Untersuchungen und Kalkulationstabellen zur Schätzung der N2-Fixierleistung und der N-Flächenbilanz beim Anbau von Lupinus albus und Lupinus luteus in Reinsaat und von Vicia faba und Pisum sativum in Reinsaat und im Gemenge mit Avena sativa

Abstract

In 1999 a three year lasting field experiment with different crop legumes from one to four species on four varying field sides in Lower Saxony was started. In detail Vicia faba, Pisum sativum as green pea and as grain crop, Lupinus albus and Lupinus luteus (only on two of the four sides) were integrated as sole crops (open sowing). Vicia faba and Pisum sativum were grown in mixture with Avena sativa, harvested as total plant silage (BBCH 79) and as a grain crop (BBCH 89 to 99). The chief purpose was to develop an improved calculation model to estimate the symbiotic nitrogen fixation rate in legume cultivations. In order to reach this aim the nitrogen contents in root and shoot were detected and the extractable mineral N contents in soils were determined using a CaCl2 method. The amount of the nitrogen derived from soil and atmosphere in the different plant organs was detected by using 15N isotope technique. The studies integrated Brassica napus as well as Avena sativa and the 15N enrichment of the plant organs of the dicotyledon Brassica napus showed constantly higher 15N values than the monocotyledon plant Avena sativa so that Brassica napus was more suitable as a reference plant.At maturity the average amount of the N2 fixation of the monocrop Vicia faba was 193.0 kg N ha-1. Pisum sativum fixed 141.3 kg N ha-1, Lupinus albus 125.1 kg N ha-1 and Lupinus luteus 153.5 kg N ha-1 respectively. In the mixed crop systems with Avena sativa the nodulating partner Vicia faba and Pisum sativum fixed an average amount of 185.7 kg N ha-1 and 128.8 kg N ha-1 respectively. The absorption of inorganic soil N at full ripeness of Vicia faba was averaged out to 69.0 kg N ha-1. Pisum sativum as a grain crop used 52.0 kg N ha-1 of the mineral N, Lupinus albus took up 90.8 kg N ha-1 while it was 83.8 kg N ha-1 at Lupinus luteus. Vicia faba as mixed crop with Avena sativa took up 57.1 kg N ha-1 and Pisum sativum as mixed crop absorbed 63.9 kg N ha-1. The atmospherically derived N in shoots and roots of Pisum sativum at milky ripeness was about 100.4 kg N ha-1 on average and the mean amount of the soil derived N came to 51.8 kg N ha-1.In mixed stands with Avena sativa harvested as total plant silage the nodulating partner Vicia faba on average used 53.6 kg N ha-1 of the plant available N in soil and Pisum sativum 50.5 kg N ha-1. In this utilization of Vicia faba the contents of nitrogen derived from atmosphere was 122.8 kg N ha-1 on average, at Pisum sativum 100.9 kg N ha-1 were found. Only small differences between soil N and N derived from atmosphere could be determined between the tested varieties of one species.The N2 fixation is inter alia affected by numerous environmental factors like the particle size distribution of the soil, nutrients (especially nitrate), and further climatic influences. With help of the great amount of data obtained of this field trial close correlations between corn yield and the total plant N (shoot and root) accumulated and the N derived from atmosphere were found and these data were used to deduce the N balance of the tested grain legumes. By consulting the determined data and assessed amounts of N released by rhizodeposition of the leguminous plants to the soil an already existing method for calculating the N balance (SCHMIDTKE 2001) was used to hand over a model to the agricultural and water engineering advisory service. The calculation model is relatively easy because the grain yield is the factor needed to deduce the N2 fixation rate and the N balance of the grain legumes integrated in the field trial.