Soybean effects on soil nitrogen availability in crop rotations.
Vanotti M.B. | Bundy L.G.
Soybean [Glycine max (L.) Merr.] production contributes significantly to the N supply for a following corn (Zea mays L.) crop, even though soybean N budget studies indicate that N removed in grain may substantially exceed biological fixation. Information on the N status of cereal crops during the 2nd yr following soybean may help resolve this issue. This study reports on N effects of soybean on yield response of succeeding cereal crops and soil N availability based on data from a 15-yr crop rotation experiment (1977-1991) on a Rozetta silt loam soil (Typic Hapludalfs) at Lancaster, WI. We evaluated the yields of corn and oat (Avena sativa L.) succeeding soybean and alfalfa (Medicago sativa L.) in corn-soybean-corn-oat-alfalfa (CSCOM) and corn-corn- oat-alfalfa-alfalfa (CCOMM) crop rotations. Fertilizer N (0, 56, 112, and 224 kg ha-1) was applied only to corn, but NO3-N carryover usually affected oat yields as well. The legume fertilizer N replacement values based on check plot yields and the response function of 3rd-yr corn in a corn-corn-corn-alfalfa-alfalfa sequence, were equivalent to 153 and 36 kg N ha-1 for the 1st and 2nd yr after alfalfa, respectively, and 75 kg N ha-1 for the 1st yr after soybean. In the 2nd yr after soybean (CSC(O)M), oat yields were significantly lower than following corn in the CC(O)MM rotation. Preplant soil NO3 and oat N uptake (1987-1991) indicated that oat yield differences were due to lower soil N availability in the CSCOM rotation. The average soybean effect on soil N availability in the 2nd yr was equal to a soil N debit of 36 kg N ha-1. This indicates that part of the N contribution of soybean to 1st-yr corn is realized at the expense of subsequent reductions in soil N availability.
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