Two experiments were conducted to validate an approach of using plant cuticular alkanes to estimate diet composition and fecal output. In the first experiment, n-alkane patterns of the four major pasture species were determined and compared and a further two sets of pasture mixtures were prepared to validate the use of plant n-alkane patterns to estimate species composition. In the second experiment, estimates of daily fecal output of grazing sheep were compared using controlled-released devices containing either Cr 2 O 3 or alkanes. There were considerable differences in odd-numbered alkanes and in their total content between species. Results from the first experiment, where two sets of pasture mixtures were analyzed suggest that it is feasible to separate species composition using differences in n-alkane pattern. The second experiment showed that accurate estimation of daily fecal output can also be obtained using capsules containing alkanes. Key words: n-alkane, pasture, diet composition, fecal output
Soil testing for sulfur (S) is becoming increasingly important as soils become more S-deficient due to lower S inputs in fertiliser and higher offtake in product. Because of the differing rates of S supply required by a range of crops, the relative importance of the soil sulfate and organic S pools could be expected to vary between crops. A glasshouse experiment was conducted using an Aquic Haplustalf of granitic origin and an Ultic Haplustalf of basaltic origin collected from unfertilised pasture sites on the Northern Tablelands of New South Wales from Uralla and Walcha, respectively. The soil was labelled with 35S. The experiment consisted of 2 rates of S fertiliser (0 and 17·7 mg/kg soil, equivalent to 0 and 30 kg S/ha), 3 crop species (radish, corn, ryegrass), and 2 soils (granite and basalt). S was extracted using 2 extracts, mono-calcium phosphate (MCP) and 0·25 M KCl heated at 40°C (KCl-40), termed primary extracts, and the components of S in the extracts were determined. The relationship between the amount of S removed from the extract (S before planting – S after cropping) by the 2 test extractants in the – S treatment and plant S uptake was also determined. A higher S concentration was found in the KCl-40 extract than in the MCP extract in the granite soil. Conversely, the MCP extract had a higher S concentration in the basalt soil because of the relative size of the adsorbed S and ester-S pools in this soil. More than 33% of the 35S was recovered in the extracted S pool, and <11% from the organic S pool in both extractants and in both soils. Data showed a lower specific activity (SA) of the S in the MCP extract as measured by ICP than in KCl-40 in both soils and all crops. The specific activity ratio of the extractants, as measured by ICP, was closest to 1·00 for the KCl-40 extract in both soils for each crop. The removal of S from the MCP extractant during cropping was lower than plant uptake in all treatments except ryegrass in the basalt soil. The KCl-40 extract tended to underestimate S supply at low uptake and overestimate at higher uptake. The results reported in this experiment showed that the KCl-40 extract generally performed well for all 3 crops and on both soils. The data showed that the KCl-40 extract removed S from pools similar to those reached by the crops.
A grazing experiment was conducted at the Big Ridge 2 site CSIRO, Chiswick (30˚31′S, 151˚39′E), 20 km south of Armidale, New South Wales, Australia. The site was established in 1955. In March 1966, phalaris and white clover were sown and pastures were fertilised annually with superphosphate until 1993. There were 3 pasture treatments, each with 2 replicates: degraded pasture (low phalaris content), phalaris-dominant, and phalaris–white clover. The effect of pasture type on animal production (liveweight gain and wool) was only significant in 1996, when there were large differences in pasture composition and production between the 3 pasture types. n-Alkane based estimates showed that pasture degradation affected diet selection and nutrient intake and thus sheep production. The estimates in this study also showed no clear preference for a single pasture species over time and lack of strong preferential selection for clovers when sheep were grazing 3 contrasting pastures. Preferential selection of a particular species varied over time depending on the presence and availability of alternative species. Although there were large differences in total N and S intake and faecal output between the 3 pastures, the proportion of the dietary nutrient used for production was similar. This observation reveals the importance of further improving pasture and grazing management, particularly in productive phalaris–white clover pasture with high nutrient flux, to improve nutrient recycling through plant uptake and retention by animals in the grazing ecosystem, and reduce losses.
Soils of Cambodia are low in fertility and conventional rice cultivation destroys any structure that they have. Usage of inorganic fertilizers is low and farmers are encouraged to use animal manure. Much of the research conducted on crop responses to manure is based on trials where unrealistically high application rates have been used so the farmers are given false hopes as to what they might achieve through its use. Little response curve data exists on which to base fertilizer rate recommendations and general recommendations have been formulated for the different soil groups. An economic analysis comparing the general recommendation with site specific nutrient management (SSNM) recommendations has been made on the results of a published experiment and shown substantial increases in both profitability and benefit/cost ratio in using the SSNM recommendations on four soil types. Cambodian farmers, like many in the developing world, have to be careful with their limited cash resources in purchasing plant nutrients and more attention need to be paid to producing profitable and reliable fertilizer and manure recommendations.
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