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Article

Effects of Potassium Fertilizer on Sugarcane Yields and Plant and Soil Potassium Levels in Louisiana

by
Richard M. Johnson
1,*,
Katie A. Richard
1,† and
Quentin D. Read
2
1
United States Department of Agriculture, Agricultural Research Service, Sugarcane Research Unit, Houma, LA 70360, USA
2
United States Department of Agriculture, Agricultural Research Service, Southeast Area, 840 Oval Drive, Raleigh, NC 27606, USA
*
Author to whom correspondence should be addressed.
†
Current Address: American Sugar Cane League, Thibodaux, LA 70302, USA.
Agronomy 2024, 14(12), 2761; https://doi.org/10.3390/agronomy14122761
Submission received: 20 August 2024 / Revised: 13 November 2024 / Accepted: 19 November 2024 / Published: 21 November 2024
(This article belongs to the Section Soil and Plant Nutrition)
Browse Figures
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Abstract

:
The influence of potassium fertilizer on sugarcane (interspecific hybrids of Saccharum Spp.) yields and leaf and soil potassium levels was evaluated at six locations in Louisiana. The objective of this study was to determine if the sugarcane yields in Louisiana could be improved with potassium application. Different rates of potassium fertilizer (0–179 kg K2O ha−1) were applied to plant cane and ratoon sugarcane fields in Louisiana. Soil samples and sugarcane leaf samples were also collected from all experiments. Yield data were collected by harvesting plots with a single row, chopper harvester and a field transport wagon equipped with electronic load sensors. At all locations and soil types, potassium fertilizer did not increase cane or sugar yields. Soil properties data showed that significant increases in soil potassium levels did not occur until the second ratoon crop, where soil potassium increased by 30% for the high rate. Increases in plant potassium were also not observed until the second ratoon crop, where plant potassium increased by 10.5% for the high rate. The potential cause of the observed lack of response may be explained by interference from calcium and magnesium, combined with fixation by smectite and vermiculite clay minerals. Our soil and plant uptake data would suggest that repeated K applications at recommended rates, which currently vary from 90 to 157 kg ha−1, may be required to achieve the potential benefits of K fertilizer in Louisiana sugarcane soils. However, this must be verified by additional on-farm trials.

1. Introduction

Defining the nutrient requirements for sugarcane grown in Louisiana is a complicated process due to the perennial nature of the crop and the fact that Louisiana is the most northern sugarcane growing region in the world [1]. Nutrient requirements and uptake also differ between newly planted cane and successive ratoon crops [2], with older ratoons generally requiring higher nutrient amounts. Nitrogen has been identified as the predominant soil nutrient in sugarcane in terms of its contribution to crop productivity in most sugarcane producing regions of the world [3]. In terms of amounts applied, the next most important soil nutrient in sugarcane production is potassium (K). It is the most abundant cation in the cell sap of sugarcane [4] and has many functions throughout the plant [5]. Potassium has a vital role in plant water relations through its role in stomatal regulation and helps regulate 60 or more enzymes that influence plant growth [6]. The amount of K that is available in the soil at a given time is controlled by an equilibrium between soluble and exchangeable K sources and non-exchangeable and mineral sources [6]. As the plant available K sources (soluble and exchangeable) are depleted from the soil solution, additional K can be released from the mineral and non-exchangeable pools to restore the equilibrium [6]. Therefore, the amount of K available in the soil to the sugarcane crop will be a function of the amount of K in these different soil sources. Potassium fertilizer rates are typically determined from analyzing the soil for the plant available K levels, not the non-exchangeable or mineral sources of K. The most popular soil extractant used to determine plant available soil nutrients in the United States is the Mehlich III procedure [7]. While this extractant is efficient at determining exchangeable K, it does not estimate non-exchangeable or mineral forms. This can complicate recommendations for sugarcane, which is a perennial crop where soil samples are typically collected only once per four- or five-year crop cycle. The changes in the soil’s K reserves that occur over the crop cycle are typically not captured by this sampling schedule and K recommendations based on this sampling scheme may not represent the true crops needs [8]. Sugarcane uses substantial amounts of K, with a study conducted in Louisiana reporting that sugarcane removes approximately 1.2 kg of K per tonne of cane harvested [9]. These amounts are comparable to those reported for other sugarcane producing regions of the world with a Florida study [10] reporting a removal rate of 1.7 kg K per tonne and an Australian study reporting a removal rate of 1.5 kg K per tonne [11].
The response of sugarcane yields to K fertilization around the world has been found to vary considerably in the reported literature. In South Africa, K fertilization at rates up to 180 kg K ha−1 increased cane yields but had a minimal effect on sucrose concentrations [12]. In contrast, a study in Sudan [13] found significant increases in both cane and sucrose levels with K applied at rates of 72 and 144 kg K ha−1. Another study conducted in Ecuador [14] reported that sugarcane response to K was location-specific, but in two of three locations applications of 100 kg ha−1 K2O increased cane and sugar yields (only theoretically recoverable sucrose was observed to increase in the third location). It was reported that K fertilization at rates up to 162 kg K ha−1 in Brazil increased stalk diameter and production in the first ratoon sugarcane, but not in the second ratoon [15]. In another study conducted in Brazil [16], the authors reported that K fertilization at a rate of 200 kg K2O ha−1 increased cane yield by 7.9% compared to the control but did not affect sugar concentration. A study from India [17] reported that K fertilization at a rate of 50 kg K ha−1 increased cane yield, but not sucrose concentration compared to the control when KCl was used as the K source. In contrast, when K2SO4 was the K source (50 kg K ha−1) both cane yield and sugar concentrations were increased compared to the control [17]. In a more recent study conducted in South Africa [18], it was reported that K fertilization at rate up to 240 kg K ha−1 did not increase sugarcane yields on soils with high K reserves (exchangeable K > 0.25 cmol kg−1). When these reserves became depleted (exchangeable K < 0.25 cmol kg−1) due to successive cropping with sugarcane, a yield response could be obtained [18].
Results from K fertilization studies in the United States are also variable. A study conducted in Florida [19] reported that the response to K on Histisols was modest at best and the increases in tonnage observed were mostly negated by the decreases in sucrose content. In a later study on Florida Histisols [20], the authors reported significant responses to K in cane yield in plant cane, first, and second ratoon cane. Significant responses in sugar yield occurred in plant cane and first ratoon crops. In another study in Florida Histisols [21], it was reported that significant increases in sucrose yield response were obtained with added K, but these were attributable to increases in biomass. Further, investigations by the authors revealed that significant sucrose yield responses occurred in five of fourteen crop years, compared to the control [21]. In contrast, a more recent study [22] found that K fertilization on mineral soils in Florida resulted in significant sucrose yield responses in five of six locations. An extensive study was conducted in Louisiana [23] to evaluate the response of sugarcane to K fertilizer. The author reported that a majority of the forty-nine experiments conducted showed a positive response to K fertilization, although results were only significant in fourteen of the cases evaluated [23]. The author also concluded that greater responses to K were more likely in ratoon cane than with plant cane and were less likely on clay soils [23]. Another Louisiana study [24] investigated the effects of soil type and variety on the response of sugarcane to nitrogen and K fertilizers. The author reported that K fertilization at a rate of 90 kg K2O ha−1 significantly increased cane and sugar yields in both plant and ratoon cane. The authors also did note that the response in sugar yields was variety-dependent, with some varieties not showing a significant result [24]. The authors of two recent K studies in Louisiana [25,26] reported significant increases in both cane and sugar yields in plant cane and ratoon crops. In most cases, significant increases in sugar yield were obtained with 67 kg K2O ha−1, although in one study 268 kg K2O ha−1 was required to achieve a significant response, a clearly uneconomic amount. Given the lack of recent information concerning the need for K fertilization with modern Louisiana sugarcane varieties and cultural practices, the specific objective of this experiment was to determine the cane and sugar yield response of two major Louisiana sugarcane varieties HoCP 96-540 and L01-299 to supplemental K fertilizer. We hypothesize that sugarcane yields will respond positively to potassium fertilizer application.

2. Materials and Methods

2.1. Description of Experimental Fields

Potassium fertilizer experiments were first conducted in plant cane and first and second ratoon commercial sugarcane fields of HoCP 96-540 and L01-299 at three locations throughout the Louisiana sugarcane industry from 2014 to 2019. The sites selected are all representative of the major sugarcane producing regions in Louisiana. The first experimental locations were at Al Landry Farms in plant cane fields of HoCP 96-540 on light and heavy soils in Plaquemine, LA (30.21905 N, −91.19035 W). The light and heavy soils were mapped Commerce silt loam and silty clay loams, respectively (fine-silty, mixed, superactive, nonacid, thermic Fluvaquentic Endoaquepts). Plant cane, first ratoon, and second ratoon data were collected from this location in 2014, 2015, and 2016, respectively. The second experimental locations were at Naquin Farms in plant cane fields of L01-299 on light and heavy soils in Schriever, LA (29.66161 N, −90.87096 W). The light and heavy soils were mapped Cancienne silt loam and silty clay loams, respectively (fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts). Plant cane, first ratoon, and second ratoon data were collected from this location in 2014, 2015, and 2016, respectively. The third experimental locations were at Gravois Farms in plant cane fields of HoCP 96-540 on light and heavy soils in Edgard, LA (30.03819 N, −90.54945 W). The light soil was mapped as a Cancienne silt loam (fine-silty, mixed, superactive, nonacid, hyperthermic Fluvaquentic Epiaquepts) and the heavy soil as a Gramercy silty clay loam (fine, smectitic, hyperthermic Chromic Epiaquerts). Plant cane, first ratoon, and second ratoon data were collected from this location in 2016, 2017 and 2018, respectively. Rainfall and temperature data were collected from a weather station in Carville, LA, for site one and Thibodaux, LA, for sites two and three. Temperature data were within the normal range for the Carville site during the experiment and precipitation was above normal. Temperature data were also in the normal range for the Thibodaux sites, with the exception that 2014 was slightly cooler than normal. Precipitation for the Thibodaux site was slightly below normal in 2014, within the normal range for 2015, 1016, and 2018 and above normal for 2017. None of these observations would be expected to adversely affect sugarcane yields.

2.2. Potassium Treatments

Potassium fertilizer was applied at rates of 0, 45, 90, 134, and 179 kg K2O ha−1 on each side of the planted row using muriate of potash (potassium chloride) as the K source. Potassium treatments were surface broadcast in mid-April (early tillering phase and typical application time in Louisiana), and plot size was 3 rows (inter-row spacing was 1.8 m) by 15 m in length. Treatments were arranged in a randomized complete block design with six replications. Quantities of nitrogen and sulfur were maintained by cooperators as recommended for plant cane and first and second ratoon crops on silt-loam (light-textured) and silty clay loams (heavy-textured) soils [27,28]. The LSU AgCenter currently recommends nitrogen levels range from 90 to 134 kg N ha−1 and sulfur levels 28 kg S ha−1 [29].

2.3. Soil and Plant Sampling and Analysis

Soil samples (0–15 cm) were collected with a soil probe (19 mm diameter) from all plots (6 samples per plot) prior to fertilizer application and after harvest to determine soil nutrient levels. Soil samples were air-dried, ground to pass a 2 mm screen with an electric grinding mill (Straub 4E, QCG Systems, Phoenixville, PA, USA) and shipped to Waypoint Analytical (Memphis, TN, USA) for analysis. Details of the soil analyses are available in [30].
Stalk number was determined in 3 m sections during the grand growth period (June to August). Only stalks that were at least 1.2 m tall from the soil surface to the youngest visible leaf collar were counted and measured. Leaf samples (youngest fully expanded leaf) for tissue analysis were also collected during the grand growth period and oven-dried at 65 C. Samples were then ground using a Laboratory Mill (Thomas Wiley, Model 4) equipped with a 1 mm sieve. The ground plant leaf tissue (0.5 g) was analyzed by nitric acid–hydrogen peroxide digestion and ICP spectroscopy to serve as an indicator of fertilizer-use efficiency [31]. Nitric acid and hydrogen peroxide was purchased from Ricca Chemical (Arlington, TX, USA) and samples were analyzed on an Spectro ICP. Standard plant tissues and sample blanks were included in all analyses and random duplicate samples were included within each replication to ensure the repeatability of the analyses.

2.4. Yield Determination

Experimental plots were harvested with a single-row chopper harvester (John Deere, Thibodaux, LA, USA) and cane weight in each plot was determined using a modified single-axle high-dump wagon equipped with a billet sampler (John Deere, Thibodaux, LA, USA) equipped with load sensors mounted on the spindles at the end of the axle and on the wagon’s tongue where it connects to the tractor [30,32]. The sub-samples of the billeted cane were analyzed using the pre-breaker, core press method [30,33].

2.5. Statistical Analyses

Linear mixed models were fit to each response variable separately. Fixed effects were crop year (levels: plant cane, first ratoon, and second ratoon), soil type (levels: light and heavy), variety (levels: HoCP 96-540 and L 01-299), and K addition (five treatment levels, treated as a continuous predictor in the analysis). All two-way and three-way interactions were included. Random intercepts were fit to each environment (combination of location and year). Models with random slopes with respect to K addition for each environment were compared to random intercept models using likelihood ratio tests. These tests indicated that including a random slope term was not supported by the data, thus we present the random intercept models here. The plant K and soil K variables were log-transformed before model fitting. Stalk counts were modeled using a generalized linear model with a Poisson response distribution and log link function. Because some treatment combinations were missing from the stalk counts data, interaction terms including crop year and variety were excluded from the stalk counts model.
Analysis of variance was performed using Type III F-tests and Kenward–Roger approximation of denominator degrees of freedom. Marginal trends with respect to K addition were estimated averaged across all other predictors, and by each predictor variable and combination thereof. Marginal means were estimated at each level of K addition averaged across all other predictors, and by each predictor variable and combination thereof. The 95% confidence intervals around the marginal trends and means were computed again using the Kenward–Roger approximation of degrees of freedom.
Statistical analysis was carried out using R software v4.3.1 [34], including the packages lme4 v1.1-34 [35], lmerTest v3.1-3 [36], emmeans v1.8.7 [37], and car v3.1-2 [38].

3. Results

3.1. Soil Properties from Experimental Locations

The initial soil properties from the six study sites did not exhibit any conditions that would have limited or reduced K availability, with possibly one or two exceptions (Table 1). The soil pH at all six locations was within a range that would not have limited K availability with the lowest soil pH (5.7) obtained at heavy soil location at Naquin Farms and the highest pH (6.6) was at the heavy soil location at Gravois Farms (Table 1). The preliminary soil K levels tested as “medium” on the light soil test at Landry Farms and “optimum” on the heavy soil test by the Mehlich III procedure and Waypoint Laboratories classification. At Naquin Farms, the light soil test tested as “low” and the heavy soil tested as “optimum”. Finally, the light soil test at Gravois Farms tested as “low” and the heavy soil tested as “medium”. It should be noted that K fertilizer was recommended at all locations, with higher rates recommended for the light soils at all locations. It is possible that the high K soil test level at the Naquin Farms heavy soil test may have obscured the K response at that location. Two of the sites tested “low” for phosphorus, two tested “medium”, and two tested “optimum”. Calcium and magnesium tested as “medium” or above at all locations and sulfur tested “low” at two locations, “medium” at three locations, and “optimum” at one location. The organic matter levels were typical for Louisiana sugarcane soils ranging from 1.65 to 2.82% (Table 1). The CEC values are all representative of Louisiana sugarcane soils ranging from 15.0 to 24.7 cmol (+)/kg, and in all cases, the heavy soils at each site had a greater CEC than the light soil (Table 1). Finally, a majority of the (Ca + Mg)/K ratios for the test sites indicated that interference in potassium retention by Ca and Mg were possible. These data are more completely evaluated in Section 4.

3.2. Significance of the Main Effects of Crop, Soil Type, Variety, and Potassium Fertilizer

The main effects of crop year and variety did not significantly influence (p > 0.05) any yield component or the levels of K in soil or leaf samples (Table 2). In contrast, the main effect of soil type did affect cane yield, sugar yield, plant K, and soil K, with significantly greater yields and K concentrations in heavy soil.
The main effect of K did not result in a significant response (p > 0.05) with cane yield, TRS, or sugar yield, but there was a significant positive influence of K addition on the levels of soil and plant K (Table 2). There was a significant interaction between crop year and soil type for TRS, sugar yields, and stalk counts (Table 2). There was also a significant interaction between crop year and K added for the levels of soil and plant K (Table 2), with significantly greater response to K addition in the second ratoon crop year. The interaction between soil type and variety was also highly significant for all yield components and soil and plant K. Finally, a three-way interaction between crop year, soil type, and variety was also significant for cane yield, TRS, and sugar yields.

3.3. Potassium Fertilizer Effects on Sugarcane Yield Components

Cane yield did not respond to applied K fertilizer (Figure 1A) with the marginal trends showing no significant effects of added K. The trends for crop year showed greater cane yields for plant cane and first ratoon yields, as compared to second ratoon yields, but this was not significant (Figure 1B). The marginal trends effect of soil type also showed higher (but not significant) cane yields for light soil as compared to heavy soil (Figure 1C). There were also no significant differences in cane yield due to K between varieties (Figure 1D). The marginal trends for TRS did not show an overall response to K and showed no significant trend regarding crop year, soil type, or variety (Figure 2A–D). The marginal trends for sugar yields also did not show an overall effect of K addition (Figure 3A). The trends for crop year showed higher (but not significant) sugar yield for plant cane and first ratoon crops, as compared to second ratoon crops (Figure 3B). The trends for soil type also showed higher (but not significant) sugar yields for light soils as compared to heavy soils (Figure 3C). No differences were observed in the trends for varieties (Figure 3D). The overall marginal trend for stalk population were also not significantly affected by K addition. Crop year and soil type also did not influence the trends, but the trend for variety showed that L 01-299 produced more stalks than HoCP 96-540 (but was not affected by K addition).

3.4. Potassium Fertilizer Effects on Soil and Plant Potassium Levels

The overall marginal trend for the plant K levels showed a significant response to K addition (Figure 4A). This effect was primarily the result of the positive trend in plant K levels observed in the second ratoon crop, which is shown in the trend data for crop year in Figure 4B. No effects on plant levels of K were observed in the plant cane or first ratoon crop. There were also minimal (not significant) differences in plant K observed due to soil type (Figure 4C) and variety (Figure 4D). Similarly to the plant response data, the overall marginal trend data for soil K levels showed a significant positive response to K addition (Figure 5A). Also, like the plant response data, this effect was due primarily to the large increase in soil K in the second ratoon crop (Figure 5B). The marginal trend for soil type showed a much higher baseline level of K in heavy soils, as compared to the light soils (Figure 5C). However, the rate of increase in soil K with increasing K addition is greater in the light soil. Finally, the marginal trend for variety showed that soil K increased more with increasing K addition in the fields planted to L 01-299 (Figure 5D).

4. Discussion

The combined data from the six K trials did not result in any significant increases in cane yield, TRS, sugar yield, or stalk population due to K addition (Figure 1, Figure 2 and Figure 3). These results reject our research hypothesis that yields would respond positively to potassium fertilizer addition. Several explanations for these results will be considered. The yields obtained in these studies were representative or better than state average yields for the years that the studies were conducted [39] and did not appear to be depressed due to nutrient stress. This is further supported by the plant K levels which were in the sufficient to optimum range (Figure 4) with no signs of nutrient deficiencies [40]. Potassium fertilizer was applied in these trials at rates up to 179 kg ha−1, which exceeds the currently recommended LSU AgCenter rates [29] that vary from 90 to 157 kg ha−1. It is possible that higher K rates would have resulted in a yield response. A recent study from Brazil reported that K rates up to 240 kg ha−1 resulted in the best yields and economic return [41]. This possibility is currently being investigated in trials on commercial farms in Louisiana.
The soil test data that were taken prior to initiation of the trials documented that soil properties should not have limited K availability. Soil pH was in the range where lime application would not be recommended (Table 1). In Louisiana, lime is not applied until the pH drops below 5.5 on a light soil and 5.2 on a heavy soil [27]. Although, two sites tested low for phosphorus (Table 1), phosphorus is not typically applied in Louisiana sugarcane due to a lack of yield response [30]. The soil data did show that the levels of Ca and Mg in these trials were relatively high (Table 1), as compared to the levels of K (Table 1). Several other researchers have reported that Ca and Mg in the soil can interfere with the movement of K in the soil [6]. Another researcher suggested that when the ratio of (Ca + Mg)/(K) exceeds 20, a significant decrease in K uptake may occur [42]. The soil in our trials exceeded this ratio in three of the six sites and closely approached this level in two others (Table 1). However, after two years of K application both the soil and plant K levels in our study increased in the second ratoon crop, suggesting that sufficient Ca and Mg were displaced to allow for greater K uptake (Figure 4 and Figure 5). It is possible that cane or sugar yields would have shown an increase if the study was continued into the third ratoon crop.
A study from South Africa reported that leaf K content did not increase or increased slowly following high applications of K fertilizer [43]. The authors speculated that some of the soils investigated in their research exhibited strong K fixation due to high levels of smectite and vermiculite. These clay minerals are common in the Louisiana soils investigated in our study. The dominant clay mineralogy in the Southern Mississippi River Alluvium has been reported to be smectitic, which is the major land resource area where this study was conducted [44]. It was also reported that higher K applications are required in these conditions and that over time less K will be fixed and more available for crop uptake [43]. Finally, a recent study from Brazil reported that differences were obtained between fertilizer formulations, with liquid, soil-incorporated fertilizer providing improved yields over dry surface-applied fertilizer in some circumstances [45]. It should be noted that this study did not only study K fertilizer, but a combination of N, P, and K. The majority of K fertilizer in Louisiana is surface applied granular KCl, so it is possible that a liquid source may improve yields. This possibility will be investigated in future research.
Based on the soil test and plant uptake data, which did not show a significant increase in K until repeated applications of K were applied, it appears that in the fields examined in this research study, the repeated application of K might be required to overcome the combined effects of interference from Ca and Mg and potential K fixation by clay minerals. However, many sugarcane growers in Louisiana have avoided applying K, or applied lower than recommended rates, due to high prices. This practice could prevent the potential beneficial effects of K application from being realized.

5. Conclusions

The influence of K fertilizer on cane and sugar yields, plant K levels and soil properties was tested at six locations in Louisiana. The data showed that K fertilizer did not increase cane and sugar yields in the soils and locations evaluated. Soil properties data showed that significant increases in soil K levels did not occur until the second ratoon crop. Significant increases in plant K were also not observed until the second ratoon crop. One possible explanation of the observed lack of response may be the combined effects of interference in K retention from Ca and Mg and K fixation by smectite and vermiculite clay minerals. Our soil and plant uptake data would suggest that repeated K applications at recommended rates, which currently vary from 90 to 157 kg ha−1, [29] may be required to achieve the potential benefits of K fertilizer in Louisiana sugarcane soils. However, this must be verified by additional on-farm trials. Higher K rates or a change in fertilizer formulation may also be necessary to achieve a yield response. This will also be investigated in future trials.

Author Contributions

Conceptualization, R.M.J. and K.A.R.; methodology, R.M.J. and K.A.R.; formal analysis, Q.D.R.; investigation, R.M.J. and K.A.R.; resources, R.M.J.; data curation, R.M.J.; writing—original draft preparation, R.M.J.; writing—review and editing, R.M.J., K.A.R. and Q.D.R.; visualization, Q.D.R.; supervision, R.M.J.; project administration, R.M.J.; funding acquisition, R.M.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded entirely by the USDA ARS.

Data Availability Statement

The data presented in this study are available on request from the authors.

Acknowledgments

Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable. We thank Brenda King, Deise Paula da Silva, Chandler Richard, Randy Richard, Jeffrey Carrillo, and Mathew Waguespack for assistance in soil and plant sampling and harvesting in all experiments.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Estimated marginal trends of potash addition on cane yields for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
Figure 1. Estimated marginal trends of potash addition on cane yields for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
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Figure 2. Estimated marginal trends of potash addition on TRS (theoretically recoverable sugar) for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level area shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
Figure 2. Estimated marginal trends of potash addition on TRS (theoretically recoverable sugar) for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level area shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
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Agronomy 14 02761 g003
Figure 3. Estimated marginal trends of potash addition on sugar yield for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
Figure 3. Estimated marginal trends of potash addition on sugar yield for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. No slopes are significantly different from zero.
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Figure 4. Estimated marginal trends of potash addition on plant leaf potassium for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level area shown and error bars indicate standard errors of the means. Slopes significantly different from zero are shown as thick solid lines, while slopes not significantly different from zero are shown as thin dashed lines. The overall effect of potash addition on leaf K was significant (t520 = 3.65, p = 0.0003), (A). The effect of potash addition on leaf K in second ratoon was also significant (t520 = 4.70, p < 0.0001), (B).
Figure 4. Estimated marginal trends of potash addition on plant leaf potassium for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level area shown and error bars indicate standard errors of the means. Slopes significantly different from zero are shown as thick solid lines, while slopes not significantly different from zero are shown as thin dashed lines. The overall effect of potash addition on leaf K was significant (t520 = 3.65, p = 0.0003), (A). The effect of potash addition on leaf K in second ratoon was also significant (t520 = 4.70, p < 0.0001), (B).
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Figure 5. Estimated marginal trends of potash addition on soil potassium for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. Slopes significantly different from zero are shown as thick solid lines, while slopes not significantly different from zero are shown as thin dashed lines. The overall effect of potash addition on soil K was significant (: t569 = 4.53, p < 0.00010 (A). The effect of potash addition on soil K in second ratoon was significant (: t569 = 6.68, p < 0.0001) (B). The effect of potash addition in light soil was significant (t569 = 5.23, p < 0.0001) (C). The effect of potash addition on soil K in variety L 01-299 was significant (t569 = 4.38, p < 0.0001) (D).
Figure 5. Estimated marginal trends of potash addition on soil potassium for the overall trend (A) and the two-way interactions of potash addition with crop year (B), soil type (C), and variety (D). All treatments were replicated six times and data were subjected to analysis of variance. Means at each potash addition level are shown and error bars indicate standard errors of the means. Slopes significantly different from zero are shown as thick solid lines, while slopes not significantly different from zero are shown as thin dashed lines. The overall effect of potash addition on soil K was significant (: t569 = 4.53, p < 0.00010 (A). The effect of potash addition on soil K in second ratoon was significant (: t569 = 6.68, p < 0.0001) (B). The effect of potash addition in light soil was significant (t569 = 5.23, p < 0.0001) (C). The effect of potash addition on soil K in variety L 01-299 was significant (t569 = 4.38, p < 0.0001) (D).
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Table 1. Properties of soil sampled prior to initiation of plant cane potassium trials (2014, 2016) from three locations in Louisiana planted to HoCP 96-540 and L01-299.
Table 1. Properties of soil sampled prior to initiation of plant cane potassium trials (2014, 2016) from three locations in Louisiana planted to HoCP 96-540 and L01-299.
Lan
LS †		Lan HSNaq LSNaq HSGra
LS		Gra HS
Soil pH ‡5.765.915.765.716.366.62
P (mg kg−1)35.616.717.8389.712.5
K (mg kg−1)13919693.8255111133
Ca (mg kg−1)220032001440311620002316
Mg (mg kg−1)469700254816384516
S (mg kg−1)13.22312.18.510.97.7
OM (%)2.432.821.653.372.131.83
CEC (cmol (+)/kg16.022.510.224.715.017.3
(Ca+Mg)/K19.420.118.415.521.521.6
Potassium
Recommendation §		96661281510799
†—Al Landry Farms (2014), Naquin Farms (2014), and Gravois Farms (2016) light and heavy soils. ‡—Soil pH, Mehlich III levels of exchangeable soil phosphorus, potassium, calcium, magnesium, and sulfur, organic matter, and CEC (sum of bases). §—Potassium recommendations from Waypoint Analytical (Memphis, TN, USA) for sugarcane grown in Louisiana.
Table 2. Statistical significance (p-value) showing the effect of crop stage, soil type, variety, and potash added on cane yield, theoretical recoverable sugar (TRS), sugar yield, plant population, and (K) potassium concentration in the plant tissue and soil profile.
Table 2. Statistical significance (p-value) showing the effect of crop stage, soil type, variety, and potash added on cane yield, theoretical recoverable sugar (TRS), sugar yield, plant population, and (K) potassium concentration in the plant tissue and soil profile.
TraitsCane YieldTRSSugar/AStalk CountsPlant KSoil K
p-Value
Crop0.140.620.280.270.550.76
Soil0.0000010.490.0000010.290.0000010.000001
Variety0.730.930.730.00800.780.88
Potassium Added0.6950.2990.3290.5610.000290.00000721
Crop × Soil0.00180.0180.0000770.00890.270.000026
Crop × Variety0.610.170.63-1.00.93
Crop × Potassium Added0.870.7450.9410.8820.001760.000000755
Soil × Variety0.0000010.0000010.000290.00000680.0000010.000001
Soil × Potassium Added0.4740.8960.6420.9270.1940.00505
Variety × Potassium Added0.8560.1130.3190.2940.260.0183
Crop × Soil × Variety0.0000010.00440.0000035-0.0580.00018
Crop × Soil × Potassium Added0.08650.9910.1960.6950.9430.255
Crop × Variety × Potassium Added0.09990.7790.436-0.3120.267
Soil × Variety × Potassium Added0.02240.3310.1120.3880.1070.235
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Johnson, R.M.; Richard, K.A.; Read, Q.D. Effects of Potassium Fertilizer on Sugarcane Yields and Plant and Soil Potassium Levels in Louisiana. Agronomy 2024, 14, 2761. https://doi.org/10.3390/agronomy14122761

AMA Style

Johnson RM, Richard KA, Read QD. Effects of Potassium Fertilizer on Sugarcane Yields and Plant and Soil Potassium Levels in Louisiana. Agronomy. 2024; 14(12):2761. https://doi.org/10.3390/agronomy14122761

Chicago/Turabian Style

Johnson, Richard M., Katie A. Richard, and Quentin D. Read. 2024. "Effects of Potassium Fertilizer on Sugarcane Yields and Plant and Soil Potassium Levels in Louisiana" Agronomy 14, no. 12: 2761. https://doi.org/10.3390/agronomy14122761

APA Style

Johnson, R. M., Richard, K. A., & Read, Q. D. (2024). Effects of Potassium Fertilizer on Sugarcane Yields and Plant and Soil Potassium Levels in Louisiana. Agronomy, 14(12), 2761. https://doi.org/10.3390/agronomy14122761

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