摘要
There is increasing global interest in the extent to which multi-species grasslands containing increased plant diversity compared with improved grasslands can also deliver higher resource protection. The objective of this experiment was to examine nutrient returns via faeces and urine by free-ranging cattle grazing semi-natural grassland which contribute to leaching losses to ground water along with volatilisation and denitrification losses to the atmosphere. Reduction of grazing intensity has frequently been recommended to meet biodiversity and production goals in sustainable grazing systems. In this experiment beef cattle were continuously stocked on semi-natural (Lolium perenne-Cynosurus cristatus) grassland at grazing intensities which were designed to either utilise herbage growth for optimum livestock production (Moderate), or to increase biodiversity by not fully utilising herbage growth (Lenient) in three replicate blocks. Observations were made in May and September of the number and timing of individual defaecation and urination events between dawn and dusk. In addition, the quantities of fresh material excreted in individual defaecation or urination events were collected and measured. For cattle grazing the Moderate and Lenient treatments, respectively, the daily number of defaecation events was 10.0 vs. 9.3 (F prob. = 0.448) in May; 10.0 vs. 9.8 (F prob. = 0.821) in September. The estimated daily total of fresh faeces excreted animal? was 10.8 vs. 9.5 kg (F prob. = 0.503) in May; 15.3 vs. 17.4 kg (F prob. = 0.480) in September. The daily number of urinations was 13.4 vs. 13.5 (F prob. = 0.941) in May; 9.4 vs. 12.7 (F prob. = 0.077) in September. The estimated daily total amount of urine produced animal? was 9.9 vs. 10.4 kg (F prob. = 0.808) in May; 7.2 vs. 11.9 kg in September (F prob. = <0.001). Subsamples of faeces and urine were analysed for N and P concentrations. The total daily outputs of N (faeces urine) animal? were 77 vs. 75 g N day? (F prob. = 0.903) in May; 96 vs. 122 g N day? (F prob. = 0.369) and urine N as a proportion of the total N excreted was 0.51 vs. 0.58 in May (F prob. = 0.215); 0.53 vs. 0.59 in September (F prob. = 0.464). Most of the P excreted (proportionately 0.99) was excreted in the faeces for both grazing intensities in May and September. The daily numbers of excretion events animal? were similar to other published values but a lower proportion of the total daily N output was excreted as urine compared with published values for cattle grazing fertilised, improved intensive swards. The potential impact of this on losses to soil water and the atmosphere should be examined.