Recovery of Fertilizer Nitrogen in Crop Residues and Cover Crops on an Irrigated Sandy Soil
2005
Bundy, Larry G. | Andraski, Todd W.
Nitrogen fertilizer inputs for intensive, irrigated crop production on sandy soils can contribute to elevated NO₃ concentrations in groundwater. This study was conducted from 1995 to 1998 to determine the potential of a winter rye (Secale cereale L.) cover crop to recover fertilizer N from soil and crop residues and the availability of this N to corn (Zea mays L.). Nitrogen fertilizer treatments included no N and N-labeled (¹⁵N-depleted) fertilizer (NLF) applied to sweet corn at 190 kg ha⁻¹ and to potato (Solanum tuberosum L.) at 224 kg ha⁻¹ Cover crop treatments (fallow and winter rye) were established following harvest, plowed the following spring, and corn was grown with unlabeled fertilizer N at 112 kg ha⁻¹ Whole plant fertilizer N recovery averaged 54% for sweet corn and 34% for potato using the NLF (¹⁵N isotope) method, and was significantly lower than N recovery determined by the difference method. Total NLF recovery decreased between harvest and the following spring (from 66 to 43% following sweet corn and from 47 to 37% following potato), presumably due to mineralization and leaching of crop residue N. Winter rye NLF uptake averaged 2 kg ha⁻¹ and had no effect on total NLF recovery. Corn grain yields were significantly higher following potato than following sweet corn and following a winter rye cover crop compared with fallow in 2 of 3 yr. Corn NLF uptake averaged 3 kg ha⁻¹ indicating the yield benefit following potato or winter rye was due to a rotation effect rather than a direct N contribution. These results indicate that on irrigated sandy soils in this region most of the N fertilizer not removed in the harvested portion of crops will be lost by leaching during the growing season or by the following spring.
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