Effect of water deficiency on the water use and yield of soybean.

MIRASSÓN, H.; BREVEDAN, R.E.; BAIONI, S.S.; FIORETTI, M.N.

Beijing, China

Conferencia; First International Conference on the Theory and Practices in Biological Water Saving.; 2006

Soybean is the most important crop in Argentina, that it is the third largest producer in the world. Soybeans are grown in many areas where rainfall is scarce and intermittent periods of water stress of some degree and duration is almost certain to occur during the soybean ontogeny. The magnitude of the seed yield reduction that occurs when soybean are under water stress is dependent upon the timing of the stress. Soybeans are sensitive to both the amount and distribution of moisture. The objective of this research was to measure under water-deficiency -at different reproductive growth stages- and under well-irrigated conditions, the water use and yield of soybeans . The field study was conducted in Ascasubi (Buenos Aires province, 39°23’S 62°37’W). The soil was sandy loam. The soil profile did not have any physical constraint up to 1.60 m. A soybean maturity group III cultivar was used. The plant population was 350,000 plants ha-1. After planting, aluminum access tubes 1.50 m in length were installed near the center of each plot. Soil moisture content was determined weekly with a neutron probe (Troxler model 1255 with scalimeter model 2600) during the growing season in 0.25-m increments up to 1.50 m. Soil water content at the first sampling date was considered as the initial soil water content. The total water use by each crop to a depth of 1.50 cm was estimated by subtracting the soil water content at or near the crop’s harvest date from the initial soil water and adding the precipitation within that period. Water lost through percolation was not taken into consideration because with the prevailing precipitation pattern would be negligible. Four treatments were applied. There were three water deficient treatments, that were irrigated throughout the growing season except for a 20-day drought period, applied at different crop reproductive stages (Fehr and Caviness. 1977. Spec. Rep. 80. Coop. Ext. Serv., Agric. Exp. Stn, Iowa Sate Univ, USA.): treatment 1, the stress period included R1 to R3 stages, treatment 2, R4 and part of R5, treatment 3, part of R5 and R6. Treatment 4 was irrigated throughout the whole growing season. The experiment was set in a completely randomized block design, with 4 treatments and 6 replications. Each plot consisted of 6 rows, 0.35 m apart and 6 m long. The total water use by the well irrigated control (treatment 4) was 45.2 cm. Most of that occurred during the reproductive period. The water use decreased from treatments 1 (42.6 cm) to treatment 2 (37.6 cm) and 3 (38,4 cm). Yield in the control treatment was 2723 kg ha-1 and was reduced up to 29% in treatment 3, the lowest yielding treatment.