Characterization Of Phosphorus Flow Of Dairy-farmland System And Management Approaches In Hebei Province

The increasing demand for milk in China is causing a rapid increase in China’s dairy cattle population. Meanwhile, the impacts of changes in production modes(e.g. collective vs intensive mode) of dairy cattle on the fates of manure phosphorus(e.g. P inputs and outputs) are evident. In order to explore the characteristics of P flows through the cow-farmland system in Hebei, a survey of investigating feed P inputs and manure and milk P outputs across 44 collective dairy operations and 20 intensive dairy operations in Hebei was carried out in this study. The characteristics of P flows through collective- and intensive cow-farmland systems were examined at individual cow and dairy operation level, respectively. The main results are as follows:(1) Among the intensive and collective operations, the former operation had relatively stable feed P contents(average 0.38% with variation coefficient of 20%, n=20); although the average was in agreement with the recommendation(0.38%-0.42%), 30% of the intensive dairy operations were greater and 20% of the intensive dairy operations were less than the recommendation; for the collective dairy operation in China, the average feed P content was 0.44%, which was greater than the recommendation, also it was associated with greater variation 32%(n=44), most importantly, it was found that about 59% of the collective operations had greater and 20% of them had less feed P contents than the recommendation, which hinted that only about 16% of the collective operations were characterized with reasonable feed P contents.(2) At the individual milking cattle level, the average P-input during one year for intensive and collective operation is 21.9kg/head and 20.3kg/head, respectively; whereas, at the operation level considering lactating cows, dry cows and heifers, the average P-input of a year is 12.6kg/head for intensive operations and 14.6 kg/head for collective operations.(3) The utilization efficiencies of feed P during one lactation period(LPUE) and one year(DPUE) for the intensive operations were 30.6% and 27.9%, respectively and the LPUE and DPUE for collective operations were 22.8% and 20.8%, respectively, where the LPUE and DPUE of intensive operations were about 34% and 25% greater than those of collective ones. At the operation level, the annual P utilization efficiency(APUE) of intensive operations was 27.3%, which was about 27% greater than the value of 21.5% for collective operations. Meanwhile, smaller variation(28%) in the APUEs among different intensive operations was observed in contrast to collective operations(34%). Furthermore, the LPUE, DPUE and APUE were all positively correlated to the milk productions within respective production modes, especially in intensive operations due to their determination coefficient R2 of 0.41, 0.49 and 0.54, respectively. It was also observed that the LPUE, DPUE and APUE were all negatively correlated to feed P inputs within respective production modes, and the R2 for intensive ones were 0.64, 0.62 and 0.65, and 0.54, 0.57 and 0.53 for collective ones.(4) For the manure P outputs, they were highly correlated to their P inputs with a R2 of 0.9 both in intensive and collective operations. At the individual animal level, the manure P-outputs of intensive operations during one lactation period and one year were about 4% and 3% lower than the collective operations. At the operation level, the annual P inputs of intensive ones were about 14% less than the collective ones and the manure P outputs were about 21% less than the latter operations. With the application of cattle manure to the wheat-maize rotation, land requirement for intensive and collective operations were estimated to be about 0.27 and 0.34 hm2/head.(5) Scenario analysis at individual milking cow level showed that, in contrast to the current situation Scenario, reducing feed P inputs of intensive and collective operations(scenario 1) can lower the manure P outputs by 27% and 34%, and this would improve the P use efficiency and decrease land requirements by intensive and collective operations from 0.72 hm2/head and 0.54 hm2/head to 0.41 hm2/head and 0.35 hm2/head. With a further improvement in feed P digestibility(Scenario 2), the DPUE of intensive and collective operations can be up to 36.3% and 30.8%, respectively, which were about 36% and 57% greater than those in current situation Scenario and the land requirement can be further reduced to 0.33 hm2/head and 0.29 hm2/head, respectively.