As farming intensification increases, so does the need for greater precision in fertiliser application. Intensification brings a greater risk of negative impacts on farm profits and on the environment through errors and inefficiencies in fertiliser application.

Recommendations and nutrient management plans from fertiliser and agricultural consultants assume the fertiliser material will be spread evenly and accurately over the target area at the target application rate. Poor spreading can negate the best management plans and result in significant production losses and loss of nutrients to water. Knowing what should be done is important. Knowing what is actually done is important too.

Most fertiliser applicator manufacturers provide guidelines to calibrate equipment. However, usually only the bulk application per hectare is determined, not the uniformity of application. This is a critical omission, as poor distribution significantly impacts yield and increases risk of leaching losses.

Excessive variation is undesirable as it has a negative impact on crop or pasture performance and can increase leaching losses.

Søgaard and Kierkegaard* concluded that a spatial coefficient of variation less than 20% was necessary to prevent loss of profit in agronomic crops. This will always be a function of the nutrient used and a plants response to it, the economic relationship between plant growth and fertiliser input as well as costs involved in applying the fertiliser. It is now generally accepted that for nitrogen fertilisers, the CV should not exceed 15%. For other fertilisers types a CV not exceeding 25% is acceptable (Yule and Grafton, 2013#).

The guidelines presented in this course are designed to provide a cost-effective method for farmers to quickly check actual performance to assure themselves and others their applications are as expected.

* Søgaard, H.T. and Kierkegaard, P. 1994. Yield Reduction Resulting from Uneven Fertilizer Distribution, Trans. of ASAE, Vol. 37(6), Pp 1749 – 1752
# Yule, I.J. and Grafton, M.C.E. 2013. New Spreading Technologies for Improved Accuracy and Environmental Compliance.