J. Mabry McCray

Sulfur Distribution and Transformations in Everglades Agricultural Area Soil as Influenced by Sulfur Amendment

Nutrient export from the Everglades Agricultural Area (EAA) has been implicated in causing sulfur (S) enrichment of Everglades wetlands. However, quantification of the S budget and transformations in EAA soils is inadequate. The objective of this study was to quantify various S fractions and investigate how elemental S amendment affects S dynamics in EAA soils. Reduced S compounds were not detected in soil before elemental S application. Organic S was the major form of S, comprising 87% of total S, followed by extractable SO4-S (13%). Extractable SO4-S for soils receiving 448 kg S ha−1 was 36%, 131%, 201%, and 270% higher than for unamended soils at 2, 6, 9, and 13 months, respectively. Elemental S was significantly higher in soils receiving 448 kg S ha−1 (482 mg kg−1) than in soils receiving 224 (111 mg kg−1) and 112 kg S ha-1 (55 mg kg−1) and unamended soil (0 mg kg−1) at 2 months after S application. Similar to extractable SO4-S, elemental S significantly decreased during the growing season. Sulfur application did not affect the sulfatase activity, however, mineralizable S increased concurrently with S application rate, and the effects continued throughout the growing season. This result was largely attributed to the oxidation of the applied elemental S. Our results suggest that large-scale S application in the EAA soils is likely to increase SO42− concentrations in soils, which poses a potential risk of SO42− export to sensitive Everglades wetlands.

SEASONAL CHANGES IN NUTRIENT AVAILABILITY FOR SULFUR-AMENDED EVERGLADES SOILS UNDER SUGARCANE

The objective of this study was to evaluate effects of elemental sulfur (S) addition on soil pH and availability of macro- and micronutrients during the sugarcane growing season. Sulfur application did not significantly reduce soil pH when applied at 0 to 448 kg S ha−1 due to the high soil buffering capacity. Water extractable phosphorus (P) and potassium (K) for soils receiving the highest S rate were 188% and 71% higher than for unamended soils only at two months after application, indicating a short-term enhancement of macronutrient availability. Soil amended with 448 kg S ha−1 contained 134% more acetic acid-extractable zinc (Zn) than unamended soil, although stimulatory effects did not extend beyond two months. Sugar yield was not affected by S addition, averaging 17 Mg sugar ha−1. The failure of S to enhance nutrient availability throughout the growing season indicates the limited benefit of applying elemental S to reduce pH and increase nutrient availability to sugarcane.

CALIBRATION OF SUGARCANE RESPONSE TO CALCIUM SILICATE ON FLORIDA HISTOSOLS

Silicon is considered a beneficial nutrient for sugarcane (Saccharum spp.) and yield responses to Si applications on Florida organic soils have been well documented. Growers need calibrated Si recommendations to be able to make cost-effective decisions regarding Si applications. The objective of this study was to develop a soil-test Si calibration based on yield responses to Ca silicate on Everglades Histosols. Twelve paired commercial field comparisons and three small-plot tests of Ca silicate application were conducted. Strong responses in t cane ha−1 and t sucrose ha−1 were determined with acetic acid-extractable soil Si <15 g m−3, with some response to approximately 25 g m−3. Recommendations were developed over this range with a maximum Ca silicate rate of 6.7 t ha−1. Optimum leaf Si concentration was determined to be ≥ 6.0 g kg−1, with 0.95 and 0.80 relative yield at 5.0 and 2.5 g kg−1, respectively.

Boundary Lines Used to Determine Sugarcane Production Limits at Leaf Nutrient Concentrations Less than Optimum

Foliar nutrient analysis is a useful diagnostic tool to complement soil testing as a best‐management practice with sugarcane (Saccharum spp.). This study was conducted to determine sugarcane production limits at leaf nutrient concentrations less than optimum. Eight Florida sugarcane growers participated in a survey of leaf nutrient values in 2004, 2005, and 2006. A total of 412 leaf samples were collected from individual commercial sugarcane fields, from which there were 389 harvest data/leaf data combinations. Fields were selected to be representative of plant cane, first ratoon, and second ratoon crops; mineral and organic soils of the area; and major commercial sugarcane cultivars. Leaf silicon (Si), magnesium (Mg), and manganese (Mn) concentrations had the strongest correlations with tons sugarcane ha−1 on organic soils, and leaf nitrogen (N), Mg, and Si concentrations had the strongest correlations with tons sugarcane ha−1 on mineral soils. Boundary lines were used to define practical limits of tons sugarcane ha−1 for leaf nutrient concentrations less than optimum. A table was developed that provides approximate leaf concentrations of nine nutrients at which 10 and 25% losses in relative tons sugarcane ha−1 were estimated. Boundary‐line analysis indicated that sugarcane production was most limited nutritionally in survey fields by insufficient Mg, iron, N, and Si on mineral soils and by insufficient Si and Mn on organic soils.

Sugarcane Yield Response to Furrow-Applied Organic Amendments on Sand Soils

Organic amendments have been shown to increase sugarcane yield on sand soils in Florida. These soils have very low water and nutrient-holding capacities because of the low content of organic matter, silt, and clay. Because of high costs associated with broadcast application, this field study was conducted to determine sugarcane yield response to furrow application of two organic amendments on sand soils. One experiment compared broadcast application (226 m3 ha−1) of mill mud and yard waste compost, furrow application (14, 28, and 56 m3 ha−1) of these materials, and no amendment. Another experiment compared furrow applications (28 and 56 m3 ha−1) of mill mud and yard waste compost with no amendment. There were significant yield (t sucrose ha−1) responses to broadcast and furrow-applied mill mud but responses to furrow applications were not consistent across sites. There were no significant yield responses to yard waste compost suggesting that higher rates or repeated applications of this amendment will be required to achieve results comparable to mill mud. Results also suggest that enhancing water and nutrient availability in the entire volume of the root zone with broadcast incorporation of organic amendments is the more effective approach for low organic matter sands.

Phosphorus Fertilizer Calibration for Sugarcane on Everglades Histosols

A calibrated soil test for phosphorus (P) fertilizer application to sugarcane (Saccharum spp.) grown on organic soils in southern Florida is an important best-management practice for minimizing P loads in water draining to the Everglades. The current calibration uses water as the soil extractant, which has the limitations of being very sensitive to pH and being most applicable to short-season crops. Phosphorus fertilizer rate studies at six locations (20 total crop years) were analyzed to develop an updated soil-test P calibration for sugarcane on organic soils. Phosphorus extracted with water, acetic acid, and Bray 2 did not consistently relate well to crop response. A new P soil-test calibration for sugarcane is proposed based on Mehlich 3 soil extraction, with a maximum rate of 36 kg P ha−1 with ≤ 10 g P m−3 in preplant soil samples and no P recommended with >30 g P m−3.

Sugarcane yield and plant nutrient response to sulfur-amended Everglades histosols

ABSTRACT High soil pH causes leaf nutrient deficiencies and reduces sugarcane yield. Soil pH in Florida histosols has been increasing as these soils subside and depth to limestone is decreased. A factorial experiment of four sulfur (S) rates and three added calcium carbonate (CaCO3) levels in soil was designed to determine S-amendment effectiveness in reducing pH and increasing nutrient availability in sugarcane as calcium (Ca) carbonate levels were increased. Sulfur-amendment and increased CaCO3 level had limited effects on yield and leaf nutrient concentrations during the growing season. Most leaf nutrients were within optimum range except nitrogen (N), phosphorus (P), iron (Fe), and manganese (Mn). Unexpected increases in Mn concentrations with added CaCO3 were associated with reducing conditions due to increased soil bulk density. High soil pH caused Mn deficiencies in the plants. Soil pH, P and Mn concentrations were important factors in predicting sugarcane yield.

Sugarcane yield response to calcium silicate on Florida mineral soils

Abstract Silicon (Si) is a beneficial nutrient for sugarcane (Saccharum spp.) and yield responses to Si amendment have been determined on soils with low soluble Si. Because a soil test Si calibration has not been published for sugarcane grown on Florida mineral soils, the objectives were to determine sugarcane yield response to silicon soil amendment on two mineral soils (Entisol and Spodosol) and to relate sucrose yield to soil-extractable Si. Calcium silicate application rates were 0, 3.4, and 6.7 Mg ha−1 (Site 1) and 0, 2.2, 4.5, and 6.7 Mg ha−1 (Site 2) in small-plot (120 m2 plot−1) experiments, with Si application resulting in significant increases in biomass and sucrose ha−1. Calcium silicate requirements of 6.7 and 4.3 Mg ha−1 were determined with initial acetic acid-extractable Si of 21 and 46 g m−3, respectively. Nonlinear models indicated that Si amendments will be required with acetic acid-extractable Si <105 g m−3.

Influence of Elemental Sulfur on Sugarcane Yield on Histosols with Near-Neutral pH

ABSTRACT Soil subsidence of Florida Histosols caused by microbial oxidation following drainage of these soils has resulted in decreased depth. Soil pH has increased from tillage operations and vertical movement of carbonates from underlying limestone bedrock through evapotranspiration and seepage irrigation. This study was conducted to determine sugarcane (Saccharum spp.) yield response to banded elemental sulfur (S) (granular 90% S and granular 80% S with 5% manganese (Mn)) in soils with unamended pH ranging from 6.5 to 7.2. Four field experiments were established as small-plots on Histosols in the Everglades Agricultural Area (EAA). Each experiment was a randomized complete block design with six replications and elemental S rates of 0, 90, 224, and 448 kg S ha−1. Less than optimum leaf Mn at two locations were associated with Mehlich 3-extractable Mn<5 g m−3. There were no sugarcane yield responses to elemental S with unamended pH<7.2, although S significantly reduced in-row pH. Abbreviations: EAA, Everglades Agricultural Area; ICP, inductively coupled argon plasma; KSM, kg sucrose Mg−1 cane; MAP, monoammonium phosphate; M3-Mn, Mehlich 3-extractable Mn; RCB, randomized complete block; STM5, granular 80% S with 5% Mn; MCH, Mg cane ha−1; MSH, Mg sucrose ha−1

Influence of compost/sludge application on sugarcane yield and nitrogen requirement on a sand soil

ABSTRACT Mineral soils in southern Florida are very low in organic matter content and most of the nitrogen (N) for sugarcane (Saccharum spp.) must be supplied in split fertilizer applications. Information is needed regarding how the interaction of organic amendments and fertilizer N influences sugarcane yields. A field study on a sand soil (Alfisol) was established to determine (1) potential sugarcane yield benefits of a compost/sludge amendment, and (2) the influence of the amendment on N fertilizer requirement. A split-plot Latin square design was used with five N rates (main plots) and presence or absence of compost/sludge broadcast at 113 m3 ha−1 (subplots). Annual N rates were 0, 67, 134, 202, and 269 kg N ha−1. Compost/sludge application increased cumulative t sucrose ha−1 by 36% averaged across N rates. The amendment also lowered annual N requirement by an average of 38%, but maintenance applications of compost/sludge will be required every four years.