Leaf yellowing (chlorosis) is not unique to Concord grape, yet occurs with great intensity in the arid, irrigated central Washington state growing region. Past research on nutrients has not shown a clear cause and effect relationship between soil and/or plant nutrient status and chlorosis. We investigated both nutritional and climatic conditions for their association with chlorosis occurrence. Six vineyard sites were selected, 2 each with no history of chlorosis (achlorotic), occasional chlorosis, and annually reoccuring chlorosis (chronically chlorotic) and monitoring sites in chlorotic and achlorotic areas were established. Nutrient elements K, Ca, Mg, Mn, and Cu plus the nonnutrient elements Na and Al were monitored in soil (surface, 0 to 30 cm, and subsurface, 30 to 75 cm, depths) and leaf tissue (both petioles and blades) prebud burst (soil only), at bloom, and preveraison at 650 degree days at all vineyard sites for the 2001, 2002, 2003, and 2004 growing seasons. In addition, both soil temperature and moisture were monitored. To evaluate the intensity of chlorosis at each site, chlorotic vines were GPS marked and mapped post-bloom each year. Overall, chlorosis incidence was more widespread in 2001 and 2003 than in 2002 or 2004. There were few relationships with soil or tissue nutrient concentrations. However, soil moisture was consistently higher and soil temperature lower in the period between bud burst and bloom in the chlorotic sites. This suggests that a cold, wet soil environment prior to bloom impedes grape root growth and/or function and triggers plant chlorosis. Yearly differences strongly support this finding.
Small conifers often must coexist with the components of early plant succession for prolonged periods of time in forest regeneration. Forest regeneration and the management of perennial horticultural crops are similar in this respect, since individual “crop” plants in both instances usually occur in close proximity to each other or associated species. Association of the crop with its neighbors may be detrimental in both situations (10, 15), but other interactions also are possible (8). Thus it is necessary for forest managers and horticulturists to recognize the physical, physiological, and environmental components that influence the outcome of plant-to-plant associations. It also is necessary for land managers (foresters, horticulturists, etc), to understand the consequences of their actions, since short-term impacts on vegetation can have long-term influences on environmental resource availability, subsequent vegetation, and the populations of other organisms. Long-term impacts of management are not exclusive to forest regeneration, but the need for prediction may be most obvious there because of the relative longevity of forest communities in comparison to most of those in agriculture.
In arid and semiarid areas, wine grapes are frequently managed using regulated deficit irrigation (RDI) to control vegetative growth. To understand the distribution of soil moisture using RDI in a drip-irrigated vineyard, we collected soil samples after several irrigation events around six drip emitters in two ‘Cabernet Sauvignon’ and two ‘Merlot’ vineyards from late July through Mar. 2002 and 2005. The March sampling depicts soil moisture status before budbreak after winter precipitation. Soil samples were collected in four depth increments at 16 locations in a half-circle radius from immediately below the emitter to a depth of 60 cm. Both gravimetric and volumetric soil moisture content were determined. Soil moisture varied by depth, distance from the emitter, and sampling time. During late-season irrigation events, 50% to 75% of the sampled area contained plant-available water, which was less than expected. When calculated as plant-available soil moisture, regardless of time of sampling, soil sampled across a 0- to 45-cm depth provided the most representative indication of soil moisture status. Additionally, sampling directly under the emitter or directly under the drip line could result in skewed measurements compared with the sampled area. The data suggest that collecting soil samples within a 20- to 40-cm radius, either diagonal or perpendicular to the drip line emitter position, will best reflect the amount of plant-available soil water. Additionally, monitoring should be conducted on both sides of the row around each emitter selected and then averaged to avoid any patterns from hilling or disruption in water flow patterns.
Concord grape (Vitis labrusca L.) accounts for a majority of juice grapes produced in Washington State. Because synthetic nutrients are not permissible in USDA organically-certified production systems, legume cover crops are used to supply nitrogen (N) to the crop. In order to supply a sufficient amount of N, the cover crop must successfully establish and produce large quantities of biomass. This study evaluates how the planting date influences emergence and biomass production of hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam.] when used as legume green manures. The research was conducted on a commercial vineyard and a research vineyard from 2003–05. Treatments for the study consisted of yellow sweet clover and hairy vetch planted in both the spring and fall. Plots receiving soluble N sources were planted with wheat (Triticum aestivum L.) or rye (Secale cereale L.). Because of the large relative seed sizes of rye, wheat, and hairy vetch compared to yellow sweet clover, these treatments established faster with good stands in 2004. In 2005, clover plots had high emergence and biomass production because of water management modifications. Biomass data from the commercial vineyard in May 2005 indicates that fall-planted vetch produced more biomass than spring-planted vetch. Fall-planted hairy vetch and yellow sweet clover in the research vineyard showed higher biomass production than spring- and fall-planted hairy vetch and yellow sweet clover. When hairy vetch and yellow sweet clover are planted in the fall, they generally have better seedling emergence and biomass production due to the heightened aggressiveness exhibited by competing weed species during late spring and summer.
Legume cover crops can be used to provide nitrogen (N) to organically produced Concord (Vitis labruscana Bailey) grape. The cover crop must be incorporated at a time such that subsequent N mineralization is synchronous with plant demand to maximize the amount of N available to the grape plant. The objectives of this research were to 1) evaluate the effectiveness of hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam.] in providing N to organically grown Concord grape, 2) examine the synchronization of N release from mineralization after incorporation of cover crops with plant N demand, and 3) compare soluble, more readily available sources of N to legume cover crops in providing N to grape. This work was conducted on two Concord vineyards, one commercial (COM) and one research (RES) vineyard. Both vineyards were overhead sprinkler-irrigated and plots were established in a Latin square design with four or six replicates of each treatment. Treatments consisted of hairy vetch and yellow sweet clover planted in either the spring or fall, 112 kg·ha−1 N added as either urea or blood meal, and a 0 kg·ha−1 N control. Soils were sampled weekly (0 to 30 cm) from budbreak to cover crop plot treatment establishment and were analyzed for soluble (NO3-N and NH4-N) N. Soluble N release in the plots was monitored with ion exchange membranes (plant root simulators). Grapes were harvested and evaluated for yield and °Brix. Legume and fertilizer treatments resulted in increased N availability from grape bloom until veraison. As a result of rapid nitrification, NH4-N was less useful than NO3-N in determining N mineralization patterns. Available N peaks as high as 40 mg·kg−1 NO3-N were well timed with the critical N demand period for Concord grape. Soluble N sources (urea and blood meal) peaked higher than plant sources. No differences were detected between legume treatments. Legume covers did, however, supply more available N per unit of biomass to the soil than a small grain cover. Yield and oBrix varied by year but not by treatment, suggesting that the cover crop or plant and soil N reserves provided sufficient available N to the grape through the study period.
The effects of water stress on internal water potential components and specific physiological processes were investigated in field grown potatoes (Solanum tuberosum L. cv. Viking). Leaf water potential (ψleaf) as estimated by the pressure chamber, was not directly related to soil water potential (ψsoil) until a specific minimum ψsoil was attained. Subsequently ψleaf did not increase in response to increases in ψsoil. Water stress affected physiological processes such as stomatal resistance, photosynthesis and enzyme activity. A decline in ψleaf was apparently responsible for increased stomatal resistance and decreases in photosynthetic rates. The activities of ribulose diphosphate carboxylase and phosphoenolpyruvate carboxylase decreased as ψleaf declined. The relationship between water stress and physiological processes and the inability of ψleaf to respond to increases in ψsoil after a maximum stress may partially explain the extreme sensitivity of potatoes to even mild water stress.
The ability to monitor plant nutrient status of high value horticultural crops and to adjust seasonal nutrient supply via fertilizer application has economic and environmental benefits. Recent technological advances may enable growers and field consultants to conduct this type of monitoring nondestructively in the future. Using the perennial crop apple (Malus domestica) and the annual crop potato (Solanum tuberosum), a hand-held leaf reflectance meter was used to evaluate leaf nitrogen (N) status throughout the growing season. In potato, this meter showed good correlation with leaf blade N content. Both time of day and time of season influenced leaf meter measurement, but leaf position did not. In apple, three different leaf meters were compared: the leaf spectral reflectance meter and two leaf greenness meters. Correlation with both N rate and leaf N content were strongest for the leaf reflectance meter early in the season but nonsignificant late in the season, whereas the leaf greenness meters gave weak but significant correlations throughout the growing season. The tapering off of leaf reflectance values found with the hand-held meter is consistent with normalized difference vegetation index (NDVI) values calculated from satellite images from the same plots. Overall, the use of leaf spectral reflectance shows promise as a tool for nondestructive monitoring of plant leaf status and would enable multiple georeferenced measurements throughout a field for differential N management.
Collection and estimation of root material are likely some of the greatest challenges of whole-plant sampling. As with other perennial crops, season of sample collection is also a challenge in grape whole-plant sampling. Our interest is in collecting grape whole-plant samples from an established (>25-year-old) vineyard to study plant nutrient partitioning. Before launching into routine sampling, two techniques were compared for very fine, fine, and coarse root distribution. For very fine and fine root sampling, soil cores were collected in a radial pattern around the vine trunk at eight sample points, each either 20, 60, 120 cm from the trunk or 50, 100, and 150 cm from the trunk. Roots were washed from the soil material, separated into fractions and weighed. For evaluation of techniques for sampling fine and coarse roots, roots were either excavated by tracing them from the trunk in about a 1-m3 soil volume or by extracting about the same soil volume using a backhoe and shaking the soil free of the roots. Overall, the more narrow soil core sampling gave a greater total root mass and both the tracing and backhoe methods gave similar results. In addition, pruning weight measurement is also frequently measured in grape research. We compared using the NDVI (Normalized Difference Vegetation Index) device, the “Greenseeker”™, with pruning mass to determine if this device could be used as a non-destructive measurement for grape pruning weight.
Understanding water and nutrient movement in arid climate-regulated deficit, drip-irrigated vineyards is imperative for understanding grape vine canopy management. However, little research has been conducted in these environments to aid in the understanding of where the vine accesses nutrients and/or soil water and how that translates into soil and/or plant tissue sampling approaches. We used bromide (Br) as a tracer to study nitrate movement in soils as well as into grape leaves in two ‘Merlot’ vineyards in central Washington State. Bromide movement closely followed water movement. Although Br was detectable in grape petioles, it was not detectable in leaf blades, likely as a result of a dilution factor related to the amount of tissue. Relationships between soil Br and soil moisture as well as petiole and soil Br concentrations suggests that soil sampling for nitrate should be taken from a diagonal position between the vine and the emitter, between 20 and 60 cm from the drip line. This is consistent with the recommendation for soil moisture sampling in a published companion study.