Soil Type & Preparation for Planting
Soils Are Variable
Identifying the soil type is an early step in establishing an orchard. Recognizing soil variability will help to identify conditions that affect tree vigor. Stratified soils in root zone may cause poor drainage, and subsequent water logging reduces aeration. Severely compacted soils inhibit root growth and water percolation.
Determining Soil Type
Soil surveys and soil maps give the grower access to a large database of information about regional soil types. Links to two examples are provide here. Using a database is not a substitute for onsite sampling and analysis.
Web Soil Survey (USDA Natural Resource Conservation Service)
UC Soils-To-Go (University of California)
Soils are modified by methods such as deep tillage and soil mixing to promote uniform movement of water through the root zone, maintain aeration ane increase root growth. Soils that may need modification include:
- Claypan: these soils have a clay layer that typically starts at a depth of 12 - 24 inches, that gradually changes to a clay-loam. Tillage to mix the soil is an effective modification of this type of soil. Moldboard and dics plows are effective in mixing claypan soils.
- Hardpan: simiar to claypan, however, the presence of minerals hardens the layers, resulting in an absolute barrier to water percolation and root growth. Fracturing and breaking is required to modify this type of soil. Backhoe pits provide information regarding ripping depth and shank spacing. If the hardpan layer cannot be effectively shattered down to permeable soil, the site should not be considered for fruit and nut tree production.
- Plowpan: this is a shallow soil, the result of repeated tillage to the same depth. Fracturing is an effective modification of this soil type.
- Stratified: this is a layered soil, with abrupt changes in texture. Mixing is an effective modification of this type of soil.
- Modifying Orchard Slope: Orchards that are flood or furrow irrigated must be graded to a uniform slope. The final grade for medium to fine-textured soils should be 0.08% to 00.4%, depending on the length of the field and rate of water discharge. If cuts exceed 0.6 feet, two separate cuts should be done, over a two-year period to stabilize the grade. For fields requiring cuts of more than a foot, micro-irrigation should be considered.
- Filling Areas: fill areas usually require more soil than is availabe from scrapped off spots, because scrapping damages soil structure, increasing density. Fill soil should contain some clods, indicating maintenance of soil structure. Additional ripping and re-leveling is desireable to alleviate compaction, especially where deep filling is required.
- Land Leveling is undertaken to improve water coverage and drainage. Detailed information is available on the Land Preparation (IRRI), although this website has an agronomic focus.