, can play a crucial role in further narrowing the nutrient uptake yield gap by extending the period of active nutrient absorption. Incorporating a late-maturing cultivar, such as Panamera, into the INM strategy alongside mulch and full recommended fertilizer rates further reduced the yield gap by an additional 7 t/ha. This cultivar is characterized by a prolonged nutrient uptake window, lower N demand (less than 120 kg N/ha), and vigorous early-season canopy development that promotes light interception and dry matter accumulation. Additionally, the robust early canopy development promotes efficient early nutrient uptake to support canopy growth, while the resulting high canopy cover shades the soil surface, moderating soil temperatures and likely reducing volatilization losses. The full INM approach, integrating recommended fertilizer rates, soil cover, and a late-maturing cultivar, closed 83–84% of the nutrient-inspired yield gap. However, a residual gap of approximately 7 t/ha (15–16%) remained, likely attributable to persistent nutrient losses, which are not fully mitigated by current INM strategies. It is also worth noting that the presence of a restrictive soil layer at 0.8 m depth at the experimental site likely limited deep leaching losses, as potato root systems are predominantly confined to the upper 0.8 m of soil [63]. Consequently, persisting nutrient losses were more likely to occur through upward movement via volatilization or remain in the soil post-harvest, as supported by the soil test results (Table 2) that indicated residual nutrient levels. Additionally, both Panamera and Sababa cultivars are highly susceptible to water deficits across all growth stages [35]; thus, the imposed irrigation deficit likely had a particularly negative impact on the late-maturing Panamera cultivar. Furthermore, achieving the theoretical yield potential requires perfection in the management of all other yield-determining production factors, including optimal plant population, balanced supply of all 17 essential nutrients, and comprehensive pest and disease control from planting to harvest [64]. Such ideal conditions are rarely met under practical field conditions, even in well-managed experimental plots, thus making the complete elimination of the yield gap improbable.

3.6. Fertilizer-Driven Variations in Potato Yield, Canopy Development, Biomass Accumulation, and Growing Length

Potato yield and growth parameter responses varied significantly (p < 0.001) across the different fertilizer application rates in both the 2022/23 and 2023/24 growing seasons (Figure 4). Yields increased with increasing fertilizer input, with the lowest average yields (14 t/ha and 8 t/ha, respectively) obtained from nutrient-deprived plots, while the highest average yields (35 t/ha) were recorded under the full recommended fertilizer application rate. Although average yields were statistically higher under full fertilizer application compared to reduced rates, the differences were relatively marginal, 4 t/ha and 7 t/ha in the 2022/23 and 2023/24 seasons, respectively. These findings suggest that, while there is a clear need to increase fertilizer use in SSA to improve productivity, blanket high-rate recommendations may not be practical or economically viable for financially constrained farmers [15,30]. Instead, applying moderate fertilizer rates can substantially raise yields (from 6–10 t/ha baseline to 28–31 t/ha) without imposing prohibitive input costs. The observed yield responses were closely aligned with growth indicators, including canopy cover, shoot biomass, and time to maturity, which are vital determinants of potato productivity. Fertilizer application significantly enhanced these parameters, resulting in denser, more vigorous canopies that efficiently intercepted solar radiation, thereby enhancing photosynthesis and promoting tuber growth. Increased nutrient availability also stimulated vegetative development, as evidenced by greater shoot dry biomass due to enhanced cell division, leaf expansion, and prolonged vegetative duration [44]. These improvements translated into higher assimilate production and more efficient partitioning to tubers, supporting increased yield. Conversely, nutrient-deprived plots exhibited poor growth performance, with significantly lower canopy cover and biomass, reduced leaf area, and shortened days to physiological maturity as a result of early defoliation, all of which constrained tuber development and limited yield potential.

3.7. Mulch-Induced Changes in Potato Yield, Canopy Cover, Biomass, and Growth Duration

Mulch application significantly improved potato yields across both growing seasons, highlighting its role as a vital component of the INM strategy. Yield differences of 10 t/ha and 6 t/ha were observed between mulched and non-mulched fields in the 2022/23 and 2023/24 seasons, respectively (Figure 5A,B), with mulched plots consistently outperforming their non-mulched counterparts. These yield gains align with the widely recognized benefits of mulching, which include moderation of soil temperatures, conservation of soil moisture, suppression of evaporative and volatilization losses, and improved nutrient retention and availability [54,65,66]. Within the framework of CA, mulch contributes to the principle of permanent soil cover, which is critical for enhancing soil fertility, maintaining organic carbon inputs, and supporting beneficial biological processes that collectively sustain crop productivity [67]. In addition to yield improvement, mulch influenced key growth traits that contribute to yield formation (Figure 5C–H). Potato fields without mulch exhibited a shortened growing period, with maturity accelerated by 4 to 7 days relative to mulched plots (Figure 5G,H). The absence of ground cover led to direct exposure of the soil to sunlight, elevating soil temperatures and exacerbating nutrient and moisture losses via volatilization and evaporation [68]. These stress conditions prompted early senescence, limiting vegetative growth and reducing canopy cover and shoot biomass [69]. Under such stress, plants may shift assimilate allocation toward tuber development at the expense of vegetative structure, resulting in smaller canopies and ultimately reduced yield and tuber quality. This stress-induced early maturity response, although adaptive [70], restricts the crop’s ability to accumulate biomass and maintain photosynthetic activity over a longer duration, which is crucial for high yield potential. Taken together, these results demonstrate that mulch not only enhances yield directly but also contributes to crop growth resilience by creating a more favourable hydrothermal environment. Its integration into INM systems is, therefore, essential, particularly in regions prone to nutrient and moisture stress, as it offers both agronomic and ecological benefits necessary for sustaining potato production under challenging climatic and soil conditions.

3.8. Genotypic Variation in Potato Yield, Canopy Development, Biomass, and Crop Maturity

Significant differences (p < 0.05) in potato yield were also observed among the selected potato cultivars across both seasons (Figure 6). The late-maturing cultivar Panamera consistently produced the highest average yields (31 t/ha and 28 t/ha in the 2022/23 and 2023/24 seasons, respectively), coupled with high canopy cover and aboveground biomass accumulation. The extended growth duration allows for high tuber bulking potential and better resource utilization, often resulting in higher total yields. However, Panamera was statistically comparable to Sababa and Mondial in the respective seasons, reflecting the high yield potential of these cultivars. In contrast, Tyson consistently underperformed, likely due to traits such as early maturity, limited shoot biomass, and reduced canopy cover—factors that shorten the nutrient uptake window, lower photosynthetic capacity, and ultimately reduce dry matter partitioning into tubers.

4. Conclusions

This study aimed to identify an INM strategy centered on judicious inorganic fertilizer use, strategic cultivar selection, and soil surface cover to close the nutrient-based yield gap in potato production under high temperatures and marginal soils of SSA. The findings revealed a substantial nutrient-related yield gap of 42–45 t/ha, with approximately half attributed to limited fertilizer use (21–24 t/ha) (a common constraint in SSA), while the remaining gap (nutrient loss and nutrient uptake-based yield gap) was linked to inefficient nutrient management. The integration of fertilizer application (full or halved rates) with soil surface cover and a late-maturing cultivar significantly improved productivity, doubling average global potato yields and achieving 35–43 t/ha. While the judicious application of fertilizer remains critical for improving yields in SSA, our findings provide strong empirical support that fertilizer use alone is insufficient to close crop yield gaps. In alignment with the fourth principle of CA, nutrient inputs must be complemented by practices that enhance nutrient use efficiency and soil health. This study demonstrates that integrating fertilizer application with nutrient loss-mitigating and nutrient uptake-enhancing strategies results in significantly greater yield and resource use efficiency. Therefore, for the principle to be more holistically framed, we support the view that the fourth principle of CA should be adopted and presented as Integrated Nutrient Management moving forward. However, it is important to note that reducing fertilizer rates within the INM framework, when combined with mulching and the Panamera cultivar, offers a more accessible and sustainable crop nutrition strategy. This approach sustains high yields, enhances nutrient uptake, and minimizes nutrient losses, making it particularly suitable for resource-constrained farmers. Notably, mulching demonstrated greater yield advantages under reduced fertilizer rates, indicating its critical role in enhancing fertilizer efficiency. Finally, we recommend that future research include a comprehensive cost-benefit analysis to evaluate the economic viability of incorporating mulching into low-input systems. Although mulching provides agronomic benefits, its adoption may be limited by the added costs, particularly among resource-constrained farmers. A clearer understanding of the economic returns of INM strategies will be vital to promoting adoption and scaling up sustainable potato production in SSA.

Author Contributions

Conceptualization, J.N. and S.H.; methodology, J.N. and S.H.; formal analysis, J.N.; investigation, J.N.; resources, N.Z.N., L.S. and S.H.; data curation, S.H.; writing—original draft preparation, J.N.; writing—review and editing, J.N., S.H. and N.Z.N.; visualization, J.N.; supervision, S.H. and N.Z.N.; project administration, J.N. and S.H.; funding acquisition, S.H. and N.Z.N. All authors have read and agreed to the published version of the manuscript.

Funding

This project was funded by the National Research Foundation (NRF) through the ERA Net Co-fund on Food Systems and Climate (grant No. 134115), and the European Union’s Horizon 2020 (grant No. 86255) to cover running costs, while FoodBev SETA provided a scholarship for J.N.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

The authors would like to express their gratitude to Wesgrow® for potato tuber seeds essential for conducting this research.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Minimum and maximum temperatures and rainfall at the Sykerfuil experimental farm during the 2022/23 (A) and 2023/24 (B) growing seasons.
Figure 1. Minimum and maximum temperatures and rainfall at the Sykerfuil experimental farm during the 2022/23 (A) and 2023/24 (B) growing seasons.
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Figure 2. Yield contributions of integrated nutrient management components toward achieving maximum potato yields during the 2022/23 (A) and 2023/24 (B) growing seasons.
Figure 2. Yield contributions of integrated nutrient management components toward achieving maximum potato yields during the 2022/23 (A) and 2023/24 (B) growing seasons.
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Figure 3. Yield responses to integrated nutrient management (INM) strategies and their components in closing nutrient- and management-related yield gaps during the 2022/23 (A) and 2023/24 (B) growing seasons. Only negative error bars are shown to avoid overlapping with the yield gap line. Positive errors are symmetrical and equal in magnitude.
Figure 3. Yield responses to integrated nutrient management (INM) strategies and their components in closing nutrient- and management-related yield gaps during the 2022/23 (A) and 2023/24 (B) growing seasons. Only negative error bars are shown to avoid overlapping with the yield gap line. Positive errors are symmetrical and equal in magnitude.
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Figure 4. Potato yield (A,B) and growth parameters (C–H) as influenced by fertilizer application during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
Figure 4. Potato yield (A,B) and growth parameters (C–H) as influenced by fertilizer application during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
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Figure 5. Potato yield (A,B) and growth parameters (C–H) as a function of soil surface cover during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
Figure 5. Potato yield (A,B) and growth parameters (C–H) as a function of soil surface cover during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
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Figure 6. Potato yield (A,B) and growth parameters (C–H) as influenced by genotypic variation during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
Figure 6. Potato yield (A,B) and growth parameters (C–H) as influenced by genotypic variation during the 2022/23 (top) and 2023/24 (bottom) growing seasons. Treatments sharing the same letter are not significantly different at p ≤ 0.05.
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Table 1. Time to maturity, growing cycle, nutrient uptake time advantage, and nutrient response characteristics of the potato cultivars.
Table 1. Time to maturity, growing cycle, nutrient uptake time advantage, and nutrient response characteristics of the potato cultivars.
CultivarTime to Maturity (days) Growing Cycle * Nutrient Uptake Advantage (days)Nutrient Response Characteristics
Sababa100–105Early maturing0-
Mondial110–115Mid-late maturing 10Sensitive to nitrogen spikes
Tyson105–110Mid maturing5Low nitrogen requirement (<120 kg N/ha)
Panamera115–120Late maturing15-
* Nutrient uptake advantage for each cultivar was determined based on the difference in maturity time when compared to the early-maturing cultivar, which was used as the benchmark.
Table 2. Soil nutritional status of the experimental site before planting and the applied fertilizer application rates per growing season.
Table 2. Soil nutritional status of the experimental site before planting and the applied fertilizer application rates per growing season.
NutrientSoil TestCrop RequiredDeficit100% Fertilizer Application Rate50% Fertilizer Application RateTotal Soil Available Nutrients
100%50%Control
----------------------------------------------------------------------kg/ha----------------------------------------------------------------------
Season             2022/23
N6024018024012030018060
P7515580804015511575
K22032010010050320270220
Season             2023/24
N3024021024012027015030
P515515015075155805
K8032026026013034021080
Table 3. Actual potato yields and corresponding yield gains attributed to individual integrated nutrient management components across the 2022/23 and 2023/24 growing seasons.
Table 3. Actual potato yields and corresponding yield gains attributed to individual integrated nutrient management components across the 2022/23 and 2023/24 growing seasons.
Fertilizer Application Rate (%)Yield
(t/ha)		Yield Gain/Loss
(t/ha)		Mulch ApplicationLate Maturing CultivarTotal Yield Gains
Yield (t/ha)Yield Gain/Loss (t/ha)Yield (t/ha)Yield Gain/Loss(t/ha)
08+016+824+8+16
5022+1438+1641+3+33
10029+2136+743+7+35
Fertilizer Application Rate (%)Yield
(t/ha)		Yield Gain/Loss
(t/ha)		Mulch ApplicationLate Maturing CultivarTotal Yield Gains
Yield (t/ha)Yield Gain/Loss (t/ha)YieldYield Gain/Loss
05+09+411+2+6
5021+1632+1135+3+30
10029+2436+743+7+38
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MDPI and ACS Style

Ntuli, J.; Ngobese, N.Z.; Sithole, L.; Hadebe, S. Disentangling and Closing the Nutrient-Based Potato Yield Gap Using Integrated Nutrient Management Under Temperate Environments of Sub-Saharan Africa. Horticulturae 2025, 11, 835. https://doi.org/10.3390/horticulturae11070835

AMA Style

Ntuli J, Ngobese NZ, Sithole L, Hadebe S. Disentangling and Closing the Nutrient-Based Potato Yield Gap Using Integrated Nutrient Management Under Temperate Environments of Sub-Saharan Africa. Horticulturae. 2025; 11(7):835. https://doi.org/10.3390/horticulturae11070835

Chicago/Turabian Style

Ntuli, Jabulani, Nomali Ziphorah Ngobese, Lucky Sithole, and Sandile Hadebe. 2025. "Disentangling and Closing the Nutrient-Based Potato Yield Gap Using Integrated Nutrient Management Under Temperate Environments of Sub-Saharan Africa" Horticulturae 11, no. 7: 835. https://doi.org/10.3390/horticulturae11070835

APA Style

Ntuli, J., Ngobese, N. Z., Sithole, L., & Hadebe, S. (2025). Disentangling and Closing the Nutrient-Based Potato Yield Gap Using Integrated Nutrient Management Under Temperate Environments of Sub-Saharan Africa. Horticulturae, 11(7), 835. https://doi.org/10.3390/horticulturae11070835

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