Effects of ammonium depot (Cultan~(R)) fertilisation on plant and soil nitrate content and metabolism of kohlrabi plants

摘要

Ammonium-based vegetable fertiliser (CULTAN~(R)) improved product quality by reducing nitrate content of kohlrabi tubers by 45 percent without affecting either tuber size, weight or yield. Residual nitrate in the soil at harvest was also reduced byaround 45 percent when compared with conventional nitrate-based fertilisation. Ammonium fertilisation enhanced leaf chlorophyll synthesis, particularly of chlorophyll a, and hence induced a closer chlorophyll a:b ratio of 2.67:1 relative to 2.88:1 in nitrate-fed plants, and stimulated epicuticular wax formation two-fold. The enhanced epicuticular wax, in the form of dendrites, of ammonium-fed kohlrabi leaves reflected 20-25 percent more light in the visible and photosynthetically active range than nitrate-fed leaves. This effect was compensated for by the lower chlorophyll a:b ratio of the ammonium-fed plants which indicates enhanced efficiency of the photosystems and light harvesting complex, resulting in an overall unchanged net photosynthesis. The dendritic wax structure also increased the contact angle from 108 deg to 151 deg, with quicker drying after precipitation, thereby reducing pathogen infection and increasing the potential to wash off spores during precipitation.