Light intensity effects on growth, physiological and nutritional parameters of tropical perennial legume cover crops

Authors: Baligar, Virupax; Elson, Marshall; HE, ZHENLI - University Of Florida; LI, YUNCONG - University Of Florida; PAIVA, ARLECELIO - University Of Santa Cruz - Brazil; AHNERT, DARIO - University Of Santa Cruz - Brazil; ALMEIDA, ALEX-ALAN - University Of Santa Cruz - Brazil

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2020
Publication Date: 10/6/2020
Citation: Baligar, V.C., Elson, M.K., He, Z., Li, Y., Paiva, A.D., Ahnert, D., Almeida, A.F. 2020. Light intensity effects on growth, physiological and nutritional parameters of tropical perennial legume cover crops. Agronomy. https://doi.org/10.3390/agronomy10101515.
DOI: https://doi.org/10.3390/agronomy10101515

Interpretive Summary: Soils under cacao are degraded due to soil erosion and leaching loss of nutrients. Fast growing perennial legume cover crops before and during the early stages of cacao establishment could reduce soil degradation and suppress weeds. However, growth and persistence of perennial legume cover crops in cacao plantation are affected by the level of light at their canopy levels. In this paper we report the existence of intraspecific differences for growth and macro and micronutrient use efficiency in cover crops when grown at low levels of irradiance. This information will be useful to farmers to select the most beneficial legume cover crops to grow in cacao plantation and for plant breeders to use in developing superior efficient leguminous cover crops to reduce soil degradation in plantation crops.

Technical Abstract: In early stages of establishment of plantation crops such as cacao, perennial legume cover crops provide vegetative cover to reduce soil and nutrient loss by erosion. Light intensity at cover crop canopy levels greatly influences their adaptability and optimum growth. As tree crops mature, understory cover crops suffer from inadequate levels of light intensity. A greenhouse experiment was undertaken with nine perennial legume cover crop species (Calopo, Ea-Ea, Jack Bean, Lab-Lab, Mucuna ana, Mucuna preta, Cowpea, Black Pigeon Pea, and Mixed Pigeon Pea) to assess the effects of three photosynthetic photon flux densities (PPFD, µmol m-2 s-1) 180 (inadequate), 450 (moderate) and 900 (adequate) on growth, physiological and nutrient uptake parameters. PPFD had highly significant effects on growth parameters of leaf, shoot and root and increasing light intensity from 180 to 900 µmol m-2 s-1 increased all growth parameters, with the exception of specific leaf area. In all the legume cover crops increasing light intensity significantly increased net assimilation rates (NAR), SPAD index, and net photosynthesis (PN) and its components, stomatal conductance (gs), evapotranspiration (E) and vapor pressure deficit (VPD). Cover crop species, PPFD and their interactions significantly affected water flux (Vo) and various water use efficiency parameters (WUE TOTAL, WUEINST and WUE INTR). Increasing PPFD increased WUE in all the cover crops. Species and PPFD had highly significant effects on uptake of macro- and micronutrients. Overall uptakes of all nutrients were increased with an increase in PPFD from 180 to 900 µmol m-2 s-1. Crop species and PPFD had significant effects on influx (IN) and transport (TR) of macro- and micronutrients. With few exceptions nutrient use efficiency (NUE) of the nutrients were significantly influenced by species, PPFD and their interactions. With the exception of Mn, increasing PPFD from 180 to 900 µmol m-2 s 1 enhanced NUE for all the nutrients.