Over the past 50 years, improvements in peanut varieties have more than doubled yields, with an average increase of 46 lb/ac per year (Holbrook, 2019). However, the greater nutrient demands of these high-yielding varieties raise concerns that current fertilizer recommendations, particularly for sandy soils with low potassium (K) holding capacity, may be insufficient. In Florida, where peanuts primarily grow on sandy soils (Wright et al., 2021), K is crucial for plant growth and yield, and its deficiency can reduce both yield and kernel quality (Borah et al., 2021; Meena et al., 2022; El-Mageed et al., 2023; Khan et al., 2023).

Recommendations for K fertilization in the Southeastern U.S. vary depending on soil type and the existing levels of potassium (K) in the soil. Research has demonstrated varying crop responses to K application rates ranging from 45 lb/ac (54 lb/ac K₂O) to 89 lb/ac (107 lb/ac K₂O), with some studies suggesting that higher rates may further enhance yield. Additionally, split K applications have been proposed as a strategy to reduce nutrient losses and improve uptake efficiency. However, research on peanuts has yielded mixed results. Studies conducted in India have shown benefits from split applications, while research in Florida found no significant advantage on sandy soils (Chinnasamy, 1993; Dudhade et al., 2021; Ponnuswamy et al., 1996; Patro et al., 2018; Harris, 2017; Donaghy, 2020).

Currently, Mehlich-3 soil-test K (STK) fertilization recommendations in Florida are 83 lb/ac (100 lb/ac K₂O) for soils testing low in K, 33 lb/ac (40 lb/ac K₂O) for soils testing medium, and no K for soils testing high (Mylavarapu, Wright, & Kidder, 2022). The inconsistencies observed across the literature underscore the importance of developing site-specific K management strategies to optimize both yield and quality.

Objectives

Our study objectives were to (1) evaluate the combined impacts of different rates and timings of K fertilizer application in locations differing in their Mehlich-3 STK on pod yield and quality traits of peanuts, and to (2) provide K-management recommendations that are likely to optimize peanut responses to K fertilization in sandy soils in North Florida.

Site selection and weather conditions

Research plots were established at the Plant Science Research and Education Unit (PSREU) of the University of Florida in Citra, FL during the spring-summer growing seasons of 2014 and 2015. Three field sites named “Hilltop”, “Citra”, and “Sesame” were selected according to their STK indexes from a March 2014 survey of several possible sites.

These three sites provided a range in Mehlich-3 STK indexes for studying responses to K fertilization under varying soils with differing concentrations of STK. Results of the preliminary site survey showed that Hilltop and Citra were in the low Mehlich-3 STK index category (≤35 mg kg-1 K), and Sesame was in the medium category (36 – 60 mg kg-1 K; Mylavarapu et al., 2022 and Table 1).

Table 1. Pre-fertilization Mehlich-3 soil test Ca and K values (mg kg-1). Values were averaged from 12 plots within each field sampled at a depth of 0-15 cm on the day before the first fertilization and planting.

Site	Year	Ca mg kg-1	K mg kg-1
Hilltop	2014	395	2
Citra	2015	495	26
Sesame	2014	729	40

Note: STK values ≤ 35, 36-60, and >60 mg kg^-1, are considered low, medium and high, respectively, according to the standardized fertilization recommendations for agronomic crops, of the University of Florida (Mylavarapu et al., 2022).

 

Excessive rain and irrigation could leach K below the root zone in sandy soils with low cation exchange capacity. We managed irrigation by monitoring soil moisture with tensiometers. There were four potentially leaching rains but three of the four rains occurred during the latter part of the growing season, well after the final 60-day K applications. Based on this, we conclude that K leaching from rainfall did not significantly impact crop responses to K fertilizer rate or timing treatments.

Treatments and experimental design

The study included five potassium (K) fertilizer rates: 0, 50, 100, 150, and 200 lb/ac of K₂O (equivalent to 0, 40, 83, 125, and 166 lb/ac of K applied as KCl). These rates were applied across four timing strategies:

• 

  P: 100% pre-plant,

• PB: ⅔ at planting and ⅓ at early bloom,
• PB60: ⅓ at planting, ⅓ at early bloom, and ⅓ at 60 days after planting, and
• B60: ½ at early bloom and ½ at 60 days after planting.

Early-bloom applications coincided with early flowering, which occurred 30 days after planting in both 2014 and 2015.

The data analysis used Relative Yield (RY) as the primary dependent variable, standardizing yields across years and locations for replication (Pearce et al., 2023). RY was calculated as the ratio of each plot’s yield to the maximum attainable yield at that site-year, expressed as a percentage. ANOVA was conducted for each dependent variable (pod yield, leaf K (LKH), total sound mature kernels (TSMK), and extra-large kernels (ELK)), with fixed effects such as K fertilization rate, timing, and site. Tukey’s HSD test was used for mean separation, and quadratic plateau regression modeled the impact of K rate on RY. Additional research method information is available in (Zubieta, Rahman, Hochmuth, Drew, & Matcham, 2025)

LKH (leaf K concentration near harvest) was assessed as an indicator of plant K nutritional status in relation to K fertilization. Sufficiency in leaf-K is associated with optimal yield. Plant nutrient testing also aids in predicting yield and quality attributes, facilitates in-season nutrient management decisions, and allows farmers to reduce the risk of nutrient runoff and environmental impact.

Potassium Fertilization Rate and Yield Response

The effects of K fertilization rate on peanut pod yield were influenced by site conditions. Both potassium rate and timing interacted significantly with site to affect pod yield. In Hilltop and Citra, peanut pod yield (RY) increased quadratically with potassium fertilization, reaching a plateau after a certain K rate. The K rates needed to achieve the goal of 99% RY were 143 lb/ac (172 lb/ac K2O) Hilltop and 73 lb/ac (87 lb/ac K2O) in Citra (Figure 2).

Figure 2. Quadratic plateau regression models of the relationship between potassium fertilization rate (kg ha-1) and RY (%) in Hilltop (a) and in Citra (b). The break point, denoted with a grey dotted line, in each regression represents the highest K rate that was likely to reach the 99% RY goal.
Note: K multiplied by 1.2 gives K2O. In Figure 2a, RY is maximized with 160 kg/ha K, or 143 lb/ac K or 172 lb K2O per acre. In Figure 2b, RY is maximized with 82 kg/ha K, or 73 lb/ac K or 87 lb/ac K2O. 

 

K Fertilization Timing and Yield

K fertilization timing had varying effects on pod yield across different sites. In Citra, the B60 timing resulted in a 17% lower yield compared to other timings, which averaged 2891 lb/ac. In Hilltop, the PB60 timing led to a 7% lower yield than PB, but other timings showed no significant differences. Yields in Sesame were consistent across timings, averaging 7387 lb/ac.

The TSMK was highest in Hilltop (78.5%) and similar in Citra and Sesame (75.6% and 76.1%). ELK varied by site: in Citra, ELK increased with K rates, while Hilltop and Sesame showed no significant changes.

LKH and Yield Relationships

Both the fertilizer rate and site affected LKH but not by fertilization timing. We observed higher LKH values in Citra with K rates of 125 lb/ac K (150 lb/ac K2O) and 166 lb/ac K (200 lb/ac K2O). Similarly, in Hilltop, we recorded the highest LKH with the same rates. Sesame’s LKH increased with higher K rates, but we did not note significant differences between treatments.

LKH was positively correlated with RY in Citra and Hilltop. However, no significant relationship was found in Sesame. Critical leaf-L concentration near harvest was shown to be 0.9 to 1.0 % in the most recently matured whole leaf.

Discussion:
Role of K in Peanut Growth and Yield

K is crucial for peanut growth, influencing carbon fixation, enzyme activation, and nutrient uptake (Basha & Rao, 1980; Borah et al., 2012). Improved soil K availability leads to increased growth and yield, particularly in soils with low K levels, as observed in our study. Our findings suggest that K fertilization improves pod yield significantly in low-STK sites.

Relevance of Current Fertilization Recommendations

The University of Florida’s current K recommendations, of 33 or 83 lb/ac K (40 or 100 lb/ac K2O) for medium or low Mehlich-3 K soils, respectively, may be inadequate for sandy soils with low STK (Mylavarapu et al., 2022). In our study, the optimal K fertilization rates ranged from 73 to 143 lb/ac (87 to 172 lb/ac K2O) for two sites testing low in STK, surpassing the existing recommendations for soil with low STK. In contrast, Sesame (a medium-STK site) showed no significant response to K fertilization, raising questions about the overestimation of K needs in medium testing soils, based on current Mehlich-3 calibration.

Split Applications and Timing Considerations

Our study found that split applications of K did not result in increased yields or quality. Given the low leaching rainfall in the region during this study, applying K at planting appears to be sufficient for low-STK sites.

Implications and Future Research

Our results highlight the importance of using soil testing to predict the optimal K fertilizer rates. Over-fertilization, and the associated increased input costs, should be avoided, especially in areas where K availability is sufficient. Further research is needed to explore the effectiveness of split K applications under high rainfall conditions.

Takeaway Messages

Producers need to carefully tailor K fertilization rates to the site’s soil K levels to maximize peanut yield.
Current K recommendations for sandy soils may be too low for low-STK conditions.
Split K applications are unlikely to improve yields in regions with low leaching rainfall.
Soil testing remains a critical tool in optimizing K fertilization and preventing over-fertilization.

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Authors: Aadil Rahman (UF/IFAS Dept of Agronomy), Emma Matcham (Ohio State University Dept of Horticulture and Crop Science), and George Hochmuth (UF/IFAS Dept of Soil, Water, and Ecosystem Sciences). Published to the blog by Mike Loizzo.
Featured image photo by Tyler Jones, UF/IFAS Communications

References:

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Borah, B. (2021). Potassic fertilizer management for sustainable groundnut productivity in India: a review. Agricultural Reviews, 42(4), 398-405. https://doi.org/10.18805/ag.R-2037

Chinnasamy, C. (1993). Studies on the effect of split application of nitrogen and potassium on the yield performance of irrigated groundnut (VRI 2) under various methods and times of application. M.Sc. (Ag.) Thesis, Tamil Nadu Agricultural University, Coimbatore.

Donaghy, W. (2020). Potassium fertilization rate and timing effect on biomass and nutrient partitioning in peanut (Arachis hypogea L.). [Master’s thesis, University of Florida]. Agronomy Department, Gainesville, FL. Available at https://original-ufdc.uflib.ufl.edu/AA00076988/00001

Dudhade, D.D., Amolik, V.L., & Gadakh, S.S. (2021). Effect of potash levels and apportioning time on yield and economic of summer groundnut under drip irrigation. International Journal of Chemical Studies, 9(3), 303-306.

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