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Title: High retention of N P nutrients, soil organic carbon, and fine particles by cover crops under tropical climate

Author
item WANG, Q - University Of Florida
item LI, Y - University Of Florida
item KLASSEN, W. - University Of Florida
item Alva, Ashok

Submitted to: Agronomy for Sustainable Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2011
Publication Date: 10/7/2011
Citation: Wang, Q., Li, Y., Klassen, W., Alva, A.K. 2011. High retention of N P nutrients, soil organic carbon, and fine particles by cover crops under tropical climate. Agronomy for Sustainable Development. 32:781-790.

Interpretive Summary: Cover crops provide soil cover during offseason against wind erosion. This vegetation is plowed in during spring in preparation for planting the main crop. The cover crops biomass when incorporated into the soil will undergo decomposition and subsequently release biomass nutrients into plant available forms for the subsequent crop. the estimate of this transformation of nutrients is important to calculate the actual nutrient requirement that needs to be applied for the subsequent crop in question. In this study mineralization of nutrients from sunnhemp and sudangrass biomass was evaluated in a sandy and loamy soils at 20, 25, and 30 degrees C. The results revealed that rate of mineralization was greater in a sandy soil as compared to that in a loamy soil. Mineralization increased with increasing temperatures.

Technical Abstract: Cover cropping system has shown a potential to improve soil quality and carbon sequestration but the residue decomposition rates determined by biotic and abiotic factors play a crucial role to reach such objectives. Legume and non-legume cover crop residues were applied to the surface of two soils in contrast to soil alone (CK) contained in decomposition monitoring apparatuses at three temperature regimes in a phytotron system to investigate their turnover of organic carbon (C), nitrogen (N), and phosphorus (P). The two cover crops were sunnhemp (Crotalaria juncea L.) –(SH) and sorghum sudangrass (Sorghum bicolor × S) – (SS), soils were the Krome gravelly loamy (KGL) soil from south Florida, and Quincy fine sandy (QFS) soil from southeast WA, three temperatures were 20, 25, and 30 oC, and soil moisture all controlled at 75% of the field capacity. The self-designed decomposition monitoring apparatus consisted of bottom caped PVC cylinder, a soil solution sampler, a vial holder with a Ziploc bag on the top. Carbon dioxide (CO2) release was monitored and soil solution analyzed for N and P for 360 days. The results displayed a convenient and practical approach to monitor residue decomposition under undisturbed and aerobic conditions. All experimental factors significantly influenced the mineralization of C, N (NO3-N) and P. On average, the QFS soil had greater mineralization rate than the KGL soil, a high temperature generally increased C and N, and applying cover crop residues improved the mineralization of C and NO3-N. Ortho-P concentrations in the KGL soil was much lower than those in the QFS soil regardless any treatment, which might be attributed to the high binding capacity of the KGL soil with high pH and abundance of CaCO3. The kinetic mineralization of organic C was well fitted to an exponential first order model, and a power rise model and a zero order linear model were well fitted to describe the cumulative N and P mineralization with time. The results suggest that the cover crop residue mineralization of C, N and P depends not only on the residue quality (e.g., C:N ratio), biotic traits of residues, some abiotic factors, such as soil type and temperature, are critical to determine its mineralization as well.