Invasive annual grasses, such as medusahead, can reduce forage production capacity and interfere with revegetation projects in California rangelands. Because of the taxonomic similarity to other more desirable grasses, achieving selective control of invasive annual grasses can be difficult. In selectivity trials conducted in Yolo and Siskiyou counties, CA, the herbicide imazapic gave control of many nonnative annual grasses yet provided some level of selectivity to specific perennial grasses used in revegetation projects throughout the western United States. The selectivity difference between newly seeded perennial and annual grasses was greater with PRE applications than with POST treatments. Both perennial and annual grasses within the tribe Hordeae were more tolerant to imazapic than other grass species. In addition, field experiments were conducted at three sites in northern California (Yuba, Yolo, and Lassen counties) and one in southern Oregon (Lake County) to test the response of imazapic to varying management conditions. Imazapic was applied PRE in fall (and also spring in Lake County) at rates from 35 to 210 g/ha on undisturbed rangeland, in comparison with rangeland cleared of standing plant material and thatch by either tillage, mowing and raking, or burning. Imazapic generally showed enhanced weed control when applied following disturbance. Rates as low as 70 g/ha, if combined with thatch removal, provided significant suppression of medusahead. In addition, disturbance alone generally reduced medusahead cover in the following year. Although imazapic showed potential for control of medusahead and other annual grasses, its selectivity window was relatively narrow.

Predictive equations for alfalfa quality (PEAQ) based on height of the tallest stem and maturity stage of the most mature stem in a sample were developed to estimate neutral‐detergent fiber (NDF) and acid‐detergent fiber (ADF) concentrations in alfalfa (Medicago sativa L.). Field testing of these equations is limited outside the state of Wisconsin where they were developed. Our objectives were to test these equations for estimating alfalfa NDF and ADF across a wide geographic area and to evaluate the performance of PEAQ on a whole‐field basis by using within‐field subsampling. Alfalfa samples varying in height and maturity were collected throughout the growing season from fields in New York (n = 28), Pennsylvania (n = 23), Ohio (n = 48), California (n = 45), and Wisconsin (n = 48) in 1994 to 1996. Additional samples were collected in Ohio and Wisconsin from producer‐managed fields in which 5 to 10 subsamples per field were taken on each sampling date (n = 296 subsamples from 51 fields). Observed NDF and ADF values were regressed on estimated values. The accuracy of PEAQ in other states was at least equal to that observed in Wisconsin. Across all states, regression equations for NDF and ADF were slightly biased (b ≠ 1.0 and/or y‐intercept ≠ 0 at P < 0.01); however, prediction errors were sufficiently low to allow use of PEAQ as a preharvest management tool. Root mean square error values ranged from 19.1 to 23.9 g kg−1 for NDF and 15.0 to 19.0 g kg−1 for ADF. Prediction errors were 16.2 g kg−1 for NDF and 13.2 g kg−1 for ADF across Ohio and Wisconsin when regressing observed means on estimated means of five subsamples per fieldsampling date combination. We conclude that predictive equations for alfalfa quality based on a combination of stem height and maturity were robust across a wide range of environments.

California's interior grasslands have undergone dramatic changes during the last two centuries. Changes in land-use patterns and plant introductions after European contact and settlement resulted in the conversion of perennial-dominated grasslands to exotic annual grasses. More recently, the annual grasslands have been heavily invaded by the deeply rooted late-maturing forb yellow starthistle. This series of invasions and conversions has changed the community structure and phenology of the grasslands. We hypothesized that these changes have resulted in significant differences in soil water–use patterns in the grasslands. We studied soil water depletion and recharge patterns of three grassland community types dominated by perennial grasses, annual grasses, or yellow starthistle with contrasting phenology and rooting depths for 4 yr. Soil moisture measurements were taken every month from March to December in 1998, 1999, and 2000 and every other month in 2001. Measurements were taken with a neutron probe at depths of 30 to 150 cm at 30-cm intervals. The results indicate that the yellow starthistle community maintained a significantly drier soil profile than the annual grass community. The perennial grass community maintained an intermediate soil water content that was not significantly different from either of the other two communities. Significant time by community and depth by community interactions indicated that the yellow starthistle community continued depleting soil moisture later into the season and at deeper depths than the other grass communities. This study demonstrates the effect of plant invasion on soil water recharge and depletion patterns in California grasslands.

Companion crops have been used in alfalfa (Medicago sativa L.) establishment to increase forage yield and decrease weeds. When oat (Avena sativa L.) is used as a companion crop, the typical seeding rate is 50 to 75 kg ha−1. In irrigated situations this seeding rate has depressed alfalfa yield and stand density. This study was conducted under irrigated conditions to evaluate alfalfa yields, forage composition at first harvest, and alfalfa and weed densities at four oat seeding rates; 0 to 36 kg ha−1. Two field experiments were established at Madera and one at Courtland, CA. The interplanting of oat with alfalfa increased first‐harvest forage yields 2.45 to 8.62 Mg ha−1, relative to alfalfa planted alone. Alfalfa yields at subsequent cuttings during the first season were reduced by the oat companion crop. By the last cutting in the first season and all cuttings in the second season, yields were equal for all treatments. First‐season forage yields were increased 1.54 to 5.05 Mg ha−1 by an oat companion crop. The oat component of the first cutting ranged from 71 to 98%. Alfalfa and weed biomass were both reduced by the oat companion crop. The oat companion crop reduced alfalfa stand density during establishment, but density was higher at the beginning of the second season at two of the three sites when the oat seeding rate was 18 kg ha−1. Alfalfa established with an oat companion crop had an average of 30% fewer weeds in the second year when 9 kg ha−1 were used and almost 50% fewer weeds at 18 kg−1. Thus, the seeding rate of an oat companion crop considered best for optimizing yields and reducing weeds under irrigation in California is approximately 18 kg ha−1.

roundwater is a vital resource in California, providing approximately 38% of the state's water supply in normal years and at least 46% in dry years (DWR 2014). During the recent drought (water years 2011-2012 through 2015-2016), the majority of groundwater wells (90%) experienced a drop in groundwater levels of at least 10-50 ft (3-15 m) while some wells (8%) showed declines in groundwater level of more than 50 ft (>15 m) (DWR 2017). Groundwater overdraft persisted for most of the 20th century but the rate has dramatically increased since 2000 to about 7.2 million acre-feet (ac-ft), or 8.9 cubic kilometers (cu km) per year between 2006 and 2010 (Faunt 2009; Scanlon et al. 2012). State legislation now requires the implementation of groundwater sustainability plans to ensure that all groundwater basins are managed sustainably by 2040 (SWRCB 2014). Managed groundwater recharge on agricultural lands in winter, when surplus surface water often is available, is one promising strategy for replenishing RESEARCH ARTICLE Managed winter flooding of alfalfa recharges groundwater with minimal crop damage Over 90% of the water applied to sites in Davis and Scott Valley percolated to recharge groundwater, making this a viable practice on highly permeable soils.