In 2007-2009, at the Experimental Agricultural Station in Lipnik near Stargard Szczeciński, a field experiment was performed on acid brown soil of the good wheat complex. This soil in the topsoil contained 8.2 g kg-1 of organic C, had a slightly acid reaction and a low contents of available forms of P (30.1 mg kg-1) and K (45 mg kg -1). During the growing season the ground water level re-mained below 3.0 m.The aim of the studies was to compare the yield potentials of corn and two hybrids of sweet sorghum cultivated in conditions of various humidity of the light soil. On the plots with and without drop irrigation, sweet sorghum (the Sucrosorgo-506 and Rona-1 varieties) and corn (the variety Oldham FAO-250), of which the latter was the species compared. The times and doses of irrigation were determined based on indications of soil tensiometers. To the irrigation a dropping line of a capacity of 2.4 l h-1 of water and emitters spaced 30 cm apart was used. The combined doses of water depended on the timing and amount of rain-falls and were: in 2007 - 40 mm, in 2008 - 150 mm, in 2009 - 110 mm. The plant density of corn was 111 000 ha-1 (60 x 15 cm), and that of sorghum 222 000 ha-1 (30 x 15 cm). The dry yield of shoots of Sucrosorga-506 was significantly higher than that of corn and sorghum of the Rona-1 variety. Irrigation increased the dry yields of Sucrosorga-506 by 7.1 t ha-1, corn by 4.8 t ha-1 and sorghum of the Rona-1 variety by 2.9 t ha-1. Irrigation more decreased the contents of dry matter in shoots of sorghum varieties than in those of corn and also influenced the yield structure. Irrigation increased the weight of corn cobs and the yield of shoots and panicles in sorghum varieties, but decreased the weight of their other organs. The productivity of 1 mm of irrigated water expressed in yields of dry matter was high-est for Sucrosorga-506 (98.6 kg mm-1 ha-1) and corn (80.1 kg mm-1 ha-1), and much lower for the Rona-1 variety of sorghum (42.2 kg mm-1 ha-1).
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