This is why the definition focuses on maximising their use efficiency. Agronomic efficiency (AE) is defined as the extra produce generated (in kg) per unit of nutrients applied (in kg).

  • Fertiliser and improved germplasm. In terms of response to management, two general classes of soils are distinguished: (i) soils that show acceptable responses to fertiliser (Step A – blue line, Figure 2) and (ii) soils that show minimal or no response to fertiliser due to other constraints besides the nutrients contained in the fertiliser (Step B – green line, Figure 2). We have classified above soils as ‘responsive soils’ and ‘poor, less-responsive soils’ respectively. In some cases, where land is newly opened, or where fields are close to homesteads and receive large amounts of organic inputs each year, a third category of soil exists where crops respond little to fertiliser as the soils are fertile. These soils need only maintenance fertilisation and are termed ‘fertile, less responsive soils’.