Rainfall Variability and Soybean Yield in Paraná State, Southern Brazil
Abstract
Agriculture (the agricultural exports flagship from southern Brazil) is highly dependent on temporal rainfall distribution. However, the technology used in the field has been altering this relationship. Such technology, in addition to minimizing the effects of climate variability, has increased the annual soybean yield observed in the trend analysis, which was positive in 17 of the municipalities studied. The aim of this study was to analyze the rainfall variability and soybean production in one of the areas of greatest soybean production in southern Brazil by applying the quartile, percentile, Pettitt (homogeneity - break results) and Mann-Kendall (trend) tests. The results indicate a significant relationship between annual rainfall variability (1999-2000; 2009-2010) and soybean yield (kg/ha), particularly during the growing season of 2009-2010 when the yield variation between municipalities was low. It was concluded that the statistically significant correlations indicate that the soy dependence ranges from 22% to 50% in certain municipalities.
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Introduction
The potential impact of climate change on agricultural production has often been evaluated on national and regional scales. In much of the tropics, rainfall is the main factor responsible for annual fluctuations in the grain yield. Between 60% and 70% of agricultural production is explained by interannual rainfall variability (Camargo 1984; Göpfert et al. 1993; Pereira et al. 2002; Goldblum 2009).
A correlation analysis by Krishna Kumar et al. (2004) described indicators of the effects of monsoonal rains and its potential (surface temperatures and sea level pressures in the Pacific and Indian Oceans) to affect in agricultural yield in India. The conclusion was that there is a significant correlation between the total annual yield in India (except for sorghum and sugarcane) and the total rainfall during the summer monsoon.
Goldblum (2009) reported that corn yield in the United States is negatively correlated with the temperatures in July and August in much of the state of Illinois and positively correlated with rainfall in September (in the central portion of the state) and rainfall in July and August in most of southern and northern Illinois. The soybean yield is negatively correlated with the mean monthly temperature in central and southern Illinois during the summer and positively correlated with rainfall in July and August in the same regions.
Penalba et al. (2007) analyzed the impacts of climate variation on agriculture in the primary agricultural region of Argentina, the Pampas. Simple correlations between certain variables quantitatively confirm that the air temperature and rainfall are the main climate factors that determine the variation in agricultural production.
Farming practices in Brazil have changed in the last 30 years, particularly with regard to agricultural modernization and techniques for minimizing climatic influences on productivity (Assunção 2002; Wilhelmi et al. 2002).
In developing countries, the relationship between the annual production of some commodities and droughts is often considered by researchers in the biological and natural sciences due to the agricultural conditions in these countries. After all, droughts can seriously affect the growth and development of plants (Rodrigues et al. 2015). These concerns are observed in countries in which capitalism is peripheral, which are more vulnerable to droughts because there is less investment in technology to minimize these effects; they are derived from policies focused on grain yield and justified by the need to produce food. Therefore, losses and annual fluctuations in the yield of grains such as soybeans economically impact the manufacture of many other products.
Almeida and Sant’Anna Neto (2007) concluded that in Brazil, particularly in the states of Rio Grande do Sul, Paraná and Mato Grosso, the soybean yield is correlated with and depends on the rainfall, which is increased in subtropical latitudes and decreased in tropical ones.
Because soybeans are one of the most important agricultural products in the world (Rodrigues et al. 2015) and are currently acquiring a central role in food security and the world food demand (Sentelhas et al. 2015), the aim of this study was to analyze the rainfall variation and its impact on soybean productivity during the growing season of October to April in producing areas in the state of Paraná, southern Brazil, during the agricultural years of 1999-2000 to 2009-2010.
Conclusion
We conclude that the historical rainfall series is homogeneous because of the low break results, although there is a marked increasing trend in the rainy season totals (October-April) exclusively at the rainfall stations located in the areas with a predominantly tropical climate (central and northern water basins). There were significant increasing trends in soybean yields in 15 (11%) of the municipalities. In general, there is a marked relationship between the analyzed variables, particularly in growing seasons of unusual rainfall: the extremely dry, dry, rainy and extremely rainy years. It was found that soybean yield among the municipalities is negatively correlated decreased total annual rainfall and positively correlated with rainfall when rainy periods occur. There was a significant correlation between the increased rainfall and increased yield. There was an increasing trend of both the annual rainfall and total soybean yield, particularly in the central and northern regions of the basin. There was no significant trend of increased soybean yield in most municipalities; increases occurred in only 17 of them (13%). This result is considered an indicator of what has been occurring in recent decades in Brazil and other countries in the developing world that are soybean producers, such as Argentina and India. These countries have become major commodity producers to support the constantly growing needs of consumers. The statistically significant correlations indicate that the soy dependence ranges from 22% to 50% in certain municipalities. Although the results indicate correlations, this type of dependence in Brazil has been decreasing, particularly in crops that are important for export. This is a consequence of the investments in science, technology and innovation in agribusiness, which is supported by the results indicating a trend of increasing yield in the municipalities of the northeastern basin. This pattern may be attributed to the current context of global markets, in which increases in income and decrease in costs and risks are basic requirements for competitiveness. To reduce yield losses caused by the annual rainfall variability, crops with different characteristics, such as drought-tolerant cultivars, and different types of crop management can be used (Farias et al. 2009; Battistti and Sentelhas 2015). However, this solution is not available to small and medium landowners, who do not have access to technological innovation due to either financial inability or lack of access to information. This situation occurs in regions with unequal peripheral capitalism, such as Brazil and its infrastructure-poor municipalities, including some examples in the state of Paraná.
