Soil Management for Orchards and Vineyards
Cover Crops for Orchards and Vineyards
Conservative and sustainable soil management techniques, such as cover cropping, have been essential in safeguarding soil health. A cover crop is any crop grown to provide soil cover, regardless of whether it is later incorporated. Cover crops are grown primarily to prevent soil erosion by wind and water. Vineyard cover crops can be managed a number of different ways. Most commonly, crops are seeded in every alley to provide cover throughout the orchard or vineyard (Figure 19.7). They can also be planted in alternate alleys, each with a solid stand of a different cover (e.g., grass and legume), or alternating with alleys that are clean cultivated (Figure 19.8).
Challenges in Growing Cover Crops
Cover crops have many potential benefits, but there are also important trade-offs and management implications to consider when deciding whether to use cover crops and which crop or mixture of crops to choose.
Water Use
Although there are many benefits in growing cover crops as discussed in Chapter 16, cover crops use water and will increase the total orchard and vineyard water requirement. In spring, cover crops can deplete stored soil moisture from winter rains that would otherwise be available to trees and vines. This is particularly a problem with young trees and vines need for water, which can reduce tree and vine growth and delay development in the early stages of establishment.
Nutrient Demand
Cover crops can also compete with the trees or vines for nutrients. For example, winter annual grasses require large quantities of nitrogen and, if allowed to mature, can delay nitrogen availability to the trees or vines and reduce plant vigor.
Risk of Frost
The growth habit of certain cover crop species can alter microclimate in the orchard or vineyard. This is especially important in the early spring or late autumn season when frost events are more likely to occur. The presence of a high-biomass producing cover crop can reduce the heat transfer from the orchard or vineyard floor at night due to reductions in soil warming during the day and cooling via plant transpiration. Orchards and vineyards with clean cultivated soil typically absorb more solar radiation throughout the day and release the stored heat at night.
Orchard and Vineyard Shading
Some cover crop species are more shade tolerant than others and are therefore better adapted for use as cover crops in orchards. Orchard shade is of less importance for winter green manure and annual reseeding cover crops than for perennial sods since stand establishment and growth take place after leaf fall, when more light reaches the orchard floor.
Cover Crop Types
Choosing a cover crop depends largely upon the objectives in the overall orchard and vineyard management plan. There are three main categories of cover crops—legumes, grasses, and brassicas.
Legumes
Legumes have a major role in the process of biological nitrogen fixation enhancing available forms of ammonia and nitrates (after organic nitrogen is mineralized) that is crucial for the nutrient cycle and plants’ healthy growth and development. This sustainable practice increases soil’s fertility and reduces fertilizer requirements over time. A cover crop’s ultimate nitrogen contribution to the orchard and vineyard depends on the mass of cover crop produced, the types and relative amounts of legumes and nonlegumes it contains, and how the cover crop is managed.
Grasses
The most utilized cover crops in orchards and vineyards are grasses because these plants have several mechanisms to enhance soil quality and prevent water loss. Characteristics of grasses include large seed production and growth in semi-shaded conditions, which allows vegetation coverage to be present in orchards and vineyards throughout the year. Additionally, grasses are hardy plants that can withstand drought or water scarcity. In vigorous orchards and vineyards, grass can take up nitrogen and tie it up over time. Unlike legumes, nitrogen in grass is not readily available to trees or vines for uptake when the plants decompose; however, grass cover crops can provide a substantial amount of biomass that, over time, may aid in increasing orchard or vineyard soil organic matter.
Brassicas
Brassicas can rapidly increase biomass by producing deep taproots, which enhance their weed suppression abilities and alleviate soil compaction. Deep root systems can extract nitrogen from deeper and shallow soil strata, therefore, enhancing the nutrient cycling process.
Annuals
Annual cover crops are chosen for multiple reasons in orchards or vineyards. One reason to grow annual cover crops rather than perennial cover crops is to provide seasonal soil conservation in the winter months followed by removing the cover crop by tillage or mowing in the spring or the dry season (summer). Disking or mowing in late March will reduce the risk of frost.
Perennials
Perennial species are most commonly used in orchards or vineyards planted on deep, fertile soils where overly vigorous vines are a problem. Perennial cover crops provide a firm platform for machinery and foot traffic, which can be extremely important during wet periods of the growing season. But this living mulch can also become a liability during extended droughts if trees and vines are not deeply rooted or if the cover crop is active during hot, dry periods of the season.
Planting Cover Crops
Climate permitting cover crops should be planted between harvest and leaf fall when soil is still warm for rapid germination and seedling growth. Germination and early stand establishment are substantially improved if rainfall occurs or irrigation water is applied soon after planting. Orchard and vineyard pruning operations can conflict with cover crop seeding because equipment traffic associated with pruning can damage the cover crop seedbed and emerging seedlings
Cover Crop Termination
The most common methods used to terminate winter cover crops is by winter-kill, mowing, tillage, a combination of mowing and tilling, roller-crimping, herbicides, and grazing. Cover crops vary in their hardiness over winter. Cover crops that die during freezing temperatures in winter create a mulch-like mat on the soil surface that can help protect the soil from erosion. The absence of a living cover crop to manage in the spring can allow for early planting of another cover crop or a cash crop and provides an opportunity for no-till planting. Mowing is often used to quickly terminate a cover crop before it goes to seed.
Cover Crop Rotation
Over time, cover crops can develop pests and pathogens that make it difficult to reseed the same species year after year. Sometimes, growers will use completely different species from year to year, such as mustards or radishes, followed by legumes, which are then followed by annual grains.
Click on the following topics for more information on soil management for orchards and vineyards.
