Sulphur cycling in New Zealand hill country pastures. I. Laboratory sulphur, nitrogen and carbon mineralization studies |
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| Authors: | K SAKADEVAN M J HEDLEY A D MACKAY |
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| Institution: | Department of Soil Science, Massey University, Palmerston North, New Zealand;DSIR Grasslands, Private Bag 11008, Palmerston North, New Zealand |
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| Abstract: | Large leaching losses of sulphate contribute to the inefficient use of sulphur (S) fertilizer in some grazed hill country pastures in New Zealand. Laboratory mineralization studies were conducted to measure S, nitrogen (N) and carbon (C) mineralization rates and the potential for S leaching from surface soils of low (LS, 0–12°) and medium (MS, 13–25°) slope positions on hill country pastures. The soils differed in C, N and S contents as a result of different fertilizer histories and the uneven redistribution of nutrients by the grazing animal. Soils were incubated in columns for 140 d and leached periodically with 0.01 M KCl to remove mineralized sulphate, nitrate and ammonium. The net amounts of N and S mineralized were greater in soils on low slopes than medium slopes and in soils from pastures which had received fertilizer continuously, compared with those hill pastures that had not received single superphosphate fertilizer in the previous 7 years. In both cases more mineralization was associated with smaller soil C:nutrient ratios. However, the amounts of C mineralized were greater in soils from medium slopes where C:nutrient ratios were larger. In general, the ratio of N:S mineralized was smaller than the N:S ratio of the soil organic matter, suggesting that N is conserved while S remains in the soil solution susceptible to leaching. It is suggested that the extent of S leaching loss under field conditions will reflect S mineralization potential. |
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