Improving cropland N, P and K nutrient budgets through local and global data

Cropland nutrient budgets show the difference between the inputs and outputs of nutrients to an area of land over a specified period of time. They are useful to aid decision-making for nutrient management, both from an agricultural and environmental point of view, and can indicate ‘hot-spot’ locations with a surplus or deficiency in nutrients. Estimates of cropland nutrient budgets at national to global scales typically rely on average nutrient concentrations of crop components removed from the soil. Given the wide-spread use of nutrient budgets it is important that more locally relevant coefficients or models are developed. Using maize as an example, we assessed how much a country’s estimated nutrient removal is affected when using global (Tier 1), regional (Tier 2) or national/sub-national (Tier 3) estimates of harvest index and nutrient concentrations of crop products and crop residues. Estimates of cropland removal of nitrogen, phosphorus and potassium varied substantially (up to 54%), depending on which Tier approach was used. This had considerable impact on national nutrient budgets. Therefore, if Tier 2 data are not available, Tier 3 offers a methodology to overcome such data limitations through the application of models, trained on localized but widely available data for countries. The methodology used for maize will also be applied to other crops to improve cropland nutrient budgets and estimates of crop nutrient use efficiencies.