| Litter (dead plant material) is important in pasture for its role in conserving soil water. Litter traps winter precipitation, slows runoff, and reduces evaporative losses. Litter can also trap moisture above the soil surface making it unavailable to plants. Grazing impacts litter by reducing the amount of plant material returning to the soil as litter. It also increases the decomposition of litter through treading and trampling the surface, and the deposition of greater amounts of mineral nutrients in urine and feces. Optimum litter benchmarks for healthy pasture, ranging from 600 kg/ha -- 1600 kg/ha, have been determined for grazing regions of Alberta. Similar data has not been published for Manitoba. Three studies were undertaken from 2006 to 2007 to examine litter in southwestern Manitoba pastures. In the first study the relationship between litter, soil microclimate and forage yield was tested across five pasture sites. Litter was applied to bare soil at rates from 0 kg/ha to 3000 kg/ha. The amount of litter biomass was not strongly related to soil moisture, though near-surface soil temperatures were reduced when litter was present. Further, the presence of litter did not influence yield. The objective of the second study was to measure the effect of different grazing strategies on the litter layer of six pastures in southwest Manitoba. Four grazing systems (continuous, time-controlled, twice-over, and stockpiled) were simulated using different frequencies of defoliation. It was found that after three years of simulated grazing, litter was present in largest quantities in the least-frequently grazed treatments. Litter ranged from 1000 kg/ha under the continuous grazing treatment to 3711 kg/ha in the ungrazed control. Litter amounts under time-controlled grazing averaged 1130 kg/ha, while twice-over averaged 1736 kg/ha. The third study involved a field survey assessing the quantity of litter present in native pastures in different ecoregions of Manitoba. Litter biomass was measured in grazing exclosures located in twelve pastures across the province that were lightly clipped twice per year. Litter in these cages was extremely variable, ranging from 825 kg/ha to 3750 kg/ha. Over two years of study, litter biomass averaged 1902 kg/ha. Through this research, the value of litter as an indicator of sustainable pasture management was confirmed, though it remains unclear whether litter is important to pastures from the perspective of soil microclimate. |
