Einfluss von Aussaatstärke, Bodenbearbeitung und Anbaumuster auf den Ertrag von Erbsen-Hafer-Gemengen

Abstract

In a two-year field experiment (2002/2003) on a loess soil near Göttingen, pea and oat were grown as sole and intercrops at a range of densities. The trial was carried out under conventional and reduced tillage system. Within the 16 examined pea-oat intercrops which followed the response surface design, two different replacement series arose.In both years, advantages of the intercrops over sole crops could be measured. Thereby, highest yield advantages were found for intercrops with densities above the recommended sole crop densities. This shows that pea and oat were not competing for exactly the same resources and that intercrops used resources more efficiently than sole crops. To reach maximal grain yields, optimal seed density was 87.5-100% of recommended sole crop density (70-80 pea seeds m-2). Optimal seed density of oat varied depending on soil-N content: at low Nmin values oat could be sown with higher densities (150-300 seeds m-2) than at high Nmin values (75-150 seeds m-2). As pea is responsible for reaching high grain-N yields in intercrops in the first place, optimal oat density for high grain-N yields could be reduced even further (38-75 seeds m-2), while optimal pea density was still 100% of recommended sole crop density. The higher the pea density in the intercrops, the higher was the amount of N fixed from atmosphere. However, intercrops with high pea densities showed similar low residual Nmin values as sole cropped oat, so that intercropping significantly reduced the risk of N losses after harvest compared to sole cropped pea. Intercropped pea at high densities fully compensated for the lower Nmin uptake of oat at lower oat densities. Intercropped oat was possibly forced to take up more soil N from deeper soil layers and therefore additionally reduced the risk of soil N losses through leaching from deeper soil layers. So even when taking the risk of soil N losses into account, highest yielding intercrops could be recommended.Tillage systems hardly influenced yields and competition processes in pea-oat intercrops. Contrary to expectations, N uptake from atmosphere by pea was not increased in the reduced tillage system. This can be traced back to similar Nmin values and N mineralization in the soil under both tillage systems. Intercropped pea under reduced tillage showed even higher N2 fixation compared with conventional tillage. Soil parameters such as e.g. bulk density could have led to a higher competitive ability and N2 fixation of intercropped pea under conventional tillage.Both experimental designs were suited for the use in field experiments and enabled statements about competition processes, resource complementarity and optimal intercropping densities. The response surface design showed the advantage of being able to separate intra and interspecific competition and therefore enabled valuable insights in the competition processes of pea-oat intercrops. Additionally, the response surface design was unaffected by insufficient field emergences, as due to its lack of dependence on sole crops and total densities numbers of plants m-2 instead of seeds m-2 can be used for the evaluation. Due to their density dependence, the determined RYT values had to be interpreted with caution. Low RYT values e.g. emerged from low total densities. Interpretations of the NDI values for the response surface design were difficult as reference values are hardly available. Both experimental designs were only able to find optimal densities within the examined range of densities. Therefore for both experimental designs, knowledge about the approximate scale of the optimal densities of the intercrops is of high importance when planning field experiments. The present experiment was able to show that ex-perimental effort for the response surface design could be reduced, as sole crops could be omitted. However, when using the replacement series design, an investigation of different replacement series as well as different densities within a replacement series can be recommended. It is also very important to consider identical growth conditions for the species in sole and intercrops.