Evaluation of Three Cover Crops and Their Termination with a Roller Crimper to Produce In Situ Mulch Under Tropical Conditions

Smallholder tropical farmers rely upon on-farm inputs such as cover crops (CC) to provide ecological and economical means for the management of soil quality and pest management. Roller-crimper technologies for the termination of CC to produce in situ mulch were developed in temperate climates where seasonal changes impede CC re-growth. Information on CC response to termination with a roller-crimper and resulting weed suppression is limited or non-existent for tropical environments. The objective of this project is to; 1) evaluate three CC under tropical environmental conditions produced with zero external inputs, 2) to determine CC re-growth levels post termination with a roller crimper, and 3) to evaluate CC surface residue on weed development. Sunn hemp (SH; Crotalaria juncea (L.) cv IAC-1), lablab (LL; Lablab purpureus (L.), cv Rongai), and sorghum sudan (SS; Sorghum bicolor x S. sudanense L. cv Mega Green) were planted November 1, 2011 (Year 1) and again on October 4, 2012 (Year 2) by broadcast seeding. Cover crops were terminated with a roller-crimper 112 days after planting (DAP) in year 1 and 55 DAP in year 2. CC and weed biomass data was determined before termination and CC regrowth and weed biomass was determined post-termination. Sunn Hemp produced the highest level of CC biomass at 8,091 dry matter (DM) kg/ha which was greater than either the SS or LL at 5,182 or 4,382 DM kg/ha, respectively, in year 1 (p<0.0001). Year 2 resulted in lower CC biomass than year 1 for both SH and SS at 3,589 and 4,424 DM kg/ha, respectively, (p<0.0001), with no difference in biomass between SH and SS within year 2. Lab lab failed to establish in year 2 from extensive army worm herbivory. Cover crop vegetative biomass yields in year 1 resulted in the contribution of 177 kg/ha nitrogen (N) from SH which was more than SS at 112 kg/ha N or LL at 89 kg/ha N (p<0.05). In year 2, there was no difference in N contribution to the farm system between SS and SH. In both years, weed biomass at CC termination was greatest for LL and similarly low for both SH and SS (p<0.05). SH responded favorably to termination with a roller-crimper and SH had the lowest level of regrowth. This was supported by the high amount of both SS and LL re-growth harvested in year 1 and again in year 2 for SS (p<0.0002). However, SH regrowth was greater in year 2 compared to year 1 which could be attributed to differences in SH maturity and lower plant stem lignification. Both SH and SS were effective in suppressing weeds following termination where LL was not. SH performed well as a cover crop producing high biomass levels and inhibiting weed development. Sorghum sudan performed well as a cover crop with excellent weed suppression, but was not effectively terminated with a roller-crimper with extensive regrowth. SH responded favorably to termination with a roller-crimper by exhibiting a high kill rate that produced in situ mulch that inhibited weed development.