Response of nine soybean lines to soil moisture conditions close to saturation

Abstract

The effects of two constant water table treatments, maintained at 3 and 15 cm below the soil surface (CWT 3 and CWT 15, respectively), were compared with the effect of overhead irrigation (OHI) on dry matter production of nine soybean (Glycine max) lines, grown for 36 days in beds of soil in the glasshouse. The lines represented a range of maturity groups. Water for each irrigation treatment was supplied with, or without, dissolved inorganic nitrogen (100 ppm N), on a split plot basis. CWT 15 plants accumulated 37% more dry matter, and 35 times more nodule dry matter, than did OH1 plants. CWT 3 plants became very chlorotic within a week of imposing the water table, but recovered to produce only 18% less dry matter than the OHI plants. CWT 3 plants accumulated the greatest amount of nodule dry matter, and this fraction accounted for 5% of total plant dry weight in some lines. Plants in both of the water table regimes were taller than the OHI plants, even for lines that flowered in 21 days, and this effect reduced the cultural disadvantage of short stature normally noted in early flowering lines. Nitrogen application marginally increased shoot proportion, plant height and node number, but decreased nodule mass in CWT 15 and OHI plants. The study indicated that soybeans can respond well to permanent water tables maintained close to the soil surface, and attain rapid early growth independent of applied nitrogen. Projections suggest that high yields of seed are feasible in 80-85 day soybean crops growing on a controlled water table system. This system also may promote other operational efficiencies related to a shortened cropping cycle, simplified water management, and weed control.