Donald L. Lancaster

Control of Medusahead (Taeniatherum caput-medusae) and other Annual Grasses with Imazapic

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. Nomenclature: Imazapic, medusahead, Taeniatherum caput-medusae (L.) Nevski, ELYCM

Assessing Nitrogen Fertilization Needs for Irrigated Orchardgrass in the Intermountain Region of California

Nitrogen fertilization is a critical component of maximizing yield for grass hay production. However, the steady increase in fertilizer price along with concerns for off-site N movement make prudent use of N important. On-farm studies in northeastern California were conducted in irrigated orchardgrass to examine the influence N fertilizer rates and application times have on forage yield, forage quality, soil nitrate, and economics for retail hay. N rates up to 400 lb/acre increased annual yield and net return in a three-cut system. N fertilizer also increased crude protein. Applying fertilizer in split applications gave higher yield, crude protein, and economic return for second and third cut compared to a single fertilizer application at grass green-up. Apparent N recovery decreased with increasing fertilizer rate and ranged from 80 to 38%. N fertilizer did not influence forage neutral detergent fiber. At the highest N fertilizer rates, forage NO3-N at first and second-cut was above 1500 ppm. Fertilizing with N at 600 lb/acre/season elevated fall soil NO3-N at the 24 to 36-inch soil depth compared to the control at multiple sites. Split applications of N fertilizer are imperative to maximize yield, crude protein, and economic return, but excessive N fertilization can increase the likelihood of high forage nitrate and nitrate accumulation below the root zone. Introduction Orchardgrass (Dactylis glomerata) is a popular irrigated grass species grown in the intermountain region of California. Orchardgrass is desired for hay, and it produces high quality forage with proper irrigation and fertilization. Most intermountain orchardgrass fields are managed with efficient irrigation systems (center-pivot, wheel-line, or laser-leveled flood) and cut for hay three times per season. Grass hay prices are high — hay for horses often brings a price greater than dairy-quality alfalfa (4) — making grass hay more valuable than pasture. With high fuel, fertilizer, and energy costs, producers must maximize yield and production efficiency to be Fig. 1. Unfertilized orchardgrass (right) and orchardgrass fertilized with 100 lb N per acre at grass green-up (left) at first-cut harvest. 18 June 2008 Forage and Grazinglands profitable (2). N fertilization is necessary to obtain high grass yields, but applying too much or too little N has negative economic or environmental consequences. Several studies have examined N fertilization of cool-season perennial grasses (2,3,8,10). These studies showed that forage yield increases with increasing N rate, but apparent N recovery (ANR) decreases with high N rates. They also found split applications of N usually produce higher yields compared to applying all the N in early spring. Discrepancies between published studies emerge with optimal N fertilization rates, application timings, and ANR and are likely the result of differences in climate, soil, and management between experiments (9). Management practices, cutting schedules, economics, and soils in the intermountain region of California differ greatly from previous N fertilization research published in the literature, especially since many of these studies were conducted under rain-fed systems east of the Mississippi. Thus, our objective was to determine the optimum N fertilization rate and timing to maximize yield, N use efficiency (NUE), ANR, and returns for orchardgrass grown for retail hay in the intermountain region of California. N Fertilization Study The study was conducted at four orchardgrass sites (McArthur, Ft. Jones, Doyle, and Lookout) in 2005 and two orchardgrass sites (Montague and Susanville) in 2006. Sites’ soil and climate attributes are shown in Table 1. The experiment at every site was a completely random design with 4 replicates and 8 N fertilization treatments. Plot size was 20 by 20 ft. Soil samples were collected at each site before initiating the experiment, and sites were fertilized with phosphorus, sulfur, or potassium if the pre-treatment soil test suggested a deficiency. Watermark soil moisture sensors (Irrometer Co., Riverside, CA) were buried at an 8-inch depth at all sites before N treatments were applied to measure soil moisture throughout the growing season. Table 1. Site soil and climate attributes. N treatments were applied by hand in the form of urea (46-0-0) at the rates listed in Table 2. Treatments totaled 100, 200, 300, 400, or 600 lb of N per acre for the entire season. N application rates at grass green-up in March were 0, 100, 200, or 300 lb/acre. Split application rates after first and second cutting were 0, 50, 100, or 200 lb/acre and were applied immediately before the first Site Soil type Mean annual temperature (°F) Mean annual precipitation (inches) Elevation (feet) Doyle Calpine sandy loam Aridic Haploxerolls 50.6 11.4 4275 Ft. Jones Stoner gravelly sandy loam coarse-loamy, mixed, active, mesic Typic Haploxerepts 50.5 20.6 2747 Lookout Modoc sandy loammesic Vitritorrandic Durixerolls 48.5 15.8 4144 McArthur Esperanza loam fine, smectitic, mesic Pachic Argixerolls 50.6 19.1 3311 Montague Montague clay fine, montmorillonitic, mesic Typic Chromoxererts 51.7 19.5 2634 Susanville Mottsville gravelly loamy course sand mixed, mesic, Torripsammentic Haploxeroll 49.4 14.3 4258 18 June 2008 Forage and Grazinglands irrigation after first and/or second harvest. All fertilizer applications were incorporated into the soil with rainfall or irrigation ≥ 0.5 inch within one to two days of application. The first harvest occurred when grasses were in the flowering stage, and the second and third harvest occurred 40 to 50 days after the previous cutting. Drought stress occurred in mid-summer at the Doyle, Lookout, and Ft. Jones sites in 2005. Therefore, the crop at these sites was only harvested twice, once at flowering and again in early fall. Yield was measured by harvesting a 3by 20-ft strip at a 3-inch stubble height from each plot with a Carter Harvester (Carter Mfg. Co. Inc., Brookston, IN). Forage samples were oven-dried at 140°F for dry matter (DM) determination and forage quality analysis. Dried forage samples were analyzed for total extractable nitrate N (NO3-N), total N (N), total crude protein (CP) and neutral detergent fiber (NDF) using University of California ANR Analytical Lab preparation and analyses methods (UC ANR Analytical Lab, Davis, CA) (7). In the fall after the last cutting, soil was sampled for NO3-N at three depths: 0 to 12 inches, 12 to 24 inches, and 24 to 36 inches. Soil cores were taken from 10 random locations in each plot for three fertilization treatments (unfertilized, 100-100-100, and 200-200-200). Soil was air-dried and analyzed for NO3-N using University of California ANR Analytical Lab methods (UC ANR Analytical Lab, Davis, CA). Yield, forage quality, and soil nitrate data were analyzed by analysis of variance (ANOVA) followed by a comparison of treatment means using Fischer’s least significant difference (LSD) at P ≤ 0.05. Regression analysis was used to determine the relationship between first-cutting yield and N fertilizer rate applied in early spring (SAS Institute Inc., Cary, NC). Site data were pooled for analysis if a site by treatment interaction was not significant at P ≤ 0.05. Influence on Forage Dry Matter Yield and NUE Both N fertilizer rate and application timing had a significant effect on orchardgrass yield (Table 2). First-cut harvest produced more forage than secondor third-cut harvest (Table 2). First-cut orchardgrass yield increased rapidly from 0 to 100 lb N per acre, however the yield response diminished at rates above 100 lb N per acre (Fig. 1). At the moisture-stressed 2-cut sites, orchardgrass yield almost doubled from 0 to 100 lb N per acre, but the yield increase from fertilization lessened from 100 to 200 lb N per acre, and leveled off at fertilizer rates above 200 lb N per acre (Fig. 1). At 3-cut sites, the relationship between first-cut yield and fertilizer was similar to 2-cut sites, but yield at 3-cut sites increased slightly from 200 to 300 lb N per acre (Fig. 1). Applying N fertilizer in split applications produced higher secondand thirdcut yield compared to applying all N at grass green-up (Table 2). Second-cut yield was 0.26 to 0.66 ton/acre higher if fertilizer was applied at 100 lb N per acre in early spring and 100 lb N per acre after first cutting (100-100) compared to 200 lb N per acre in early spring (200-0) (Table 2). Second-cut yield was 0.15 to 0.78 ton/acre higher if fertilizer was applied at 200-100 compared to 300-0 (Table 2). Split applications of N fertilizer were essential for increasing third-cut yield. Even at the highest single N rate (300 lb/acre), yield did not differ from the unfertilized plots if fertilizer was only applied in early spring (Table 2). In contrast, applying fertilizer in split applications at 100-50-50, 100-100-100, or 200-100-100 increased third-cut yield by at least 190% compared to unfertilized plots (Table 2). 18 June 2008 Forage and Grazinglands Table 2. The effect of nitrogen rate and application time on orchardgrass yield and nitrogen use efficiency. x N use efficiency represents lbs of additional forage for each lb of applied N. It was calculated as [(total yield at Nx – total yield at N0) * 2000 ÷ lb N per acre applied at Nx], where x = N rate > 0. y N fertilizer treatments shown as lb of N per acre applied: at spring green-up – after first cut – after second cut. Orchardgrass sites 100% Dry matter yield (tons/acre) N use efficiencyx (lbs) 1st cut 2nd cut 3rd cut Total 2-cut 0-0y 1.51 0.88 2.39 100-0 2.71 1.11 3.82 29 100-50 2.75 1.68 4.43 27 200-0 3.05 1.50 4.55 22 100-100 2.82 1.96 4.78 24 300-0 3.13 1.66 4.79 16 200-100 3.13 2.15 5.28 20 200-200 3.08 2.27 5.36 15 LSD (P = 0.05) 0.27 0.28 0.42 4 3-cut 0-0-0 1.93 0.91 0.41 3.26 100-0-0 3.22 1.31 0.54 5.08 35 100-50-50 3.29 1.77 1.22 6.28 30 200-0-0 3.42 1.29 0.49 5.20 18 100-100-100 3.25 1.95 1.37 6.58 22 300-0-0 3.86 1.37 0.55 5.78 17 200-100-