• Integrating Ecological Stoichiometry to Understand Nutrient Limitation and Potential for Competition in Mixed Pasture Assemblages

      Ball, K. R.; Woodin, S. J.; Power, S. A.; Brien, C.; Berger, B.; Smith, P.; Pendall, E.; Department of Environmental Sciences, University of Arizona (Springer Science and Business Media LLC, 2021-06-29)
      Purpose: Much is known about growth and nutrient uptake traits and ecological stoichiometry in natural systems. However, these concepts have been comparatively understudied in agricultural systems despite their potential to infer nutrient limitation and interspecific resource competition. Methods: This study established a model mixed pasture system to assess tissue C:N and C:P stoichiometry and aboveground biomass (AGB) in a grass (Phalaris aquatica) and legume (Trifolium vesiculosum) under factorial inputs of high and low nitrogen (N) and phosphorus (P), in monoculture and mixture. Due to inherent trait diversity, we expected grass and legume growth, shoot vs root stoichiometry and N:P homeostasis to differ in response to nutrient limitation and between monoculture and mixture. Results: Grass AGB was greater with N addition and in mixture, and legume AGB was decreased by N but increased by P, more so in mixture. Nutrient limitation in grass was determined via a strong coupling of growth with shoot stoichiometry, by which AGB decreased and C:N increased under N limitation. Legume growth was not correlated with tissue stoichiometry, but potential for growth limitation by N and P was detected via increased shoot C:N under low N and P, and C:P under low P. Legume shoot N:P was more homeostatic than grass, and grass shoot N:P homeostasis was greater in mixtures than in monocultures. Conclusions: Integrating ecological stoichiometry alongside trait-based ecology is a useful tool for predicting how fertiliser management may affect nutrient balance and species dominance in mixed pasture agroecosystems. © 2021, Sociedad Chilena de la Ciencia del Suelo.
    • 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

      Ball, K.R.; Baldock, J.A.; Penfold, C.; Power, S.A.; Woodin, S.J.; Smith, P.; Pendall, E.; Univ Arizona, Dept Environm Sci (ELSEVIER, 2020-08-07)
      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.