Solar radiation use efficiency by soybean under field conditions in the Amazon region

Paulo Jorge De Oliveira Ponte De Souza Souza,Leila Sampaio,José Renato Bouça Farias,Aristides Ribeiro,Renata Silva Loureiro,Edson José Paulino Da Rocha,Carlos Capela Bispo

doi:10.1590/s0100-204x2009001000001

Abstract

The objective of this work was to evaluate the efficiency of soybean (Glycine max) in intercepting and using solar radiation under natural field conditions, in the Amazon region, Brazil. The meteorological data and the values of soybean growth and leaf area were obtained from an agrometeorological experiment carried out in Paragominas, Pará state, during 2007 and 2008. The radiation use efficiency (RUE) was obtained from the ratio between the above-ground biomass production and the intercepted photosynthetically active radiation (PAR) accumulated to 99 and 95 days after sowing, in 2007 and 2008, respectively. Climatic conditions during the experiment were very distinct, with reduction in rainfall in 2007, which began during the soybean mid-cycle, due to the El Niño phenomenon. An important reduction in the leaf area index and biomass production was observed during 2007. Under natural field conditions in the Amazon region, the values of RUE were 1.46 and 1.99 g MJ-1 PAR in the 2007 and 2008 experiments, respectively. The probable reason for the differences found between these years might be associated to the water restriction in 2007 coupled with the higher air temperature and vapor pressure deficit, and also to the increase in the fraction of diffuse radiation that reached the land surface in 2008.

Highlights

In recent years, the agricultural frontier in the Amazon has been advancing at an increasing rate, and the soybean crop has often been considered the main responsible for this (Dantas & Fonteles, 2005), which is a troublesome fact because of the impacts it causes on the regional climate pattern (Fearnside, 2001; Costa et al, 2007)
In 2006, the cultivated area in Pará state reached 90,000 ha, with a mean productivity of 3 Mg ha-1 (Governo do Pará, 2009). These changes in the Amazon land use may cause serious environmental impacts, such as the decrease in local precipitation, in comparison to the reduction caused by land for pasture (Costa et al, 2007), it is important to highlight that the expansion of soybean culture towards low latitudes has occurred as a strategy to supply the increasing population growth and the consequent demand for food and biofuel
In 2007 precipitation was reduced, with a total monthly amount lower than the normal rain regime and lower than the amount observed in 2008 (Figure 1), which resulted in lower values of fraction of transpirable soil water in the first year (Figure 2)

Summary

Introduction

The agricultural frontier in the Amazon has been advancing at an increasing rate, and the soybean crop has often been considered the main responsible for this (Dantas & Fonteles, 2005), which is a troublesome fact because of the impacts it causes on the regional climate pattern (Fearnside, 2001; Costa et al, 2007). In 2006, the cultivated area in Pará state reached 90,000 ha, with a mean productivity of 3 Mg ha-1 (Governo do Pará, 2009) These changes in the Amazon land use may cause serious environmental impacts, such as the decrease in local precipitation, in comparison to the reduction caused by land for pasture (Costa et al, 2007), it is important to highlight that the expansion of soybean culture towards low latitudes has occurred as a strategy to supply the increasing population growth and the consequent demand for food and biofuel. Such relation is defined as the efficiency with which the captured radiation is used to produce new material (Black & Ong, 2000), and it has been successfully used as a tool to simulate the growth of different cultures (Albrizio & Steduto, 2005)

Objectives

Methods

Results