Common bean in highly variable weather conditions, on sandy soils, and food security in a subtropical environment

Common bean is a vital component of food security and reduction in malnutrition in developing nations of the world. In a year of low rainfall and high temperature during flowering and high rainfall during grain filling, we studied the effects of (1) water availability and tillage on soil structural formation and on water retention, growth and productivity of common bean, and (2) time series analysis of soil available water and its relationship with related atmospheric variables. Soil management systems consisted of no-tillage (NT), conventional tillage (CT), chiseling 2 days before sowing (Ch0), and 1 year before sowing (Ch1), in complete randomized block design and four replications. Air temperature, rainfall, soil available water, and air capacity were monitored throughout the 78-days bean cycle, and time series analysis of data was performed. Water availability in topsoil reached limiting values, close to the permanent wilting point, limiting proper development of bean at flowering. Water availability was higher in periods of limited rainfall in untilled soils (NT and Ch1). Low soil availability of water and high air temperatures during flowering and grain filling stages affected grain production but grain yield did not differ statistically among tillage systems, which was similar to the average yield obtained in the state of Rio Grande do Sul. Temporal distribution of soil available water did not correlate with daily rainfall but correlated with air temperature. Time series analysis was adequate for estimating soil available water from its previous and related variables. Conservation agriculture (no-tillage and old-chiseling) improves water conditions in soil, but with long periods of water deficit there is no guarantee for high food production; thus, supplementary irrigation may still be necessary to reduce the combined effects of abiotic factors of air temperature and rainfall.