To combat falling productivity comprehensive nutrient budgeting is essential for improving farm productivity and agricultural resilience.
Understanding nutrient budget requires careful measurement of the difference between what is being exported within crops or being lost from the land (e.g., as soil adhering to roots, through erosion, leaching or loss to the atmosphere), as well as, what nutrients may be being imported through natural processes (weathering of parent material, nitrogen fixation, decay of plants, rainfall, bird or animal droppings).
Knowing what natural or artificial fertiliser inputs are required to balance this nutrient budget enables farmers to reach an optimal outcome where production is sustained, while costs are minimised, and environmental impacts avoided.
For example, nutrient imbalance has been a persistent issue in soils used for sugar cane in Fiji. Production began in the 1880s and fertiliser use increased after the Second World War. Up to the 1980s, the use of particular fertilizers resulted in excess inputs of N and less than appropriate inputs of P and K (Morrison et al., 1985, 2005). After significant debate and review, blended fertilisers were introduced in the early 1990s and this has led to a more balanced input of N, P and K. However, topsoil Ca and Mg contents have dropped dramatically and this has been attributed to a continuous removal of Ca and Mg in harvested cane and by erosion. In most years, less than replacement quantities of these elements are being added in fertilisers. Another contributing factor has been a dramatic decrease in liming on sugarcane farms.
