Light Intensity Effects on the Growth, Physiological and Nutritional Parameters of Tropical Perennial Legume Cover Crops

V C Baligar,D Ahnert,A A F Almeida,M K Elson,Y Li,Z He,A De Q Paiva

doi:10.3390/agronomy10101515

Abstract

In the early stages of the 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 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 (PPFDs, µmol m−2 s−1) 180 (inadequate light), 450 (moderate light) and 900 (adequate light) on growth, physiological and nutrient uptake parameters. PPFD had highly significant effects on leaf, shoot and root growth parameters and increasing the 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 the light intensity significantly increased the net assimilation rates (NAR), SPAD index and net photosynthesis (PN) and its components, stomatal conductance (gs), transpiration (E) and vapor pressure deficit (VPD). Cover crop species, PPFD and their interactions significantly affected water flux (Vo) and various water use efficiency parameters (WUETOTAL, WUEINST and WUEINTR). Increasing the PPFD increased the WUE in all of the cover crops. Species and PPFD had highly significant effects on the uptake of macro- and micronutrients. Overall uptakes of all nutrients were increased with increases in the PPFD from 180 to 900 µmol m−2 s−1. With few exceptions, the nutrient use efficiency (NUE) of the nutrients was significantly influenced by species, PPFD and their interactions. Except for Mn, increasing the PPFD from 180 to 900 µmol m−2 s −1 increased the NUE for all the nutrients.

Highlights

Fast growing cover crops before and during the early stages of establishment of widely spaced perennial crops such as cacao, coffee, oil palm and rubber can reduce soil erosion, reduce nutrient losses, suppress weeds and improve soil health [1]
Cover crops are grown as understory plants they do not receive full sunlight and as upper story trees grow the amount of photosynthetic photon flux density (PPFD) received at the cover crop canopy is reduced
The cover crop species studied in this experiment showed significant interspecific differences for growth parameters at inadequate to adequate light intensities

Summary

Introduction

Fast growing cover crops before and during the early stages of establishment of widely spaced perennial crops such as cacao, coffee, oil palm and rubber can reduce soil erosion, reduce nutrient losses, suppress weeds and improve soil health [1]. Establishment of fast growing cover crops can reduce soil loss by erosion, minimize nutrient loss by leaching and increase organic matter and N content, thereby restoring soil productivity [1,2,3,4,5,6]. Cover crops are grown as understory plants they do not receive full sunlight and as upper story trees grow the amount of photosynthetic photon flux density (PPFD) received at the cover crop canopy is reduced. In tropical regions, incoming PPFD is around 1800 μmol m−2 s−1 [7]

Methods

Results

Conclusion