Influence of cultivation on soil nitrogen pools |
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| Abstract: | Abstract Exchangeable NH4, organic N, and fixed NH4, were followed in three soil layers (0–25, 25–50, and 50–75 cm) of plots under conventional and minimum tillage in a 10—year field experiment. The main effect of both tillage treatments was a marked increase of fixed NH4 during the first two years which was attributed to the heavy application of N fertilizers because soils were not fertilized prior to the experiment. Due to spatial variability of soil composition, a statistically significant increase over the 10—year was observed for total and fixed NH4 only in the surface layer of conventionally tilled soils, probably due to thorough mixing caused by intense cultivation. In this layer the organic N pool did not appear to vary with the years, while the fixed NH4 pool was influenced by N fertilization. A general trend was a uniform increase of the ratio between fixed NH4 and total N. Under conventional tillage, the trend was similar for the three soil layers while the reduced amount of fixed NH4 present in the upper soil layers (0—25 and 25–50 cm) was assumed to be caused by root absorption. Under minimum tillage, the increase of fixed NH4 ratio was limited to the first 50 cm of soil, and was less pronounced in the top layer where maximum root accumulation is generally expected to be present. The data support the importance for crops of the fixed NH4 pool. |
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