Orchard Floor Management Systems
An ideal orchard floor would be easy to maintain, aid the growth of trees and fruit, maintain soil structure, reduce erosion, not block the radiation of heat from the soil on frosty nights, and not compete with trees for water or nutrients. In practice, no single orchard floor management system accomplishes all of these goals. Current systems balance the ideal against real world conditions.
Several general systems for managing orchard floors, listed below, are available and each has advantages and disadvantages to consider before choosing one.
- Grass alleys between tree rows with vegetation-free strips in the tree row;
- Solid vegetation cover;
- Total clear cultivation;
- Mulches in the tree row with vegetation or clear soil between rows.
Grass Alleys with Vegetation-free Strips
This is the most widely adopted method of orchard floor management. It has many of the advantages of both solid grass cover and clean cultivation. Usually, herbicides or cultivation are used to establish a vegetation free zone of 2.5 to 3 feet on each side of a row of trees, giving a total strip width of 5 to 6 feet. A cover crop, usually a sod forming grass, is planted and maintained in the alley between the tree rows. This strip provides an area where roots can grow without competition from weeds or grass sod. In orchards with a vegetation free zone, most of the root growth occurs in the vegetation free area, especially for young trees. The grass alley provides a solid path for equipment travel, helps prevent soil erosion, helps maintain soil structure, and aids water infiltration. Depending on the cover crop sown, weed invasion can be minimized and sod establishment can be fairly quick.
Solid Vegetation Cover
Solid vegetation cover, usually grasses, has been used by many growers in the past. It is particularly effective on steep slopes where erosion is a severe problem. It is least competitive in mature orchards planted on vigorous rootstocks (MM.111, MM.106, or seedling). However, solid vegetation cover has major drawbacks. Vegetation competes with fruit trees for water and nutrients which reduces tree vigor and results in decreased yields and small fruit size. Vegetation growing right up to tree trunks is also difficult to mow. Mowing equipment can damage trees if operated too close to them. Vegetation surrounding tree trunks creates a favorable habitat for rodents. During the winter when other food is scarce, rodents will feed on tree trunks up to the snow line. In severe cases rodents will completely girdle the tree leading to tree death.
In this system no vegetation remains on the orchard floor. Growers can either use herbicides to kill all vegetation or shallow cultivation. Cultivation may improve water infiltration of some soils, but frequent shallow cultivation damages feeder roots near the soil surface and is energy intensive. Soil erosion on all but very flat sites can be increased with bare soil from either cultivation or herbicide use. Bare soil does not provide good traffic support when soils are wet and may lead to additional soil compaction from heavy equipment. Creation of a disking pan is a common result. During the driest part of the summer, bare ground in the orchard results in increased dust, which will exacerbate mite problems in the orchard canopy.
Mulches conserve soil moisture and will initially inhibit weed growth around trees. Effective mulches include straw, sawdust or shavings, hay, leaves, chipped prunings, or shredded newsprint. Mulches are expensive to obtain and apply on an annual or biennial basis. They do not control weeds effectively for long periods, especially perennial weeds. Organic mulches may bring in additional weed seeds and/or new weed species. As they decompose, some organic mulch materials tie up available soil nitrogen.
Development of synthetic plastic film and spun bonded polyester fabric mulches has added an additional management option. However, these products must be covered with an organic mulch to prevent photodegredation of the material. These products are typically applied to the soil and the trees are planted into the weed barrier.