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

item Wang, Q
item Li, Y
item Klassen, W
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.C., 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. DOI: 10.1007/S13593-011-0054-9.

Interpretive Summary: Cover crops play various beneficial roles to contribute to sustainable agriculture. The influence of four cover crops (sunn hemp, velvetbean, cowpea, and sorghum sudangrass) grown on a gravelly loam soil as compared to weedy fallow condition was evaluated on transport of N, P, and clay fraction under two rain intensities (5.8 and 11.6 mm/d). The amount of clay fraction at the end of leaching was greater at the lower soil layer (20-30 cm) than those at the 0-10 and 10-20 cm depths in weedy fallow treatments thus indicating greater leaching under this treatment. The cover crops helped maintain clay fraction in the surface soil due to lower leaching losses. High rainfall intensity leached greater amount of N than that with low rainfall intensity across all cover crops and weedy fallow. Sunn hemp cover crops appear to be the most effective in accumulation of N, thereby, decreasing leaching losses.

Technical Abstract: Conservation of soil and water is fundamental to the development of sustainable agriculture. Transport of nitrogen (N) and phosphorus (P), and fine soil particles down the soil profile of a gravelly loam soil (loamy-skeletal, carbonatic, hyperthermic Lithic Udorthents) was investigated under various summer cover crops and two simulated rainfall intensities (5.8 and 11.6 mm d-1) in a mesocosm system. The cover crops were sunn hemp (SH) [Crotalaria juncea (L.) ‘Tropical sunn’], velvetbean (VB) [Mucuna deeringiana (Bort.)Merr.], cowpea (CP) [Vigna unguiculata (L.) Walp ‘Iron clay’], and sorghum sudangrass (SS) [Sorghum bicolor × S. bicolor (Piper) Stapf.] in contrast to weedy fallow (WF) as a control. Under the high rainfall intensity, the sum of N (NO3-N plus NH4-N) in the leachate ranged from 3.4 to 16.1 kg N ha-1 for cover crops and 8.8 kg N ha-1 for WF, in contrast to 0.5 to 1.9 for the same cover crops and 10.2 kg N ha-1 for WF under the low rainfall intensity. Among the cover crops, SH was the most effective species, which can obtain as much as 376 kg ha-1 N, 27 kg ha-1 P under high rain intensity, and 247 kg ha-1 N and 22 kg ha-1 P under low rain intensity via biomass accumulation. The amounts of soil organic carbon associated with fine soil particles in the root zone under SH and SS were 5-7% greater than those in WF. The result suggests that SH, as a promising summer cover crop, demonstrates a superior ability to reduce the downward migration of fine soil particles and conserve soil nutrients and water.