Final Report for FS12-258
Project Information
Introduction
This project investigates the problems of excessive canopy and weed control in a southern vineyard through soil analysis while employing a variety of ground covers. The shading as a result of canopy overgrowth has precluded harvest in this Traminette plot and has proven to be a regional challenge in other vineyards growing this and other varieties. Excessive canopy growth was attributed to excessive available nitrogen (N) in the soil, although no fertilizer additions have been applied in the past 5 years. The experimental approach was based on the hypothesis that excessive N was the main contributor to excessive canopy growth. The addition of high carbon materials (e.g. straw or wood mulch) will immobilize N into the organic N fraction of the soil, making it unavailable for plant use until this material is mineralized into a plant available form. The use of a cover crop will utilize available N in the soil that is incorporated into the plant biomass, rendering it unavailable until that material decomposes and goes through the mineralization process described above. Both mechanisms will reduce the amount of plant available N and would reduce N uptake by grape, to reduce the early season vigor experienced with this variety. Further, the use of ground cover (cover crop and mulch) can suppress weed pressure by shading, out competing, or creating a physical barrier to weed growth. After project initiation and first year data analysis, it was concluded that other factors such as Traminette vigor were more influential than native soil fertility levels, but the treatments established in 2012 remained in place for 2013 to confirm these results.
2012 offered a major challenge to the study design consequent to minimal rainfall as affecting rye grass stands and the usual weed pressure. I consider this to be somewhat ironic as I had previously suspected the frequent summer rains to play a significant role in the genesis of excessive canopy (along with particular varietal characteristics and nitrogen availability). Obviously the rainfall threshold to allow excessive vigor falls below the offerings of even an historically dry southern climate. 2013 was also plagued with challenges, a late freeze after budbreak followed by excessive rainfall during the remainder of the growing season.
No difference in canopy density could be demonstrated between plots pruned more vigorously pre-budbreak and those pruned in routine fashion as guided by UK viticulture specialists. Consequent to this fact we propose to alter plot management as pertains to differential pruning. All plots will be pruned in identical fashion prior to budbreak. Mid-summer selective pruning and leaf-pulling will be employed in those plots previously pruned more vigorously in early spring. If nitrate availablility and the effects of various ground covers do not offer a solution to this ubiquitous problem, a second pruning may represent the only viable answer, despite its cost.
Research
The approach consisted of initial soil analysis following by various multiple plot applications of woodchip mulch, wheat straw, rye, Gramoxone/Chateau herbicide combination, and additional pruning treatments. Soil samples were collected to a depth of 12 inches, in 6 inch increments (April 2012 and February 2013) and analyzed for plant available phosphorus (P), potassium (K), pH, buffer pH, calcium (Ca), magnesium (Mg), zinc (Zn), soil organic matter (SOM), total N (TN), and soil nitrate. Tissue samples (petiole) were collected prior to verasion and analyzed at Waters Agricultural Laboratories. Weed pressure for individual plots was visually rated and combined across treatments.
Initial Results and Observations
- Soil nitrate (NO3) levels were near baseline for Kentucky soils. (anything less than 10 ppm would be considered normal baseline for this region.)
- NO3 samples were lower in 2013 than 2012, but at these levels probably a function of sampling time more than treatment effects.
- Tissue samples low in nitrogen and phosphorus.
- Pruning demonstration conducted by University of Kentucky viticulture staff to address appropriate spring pruning of this variety on a Geneva Double Curtain trellis system
- Driest early spring and summer in more than 30 years (documentation to follow) resulted in poor rye grass stand precluding valid assessment of those plots in terms of both weed control and soil nitrate impact
- Weed pressure somewhat reduced in 2012 as consequence of dry conditions
- In terms of weed suppression, method effectiveness in decreasing order as follows: Gramoxone/Chateau (fortunately had rainfall 3 days after application), wood mulch, straw, and lastly rye grass (poor stand)
- No difference in canopy density could be demonstrated between either different ground cover plots or between different pre-bud break pruning
- No commercial crop could be harvested because of poor quality (low brix) and diseased (invariable consequence of shading/poor air circulation) fruit
Project Outcomes
Environmental conditions during the timeframe of this study were challenging. A major drought in 2012, followed by a late spring freeze and excessive moisture in 2013 partially compromised the results of this study. Ground cover treatments showed varying degrees of success, but not equal to or better than standard grower practices. Additional pruning, above University Extension recommendations was not sufficient to reduce canopy growth in the Traminette grape.
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Table 1. Soil nutrient analysis for phosphorus (P), potassium (K), soil organic matter (SOM), total nitrogen (TN), and nitrate in 2012.
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Reported in lb/A
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%
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ppm
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Treatment
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Depth
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P
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K
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SOM
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TN
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Nitrate
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Control
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0-6
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52
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572
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2.55
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0.15
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5.7
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Control
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6-12
|
4
|
246
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0.94
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0.06
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4.5
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Add. Prune
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0-6
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29
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581
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2.47
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0.15
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7.4
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Add. Prune
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6-12
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2
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251
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0.73
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0.06
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4.7
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Rye 1
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0-6
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32
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509
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2.31
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0.14
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8.0
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Rye 1
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6-12
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7
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278
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1.09
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0.07
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5.3
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Rye 2
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0-6
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37
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503
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2.52
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0.15
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8.9
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Rye 2
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6-12
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3
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251
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0.80
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0.06
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4.1
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Straw
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0-6
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40
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593
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2.52
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0.15
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5.7
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Straw
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6-12
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3
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256
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0.80
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0.06
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4.1
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W. Mulch
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0-6
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39
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553
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2.87
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0.17
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7.9
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W. Mulch
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6-12
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3
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246
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0.87
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0.06
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5.6
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Table 2. Soil nutrient analysis for phosphorus (P), potassium (K), soil organic matter (SOM), total nitrogen (TN), and nitrate in 2013.
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|
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Reported in lb/A
|
%
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ppm
|
||
|
Treatment
|
Depth
|
P
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K
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SOM
|
TN
|
Nitrate
|
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Control
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0-6
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45
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512
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2.68
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-
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5.6
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Control
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6-12
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5
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257
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0.96
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-
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2.6
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Add. Prune
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0-6
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27
|
581
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2.69
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-
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6.1
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Add. Prune
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6-12
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2
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283
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0.81
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-
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2.5
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Rye 1
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0-6
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48
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627
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2.79
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-
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5.3
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Rye 1
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6-12
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3
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284
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0.85
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-
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3.2
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Rye 2
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0-6
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38
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528
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2.64
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-
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5.8
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Rye 2
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6-12
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4
|
261
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0.87
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-
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3.2
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Straw
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0-6
|
39
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639
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2.58
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-
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6.3
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Straw
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6-12
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4
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285
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0.94
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-
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4.8
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W. Mulch
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0-6
|
31
|
569
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2.91
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-
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4.1
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W. Mulch
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6-12
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3
|
280
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0.91
|
-
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3.7
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- TN data was not collected in 2013