Characterization Of Nitrogen Flow Of Dairy-farmland System And Management Approaches

With the increasing demand for milk in China, Chinese dairy cattle populationincreased rapidly; meanwhile, the changing management practice in dairy milkproduction had strongly impacted the N flows. To indicate the characteristics of Nflows of different dairy-farmland systems, the N input, output as well as its utilizationof22small dairy holders in collective operations and16intensive dairy operations inHebei province were investigated. The N flows were analyzed at individual cattle,dairy operation and dairy-farmland level to explore the impact of farm size on theenvironmental risk of N. The main results are as follows:(1) The results showed that the average milk yield of intensive dairy operationswas6587kg cow-1yr-1(varied from5000to8000kg cow-1yr-1), which was higherthan collective dairy operations that was4958kg cow-1yr-1(varied from2000to7000kg cow-1yr-1). It also indicated that intensive dairy operations have steadiermilk production than the collective ones. Although N inputs among different dairyoperations are characterized with large variability, but no significant linear relationswere found against the size of dairy operations. Annually N input in collective dairyoperations was120.0kg cow-1yr-1, that was less than136.8kg cow-1yr-1N input inintensive dairy operations. But N input on the basis of1ton milk production was26.8kg in collective dairy operations, which was higher than22.1kg N input inintensive dairy operations. Of all the investigated dairy operations, both collective andintensive dairy operations N input per1t milk (per LU=600kg head-1) is29.7kg (112.0kg cow-1yr-1)和30.5kg (117.4kg cow-1yr-1), respectively.(2) This study also showed that the annual utilization efficiency of feed nitrogen(ANUE) of dairy cows and the utilization efficiency of feed N during one lactation(LNUE) were25%and27%in intensive dairy operations, respectively, which washigher than the ANUE and LNUE of21%and24%in collective dairy operations. Ofall the investigated dairy operations, the LNUE of both collective and intensive dairyoperations negatively correlated to the feed N-input, and the correlation coefficientwas-0.9170(n=16, p <0.01) for intensive dairy operations and-0.6182(n=24, p < 0.01) for collective dairy operations, respectively. At dairy operation level, thenitrogen use efficiency of intensive and collective dairy operations was21%and19%,respectively, which are lower than LNUE and ANUE of dairy cows. Nitrogenutilization efficiency of intensive dairy operations are negatively correlated to thenitrogen input of LU (600kg head-1)(r=-0.6296, P <0.01), similar correlation isalso obtained in collective dairy operations (r=-0.9344, P <0.01). However, N outputof dairy operations varies with the size of dairy operations, and in collectiveoperations the N use efficiency and N output are significantly correlated but no suchrelation in intensive dairy operations.(3) Meanwhile, N losses from intensive and collective operations toenvironment are9.7kg and10.3kg, respectively. At dairy operation level,environment nitrogen emissions of intensive dairy operations and collective dairyoperations per1t milk were9.7kg and10.3kg, equivalent to36.2kg and40.2kg per600kg live unit, respectively. The main source of nitrogen losses were frommanure-N via NH3volatilization losses accounting for88%of the total losses.(4) Scenario analysis showed that optimizing the dairy feed-input would not onlyimprove the nitrogen use efficiency of dairy, especially for collective dairy, and alsoreduce N excretion and the resulted environmental losses. Improvement of manuremanagement measures can effectively increase the rate of returning the manure.(5) Both dairy mode in different extent reflects with farmland production systemis not closed, dairy farm in the N-flow between different regions mainly as a nutrienttransport, transfer the feed-n to farmland system and environment. Intensive dairyoperations (with internal farmland) per1t milk (per LU) can transfer19.3kg (73.7kg)of import feed n and9.3kg (35.7kg) of local farmland nitrogen, intensive dairyoperations (no internal farmland) per1t milk (per LU) can transfer19.6kg (73.2kg)of import feed n and4.3kg (16.0kg) of local farmland N, while collective operationstransit17.2kg (65.7kg) of import feed n and10.1kg (39.4kg) of local farmlandnitrogen.