Soil organic carbon and nitrogen pools are increased by mixed grass and legume cover crops in vineyard agroecosystems: Detecting short-term management effects using infrared spectroscopy

The incorporation of cover crops in orchards and vineyards can increase soil organic carbon (OC) and improve nitrogen (N) availability. This study compared how three herbaceous under-vine cover crop assemblages affected OC and N pools in four edaphically distinct vineyard agroecosystems. Using physical fractionation and soil spectral analysis we: 1) compared effects of grass and legume mono- and poly-cultures on total, coarse (>= 50 mu m) and fine (< 50 mu m) pools of OC and total N (TN), as well as extractable N (ExN), and 2) assessed predictions of OC and TN pools by infrared spectroscopy (IRS) and partial least squares regression analyses (PLSR). Compared with the control treatment, total, coarse and fine fraction OC were greater in the presence of grasses and legumes; ExN was increased 38% by legumes, and 78% in legume-grass mixture. With initial calibration, we used one soil spectral analysis to successfully derive models predicting contents of OC in the whole soil, and the allocation of OC to coarse and fine fractions. In addition to demonstrating the efficacy of incorporating grass and legume cover crops into vineyard cropping systems to improve OC and the storage and availability of N across diverse soil types, this study confirms the ability of IRS/PLSR to predict changes in OC concentrations related to differential ground cover management. IRS/PLSR is an important and practical approach for the rapid quantification of short-term management impacts on SOM pools, contributing significantly towards improved under- standing of soil C and N dynamics in vineyard agroecosystems.