Rao S. Mylavarapu

ESTIMATING CHEMICAL PROPERTIES OF FLORIDA SOILS USING SPECTRAL REFLECTANCE

This study was conducted to develop fundamental relationships between soil properties from three representative Florida soil orders and their spectral characteristics. The ultimate goal of this work is to develop a real–time soil property sensor for use in effective farm management. A total of 270 samples collected from the three representative soil orders (Alfisol, Entisol, and Ultisol) in Florida were used for analysis. Soil samples were obtained from 0 to 15 cm depth at 15 sampling points within three specific fields of 2.0 ha each of the three soil orders at six different times of the year, assuring a wide range of sample variability in sampling times and locations. Reflectance of the soil samples was measured in the range of 400 to 2498 nm with a 2 nm increment, and the corresponding nutrient content (P, K, Ca, and Mg) along with pH and soil organic matter content was measured for each of the samples. Partial least squares analysis was used to build prediction models with a calibration data set of 180 randomly chosen samples. The remaining 90 samples were used to validate the models. The prediction models for measured soil chemical properties for the three soil orders yielded R2 values of 0.24 to 0.88. This result could be useful in the development of a soil nutrient sensor for site–specific crop management.

Environmentally Responsible Potato Production Systems: A Review

ABSTRACT More than 500,000 hectares of land is planted to potato crop each year in the United States. Intensive nutrient-management practices for potato cultivation have led to increased concerns about nitrate leaching in these soils. Studies on nitrogen (N) uptake characteristics of potato roots have shown that N fertilizers are applied in excess of the optimal rate for maximum yield. This paper discusses all current and relevant research on nutrient and water management issues that have lead to improved nitrogen use efficiency for successful potato production and minimized groundwater impacts. Specific topics within the nutrient-management section include mineral fertilizers, nutritional requirements, N uptake and the root system, slow and controlled-release fertilizers, organic sources of nutrients, and nitrification inhibitors. Research on alternate methods of irrigation currently in use and available for potato production is discussed. Application of prediction models to optimize all the components for sustaining both economical and environmental goals is also discussed, with an emphasis on the immediate need for linking nutrient management traditionally aimed at crop yields with the preservation of water quality in all future research programs.

Reflectance spectroscopy for routine agronomic soil analyses

Near-infrared reflectance spectroscopy is a demonstrated tool for quantitative analysis of numerous soil properties. Reported advantages include analytical precision, predictive accuracy, and reduced costs and processing times. A library (N = 1933) representing all major soil orders in Florida was assembled from samples submitted to the University of Florida Extension Soil Testing Laboratory for routine testing during 2004-2005. High-resolution diffuse reflectance spectra from each sample in the visible/near infrared were used to predict observations made using standard laboratory analytical procedures for soil pH, Mehlich-1-extractable P, K, Ca, Mg, Cu, Mn, and Zn, percentage of organic matter, and saturated hydraulic conductivity (Ksat). Calibrations were immediately applicable for organic matter and Al, based on relative performance determinant values (RPD = standard deviation/standard error of validation > 2.0). Models for pH, P, Ca, and Ksat showed moderate accuracy (1.5 < RPD < 2.0), whereas those for K, Cu, Mg, Mn, Zn, and Fe exhibited low efficiency (RPD < 1.5), indicating a need for further refinement before near-infrared reflectance spectroscopy is a viable alternate method to standard laboratory procedures. Prediction of soil fertility and productivity based on published Florida soil diagnostic categories showed effective discrimination for pH, P Mg, Mn, Cu (phytotoxicity), and Ksat. Our study showed that prediction efficiency is a strong function of mean nutrient/analyte concentration in the soil. We further demonstrated that near-infrared reflectance spectroscopy error rates were comparable to, and in some cases smaller than, laboratory analytical error rates, suggesting that the observed low spectral prediction efficiency may be substantially because of uncertainty in the laboratory data.

Concentration of cadmium in cacao beans and its relationship with soil cadmium in southern Ecuador.

Cadmium (Cd) content in cacao beans above a critical level (0.6 mg kg(-1)) has raised concerns in the consumption of cacao-based chocolate. Little is available regarding Cd concentration in soil and cacao in Ecuador. The aim of this study was to determine the status of Cd in both, soils and cacao plants, in southern Ecuador. Soil samples were collected from 19 farms at 0-5, 5-15, 15-30, and 30-50 cm depths, whereas plant samples were taken from four nearby trees. Total recoverable and extractable Cd were measured at the different soil depths. Total recoverable Cd ranged from 0.88 to 2.45 and 0.06 to 2.59, averaged 1.54 and 0.85 mg kg(-1), respectively in the surface and subsurface soils whereas the corresponding values for M3-extractable Cd were 0.08 to 1.27 and 0.02 to 0.33 with mean values of 0.40 and 0.10 mg kg(-1). Surface soil in all sampling sites had total recoverable Cd above the USEPA critical level for agricultural soils (0.43 mg kg(-1)), indicating that Cd pollution occurs. Since both total recoverable and M3-extractable Cd significantly decreased depth wise, anthropogenic activities are more likely the source of contamination. Cadmium in cacao tissues decreased in the order of beans>shell>>leaves. Cadmium content in cacao beans ranged from 0.02 to 3.00, averaged 0.94 mg kg(-1), and 12 out of 19 sites had bean Cd content above the critical level. Bean Cd concentration was highly correlated with M3- or HCl-extractable Cd at both the 0-5 and 5-15 cm depths (r=0.80 and 0.82 for M3, and r=0.78 and 0.82 for HCl; P<0.01). These results indicate that accumulation of Cd in surface layers results in excessive Cd in cacao beans and M3- or HCl-extractable Cd are suitable methods for predicting available Cd in the studied soils.

Distribution and fractionation of phosphorus, cadmium, nickel, and lead in calcareous soils amended with composts.

Abstract Composts improve organic carbon content and nutrients of calcareous soils but the accumulation and distribution of phosphorus and heavy metals among various fractions in soil may vary under the south Florida conditions. The accumulation of P, Cd, Ni, and Pb with depth and the distribution of water soluble, exchangeable, carbonate, Fe–Mn oxides, organic and residual forms of each element were investigated in soils amended with municipal solid waste (MSW) compost, co-compost and biosolids compost and inorganic fertilizer (as control). Total concentrations of P, Cd, Ni, and Pb were higher in the 0–22 cm soil layers and decreased considerably in the rock layers. These elements were in the decreasing order of P ≫ Pb > Ni > Cd. Amounts of water soluble and exchangeable forms of P, Cd, Ni and Pb were negligible at 0–22 cm soil depths except for Cd in the 10–22 cm depth. Amending calcareous soil with either organic or inorganic amendments rendered phosphorus, nickle and lead in the residual form followed by Fe–Mn oxides form in the 0–10 and 10–22 cm soil layers. Cadmium was predominantly in the Fe–Mn oxides fraction followed by the residual and carbonate forms in both soil layers. A significant positive correlation was found between various organic carbon fractions and organic forms of P, Cd and Pb in the surface soil layer. Soil amended with MSW compost had higher concentration of Cd in the organic fraction whereas, co-compost and MSW compost amended soil had higher concentrations of organic Ni fraction in the 0–10 cm soil layer.

Comparing phosphorus indices from twelve southern U.S. states against monitored phosphorus loads from six prior southern studies.

Forty-eight states in the United States use phosphorus (P) indices to meet the requirements of their Natural Resources Conservation Service (NRCS) Code 590 Standard, which provides national guidance for nutrient management of agricultural lands. The majority of states developed these indices without consultation or coordination with neighboring states to meet specific local conditions and policy needs. Using water quality and land treatment data from six previously published articles, we compared P loads with P-Index values and ratings using the 12 southern P indices. When total measured P loads were regressed with P-Index rating values, moderate to very strong relationships (0.50 to 0.97) existed for five indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina) and all but one index was directionally correct. Regressions with dissolved P were also moderate to very strong ( of 0.55 to 0.95) for the same five state P indices (Arkansas, Florida, Georgia, North Carolina, and South Carolina); directionality of the Alabama Index was negative. When total measured P loads were transformed to current NRCS 590 Standard ratings (Low [<2.2 kg P ha], Moderate, [2.2-5.5 kg P ha], and High [>5.5 kg P ha]) and these ratings were then compared to the southern-Index ratings, many of the P indices correctly identified Low losses (77%), but most did not correctly identify Moderate or High loss situations (14 and 31%, respectively). This study demonstrates that while many of the P indices were directionally correct relative to the measured water quality data, there is a large variability among southern P indices that may result in different P management strategies being employed under similar conditions.

Root distribution under seepage-irrigated potatoes in Northeast Florida

Much of commercial potato production in Florida is irrigated using sub-surface seepage irrigation. A perched water table is maintained during the season within 50 cm below the top of the potato ridge. Fertilizer placement is critical in this system to maximize plant uptake and to minimize leaching potential. Optimal placement of fertilizers is dependent on root distribution. The objectives of this study were to develop and test a new methodology to spatially describe potato root distribution as affected by nitrogen rate and irrigation system. Soil slices containing representative samples of the potato root system at full flowering were taken from plots fertilized with ammonium nitrate at 168, 224, and 280 kg N ha−1. The proposed sampling methodology performed satisfactorily. Root length density (cm root cm−3 soil) and specific root length (cm root mg−1 root dry weight) were not affected by nitrogen rate, but were affected by spatial position in the soil profile. The highest root length density value (0.72 average) was observed within 12 to 15 cm of the seedpiece. Low root length density values averaging 0.036 were observed between 24 and 36 cm from the top of the ridge. Specific root length values indicated a relatively homogeneous root system in terms of the quantity of invested biomass by unit of root length except in the two central units below 24 cm from the top of the ridge where thickened roots caused significant lower values averaging 6.47 as compared with the average of 15.87 from the surrounding Units in the slice. Root thickening in deep apical roots suggested aerenchyma formation promoted by a combination of saturated soil conditions in the root zone caused by inappropriate irrigation management and soil compaction. Fertilizer placement under the seedpiece should be a good alternative to increase potato nitrogen uptake under seepage irrigation.ResumenLa producción comercial de papa en la Florida es irrigada por percolación sub-superficial. Durante la temporada de producción el nivel freático se mantiene a 50 cm por debajo de la cima del caballón donde la papa ha sido sembrada. La localización del fertilizante es un punto crítico en este sistema para maximizar la absorción y minimizar el potencial de lixiviación. La localización óptima del fertilizante depende de la distribución de las raices. Los objetivos de este estudio fueron desarrollar y validar una nueva metodología para describir espacialmente la distribución de las raices de la papa bajo efecto de la dosis de nitrógeno y el sistema de irrigación. En plena floración de la papa fueron muestreados perfiles de suelo conteniendo muestras representativas del sistema radicular de parcelas fertilizadas con nitrato de amonio en dosis de 168, 224, y 280 kg N ha−1. La metodología propuesta funcionó satisfactoriamente. La densidad de longitud de raíces (cm raiz cm−3 suelo) y la longitud radicular específica (cm raiz mg−1 peso seco de raiz) no fueron afectadas por la dosis de nitrógeno pero si por su posición espacial en el perfil del suelo. Los valores mas altos de densidad de longitud de raíces (0.72 en promedio) fueron observados en una zona de 12 a 15 cm circundando la semilla. Entre 24 y 36 cm de profundidad fueron observados valores bajos de densidad de longitud de raíces con 0.036 en promedio. Los valores de longitud radicular específica indicaron un sistema radicular relativamente homogéneo en términos de la cantidad de biomasa invertida por unidad de longitud radicular excepto en los dos ambientes centrales por debajo de 24 cm de profundidad donde raíces engrosadas causaron bajos valores significativos promediando 6.47 comparados con el valor promedio de 15.87 observado en el resto de los ambientes estudiados. El engrosamiento apical en raíces profundas sugieren la formación de aerénquima promovido por la combinación de saturación del suelo en la zona radicular causada por manejo inapropiado de la irrigación, y compactación del suelo. La colocación del fertilizante debajo de la semilla de la papa podría ser una buena alternativa para incrementar la absorción de nitrógeno en condiciones de irrigación por percolación.

Phosphorus soil tests for environmental assessment in subtropical soils

Abstract Soil test phosphorus (P) is used to evaluate the nutritional status of a soil in relation to a crops yield response. Recently, there is interest to calibrate agronomic soil tests to predict risk of P transport in runoff. An experiment was conducted to evaluate the relationships among three agronomic soil test P extraction methods (Olsen, Bray1, Mehlich3) and dissolved P in water (0.01 M CaCl2 extractable P) in five representative soils of tropical and subtropical areas in Puerto Rico and Florida. The soils were of the series Astatula (Entisol), San Antón (Mollisol), Caguabo (Inceptisol), Corozal (Ultisol), and Bayamón (Oxisol). Soils were amended with three inorganic P levels as triple super phosphate, three organic P levels as broiler litter, and their combinations in an incomplete factorial design for a total of 11 treatments. Soils were sampled during 46 weeks and soil test P was measured. Exploratory statistics were used to evaluate relationships among the variables. Relationships using the Astatula soil were studied separately as inherently high soil test P values influenced regressions greatly. A near 1:1 relationship between soil test P extracted using Bray1 and Mehlich3, and Mehlich3 and Olsen extractants was obtained. In general, improved relationships were obtained using individual soils as soil pH and mineralogy influenced the amount of P extracted. Critical soil test concentrations to reach dissolved P concentrations of 1 mg P L−1 were (95% confidence intervals in parenthesis) 179 (174–185), 197 (190–207), and 252 (243–266) ppm for Olsen, Bray1, and Mehlich3 extractants, respectively for all soils combined excluding Astatula. The critical values obtained in combination with soil-landscape information can be used to establish guidelines for P management in agricultural soils.

Potato (solarium tuberosum l.) yield and internal heat necrosis incidence under controlled-release and soluble nitrogen sources and leaching irrigation events

Best management practices (BMPs) have been developed for northeast Florida potato production with the objective of reducing N fertilizer use while main-taining tuber yield and quality. However, rainfall timing and intensity can affect soil N availability, tuber yield, and quality. Objectives of this study were to determine the influence of fertilizer source (soluble and controlled-release) and timing of leaching irrigation on tuber yield and quality of ‘Atlantic’ potato in a seepage-irrigated production system. The experiment was conducted in 2004 and 2005 as a split-split plot with four replications. Main effects were leaching irrigation treatments (no-leaching irrigation and leaching irrigation at 2, 4, 8 and 12 weeks after planting [WAP]), N source (ammonium nitrate [AN] at 224 kg ha-1 or controlled-release fertilizer [CRF] at 196 kg ha-1), and supplemental N sidedress application (34 kg N ha-1). In 2004, total and marketable tuber yields for plants in the 8 and 12 WAP leaching treatments were 10% and 11% lower, respectively, than plants in the no-leaching treatment. In 2005, marketable tuber yields from plants in the no-leaching treatment were significantly higher than plants in the 4, 8 and 12 WAP leaching treatments. Plants in CRF treatments produced significantly higher marketable tuber yields in both years compared with plants in AN fertilizer treatments. Supplemental N sidedressing did not improve tuber yield or quality in either year. Plants in the CRF treatment had a higher incidence of tubers with internal heat necrosis (IHN) in 2004 and 2005 compared with plants in the AN fertilizer treat-ment. This suggests that under severe leaching pres-sures, CRF needs a faster soil nutrient “recharge” to reduce plant nutrient stress. Plants in the CRF treatment averaged 12% higher marketable tuber yields with 13% less N applied compared with the AN treatment. Overall, CRFs are well suited as a BMP for northeast Florida potato production.ResumenPara la producción de papa en el noreste de Florida se han desarrollado unas mejores prácticas de mane jo (BMPs) con el objeto de reducir el uso de la fertilización con N mientras se mantiene el rendimiento y la calidad del tubérculo. Sin embargo, el momento e intensidad de lluvias pueden afectar la disponibilidad de N en el suelo, la calidad y rendimiento de tubérculos. Los objetivos del presente estudio fueron determinar la influencia de la fuente del fertilizante (soluble y de liberación controlada) y momento de irrigación por lixiviación sobre el rendimiento y calidad del tubérculo de papa ‘Atlantic’ con el sistema de producción subirrigado. El experimento se realizó en 2004 y 2005 como parcela subdividida con cuatro repeticiones. Los efectos principales fueron los tratamientos de irrigación por lixiviación (irrigación sin y con lixiviación a las 2, 4, 8 y 12 semanas después de la siembra [WAP]), fuente de N (nitrato de amonio [AN] a 224 kg ha--1 o liberatión controlada de fertilizante [CRF] a 196 kg ha-1) y aplicación suplementaria en bandas de N (34 kg N ha-1). En 2004, el rendimiento total y comercial de tubérculos en los tratamientos de lixiviación de 8 y WAP fueron 10% y 11% más bajos, respectivamente que en plantas en el tratamiento sin lixiviación. En 2005, el rendimiento de tubérculos comerciables de plantas en el tratamiento sin lixiviación fueron significativamente más altos que en plantas en los tratamientos con lixiviación de 4, 8 y 12 WAP. Las plantas en los tratamientos CRF dieron rendimientos más altos de tubérculos en ambos años en comparación con plantas de los tratamientos con fertilizante AN. El tratamiento con N suplementario en bandas no mejoró el rendimiento o la calidad de los tubérculos en ambos años. Las plantas en el tratamiento CRF tuvieron una alta incidencia de necrosis interna (IHN) en 2004 y 2005 en comparación con plantas en el tratamiento del fertilizante AN. Esto sugiere que bajo severa presión de lixiviación, el CRF necesita una “recarga” más rápida de nutrientes para reducir el estrés de la planta por nutrientes. Las plantas en el tratamiento CRF dieron un 12% más de tubérculos comerciables con 13% menos de N aplicado en comparación con el tratamiento AN. Los tratamientos CRF convienen más como un BMP para la productión de papa en el noreste de Florida.

Nitrate-nitrogen concentrations in the perched ground water under seepage-irrigated potato cropping systems.

Excessive nitrogen rates for potato production in northeast Florida have been declared as a potential source of nitrate pollution in the St. Johns River watershed. This 3-yr study examined the effect of N rates (0, 168, and 280 kg ha(-1)) split between planting and 40 d after planting on the NO(3)-N concentration in the perched ground water under potato (Solanum tuberosum cv. Atlantic) in rotation with sorghum sudan grass hybrid (Sorghum vulgare x Sorghum vulgare var. sudanese, cv. SX17), cowpea (Vigna unguiculata cv. Iron Clay), and greenbean (Phaseolus vulgare cv. Espada). Soil solution from the root zone and water from the perched ground water under potato were sampled periodically using lysimeters and wells, respectively. Fertilization at planting increased the NO(3)-N concentration in the perched ground water, but no effect of the legumes in rotation with potatoes on nitrate leaching was detected. Fertilization of green bean increased NO(3)-N concentration in the perched ground water under potato planted in the following season. The NO(3)-N concentration in the soil solution within the potato root zone followed a similar pattern to that of the perched ground water but with higher initial values. The NO(3)-N concentration in the perched ground water was proportional to the rainfall magnitude after potato planting. A significant increase in NO(3)-N concentration in the perched ground water under cowpea planted in summer after potato was detected for the side-dressing of 168 kg ha(-1) N applied to potato 40 d after planting but not at the 56 kg ha(-1) N side-dress. Elevation in NO(3)-N concentration in the perched ground water under sorghum was not significant, supporting its use as an effective N catch crop.