Do Foliar Fertilizers Promote Increased Productivity of Tropical Grasses?

Abstract

Foliar fertilizers are low-cost agrochemicals used in pastures, and further research is needed regarding their impact on tropical grasses. Therefore, the objective of this research was to evaluate the effects of foliar fertilization on the development of tropical grasses. Two experiments, consisting of five treatments and four replicates, were carried out. Each experiment was carried out using the following grasses: Zuri grass (Megathyrsus maximus Jacq. cv. Zuri) and ipypora grass (hybrid of Urochloa brizantha × Urochloa zizizensis). In each experiment, ten treatments were evaluated using a 2 × 5 factorial design with four replications. Treatments combined two soil fertilization strategies (with and without nitrogen) and five foliar fertilization strategies, which consisted of a control treatment without foliar fertilization and four application times: immediately after defoliation (0 leaves) and with 1, 2, and 3 expanded leaves. The grass height, tiller population density (TPD), leaf number (LN), forage dry mass (FDM), individual leaf mass (ILM) were evaluated. In the absence of soil fertilization, foliar fertilizer application had no effect on the development of the grasses (p > 0.05). Foliar fertilization did not affect the FDM of Ipyporã and Zuri grass under any of the conditions evaluated (p > 0.05). When applied in the soil fertilize with nitrogen, foliar fertilizer increased LN by 24% for two grasses (p < 0.05). For Zuri grass, foliar fertilization reduced individual leaf mass by 19% (p < 0.05). Thus, foliar fertilizer does not increase the productivity of tropical grasses, with small effects on the leaf’s appearance in Ipyporã and Zuri grass, without altering the forage mass, which necessitates new studies with agrochemicals, new doses, and concentrations of nitrogen.

1. Introduction

High-efficiency agricultural production systems demand more precise and sustainable nutritional strategies, among which foliar fertilization stands out. This technique consists of applying agrochemicals directly to the leaves, especially at times of greater physiological demand from plants or in conditions where the absorption of nutrients by roots is limited [1]. This practice has been shown to be effective in providing nutrients, which can favor plant metabolism and thus improve productivity, often contributing to the quality of agricultural products [2].

Agrochemicals with nutritional purposes have been developed for specific agronomic purposes aimed at improving the physiological and productive performance of plants. Unlike the conventional use of the term, which is often only associated with agricultural pesticides, agrochemicals also include fertilizers, growth regulators, and biostimulants, among other products designed to optimize plant metabolism and crop yield.

In the case of foliar fertilization, these inputs play a strategic role by acting directly on active plant tissues, promoting positive responses and complementing nutrition via soil. The efficiency of foliar fertilization is related to several factors. Among them, the possibility of splitting doses, the reduction in losses due to leaching or fixation in the soil and the lower environmental impact than traditional forms of fertilization stand out [3]. There are positive results with the application of micronutrients through foliar fertilization [4], which reinforces the potential of this technique to contribute to more efficient and sustainable production systems.

However, the effectiveness of foliar fertilization using macronutrients remains controversial. Some studies have reported no significant effect on the development of grasses [5] or legumes [6]. In sugarcane, for instance, foliar nitrogen application did not increase productivity, although it enhanced nitrogen uptake [7] and elevated the concentrations of nitrogen, zinc, and boron in plant tissues [2]. In Lolium perenne L., foliar fertilization did not increase crop productivity in two studies [8,9], though one of them did observe a reduction in weed infestation [9].

Despite its widespread use in high-value crops such as vegetables and grains, there is still a notable lack of research evaluating the effectiveness of foliar fertilization in forage species used in grazing systems. This gap is particularly relevant in tropical regions, where soils frequently suffer from nutrient leaching and chemical fixation, limiting root nutrient uptake. A deeper understanding of foliar fertilization mechanisms in tropical forages could help overcome these limitations, ensuring faster and more efficient nutrient absorption. In the face of climate variability typical of tropical areas, characterized by alternating drought and intense rainfall, adaptive strategies such as foliar fertilization can provide a rapid response alternative, supporting consistent forage growth under unstable environmental conditions.

Therefore, targeted research in this area can contribute to the development of more effective application strategies and optimized nutrient formulations, particularly by identifying which nutrients are most efficient when applied via foliar fertilization. Such advancements have the potential to significantly enhance pasture productivity, resulting in both economic benefits and reduced environmental impacts. In this context, the present study aimed to evaluate the effects of foliar fertilization on the morphological development of tropical forage species, focusing on the cultivars Urochloa hybrid cv. BRS RB 331 Ipyporã and Megathyrsus maximus cv. BRS Zuri, to assess the potential of this practice to increase pasture productivity.

2. Materials and Methods

2.1. Experimental Design

Four studies were carried out in a greenhouse in a completely randomized design at the Federal University of Rondonópolis (latitude 16°28′ S, longitude 54°38′ W and altitude 284 m). In each experiment, ten treatments were adopted in a 2 × 5 factorial scheme and with four replications. Treatments consisted of five fertilization strategies, in which the foliar fertilizer was applied on the day of defoliation (no expanded leaves), and subsequently with 1, 2, and 3 expanded leaves, and an additional treatment without foliar fertilization (control). Two soil nitrogen fertilization strategies were tested (with and without nitrogen). Each experimental plot consists of a pot with 5 L of soil containing 5 plants.

In studies 1 and 2, the forage used was an interspecific hybrid of Urochloa spp., cultivar BRS Ipyporã (U. ruziziensis × U. brizantha). In studies 3 and 4, the forage used was Megathyrsus maximus Jacq. cv. BRS Zuri (sin. Panicum maximum Jacq. cv. BRS Zuri). In experiments 1 and 3, a low nitrogen fertilization dose (100 mg dm⁻³) was applied to the soil, and in experiments 2 and 4, a high nitrogen fertilization dose (200 mg dm⁻³) was applied in the soil (Figure 1).

2.2. Experimental Establishment

The soil used in all studies was collected from the 0–20 cm layer of Red Oxisol soil (

Table 1. Chemical and particle size characterization of the Oxisol.

pH	P *	K	Ca + Mg	Al + H	CEC	V	M	Sand	Silt	Clay
CaCl2			cmolc dm−3			%		%
6.0	3.4	117	4.3	1.7	6.3	73	0	57.5	5.0	37.5

* Mehlich-1 method; CEC: cation exchange capacity; V: base saturation; M: aluminum saturation.

). After collecting, soil was sieved through a 4 mm mesh and transferred to the pots. Then, it was fertilized with phosphorus at a dose of 300 mg dm⁻³ in the form of triple superphosphate (36% P₂O₅). The phosphate fertilizer was incorporated superficially (0 to 2 cm), and 30 seeds were immediately sown per pot. Ten days after sowing, thinning was carried out, and 5 uniform plants were maintained per pot. After thinning, nitrogen fertilization was added in a 50 mg dm⁻³ N dose via urea (Figure 1).

Thirty days after thinning, a uniformity cut was performed, followed by foliar fertilization. The residue heights of the Ipypora and Zuri grasses were 15 and 30 cm [10,11], respectively. The foliar fertilizer consisted of the following nutrient concentration: 14% N; 12% P₂O₅; 12% K₂O; 0.38% Mg; 10.2% S; 0.24% Cu; 0.18% Mn; and 0.63% Zn. A solution was applied with a foliar fertilizer dose of 2 kg ha⁻¹ and a water volume of 200 L ha⁻¹, which resulted in a solution with a concentration of 10 g L⁻¹. This was based on the technical recommendations of the manufacturer.

In the experiments in which nitrogen was applied to the soil, fertilization was carried out on the same day as foliar fertilization using urea. The experiments in which a nitrogen dose of 100 mg dm⁻³ was applied to soil were called “low soil N” (experiments 1 and 3). When a nitrogen dose of 200 mg dm⁻³ was applied to soil, it was called “high soil N” (Experiments 2 and 4). The evaluations were carried out every time the Ipypora and Zuri grasses reached heights of approximately 30 and 75 cm, respectively [10,11]. The pots were irrigated daily using the gravimetric method [12].

2.3. Data Collection

Thirty days after the uniformity cut, the plant height was measured using a graduated ruler, and the number of tillers was counted in each experimental unit, and subsequently, the plants were harvested. After the forage was harvested, the number of leaves was counted, and the forage mass was packed in paper bags, dried in an air circulation oven at 55 ± 5 °C for 72 h and then weighed. Treatments were reapplied and reevaluated when the grasses reached approximately the same height as the standard cut. Individual leaf mass (ILM) was calculated by dividing the total dry mass of the leaf blades by the total number of leaves.

To compare the foliar fertilizer application with the control (no application), the Scheffé test was employed. The influence of fertilization timing was evaluated through regression analysis. Comparisons among soil fertilization methods were not conducted, as this was beyond the scope of the present study. Moreover, the efficacy of nitrogen fertilization via soil has been extensively documented in previous research [13]. All statistical analyses were conducted at a significance level of 5%, through SISVAR, version 5.8.

3. Results

In experiment 1, no effect of foliar fertilization was observed (p > 0.05) on Ipypora grass in any of the levels of soil fertilization (without nitrogen fertilization in the soil and with low application of nitrogen in the soil) (

Table 2. Productive characteristics of Ipypora grass subjected to different foliar fertilization strategies associated with a low dose of nitrogen in the soil (experiment 1). TPD: tiller population density, LN: leaf number, FDM: forage dry mass, ILM: individual leaf mass, L: linear, Q: quadratic, CV: coefficient of variation.

Variables	Number of Leaves After Defoliation					Contrast	Regression		CV (%)
	0	1	2	3	Control	With Foliar × Without Foliar	L	Q
Low N fertilization in the soil
Height (cm)	32.87	33.50	30.75	31.12	35.62	0.115	0.362	0.942	16.98
TPD (tiller pot−1)	55.62	55.62	48.37	53.50	50.00	0.312	0.324	0.406	15.38
LN (leaves pot−1)	109	115.75	100.87	113.62	103.62	0.389	0.939	0.611	16.74
FDM (g pot−1)	20.97	19.64	19.57	20.72	21.70	0.286	0.866	0.260	16.82
ILM (g)	0.19	0.17	0.19	0.18	0.21	0.090	0.878	0.632	14.62
Leaves per tiller	2.01	2.09	2.11	2.16	2.09	0.979	0.519	0.942	21.02
Without N fertilization in the soil
Height (cm)	37.87	33.62	32.37	35.00	38.25	0.281	0.445	0.238	23.04
TPD (tiller pot−1)	30.75	36.37	38.50	35.87	34.25	0.613	0.066	0.053	15.84
LN (leaves pot−1)	70.00	71.62	79.87	75.50	65.25	0.221	0.451	0.693	25.70
FDM (g pot−1)	16.09	17.06	15.57	16.15	15.29	0.312	0.764	0.799	14.11
ILM (g)	0.23	0.24	0.21	0.21	0.24	0.299	0.197	0.892	17.82
Leaves per tiller	2.38	1.98	2.04	2.11	1.91	0.327	0.388	0.225	25.78

). No effect of timing fertilization (p > 0.05) of foliar fertilizer was observed in Ipypora grass on any variables measured in experiment 1 (Table 2).

In experiment 2, a significant linear effect (p < 0.05) was observed for TPD of Ipypora grass under high soil nitrogen fertilization, whereas a significant quadratic response (p < 0.05) was detected in the absence of soil nitrogen fertilization (

Table 3. Productive characteristics of Ipypora grass subjected to different foliar fertilization strategies associated with a high dose of nitrogen in the soil (experiment 2). TPD: tiller population density, LN: leaf number, FDM: forage dry mass, ILM: individual leaf mass, L: linear, Q: quadratic, CV: coefficient of variation.

Variables	Number of Leaves After Defoliation					Contrast	Regression		CV (%)
	0	1	2	3	Control	With Foliar × Without Foliar	L	Q
High N fertilization in the soil
Height (cm)	40.25	39.87	43.87	39.12	39.50	0.083	0.641	0.208	10.55
TPD (tiller pot−1)	74	75	72	67	62	0.069	0.047 1	0.413	19.62
LN (leaves pot−1)	140.87	141.00	152.62	140.37	115.87	0.036 *	0.169	0.095	23.31
FDM (g pot−1)	27.50	31.14	29.55	31.08	25.95	0.096	0.665	0.072	19.67
ILM (g)	0.70	0.78	0.69	0.78	0.65	0.091	0.788	0.590	18.50
Leaves per tiller	0.30	0.30	0.33	0.28	0.42	0.979	0.519	0.942	21.02
Without N fertilization in the soil
Height (cm)	34.25	35.12	36.00	37.87	33.87	0.319	0.715	0.182	13.69
TPD (tiller pot−1)	34	39	40	39	36	0.297	0.527	0.012 2	14.79
LN (leaves pot−1)	69.62	68.87	72.25	61.50	74.25	0.322	0.915	0.537	22.50
FDM (g pot−1)	18.59	19.88	18.45	19.49	19.34	0.839	0.741	0.920	15.49
ILM (g)	0.27	0.30	0.27	0.32	0.28	0.669	0.788	0.597	27.48
Leaves per tiller	2.11	1.78	1.83	1.57	2.05	0.274	0.588	0.065	27.75

¹ y = 75.6 − 2.4x (R² = 0.75); ² y = 34.1 + 6.1x − 1.5x² (R² = 0.99). * significant differences were determined using the Scheffé test (p < 0.05).

). Under conditions of high soil nitrogen input, the application of foliar fertilizer resulted in an increased number of leaves in Ipypora grass. However, no significant differences were observed in forage mass (p > 0.05) under these conditions (Table 3).

In experiment 3, the application of foliar fertilizer had no significant effect (p > 0.05) on the development of Zuri grass (

Table 4. Productive characteristics of Zuri grass subjected to different foliar fertilization strategies associated with a low dose of nitrogen in the soil (experiment 3). TPD: tiller population density, LN: leaf number, FDM: forage dry mass, ILM: individual leaf mass, L: linear, Q: quadratic, CV: coefficient of variation.

Variables	Number of Leaves After Defoliation					Contrast	Regression		CV (%)
	0	1	2	3	Control	With Foliar × Without Foliar	L	Q
Low N fertilization in the soil
Height (cm)	62	62	57	63	54	0.290	0.806	0.322	12.49
TPD (tiller pot−1)	46	46	46	40	40	0.136	0.068	0.213	16.02
LN (leaves pot−1)	52	46	37	42	42	0.469	0.011 1	0.085	19.12
FDM (g pot−1)	24.87	23.09	21.04	24.74	22.15	0.994	0.766	0.144	21.12
ILM (g)	0.22	0.24	0.30	0.28	0.26	0.835	0.030 2	0.472	23.1
Leaves per tiller	2.30	2.04	1.69	2.15	2.12	0.691	0.273	0.036	21.86
Without N fertilization in the soil
Height (cm)	56	59	57	59	59	0.572	0.396	0.832	8.64
TPD (tiller pot−1)	26	21	20	27	24	0.677	0.820	0.030 3	26.33
LN (leaves pot−1)	20	19	19	21	38	0.736	0.775	0.525	30.66
FDM (g pot−1)	13.45	15.46	13.04	13.33	25.27	0.206	0.448	0.296	17.14
ILM (g)	0.38	0.41	0.35	0.32	0.36	0.935	0.184	0.530	32.53
Leaves per tiller	1.69	1.85	1.88	1.71	1.56	0.356	0.932	0.495	33.91

¹ y = 50.1 − 3.9x (R² = 0.62); ² y = 0.224 + 0.024x (R² = 0.72); ³ y = 26.2 − 8.8x + 3x² (R² = 0.97).

). However, under conditions of low soil nitrogen availability, the timing of foliar fertilization significantly influenced (p < 0.05) plant development, with a linear effect (p < 0.05) observed for both the number of leaves and the individual leaf mass of Zuri grass (Table 4).

Under high soil nitrogen conditions, foliar fertilization significantly influenced both the number of leaves and the individual leaf mass of Zuri grass (p < 0.05), although it had no effect on total forage mass (p > 0.05) (

Table 5. Productive characteristics of Zuri grass subjected to different foliar fertilization strategies associated with a high dose of nitrogen in the soil (experiment 4). TPD: tiller population density, LN: leaf number, FDM: forage dry mass, ILM: individual leaf mass, L: linear, Q: quadratic, CV: coefficient of variation.

Variables	Number of Leaves After Defoliation					Contrast	Regression		CV (%)
	0	1	2	3	Control	With Foliar × Without Foliar	L	Q
High N fertilization in the soil
Height (cm)	85.00	84.75	82.37	89.25	85.12	0.927	0.274	0.098	7.03
TPD (tiller pot−1)	52	55	43	48	47	0.536	0.199	0.852	22.34
LN (leaves pot−1)	129	100	92	103	85	0.012 *	0.015 1	0.014 2	19.31
FDM (g pot−1)	36.2	28.4	28.1	36.1	33.8	0.914	0.826	0.013 3	17.58
ILM (g)	0.289	0.306	0.333	0.353	0.396	0.002 *	0.014 4	0.907	15.98
Leaves per tiller	2.55	1.86	2.49	2.23	1.83	0.821	0.844	0.560	45.08
Without N fertilization in the soil
Height (cm)	79.00	74.50	70.87	76.12	71.50	0.150	0.222	0.035 5	8.37
TPD (tiller pot−1)	25	20	20	21	25	0.4797	0.089	0.155	21.75
LN (leaves pot−1)	29	27	24	27	28	0.758	0.376	0.312	26.17
FDM (g pot−1)	14.2	12.6	12.9	14.5	13.7	0.895	0.793	0.128	21.08
ILM (g)	0.478	0.500	0.530	0.540	0.497	0.769	0.261	0.837	24.22
Leaves per tiller	1.28	1.43	1.27	1.39	1.38	0.826	0.766	0.898	28.92

¹ y = 118.9 − 8.6x (R² = 0.48); ² 128.9 − 38.6x + 10x² (R² = 0.99); ³ 36.24 − 11.91x + 3.95x² (R² = 0.99); ⁴ y = 0.2874 + 0.0219x (R² = 0.99); ⁵ 79.4 − 8.5395x + 2.4375x² (R² = 0.90); * significant differences were determined using the Scheffé test (p < 0.05).

). In contrast, in the absence of soil nitrogen, foliar fertilization did not result in significant changes in any of the evaluated variables (Table 5).

4. Discussion

The response to foliar fertilization depends on the grass and nitrogen fertilizers applied to the soil. For Ipypora grass, foliar fertilization did not influence any of the variables when low N fertilization dose or the absence of N fertilization was used in the soil (Table 2). When there was high fertilization in the soil, foliar fertilizer increased the number of leaves on Ipypora grass, but did not increase the forage mass (Table 2). The increase in the number of leaves comes from the greater rate of leaf appearance, which is an effect of nitrogen fertilization [14,15]. However, the amount of nitrogen applied through foliar fertilization was so small that it was probably not enough to promote an increase in the size and mass of each leaf that would result in an increase in forage mass, which was not identified in this study.

For Zuri grass, similar to Ipypora, foliar fertilization did not change any of the variables when low N fertilization or the absence of N fertilization was used in the soil (Table 2). However, when nitrogen was applied to the soil in high quantities, foliar fertilization increased the number of leaves and reduced the mass of each leaf so that it did not change the forage mass.

In this way, phenotypic plasticity was identified as a small dose of nitrogen through foliar means, resulting in a change in morphology without an increase in productivity. This phenotypic plasticity is similar to observations of tiller density in other studies [16]. Under these conditions, the plants compensate for the low density with greater allocation in biomass per structural unit, which guarantees a certain level of productivity maintenance, even under nutritional limitations.

Given the results with Ipypora and Zuri grasses, the application of nitrogen foliar fertilizer did not result in an increase in forage mass, which demonstrates that there is no possibility of increasing the pasture’s support capacity. The impacts of foliar fertilization are indirect. In sugarcane, although foliar fertilization with nitrogen does not increase productivity, there has been an increase in nitrogen uptake [7]. Furthermore, although foliar fertilization with nitrogen does not increase productivity of Lolium perene L., one study reported a reduction in weed infestation [9]. This reduction comes from changes in grass morphology, which favor competition with weeds.

With respect to when to carry out foliar fertilization, the main hypothesis of this study is that the greater the number of expanded leaves is, the greater the response to foliar fertilization, since there would be a greater leaf area to intercept the sprayed fertilizer [16]. However, for Ipypora grass, this effect was identified only for TPD in the experiment with a high nitrogen dose fertilization in the soil.

For Zuri grass, the timing of foliar fertilization also changed the TPD when there was low nitrogen dose fertilization in the soil (Figure 2). While the greater number of leaves favored the tillering of Ipypora grass, for Zuri grass, the greatest tillering occurred when foliar application occurred on 0 and 3 expanded leaves. In this case, the early application of foliar fertilizer, immediately after cutting, may have anticipated the assimilation of nitrogen, favoring the allocation of resources for the initial growth and formation of new leaves to the detriment of the emission of new tillers, which is a phenomenon observed in grasses managed under fractional fertilization [16,17,18]. However, these results need to be better studied, especially regarding the plant anatomy of the grasses studied, as well as identifying whether the assimilation of nutrients occurred through foliar or root means, as there are crops in which the greatest contribution of N to regrowth comes from the roots [19].

Under high nitrogen fertilization in the soil (Table 5), the timing of foliar fertilization also influenced leaf expansion in Zuri grass. The later the fertilization process is, the lower the number of leaves and the greater the mass of each leaf, which is also characterized as phenotypic plasticity. Nutrients, mainly nitrogen, from leaf fertilizer accelerated the expansion of leaves, but the amount of nutrients was not enough to maintain or increase the mass of each leaf.

In general, the application of foliar fertilizer to tropical grasses, when synchronized with specific periods of plant development and associated with adequate levels of nitrogen in the soil, promotes changes in leaf appearance, leaf mass, and tillering without influencing forage mass. Foliar fertilizer does not increase the forage mass and TPD, which are variables that affect the carrying capacity, soil cover, weed suppression, and pasture permanence.

In general, no significant differences were observed in the development of Ipyporã and Zuri grasses with or without foliar fertilizer application. A response to foliar fertilization was only evident when high levels of nitrogen were applied to the soil and affected only leaf numbers and individual leaf mass for Zuri grass (Table 5) and leaf numbers for Ipyporã grass (Table 3). These findings suggest that adequate soil nitrogen fertilization is essential to elicit a response to foliar fertilizers, as nitrogen is one of the most extracted nutrients in forage grasses [20], and it plays a crucial role in promoting significant changes in grass growth and development [14,15,21].

The limited response to foliar fertilization may be explained by the low doses typically applied, as higher concentrations, particularly of nitrogen-based fertilizers, can lead to phytotoxic effects in plants [22]. Consequently, positive effects of foliar fertilization with macronutrients on forage productivity are rarely reported in the literature. In the present study, considering the sufficient nitrogen supply via soil fertilization, it is likely that the observed changes in leaf number were due to the action of micronutrients contained in the foliar fertilizer.

Therefore, the application of foliar fertilizers should be seen as a complementary strategy and not a substitute for soil fertilization. However, it is essential to consider the economic viability of this practice, as there was no increase in forage mass in any of the experiments. New studies should consider more concentrated foliar fertilizers or application in greater quantities, as there are promising results with Panicum maximum CV. Mombasa with fertilization dose of 60 kg ha⁻¹ was used, and in order to avoid phytotoxicity in the plants a spray solution of 400 L ha⁻¹ [1] was required. Another relevant aspect is identifying how many nutrients applied through spraying are absorbed by the roots when they come into contact with the soil, or are how many are included in the plant through the leaves.

5. Conclusions

The response of tropical grasses to foliar fertilization varies depending on the forage species, the level of nitrogen fertilization in the soil, and the moment of application. When there is an absence or low availability of nitrogen in the soil, there is no effect of foliar fertilization. For Ipypora grass, the effects of foliar fertilization were affected by the presence of high nitrogen fertilization in the soil affecting the number of leaves and changes in the tiller population density. In the case of Zuri grass, foliar fertilization affects the number and mass of leaves when associated with nitrogen fertilization in the soil or when applied at specific times of growth, even when there is low nitrogen in the soil. Regardless of the grass, the forage mass is not influenced by the application of foliar fertilizer.

Future research should focus on optimizing foliar fertilization rates as a complementary strategy to soil fertilization in pastures. Additionally, it is essential to identify which nutrients yield the most favorable responses and which are less viable for foliar application. Further studies should also evaluate nutrient absorption efficiency, forage quality, economic viability, and nutrient translocation pathways, aiming to enhance the productivity of tropical forages in grazing systems.