Effects of fallow replacement green manuring with annual legumes on soil nitrogen availability
Legume green manures are used in crop rotations to enhance soil nitrogen availability and to provide ground cover for soil conservation. The annual legumes Black Lentil, Chickling Vetch, Tangier Flatpea, and a Feedpea were grown with tall stubble snow trapping in rotation with spring wheat to determine their suitability for fallow replacement in wheat production systems in the Brown soil zone. The field experiment, conducted at Swift Current Research Station from 1984 to 1991, was designed to assess the different legume types and green manure management practices (inoculation, incorporation, and desiccation). The RCB included fallow-wheat and continuous wheat as controls. Only continuous wheat received nitrogen (N) fertilizer. Soil N availability was measured by analyzing five soil segments down to 120 cm depth for exchangeable ammonium and nitrate up to four times each year. The topsoil was also analyzed by an incubation/leaching technique to determine the potential N mineralization after three cycles of the rotation in 1990. Soil nitrate showed large treatment related variation. Nitrate values for legume green manuring were consistently higher after incorporation than after desiccation. In all treatments, topsoil nitrate was high in spring and lowest in July. In fall and spring following fallow and green manuring nitrate was high for the fallow-wheat and the legume-wheat rotations and low for continuous wheat. The initial potential rate of nitrogen mineralization reveals a lower nitrogen supplying power of the topsoil for fallow wheat than for legume/wheat and for fertilized continuous wheat.
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