Relative Nitrogen Utilization by Legume Cover Crop Species at Three Soil Temperatures

Abstract

AbstractWhen selecting a legume cover crop, one should know relative N‐fixing and N uptake capabilities, as well as growth and water use characteristics, to identify the species best adapted to the growth period and soil temperatures (season) during which the cover is crop grown. We provide information on these characteristics for eight inoculated legume species at soil temperatures of 10, 20, and 30 °C. Plants were grown in constant‐temperature water baths in a greenhouse for 105 d after establishment in 1.1 kg of Alliance silt loam (fine silty, mixed, mesic, Aridic Argiustoll) per pot. Plant samples were taken every 21 d for determinations of dry weight, total N uptake, and N2 fixed (isotope dilution method). Water use was measured daily by weighing. Total N uptake and N2 fixation were usually greatest for large‐seeded annual species during the first 42 to 63 d of the experiment. At 10 °C total N uptake and N2 fixation were greatest for hairy vetch (HV), Vicia villosa Roth and faba bean (FB), Vicia faba L. At later sampling dates, N uptake and fixation for white clover (WC), Trifolium repens L., was also relatively high. At 20 °C, soybean (SB), [Glycine max (L.) Merr.] exhibited outstanding growth and N uptake throughout the 105 d. For the first 42 d, FB performance also was superior to other species. At 30 °C, N uptake and fixation by SB was more than double that of any other species at all sampling dates. Quantity of N2 fixed per unit water used was greatest at 10 °C for WC, followed closely by HV and field pea (FP) Pisum sativum L.; at 20 °C, SB followed by WC and lespedeza (LD), Lespedeza stipulacea Maxim.; and at 30 °C, LD followed by SB. Our results suggest that under many situations (early spring) some grain legumes, such as and FB, may be a better cover crop than many species commonly used.