Predicting Nitrogen Availability to Rice: II. Assessing Available Nitrogen in Silt Loams With Different Previous Year Crop History1
- J. L. Sims and
- B. G. Blackmon2
Soil test methods that measure NH44-N in silt loams before and after incubation under waterlogged conditions were evaluated as predictors of N availability to ‘Nato’ rice (Oriza sativa L.) grown in the greenhouse. Eighteen soils for each of five previous year crop histories were utilized. All so ls were from crop rotations containing rice.
Coefficients of determination (r2) for the regression of N uptake by rice on NH4+-N after 6 days incubation of soil from the different crop histories increased in the order of cotton (Gossypium hirsutum L.) < rice < lespedeza (Lespedeza striata Thumb.) < soybean (Glycine max L.) < reservoir (irrigation water storage or fish production), and ranged from .12 to .77. Exchangeable Ca was inversely related to N uptake and accounted for significant percentages of variation in uptake on all soils except those from reservoirs. Exchangeable Ca was not related to NH4+-N production during incubation. For all previous year crop histories NH4 -N in soil after 6 days incubation was a better single predictor of N uptake by rice than soil organic matter values.
Initial NH4+-N content of reservoir soils was about 5 times greater than in soils of other crop histories. The amount in these silt loam soils from reservoirs (55 kg N/ha) was about half that found in previous studies for reservoir soils of clay texture. Multiple regression analyses indicated that including initial NH4+-N together with NH4+-N production during incubation improved the prediction of N uptake over NH4 -N production values alone. Including exchangeable Ca together with initial NH4+-N and NH4+-N production values improved the prediction on all soils except those from reservoirs.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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