Comparison of Some Approaches to Determine Spatial Dependence of Soil Properties

Knowledge of variability and spatial structure of soil properties is essential for optimal design for collecting soil samples and effectively applying management decisions in the field. The objective of this study is to compare some approaches for characterizing, and comparing spatial dependence of isotropic second-order stationary processes. The evaluated approaches are the nugget to sill ratio (NR), normalized (by fitted sill) semivariogram, correlograms, and two integral scales. Soil samples, collected at a regular 50 m × 50 m grid from 0-15 cm depths, were analyzed for sand and clay, bulk density (b), saturated hydraulic conductivity (Ks), wilting point, available water content (AWC), pH, electrical conductivity (EC), nitrate-nitrogen (NO3- N), and chloride (Cl) were determined. Geostatistical software (GS+, Gamma Design Software, Plainwell, MI) was used to estimate the variance structure of various measured soil properties. Analysis include using data on the spatial variability of various properties from four published studies. NR displayed spatial dependence ignoring the influence of range, normalized semivariogram and correlogram provided the visual comparison, and both integral scales incorporated the influence of range and provided single number spatial dependence summaries. Either of the integral scale formulations can be used to characterize the spatial dependence of soil properties from agricultural fields

Numerical Evaluation of Nitrate Distributions in the Onion Root Zone under Conventional Furrow Fertigation

HYDRUS (2D/3D) model was used to simulate spatial and temporal distributions of nitrate-nitrogen (NO3-NNO3-N) within and below the onion root zone under conventional furrow fertigation with the urea-ammonium-nitrate (UAN) liquid fertilizer. The simulated water contents in the furrow irrigated onion field agreed well with the measurements. Simulations produced similar patterns of the measured NO3-N concentration profiles throughout the growing season. NO3-N concentrations remained higher and accumulation of NO3-N was observed within the root zone. Higher NO3-N within the root zone was dependent on the rate of the UAN fertilizer application, quantity of NO3-N removed by root uptake, and NO3-N drainage fluxes below the root zone. Simulations also suggested that NO3-N below the root zone during different growth stages remained much higher than a recommended (for drinking water) standard concentration level (10 mg L-1). This resulted in higher NO3-N drainage fluxes, particularly during the fertigation events between the establishment and vegetative growth stages. This indicates the need to apply most fertigation events at an early stage of bulb formation to provide the maximum NO3-N demands by onions and to reduce potential NO3-N leaching

Available plant nutrients in soil as influenced by planting methods and herbicidal treatments

Rice (Oryza sativa L.)-wheat (Triticum aestivum L.) is the predominant cropping system of North Indian region. Due to continuous following of rice-wheat cropping system every year, weed infestation particularly in wheat, has emerged a major problem resulting in reduced wheat yield and nutrient mining. Integration of suitable planting methods, along with effective weed control measures, can reduce the weed infestation and nutrient mining from the soil and can enhance available plant nutrients in the soil. To evaluate the influence of different planting techniques and weed control practices in wheat on available plant nutrients in soil, a field study was conducted at the department of Agronomy, Punjab Agricultural University, Ludhiana (India) for two consecutive years. The treatments comprised of five planting techniques: conventional tillage, zero till sowing without rice stubbles, zero till sowing in standing rice stubbles , zero till sowing after partial burning of rice stubbles and bed planting and five weed control treatments i.e. clodinafop 60 g/ha, clodinafop 60 g/ha fb 2, 4-D 0.5 kg/ha, sulfosulfuron 25 g/ha, mesosulfuron + iodosulfuron 12 g/ha and unweeded (control). The experiment was conducted in split plot design with planting methods in the main plot and herbicidal treatments in the sub plot with three replications. The results of the study showed that zero till sowing of wheat in standing rice stubbles observed significantly higher soil organic carbon, available nitrogen, phosphorus and potassium than conventional till wheat sowing after removal of rice residues. Although partial burning of rice stubbles also showed positive trend in soil organic carbon, available nitrogen, phosphorus and potassium but retort was less distinct than rice stubbles without burning. Further, zero tillage alone also showed improvement in soil organic carbon and available nitrogen, phosphorus and potassium over conventional tillage. Application of herbicides did not diverge soil organic carbon, but significantly improved the available nitrogen, phosphorus and potassium content in soil than the unweeded (control)

Nitrate-Nitrogen Leaching from Onion Bed under Furrow and Drip Irrigation Systems

Water is a limited resource for crop production in arid areas of Southern New Mexico. The objectives of this study were to estimate the amount and depth of water and nitrate-nitrogen (NO 3 -N) fronts, water and NO 3 -N balances, and irrigation efficiencies for two onion (Allium cepa L.) fields under furrow and drip irrigation systems. Monthly soil samples were analyzed for −1 for drip-irrigated fields. The irrigation efficiencies varied from 78 to 80% for furrow-and 83% for drip-and N application efficiencies (NAEs) were 35 to 36% for furrow-and 38 to 39% for drip-irrigated fields. Small N fertilizer applications, delayed until onion bulbing starts, and water applications, preferably through drip irrigation, are recommended to reduce deep percolation and increase nitrogen and water efficiencies

Numerical Evaluation of Nitrate Distributions in the Onion Root Zone under Conventional Furrow Fertigation

HYDRUS (2D/3D) model was used to simulate spatial and temporal distributions of nitrate-nitrogen (NO3-NNO3-N) within and below the onion root zone under conventional furrow fertigation with the urea-ammonium-nitrate (UAN) liquid fertilizer. The simulated water contents in the furrow irrigated onion field agreed well with the measurements. Simulations produced similar patterns of the measured NO3-N concentration profiles throughout the growing season. NO3-N concentrations remained higher and accumulation of NO3-N was observed within the root zone. Higher NO3-N within the root zone was dependent on the rate of the UAN fertilizer application, quantity of NO3-N removed by root uptake, and NO3-N drainage fluxes below the root zone. Simulations also suggested that NO3-N below the root zone during different growth stages remained much higher than a recommended (for drinking water) standard concentration level (10 mg L-1). This resulted in higher NO3-N drainage fluxes, particularly during the fertigation events between the establishment and vegetative growth stages. This indicates the need to apply most fertigation events at an early stage of bulb formation to provide the maximum NO3-N demands by onions and to reduce potential NO3-N leaching

Cluster and Principle Component Analysis of Soybean Grown at Various Row Spacings, Planting Dates and Plant Populations

Increased light interception (LI), along with concomitant increases in crop growth rate (CGR), is the main factor explaining how cultural factors such as row spacing, plant population, and planting date affect soybean yield. Leaf area index (LAI), LI, and CGR are interrelated in a “virtuous spiral” where increased LAI leads to greater LI resulting in a higher CGR and more total dry matter per area (TDM). This increases LAI, thus accelerating the entire physiological process to a higher level. A greater understanding of this complex growth dynamic process could be achieved through use of cluster analysis and principle components analysis (PCA). Cluster analysis involves grouping of similar objects in such way that objects in same cluster are similar to each other and dissimilar to objects in other cluster. PCA is a technique used to reduce a large set of variables to a few meaningful ones. Seasonal relative leaf area index (RLAI), relative light interception (RLI), and relative total dry matter (RTDM) response curves were determined from the data by a stepwise regression analysis in which these parameters were regressed against relative days after emergence (RDAE). Greatest levels of RLAI, RLI and RTDM were observed in soybean planted early on narrow row spacings and recorded greater plant population. In contrast, lower levels of these parameters occurred on plants with wide row spacings at late planting dates. For farmers, these results are useful in terms of adopting certain cultural practices which can help in the management of stress in soybean