Opportunities for variable rate application of nitrogen under spatial water variations in rainfed wheat systems—an economic analysis

Abstract

In fields of undulating topography, where rainfed crops experience different degrees of water stress caused by spatial water variations, yields vary spatially within the same field, thus offering opportunities for variable rate application (VRA) of nitrogen fertilizer. This study assessed the spatial variations of yield gaps caused by lateral flows from high to low points, for rainfed wheat grown in Córdoba, Spain, over six consecutive seasons (2016–2021). The economic implications associated with multiple scenarios of VRA adoption were explored through a case study and recommendations were proposed. Both farm size (i.e., annual sown area) and topographic structure impacted the dynamics of investment returns. Under current policy-price conditions, VRA adoption would have an economic advantage in farms similar to that of the case study with an annual sown area greater than 567 ha year−1. Nevertheless, current trends in energy prices, transportation costs and impacts on both cereal prices and fertilizers costs enhance the viability of VRA adoption for a wider population of farm types. The profitability of adopting VRA improves under such scenarios and, in the absence of additional policy support, the minimum area for adoption of VRA decreases to a range of 68–177 ha year−1. The combination of price increases with the introduction of an additional subsidy on crop area could substantially lower the adoption threshold down to 46 ha year−1, making VRA technology economically viable for a much wider population of farmers.

Use of supervised and unsupervised approaches to make zonal application maps for variable-rate application of crop growth regulators in commercial cotton fields

“…Therefore, for VR applications to be more profitable in these scenarios, other operational costs must not exceed the margin of savings they provide from the applied input. As noted by Lawes and Robertston (2011) (Plant, 2001;Lawes and Robertson 2011;Fabiani et al 2020;Tenreiro et al 2023); studies that found no significant differences from a uniform rate approach (Boyer et al 2011); and studies that noted that the overall economic benefits of this type of management in small-scale farming are low (Späti et al 2021).…”