Balanço de radiação e energia numa cultura de soja irrigada.

Abstract

This research was conducted at the experimental station of CPATSA / EMBRAPA, in the irrigated perimeter of Mandacaru, Juazeiro-BA, aiming to study the behavior of irrigated soybean (Glycine max. (L.) merrill) cultivated in semi-arid conditions of the Brazilian Northeast. We tried to evaluate the components of the energy and radiation balances, comparing the measured results with those obtained by conventional empirical formulas, aiming to adjust them to the local and culture conditions. Observations occurred throughout the experimental period between September and December 1987, with continuous daytime recordings and hourly readings of the radiation balance (Rn); global radiation (Rs4); and reflected shortwave radiation (Rt). Hourly measurements of crop evapotranspiration (ET ^), soil heat flow (G), dry and wet bulb temperatures and foliage temperature were also performed. Weekly dry matter yield, leaf area index (LAI) and crop height (h) were evaluated every three days. The albedo (a) ranged from 0.12 at the beginning of the observations to a maximum of 0.25 in the flowering phase, showing daily fluctuations, especially after irrigation. IAF and h reached maximum values ​​of 8.5 to 8 9.2 cm, respectively. The results show that the daily estimation of Rs ^ / by hourly readings can present considerable errors, depending on the cloud cover and type. The best estimates of Rn were obtained by the PENMAN equation (1948), adapted to local and cultural conditions. The available radiant energy balance represented 62% of the global radiation incident during the experimental period. The energy used for evapotranspiration considerably exceeded Rn, while 1.45% of the radiation balance was used for dry matter production.