Plant secondary compounds (PSCs) can be vital to a sustainable agriculture system. PSCs help plants attract pollinators, recover from injury, protect from ultraviolet radiation, increase drought tolerance, and aid in defense against pathogens, diseases, and herbivores. Therefore it is important to understand what affects the fluctuations in concentration of PSCs, as well as the impact of these compounds on soil function. We determined 1) how plant diversity (monocultures vs. two-way mixtures) affects concentration of primary and secondary compounds, 2) how different management practices (animal impact vs. machine harvesting) affect soil quality, nutrient cycling, and PSC concentration, and 3) how cattle manure from different diets, containing different PSCs, influences soil characteristics. Endophyte-infected tall fescue (Schedonorus phoenix), saponin-containing alfalfa (Medicago sativa), and tannin-rich sainfoin (Onobrychis viciifolia) were planted in strips of monocultures or two-way mixtures of grass-legume in a completely randomized block design with split-split plot. Cattle strip-grazed the plots from May to September, while similarly planted ungrazed treatments were hayed. Tall fescue, alfalfa, and sainfoin were analyzed for ergovaline, saponins, and extractable tannins, respectively. Soil fertility, microbial activity, and bulk density was measured in all plots. Manure from each diet (alfalfa/fescue and sainfoin/fescue) was freeze dried, incorporated into soil at two rates (1-cattle excretion at 3.74 kg dry manure/cow/day, and 2-upper rate of manure fertilization at 350 kg N/hafs) and incubated in the lab at 25°C for 8 weeks. Soil nitrate and enzyme activities were measured at 0, 3, 7, 14, 21, 28, 42, and 56 days. Dehydrogenase enzyme activity was greater in the upper rate than lower rate of manure fertilization (P < 0.05). The alfalfa diet induced greater dehydrogenase activity than the sainfoin diet, suggesting microbial inhibition from tannins. Further results, conclusions, and implications for management will be presented.
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