California is the leading dairy state in the United States. The total sale of milk and its products represents about $6.3 billion annually out of the $50 billion generated from all agricultural production in the state. However, methane emissions from dairy manure and enteric fermentation represented nearly half of all annual methane emissions in California, with dairy manure accounting for 25%, and enteric fermentation for 20%. Methane emissions originating from manure are produced primarily from anaerobic settling basins and lagoons, which are the most common manure storage systems in the state. To achieve sustainability on dairy farms and to comply with state regulations for air and climate pollutants, dairy farms have implemented technologies such as anaerobic digestion and alternative manure management technologies. In addition, governmental incentive programs have been deployed to partially fund these technologies for eligible dairies in the state. The present article reviews the design and operations, effectiveness, and economics of the most common technologies employed in Californian dairies in reducing methane emissions. The technologies studied include anaerobic digesters, mechanical separators, compost-bedded pack barns, manure vacuuming followed by drying, and weeping walls. The current status and estimated effectiveness of government incentive programs are reviewed and recommendations for improvements presented. Finally, future trends and research needs for mitigating the emissions in Californian dairies are identified.

Annual crop production in California is mostly dominated by warm‐season species that require irrigation. Irrigation has been restricted due to drought and policy and may become more uncertain due to climate change. To adapt to these changes, more cool‐season crop options that require less water than summer annuals are needed. Wheat is the most common cool‐season crop, and in other parts of the world canola (Brassica napus L.), and other Brassica oilseed species have diversified and improved the productivity and profitability of cereal‐based agricultural systems. We evaluated multiple canola and camelina [Camelina sativa (L.) Crantz] varieties across diverse agro‐ecological environments throughout California. Yield potential and viability of these oilseed species as complements to wheat were assessed. Canola achieved high mean yields and seed oil content, a very high yield potential, and showed only limited genotype × environment interaction. Using short‐season spring‐type varieties and suitable agronomic management, mean seed yields could be expected to reliably exceed 3000 kg/ha, with a mean seed oil content of 45%. Camelina yields were lower (1000 kg/ha with a mean seed oil content of 30%) and more variable than canola, and displayed high genotype × environment interactions and yield instability. Camelina did not mature earlier than the best yielding canola varieties. Camelina is not economically competitive with canola or wheat, but may be viable for specialized uses in California, especially in low rainfall locations, but this requires further investigation. Given these promising results, Brassica oilseed variety evaluation and agronomic studies should continue in California.

Core Ideas: The accuracy of the Agricultural Production Systems Simulator crop model for simulating canola production in California was tested. The crop model accurately predicted canola yields across the state. Simulations support observations from multi‐environments trials that canola has both high mean yields and yield potential in California. The simulation results suggest canola is a viable alternative crop for diversifying cool‐season annual cropping in California. Canola could maintain economically viable yields under climate change scenarios projected for the region. The agricultural sector of California is one of the most economically valuable and diverse in the world, but is dominated by perennial tree, vine and forage crops, as well as warm‐season annual species that are dependent on irrigation. The diversity of less water‐intensive annual cool‐season crops is limited and wheat (Triticum aestivum L.) is the primary crop. Canola (Brassica napus L.) could diversify annual cool‐season cropping in the state. Our study used field data from a multi‐environment canola variety trial to test the ability of the Agricultural Production Systems Simulator (APSIM) model to simulate canola production in California. APSIM was able to accurately simulate canola yields in diverse regions, and consequently was used to investigate the yield potential of canola in California, using different irrigation management strategies, under both current and anticipated future climate scenarios. These simulations predict that canola should have high mean yields throughout California, given suitable management and variety selection. The long‐term mean yield for short‐season, spring‐type, canola in the central valley of California is predicted to be more than 4800 kg/ha with supplemental irrigation. Under rain‐fed conditions in the northern central valley mean yields are predicted to be 3500 kg/ha. This should make canola economically competitive with cool‐season cereals. Without additional improvements in variety adaptation or management changes, our simulations suggest the yield of canola in California will decline modestly, but remain economically viable, under future climate scenarios.

Salinity and trace mineral accumulation threaten the sustainability of crop production in many semi-arid parts of the world, including California’s western San Joaquin Valley (WSJV). We used data from a multi-year field-scale trial in Kings County and related container trials to simulate a forage-grazing system under saline conditions. The model uses rainfall and irrigation water amounts, irrigation water quality, soil, plant, and atmospheric variables to predict Bermuda grass (Cynodon dactylon (L.) Pers.) growth, quality, and use by cattle. Simulations based on field measurements and a related container study indicate that although soil chemical composition is affected by irrigation water quality, irrigation timing and frequency can be used to mitigate salt and trace mineral accumulation. Bermuda grass yields of up to 12 Mg dry matter (DM)·ha⁻¹ were observed at the field site and predicted by the model. Forage yield and quality supports un-supplemented cattle stocking rates of 1.0 to 1.2 animal units (AU)·ha⁻¹. However, a balance must be achieved between stocking rate, desired average daily gain, accumulation of salts in the soil profile, and potential pollution of ground water from drainage and leaching. Using available weather data, crop-specific parameter values and field scale measurements of soil salinity and nitrogen levels, the model can be used by farmers growing forages on saline soils elsewhere, to sustain forage and livestock production under similarly marginal conditions.