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-w inter periods during a three-year field experiment on two Danish soils , a sandy loam and a coarse sand. Both soils were grown with spring ba rley and on the coarse sandy soil a catch crop was undersown in one tr eatment. 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 leac hing. The unfertilized soil differed from the fertilized treatments wi th a lower N-uptake and a decreased N-leaching, especially on the sand y loam soil. The type of fertilization did not influence the net N-min eralization very much. The N-balances were based on the store of miner al nitrogen in spring and at harvest, as well on the N-input and N-out put, which included N fertilization, net N mineralization, and N-uptak e, N-leaching and N-denitrification. The deviations in N-balance were strongly influenced by the high variations found for the N-pools inclu ded in the N-balance and only to a minor extent by the climatic condit ions and the type of soil.