Timing of application

Fertiliser application should be timed to achieve maximum plant uptake, thereby reducing losses of nutrient to the environment. Ideal timing will be affected by the solubility (mobility) of the nutrient or fertiliser used, crop stage and rate of growth (and therefore its nutrient demand) and the nutrient fixing capability of the soil. Consider also the amount of rainfall and/or irrigation experienced or expected.

Applying fertiliser long before the plant will take up the nutrient exposes the nutrient to potential loss. This is particularly so with nitrogen fertilisers. Maximum responses and minimal nutrient losses will usually occur if fertiliser is applied when plants are growing rapidly. It is especially important to apply highly mobile nutrients at times when plants are actively growing to avoid losses to the environment between application and plant uptake, and thus to maximise the return on the investment. This is particularly important when highly soluble nutrients are applied in high rainfall or irrigation situations.

Application of fertiliser in relation to soil and air temperatures is also important because these conditions affect plant growth and hence nutrient use. For example, applying nitrogen fertiliser to ryegrass when soil temperatures are less than 6°C and falling is likely to be ineffective in stimulating pasture growth because ryegrass stops growing at soil temperatures below 4°C. If it will be some time before temperatures rise and the ryegrass starts to grow again (and take up the nitrogen), the nitrate may be lost through leaching. Nitrogen fertiliser application should be delayed until the pasture is actively growing, especially if considerable rainfall is expected in the meantime.

Fertiliser often requires water to move it to a site where it can be taken up by plants and, in the case of nitrogen, where it is protected from gaseous losses. Timing of fertiliser application in relation to irrigation or rainfall can be critical to determining the risk of gaseous loss.