Soil Preparation

Soil Type

Recognizing soil variability will help to identify conditions that will 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.

Common soil types requiring modification include claypan, hardpan, plowpan and stratified. (For preparation of these soil types, see below.)
Use the soil surveys: USDA Natural Resource Conservation Service soil surveys. Online surveys can be accessed through the University of California website: UC Soils-To-Go
Sampling for soil type: digging backhoe pits, 6 -7 feet deep, or using core-sampling methods will provide a profile of the site. Generally, one pit per 20 acres is advised, locating the pits in both good and troubled areas. Arial maps and observations of row crops grown on the field will help to determine these areas.
Testing for soil type: soil samples can be taken every 1-2 feet from each pit or core. Composite samples are created by mixing the soil for each depth from several pits or cores. About 1.5 lbs of each composite sample can be taken to a local lab specializing in soil testing.

Physical Preparations of Common Soil Types

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.

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.

Land Leveling

Organic residues: remove crop and weed residues from previous plantings.
The 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.
The fill: 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.