«University of California Division of Agriculture and Natural Resources Committee of Experts on Dairy Manure Management September 2003 February 2004, ...»
C. How do factors such as frequency of flushing, recycling of water for flushing and retention time in ponds affect losses?
Use of a universal animal ‘emission factor’ for reactive N compounds (e.g., ammonia) from commercial dairies is not possible because of the limited number of field measurements on which they are based and the wide emission variability among and within dairies. We concur with the National Research Council (NRC, 2003), that there is no single emission factor that could possibly describe atmospheric N losses from dairies.
To determine atmospheric N losses from existing dairies, we concur with NRC (2003) in recommending the use of process-based models coupled with a whole-farm and farm component N balance approach that describes potential atmospheric N losses for the different farm component processes. The process-based model approach coupled with total N balance predicts atmospheric N losses between excretion and land application and helps manage nutrient application rates to crops at agronomic rates. The Committee emphasizes however, that while this approach is technically viable, it requires extensive data measurement, record keeping, and is associated with significant estimation errors.
There are insufficient data available to quantify atmospheric N losses associated with effects of frequency of flushing, use of recycled water for flushing and time spent in retention ponds.
However, in general, more frequent flushing, of fresh water for flushing and shorter residence times in lagoons will tend to decrease ammonia volatilization. However the quantitative impact of these strategies is unknown at this time.
In light of these findings and in light of California-specific conditions, we suggest that atmospheric N losses from liquid manure (i.e., freestalls and flush lanes and lagoons) used for dairy planning and permitting purposes, are considered to range between 20% and 40%. The use of a single number (“emission factor”) is strongly discouraged. Note, that these losses do not include atmospheric N losses in the land application (crop production) area.
4. Crop Nitrogen Requirements A. Is the Western Fertilizer Handbook appropriate to determine crop nitrogen requirements on California dairy farms?
Both field and modeling studies reviewed and implemented for this report consistently show that the N input requirements for forage crops will generally be in the range of 140% to 165% of the crop N harvest removal, assuming that the manure application would consist of lagoon water which is approximately 75% NH4-N. As stated above, inputs include not only manure and fertilizer N but also atmospheric N sources and nitrate present in irrigation water. Investigations of the crop N recovery in several field experiments showed that the appropriate N loading rate that minimizes N leaching and maximizes N harvest is between 140 to 150% of the N harvested.
Computer models indicated a somewhat larger range of 140% to 165%. While field studies provided important feedback on loss pathways and loss rates as well as mineralization rates, model simulations were well suited to study the dynamic behavior of the soil nitrogen pool and its interaction with the crop N uptake. Simulations are particularly valuable to understand the role of various loss pathways. Field mineralization, volatilization, and denitrification rates for specific field conditions can be obtained from detailed field and laboratory studies using standard model calibration and validation approaches.
The combined evidence from laboratory, field, and modeling studies indicates that precise nutrient management, while plausible in principle, may be problematic when implemented in full-scale production systems, as it requires careful timing of the N applications, close monitoring of the amount of N and water inputs, and best management of crop production. More importantly, the growers must show flexibility to make necessary adjustments on N inputs during the course of a growing season to achieve satisfactory results.
With respect to the potential for groundwater degradation, all of the computations and field observations point to a fundamentally critical issue: Given that practically achievable leaching fractions in border check and furrow systems are 15 to 30%, nitrate leaching is at best in the range of 10% to 15% of the N applied. Based on the above-described NIR of 140 to 165% of N removal at harvest, at annual crop yields that typically remove 400 – 600 lbs N ac-1 yr-1, input requirements will be in the range of 560-990 lbs N ac-1 yr-1. Hence, nitrate-nitrogen leaching losses – under optimal irrigation and nutrient management – will be in the range of 55 to 150 lbs N ac-1 yr-1. Assuming recharge rates in irrigated systems of 1 – 2 acre-feet per acre per year (300 – 600 mm per year), the nitrate concentration in the leachate is in the range of 10 to 55 ppm (mg L-1) NO3-N, which is at or above the regulatory limit for drinking water quality (10 mg L-1) and at or significantly above the average measured leachate value for other California farming systems (15 mg L-1, Rible et al. 1979). The potential for denitrification in the unsaturated zone below the root zone (not considered in this report) and within the Central Valley aquifers therefore becomes a key factor in determining, whether such (optimal) leaching water quality conditions will still cause groundwater degradation or whether denitrification naturally attenuates nitrate levels to non-degrading levels.
5. Phosphorus and Potassium Requirements A. Should the application of phosphorus and potassium be limited?
B. If so, what should the limits be and under what circumstances?
Currently available literature data and the limited amount of recent research in the San Joaquin Valley on the nutrient cycle of P and K in dairies does not allow for a conclusive finding on the question of phosphorus and potassium status in field soils used for application of animal waste.
However, trends are certainly apparent that dairyman will need to monitor the increased application of both P and K to determine the impact on forage nutrient levels and animal performance.
6. Salt Excretion and Land Application of Salt A. How much salt is generated by a cow?
B. Are there differences in the amount of salt generated between dry and wet stock?
C. How much salts are removed by various solids separation methods?
D. What are “reasonable” salt loading rates in typical Central Valley cropping patterns?
The excretion of salts can be expected to vary dramatically due to on-farm management decisions and practices. Regardless, daily consumption and excretion of salts will be dramatically lower for dry vs. lactating stock, although even this can be affected by management decisions.
From a dietary point of view, exact salt excretion data are currently unavailable except for Na+, K+, Cl-, and total N excretion. Excluding uncontrolled provision of salt to lactating dairy cows, a summary of six groups of cows on three commercial California dairies suggests that the average lactating dairy cow will excrete 1.29 lb (585 g) day-1 of Na+-K+-Cl- salts and the average dry cow will excrete 0.63 lb (287 g) day-1 (also Na+-K+-Cl- salts only). Assuming an annual division of 305 days lactating and 60 days dry, the average dairy cow will excrete 427 lb (194 kg) year-1 of Na+-K+-Cl- salts. That these values are less than values reported by the 1973 UC Committee of Consultants Water Quality Task Force reflects the fact that comparable data for other salts (Ca2+, Mg2+, HCO3-, SO42-) are not available.
Analysis of manure data, geochemical modeling, and observations of groundwater recharge quality in the San Joaquin Valley dairies suggests that the salinity contribution (defined as the mass of total dissolved solids) from manure, under proper nutrient management practices that seek to maximize the use of lagoon water as a source of fertilizer, is on the order of 1786 – 3572 lbs ac-1 yr-1 (2000 – 4000 kg ha-1 yr-1). For comparison, the salt loading from irrigation water alone, depending on the source of the irrigation water, is on the order of 357 lbs ac-1 yr-1 (400 kg ha-1 yr-1) for lower salinity water sources (e.g., Sierra Nevada watersheds) to nearly 4,000 kg ha-1 yr-1 for higher salinity water sources (e.g., State Water Project).
At the regional scale, dairies are only one of several sources of salinity to the Central Valley’s groundwater and surface water supply. Locally, they add significant additional salinity to bgroundwater. The long-term impacts from dairies as well as those from other salinity sources (municipal wastewater treatment plants, food-waste dischargers, etc.) are still not well understood. Increasing salinity in California’s waters is an issue that must be dealt with as part of an integrated long-range water resources management plan.
Chapter 1 - Introduction
1.1 The Dairy Industry in California Dairying is an important agricultural industry in California as it is the number one dairy state in the nation with approximately 1.7 million lactating cows. As of December 2003, the state’s output in milk and cream accounted for approximately $4.6 billion of California’s nearly $30 billion in annual agricultural income.
1.2 Regulatory Framework Federal, State and Local regulatory agencies can regulate dairy facilities. The Central Valley Regional Water Quality Control Board and the San Joaquin Unified Air Pollution Control District are the primary agencies. County agencies in San Joaquin, Merced, Madera, Kings, Tulare and Kern also regulate dairy facilities.
Multiple efforts are underway to address environmental concerns related to animal confinement at the federal, state, and local level. The US EPA promulgated the Concentrated Animal Feeding Operations (CAFO) Final Rule on Dec. 15, 2002, and it was published in the Federal Register on Feb. 12, 2003. US EPA identified existing and potential concerns during the Rule making process. The new Rule requires that all CAFOs apply for an NPDES permit by April 13, 2006.
The Rule has recently been challenged in court and is currently being revised. The Central Valley Regional Water Quality Control Board is developing guidelines under both federal (NPDES permit) and state regulations. California regulations governing discharges from confined animal facilities are contained in Title 27 of the California Code of Regulations and in the Porter-Cologne Water Quality Control Act (California Water Code Division 7).
The San Joaquin Valley Unified Air Pollution Control District adopted its implementation plan for SB 700 on May 20, 2004, and some dairy operators were required to request coverage under the new permit structure. Most dairy operators are required to develop and implement Conservation Management Practices to reduce fugitive dust emissions. The South Coast Air Management Control District has finalized Rule 1127 and will begin the implementation phase to reduce dust emissions.
Key to many of the regulations is the need to develop manure management plans to include environmental compliance. Though not a regulatory agency, the USDA Natural Resources Conservation Service is developing Guidance for California’s Comprehensive Nutrient Management Plan (CNMP). This process would provide key information for consultants and producers to adequately document nutrient application and crop nutrient uptake and identify management practices to reduce atmospheric emissions.
1.3 Environmental Concerns of Regulatory Agencies Manure generated in dairy production facilities can impact the environment (National Center for Manure and Animal Waste Management, 2001). Water quality impacts from nitrate and salts from land applied manure are key concerns to the Central Valley Regional Water Quality Control Board and are the catalyst for this report. Emissions from manure deposited in corrals, holding pens, and lagoons may also have adverse effects on air quality. Local air districts are concerned with ammonia, volatile organic compounds (VOCs), hydrogen sulfide and particulate matter (PM) emissions. Methane emissions occur but are not a regulated compound.
Potential water quality impacts from improper handling and disposal of dairy manure include accidental or intentional discharges or inadequate management of nutrients that cause pollutants to reach surface water or to recharge to groundwater. Other concerns related to the potential contribution of manure discharge to surface waters were included in the CAFO rule, and include microbes, antibiotic metabolites and organic compounds (US EPA CAFO Rule, 2003).
The San Joaquin Valley Air Basin (SJVAB) is not in compliance with the Clean Air Act. For ozone, the US EPA reported the basin’s air quality to be in the “Non-attainment/Extreme” category, and for PM10, in the “Non-attainment/Serious” category. In general, ozone is not emitted to the air from specific sources, but its precursors VOCs and NOx are emitted. Ozone is the product of photochemical reactions of N oxides (NOx), and VOCs. These pollutants are emitted from dairies at levels that have not been studied conclusively. Ruminant animals generate methane and certain VOCs (e.g., volatile fatty acids, ketones, aldehydes, alcohols) as a part of their normal digestive processes. Additionally, methane is generated under anaerobic conditions in liquid manure storage ponds. There are other organic gases produced from manure and its enzymatic or microbial decomposition. Ammonia released from dairy manure is odorous and can react with NOx to form ammonium nitrate, which is classified as fine PM. Ammonia is also important because it can react with oxygen in the atmosphere and the soil to form NOx and eventually nitrate.
1.4 The Role of the University of California In 1973, the University of California, Division of Agriculture and Natural Resources, at the request of State Water Resources Control Board, formed the Water Quality Task Force of UC Agricultural Committee of Consultants (1973) to investigate generation of manure on dairies and make recommendations on management of dairy manure in California. The documents produced formed the basis for development of statewide regulations adopted in 1984.