Nitratentwicklung nach Kleegrasumbruch im Frühjahr unter der Folgefrucht Silomais

Abstract

Abstract Nitrate release under the following crop maize after ploughing a clover‐grass crop in spring After ploughing a clover‐grass crop in spring, the formation of nitrate under the following crop maize, its nitrogen uptake and yield were investigated as well as the N‐mineralization in the fallow plots. As ploughing processes the variants “rotary cultivator” and “plough” were compared.Three days before ploughing 14 kg nitrate‐N/ha were found in the soil from 0 to 90 cm depth. At all sampling dates after ploughing significant higher nitrate‐N contents were analysed in the soil of the plough variant than in the rotary cultivator variant. Under maize the highest observed nitrate contents were reached at the end of July, that is 117 kg N/ha in the plough and 65 kg N/ha in the rotary cultivator variant. In the soil without plant growth the highest nitrate values were not noticed before the end of August, namely 213 and 102 kg N/ha in the plough and in the rotary cultivator variant, respectively. During the time after these maximum values the nitrate contents in the fallow plots lessened dramatically, probably implying considerable nitrogen losses.In the maize plots, however, the continual nitrogen release could obviously be used well by the plants. Under maize there was another period of intensive N‐mineralization between end of August and the beginning of October, so that the N‐contents in both soil and maize plants approximately doubled during the last 5 weeks before harvest: from 70 to 148 (“rotary cultivator”) and from 140 to 269 kg N/ha (“plough”), respectively. This is equivalent to a mineralization rate of 1.9 and 3.1 kg nitrate‐N/ha d, respectively, in the time between the end of August and the beginning of October. This nitrogen release was only expressed by the increasing N‐uptake of the maize plants, but not by a changed nitrate store in the soil.Because of the better nitrogen supply the plough variant led to a dry matter yield which was 73 % higher than in the rotary cultivator variant (176 and 102 dt/ha, respectively).