To determine the rate of fertilizer leaving the machine and thus obtain the dose per hectare to be spread, 3 elements must be taken into account:
- The total application rate Q in kg / ha
- The working width L in m
- The forward speed of the tractor during spreading: V, in km / h
Formula for calculating the fertilizer flow rate D to be metered by the machine:
As the spreading tables are supplied by the manufacturer for information, always check the quantity of fertilizer actually leaving the machine. To do this, you must opt for a fixed station flow control (to be performed over a period of at least 30 seconds or even a minute) or over a specific distance. For the epandeur pour terreau this is important.
There are also many precision tools to help you more easily to ensure that the flow is adapted to the forward speed. DPA (flow proportional to advancement) regulation is one of them. The ideal is to use it with a GPS antenna to be able to more precisely adapt its use to the forward speed, and set up an effective fertilization.
To succeed in your distribution, calculate your regularity of spreading
To succeed in its distribution, the regularity of the spreading, defined by the contribution of the same quantity of fertilizer in all points of the plot, must be perfect.
This regularity of spreading is characterized after covering the spreading plies by the coefficient of variation (CV). It can be determined by a field test, or by computer measurements and simulations.
Once the spreading layer of a given fertilizer and spreader has been recorded, the computer superimposes these layers by simulating the progress of the tractor (figure below):
Then, the layers of the adjacent outward and return passages are combined to establish the transverse distribution curve and calculate the corresponding coefficient of variation. However, not all farmers use solid fertilizers. For users of liquid fertilizers, there are 3 important points to note:
- With nitrogen, it is necessary to take into account losses by volatilization, and increase the target dose (by 15% or more).
- A sprayer used with liquid fertilizer is more exposed to premature wear, especially with oxidation phenomena.
- It is easier to carry out the dose modulation (manual or by GPS) with a solid fertilizer spreader. The acquisition of modern sprayers, equipped with multi-jets controlled automatically is recommended.
As for border spreading, it can be done before or after spreading in the open field. It is nevertheless advisable to start with the borders and the headlands because the traces left on the ground by the passage of the tractor then serve as the opening and closing mark of the distributor during the fertilization of the rest of the plot.
