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This article in AJ

  1. Vol. 86 No. 5, p. 881-886
    Received: June 18, 1993

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Frequency of Nitrogen Fertilizer Carryover in the Humid Midwest

  1. Matias B. Vanotti and
  2. Larry G. Bundy 
  1. Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, W153706-1299



Soil tests for residual NO-3 can improve prbdiction of crop N fertilizer requirements in the humid Midwest, but their adoption as a standard procedure in fertilizer N recommendation programs depends on the frequency of significant profile NO-3-N carryover. Data from a 25-yr crop sequence experiment (1967 to 1991) on a Rozetta silt loam soil (finesilty, mixed, mesic Typic Hapludalf) at Lancaster, WI, were used to estimate the frequency and extent of N fertilizer carryover. Sequences studied included unfertilized oat (Avena sativa L.) grown after corn (Zea mays L.) that received a range of N rates. Oat yields were influenced by the residual effects of the previous year's N application in 21 of the 25 yr, with yield responses varying from 500 to 1500 kg ha−1. Soil profile measurements (0 to 90 cm) taken before seeding oat in spring 1987 through 1991 showed substantial NO-3-N carryover that was usually found below the 30-cm depth. Significant increases in profile NO-3-N content occurred at low N rates (56 to 112 kg N ha−1) in years with limited rainfall during the preceding corn growing season, but only at higher N rates under optimum corn growing conditions. Total N uptake by oat was also significantly affected by corn N treatments, and it was well correlated with profile NO-3-N. A nutrient efficiency index that characterized the yield response of oat to profile NO-3-N was used to estimate carryover NO-3-N from 1967 to 1986 oat yield data. Expected N fertilizer carryover values (P = 80%) ranged from 32 to 106 for a 168 kg N ha−1 rate, and from 63 to 151 kg NO-3-N for a 224 kg N ha−1 rate. The wide variation of expected amounts of N carryover reflects typical year-to-year changes in conditions affecting N recovery by corn and retention by soil. Results of this study indicate that significant residual profile NO-3-N occurs in most years on well-drained silt loam soils in Wisconsin, and that year-specific tests for profile NO-3-N are needed to adjust N recommendations for varying amounts of NO-3-N carryover.

Research supported by the College of Agricultural and Life Sciences, Univ. of Wisconsin-Madison, through Project 3449

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