Author
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Alva, Ashok |
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Submitted to: Journal of Sustainable Agriculture
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/1/2006 Publication Date: 12/6/2006 Citation: Alva, A.K. 2006. Sustainable nutrient management in sandy soils - fate and transport of nutrients from animal manure verses inorganic sources. Journal of Sustainable Agriculture. Vol 28: 139-155. 2006. Interpretive Summary: Estimation of nutrient leaching from sandy soils is important to develop management techniques to facilitate minimizing leaching losses. Nutrient leaching can occur from inorganic fertilizers as well as from organic sources, following the mineralization of nutrients. In this study, nitrogen and phosphorus leaching were evaluated from a Quincy fine sand subject to the following treatments: (i) unamended; (ii) 100 kg N/ha as urea; (iii) 100 kg N/ha as urea plus 100 kg P/ha as KH2PO4; (iv) 200 kg N/ha as manure. To examine the degree of vulnerability of this soil for leaching, 100 kg/ha bromide was applied as potassium bromide uniformly across all leaching columns. Leaching of bromide was completed in one pore volume of leachate indicating high vulnerability of this soil for leaching losses. In both urea and manure amended soils, the amount of ammonium-nitrogen in the leachate was considerably lower than that of nitrate-nitrogen. This is in part due to the rapid transformation of ammonium form of nitrogen into nitrate form. There was an appreciable lag time for leaching of phosphorus to occur as compared to that of nitrogen forms. Technical Abstract: A clear understanding of transformation and transport of nutrients from inorganic sources as well as organic amendments is important to manage the application of these nutrient sources efficiently in an effort to minimize the losses. With respect to nitrogen (N) management for crop production, inorganic fertilizers and organic N containing amendments are being used. Nitrogen in the organic N amendments is transformed into ammonium (NH4+) and nitrate (NO3-) forms. Although this transformation is necessary for rendering N available to plants, these N forms (in particular NO3- form) is subject to leach in the soil with the water front. Leaching column (15 cm diameter x 120 cm long) experiment was conducted using a Quincy fine sand (mixed, mesic, Xeric Torripsamments) packed to simulate the natural soil profile of 120 cm depth. The treatments included : (i) unamended; (ii) 100 kg N/ha as urea; (iii) 100 kg/ha of N and P as urea and KH2PO4; and (iv) 200 kg N/ha as manure. All columns received uniform bromide (Br-) applications at 112 kg/ha, as KBr. The columns were leached with 5 pore volumes (total of 45L) of water. The Br- was leached entirely from all the columns in the second pore volume of leachate. The extraction of the soil at the conclusion of leaching of 5 pore volumes showed negligible to below detection limits of Br-. Across all N amendments, the leaching of NH4-N was considerably lower than that of NO3-N. This is an indication of rapid transformation of NH4-N into NO3-N, and retention of NH4-N to some degree by the soil. Leaching of PO4-P was negligible in the first 3 pore volumes, but increased rapidly during the subsequent leaching. The amount of P leached was much greater for the urea plus KH2PO4 amended treatment as compared to that from the manure amended treatment. This was an indication of the slow transformation of organic P into PO4-P from manure amended treatment. The residual soil N (2M KCl extractable) after the completion of five pore volumes of water showed negligible levels of NH4-N through the entire depth of the soil column. The extractable NO3-N levels in the 0 to 30 cm depth soil were greater in the manure, and urea plus KH2PO4 treatments as compared to those in the other treatments. Despite leaching of five pore volumes of water, the extractable PO4-P concentration was greater for the manure, and urea plus KH2PO4 amended treatments as compared to those for the other treatments, across the entire depth of the soil column. |
