CATCH CROP AND ANIMAL SLURRY IN SPRING BARLEY GROWN WITH STRAW INCORPORATION

Four rates of straw (0, 4, 8 and 12 t ha(-1) yr(-1)) were incorporated in a field experiment with continuous spring barley. The experiment w as conducted on a sandy soil (5.5% clay) and a sandy loam soil (11.2% clay), After eight years, the straw incorporation was combined with ca tch-crop growing with and without winter application of animal slurry and also spring fertilization with mineral fertilizer (0, 50, 100 or 1 25 kg N ha(-1) yr(-1)). The combined experiment was conducted for thre e 1years on the sandy soil and for four years on the sandy loam soil. The effects on barley dry matter yield and N uptake are presented toge ther with the long-term effects of the straw incorporations on crop gr owth and soil C and N. Grain yield on the sandy loam was unaffected by straw incorporation. On the sandy soil the highest straw application rates reduced grain yield in the unfertilized barley. When the barley received mineral fertilizer at recommended levels (100 kg N ha(-1) yr( -1)), grain yield on this soil was also unaffected by the high straw r ates. Including a catch crop had a positive effect on the grain yield of barley on both soils. The total N uptake in grain and straw general ly increased with straw application up to 8 t ha(-1) yr(-1). With the highest straw application rate (12 t ha(-1) yr(-1)), the total N uptak e decreased but still exceeded N uptake in barley grown with straw rem oval. The barley accumulated higher amounts of N when a catch crop was included. The total N uptake in the barley was significantly higher a fter animal slurry application. The extra N uptake, however, was much lower than the amounts of N applied with the slurry. Incorporation of straw had only a small influence on N uptake after slurry application. The straw, therefore, was not able to store the applied N during wint er. In the two four-year periods before the combined experiment, grain yield on the sandy loam was generally negatively affected by straw in corporations, In the second period, N uptake began to show a positive effect of the straw. On the sandy soil, grain yield and N uptake durin g the whole period were generally positively affected by the straw inc orporations except for the highest straw rate (12 t ha(-1) yr(-1)). Th e sandy loam soil showed higher increases in C and N content after the repeated straw incorporations and catch-crop growing than the sandy s oil, When application of animal slurry was combined with the catch cro p, no further increases in soil C and N were found relative to soil wh ere a catch crop was grown without slurry application. Large amounts o f the N applied with the slurry may therefore have been lost by denitr ification or nitrate leaching.