|Ferguson, Richard - UNIVERSITY OF NEBRASKA|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2000
Publication Date: N/A
Interpretive Summary: This is a summary of crop (corn silage) usage of nitrogen and phosphorus over a 7 year period. The treatments include manure, composted manure and commercial fertilizer applied to the cropland to meet the nitrogen or the phosphorus needs of the crop. To meet the nitrogen needs of the crop, phosphorus content of the manure/compost caused an oversupply of phosphorus. To meet the phosphorus needs, there was a deficiency in nitrogen and additional commercial fertilizer was applied. Another treatment included rye grass seeded after harvest to take up the nitrogen and make it available during the next year. This has reduced nitrogen moving below the root zone. Within the past two years, there has been an increase in the nitrogen that has moved below the crop root zone where high applications of manure/compost were used. This was caused by underestimating the ability of the crop to use the nitrogen in the manure/compost. There has been an increase at the soil surface in the amount of phosphorus present in the treatments receiving manure/compost at a rate designed to supply only enough phosphorus to meet crop needs. Again, the ability of the crop to use phosphorus was underestimated. There has been an excessive amount of phosphorus accumulated at the surface of the treatments receiving the higher rate of manure/compost as expected. There has been a small increase in the phosphorus content of the soil at the second sample depth (2 ft), probably the result of a deep tillage operation in 1995. Silage yields have been equal to or greater than the commercial treatment for each of the manure/compost treatments. Manure/compost can be safely and effectively used to replace commercial fertilizer, however, care must be taken to balance applied rates to crop needs.
Technical Abstract: A long-term study was initiated in 1992 to investigate the impacts of relatively high rates of application of beef feedlot manure or composted beef feedlot manure on the accumulation and movement of N and P in soil. Irrigated corn silage has been produced annually with treatments of manure or composted manure to meet crop requirements of N or P. An inorganic N fertilizer treatment was also included. Main plots were the presence or absence of a winter cover crop. Soil P levels increased significantly with organic residue application in the top 0.6 m, but no evidence of P movement below that depth was observed. Nitrate-N accumulated in the root zone following higher rates of residue application, but crediting for residual nitrate-N with reduced residue application rates allowed the accumulation and movement of nitrate-N below the root zone to be minimized. The presence of a winter cover crop reduced nitrate-N levels in the root zone in some years. Silage yield with application of organic residues was normally equa to or greater than that from inorganic N fertilizer.