Seminar Series Abstract

Persistence and Transformation of Nitrogen Forms and Phosphorus in Two Soil Tillage Systems

Desh Duseja and Sarabjit Bhatti

Cooperative Agricultural Research Program Seminar Series
Tennessee State University, Nashville, TN
April 21, 1999

Introduction.  Increasing the popularity of conservation tillage (CN) and no-tillage (NT) in Tennessee and the United States has resulted in a 60% increase in NT acreage in Tennessee in the last six years. Information on the long-term effect of NT conditions on soil properties/nutrient dynamics is somewhat lacking.

Objectives.  The objective of this project was to delineate, under laboratory conditions, the influence of different soil/environmental conditions on P and N mineralization/immobilization in a soil (Byler silt loam) previously subjected to long-term (4 year) tillage and no-tillage. N transport/movement will be studied in the next phase of the project.

Methodology.  Soil samples collected from 0-4", 4-8", and 8-12" soil depths of previously used long-term tillage-study plots were collected. These samples were incubated at a constant temperature in the laboratory. Three replications, two moisture levels (30 and 60%), and three nutrient levels were used. Samples were incubated with or without plant material (2% w/w). Initial P rates of 0, 10, and 20 ppmw, and N rates of 0, 50, and 100 ppmw were utilized. They were analyzed at 28, 133, and 365 days after incubation for NH₄⁺ and NO₃^-, and at 28 days for available P.

Results.  Whereas the type of previous tillage history had negligible influence on NH₄⁺ and NO₃^- accumulation in soil, P availability levels were substantially increased in NT compared to CN. Similarly, increasing nutrient application rates substantially enhanced P availability, but not NH₄⁺ and NO₃^- levels. N and P immobilization seemed to be limited in spite of 2% organic matter additions. Increasing moisture levels enhanced P availability, but suppressed the nitrification process. Conditions at 4-8" soil depth were more favorable for P mineralization, but less favorable for nitrification.

Impact.  P and N accumulations in no-till land can pose a problem at normal moisture levels and with time. Perhaps the application rates should be reduced to stem nutrient losses in runoff/sediment. Immobilization of P and N in NT should not be a problem, provided O.M. of high C:N ratio is not used.

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