Soil Management for Orchards and Vineyards
Orchard and Vineyard Floor Management
Good soil management is essential for sustainable production in orchards and vineyards. Good soil-management practices in orchards and vineyards require that soil fertility is maintained; that water from rain or irrigation penetrates the soil readily and is not lost by runoff; that soil structure is not unduly compromised, despite the hauling of heavy equipment through the orchard and vineyard; and that conditions favor the growth and fruitfulness of the trees and vines from decade to decade. Orchard and vineyard floor management practices can include anything from the addition of soil amendments, cultivation, to soil conservation practices. In many instances, orchard floor management practices may be more or less compatible with particular harvesting or cultivation practices.
Soil Amendments
Manure and Compost
Periodic application of manure and compost is a proven method for improving the water-infiltration capacity of certain soils: those that suffer from weak structure due to low organic matter content. Applying manure can have many soil and crop health benefits, such as increased nutrient levels (nitrogen, phosphorus, and potassium in particular, but also micronutrients) as well as easily available carbon that will benefit the soil microbial community.
Nutrient Availability. A potential advantage of non-composted animal manures is that the nitrogen it contains will be more immediately available (unless the manure is highly weathered), whereas nitrogen in well-cured compost is more biologically stable and converts to the plant-available form over a period of years.
Organic Matter. Not only does manure and compost provide macro- and micro-nutrients to the soil but it also supplies organic matter to the soil. Organic matter is critical for increasing a soil’s available water holding capacity, serves as a slow-release fertilizer, promotes the formation and stability of aggregates, increases water infiltration, and enhance soil tilth, all of which contribute to decreasing soil erosion and increasing yields and plant health. Frequent tillage facilitates the loss of soil organic matter.
Calcium Materials
Adding calcium salts to soil and water increases the salinity as well as the soluble calcium of the irrigation water and soil water. Both of these factors improve water infiltration as the calcium promotes aggregation by binding clay particles together, which in turn promotes the stability of the soil aggregates.
Lime. Lime (CaCO3) can enhance the physical properties of acid soils (soils with pH less than 7.0) as discussed in Chapter 14. The calcium in lime helps bind clay particles together, promoting good soil structure.
Gypsum. Gypsum (CaSO4) also enhances the physical properties of soil through the addition of calcium. As discussed in Chapter 15, gypsum is a neutral salt that, when applied to slightly alkaline soil (pH greater than 7.5) or neutral soils (pH = 6.5–7.5), will improve aggregate stability with little or no effect on pH.
Cultivation Practices
Some fruit growers, especially but not limited to the West, have practiced “clean cultivation,” eliminating vegetation throughout the planting, that can be applied to both interrow and intrarow areas, or only to the intrarow. The advantages of cultivation include the immediate cessation of weed competition, breaking of soil crusts, and possible liberation of nitrogen in the short term, depending on the nature of vegetation being destroyed. The downside of cultivation include potential damage to tree and vine roots, erosion of the disturbed soil, loss of soil organic matter and soil structure, and associated input costs. It’s also difficult to move equipment through the orchard and vineyard in wet weather.
Soil Conservation Practices
Soil conservation practices help improve soil structure, reduce soil erosion, improve water-holding capacity, and provide other natural resource benefits. One such soil management practice quite often used in orchards and vineyards is maintaining a ground cover whether it by mulching, growing a cover crop, or just maintaining the resident vegetation. Other benefits with ground cover include increase in organic matter, suppression of weeds, and ability to attract beneficial insect pollinators.
Mulching
Mulch is any material applied to the soil surface. Mulches are usually organic, such as straw, wood chips, sawdust, or chipped prunings. Principal reasons for using mulches include weed suppression, water conservation and erosion management, reflectance of sunlight and heat, and slow incorporation of organic matter into the subtending soil. Under tree or vine mulches are probably more commonly used in orchards and vineyards (Figure 19.6).
Cover Crops
Among strategies to increase environmental sustainability in orchards and vineyards, cover cropping has been recognized as an effective practice to promote soil conservation and to reduce the impact of agriculture on climate changes. Beside soil protection (erosion control, aggregate stabilization, soil porosity enhancement), several ecosystem services (provisioning, supporting, and regulating functions) provided by cover crops has been observed. For example, if the slope is steep in orchards or vineyards cover crops are an effective tool for runoff control, through better infiltration of water into the soil due to the soil organic matter.
Resident Vegetation
Resident vegetation consists of all plant species growing within the orchard or vineyard. These include both native plants and invasive weeds. The diversity of native plants varies by region of orchard and vineyard production. A major advantage of this system is the lack of planting costs; however, invasive weed species may be difficult to eradicate once established.
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