Submitted to: Journal of Plant Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/5/2006
Publication Date: 8/1/2006
Citation: Baligar, V.C., Fageria, N.K., Paiva, A.Q., Silveria, A., Pomella, A., Machado, R. 2006. Light intensity effects on growth and micronutrient uptake by tropical legume cover crops. Journal of Plant Nutrition. 29:1959-1974. Interpretive Summary: In plantation crops, the soil is unprotected, especially during early growth stages, and is subjected to loss by erosion. Inclusion of fast growing cover crops in the early stages of plantation crop establishment could help to reduce soil erosion, nutrient leaching and increase organic matter buildup leading to restoration of soil productivity. Cover crops grown in plantation systems as understory plants do not receive full sun light. Cover crops that tolerate low light intensity will have greater impacts on soil fertility and productivity of plantation crops. Productivity and persistence of cover crops, in tropical plantation crops is therefore greatly influenced by light intensity at ground level and soil fertility status. An experiment was conducted under controlled conditions, with the objective of evaluating the influences of two light intensities on growth and micronutrient uptake and use efficiencies of nine tropical legume cover crops. Increased light intensity improved nutrient utilization efficiency. Regulation of light intensity through proper shade and maintenance of adequate levels of micronutrients in soil appears to be critical in a plantation system to achieve the maximum potential benefits of cover crops. Cover crops that can grow in low light intensity could be useful to plantation farmers of tropical regions to reduce soil erosion losses.
Technical Abstract: Cover crops are important components of a sustainable crop production system in plantation crops such as cacao, coffee, oil palm and banana. Optimal growth of cover crops in plantation agriculture is determined by adaptability of crop species, light intensity reaching their leaf canopies and their nutrient use efficiencies, including that of micronutrients. An experiment was conducted in a climatically controlled growth chamber to evaluate the influence of levels of light intensity on growth, and micronutrient (B, Cu, Fe, Mn, and Zn) uptake parameters in legume cover crops. Two photosynthetic photon flux density (PPFD, 200 and 400 µmol m-2 s-1) light treatments were imposed on nine legume species (joint vetch, sunhemp, crotalaria ochroleuca, showy crotalaria, hairy indigo, lab-lab, sesbania, Brazilian stylo and cowpea). Overall light intensity significantly affected the growth and micronutrient uptake and use efficiency ratios and, with few exceptions interactions between cover crop species and PPFD were also significant. Such PPFD x crop species interactions showed that cover crops used in this study differed in growth and nutrient uptake parameters under the conditions imposed. Sunhemp, cowpea, sesbania and lab-lab species were superior in producing shoot dry weight and in nutrient accumulation compared with other species at lower as well higher PPFD levels. Inter-specific differences in nutrient influx and transport were observed. Influx and transport of micronutrients was in the order of Mn > B > Fe > Zn > Cu. Overall, growth, nutrient uptake and use efficiency ratios were higher with higher PPFD than lower PPFD. Results of this study indicated that use of proper crop species at adequate light intensities are important components of successful cultivation of cover crops in plantation agriculture.