N-BALANCE FOR MINERAL-N ON SPRING BARLEY CROPPED SANDY LOAM AND COARSE SANDY SOIL WITH MINERAL AND ORGANIC FERTILIZERS

N-balance for mineral N was calculated for growing season and autumn-winter periods during a three-year field experiment on two Danish soils, a sandy loam and a coarse sand. Both soils were grown with spring barley and on the coarse sandy soil a catch crop was undersown in one treatment. The soils were fertilized with inorganic N (NPK) and organic N (pig slurry) applied in the spring and also in autumn (on the coarse sand). On the sandy loam soil the differences in N-leaching. N-uptake and net N-mineralization between the fertilized treatments were small. On the coarse sandy soil the autumn-applied slurry caused a strongly increased N-leaching, while the undersown catch crop reduced the leaching. The unfertilized soil differed from the fertilized treatments with a lower N-uptake and a decreased N-leaching, especially on the sandy loam soil. The type of fertilization did not influence the net N-mineralization very much. The N-balances were based on the store of mineral nitrogen in spring and at harvest, as well on the N-input and N-output, which included N fertilization, net N mineralization, and N-uptake, N-leaching and N-denitrification. The deviations in N-balance were strongly influenced by the high variations found for the N-pools included in the N-balance and only to a minor extent by the climatic conditions and the type of soil.