Water and Radiation Productivity in Short-Term Sequences As Opposed to Soybean Monoculture in Argentina.

Soybean occupies more than 70% of summer crop production area in Argentina, and only 30% of this area is planted as double crop after winter crops. This indicates that a great proportion of the year, land is under fallow and resource use efficiency low. The objective of this work was to quantify water (WP) and radiation productivity (RP) in soybean monoculture as compared with sequences that include a previous winter crop. A two year study was planned for comparing soybean monoculture (Sy) and Sy planted after: pea (P-Sy), short-season wheat (SWh-Sy), long-season wheat (LWh-Sy), barley (Ba-Sy) and a short-season maize (SMz-Sy), in Oliveros, Argentina (32º33’ S, 60º51’ W). Water and radiation capture (CWat and CRad) and use efficiencies (WUE and RUE) were calculated for estimating WP and RP in each sequence. Sy captured 548 MJ m^-2 and 509 mm of water, increasing by 22% in all winter-Sy sequences and 57% when SMz-Sy was planted. On annual basis, all sequences showed ca. 35% of CRad, increasing 23% over Sy. When grasses were previously planted RUE was 2.15 MJ g^-1, 70 and 64% greater than Sy and P-Sy, respectively. Ba-Sy, LWh-Sy and SMz-Sy used 717 mm, a respective 41 and 21% increase over Sy and P-Sy + SWh-Sy. All sequences showed a 71% increase in water use, as opposed to 53% of Sy. Only sequences that included grasses showed higher values of WUE than Sy. RP and WP increased ca. 2 times when grasses were in the sequence (0.75 g MJ^-1 and 1.5 g mm ^-1, respectively). Similar trend was observed with RP. SMz-Sy also showed increases of 42 and 16 % over all other sequences in WP and RP, respectively; however soybean planting in this sequence is more risky because of difficulties in having adequate soil moisture for planting.