Agriculture has long been a significant component of the United States economy. In fact, it is viewed by most of the world as the model to be followed. However, in recent years governmental and environmental groups have expressed concern over certain farm practices and have brought increasing pressure for change on the agricultural industry. Some of these concerns are valid, such as those documented by the misuse of chemicals or short sighted farming practices. In order to maintain its economic dominance, agriculture must adopt new technologies to alleviate these concerns.
There are nearly 60 million acres of irrigated cropland in the United States. Most of this acreage receives some type of surface irrigation. Newer technologies like drip irrigation are proven to have significant advantages over traditional surface irrigation systems. Placing the drip emitter beneath the soil surface - called subsurface drip irrigation (SDI) - holds the potential for additional benefits to the grower (see photos).
Significant technical advances have been made recently in the use of SDI. It is now considered by many to be a viable alternative to other forms of irrigation (flood, furrow, sprinkler, micro, etc.). It has applications in row crops and permanent crops, and life expectancy of the SDI system may be 20 years or longer.
The potential for production increases with SDI covers the full range of irrigated crops. Examples include alfalfa, which would benefit from continued irrigation while cuttings are drying in the field. Subsequent growth could lead to additional cutting(s) and tonnage. Lower quality water can be used with SDI to successfully grow crops where other systems fail. As competition grows for potable water, growers may be forced to use reclaimed or recycled water sources.
Trees and vines will benefit from SDI due to reduced compaction from equipment entering wet fields, as is the case with other irrigation methods. Farming efficiency is increased because cultural practices can be performed on an as-needed basis. Significant reduction in the use of pre-emergent herbicides and related tractor time is also expected. The collective benefit will be reduced negative impact on soil, water and air resources.
Little information is available in the technical literature on use of SDI in vineyards. More information on SDI would be beneficial to grape growers, irrigation consultants, and irrigation equipment suppliers. Integrating SDI with other technologies has the potential for enhancing overall farm profitability. This project evaluates the interaction between trellis system, irrigation system and amount of irrigation. The specific objectives of this project were as follows:
- To evaluate the effect of trellis system, irrigation method, and deficit-irrigation scheduling.
- To evaluate the effect of trellis system, irrigation method, and deficit-irrigation scheduling on growth, yield, components of yield, and fruit composition.
- To evaluate performance of above ground drip (AGD) and subsurface drip irrigation (SDI) systems.
MATERIALS AND METHODS
This study is being conducted in a 15-acre Sauvignon Blanc vineyard located on the California State University, Fresno Agricultural Laboratory. The vines are grafted to Freedom rootstock and were planted in 1992 on a spacing of 8' x 12' (vine x row). The soil type is Hanford Sandy Loam and the row direction is north to south.
The irrigation systems are comprised of emitters suspended along the vine row from a wire 18 inches above the ground or emitters placed in the center of the vine rows at a depth of 20 inches (subsurface). Both installations use drip tubing 0.63 inches in diameter with two 0.5 gallons-per-hour inline emitters, spaced 48 inches apart. The subsurface emitters have the herbicide Treflan incorporated in them during the manufacturing process to prevent root intrusion. Caution needs to be exercised with Treflan impregnated products, as excessive heat will significantly reduce its efficacy. Tubing was replaced on this project due to excessive exposure to the sun before installation. Above ground irrigation was applied at a rate of 0.8 of crop evapotranspiration (Etc). The subsurface irrigations were done with three different water application rates; 0.8, 0.6, and 0.4 Etc.
Four trellis systems were used in conjunction with each of the irrigation treatments. Minimally-pruned vines received no dormant season pruning. However, these vines were trimmed after berry set, under the vine row, at a height of 30 inches from the soil surface. Data was analyzed as a two-factor factorial.
Data was collected during the 1996 and 1997 growing seasons. The experimental design used is a randomized complete block with four blocks. Experimental units consisted of five rows of approximately 70 vines each. Data was collected from five vines in the middle of each row. One hundred berries were collected from the apex of basal clusters on randomly selected shoots prior to harvest. Berry samples were transported to the laboratory and stored at approximately 34F until analysis. All samples were analyzed within two days of sampling. At the time of analysis, berries were crushed and the resulting juice filtered through cheesecloth. Soluble solids were measured using an Abbe refractometer (Leica Mark II). A Corning pH/ion analyzer (model 350) was used to deter-mine titratable acidity and pH (Zoecklein et al., 1994).
At harvest, yield and cluster number were determined for each of the five vine plots. Mature nodes were counted in winter before dormant pruning. A node was considered to be mature when both adjacent internodes had periderm. Data was subjected to a factorial analysis of variance, with training system and irrigation method as factors (Little and Hills, 1978). Means were separated by Duncan's multiple range test at the 5-percent level.
Treatments involved in the study are listed below. Trellis system treatments are as follows:
- Standard two-wire vertical trellis (BC)
- Open lyre (OL)
- Geneva double curtain (GDC)
- Minimal pruning (MP)
Irrigation scheduling treatments are as follows:
- Above ground drip with water application of 0.8 of evapotranspiration (Etc)
- Subsurface drip irrigation (SDI) with water applica- tion of 0.8 Etc
- SDI with water application of 0.6 Etc
- SDI with water application of 0.4 Etc
RESULTS AND DISCUSSION
The effects of irrigation method and training system on yield and components of yield for 1996 are presented in Table 1. Irrigation method had a significant effect on yield per vine, clusters per vine, and cluster weight. Yields were highest in the plots which were irrigated to 80 percent of crop evapotranspiration. The 0.6 and 0.4 Etc treatments were significantly lower in yield, but similar to each other. Clusters per vine were highest for 0.8 Etc AGD irrigation and lowest for 0.4 Etc SDI. The clusters per vine data for 0.8 and 0.6 Etc SDI treatments were intermediate. Cluster weights were highest for the two 0.8 Etc treatments and lowest for the 0.4 and 0.6 Etc treatments. Berry weights and berries per cluster were not statistically different.
Yield was significantly higher for the open lyre and minimal pruning treatments in 1996 (Table 1). Minimally-pruned vines produced the highest number of clusters per vine, followed by OL, GDC, and BC, respectively. Cluster weights were highest for BC, lowest for MP, and intermediate for OL and GDC vines.
Both irrigation method and training system had a significant effect on fruit composition in 1996 (Table 2). Soluble solids were highest in the 0.8 Etc SDI treatments and lowest in 0.8 Etc AGD plots. SDI plots irrigated at 0.4 and 0.6 Etc showed the highest pH and 0.8 Etc AGD vines produced the lowest pH. There were no significant effects of irrigation method on titratable acidity of the juice.
Vines trained to BC and GDC produced significantly higher soluble solids and pH in 1996 (Table 2). Juice pH was statistically lowest for minimal pruning and intermediate for open lyre trained vines. Titratable acidity levels were similar for BC, open lyre, and GDC vines, with MP vines significantly lower than the other three. In general, fruit composition responses to treatment were inversely related to yield responses to treatment, except for a lower than expected titratable acidity in the minimally pruned plot.
Irrigation method had no significant effect on growth in 1996 (Table 3). However, training system had a significant impact on vine growth. MP vines produced more shoots per vine than all other treatments. Shoots per vine on OL and GDC vines were intermediate, but not different from each other. Bilateral cordon, open lyre, and GDC vines matured more nodes per vine than did the minimally pruned treatment vines. Nodes retained per vine were significantly highest for MP vines, with BC, open lyre, and GDC vines lowest and all similar to each other. Although not statistically analyzed, pruning weights were higher in BC vines, at approximately six pounds. Open lyre and GDC vine pruning weight were approximately four pounds.
1997 Irrigation method had a significant effect on yield per vine, clusters per vine, and cluster weight in 1997. As in the previous year, yields were highest in the plots which were irrigated to 80 percent of crop evapotranspiration. The lower irrigation treatments resulted in lower yields, repeating the results of 1996. Clusters per vine in the irrigation treatments appear to follow the results of 1996, but the data showed so much variance within the blocks that there is statistically no significant difference when separated by the Duncan's Multiple Range test. Berry weights were lower overall in the 0.4 Etc, and there were no significant differences in the number of berries per cluster among the irrigation treatments.
Highest yields were repeated in 1997 with the open lyre and minimal pruning treatments (Table 4). Minimally-pruned vines produced the highest number of clusters per vine, followed by OL, GDC and BC, respectively. This substantiated the data reported in 1996. Cluster weights were again highest for BC and lowest for MP.
Fruit composition was significantly affected by irrigation method and trellis system in 1997 (Table 5). Juice pH was lowest for minimal pruning, indicating a lower maturity level of this treatment on the date of harvest. As soluble solids increased in the vines so did pH, with a corresponding drop in titratable acidity. This reflects vine balance, for all treatments, as the vines matured.
Irrigation treatment had no significant effect on growth in 1997 (Table 7). Training system had a significant impact on vine growth, as was apparent in 1996. Again, the MP vines produced more shoots per vine, and retained nodes per vine were substantially higher. Although pruning weights were higher for all pruned treatments in 1997, they were again higher in the bilateral cordon treatment than in the divided canopy treatments.
Overall crop yield was higher for all treatments in 1997 due to vintage variance. However, crop levels were consistent among treatments with 1996, showing a significantly higher yield for the open lyre and minimally-pruned plots. The open lyre treatment showed very high yields in both 1996 and 1997 (statistically equal to MP) with good soluble solids and acid balance. Increased yields resulted from higher number of clusters per vine in both of these treatments. However, the minimally-pruned plots are mechanically harvested, giving a distinct cost and labor saving advantage over the open lyre treatment. The minimally pruned treatments showed lower soluble solids when harvested on the same date as other treatments. This is a direct result of the increased bunch count and yield, and it should be noted that although this trellis treatment matures more slowly, it would have reached maturity in warm climates if comparison between treatments had not required harvest on the same day.
When irrigation treatments dropped below 80 percent of evapotranspiration, yields dropped. Yields of the 0.4 Etc were statistically lower in the SDI treatment as a result of lower cluster and berry weights. The potential benefits from utilizing SDI technology in conjunction with other evolving technologies should be encouraged. Crops such as wine grapes that are moving towards more mechanization can benefit from SDI applications. Traditional placement of drip lines above ground is highly susceptible to damage during machine harvesting. Pressures to mechanize the harvesting and other cultural practices will continue to rise as labor supplies become less reliable.
At present, the most likely candidates for SDI systems are relatively-high-value crops. Use of SDI on other crops will likely accelerate. Utility companies can support the transition by the continuing the practice of offering favorable pricing of off-peak power. This should encourage the use of systems such as drip irrigation which are easily automated.
Little, T.M. and F.J. Hills. 1978. Agriculture Experimentation. 350 pp. John Wiley and Sons, New York.
Zoecklein, B.W., K.C. Fuglesang. B.H. Gump, and F.S. Nury. 1994. Wine Analysis and Production 621 pp. Chapman and Hall, New York.
- Drip in Irrigation
- Epperson's Market, Inc.
- Georgia-Pacific, Inc.
- GeoFlow Irrigation, Inc.
- HIT Products
- Netafim Irrigation, Inc.
- Sonoma Grapevines
- Sunridge Nursery
- Vineyard Industry Products
- Wade Irrigation
- California Agricultural Technology Institute
- American Vineyard Foundation