Nitrogen Use Efficiency of Winter Wheat among Landscape Positions

Abstract

Spatially variable N fertilizer application may reduce environmental impacts and increase the economic return of N fertilization. To achieve these benefits, N recommendations must account for within‐field differences in the amount of N required to produce a unit of yield (unit N requirement, UNR). Component analysis was used to determine the sources of variation in the UNRs of winter wheat (Triticum aestivum L.) among landscape positions. The UNRs were divided into two components, N uptake efficiency (plant N/N supply) and N utilization efficiency (grain yield/plant N) observed in N rate trials (0–140 kg N ha−1 fall applications) established on footslope, south backslope, shoulder, and north backslope positions of two farms for 2 yr. Variation in the UNR among the 16 landscape positions studied was most associated with differences in N uptake efficiency (r = −0.80), although N utilization efficiency (r = −0.62) also contributed to the variation. Nitrogen uptake efficiency among landscape positions declined as more fertilizer was required to reach optimum yield (r = −0.56) due to low N fertilizer uptake efficiencies (Δplant N/ΔN fertilizer). Nitrogen fertilizer uptake efficiency was related to the degree of apparent N loss (r = −0.87), indicating that N availability limited N uptake efficiency among landscapes. Overall, low N fertilizer uptake efficiencies (<50%) and high N loss percentages (>50%) indicate the need to reduce N losses and lower UNRs, particularly on north‐facing backslopes susceptible to N leaching.

Soil Fertility in relation to Landscape Position and Land Use/Cover Types: A Case Study of the Lake Kivu Pilot Learning Site

“…Many other studies on volcanic soils demonstrated that N turnover in the volcanic soil may not be solely interpreted in terms of C/N ratios [48][49][50]. Perhaps temperature differences, the level of weathering of the parent rock, landuse/cover change, soil management, and hillslope processes and interactions explain the differences in C/N ratios between the two soils of volcanic origin [50][51][52][53].…”

Variability in Optimum Nitrogen Rates for Maize

“…Fiez et al (1995) suggested that the different N response between and within fields was due to spatial and temporal variations in crop demand. The optimum N fertilizer rate changes dramatically from one maize field to the next because it is affected by the complex interactions of spring precipitation, temperature patterns, soil organic matter, and crop development (Scharf, 2001;Scharf et al, 2005).…”

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

“…While a portion of this variability was teased out by differences in year-to-year precipitation, other environmental, genetic, and management factors contribute to within-site variability, such as landscape elevation, slope, aspect (Mulla et al, 1992;Fiez et al, 1994;Yang et al, 1998), subsoil constraints , spring rainfall , crop rotation (Hammel, 1995), nutrient availability (Fiez et al, 1995), onset of drought and temperature stress (Gizaw et al, 2016), and crop genetics . Despite the heterogeneity of the landscape, iPNW growers still commonly apply single rates of fertilizer, particularly in the higher precipitation areas (Mahler et al, 2014).…”

“…In addition to conserving soil water, the reduction or elimination of tillage is a strategy to combat water and wind erosion (Singh et al, 2012;Williams et al, 2014) in combination with continuous annual cropping (Thorne et al, 2003;Feng et al, 2011). Heterogeneous topography also challenges nutrient management due to significant variability in plant-soil-nutrient interactions and crop performance (Fiez et al, 1994(Fiez et al, , 1995 with opportunities for site specific N fertilizer management to mitigate differences in water and N use efficiencies across the landscape (Miao et al, 2011). A combination of these alternative cropping system strategies may increase productivity and economic returns (Tanaka et al, 2002;Alam et al, 2015;Babu et al, 2016), and multiple strategies may be needed (Kirkegaard and Hunt, 2010;Snapp et al, 2010).…”