Evaluation of Three Cover Crops and Their Termination with a Roller-Crimper to Produce Residual Surface Sheet Mulch On Cover Crop Re-Growth and Weed Development Under Tropical Environmental Conditions.

Tropical smallholder farmers operating under low-external-input conditions rely upon non-intensive on-farm inputs such as cover crops (CC) to provide ecological and economical means for the management of soil quality, soil fertility, and pest management.  Roller-crimper technologies for the termination of CC to produce residue based surface sheet mulch were developed in temperate climates where environmental seasonal changes impede CC re-growth.   Information on the response of CC 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 residue re-growth levels, and 3) to evaluate weed suppression capabilities after termination with a roller-crimper to produce surface sheet mulch.  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 by broadcast seeding.  The experimental design was a RCBD with 3 replications.  Cover crops were terminated with a roller-crimper 112 days after planting.  Plant data was collected on CC and weed biomass production prior to termination; and CC residue height, weed biomass, and CC re-growth biomass were determined 30 days after termination.  Sunn Hemp produced the highest level of CC biomass at 8,091 dry matter (DM) kg/ha which was significantly greater than either the SS or LL at 5,182 DM kg/ha and 4,382 DM kg/ha, respectively (p<0.0001).  Cover crop vegetative biomass yields 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).  No difference in phosphorus or potassium contribution was seen between the three CC evaluated.   Weed biomass at CC termination was greatest for LL with 264 DM kg/ha graminaceous weeds (GW) and 218 DM kg/ha broad leaf weeds (BLW) compared to SS with 18 DM kg/ha GW and 31 DM kg/ha BLW or SH with <1 DM kg/ha of either GW or BLW (p<0.05).  Sunn hemp had a favorable response to termination by a roller-crimper.  This was evident in the amount of CC re-growth and weed biomass harvested post-termination from the SS and LL compared to SH.  Sun hemp had significantly less re-growth, GW, or BLW than SS or LL with less than 1 DM kg/ha for all three measurements (p<0.05).  Lablab had the most re-growth and non-killed LL vegetation measuring 2,480 DM kg/ha (p<0.05) with 1,436 DM kg/ha GW and 444 DM kg/ha BLW.  For SH and SS there was less than 1 DM kg/ha of either GW or BLW, but SS had 1,436 DM kg/ha of CC re-growth compared to zero re-growth for the SH CC.  Sunn hemp performed well as a tropical cover crop producing the highest biomass levels and inhibiting weeds during CC growth. Sunn hemp responded well to termination with a roller-crimper by exhibiting a near 100% kill resulting in surface sheet mulch that inhibited weed development for over 30 days.