Precision fertilizer spreading, pure benefit

The effects of uneven fertilizer spreading remain invisible in most cases.

Only drastic variations are visible as dark and light stripes. However, losses set in long before any variation becomes visible to the naked eye. The cost of uneven spreading is mainly due to lost yield and lost quality. But the environmental burden and additional fertilizer cost shall not be neglected either. How to evaluate the cost of uneven fertilizer spreading?

Spreading profile and yield profile

This figure shows a typical cumulative spreading profile obtained with a trapezoidal configuration upon three fertilizer applications. The desired fertilization rate of 200 kg/ha has been applied on average, but the variation coefficient reaches 27 %. The mean yield is 79,9 dt/ha, whereas the potential yield amounts to 83,7 dt/ha. The lost yield is 3,8 dt/ha, representing lost earnings of 76 €/ha (at a wheat price of 200 €/ha).

Spreading variability

Marked color differences appear only when spreading variability exceeds 30%, significantly reducing yield and increasing the risk of lodging.

Calculating yield losses

The yield losses due to spreading variations can be calculated using the fertilizer response curve. This figure shows a typical response curve for wheat.

This table indicates the lost yield for different variation coefficients and fertilization at the agronomic optimum. For fertilization at the economic optimum, the variation coefficient has an even higher impact on yield.

This table indicates expected losses for different crops and variation coefficients with and without lodging.

Consequences of uneven fertilizer spreading

Spreading problems remain undetected in most cases. For variation coefficients below 25% they remain barely visible to the naked eye, while yield drops already significantly. As soon as marked color differences appear, the variation coefficient already exceeds 45%. Besides diminished yield and the risk of lodging, uneven spreading has other consequences on crops:

  • Reduced quality (protein and oil content)
  • Increased environmental burden
  • Higher risk of infections
  • Impaired threshing
  • Higher desiccation cost

Ammonium nitrate or urea?

Spreading nitrogen fertilizer precisely increases margin and reduces environmental burden. Using high quality fertilizers of known origin ensures good spreadability and even nutrient supply. However, when it comes to spreadability, fertilizer types are not equal. Ammonium Nitrate, due to a higher bulk density and lower nitrogen concentration, offers more homogeneous spreading characteristics than urea. Wind can further degrade spreading homogeneity with urea, resulting in significant local over- or undersupply.