Emergence of Forage Legume Seedlings as Influenced by Water Potential and Soil Strength

ABSTRACT The effects of water potential and soil strength on seedling emergence of 3 forage legume species, desmanthus (Desmanthus virgatus CPI 91146), glycine (Glycine latifolia CQ 3368) and cowpea (Vigna unguiculata cv. Red Caloona) were studied in red-brown earth and black earth under a controlled temperature in a growth chamber. 3 water potentials, -10, -300 and -750 kPa were applied in both soils. To achieve the desired levels of water potential, the soils were placed in columns of dialysis membrane and suspended in polyethylene glycol (PEG) solutions (molecular weight 10,000) of different concentrations until equilibrium was maintained making sure that the soil did not come in contact with PEG. Soil strength increased with decreased water potential and the effect was more rapid in red-brown earth than in black earth. Seedling emergence black earth occurred at water potentials of-10 and—300 kPa (soil strength of 0.64 and 1.98 kg/cm2 respectively) while in the red-brown earth seedling emergence was restricted to—10 kPa (soil strength of 1.75 kg/cm2). However, cowpea showed a greater emergence force by emerging at water potential of -750 kPa (soil strength 2.66 kg/cm2) in the black earth and at -300 kPa (soil strength of 5.27 kg/cm2) in the red-brown earth. Time to emergence increased with decreasing water potential and increased soil strength. Seedling emergence was rapid at both 0.64 and 1.75 kg/cm2 and delayed above this soil strength. It was concluded that low water potential and high soil strength restrict seedling emergence.