Submitted to: Plant Nutrition Colloquium Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2005
Publication Date: 9/14/2005
Citation: Green, V.S., Dao, T.H., Cavigelli, M.A. 2005. Characterizing bioactive phosphorus of soil aggregates in conventional and manure-based cropping systems. In: C.J. Li et al. (eds). Plant Nutrition for Food Security, Human Health, and Environmental Protection. Tsinghua University Press, Beijing, China. p. 1166-1167. Interpretive Summary: Soils repeatedly treated with large amounts of manure accumulate inorganic and organic phosphorus (P) in the near-surface zone. Elevated levels of soil P have been associated with P discharges in runoff and impairment of the quality of nearby water bodies. Organic farming systems depend heavily upon organic sources of nutrients, largely from animal manures. These farming practices require tillage to mechanically control weeds. They also involve high inputs of organic matter such as plant residues and manure, which increase soil structural stability. Similarly, reduction or elimination of tillage in conservation systems promotes soil structural stability. Conservation tillage often results in a stratified distribution in nutrients in the near-surface zone. These crop production systems are growing in popularity, yet it is not known how the net effect of increased aggregation, organic matter inputs, and P stratification in no-till (NT)and manure-amended systems affect sediment-bound phosphorus losses compared to conventional cropping practices. The results showed that reducing tillage in corn-soybean-wheat rotations greatly influenced macroaggregate development, particulate P distribution in high organic matter manure-amended soils. As soil is selectively eroded, smaller aggregates were observed to be eroding preferentially. Reduction in tillage has a beneficial effect on the development of large water-stable macroaggregates and sequestration of P under NT management. The ligand-based phytase-hydrolyzable phosphorus method developed at BARC showed that soil management practices should focus on both inorganic- and organic phosphorus fractions as both potentially contribute to water quality degradation. A balance between nutrient utilization and fertilizer and manure nutrient application is critical to avoid edge-of-field losses and potential impairment of the ecological integrity and quality of nearby streams and estuaries.
Technical Abstract: In areas of intensive animal agriculture, applications of manure often result in accumulation of inorganic and organic phosphorus (P) in the near-surface zone. Organic farming systems depend heavily upon organic sources of nutrients, largely from animal manures. A long-term field study was conducted to compare the potential losses of sediment-associated nutrients from no-till (NT), conventional till (CT), and organically managed system (ORG) that received repeated poultry manure applications. After a decade of continuous organic and conventional conservation management, all soils showed nutrient levels that were characteristic of P-enriched soils in the surface 0 to 5-cm depth. In combination with the aggregate size distribution, about 70% of soil P was concentrated in macroaggregates ranging from 0.2 to >2 mm in size in the NT treatment whereas, a greater percentage of soil P was found in microaggregates of <0.2 mm in CT and ORG treatments. The high intensity and frequency of tillage in CT and ORG treatments negated the benefits of the high carbon loading from cover crops and poultry manure applications, resulting in soil conditions that were less conducive to the formation and/or stability of large macroaggregates than those under NT management of these Ultisols. Nutrient management practices for erosion-prone manure-amended lands should focus on both inorganic- and organic bioactive P release from soils as both are potential contributors to water quality degradation from eroded sediments and dissolved P.