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United States Department of Agriculture

Agricultural Research Service

Title: Ammonium Adsorption and Desorption in Sandy Soils

Authors
item Wang, F - UNIV SASKATCHEWAN, CANADA
item Alva, Ashok

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 1999
Publication Date: October 1, 2000
Citation: WANG, F.L., ALVA, A.K. AMMONIUM ADSORPTION AND DESORPTION IN SANDY SOILS. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL, 64:1669-1674. 2000.

Interpretive Summary: SUMMARY Losses of fertilizer nitrogen (N) through leaching from soil are both an agricultural and environmental concern because they cause inefficient use of N fertilizers for crops and pollution of our water systems. Hence knowledge of the nature of a soil with respect to its N holding and supply abilities is indispensable for establishing best strategies for management of N fertilization in the soil. This is of particular importance for sandy soils, which are usually subjected to severe leaching annually and are not well understood to date for their interactions with applied fertilizer N. In the present study, we examined ammonium (NH4) adsorption and desorption in samples of a Wabasso and a Candler sandy soil at various depths. We found that N buffering capacity of the soils, which is a measure of the potential of a soil to sustain the supply of soil NH4 to soil solution and thus to plants, ranged from 0.26 (Wabasso sub-surface) to 3.9 (Wabasso Bt horizon) cmol kg-1/(mol L-1)1/2 . This low N buffering capacity indicated a relatively poor potential N supply ability of the soils as compared to that of silt loam or clay soils. Similarly, labile NH4, a measure of direct N supply ability of a soil, was also low, ranging from 4.9 x10-3 (Candler sub-surface) to 13.8 x10-3 (Wabasso surface) cmol kg-1. The highest NH4 adsorption was in the Bt horizon sample (75.3 mg kg-1) whereas the lowest was in the sub-surface horizons of the soils (10.8 mg kg-1). Although NH4 adsorption capacity of the surface soils was greater than that of the sub-surface soils, the latter soils showed greater NH4

Technical Abstract: Leaching of fertilizer N in sandy soils is both an agricultural and environmental concern and depends, in part, on the N holding capacity of the soils in the vadose zone. We examined ammonium (NH4) adsorption and desorption in surfact (0-30 cm) and sub-surface (30-60 cm) samples of a Wavasso (sandy, siliceous, hyperthermic, Alfic Haplaquods) and a Candler (uncoated hyperthermic, Typic Quartzipsamments) sand using a batch technique. Samples of a Bt horizon (90-100 cm depth) of the Wabasso sand were also used in the study. The NH4 quantity-intensity relations showed that the potential buffering capacity (PBC) of the soils ranged from 0.26 (Wabasso sub-surface) to 3.9 (Wabasso Bt horizon) cmolckg-1M-1/2. Labile NH4, as determined from the quantity-intensity relations, was in the range of 4.9 x10-3 (Candler sub-surface) to 13.8 x10-3 (Wabasso surface) cmolc kg 1. Positive linear relationships were observed between organic C content and quantity-intensity plot parameters (potential NH4 buffering capacity and labile NH4) of all soil samples except the Wabasso Bt horizon. Although NH4 adsorption capacity of the surface soils was greater than that of the sub-surface soils, desorption of NH4 from the former soils was also stronger than that from the latter. This study clearly demonstrated that the potential NH4 buffering capacity and labile NH4 values for the sandy soils studied were much lower than those for clay and silt loam soils.

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