Planting Date Influences on Growth, Yield and Nutrient Status of Fodder Radish Under Rainfed Conditions in South Africa

Abstract

Ranked 30th globally in dryness, South Africa faces severe challenges in ensuring fodder security, which is worsened by climate change impacts on agriculture. However, there is still limited knowledge about optimising fodder radish cultivation under shifting climatic conditions. This study investigated the effects of planting dates (December to March), cultivars (Nooitgedacht, Line 2 and Endurance) and seasons (2020/21 and 2021/22) on growth, yield, and crude protein (CP) and mineral concentrations under rainfed conditions. Seasonal variation significantly (p < 0.05) influenced emergence, relative growth, and flowering across planting dates. Fresh tuber yield was highest when Nooitgedacht was planted in December (2052 and 2102 kg ha⁻¹). In contrast, January planting enhanced aboveground biomass and crude protein (CP) yield, with Endurance recording the highest biomass (1260 and 1157.95 kg ha⁻¹ DM) and tuber CP yield (19.2 and 18 kg ha⁻¹). December planting favoured tuber production, whereas January planting optimised biomass, CP yield, and persistence. Planting date and cultivar significantly affected leaf and tuber mineral concentrations. December–January plantings generally enhanced leaf P, K, and Zn concentrations. Endurance and Nooitgedacht accumulated higher micronutrients than Line 2, particularly under early planting. The late flowering of Endurance extended the grazing period, aligning with late-winter forage demand under rainfed conditions. Overall, this study offers practical guidance for improving the quantity and quality of fodder radish in diverse agricultural settings. Future work should evaluate these cultivars across more sites to confirm performance stability under variable rainfall patterns.

1. Introduction

South Africa is already ranked among the 30 driest countries in the world and faces increasing water scarcity as population growth intensifies competition among agriculture (particularly irrigation), industrial processing, and domestic consumption [1]. In rural areas, communal farmers rely heavily on livestock production, with national herds exceeding 12 million cattle, 20 million sheep, and 5 million goats [2]. Growing competition for water resources hinders progress toward Sustainable Development Goal 6 on clean water and sanitation and Goal 2 on zero hunger, as water scarcity limits agricultural productivity and threatens food security.

The growing demand for animal protein is expected to increase livestock numbers, yet productivity remains constrained by fodder insecurity [3]. Rising temperatures and the encroachment of woody species into tropical and subtropical grasslands further threaten the availability of quality forage, particularly for communal farmers who rely heavily on natural rangelands [4]. In South Africa, recurrent droughts have intensified forage scarcity, contributing to livestock mortality in several rural areas [5]. In this context, fodder radish (Raphanus sativus L.) has emerged as a valuable cover and forage crop in dry-land regions where rainfall is the primary water source, offering a promising alternative due to its rapid growth, high biomass production, and adaptability to variable water conditions, thereby enhancing fodder security in such farming systems. [6]. Fodder radish offers distinct advantages in such environments due to its quick growth, deep rooting system, and ability to improve soil structure and fertility [7,8,9,10].

Forage quality is influenced by factors such as anatomy, morphology, and chemical composition differences [11], but suitable crop management practices such as the adjustment of planting dates and fertiliser application, can effectively enhance the quality and quantity of crops [12]. Planting date is important in dry-land agriculture as it determines the crop’s exposure to rainfall and temperature variations during its growth cycle [13,14]. However, the changing climate might alter the optimum planting time for fodder radish. Therefore, selecting appropriate planting dates enhances the radish ability to establish, grow vigorously, and achieve optimal biomass production [15,16]. Optimum planting dates can considerably impact the development, emergence, vigour, and the attainment of optimal biomass productivity of fodder radish. According to Tully and Ryals [17], the duration of flowering and mineral accumulation is related to planting dates, which has significant consequences for the quality of fodder for grazing livestock.

Understanding how different fodder radish cultivars and planting dates interact under rainfed conditions can enhance resource use efficiency, forage quality, and soil health. This, in turn, supports resilient and productive agriculture in areas with limited water availability [18,19]. While Ncisana et al. [20] claimed that a nutritious diet or feed is essential for grazing livestock, supporting good health and optimising productivity. However, limited research has assessed how planting date influences the performance of recently developed fodder radish cultivars under rainfed conditions in South Africa. Understanding these responses is crucial for identifying optimal management practices to enhance fodder productivity and resilience in the country’s dry-land farming systems.

In a study exploring the impact of planting dates under irrigation on various fodder radish cultivars in Limpopo and Gauteng provinces [21], they explained that crops planted in March outyielded crops planted in February or April. Conversely, Atıs and Akar [22] reported lower biomass and CP yields with earlier planting dates. Additionally, Bellaloui et al. [23] and Bhardwaj et al. [24] discovered that earlier planting dates were associated with higher concentrations of nitrogen (N) and essential minerals such as phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), and zinc (Zn).

Fodder radish is an important forage crop for improving feed availability and quality during dormant season. Although several cultivars have been evaluated under different environmental conditions, newly developed genotypes such as Endurance and Line 2 have not been scientifically assessed for their productivity, mineral accumulation, and crude protein yield under rainfed conditions. These genotypes were specifically bred for late flowering and high-quality fodder production in late winter [20], yet their agronomic performance and nutritional value across different planting dates remain unknown. Furthermore, climate variability and shifting seasonal rainfall patterns are increasingly affecting optimal planting windows, which may alter crop growth, yield, and nutrient composition. Currently, there is limited information on how planting date interacts with these new genotypes to influence biomass production and forage quality. Although several trials have examined fodder radish production under supplementary irrigation, reported biomass yields vary widely, typically ranging from approximately 5 to 15 t DM ha⁻¹ depending on planting density and management practices. However, no studies in southern Africa including the KwaZulu-Natal Midlands have quantified yield and biomass benchmarks across planting dates under rainfed conditions without fertiliser application. Therefore, evaluating Endurance and Line 2 across different planting dates is essential to determine their suitability and to identify climate-resilient planting strategies that maximise fodder yield and nutritional value under rainfed conditions. It was hypothesised that March planting would enhance growth and yield due to best environmental conditions, especially moderate day temperatures and cooler nights, and this would allow plants to mature during cooler months and the early winter period, while January planting would improve mineral concentration, crude protein concentration, and crude protein yield, this can be attributed to enhanced soil microbial activity and nitrogen mineralisation under elevated temperatures, coupled with increased nutrient bioavailability and uptake efficiency. This study aimed to (i) evaluate the effect of planting date on growth, yield and nutrient quality of fodder radish cultivars, and (ii) identify optimal cultivar and planting date combinations for maximising biomass and CP yield under rainfed conditions.

2. Materials and Methods

2.1. Site Description

Field trials were conducted during the 2020/21 and 2021/22 growing seasons at the Department of Agriculture Research Institute, Cedara, under the Agricultural Research Council dry-land fields which are situated in the midlands of KwaZulu-Natal, South Africa (altitude 1076 m above sea level, 29°32′ S, 30°17′ E). The study site receives mean annual summer rainfall of 876 mm, with mean minimum and maximum temperatures of 14 °C and 25 °C, respectively. The soil at Cedara is characterised as deep, red and kaolinitic Hutton with a heavy clay loam texture, according to the Soil Classification Working Group [25]. The chemical properties are provided in (

Table 1. Chemical properties of the topsoil in mg kg⁻¹, unless otherwise stated (0–30 cm depth) at the experimental site.

Seasons	Nutrients	Average per 0.3 m Depth	Fertility Status
2020/2021	P	18.90	Low
	K	75.00	Low
	Ca	400.00	Low
	Mg	80.89	Low
	Na	25.40	Very low
	Clay (%)	58.00
	Silt (%)	16.00
	Sandy (%)	18.00
	pH	5.5	Moderately acidic
2021/2022
	P	19.7	Low
	K	79.00	Low
	Ca	450.00	Low
	Mg	81.00	Low
	Na	26.70	Very low
	Clay (%)	56.00
	Silt (%)	16.00
	Sandy (%)	20.00
	pH	5.10	Moderately acidic

).

2.2. Plant Material

Seeds from the Agricultural Research Council-animal production institute (ARC-RFI), Cedara seedbank, South Africa were utilised in this study. This research assessed three cultivars: Endurance, Line 2 and Nooitgedacht. The Nooitgedacht, which is considered the most popular fodder radish cultivar in South Africa, is known for its large roots but has hairy, prickly leaves. Recently, the ARC-RFI developed two new dual-purpose cultivars, Endurance and Line 2, which feature soft leaves [20]. Unlike Nooitgedacht, Endurance and Line 2 offer greater leaf bulk and superior forage quality. Notably, Endurance and Nooitgedacht cultivars are already available on the market, while Line 2 is yet to be commercialised.

2.3. Trial Layout and Design

The experiment was conducted using a randomised complete block design with a split-plot treatment arrangement and three replications over two growing seasons (2020–2022). The study consisted of two experimental factors: planting date and cultivar. The main-plot factor was planting date, with four levels: 14 December, 14 January, 14 February, and 14 March. The sub-plot factor was cultivar, with three levels: Endurance, Line 2, and Nooitgedacht. Nooitgedacht is a commercially established cultivar and was included as the control for comparison with the newly developed genotypes Endurance and Line 2. The treatments were arranged in a factorial combination of four planting dates and three cultivars, resulting in twelve experimental variants per replication and a total of thirty-six experimental units across the three replications.

The experimental area measured 144 m². Each sub-plot measured 6 m × 6 m (36 m²), with a 1 m buffer zone between adjacent plots to minimise edge effects. Plants were spaced at 0.5 m between rows and 0.5 m within rows, resulting in 12 plants per row and 144 plants per sub-plot, equivalent to a planting density of 40,000 plants per hectare. Each sub-plot consisted of six rows, of which the three central rows (18 m²) were used for data collection to avoid border effects. Figure 1 provides an overview of the meteorological conditions during the 2020/2021 and 2021/2022 growing seasons, with data from the Agricultural Research Council’s Cedara weather station.

2.4. Agronomic Practice and Data Collection

The site had been ploughed three years prior to this study and was sown with ryegrass in the intervening period. Before planting, the land was mechanically ploughed, disked, and rotovated. The chemical properties of the topsoil (0.3 m) are provided in (Table 1). No fertiliser was applied throughout the study to reflect the realities of smallholder dry-land farming, where limited access to inputs such as fertiliser and irrigation constrains production [26]. This approach ensured that crop performance was evaluated under conditions representative of actual smallholder farming practices in South Africa. The weeds were removed by hand before planting and during the experiment. Hand sowing took place at 1 cm depth. Emergence up to 10 days after planting was recorded. Data collection focused on middle-row plants to avoid border effects. Then, 12 plants per plot were marked with numbered plastic bands and used to measure plant height, leaf number, leaf length, width, leaf area. Fresh mass was measured by weighing the freshly harvested aboveground biomass (AGB), including leaves and stems from 18 m² area. The samples were then oven-dried at 75 °C for 3–4 days or until a constant weight, after which the dry biomass was recorded. Plant height was measured from the soil surface to the tip of the fully developed leaf using a tape measure. Leaf area (LA) was determined using the equation (Equation (1)) suggested by Silva et al. [27], with leaf length and the width measured on the youngest fully developed leaf using a 30 cm ruler.

$$LA=C \times L \times f$$

(1)

where C = length, in cm; L = width, in cm; and f = correction factor for radish (0.57).

The relative growth rate, relative height rate, persistence, and the number of days to full flowering were also measured. Persistence was assessed by determining the number of fodder radish plants that remained alive and productive over a period of ninety days. The relative growth rate (RGR) (Equation (2)) and relative height rate (RHR).

$$RGR={\displaystyle \frac{(\mathit{ln}M2-\mathit{ln}M1)}{t2-t1}}$$

(2)

where M₁ and M₂ represent initial and final biomass at times t₁ and t₂, respectively

$$RHR={\displaystyle \frac{(\mathit{ln}H2-\mathit{ln}H1)}{t2-t1}}$$

(3)

where H₁ and H₂ represent the natural initial and final height at times t₁ and t₂, respectively.

The number of days to full flowering was recorded from the first day of planting to the full flowering in each plot.

Ninety days after planting, an 18 m² area was excavated to harvest tubers for the measurement of tuber size and yield. Tuber length was measured with a 30 cm ruler, while tuber diameter was recorded using a digital vernier calliper. The aboveground biomass (AGB) was separated from tubers, and tubers were placed in labelled sampling bags and weighed to determine fresh mass. Tuber fresh plant material was dried at 75 °C for four days or until a constant weight was achieved. Yield was expressed as fresh and dry tuber weight (kg ha⁻¹), with tuber yield per hectare calculated based on measurements from an 18 m² area. Then, the above and belowground plant material was milled using a 1 mm sieve before chemical analysis. Milled samples were transferred into airtight sample bottles.

2.5. Mineral, Crude Protein and Crude Protein Yield

The mineral elements analysed included phosphorus (P), calcium (Ca), sodium (Na), magnesium (Mg), potassium (K), zinc (Zn), copper (Cu), manganese (Mn), iron (Fe) and aluminium (Al) [28]. Fodder radish leaves and tuber samples were dried at 75 °C for 3 to 4 days or until a constant weight, then milled to pass through a 1 mm sieve. Thereafter, subsamples weighing 0.5 g underwent dry ashing at 450 °C overnight, followed by dissolution in 25 mL of 1 M HCl. The resulting solutions were diluted fourfold with deionised water before the analysis of P, K, Ca, Mg, Na, Cu, Zn, Fe, Mn, and Al using ICP-OES (inductively coupled plasma optical emission spectroscopy). Total nitrogen, carbon, and sulfur were determined using an automated Dumas dry combustion method with a LECO TruMac CNS (LECO Corporation, St. Joseph, MI, USA; Matejovic) [29]. This involved weighing 0.125 g samples into a ceramic boat, adding a combustion catalyst (COM-CAT), and thoroughly mixing it with the sample. The boat was then placed into a horizontal furnace where the sample underwent combustion in an oxygen stream at 1350 °C. Nitrogen was measured (as N₂) using a thermal conductivity cell. The crude protein (CP) content of the herbage was calculated by multiplying the Kjeldahl nitrogen (N) value by the standard factor 6.25 (CP = N × 6.25) using Kjeldahl method [30]. Then, the crude protein yield (CP yield) (kg ha⁻¹) was determined by multiplying the dry mass of leaves and tubers by their respective CP concentrations as per Leon et al. [31].

2.6. Statistical Analysis

The normality and homogeneity of variances were assessed using the Kolmogorov–Smirnov and Levene’s tests, respectively and visualised with Q-Q plots. All parameters satisfied both assumptions, except for crude protein yield and relative growth rate (RGR), which deviated from normality and were successfully log₁₀-transformed prior to analysis. The IBM SPSS statistical software (version 25; www.spss.com, accessed on 22 February 2024) was used to perform statistical analyses, including analysis of variance (ANOVA) using a univariate general linear model. Planting date and cultivar were treated as fixed factors, while block was included as a random factor. All measured variables were used in the ANOVA as dependent variables.

The data were analysed separately for each season. A two-way ANOVA was conducted to evaluate the effects of planting date and cultivar on various plant traits, including leaf dry weight, leaf number, plant height, leaf length, leaf width, leaf area, emergence, persistence, number of days to full flowering, tuber dry weight, tuber length, and tuber diameter, mineral, crude protein, crude protein yield, and biomass yield. The LSD post hoc test was applied for means comparison, and statistical significance was determined at p < 0.05.

3. Results

3.1. Growth and Phenology

For the 2020/21 season, there was no significant interaction between cultivar and planting date for seed emergence (p = 1.000), persistence (p = 0.999), relative growth rate (RGR) (p = 0.930) or relative height rate (RHR) (p = 1.000) and number of days to full flowering (p = 1.000). Cultivar had no significant effect on emergence (p = 1.000), persistence (p = 0.998), RGR (p = 0.997) or RHR (p = 1.000), but on the number of days to full flowering (p = 0.008). However, planting date significantly affected emergence (p = 0.003), persistence (p = 0.015), (RGR) (p = 0.001), (RHR) (p = 0.005) and days to full flowering (p = 0.001) (

Table 2. Effect of planting date and cultivar on growth rate (RGR), relative height rate (RHR), persistence (%), number of days to full flowering (DFF) for 2020/2021 and 2021/2022 season.

Cultivar	PD	Emergence %	RGR	RHR	Persistence	DFF
	2020/2021
Endurance	December	95.00 aA	1.6 bA	2.8 aA	56 cA	210 aA
	January	95.00 aA	1.7 aA	2.6 bA	63 bA	210 aA
	February	95.00 aA	1.5 cA	2.6 bA	60 bA	210 aA
	March	95.00 aA	1.4 cA	2.5 cA	65 aA	210 aA
Line 2	December	95.00 aA	1.7 aA	2.7 aA	52 dA	200 aA
	January	95.00 aA	1.7 aA	2.7 aA	58 cA	200 aA
	February	95.00 aA	1.4 bA	2.7 aA	61 bA	200 aA
	March	95.00 aA	1.4 bA	2.6 bA	65 aA	200 aA
Nooitgedacht	December	95.00 aAAa	1.8 aA	2.7 aA	56 cA	180 aB
	January	95.00 aA	1.6 bA	2.6 bA	61 aA	180 aB
	February	95.00 aA	1.5 cA	2.6 bA	62 aA	180 aB
	March	95.00 aA	1.0 dA	2.6 bA	60 bA	161 bB
	2021/2022
Endurance	December	94.00 aA	2.9 aA	1.6 bA	58 cA	210 aA
	January	94.00 aA	1.9 bA	1.9 aA	65 aA	210 aA
	February	94.00 aA	1.1 dA	1.9 aA	62 bA	210 aA
	March	94.00 aA	1.8 cA	1.9 aA	67 aA	210 aA
Line 2	December	94.00 aA	2.9 aA	1.5 bA	54 cA	200 aA
	January	94.00 aA	2.0 bA	1.9 aA	60 bA	200 aA
	February	94.00 aA	1.1 cA	1.9 aA	63 bA	200 aA
	March	94.00 aA	1.8 bA	1.9 aA	67 aA	200 aA
Nooitgedacht	December	94.00 aA	2.9 aA	1.9 aA	58 cA	180 aB
	January	94.00 aA	1.9 bA	1.9 aA	63 aA	180 aB
	February	94.00 aA	1.3 dA	1.9 aA	64 aA	161 bB
	March	94.00 aA	1.7 cA	1.9 aA	62 bA	161 bB

^abcd Means within the same column and within each season followed by different lowercase letters indicate significant differences among planting date on each cultivar (p < 0.05). ^AB Means within the same column and within each season followed by different uppercase letters indicate significant differences among cultivars on each planting date (p < 0.05). Mean separation was performed using the LSD test.

).

During the 2021/22 season, no significant interaction between cultivar and planting date was observed for emergence (p = 1.000), persistence (p = 0.999) RGR (p = 1.000) or RHR (p = 0.983), number of days to full flowering (p = 1.000). Cultivar had no significant effect on emergence (p = 1.000), RGR (p = 0.991) or RHR (p = 0.991), persistence (p = 0.999) but did on the number of days to full flowering (p = 0.017), while planting date significantly influenced all parameters.

Across cultivars, emergence reached 90% by day 6 (Table 2). December plantings generally achieved the highest RGR and RHR, while late (February–March) plantings reduced growth rates by up to 64%. Line 2 and Endurance maintained superior persistence, whereas Nooitgedacht showed earlier flowering and shorter stature.

In the first season, the interaction between cultivar and planting date had no significant effect on tuber length (p = 0.210), tuber diameter (p = 0.785), number of leaves (p = 0.075), leaf length (p = 0.798), leaf area (p = 0.588), leaf width (p = 0.488), or plant height (p = 0.785). The main effect of cultivar was significant only for the number of leaves (p = 0.040) and tuber diameter (p < 0.001), but not for tuber length (p = 0.354), leaf length (p = 0.840), leaf area (p = 0.469), leaf width (p = 0.398), or plant height (p = 0.177). In contrast, planting date had a significant (p < 0.05) effect on plant height, number of leaves, leaf length, and leaf area (

Table 3. Effect of planting date (PD) and cultivar on tuber length (Tuber L.) cm, tuber diameter (Tuber D.) mm, leaf number per plant (Leaf N.), plant height (Plant H.) cm, leaf length (Leaf L.) cm, leaf width (Leaf W.) cm, and leaf area (LA) cm² for 2020/2021 and 2021/2022 seasons.

Cultivar	PD	Tuber L.	Tuber D.	Leaf N.	Plant H.	Leaf L.	Leaf W.	LA
2020/2021
Endurance	December	36 abA	56 cA	22 bB	100 bA	25 bA	28 bA	408 bA
	January	40 aA	63 aA	32 aB	111 aA	75 aA	35 aA	1506 aA
	February	21 cA	60 bA	16 cB	88 cA	21 cA	24 cA	289 cA
	March	26 bA	65 aA	15 cB	51 dA	15 dA	18 dA	159 dA
Line 2	December	37 aA	52 dB	20 bB	145 bA	21 cA	24 bA	299 cA
	January	37 aA	58 cB	30 aB	155 aA	78 aA	31 bA	1379 aA
	February	35 aA	61 bA	17 cB	86 cA	29 bA	22 bcA	247 dA
	March	40 aA	65 aA	15 cB	49 dA	21 cA	23 bA	343 bA
Nooitgedacht	December	39 aA	56 cA	29 bA	103 bA	22 bA	16 cA	351 bA
	January	34 abA	61 aA	39 aA	114 aA	74 aA	32 aA	1399 aA
	February	20 cA	62 aA	21 cA	281 cA	17 cA	20 bA	207 cA
	March	25 bA	60 bA	18 dA	52 dA	13 dA	22 bA	123 aA
2021/2022
Endurance	December	33 abA	58 cA	20 bB	100 aA	21 bA	24 bA	311 cA
	January	37 aA	65 abA	14 cB	87 bA	17 cA	20 cA	349 bA
	February	18 cA	62 bA	13 cB	50 cA	12 dB	14 dA	100 dA
	March	23 bA	67 aA	30 aA	110 abA	72 aA	31 aA	1281 aA
Line 2	December	34 aA	54 cB	18 bB	144 bA	18 bA	20 bA	215 bA
	January	34 aA	60 bA	16 bB	84 cA	16 cA	18 bA	172 dA
	February	33 aA	63 bA	13 cB	48 dA	18 bA	20 bA	261 cA
	March	38 aA	67 aA	28 aA	154 aA	75 aA	27 aA	1155 aA
Nooitgedacht	December	36 aA	58 cA	27 bA	102 bA	19 bA	21 bA	262 bA
	January	31 aA	63 aA	19 bA	80 cA	10 dA	16 cA	138 cA
	February	17 cA	64 aA	16 bA	51 dA	14 cA	12 dA	72 dA
	March	22 bA	62 bA	37 aA	112 aA	71 aA	28 aA	1179 aA

^abcd Means within the same column and within each season followed by different lowercase letters indicate significant differences among planting date on each cultivars (p < 0.05). ^AB Means within the same column and within each season followed by different uppercase letters indicate significant differences among cultivars on each planting date (p < 0.05). Mean separation was performed using the LSD test.

).

Similarly, the second season (2021/2022) follows the previous season trend. The interaction between cultivar and planting date was also not significant for the tuber length (p = 0.311), tuber diameter (p = 0.822), number of leaves (p = 0.115), leaf length (p = 0.792), leaf area (p = 0.514), leaf width (p = 0.461), and plant height (p = 0.916). The effect of cultivar remained significant only for the number of leaves (p = 0.002) and tuber diameter (p < 0.001). Planting date again showed a highly significant effect (p < 0.001) on the number of leaves, leaf length, leaf area, and plant height. For, tubers, Endurance and Line 2 produced the largest diameters (Table 3).

3.2. Aboveground Biomass and Tuber Yield

For the 2020/21 season, there was no significant interaction observed between cultivar and planting date on aboveground biomass (AGB) (p = 1.000) and dry tuber yield (p = 0.66). While significant interaction between planting date and cultivar was observed for fresh tuber yield (p = 0.007). Cultivar had a significant effect on AGB (p = 0.001) and fresh tuber yield only (p = 0.038), whereas planting date significantly influenced all parameters (

Table 4. Effect of planting date (PD), cultivar and season on aboveground biomass in kg DM ha⁻¹ and tuber yield (kg ha⁻¹) during 2020/21 and 2021/22 seasons.

Cultivars	PD	Aboveground Biomass	Tuber Fresh Yield	Tuber Dry Yield
2020/2021
Endurance	December	940 bA	1494 aC	108 cA
	January	1260 aA	581 bA	136 aA
	February	360 bB	275 cB	68 dA
	March	810 bB	325 cB	118 bA
Line 2	December	830 cB	1722 aB	89 cA
	January	1100 aB	556 bB	144 aA
	February	340 dB	304 dA	67 dA
	March	1000 bA	354 cA	117 bA
Nooitgedacht	December	900 bA	2101 aA	95 cA
	January	1050 bB	536 bC	141 aA
	February	1080 aA	262 dC	66 dA
	March	280 cC	312 cC	116 bA
2021/2022
Endurance	December	820 bB	1444 aC	58 cA
	January	1157 aA	531 bA	86 aA
	February	260 cB	225 cB	18 dA
	March	834 bB	275 cB	68 bA
Line 2	December	713 bC	1672 aB	39 cA
	January	949 aC	506 bB	94 aA
	February	238 cB	254 cA	17 dA
	March	733 bC	304 cA	67 bA
Nooitgedacht	December	896 cA	2052 aA	47 cA
	January	1080 aB	486 bC	91 aA
	February	281 dA	212 cC	16 dA
	March	916 bA	262 cC	66 bA

^abcd Means within the same column and within each season followed by different lowercase letters indicate significant differences among planting date on each cultivars (p < 0.05). ^ABC Means within the same column and within each season followed by different uppercase letters indicate significant differences among cultivars on each planting date (p < 0.05). Mean separation was performed using the LSD test.

).

Similarly, in the 2021/22 season, a significant interaction between planting date and cultivar was observed for fresh tuber yield (p = 0.004), with no significant interaction found for dry tuber yield (p = 0.24) and AGB (p = 0.96). Cultivar significantly affected AGB (p = 0.003) and fresh tuber yield only (p = 0.014), while planting date significantly influenced all parameters (p < 0.05).

Endurance planted in January consistently produced the greatest AGB in both seasons. December plantings achieved the highest fresh tuber yields, while January plantings optimised dry tuber yields. In contrast, late plantings (February-March) reduced dry yield by up to 65%.

3.3. Mineral Concentration of Leaves and Tubers

For leaf, planting date significantly affected all measured mineral elements, except for P and Mg (

Table 5. Effect of planting date and cultivar on macro (g kg⁻¹) and micro (mg kg⁻¹) minerals of fodder radish leaves.

Cultivar	Planting Date	P	Ca	Mg	K	Zn	Cu	Mn	Fe	Al
Endurance	December	1 aB	6 bA	16 aA	7 bA	10 bB	1 bA	24 cA	91 bB	44 dB
	January	1 aB	8 aA	17 aA	10 aAB	12 aB	2 aA	42 aA	229 aA	147 cA
	February	1 aA	8 aA	17 aA	10 aA	10 cA	1 cA	38 bA	108 bC	116 aC
	March	1 aA	9 aA	17 aA	5 cA	11 aA	1 bA	37 bA	248 aA	232 bA
Line 2	December	1 aB	6 aA	15 aA	6 bcA	10 bB	1 bA	27 cA	159 bA	85 cA
	January	1 aB	7 aAB	15 aA	8 abB	11 aC	2 aA	40 aA	84 cB	70 cB
	February	1 aA	7 aA	15 aA	10 aA	9 cB	1 cA	35 aA	190 aB	218 aB
	March	1 aA	7 aB	14.3 aA	5 cA	1 bA	1 bA	29 bB	184 aC	174 bC
Nooitgedacht	December	2 aA	6 bA	13 aA	7 bA	14 aA	1 bA	17 dC	66 dC	48 cB
	January	2 aA	5 cB	13 aA	11 aA	12 bA	2 aB	27 cB	82 cB	51 cC
	February	1 aA	7 abA	14 aA	11 aA	10 cA	1 cA	28 bcB	343 aA	292 aA
	March	1 aA	8 aAB	16 aA	8 bA	12 bA	1 bA	37 aA	225 bB	204 bB

^abcd means in the same column with different lowercase superscripts for planting dates from each cultivar are significantly different (p < 0.05). ^ABC different uppercase superscripts for cultivars from each planting date significantly differ (p < 0.05). LSD post hoc test was used to separate the means. P: phosphorus; Ca: calcium; Mg: magnesium; K: potassium; Zn: zinc; Cu: copper; Mn: manganese; Fe: iron; Al: aluminium.

). Cultivar did not influence Mg, Fe, and AL. For tubers, planting date significantly affected all mineral elements (Table 5). Cultivar did influence Mg, Zn, and Al. December–January plantings generally enhanced leaf P, K, and Zn concentrations, while later sowings increased Ca and Fe accumulation. Endurance and Nooitgedacht accumulated higher micronutrients than Line 2, particularly under early planting. In tubers, Line 2 planted in December recorded the highest P and Cu concentrations, while Endurance and Nooitgedacht had greater Ca and Fe under later sowings (

Table 6. Effect of planting date and cultivar on macro (g kg⁻¹) and micro (mg kg⁻¹) minerals of fodder radish tubers.

Cultivar	Planting Date	P	Ca	Mg	K	Zn	Cu	Mn	Fe	Al
Endurance	December	1.3 abB	1.9 bA	1.1 bA	17.5 aA	10.1 bC	0.4 cC	9.5 cA	79.3 dC	135.6 dC
	January	1.2 bA	2.2 bA	1.2 bA	16.5 aA	10.7 bA	0.3 cC	11.3 bB	358.1 cB	432.5 cC
	February	1.5 aA	2.8 aA	1.8 aA	14.7 aA	13.3 aA	0.9 aA	14.3 aA	890.6 aA	556.7 aA
	March	0.9 cA	1.9 bA	1.2 bA	5.0 bA	10.7 bB	0.7 bB	8.1 dA	499.6 bC	520.9 bB
Line 2	December	1.5 aA	2.2 aA	1.2 aA	17.9 aA	13.3 aB	1.6 aA	8.3 bC	85.0 cB	169.9 dB
	January	1.1 bA	2.3 aA	1.3 aA	14.8 bA	9.2 cB	0.5 bB	11.6 aB	307.3 bC	455.5 bB
	February	1.3 bAB	2.1 aB	1.3 aB	12.8 bA	9.6 cC	0.7 bB	11.5 aB	294.9 bC	281.8 cC
	March	0.8 cA	1.6 bB	0.9 bB	4.7 cA	9.8 bC	0.7 bB	7.9 bA	584.9 aA	536.7 aB
Nooitgedacht	December	1.4 aAB	2.3 aA	1.4 aA	17.6 aA	15.1 aA	0.7 bB	9.2 cB	434.8 cA	533.2 cA
	January	1.1 bcA	2.3 aA	1.3 aA	15.6 aA	9.9 cB	0.7 bA	12.3 aA	910.9 aA	1096.5 aA
	February	1.2 abB	2.2 aB	1.5 aB	15.1 aA	11.9 bB	0.5 cC	9.6 bC	353.6 dB	332.9 dB
	March	0.9 cA	1.7 bAB	1.3 aA	5.2 bA	11.0 cA	0.8 aA	7.6 dB	549.5 bB	561.6 bA

^abcd means in the same column with different lowercase superscripts for planting dates from each cultivar are significantly different (p < 0.05); ^ABC means in the same column with different uppercase superscripts for cultivars from each planting date are significantly different (p < 0.05). LSD post hoc test was used to separate the means. P: phosphorus; Ca: calcium; Mg: magnesium; K: potassium; Zn: zinc; Cu: copper; Mn: manganese; Fe: iron; Al: aluminium.

).

3.4. Biomass and Crude Protein Yield

Both biomass and crude protein (CP) yield were significantly affected by planting date and cultivar interaction (p < 0.05). January plantings produced the highest biomass and CP yields across cultivars, with Endurance reaching 1157 kg ha⁻¹ DM and 326 kg ha⁻¹ CP. February plantings consistently produced the lowest values (

Table 7. Effect of planting date and cultivar on yield (kg ha⁻¹), crude protein concentration (CP) in g kg⁻¹ DM and crude protein yield (kg ha⁻¹) of fodder radish leaves and tubers during the 2021/22 season.

Cultivar	Planting Date	Leaves			Tubers
		Yield (kg ha−1)	CP (g kg−1 DM)	CP Yield (kg ha−1)	Yield (kg ha−1)	CP (g kg−1 DM)	CP Yield (kg ha−1)
Endurance	December	814 bB	283 aA	231 bB	58 cA	210 bA	12 bA
	January	1157 aA	281 aA	326 aA	86 aA	223 aA	19 aA
	February	260 cB	234 bA	60 dA	18 dA	193 bA	4 cA
	March	834 bB	194 cA	162 cC	68 bA	179 cA	12 bA
Line 2	December	713 bC	265 aB	189 bC	39 cC	204 aA	8 cC
	January	949 aC	276 aA	263 aB	94 aA	209 aA	20 aA
	February	238 cB	241 bA	57 dA	17 dA	206 aA	3 dA
	March	733 bC	233 bA	171 cB	67 bA	135 bA	9 bB
Nooitgedacht	December	896 cA	312 aA	279 aA	47 cB	202 aA	9 bB
	January	1080 aB	241 bB	264 bB	91 aA	199 aA	18 aB
	February	281 dA	237 bA	66 dA	16 dA	192 aA	3 cA
	March	916 bA	243 bA	224 cA	66 bA	146 bA	10 bB

^abcd means in the same column with different lowercase superscripts for planting dates from each cultivar are significantly different (p < 0.05); ^ABC means in the same column with different uppercase superscripts for cultivars from each planting date are significantly different (p < 0.05); LSD post hoc test was used to separate the means.

).

4. Discussion

4.1. Growth and Phenology

Achieving high emergence is critical in forage production, as it determines stand establishment and ultimately influences yield potential. Contrary to our hypothesis that March planting would enhance growth metrics and yield across all cultivars, neither planting date nor cultivar significantly affected emergence (Table 2). Again, opposite to our study results, Ladumor et al. [32] observed a decreasing trend in seed emergence as planting dates are delayed. Additionally, Kaur and Singh [33] reported variations in the germination of different radish cultivars, while other studies [21,31,32] noted differences in time to emergence across fodder radish cultivars. However, our study results are in agreement with those of Husnain et al. [34], which revealed no effect of cultivar on the germination. A possible explanation for the consistently high emergence in this study could be the sufficient soil moisture levels available across all four planting dates, ensuring optimal conditions for emergence regardless of planting time or cultivar.

In addition, the results for RGR and flowering did not align with our hypothesis that planting in March would improve growth metrics and yield across all cultivars. Cultivars planted in December showed higher RGR (with the exception of Endurance in 2020/2021, which showed higher RGR in January). Relative height rate and tuber length partially agreeing with our hypothesis as a result of mixed responses of cultivars in line with planting date in both seasons. In contrast, Line 2 and Endurance, planted in March displayed greater tuber diameters and higher persistence values. December plantings, which received more rainfall, supported higher RGR, consistent with the findings of Stagnari et al. [35] and Ncisana et al. [36], who reported an increase in RGR under well-watered radish plots. Similarly, Silva et al. [37] observed that water-stress treatments in Salvia hispanica L. negatively affected growth metrics, including RGR, while Galmes et al. [38] noted the reduction in RGR under water-stressed conditions linked to leaf senescence and a decrease in leaf area index [39]. This suggests that correct planting date together with better selection of cultivars for rainfed conditions is ideal for optimizing the yield of these particular fodder crops.

All planting dates for Endurance and Line 2 resulted in a longer period for plants to reach full flowering than other planting dates (210 and 200 days, respectively). This is likely due to the higher soil moisture levels delaying the transition from vegetative to reproductive growth. These findings are consistent with Ncisana et al. [36], who observed that water-stressed fodder radish plants reached full flowering earlier than well-watered plants. On the contrary, Ngoasheng [21] claimed that planting fodder radish before February could lead to earlier flowering. This suggests that soil moisture is critical in determining full flowering time in most of the crops, with higher moisture concentration leading to a longer flowering period, as seen on Endurance and Line 2 during rainy months of December and January planting dates.

Line 2 planted in March showed longer tuber lengths compared to Endurance and Nooitgedacht in the same planting date. These findings align with those of Ngoasheng [21] but contradict with those of Kaur and Singh [33]. Differences were observed in the number of days to full flowering, with Endurance taking thirty-nine days longer to flower than Nooitgedacht. This outcome aligns with expectations, as Endurance and Line 2 were specifically bred for late flowering, providing high-quality forage later in the season for grazing livestock [20]. Nonetheless, these results contrast with the findings of Husnain et al. [34], who did not observe any effect of cultivar on flowering time.

The results of this study partially supported the hypothesis that planting in March would improve the growth metrics of all cultivars. For instance, in the second season, March planting resulted in higher values for the leaf length and leaf width compared to other planting dates for Line 2 and Nooitgedacht. Again, the tuber length and diameter were higher in March Line 2 in both seasons. These current study findings align with Ngoasheng [21]; meanwhile, on the contrary, Kaur & Singh [33] observed larger tubers with earlier planting dates. Specifically, cultivar height improved in March planting. Studies by Soltanbeigi et al. [40] and Kaur & Singh [33] have shown that planting date and environmental conditions significantly influenced crop height, consistent with our findings. The cooler temperatures likely contributed to this improvement. This can be attributed to the fact that fodder radish thrives in optimal maximum temperatures ranging from 18 °C to 24 °C, making the cooler conditions ideal for growth. Among the cultivars, Nooitgedacht produced more leaves, whereas Line 2 planted in March produced larger tuber diameter in both seasons. This variability aligns with previous studies [21,22,23,24,25,26,27,28,29,30,31,32,41], which attributed the differences to genetic variation and potential of certain crops under different climatic conditions.

4.2. Biomass and Tuber Yields

The January planting date excluding Nooitgedacht produced the highest aboveground biomass. Endurance consistently achieved the highest aboveground biomass. Additionally, this planting period resulted in the highest values for leaf number, leaf length, leaf width and leaf area contributing to increased photosynthetic capacity and biomass production. This is likely due to the favourable combination of sufficient soil moisture and cooler temperatures, as evidenced by Abbus et al. [42], who noted that higher temperatures can negatively impact plant growth and development. The results of the current study are inconsistent with those of Ngoasheng [21], who found that early autumn planting season (March) produced better results than wet season (February) in South Africa. However, Panwar et al. [41] reported that wet season in July planting performed best in India, likely due to the different climatic conditions and the waterlogged tolerance of the cultivars studied during their rainy season.

In terms of fresh tuber yield, both cultivar and the planting date significantly influenced outcomes. While Ngoasheng [21] found that March planting produced more tubers, our study results revealed that December (Line 2 and Nooitgedadt for both seasons) and January (Endurance for both seasons) planting produced the highest fresh tuber yield. January planting yielded the highest dry tuber yield across cultivars and seasons, likely due to the high rainfall received in December, which provided optimal soil moisture. Similarly, Kaur and Singh [33] observed higher yields with earlier planting dates, noting that delayed planting reduced overall yield.

4.3. Nutritional Quality

Our second hypothesis that planting in January would enhance mineral accumulation, CP concentration and CP yield across all cultivars was partially supported. Mineral accumulation showed variation, with December and January plantings yielding higher mineral and CP values, and the CP yield supported the hypothesis.

The planting date significantly affected the concentrations of all minerals in tubers, whereas only Ca, K, Zn, Mn, Cu, Fe, and Al were affected by planting date in leaves. These effects varied among cultivars, with some showing higher levels of specific minerals while others showed reduced levels. Previous studies by Bellaloui et al. [23] and Bhardwaj et al. [24] also found that early planting dates were associated with increased concentrations of minerals (P, K, S, Ca, Mg, Mn, Cu, Zn, and B). Our findings partially align with these results. For instance, the cultivar Nooitgedacht, planted in January and December had the highest levels of P in its leaves, while Endurance planted in January, February and March demonstrated the highest concentrations of Ca. This may be due to the higher rainfall during these months, which supported better nutrient uptake. However, the findings of Ncisana et al. [20] contrast with the present study’s results. They reported that none of the mineral concentrations improved in Endurance under well-watered conditions, while micronutrients such as Zn and Ca were higher under water-stressed conditions. Additionally, for Line 2, Fe, Mg, and Al levels increased under stress.

A similar pattern was observed in tubers, with the December and January plantings having better mineral accumulation. For example, Line 2, planted in December, had the highest P and Cu levels in its tubers, while Nooitgedacht planted in January had the highest levels of Fe and Al. This aligns with Krizek and Foy [43], who observed high Al concentrations under well-watered conditions. Ncisana et al. [20] found Fe and copper increased under water-stressed conditions. The higher rainfall in December and January (Figure 1) could explain these results, as adequate soil moisture supports nutrient availability and uptake. This highlights the strength of each cultivar in acquiring and conserving little resources from soil, especially during harsh conditions for optimal growth.

Fodder radish cultivars showed significant variation in mineral concentration, likely due to genetic factors. Understanding these differences is critical for selecting cultivars that thrive under different soil moisture levels and can meet specific nutritional requirements in livestock farming. Across all planting dates and cultivars, the mineral concentration in leaves and fodder radish tubers met the minimum requirements for various livestock classes and production levels.

The forage, specifically the leaves, of fodder radish cultivars offers a relatively high CP concentration (ranging from 132 to 267 g/kg DM), making it an excellent alternative protein for ruminants [44,45]. Nyathi et al. [46] noted that nutritional yield is determined by both nutritional composition and the amount of edible biomass; while “nutritional yield” is a relatively uncommon term in forage production, biomass and CP concentration are critical, as biomass determines feed quantity and CP affects nutritional quality. Balancing these factors is crucial for achieving optimal livestock performance by ensuring rumen fill and high-quality forage intake. Our second hypothesis, which proposed that planting in January would enhance CP concentration and CP yield across all cultivars, was partially supported by the leaves and fully supported by the tubers. For example, Nooitgedacht planted in December showed the highest CP levels in its leaves; however, this was not significantly different from the levels observed in the cultivar Endurance. Meanwhile, tubers for Line 2 and Nooitgedacht planted in December, January and February had higher values, with the March planting date having the lowest CP values in all the cultivars. The lower CP concentrations observed in March may be attributed to limited soil moisture. Kanda et al. [47] supported these findings, noting reduced protein concentration under increased water deficit. Similarly, Ncisana et al. [20] found higher CP levels under well-watered conditions and reduced concentrations under severe water-stressed conditions. Leon et al. [31] observed that Pueraria phaseoloides had the highest CP concentration in Trinidad and Tobago during the early dry and wet seasons, likely due to greater rainfall and soil moisture retention. In contrast, Atis and Akar [22] reported lower protein concentration with earlier planting dates.

Nematpour et al. [12] found that early and late planting dates could improve forage quantity and quality, similar to our study findings. This study observed the highest biomass and CP yield in the January planting date, which is an early planting date, with Endurance outperforming Line 2 and Nooitgedacht on the planting date. This contrasts with Atis and Akar [22], who reported lower biomass and CP yield with early planting. However, Salama et al. [48] supported our results, showing that some forage genotypes had higher biomass when planted early. The higher biomass and CP yield in January compared to the optimal planting date of March may be due to the increased rainfall during December and January (Figure 1). Kanda et al. [47] also observed higher protein yield under wet conditions, which aligns with our findings. The higher biomass in January was directly linked to increased CP yield, supporting Leon et al. [31], who found that high CP yield in P. phaseoloides during the late wet season was due to increased biomass production.

4.4. Synthesis and On-Farm Guidance

Overall, the results show that rainfall timing and seasonal temperature conditions are more critical than total rainfall for fodder radish establishment and productivity under rainfed conditions. Early plantings (December–January) achieved higher biomass, tuber yield, and nutritional quality, while later plantings (March) improved persistence and tuber diameter under lower moisture. Endurance and Line 2 performed best in terms of biomass and CP yield, whereas Nooitgedacht excelled in leaf production and P concentration.

For smallholder farmers in the Midland of KwaZulu-Natal, South Africa, planting between mid-December and late-January is recommended to optimise both yield and nutritional value, particularly in seasons with early rainfall onset. March planting can still provide acceptable yields under late or reduced rainfall, offering flexibility within variable rainfed systems.

5. Conclusions and Implications

This study demonstrates that planting date is a key management factor influencing the productivity, nutritional quality, and developmental patterns of fodder radish under rainfed conditions. Earlier planting improved overall forage value by enhancing biomass accumulation, crude protein yield, and mineral content, highlighting the importance of aligning crop establishment with favourable environmental conditions to maximise resource use efficiency. The superior performance of the newly developed genotypes, particularly Endurance, confirms their suitability for high-quality forage production and their potential contribution to improving feed availability during critical seasonal periods. The observed variation in flowering response among cultivars further emphasises the role of genotype in adapting to environmental cues, which is important for optimising forage utilisation and crop management. These findings provide important insights for developing climate-resilient planting strategies and demonstrate the value of selecting appropriate genotype and planting time combinations to enhance fodder production, nutritional quality, and overall system sustainability under variable rainfed environments.

6. Limitations and Future Work

This study was conducted at a single site over two seasons under rainfed conditions and without fertiliser application, which may limit the generalisation of the results across different environments. Future research should therefore include multi-location and multi-season trials that capture varying rainfall patterns, soil water content, soil types, soil physical properties, including field capacity and permanent wilting point and management practices to strengthen the understanding of fodder radish performance under diverse rainfed systems.