Browse on keywords: fertility nitrogen availability
Search results on 05/24/13
9601. Fredrickson, J.K., F.E. Koehler and H.H. Cheng. 1982. Availablility of N-labeled nitrogen in fertilizer and in wheat straw to wheat in tilled and no-till soil.. Soil Sci. Soc. Am. J. 46:1218-1222.
In a field study, wheat was grown in microplots under conventional tillage and no-till seedings to compare availability of fertilizer nitrogen for two consecutive crops. The N-labeled ammonium sulfate was surface-applied in May 1980 to a spring wheat crop which utilized 25 to 40% of the fertilizer N, with the highest uptake occurring on no-till. There was no difference in dry matter production between tillage methods. A winter wheat crop was then grown in the same microplots to assess the availability of the residual labeled fertilizer N, and in new microplots which were treated with the spring wheat straw containing 5.20 atom % N and 1.20% total N to assess the availability of straw N. Approximately 9% of the wheat straw N was taken up by the 1980 to 1981 winter wheat crop, while an average of 6% of the residual fertilizer N was utilized. Winter wheat dry matter production was highest on no-till receiving 168 kg N/ha, but no difference was found between the effects of tillage methods on the availability of straw N or on the uptake of residual fertilizer N. Therefore, decreased wheat production on no-till in the Pacific Northwest would not likely result from poorer crop utilization of fertilizer N under no-till than under convenional tillage. Overall low crop N-use efficiencies of the surface-applied fertilizer N were likey due to immobilization and denitrification.
9903. Smith, C.J., D.M. Whitfield and O.A. Gyles. 1989. Estimation of available N status of soil by wheat and barley: A-values.. Soil Biol. Biochem. 22(1):169-172..
The A-value is a measure of soil nutrient availability and is expressed as the ratio of nutrient in the plant derived from labelled fertilizer to that derived from soil. The assumptions of this model are that the A-value is constant, independent of rate of fertilizer-N addition, and that the fertilizer use efficiency of the fixing and non-fixing plant is the same. Using 15N-labelled fertilizer, an experiment was run to examine the effect of nitrogen form, rate of addition and the timing of the nitrogen fertilizer application on the A-value. The results showed a decline in A-values with increasing rate of fertilizer nitrogen. From their results, the authors concluded that considerable doubt is cast on the assumptions that the A-value is independent of nitrogen rate for all plants.