Nitratgehalte tieferer Bodenschichten bei unterschiedlichen Fruchtfolgen auf intensiv genutzten Ackerbaustandorten

Influence of rotation upon nitrate content of deep soil layers in intensiv cropping systems Soil samples were taken down to a depth of 10 m during winter 1985/86 in some fields in Lower Bavaria with and without vegetable production. Each core was cut into 50 cm increments and soil nitrate-N and exchangeable ammonium-N determined. The results can be summarised as follows:

• 1 The content of exchangeable ammonium in 0–10 m soil depth was much less than the amount of nitrate nitrogen. Effects of different supply of inorganic fertilizer upon the NH₄-content have not been observed.
• 2 In rotations without vegetables with high supply of mineral nitrogen much nitrate-N was concentrated in the root zone. However in a depth of 4–6 m the nitrate concentration was less than 50 mg/l.
• 3 In one field only the nitrate concentration in 2,8–3,8 m was 2 to 3 times higher than in comparable cases. This seems to be the result of much nitrogen mineralized but not used, because of fallow effects (winter killing without fertilization) in 1982.
• 4 The nitrate concentration in soil cores of arable land decreased generally with sampling depth. In fields with vegetable production soil layers of high nitrate content alterated with soil layers of low nitrate content.
• 5 Because of the strong correlation between the number of soil layers with high nitrate content and the frequency of vegetables in the rotation, it can be assumed that the soil layers with much nitrate are caused by unused inorganic fertilizer applied to vegetables. This hypothesis is also supported by the fact of high nitrogen efficiency (> 70%) of agricultural plants and low nitrogen efficiency (48–13%) of vegetables, caused by high amounts of fertilizer and only low nutrient requirement of vegetables.
• 6 The total amount of nitrate-N found in 0–10 m soil depth was in vegetable rotations 2 to 4 times higher than in fields without vegetable production. The nitrate concentration of the nitrate peaks found in fields with vegetable production decreased with sampling depth, but strongly differing gradients of nitrate decrease with soil depth were observed between the fields.