«University of California Division of Agriculture and Natural Resources Committee of Experts on Dairy Manure Management September 2003 February 2004, ...»
The eight dairying counties in the San Joaquin Valley (i.e. Fresno, Kern, Kings, Kings, Merced, San Joaquin, Stanislaus, and Tulare) are major production areas of alfalfa hay in the state (Table 7.12). According to the summary of the County Agricultural Commissioners’ Crop Reports (California Agricultural Statistics Service, 2003), the gross value of 2001 – 02 year alfalfa hay production in the San Joaquin Valley amounted to $534 million. For the same period, the gross value of alfalfa hay produced by Southern California counties (i.e. Imperial, Los Angeles, Riverside, and San Bernardino) was $205 million. Alfalfa hay produced in Southern California is mostly for consumption in the Chino-Corona and Hemet-San Jacinto dairy areas, where approximately 200,000 dairy cows are located. The remainder is exported to dairies in Arizona.
Generally, feeds for dairy cows are produced on nearby farmlands. For dairies in the Central Valley, some of the feed, especially alfalfa hay, may be produced and imported from outside the Central Valley. However, there are few data available on the extent of the importation. Based on the harvested acreage of hay (including green chops) and grains (corn, oat, and wheat) as reported in the 2002 County Agricultural Commissioners’ Data, it is reasonable to assume that the majority of the feed ingredients used by Central Valley dairies are raised on farmlands in the Central Valley (California Agricultural Statistical Service, 2003).
Table 7-3: Gross Values of Alfalfa Hay Production in San Joaquin Valley and Southern California Counties in 2001 – 02.
In addition to alfalfa, San Joaquin Valley counties have significant acreages of other crops that are major ingredients in dairy animal feed, such as corn silage, corn, winter forage, wheat, almond, tomato, citrus, etc. The production acreages in Fresno, Kern, and Merced counties are used as examples (Tables 7.13 to 7.15). Patterns in other counties are similar. They clearly illustrate the extent of local feed production for dairy cows in the San Joaquin Valley.
Alfalfa hay is fed not only to dairy cows but also to horses and other ruminant animals.
According to Dr. Daniel H. Putnam (CE Agronomy Specialist, UC Davis), California has a deficit in alfalfa production and imports probably 3 to 10% of its needs. While anecdotal evidence exists, there are no data to indicate the extent of the forage importation into the San Joaquin Valley. Small feed amounts may be imported to cover seasonal and temporary shortages in supply. We do not expect the imported amounts, especially alfalfa hay, to be significant as the shipping costs and distances will be considerable compared to local production. Imperial Valley and Palos Verde Valley are the closest major forage production areas outside of San Joaquin Valley. One-way shipping distance from these production areas will be 500 miles or longer.
Despite significant local productions, some grains (especially corn) and protein meals (such as soybean and canola meal) for dairy feeds may be imported from the Mid-West and Canada.
These two ingredients typically constitute 10 to 15% of the dry matter in the feed while forage typically is less than 50% of the dry matter in the feeds. The mineral contents of grains and protein meals are considerably lower than those of the forages. For example, the whole corn contains 0.03, 0.37, 0.12, 0.03, and 0.05% of Ca, K, S, Na, and Cl, respectively. As a result, the salt contribution of the grains and protein meals in the dairy feed will be far less significant than the forages and agricultural by-products which are locally produced.
Table 7-4: Production Acreages of Selected Crops in Fresno County in 2002.
At the regional scale, it therefore appears that when dairy manure is applied on croplands, the overall salt balance of the Central Valley appears is unaffected. Harvested plants absorb dissolved minerals from the soil and the land application of dairy manure simply redistributes them.
Despite the apparent regional balance, two additional issues must be considered, both of which highlight the localized increase in salt load when comparing animal farming systems (including
dairies) to other farming systems:
(1) The production of forage crops for consumption by Central Valley animals replaces the production of food and fiber crops for human consumption. Most foods and fibers are exported from the Central Valley (salt export), while forage crops remain in the Central Valley. Hence, for each animal unit in the Central Valley, there is a net increase in salt that remains in the Central Valley (via excretion and land application).
(2) The concentration of animals in dairies and other animal farming operations means that the salt loading to land is concentrated in the vicinity of dairies, where the manure is most likely to be land- applied, whereas the forage crop production (from where the salts originate) occurs over a much larger land area and is more dispersed.
As a result, salt loading in dairy areas are expected to increase (relative to non-dairy areas) and, over the long run, the salinity of groundwater underneath these areas may be affected.
Table 7-6: Production Acreages of Selected Crops in Merced County in 2002.
7.6 Summary 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.
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