Articles
MINERAL BALANCES FOR RADISH CROPS GROWN UNDER GLASS
The in- and output of water and minerals during two succesive years were determined.
At the input side, data were collected on the amount and mineral composition of the irrigation water and the fertilization.
As output items, the amount and mineral composition of the drainage water and the minerals removed by the crop mere monitored.
The evaporation was calculated from the relationship with irradiation.
Denitrification and mineralisation was estimated by random tests.
Soil analyses at the start and the end of the investigation period were used to calculate the contribution of the soil buffer.
The water balance at the holdings could only be closed if either seepage from surrounding surface water or leaching to deeper groundwater was assumed.
This is plausible considering the hydrological situation at the holdings.
The extra term in the waterbalance, brought on extra in- or output of minerals as well, which is incorporated in the mineral balance.
At some holdings less N and/or P was applied than the crop removal and led to soil depletion.
In most cases a surplus of N, P and K was found, up to 70 % of the total input, however, there was no clear relation between the surplus in minerals and the quantity leached out by the drainage system.
The total mass balance of N and K could not be closed, unexplained differences of 5 till 47% for N and 4 till 47 % for K were found.
This discrepancy could be caused by under- or overestimation of the contribution of the closing term in the waterbalance, the denitrification or the mineralisation.
The loss of K and N at some holdings, is apparently a result of the irrigation surplus.
Considering the reduction of the mineral emission should therefore be focussed on the optimization of the irrigation strategy.