Number of samples for accurate visual estimation of mean herbage mass in Campos grasslands

Abstract

The number of samples is a major issue when estimating the mean herbage mass of grazed paddocks. The aim of this study was to assess the number of samples required for accurate visual estimation of mean herbage mass in relation to the herbage mass heterogeneity and size of paddocks. Data were collected across scales of space and time (273 sampling events) from paddocks on Campos grasslands in Uruguay, using the visual estimation technique. The mean herbage mass of the paddocks ranged from 270 to 6350 kg of dry matter (DM) per hectare with coefficient of variation (CV) of 0.13 to 1.26. Twenty‐four events representing four levels of herbage mass heterogeneity (CV = 0.3, 0.5, 0.7 and 1.0) × three levels of paddock size (small, 5–13 ha; medium, 41–67 ha; large, 100–140 ha) were chosen (two replicates per group), and analyzed for the probability that the estimation error exceeded 10% of the mean (10% error probability) using the bootstrap technique. The number of samples required for controlling the 10% error probability below 0.1 increased gradually from 50 to 150 per paddock as the CV increased from 0.3 to 0.7, then sharply to 350 until the CV increased to 1.0, with no effect of paddock size. Taking account of the distribution of CV (< 0.7 in nearly 80% of the events), we propose a general recommendation to take a minimum of 150 samples per paddock for accurate estimation of mean herbage mass in Campos grasslands irrespective of the size of paddocks.

Spatiotemporal variation in aboveground biomass in a tropical grass pasture over a 22‐year period

“…The values of 0.16–0.94 (Figure 5) is close to the range of 0.20–1.16 obtained on the same land area basis (0.5 × 0.5 m) in other pastures (Do Carmo et al, 2020; Dobos et al, 2021; Shiyomi et al, 1983, 1984). The maximum would have been higher if the measurements had included occasions immediately after the rotational stocking periods in the paddock (Hirata, 2000a, 2000b, 2002; Hirata & Fukuyama, 1997; Ogura et al, 2002).…”

“…Interval (day) pastures (Do Carmo et al, 2020;Dobos et al, 2021;Shiyomi et al, 1983Shiyomi et al, , 1984. The maximum CV W would have been higher if the measurements had included occasions immediately after the rotational stocking periods in the paddock (Hirata, 2000a(Hirata, , 2000b(Hirata, , 2002Hirata & Fukuyama, 1997;Ogura et al, 2002).…”

Managing Grass Height for Birds and Livestock: Insights from the Río de la Plata Grasslands

“…Here, we found that adjusting the stocking rate and breeding strategy contributed to the promotion of grass height heterogeneity. This could be attributed to the fact that with taller grass and increased forage availability, cattle tend to selectively graze on the more palatable plants, leaving behind the less digestible, and thus less selected, plants, creating heterogeneity in grass height ( Do Carmo et al 2018 ;Tonn et al 2019 ). However, although grass height heterogeneity significantly increased after the management modifications, we did not observe changes in the abundance of grassland bird specialists.…”