Within-field variability of wheat yield and economic implications for spatially variable nutrient management

Abstract

Economic justification for varying fertiliser inputs to match crop yield potential of different areas or zones in fields is limited by lack of understanding of the relationship between the extent of within-field yield variation and economic gains from zone vs. uniform management. We conducted a survey of yield monitor data from 199 fields on the northern sandplain of the wheatbelt in Western Australia in order to document the extent of sub-field yield variation and test if variation is related to attributes such as yield and field area. The economic significance to zone management of the yield variation found in the survey along with variation in size of management zones, costs and prices, and soil fertility status was then assessed using a simple nutrient response model. Considerable variation occurred in yield within fields. Standard deviation varied from 0.2 to 1.2 t/ha and the difference in yield between the highest and lowest yielding thirds of each field varied from 0.5 t/ha in the least to 3.3 t/ha in the most variable field. Both small and large (10 to 172 ha), and low and high (0.6 to 4.9 t/ha) yielding fields exhibited variation that was potentially worth managing from an economic standpoint. Model results showed that the larger the difference in potential yield between zones, the greater the economic benefit from zone management. While yield contrast within fields can be increased with more zones, the economic advantage of more zones was small for the cases studied here. The potential economic benefits (from <$5/ha to $44/ha) increased with higher grain and fertiliser prices and depended on levels of soil nutrients in the different zones. Capturing the full value of the economic benefits in practice requires an accurate indication of yield potential in the different zones at the time when the fertiliser decision is being made. Yield maps can be utilised by growers to give estimates of within-field variation in yield potential and hence potential economic gains from variable rate application of fertiliser.

Adoption of variable rate fertiliser application in the Australian grains industry: status, issues and prospects

“…'', and ''What is holding you back in adopting PA?''. For the purposes of defining ''manageable variability'' we followed the rule-of-thumb developed by Robertson et al (2008) where a difference between zones in wheat yield potential of at least 1 t/ha would constitute enough to justify financially the use of variable rate application of fertiliser.…”

“…Published Australian studies of economic analysis of VR fertiliser in broadacre grain production include experimental comparisons, case studies of farmers who have adopted the technology, and economic modelling based on both representative and actual farms and fields (Brennan et al 2007;Robertson et al 2007;Robertson et al 2008;Robertson et al 2009). The benefits range from close to zero to around AUD50/ha.…”

Nutrient Management in Support of Environmental and Agricultural Sustainability

“…It does seem likely, however, that N 2 O emission and NO -3 leaching can be reduced by applying N in a spatially variable way, since several studies have found no loss of yield with a reduction in total N applied (e.g. [33][34][35]). Savings in these terms have rarely been identified in the literature but could be substantial in global or national terms if most emissions derive from the under-use of applied N by crops (perhaps 1-2 kg N 2 O-N ha …”

Testing the Temporal Ability of Landsat Imagery and Precision Agriculture Technology to Provide High Resolution Historical Estimates of Wheat Yield at the Farm Scale

“…Firstly, they could assist growers who have not yet adopted, or those who have recently adopted, precision agriculture technology to more readily access its benefits by extending the length of the dataset that is available for crop management decision making [34,35]. This would allow land managers to assess the spatially explicit nature of productivity, fertiliser requirements and profitability of their fields from a longer time series [36] and therefore leap-frog the time consuming process of archiving annual yield maps generally used in this assessment process.…”