Assessment of Spatially Variable Nitrogen Fertilizer Management in Winter Wheat

Abstract

Spatially variable N application may improve N use efficiency, grain yield, and net returns of winter wheat (Triticum aestivum L.) in fields exhibiting wide ranges of soil characteristics. The objectives of this study were to (i) determine the variability in optimal economic grain yield and in the amount of N required to produce a unit of grain at optimum yield, the unit N requirement (UNR), among landscape positions; (ii) evaluate landscape position as a criterion for dividing fields into units of equal productivity; and (iii) assess the economic benefits of spatially variable N fertilizer application. Replicated N rate (0 to 125 lb N/acre) experiments were established on footslope, south‐backslope (S‐backslope), shoulder, and north‐backslope (N‐backslope) positions of the hillslope profile at two eastern Washington farms in 1990 and 1991. Yield potential among these landscape positions varied by up to 63% and UNRs varied by up to 70%. Landscape position, however, was not an adequate criterion for dividing fields into equal productivity units. There was little economic benefit from variable N applications in a hypothetical case analysis if N recommendations were calculated assuming a constant UNR, however, if experimentally determined UNRs were used, variable applications increased net returns by up to $14.80. The degree of economic benefit depended on the levels of misapplication that occurred when a single N rate was applied to a field and the yield responses to N which determined the results of misapplication. Spatially variable N fertilizer management will require accurate estimates of yield potential, UNR, mineralization and available soil N to be economically viable. Research Question Due to variations in soil characteristics and yield potential, N requirements can vary widely within fields. However, farmers typically apply a single N rate across a field resulting in areas of over‐ and under‐application, which may affect water quality and grower income. Varying N rates within fields to match the site‐specific needs can reduce fertilizer misapplication. This study was designed to (i) determine the variation in grain yield and N requirements per bushel of winter wheat among landscape positions, (ii) evaluate landscape position as an indicator of yield potential, and (iii) assess the benefits of varying N fertilizer rates within fields. Literature Summary Several approaches for varying fertilizer rates within fields have been proposed. Montana researchers have varied fertilizer rates within fields by soil type. Others have intensively grid sampled soils and used the soil test results to divide fields into uniform areas based on projected yields and residual N levels. In addition to yield potential, N fertilizer recommendations are based on the amount of N required to produce a unit of grain at optimum yield, the unit N requirement (UNR). Past studies of variable N management have been based on the assumption that UNR is constant. Yet, the UNR probably varies within fields due to differences in soil and enviro...

Soil moisture and nutrient variation within an undulating Manitoba landscape

“…Explanation of systematic differences in plant-available N as a function of landscape requires integration of soil properties, N-cycling, previous management and cropping effects (Fiez et al 1994). As a result, complex patterns of net supply and crop uptake may preclude accurate prediction of soil residual nitrate levels, the most agronomically important form of mineral N, in the soil profile.…”

“…Spring residual nitrate concentrations may be spatially random (Mulla 1993), greater in convergent areas (Malo and Worcester 1975), or greater in divergent areas (Farrell et al 1996). Nonetheless, total N concentration and mineralization often increases with organic matter and convergent landscape character (Fiez et al 1994).…”

Comparison of Greenhouse Gas Offset Quantification Protocols for Nitrogen Management in Dryland Wheat Cropping Systems of the Pacific Northwest

“…For SWWW under sample project 1, we assumed that site specific N management could, on average, result in a 25 kg N ha −1 decrease in N fertilizer rate compared to uniform N management without decreasing yield (Mulla et al, 1992;Fiez et al, 1994a;Huggins, 2010;Taylor, 2016). For HRWW and HRSW under sample projects 2 and 3, we assumed that site specific N management could, on average, result in a 10 and 20 kg N ha −1 decrease in N fertilizer rate compared to uniform N management without decreasing yield or grain protein concentration, respectively (Huggins, 2010).…”

“…However, variability in wheat yield and N requirement has been observed across agricultural fields within the Palouse region of the iPNW (Mulla et al, 1992;Fiez et al, 1994a,b;Huggins, 2010). For example, Fiez et al (1994a) reported soft white winter wheat grain yield to vary by up to 63% and the UNR to vary by up to 70% in the Palouse. Sowers et al (1994) observed split N applications in winter wheat to produce similar grain yield with 25-40% less N. This indicates that variable rate and/or split N fertilizer application have the potential to reduce overall N rate without decreasing yield.…”

Utilização de sensores de dossel para adubação nitrogenada no algodoeiro

“…Esta variação, decorrente da ação de agentes naturais, assim como da ação antrópica, deve se manifestar com maior intensidade em algumas propriedades do que em outras (PRIMAVERA, 1998 A aplicação de fertilizantes em taxa variada, baseada na variabilidade do solo dentro de um campo, tem um potencial para reduzir sub e sobre doses, e assim melhorar a eficiência de uso de fertilizantes, o rendimento das culturas e o lucro líquido da propriedade (FIEZ et al, 1994).…”