Roland D. Meyer

Shallow groundwater quality on dairy farms with irrigated forage crops

Californias dairies are the largest confined animal industry in the state. A major portion of these dairies, which have an average herd size of nearly 1000 animal units, are located in low-relief valleys and basins. Large amounts of liquid manure are generated and stored in these dairies. In the semi-arid climate, liquid manure is frequently applied via flood or furrow irrigation to forage crops that are grown almost year-round. Little is known about the impact of manure management practices on water quality of the extensive alluvial aquifers underlying these basins. The objective of this work is to assess nitrate and salt leaching to shallow groundwater in a relatively vulnerable hydrogeologic region and to quantify the impact from individual sources on dairies. The complex array of potential point and nonpoint sources was divided into three major source areas representing farm management units: (1) manure water lagoons (ponds); (2) feedlot or exercise yard, dry manure, and feed storage areas (corrals); and (3) manure irrigated forage fields (fields). An extensive shallow groundwater-monitoring network (44 wells) was installed in five representative dairy operations in the northeastern San Joaquin Valley, CA. Water quality (electrical conductivity, nitrate-nitrogen, total Kjehldahl nitrogen) was observed over a 4-year period. Nitrate-N, reduced nitrogen and electrical conductivity (EC, salinity) were subject to large spatial and temporal variability. The range of observed nitrate-N and salinity levels was similar on all five dairies. Average shallow groundwater nitrate-N concentrations within the dairies were 64 mg/l compared to 24 mg/l in shallow wells immediately upgradient of these dairies. Average EC levels were 1.9 mS/cm within the dairies and 0.8 mS/cm immediately upgradient. Within the dairies, nitrate-N levels did not significantly vary across dairy management units. However, EC levels were significantly higher in corral and pond areas (2.3 mS/cm) than in field areas (1.6 mS/cm) indicating leaching from those management units. Pond leaching was further inferred from the presence of reduced nitrogen in three of four wells located immediately downgradient of pond berms. The estimated minimum average annual groundwater nitrate-N and salt loading from manure-treated forage fields were 280 and 4300 kg/ha, respectively. Leaching rates for ponds are estimated to be on the order of 0.8 m/year, at least locally. Since manure-treated fields represent by far the largest land area of the dairy, proper nutrient management will be a key to protecting groundwater quality in dairy regions overlying alluvial aquifers.

Characterizing sources of nitrate leaching from an irrigated dairy farm in Merced County, California

Dairy farms comprise a complex landscape of groundwater pollution sources. The objective of our work is to develop a method to quantify nitrate leaching to shallow groundwater from different management units at dairy farms. Total nitrate loads are determined by the sequential calibration of a sub-regional scale and a farm-scale three-dimensional groundwater flow and transport model using observations at different spatial scales. These observations include local measurements of groundwater heads and nitrate concentrations in an extensive monitoring well network, providing data at a scale of a few meters and measurements of discharge rates and nitrate concentrations in a tile-drain network, providing data integrated across multiple farms. The various measurement scales are different from the spatial scales of the calibration parameters, which are the recharge and nitrogen leaching rates from individual management units. The calibration procedure offers a conceptual framework for using field measurements at different spatial scales to estimate recharge N concentrations at the management unit scale. It provides a map of spatially varying dairy farming impact on groundwater nitrogen. The method is applied to a dairy farm located in a relatively vulnerable hydrogeologic region in California. Potential sources within the dairy farm are divided into three categories, representing different manure management units: animal exercise yards and feeding areas (corrals), liquid manure holding ponds, and manure irrigated forage fields. Estimated average nitrogen leaching is 872 kg/ha/year, 807 kg/ha/year and 486 kg/ha/year for corrals, ponds and fields respectively. Results are applied to evaluate the accuracy of nitrogen mass balances often used by regulatory agencies to assess groundwater impacts. Calibrated leaching rates compare favorably to field and farm scale nitrogen mass balances. These data and interpretations provide a basis for developing improved management strategies.

Effects of Dairy Manure Nutrient Management on Shallow Groundwater Nitrate: A Case Study

The effect of three different liquid manure treatments on irrigated crop nutrient uptake, crop yield, soil water quality, and groundwater quality are investigated for a typical California dairy. Animals are housed in open feedlot barns surrounded by exercise yards (corrals). Flush lanes are used to remove manure, from which solids are separated and sold off-farm. The liquid manure is stored in ponds (lagoons) and applied through the existing irrigation system on forage crops. We contrast conventional manure application practices, which largely ignore the nutrient value of the manure, with targeted manure applications designed to fully replace commercial fertilizer applications and to match the crop nutrient uptake. The targeted manure applications are split into two treatments, one that accounts only for the ammonia-N in the manure, and a second treatment that accounts for both ammonia and organic nitrogen. The three treatments are implemented sequentially in the same two fields over a seven year period. The fields have a loamy sand soil and are border flood irrigated. Shallow groundwater quality monitoring at and immediately below the water table occurred almost continuously throughout the seven year period. Grower’s records are used to describe the timing and approximate amount of manure applications and crop management during the conventional treatment period. Detailed crop nutrient uptake, irrigation flow, manure nutrient, and soil nutrient concentration measurements are made at each irrigation during the three year period of targeted manure management. Conventional treatments resulted in elevated nitrate-nitrogen concentration at the water table, averaging approximately 100 mg/l. With targeted manure management, nitrate-nitrogen concentrations at and immediately below the water table were reduced by over 50% in the first two years of targeted manure management. Balancing the nutrient application by also accounting for the organic nitrogen in the manure application further reduced the nitrate levels in shallow groundwater. We show that a detailed field nitrogen balance coupled with a simplified site-specific groundwater model provides a practical tool to predict the impact of these treatments on shallow groundwater quality.

Monitoring Shallow Groundwater Nitrogen Loading from Dairy Facilities with Irrigated Forage Crops

Californias dairies are the leading confined animal industry in the state. A majority of these family-owned dairies with an average herd-size of nearly 1,000 animal units are located in low-relief valleys and basins. Little is known about the impact of traditional and proposed dairy farming practices on water quality in the extensive alluvial aquifers underlying these basins. We have recently completed a long-term monitoring study of nitrate-nitrogen leaching on dairies in a relatively vulnerable hydrogeologic region.The extensive shallow groundwater monitoring

Matching Dairy Lagoon Nutrient Application To Crop Nitrogen Uptake Using A Flow Meter And Control Valve

A system has been developed to apply targeted application rates of diluted manure nitrogen onto cropland through an irrigation system by using a control valve in conjunction with a flow meter and quick test for nitrogen. With this system, a grower performs a preliminary determination of the nitrogen concentration in his lagoon water and estimates how long it will take to irrigate a given acreage. Using a look-up table or computer spreadsheet, a target flow rate (gpm) is determined which will result in the application of the desired number of pounds of nitrogen per acre. This figure is provided to the irrigator, who adjusts a valve on the pond outlet until the flow meter displays the target gpm. The number of gallons displayed on the meter totalizer is recorded at the beginning and end of each field or check and samples are taken periodically during the irrigation and later analyzed to confirm that the N concentration in the pond did not changed over the course of the irrigation. Totalized flow and concentration information is entered into a computer spreadsheet that calculates the amount of nitrogen actually applied. Any deficiency or excess (due mainly to the irrigation taking longer or slower than expected) can be corrected in subsequent applications irrigations. Validation of this system was conducted on ten individual irrigation basins, or checks, located in three fields. The average area in each check was 4.6 acres. On nine of the ten irrigation checks total nitrogen application for the season was within 15% of the intended application rate as measured by the flow meter totalizer. Average application rates for the entire field was within 3% of the target rate on two fields and 17% off the target on the third field. The flow meter/valve system was installed on four cooperating dairies, and the lagoon nutrient applications were managed by the irrigators. The system is proving to be sufficiently simple and practical for the average dairy producer to operate, although none of the participating dairies was able to achieve a balance of nitrogen application with uptake in the first season of use. Yields from both the replicated and all demonstration fields where lagoon water nutrients were used exclusively were comparable to those obtained using conventional practices which supplement manure applications with commercial fertilizers. This method of using a flow meter and valve to apply targeted rates of lagoon nutrients is being implemented on a number of commercial dairies in the region. Overall considerations for designing this and other aspects of a diluted manure transport, storage and land application system are discussed.