Measuring production of continuously grazed hill pastures

Abstract

<jats:p>Estimates of pasture production are critical for comparing treatment effects in research trials, as inputs to decision support models, and for on-farm use in constructing grazing plans. We compared two techniques for measuring pasture production, over 2 years in 36 paddocks continuously grazed with sheep, on hill country at the Ballantrae Research Station. One technique (Cut method) involved harvesting pasture regrowth after trimming to a standard height. The other (Model method) calculated pasture production as the sum of grazing animal intake (estimated using a spreadsheet-based model with inputs including animal performance and pasture quality) and changes in pasture cover (above-ground biomass). Annual pasture production estimates were reasonably well correlated (R2 = 0.66), but those using the Cut method were 55% greater than using the Model method. Agreement was best in spring and summer, and poorest in autumn and winter. Factors contributing to these discrepancies included the contrasting starting conditions for the pasture at the start of each measurement period (shorttrimmed for the Cut method, and patch-grazed for the Model method); the effect of grazing in the Model method maintaining pastures in a more vegetative state; and the greater losses from senescence and decay in the Model method pastures. The potential for errors using the Model method was high where measurement periods were short, as accuracy of measurement of pasture cover can be suspect. The Model method probably better quantified net pasture production in grazed pastures. Keywords: grazing, hill pasture, intake, model, pasture production</jats:p>

Analysis of Herbage Mass and Herbage Accumulation Rate Using Gompertz Equations

“…Where the herbage mass is below the optimum for HAR i‐max , it can be concluded from the HAR i –herbage mass curves that measured HAR within the exclosure cage will exceed the actual HAR under continuous stocking. Field et al (1981) and Devantier et al (1998) compared forage production predicted from livestock production with measurements using exclosure cages under continuous grazing, and found the measurements overestimated forage production predicted from livestock production by 33 and 55%, respectively. The difference between measured pasture growth rate within an exclosure cage, and actual pasture growth under continuous stocking will depend on the relative differences in actual herbage mass present.…”

A measurable effect of feral grazing on pasture accumulation rate

“…mice, invertebrates) while non-exclosure techniques (rising plate, visual, modelling) measure a pasture sward open to feral consumption. In most cases, these nonexclosure techniques have given lower estimates of pasture accumulation (Field et al 1981;Piggott 1997;Devantier et al 1998). One possible contribution to this difference highlighted by this study is the extent to which feral animals (e.g.…”

“…There is an interesting postscript to this study. Comparative assessments of pasture accumulation rate using different techniques show variation in estimates (Devantier et al 1998). Cage-cutting techniques effectively exclude all but the smallest herbivores (e.g.…”

Floristic composition and above-ground net primary production in natural grasslands on basaltic deep soils

“…The implementation of controlled grazing where grazing time and defoliation intensity can be adjusted allows mitigating the degradation process of the natural field, and could sometimes reverse it (5)(6) . Traditionally, the aboveground net primary production of pastures (ANPP), that is, the amount of biomass accumulated per unit area, was estimated from biomass cuts carried out in the field (7) . Nowadays, it is possible to estimate ANPP by remote sensors using synthetic images of improved vegetation index that detect the fraction of photosynthetically active radiation that is absorbed by plants (fPAR).…”