Impact of different cover crops and termination methods on collard yield

Authors: Kornecki, Ted

Submitted to: European Agrophysical Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2019
Publication Date: 1/15/2020
Citation: Kornecki, T.S. 2020. Impact of different cover crops and termination methods on collard yield. European Agrophysical Journal. 6(4):50-66.

Interpretive Summary: A field experiment during three years at Northern Alabama evaluated the effects of six summer cover crops and their management: rolling and flail mowing on collard green yield in no-till system. Cover crop termination rates were lower than recommended >90% to plant the cash crop into the residue cover. These lower termination rates for rolled residue were associated with regrowth and regeneration of already rolled plants. In addition, uneven soil surface across the width of the roller inhibited termination rates, as plant stems in depressions (voids) were not crimped by crimping bars and able to recover. Trailing cover crops such as velvet bean and iron clay peas are generally more difficult to terminate because of their long stems that do not tent to crush like much taller crops. To increase cover crop termination rates, multiple passes of the rolling/crimping operation or applying supplemental herbicides may be necessary. During three growing seasons, with exception of iron clay pea, volumetric soil moisture content during evaluation have showed that rolled plots consistently held more VMC than the standing cover crops. In 2013 growing season, the yield for collards were significantly higher compared to 2014 and 2015. This higher collard green yield was associated with the presence of legume cover crops, and most likely these legumes released fixed nitrogen upon their decomposition. Overall, because of less weed pressure, collard green yield was higher for flail mowed cover crops producing 11,875 kg ha-1 compared to 7,349 kg ha-1 for rolled/crimped cover crops.

Technical Abstract: A three-year experiment was conducted in Cullman, AL, to determine the impact of iron clay pea, sunn-hemp, soybean, velvet Bean, sorghum sudan, and pearl millet cover crops terminated with two methods (rolling and flail mowing) on collard (brassica oleracea var. acephala, L.) yield. Overall, each of the three growing seasons (2013, 2014, and 2015) produced significant differences in cover crop biomass production among cover crops. Across three growing seasons sorghum Sudan and Pearl Millet generated the highest biomass (23,752 and 23,333 kg ha-1 respectively). During the same period, sunn hemp produced 10,908 kg/ha-1 and soybean, velvet bean and iron clay pea produced lower biomass (6,754, 6,068, and 4,360 kg ha-1, respectively). Termination rates of cover crops used in this study were mostly below 90%. Termination rates above 90% have been recommended by agricultural extension services to plant cash crop into cover crop residue. In all three growing seasons volumetric soil moisture content during evaluation have showed that plots with rolled residue consistently held more VMC than the standing cover crops, indicating that rolled cover crop residue better preserved soil moisture content. Collard green yield was significantly different in each growing season for different covers and termination methods. Averaged over three growing seasons, the highest collard yield was observed for iron clay pea (12,623 kg ha-1), Velvet bean (11,020 kg ha-1) and Sunn hemp (10,802 kg ha-1). Data suggest that higher collard yield was obtained with legume cover crops with the benefit of released nitrogen into the soil and utilized by collards. In addition, across all years, the average collard green yield was higher for cover crops which were flail mowed (11,875 kg ha-1) compared to rolled/crimped cover crops (7,349 kg ha-1).