Search

Summer annual grass‐legume mixtures may provide supplemental grazing for livestock when cool‐season pastures are less productive, but nitrogen fertilizer recommendations for these mixtures are not well established. Inputs to these systems are often high, so optimizing N fertilizer rates may increase appeal to producers. This study evaluated the effects of increasing botanical diversity and N fertilizer application on the yield and botanical composition of summer annual mixtures in four environments in Kentucky. Nitrogen fertilizer rates of 0, 56, 112, 168, and 224 kg N ha–1 were applied to a sudangrass [Sorghum bicolor (L.) Moench × Sorghum sudanese (P.) Stapf] monoculture, a three‐species mixture, and an 11‐species mixture. In three out of four environments, sward biomass increased as N application increased (average of 15 kg dry matter (DM) ha–1 increase per kg N ha–1; p <.05). Mixture complexity had no effect on forage DM accumulation in three out of four environments (4,000, 5,830, and 7,280 kg DM ha–1 averaged over mixture for three environments; p >.05). Mixtures were overwhelmingly dominated by grasses, resulting in low functional diversity. Legumes did not respond to N (p >.05), but their contribution to sward DM was <4%. Species compatibility should be a priority when utilizing multi‐species mixtures. If a stronger legume component is desired, care must be taken to provide management that favors these species, such as reduced grass‐seeding rates to limit competition, especially during initial establishment. Core Ideas: 224 kg N ha–1 increased yield by 1.9 times over no N in three out of four environments.Mixtures did not outyield monocultures and were dominated by high‐yielding species.Legumes are not competitive when planted with high seeding rates of summer annual grasses.Annual pastures should utilize compatible species to reduce competitive dominance. [ABSTRACT FROM AUTHOR]

Relationships of forage nutritive value (NVAL) and quantity with individual animal performance on pasture have long been evaluated, but there have been few attempts to describe the specific roles or relative importance of NVAL and quantity in determining animal response. The objective of this review was to more clearly define these roles based on a comprehensive assessment of pastureland literature and the application of a meta-analysis. It is clear that quantity and NVAL interact. When pastures present a wide range in forage mass, 60 to 90% of variation in average daily gain (ADG) can be explained by quantity, but there may be no relationship of NVAL with ADG. If pastures present only high forage mass, there may be no relationship between quantity and ADG, but NVAL may explain more than 50% of variation in ADG. The meta-analysis and a review of studies that evaluated forages of differing NVAL across a range of forage mass provided evidence that NVAL (i) sets the upper limit for ADG, (ii) determines the slope of the regression of ADG on stocking rate (SR), and (iii) establishes the forage mass at which ADG plateaus. In contrast, forage quantity determines the proportion of potential ADG that is achieved and is the primary driver for direction of the ADG response (negative) to increasing SR. Thus, the literature supports a conclusion of interaction among forage NVAL and quantity in affecting individual animal performance on pasture, but it suggests that the roles of each are quite well defined. [ABSTRACT FROM AUTHOR]