Abstract
Best management practices (BMPs) are being implemented to reduce non-point sources pollution in China and worldwide. There are many types of agricultural BMPs, but their effectiveness differs from farm to farm, depending on where they are applied, how they are applied, and how they are impacted by weather. Two farms (village Nan Wayao, VNWY and village Liu Jianfang, VLJF) with differing farm systems (crop-based mixed farm and dairy-based farms) located in the upper watershed of Miyun reservoir, Beijing, China were selected. We used the Integrated Farming System Model (IFSM) based on these two farms information to estimate total phosphorus (TP) and total nitrogen (TN) loss from 2000 to 2014, to identify (1) causes of farm nutrient imbalances, (2) key factors causing the imbalances, and (3) viable BMPs to reduce source and TN runoff at the farm scale. Results indicated that these farms had TP losses ranging from 8.2 to 160 kg/ha/year and TN losses from 73.7 to 1391.6 kg/ha/year. Using IFSM, physical (i.e., soil bulk density, available water content, and soil-P) and economic (i.e., diesel and farm loan interest rates) factors are more influential in determining nutrient loss from VNWY than VLJF. Rainfall patterns had a little effect on nutrient use and loss on the dairy farm in VLJF. Changes in available water content and soil bulk density had greater impact on the return for VNWY than VLJF, while changes in loan interest rates were more influential on VLJF. Maximum reductions in nutrient loss were obtained with implementation of the BMPs conservation tillage, reduced fertilizer and manure applications, buffer strips, and storage of poultry manure.
Highlights
Farm characteristics data were obtained by farm interviews and consists of detailed information on crop type and extent, soil types, soil attribute data such as soil bulk density (SBD), available water content (AWC), and slope, type of dairy cows, numbers of cows of different ages, manure handling strategies, and equipment and structures used in managing the livestock and crops
As average relative errors were under 20%, Integrated Farming System Model (IFSM) estimates can serve as datasets for further analysis of Best management practices (BMPs) effectiveness (Table 4)
For the VNWY, the predicted average nutrients surplus of total nitrogen (TN) and total phosphorus (TP) are 73.7 and 8.2 kg/ha/year, respectively, which is significantly higher than other areas with similar geographic features
Summary
Nonpoint sources are difficult to control, due to their diffuse nature, complex controlling mechanisms, uncertain flow pathways, and spatial and temporal variability [1,2,3,4]. Differences in geographical characteristics such as soil type, slope, and soil-p concentration can influence BMP effectiveness for different farms at a watershed scale Farm characteristics, such as animal density, cropping strategies, and manure management can impact BMP benefits [10]. Farmer adoption of BMPs is a primary step in water quality improvement, and BMP adoption rates are typically closely related to their cost [11]. Economic losses as a result of implemented BMPs are typically borne by farmers, who may be reluctant to adopt expensive BMPs. economic interests between private and public sectors differ. Many studies have evaluated BMP combinations in different regions of the world using simulation models [15,16], none of these studies have focused on the types of BMPs appropriate for typical farms in north China. An optimal combination of BMPs is obtained for the study farms that addresses P and N losses while ensuring the long-term sustainability of farms
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