Mineralkvävedynamik och växtnäringsutlakning på en grovmojord i södra Halland med handels- och stallgödslade odlingssystem med och utan insådd fånggröda

During a three-year period studies of nitrogen dynamics, the utilization ratio of nitrogen by crops, and the leaching of nitrogen by tile drainage water in sandy soil in south-western Sweden. The field was divided into ten separate tile-drained plots, each with an area of 0.16 hectare. The amount of drainage water from each plot was measured and water samples were collected twice a month and weekly during flood periods. The water samples were analyzed for pH, electrical conductivity, nitrogen, phosphorus an potassium. The fertilizer regimes were: Unfertilized, commercial fertilizer according to general recommendations (90-110 kg/ha), liquid manure (pig slurry) in spring or autumn (90-110 tot. N kg/ha) supplemented with commercial fertilizer applied in the spring (45-55 N kg/ha) and treatments with double amount of liquid manure applied in spring or autumn also supplemented with commersial fertilizer. all treatments were grown with and without a catch crop exept the treatments with autumn application of mature that are required by law to be followed by a green cover during the winter. During the first two years, Ialian ryegrass, and in the year perennial ryegrass wass grown as catch crop. The ryegrass was undersown in the main crop. The grop rotation was: Oat (1989), spring wheat (1990) an barley (1991). The treatments with ryegrass were ploughed in the spring whereas the other treatments were ploughed in the autumn after stubble cultivation following harvest. The catch crop reduced the spring leaching substially in the single dose treatments with only commersial fertilizer and in th combined system with both manure and commercial fertilizer. The reduction was as high as 74 and 78 %, respectively, but in the treatment with a double dose of pig slurry the reduction stopped at 50 %. When pig slurry was applied in the autumn, the losses were doubled compared to spring application in spite of the catch crop. The unfertilized treatment (8 years) without a cac crop had 50 % less leaching compared with treatments with springapplied normal doses of fertilizers without a catch crop. The yield in the unfertilized treatment was only 34 % of the yield in the treatment with a normal dose of commercial fertilicer. The treatment with a singel dose of manure and half a dose of commercial fertilizer, bothe appliedin the spring, gave 7 % higher yield but a more lodged stand compared with the treatment with a single dose of commercial fertilize. The last two treatments had the best nitrogen utilization ration (82 % of applied N was taken away by the grain yield). A double dose of manure lowered both the yield and the nitrogen utilization ratio indipendent of time of application. The main reason for this was higher lodging tendency and higher leaching values. The cath crop lowered the yield (7-24 %) both in 1989 and 1990 in the treatment with spring-applied fertilizers. Also the fertilizer utilization ration was lower in the catch crop treatments. But in 1991 the diffferences were smaller. The main reason for this seems to be a delivery by mineralization from organic nitrogen from earlier ploughed-in catch crops. Important reasons for the drop in yield in the treatments with a catch crop seem to be competition with the main crop and large deficiency of mineral nitrogen in the early spring compared with treatments without a catch crop. Any net immobilization of nitrogen following the ploughing-in of cath crop could not be verified. At the time of yellow ripeness for the cereals, the intersown ryegrass had taken up 7-14 N kg/ha in the standing crop (above ground) and in the middle of November 11-90 N kg/ha, most in treatments were the nitrogen supply was good, such as in treatments with autumn application of manure or in treatments where the frequent use of manure had enlargeed the mineralization capacity of the soil. In the autumn the dry matter content of the catch crop varied between 800-2700 kg d.w. per hectare. From last autumn to early spring the N content of ryegrass changed only very little. The catch crops decreased the amount of mineral nitrogen in the soil (0-90 cm) from the time of yellow ripeness to late autumn exept in the treatments with autumn-applied manure. In treatments without a catch crop, the nitrogen mineralization capacity of the soil. In late autumn the dry matter content of the ryegrass changed only very little. The catch crops decreased the amounts of mineral nitrogen in the soil 80-90 cm) from the time of wellow ripeness to late autumn exept in the treatments with autumn-applied manure. In treatments without a catch crop, the nitrogen mineralization increased in the storage of mineral nitrogen throughout the autumn, leading to a higher leaching during the following winter compared with treatments with a catch crop. In the treatments with a catch crop, the mineral nitrogen storage continued to be fairly small until the time of spring ploughing. During the time from spring ploughing with a catch crop than in corresponding treatments without a catch crop. Yearly application of manure enlarged the delivery of mineral nitrogen from the soil compared with to treatments without manure. The delivery was also lowered in the treatment without any fertilizer application. Calculations show that a frequent manure addition gave an enlarged nitrogen leachong magnitude, as well as increased ammoniavolatilization and denitrification. In the autumn-ploughed treatments without a catch crop, the net mineralization of nitrogen from the time of yellow ripeness to early spring was higher than in the treatments with catch crop and spring ploughing. However, during the growing season, the minratlization was higher in the treatments with a catch crop and spring ploughing. Thus, it seems as if anutumn ploughing stimulates the mineral N-mobilization during winter. In the treatments with a spring ploughed catch crop, the net mineralization during growing season is enlarged. The amounths of nitrogen mineralization also increased during the years, suggesting an additional influence of several years durration given by the ryegrass residues. The combination of a cath crop and spring ploughing therefore seems to both diminish leaching losses though retention of nitrogen in plants and plant residues, and futher offer a possibility to govern nitrogen prosesses in the soil in such a way that nitrogen ta a greater extent will released when it can be utilized by the crop