Growth and Yield of Cultivated Grape with Native Perennial Grasses Nodding Needlegrass or California Barley as Cover Crops

Two California native perennial grasses, nodding needlegrass [Nassella cernua (Stebbins & R.M. Love) Barkworth] and California barley [Hordeum brachyantherum Nevski ssp. californicum (Covas & Stebbins) Bothmer, N. Jacobsen & Seberg], were compared with a conventional grass cover crop, ‘Blando’ brome (Bromus hordeaceus L.), as well as resident (weedy) vegetation and a clean cultivated control for effects on growth and yield of cultivated grape (Vitis vinifera L. cv. Barbera). Statistical analyses did not reveal yield differences between treatments with floor vegetation (the native grasses, ‘Blando’ brome, and resident vegetation) and clean cultivation, the cover crop treatments (the native grasses and ‘Blando brome’) and clean cultivation, nor the native grass treatments versus treatments with non-native floor vegetation (‘Blando’ brome and resident vegetation). However, there was a significant difference between the two native grasses with the average yield of nodding needlegrass 26.2% higher than that of California barley. Treatments did not differ in 8Brix, berry weight, or pruning weight. At the end of the study, vine trunk diameter was 7.1% higher under the cover crop treatments than resident vegetation. Given these results, in vineyards where a neutral effect on growth or yield is desired, nodding needlegrass would be suitable as a permanent cover crop, whereas California barley would not. Managing floor vegetation is a prime managing the resident vegetation or a planted consideration for vineyard managers. The cover crop (Elmore et al., 1998). The typical benefits of removing resident (weedy) vegemethod of cover cropping is to plant an tation are well known: weeds can compete annual grass, legume, or blend in the fall, with the vines for water, nutrients, and even allow it to grow in winter and early spring, light, and the traditional method of protecting and cultivate it by midspring so as to minimize vine growth and yield is to keep the vineyard competition with the vines. The disadvantage free of floor vegetation either through use of to this is that during the grape-growing herbicides or cultivation. However, a vineseason, the soil remains uncovered and can yard floor with no vegetative cover has its be colonized by weeds. Permanent cover drawbacks, which includes increased dust crops under nontillage are rare in California; (impeding photosynthesis and increasing although they provide continuous soil cover, vine susceptibility to spider mites) and inthere are concerns about excessive competi­ creased rate of organic matter decomposition tion. Perennial legume cover crops that have leading to a decline in soil structure and been suggested for vineyard use (Ingels et al., poorer water penetration (Gulick et al., 1998) such as white clover (Trifolium repens 1994). On slopes with no floor vegetation, L.) and strawberry clover (Trifolium fragife­ there is an increased risk of erosion. rum L.) require summer water, making their It has become common in California for management all but impractical except in practitioners to maintain vineyard floor vegareas with abundant irrigation water or a high etation for at least part of the year either by soil water table. Non-native grasses main­ tained during the growing season compete with the grapevines for water and nitrogen Received for publication 30 July 2009. Accepted and have led to reductions in grapevine vigor for publication 30 Oct. 2009. and yield. A cover crop of ‘Berber’ orchardI thank the University of California Sustainable grass (Dactylis glomerata L.) increased water Research and Education Program, which provided stress and lowered vigor and yield of ‘Caber­ funding for this study. net Sauvignon’ by ;50% (Wolpert et al., I thank assistants Jose Cantu, Abebe Gebreheiwet, 1993). Costello and Daane (2003) found Kimberly Miyasaki, and Juliet Schwartz and Scott summer floor vegetation dominated by barnStewart of Conservaseed (Rio Vista, CA). yard grass (Echinochloa spp.) and large Current address: Horticulture and Crop Science Department, Cal Poly State University, 1 Grand crabgrass [Digitaria sanguinalis (L.) ScoAvenue, San Luis Obispo, CA 93407. poli] decreased leaf nitrate–nitrogen concen­ e-mail [email protected]. tration and vigor of ‘Thompson Seedless’. Self-reseeding annuals can provide cover cropping benefits while minimizing in-sea­ son competition (Bugg et al., 1996). These can be grasses or legumes, which, under nontillage, set seed and senescence in the spring, leaving a dead mulch, which can outcompete weeds. The seed then germinates with the fall rains and a new stand is established. ‘Blando’ brome, a self-reseeding cover crop commonly used in California vineyards, has been found to use only a mod­ erate amount of water (Gulick et al., 1994; Prichard et al., 1989). However, self-reseed­ ing annuals need to be replanted every few years to revitalize the stand. A potential alternative cover cropping system for orchards or vineyards in Califor­ nia, and perhaps other regions with a Medi­ terranean climate, is the use of native perennial grasses. These grasses should be well suited as cover crops in that their phenology is opposite that of the grapevine, i.e., their dormant period is during the sum­ mer dry season when the vines are active. Therefore, they should provide the advan­ tages of a perennial cover crop without the disadvantage of excessive competition with the vines for water and nutrients, although this would depend on the degree of native grass summer dormancy. Since the early 1990s, there has been increased interest in the use of native grasses among commercial orchardists and viticulturists in California (Ingels, 1998). The object of this study was to test the competitive effect on the grapevines of two California native grasses, nodding needlegrass and California barley. Each is a peren­ nial bunch grass, which blooms in midspring and sets seed in late spring. California barley has a maximum height of 0.5 m and nodding needlegrass 0.8 m (USDA-NRCS, 2008). These were compared with ‘Blando brome’, a self-reseeding annual native to Europe; resident vegetation, which consisted of nat­ uralized grasses and forbs from Europe and Asia; and a clean cultivated control. From the same study, data were collected on soil water content and leaf water potential from the nodding needlegrass and clean cultivated treatments and are presented in another paper. Materials and Methods The experiment was conducted in 1998 and 1999 at the Kearney Agricultural Center in Parlier (Fresno County), CA. Soil type at the site was a Hanford fine sandy loam. The vineyard was a 0.4-ha block, cv. Barbera, planted in 1989, on 2.1 m (in row) · 3-m (between row) spacing. Vines were trained to a bilateral cordon and spur pruned and trellised with a single catch wire. Plot size was five rows by six vines and treatments were replicated three times in a randomized complete block design. The viticultural cli­ mate was categorized as a Winkler Region V with ;2500 growing degree-days above 10 °C between 1 Apr. and 31 Oct. in the northern hemisphere (Winkler et al., 1974). HORTSCIENCE VOL. 45(1) JANUARY 2010 154 The cover crops were established in Nov. 1996 planting at a rate of 13.2 kg·ha . Treatments were 1) nodding needlegrass [Nassella cernua (Stebbins & R.M. Love) Barkworth]; 2) California barley [Hordeum brachyantherum Nevski ssp. californicum (Covas & Stebbins) Bothmer, N. Jacobsen & Seberg]; 3) ‘Blando’ brome; 4) resident veg­ etation; and 5) a clean cultivated control. Resident vegetation consisted of winter an­ nuals, primarily soft chess (Bromus mollis L.), foxtail barley (Hordeum murinum L. ssp. leporinum), spotted cat’s ear (Hypochoeris radicata L.), annual ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot], filaree (Erodium spp. L.), and cudweed (Gnaphalium sp. L.). Cover crop and resident vegetation management consisted of one mowing in the middle of June of each year. Vines were drip-irrigated at 80% of full evapotranspiration throughout the season from 1 May to 1 Nov. of each year. Daily reference evapotranspiration figures were accessed from the California Irrigation Man­ agement Information System weather station located on-site and monthly crop coefficient values from Williams et al. (2003). Estimated water applied was 503 mm in 1998 and 538 mm in 1999. Between-row weed control in the clean cultivated treatment was undertaken every 2 weeks during the growing season by use of a tractor-drawn rototiller. For the entire study site, in-row weed control was accomplished by application of glyphosate (2.6 kg glyph­ osate acid equivalent/ha) in March and May applied in a 1-m wide band. All samples were taken from the middle three rows each plot (with the outer two rows a buffer) and middle four vines of each row (with the outer two vines a buffer). Just before harvest in each year, 50 berries per plot were randomly sampled, weighed, and percent sugar (°Brix) estimated with a hand­ held refractometer (Leica Microsystems Inc., Buffalo, NY). Yield was estimated by har­ vesting and weighing the fruit from four randomly selected half-vines per plot (29 Sept. 1998 and 13 Sept. 1999). In January after each field season, four randomly se­ lected vines per plot were pruned and the brush weighed as an estimate of vine vigor. As an estimate of the effect of the cover crops on vine vigor since cover crop establishment, trunk diameter was taken with a pair of digital calipers (Mitutoyo Co., Kanagawa, Japan) in Feb. 2000 measuring four randomly selected vines per plot at a height of 0.3 m. Yield, berry weight, °Brix, and pruning weight were analyzed by repeated measures analysis of variance (ANOVA) using a log 10 transformation and using year as the repeated measures variable and planned orthogonal contrasts for mean separation (PROC GLM; SAS Institute, 2003). For purposes of the orthogonal contrasts, the variable ‘‘floor veg­ etation’’ pooled the treatments with vine­ yard floor vegetation (nodding needlegrass, California barley, ‘Blando’ brome, and resident vegetation), ‘‘cover crop’’ pooled the planted cover crop treatments (nodding needlegrass, California barley, and ‘Blando’ brome), ‘‘na­ tive grasses’’ pooled the native grasses (nod­ ding needlegrass and California barley), and ‘‘non-native floor vegetation’’ pooled ‘Blando’ brome and resident vegetation. Trunk diameter data were analyzed by oneway ANOVA (PROC GLM; SAS Institute, 2003). Differences between means were con­ sidered significant when P # 0.05.