Enhancing Tropical Conservation Tillage Cropping Systems with Sunn Hemp (Crotalaria juncea) Cover Crop Residue As in Situ Mulch in the Production of Organic Calabaza Pumpkin (Cucurbita moschata).

In the tropics, accelerated soil fertility decline and soil degradation is attributed to extensive tillage. Farmers typically soil incorporate crop residue prior to vegetable field soil preparation, and rely upon mechanical soil disturbance as a primary means to suppress weeds. Problematic weed control in reduced tillage cropping systems is cited as a primary reason by farmers not to adopt conservation tillage practices. Innovative conservation tillage practices that utilize cover crop residues as in situ mulch could benefit soil quality and suppress weeds. The primary objective of this research is to evaluate an integrated approach to soil conservation and weed management by utilizing sunn hemp (Crotalaria juncea L. cv. Tropic Sunn) cover crop residue as in situ surface mulch in reduced tillage tropical organic vegetable cropping systems. Experiments were conducted at two independent, on-farm field sites on St. Croix, USVI that began in 2016 and ended in 2017. Sunn hemp was established in both experimental fields on September 16, 2016 and mechanically terminated with a roller-crimper on January 18, 2017. Three treatments were replicated three times in a randomized complete block design. Treatments included: 1) sunn hemp mulch (SHM), 2) sunn hemp mulch plus hay (SHM+hay), and 3) sunn hemp mowed and soil incorporated that served as a check plot (SH+none). A tractor mounted minimum-till ripper was used to make planting furrows (1.5 m apart) in all treatments; then direct seeded with Calabaza (West Indian) pumpkin (Cucurbita moschata). In-row seed spacing was 1.2 m with rows spaced at 1.5 m for an estimated 5,382 pumpkin plants/ha. Row and row-middle weed populations were assessed at 3, 6, 9, and 12 weeks after planting (WAP). Following each weed sampling all weeds were removed from each plot by hand labor. Hay mulch was applied to the pumpkin SHM+hay treatment directly following the 3-week weed assessment. Above-ground biomass of sunn hemp at termination did not differ between fields; and measured 5,563 kg ha^-1 in field 1 and 5,701 kg ha^-1 in field 2. Overall, weed biomass results (at 3, 6, 9, and 12 WAP) indicate that there was either no difference in weed biomass across treatments or that the SHM+hay treatment had less weeds than both the SHM and SH+none treatments, which were similar. Total pumpkin yield differed by field, but not by treatment yielding a mean of 56,027 kg ha^-1 (10.4 kg ha^-1 per plant). However, the two greatest pumpkin yields were measured in the SHM+hay and SHM treatments in field one at 79,973 and 70,796 kg ha^-1, respectively. Unmarketable yield did not differ by treatment or field with a mean of 795.5 kg ha^-1 accounting for approximately 1% of the total harvest. Results indicate that pumpkin cropping systems that soil incorporate SH residue (full tillage) did not provide increased weed suppression compared to conservation tillage pumpkin production systems when planted into in situ SH mulch. Therefore, conservation tillage when integrated with cover crop mulching strategies can provide alternatives to full tillage with similar or reduced weed biomass without sacrificing pumpkin yields.