2017 ASHS Annual Conference

In the tropics, accelerated soil fertility decline and soil degradation is attributed to extensive tillage. Farmers typically soil incorporate cover crops prior to vegetable field soil preparation, and rely upon mechanical soil disturbance as a primary means to suppress weeds. Alternative conservation tillage practices coupled with cover crop residue mulching strategies 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 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 randomized and replicated three times in a split plot design; then direct seeded with either calabaza (West Indian pumpkin) pumpkin (Cucurbita moschata) or okra (Abelmoschus esculentus). Treatments included: 1) sunn hemp mulch (SHM), 2) sunn hemp mulch plus hay (SHM+hay), and 3) sunn hemp mowed and 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. In-row seed spacing was 1.2 and 0.6 m for pumpkin and okra, respectively. Row and row-middle weed populations were accessed at 3, 6, 9, and 12 weeks after planting (WAP). Following each weed sampling all weeds were removed from each plot by hand labour. Hay mulch was applied to the pumpkin SHM+hay treatment directly following the 3-week weed assessment and to the okra SHM+hay treatment directly following the 9-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. At 3 WAP, there was no difference in total weed biomass between crops or treatments. Rows had nearly four times more weeds (77.4 kg ha^-1 of total weeds) compared to row-middles (19.8 kg ha^-1 of total weeds) due to in-row drip irrigation. At 6 WAP, differences in total weed biomass were only observed in treatment rows and did not differ by crop. The SHM+hay (38.8 kg ha^-1) treatment was less weedy than either the SHM (110.8 kg ha^-1) or the SH+none (118.2 kg ha^-1) treatment. At 9 WAP, there were no differences in total weed biomass for crop, treatment, or by row/row-middle. These results indicate full tillage incorporation of SH cover crop residue does not provide increased weed suppression compared to SH cover crop residue managed with conservation tillage in subsequent direct seeded pumpkin and okra crops. Therefore, conservation tillage when integrated with cover crop mulching strategies can provide alternatives to full tillage with similar or reduced weed biomass.