L. J. Grauke

Table of Contents

The productivity and profitability of an orchard are closely linked to the quality of its site. Most sites have features that limit production if neglected. The challenge of site evaluation is to address those features which can be overcome with management and to recognize those which cannot. This allows for the design of an efficient orchard system, and a more accurate prediction of production from that system. Under some conditions, the expense of necessary management cannot be justified using the best estimates of that site's potential productivity. Ultimately, only the individual making the investment in time and money can determine whether to take the risk. Even the best sites often need extensive preparation prior to the planting of an orchard. Many advantageous cultural practices can be easily performed prior to planting but are difficult afterward. The purpose of this chapter is to provide general information useful in the selection and pre-plant preparation of orchard sites.

The purpose of a site evaluation is to determine whether or how well a particular site will perform a specific function. Evaluations are conducted to determine whether to purchase a particular tract of land, which crop to plant on land already owned, or how to overcome limitations to production in established orchards. The extent and focus of the evaluation are obviously altered by the objectives of the evaluator. The purpose of this section is to provide a treatment of the subject that will be useful to readers with a broad range of objectives.

Climate is the most important factor determining the adaptation of a particular crop to a site. Climatic factors of temperature, moisture, light (photoperiod) and wind determine which crop species and cultivars will survive and which will thrive. Information on distribution of native plant species is provided in appropriate chapters in this book and has been accumulated in atlas form by Little (1971, 1977).

If the projected orchard is of a species native to the U.S., and if the orchard is planted within the native distribution range of that species, site evaluation can be as simple as noticing that thrifty native trees occur on the site. Although such observations may verify tree survival on the site, more thorough evaluation is necessary to determine site limitations and to predict orchard profitability.

In the southwestern U.S., the natural vegetation on a site may be a good indicator of soil and subsoil texture, water availability, salinity, or alkalinity. Mesquite trees (Prosopis juliflora) usually indicate very permeable, well drained soils having a low water table. The soils are usually nonsaline and suitable for agriculture if water is available. Greasewood (Sarcobatus vermiculatus) is a very salt and alkali tolerant plant that indicates a fine textured, impervious soil with high salinity and exchangeable sodium, probably needing drainage and leaching. Richards (1954) offers much useful information on the soil salinity conditions indicated by many native woody plants. Plants that indicate soil problems might disqualify a site for a particular use. As mentioned above, a thorough site evaluation needs to be made even if the target species occurs on the site.

An important index of climate is the duration of the growing season, as measured by the mean number of days between the last 32 F temperature in the spring and the first 32 F date in the fall (Fig. 2)(Baldwin, 1975). When data on cultivar phenology are available (eg. Nelson et al., 1987), cultivar adaptation in relation to length of the growing season can be projected.

If the site is within the adapted range of the species, care should be taken to insure the use of climatically adapted rootstocks as well as scion cultivars. Local nurserymen often use rootstocks that have been empirically tested and proven for their locations. For native nut species, rootstocks for the prospective orchard should be grown from seed collected within an area up to 150 miles south of the planting site, unless specific recommendations to the contrary can be justified (Bey, 1980). This recommendation is based on research conducted for black walnut, but is consistent with observations made on the performance of pecan in provenance tests (Harris and Tauer, 1987). More specific boundaries for seed collection zones for black walnut have been provided (Deneke et al., 1980)(Fig. 3, Table 1), and can be extrapolated for other crops until better information is available.

The amount and distribution of precipitation is critical to the evaluation of climate at the most general level. This information is provided in detail for specific collection sites by state and is available in annual summaries of climatological data from the local Office of State Climatology or the National Oceanic and Atmospheric Administration (NOAA). County Soil Survey reports generally include useful long term summaries of temperature and precipitation. A generalized map of annual precipitation is provided (Fig. 4)(Baldwin, 1975).

Site parameters such as topography, soil texture, and soil depth influence the runoff, infiltration rate, and availability of moisture to plants. Furthermore, the amount of water required for adequate crop performance varies with species, and within species as a function of competition due to tree density, ground cover, and ultimate tree size. These factors must be evaluated collectively to determine the need for supplemental irrigation. If supplemental irrigation is required, the quality of water available becomes critical. Water quality varies as a functon of source (surface vs. well), aquifer, well depth, etc. In states with extensive oil and gas drilling activity, disposal of saltwater associated with drilling has resulted in pollution of some aquifers (Whitfield, 1980). Information on the quality of water in certain aquifers and alluvial systems is available from a number of sources, including the U.S. Geologic Survey, the U.S. Army Corp of Engineers, state Water Development Boards, and state Departments of Public Works.

If water wells are present on a site, water quality should be determined by sample analysis. Procedures for submitting water quality samples should be obtained through local County Extension Agents. Interpretation of water quality data is often provided with the analysis or can be accomplished with the aid of references available from the USDA (Richards, 1954) or state agricultural experiment stations (Longenecker and Lyerly, 1974; Jacobs and Whitney, 1971). More information concerning water quality is available in the chapter on irrigation.

Accurate information on the frequency distribution of seasonal wind data by speed class and direction is useful in determining efficient configurations for pollination of anemophilous species. Wind speed and direction are mapped for key locations within states and information is available from the local Office of State Climatology or the NOAA. Sustained high winds coupled with low humidity tend to shorten the period of effective pollination, both by speeding pollen dehiscence and by reducing the period of pistillate receptivity (Woodroof and Woodroof, 1929). Conversely, high humidity delays pollen dehiscence and extends the period of pistillate receptivity. Woodroof and Woodroof (1929) reported that pecan pollen continued maturation but did not dehisce if relative humidity exceeded 85%, with subsequent dry conditions resulting in heavy shed. Pecan stigmas dried as much in 24 hours under dry windy conditions as they dried in 2 weeks in damp cloudy weather. Wind borne sand particles may physically damage receptive stigmas in some portions of the southwestern U.S. Accurate prediction of site effects requires knowledge of microsite conditions as well as crop phenology. Adverse conditions may be partially compensated in several ways: by orchard configurations which reduce the extent of exposure; by judicious cultivar selection to insure adequate overlap of pollen shed and pistillate receptivity from multiple parent combinations; or by supplemental applications of pollen.

Some sites experience frequent winds of sufficient speed to result in complications to tree establishment or extensive breakage of bearing limbs. Although such information might not disqualify a site, it could be helpful in tailoring efficient management to that site.

Some weather events that can be devastating to nut tree orchards may occur rather frequently, but unpredictably on some sites. Hail, hurricanes, tornadoes, and glazing ice storms can completely destroy a crop and reduce subsequent crops for several years, even if the trees are not destroyed. Information concerning the frequency of occurrence of such events may be helpful in evaluating the management risk involved. Often, an awareness of a potential problem allows for the development of a plan of action if the problem does occur. Although production agriculture is generally at risk to occasional weather related disasters, casualty losses can usually be claimed for ASCS disaster payments or claimed as a loss on tax returns.

The term 'physiography' means 'physical geography' and refers, in general, to the lay of the land. Local geographic features such as lakes often result in significant modifications of local climatic conditions. The modifying influence of the Great Lakes on the Hardiness Zone map (Fig. 1) is an example of such effects, but more subtle effects are common and may not be of sufficient scale to appear in broad treatments of climate.

The aspect, or exposure, of a slope influences the radiation that slope receives with southern and western exposures being warmer and drier than northern or eastern exposures. This may significantly influence the performance of trees on that slope. In native stands, species may vary in abundance as a function of aspect. McCarthy and Wistendahl (1989) reported Carya spp. to be found primarily on upper slopes in a southeastern Ohio forest. However, C. ovata was most abundant on the north facing slopes, while C. glabra and C. tomentosa were most abundant on south facing slopes. They determined that topography, with its resultant influence on microclimate and soils, was the best "predictor" for distribution, abundance, and regeneration patterns of the hickories.

The tendency of a site to flood is a function of both its topographic and climatic conditions and is usually addressed in the Soil Survey. Flooding can be either beneficial or devastating, depending on the extent and duration. Tree damage may result from the force of the current, extended inundation (which will drown the trees), extensive deposition of sediment over the crown of the tree, scouring of soil away from the roots, or physical scarring by drifting debris or at cleanup. Natural vegetation along stream channels can act as a screen to prevent the movement of debris onto adjacent land and will help reduce the velocity of flood water, thus reducing scour and deposition on adjacent land (Begg, 1985).

Topography also influences the flow of air on a site. Cold air tends to "flow" along land surface contours, much like water. In low areas, or even on slopes where a barrier blocks that flow, freeze pockets may develop. "Air drainage" is a term used to describe the ability of the site to move air. Air drainage influences not only the temperature, but the humidity and therefore the disease potential of microclimates on the site. Such microclimate variations may be so subtle as to be negligible, but their recognition may be critical to efficient management of some sites.

The topography of the site will influence management operations from irrigation delivery and erosion control to harvest operations. As the most readily apparent site variable, it is also the first to disqualify a site for certain orchard operations.

The Food Security Act of 1985 placed restrictions on the use of certain types of land in its Sodbuster and Swampbuster provisions. The local office of the Agricultural Stabilization and Conservation Service (ASCS) should be contacted to determine if the site has been designated as Highly Erodable Land (HEL) or Hydric land. In each case, tree crops can be established, but limitations are imposed on the type of cover crop allowed, with annual crops being prohibited.

The use of adjacent land also impacts management of a site; forests surrounding a nut orchard are a source of pests and predators; adjacent row crops sprayed by airplane may create problems with pesticide drift; heavily populated adjacent areas may restrict some management options for pesticide control. Although such considerations are rarely sufficient to disqualify a site, their occurrence and the extent to which they impact management should be recognized in the evaluation.

The position of the prospective site in relation to access roads, and proximity to potential markets may have economic implications under some conditions and should be recognized as a factor in evaluating the site.

Soils are complex and dynamic bodies, showing the integrated effects of climate and biotic activity, acting on the unconsolidated remnants of the parent material in a given topography over time. Soils are three-phase systems, comprised of solid, liquid and gas. Generally, mineral soils contain from 40 to 70% solid material, with the remaining 30 to 60 % being a combination of liquid and gas phases, depending on environmental and cultural conditions. As media for plant growth, soils must provide anchorage, water, air, and nutrients. Their ability to perform those functions is determined largely by physical properties (depth, texture, and structure). It is helpful to approach the evaluation of a soil with these functions in mind, since limitations in a particular area may be addressed by specific management. Species differ in their adaptations to soils and potential variation in soil adaptation occurs within species, underscoring the need to use adapted rootstocks. Detailed information concerning site requirements for particular species is provided in appropriate chapters in this book. Although the

conditions for considering a site acceptable may change with species, the procedures outlined here for evaluating sites are broadly applicable.

An important source of information about the soils at a potential orchard site is the Soil Survey for the County in which the site occurs. Soil Surveys are available from the state or district offices of the Soil Conservation Service and are generally provided without charge. The orchard site should be located on one of the aerial photograph based maps in the back of the survey (facilitated by referring to the Index to Map Sheets which preceeds those maps). On the aerial maps, soils are delineated into mapping units with each delineation being identified by symbols on the map and defined in the map legend that precedes the maps. The text of the Soil Survey provides descriptions of the various soil mapping units. Descriptions are provided for key physical and chemical properties in the horizons of a representative soil profile to a depth of 6 feet or greater. Tables in the Survey provide quantitative information on soil density, pH, depth to water tables, and other useful information.

Soil depth establishes the boundaries of root penetration. If the soil is visualized as a three-dimensional body, it is obvious that as soil depth increases, potential root volume increases, along with the soil's ability to buffer shortfalls of climate and management. Several reports (Hunter, 1955; Gammon et al., 1956; Hunter and Hammar, 1961) indicate that pecan tree survival and performance during periods of drought was increased as soil depth increased. Under drought conditions, Hunter (1955) observed less defoliation of pecan trees growing on a deep soil having sandy texture (poor water-holding capacity), than on more shallow soils of finer texture (better water-holding capacity). This indicates the need to integrate effective root volume, or soil depth, in evaluating the true "water-holding" capacity of a soil.

The effects of a shallow soil are most quickly communicated to the tree via its reduced water supply. Such effects may be partially compensated by careful management in the early age of an orchard, but become progressively more limiting as trees increase in size (and therefore water use). The effects of tree crowding will be more accentuated on such sites. One potential management compensation is the use of wider initial tree spacings. The reduction of competition by weeds is also more critical on such sites.

Some soils have reduced depth due to inherent pans (horizons or layers which are hardened, compacted, or very high in clay content). Soil water tends to accumulate above such zones, forming seasonal perched water tables that may damage roots. Under certain management practices, other soils may have a tendency to develop compacted zones that can also result in altered patterns of water movement and root development. Soils with inherent pans should usually be avoided as orchard sites. Soils with a tendency to form pans should be carefully managed to reduce traffic and, if necessary, to disrupt the pan. Other conditions that may limit depth of rooting are addressed in the following section.

Soils are divided into textural classes on the basis of the percentages of sand (50-2000 um dia.), silt (2-50 um dia.), and clay (<2 um dia). Differences in particle size influence the movement and availability of soil water, air, and nutrients. In general, medium textured (loamy) soils are to be preferred over fine (clay) or coarse (sandy) textured soils. All textural classes which end with "loam" are medium textured. Medium textured soils generally have an adequate balance of friability, water-holding capacity, aeration, and nutrient supplying ability. Coarse textured soils are typically very friable and well aerated, but have little water-holding capacity or inherent fertility. Proper management can make such soils very productive, since irrigation and fertilization are manageable functions. Coarse textured soils are preferred for nursery operations, since they are easier to work over a broad range of moisture, they are "warmer" in spring, they contribute to more extensive root development, and they are more easily dug at harvest. Fine textured soils often limit water infiltration and aeration, limiting production and creating challenges for management.

Many soils are composed of horizons having different textural classes. In recently formed alluvial soils, textural horizons may be due to "stratification". Stratification refers to the deposition of the soil in distinct layers. Stratified soils may contain internal horizons of sand. Internal horizons of sand can effectively limit root penetration and reduce the effective depth of a soil (Alben, 1955). Unstratified soils are therefore generally preferable to stratified soils. In older soils, much of the horizon formation may be due to weathering over time. One common weathering phenomenon is the accumulation of clay-sized particles in lower horizons, sometimes resulting in compacted clay layers that limit root development. Although not ideal, soils with internal drainage problems can often be managed. Management options include ripping or inversion plowing, depending on the nature of the problem.

Soil structure is the organization of the primary sand, silt or clay particles into compound units. These units greatly influence the movement of water, air, nutrients, and roots in the soil. Management practices such as plowing or discing influence the structure of the soil, but not the texture. Structure is described in terms such as 'platy', 'prismatic', 'columnar', 'blocky', 'granular', or 'crumb'. Some structural types (e.g. prismatic and columnar) are often found in subsoils of arid to semi-arid regions, while others (e.g. blocky and subangular blocky) are associated with heavy subsoils of humid regions. Optimum structure varies with textural class. In general, granular structure is desirable, with blocky, prismatic, platy, and massive (clay) structure being progressively less desirable for nut tree orchard sites.

Several aspects of the site should be collectively evaluated to determine the availability of water to trees. As mentioned above, the extent and distribution of precipitation is a critical aspect. The topography of the site in conjunction with the soil's infiltration rate will largely determine movement of water off of or into the soil. The depth of the soil and its texture and structure determine the speed and extent of water movement through the soil and its storage capacity. Two important hydrologic features to evaluate for the site are the depth to a groundwater table and the presence of seasonal, fluctuating high water tables. Information on the depth to water tables is often provided in the Soil Survey. The Soil Conservation Service or Corp of Engineers often maintain detailed local records of seasonal fluctuations in water table levels as recorded at piseometers throughout the area, especially along rivers.

A groundwater table is the upper surface of a zone of saturation, or free water, in the soil. A water table will establish the depth of root development in soils that do not have other structural limitations. "Permanent" water tables occur at a relatively constant depth during all seasons, although seasonal or even diurnal fluctuations are possible (Prichett and Fisher, 1987). If the groundwater table is sufficiently deep, this provides deep soil moisture, contributing to deep root development. A permanent water table at a depth of about 6 feet is ideal for pecans and walnuts. Permanent water tables closer to the surface result in reduced soil volume for root development, and are a liability rather than an asset if within 2 feet of the surface.

"Seasonal" high water tables fluctuate, being closer to the surface during the wet seasons of the year. Depending on the duration of the table and the tree species, seasonal high water tables can be a liability. Deep roots that develop during the dry period of the year may be killed when those areas of the soil profile are saturated and anaerobic in the wet season. Pecan trees growing on dense clay soils in Louisiana often have restricted root depth due to seasonal high water tables which may be present from December to April. The greater the extent of fluctuation in water table level, the greater is the damage to established trees on a site. Trees on deep, well drained sites have been killed by elevations of the water table caused by damming of nearby streams; over-irrigation on deep soils with an impervious layer may kill trees. Irrigation induced high water tables can be predicted, based on depth to fine textured or mottled horizons.

Nut tree species generally require well-aerated soils. The most useful parameter to use in the evaluation of native soil aeration is soil color: red, brown and black soils are well aerated, gray soils are very poorly aerated, and yellow or brownish-gray soils are intermediate. Mottling (spots or blotches of different color interspersed with the dominant color) also indicates inhibited air movement.

Poorly aerated soils and subsoils are typically very tight, hard, or compacted. Water infiltration and percolation is reduced. In subsoils, this may result in perched seasonal high water tables, further reducing soil depth. As mentioned above (see Soil Depth) the effects of a shallow soil are typically communicated to the tree via reduced moisture availability. The association between poor aeration and inadequate moisture often leads managers to the erroneous conclusion that moisture is the limiting factor. Unfortunately, if the primary site limitation is poor aeration, the establishment of an expensive irrigation system will not be justified. Soil aeration should be critically evaluated in the design of irrigation systems.

For pecan, the criteria of soil evaluation have been extensively reported (Skinner, 1924; Carter, 1931; Skinner et al., 1938; Brison, 1978). These reports offer descriptions of soils well adapted to pecan in contrast to poorly adapted soils. Baker and Broadfoot (1984) have provided a site index for production of pecan timber that translates descriptions of soils into a numerical system. This allows for increased resolution of site limitations and provides a basis for quantified comparisons of sites (Table 2). Partial verification of the applicability of the index as a tool for orchard site evaluation is obtained from a review of the old literature. Skinner (1924) reported pecan production in uniformly managed blocks of particular cultivars as a function of soil type from several Georgia orchards. During the five years of observation, yield of 'Schley' trees on Orangeburg sandy loam was 16% greater than the yield of uniformly managed 'Schley' trees on Norfolk sandy loam. 'Alley' trees on the Greenville sandy loam produced 29% greater yields than if grown on Norfolk soil. In another orchard, 'Frotscher' trees on Greenville and Norfolk soils produced 27% and 23% greater yields respectively than trees on the Susquehanna sandy loam. 'Moneymaker' trees on Greenville and Norfolk soils produced 49% and 43% greater yields respectively, than 'Moneymaker' trees on the Susquehanna soil. Based on this information and ignoring the possibility of interaction between cultivar and soil series, the following ranking of soils could be established: Greenville > Orangeburg > Norfolk > Susquehanna. The site index for each of these soils was determined, based on information provided by Soil Surveys published for the counties in or near the original Georgia orchards. The following was obtained, expressed as % of total possible points: Greenville, 74%; Orangeburg, 71%; Norfolk, 69%; Susquehanna, 52%.

On a broader scale, I have applied this site index in Louisiana to established orchards representing a wide range of productivity and have found close correlation between predicted and actual site performance. Furthermore, the increased resolution of site limitations provided by the index has been useful in directing management inputs to overcome site limitations.

Soil requirements of walnut are similar to those of pecan (Ponder, 1981; Begg, 1985). As a result, the pecan site index may be useful in evaluating walnut orchard sites.

Nutrient elements necessary for tree growth may be deficient or excessive on a particular site. The evaluation of the nutrient status of a prospective orchard site should be conducted to disqualify sites with limitations due to toxic concentrations as well as to direct preplant soil amendments.

The first step in the sampling of a site is to determine the soil management areas. Soil management areas should be based on site topographic and soil texture and depth changes that will influence management of the area. In the absence of better information, major soil changes as indicated on the Soil Survey map of the site may be used. Soil management areas should establish the boundaries of orchard blocks (Fig. 5)(Wildman, 1985).

The need for specific sampling methods depends largely on the target of the analysis, which will generally reflect local soil conditions. In order to determine the general salt content of the soil, the entire soil profile should be represented. This is often accomplished by sampling the surface soil (0-12 inches) and the subsoil to a depth of at least 3 feet. Samples submitted for analysis should be composite samples: combine samples taken from a particular depth within a particular soil management area (Longenecker and Lyerly, 1974). (For more detailed information concerning sampling of saline or alkaline soils, see Richards, 1954).

Several elements may exist in sufficient quantity to limit tree growth. Total soluble salts can be estimated from an electrical conductivity measurement of a saturation extract (ECe). Very few plants are effected if the conductivity of an extract from saturated paste is less than 0-2 mmhos/cm (<1000 ppm soluble salts in soil), but salt sensitive plants show reduced yields at conductivities of 2-4 mmhos/cm. Many crops will have yield reduction when conductivities are in the range of 4-8 mmhos/cm (Richards, 1954).

Specific ions may be damaging in high concentrations, and most fruit and nut crops are especially sensitive to chloride and sodium salts. Pecan and walnut are also especially sensitive to boron.

If irrigation is planned, water quality should also be evaluated in relation to salt concentration. For optimum system design, water quality information should be integrated with information on soil infiltration and percolation rates. Seasonal high rainfall might help leach harmful elements and prevent their accumulation from moderately salty irrigation waters (see Richards, 1954).

Site preparation for nut tree orchard establishment may require as much as two years prior to planting, depending on the extent of leveling and grading required. Planning must necessarily precede the actual preparation. It is appropriate that the

establishment of an orchard which may stand for over one hundred years should be premeditated.

Efficient orchard management systems are based on an understanding of the critical site limitations, their variation across areas in the orchard, and the subtle differences in management required for each area. Orchard blocks should be established on the basis of this understanding. Blocks might be based on differences in soil depth, texture, or topography, but should allow for uniform management of similar areas, with adjusted management possible for critically different areas. If soil depth varies greatly, areas may require irrigation at different frequencies. This will be critical in the design of an efficient irrigation system. Access roads to orchard blocks may serve to further delineate their boundaries (Fig. 5). Diagrams of the critical soil management areas are the first step in orchard mapping. Accurate mapping of the orchard system provides a valuable foundation upon which to build orchard records.

Detailed information concerning the surface grade of the land is necessary to plan some irrigation and leveling operations. Local ASCS offices often provide the service of evaluating existing surface grade and can provide a cut sheet to be used in leveling the land to establish surface drainage or to facilitate irrigation.

If leveling is required, it is beneficial to make major cuts and fills one year, grow an annual cover crop to facilitate settling, and make final adjustments in grade the second year. Major changes in the distribution of nutrient elements accompany leveling operations: Zn is concentrated in the upper 6 inches of the soil and is dramatically reduced in areas of cut; Ca and Mg levels are generally higher in subsoils and may be increased in areas of cut. It is advisable to rip both cut and fill areas to loosen the soil as deeply as possible.

Many soils have internal layers which restrict water and root movement, but will respond to deep tillage which breaks the layer, allowing internal drainage and thus increasing root depth. Soils can be ripped or inversion plowed, depending on the nature of the restriction. "Ripping" is the process of pulling deep parabolic or V shanks through the soil, and is also called "subsoiling". This procedure is used for disrupting compacted zones, but results in little mixing of strata. If the shanks are spaced too far apart, adequate disruption of the restrictive layer is not accomplished. For best results, the distance between ripper channels should be equal to or less than the depth of ripping. In common practice, ripping is targeted to a depth of about 24 inches, with shanks spaced 18-20 inches apart. Deeper ripping is possible with heavy equipment.

In order to mix restrictive internal clay horizons, deep inversion plowing is practiced. This can be accomplished by moldboarding or deep discing. Inversion plowing to a depth of 3 feet can be accomplished. Care should be excercised to avoid creating a layer of clayey material over a layer of coarser texture.

Both ripping and deep plowing can be expensive operations, with expense increasing with depth of the treatment. As a result, the operations should only be undertaken when their need has been established by on-site sampling. Adequate sampling will establish both the depth of the problem strata and the extent of the area affected by it. The cost of extensive, very deep tillage will be hard to justify. Furthermore, compaction zones may recur under some soil conditions.

The analysis obtained from the soil samples taken during the evaluation phase can be used to direct preplant soil amendments, if necessary. It is easier to uniformly apply and deeply incorporate additions of lime and phosphorus prior to planting than after. Targeted soil levels of those amendments vary with species and may be influenced by cover crop; legumes respond to both high calcium and high phosphorus. Ultimately, local Extension professionals should be consulted in relation to the needs of specific target crops on particular sites. Recommendations will be based on information gathered from the soil sample.

Routine soil and leaf sampling are important to monitor the nutrient status of the trees and to establish management patterns in the early life of the orchard. Detailed information on those topics is presented in the chapter on Mineral Nutrition.

Site evaluation is the process of gathering and interpreting critical information concerning the ability of the prospective site to perform its intended function. Important factors to consider have been introduced, along with sources of more detailed information. If adequate information has been obtained in the evaluation stages, the grower has the opportunity to address some site limitations in pre-plant site preparation. The difference between a good site and a poor one will be manifested throughout the life of the orchard. The difference between good and poor management begins well in advance of tree planting: the good manager knows and addresses the site's limitations.

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Baldwin, J. L. 1975. Weather atlas of the United States. Environmental Data Service. US Government Printing Office, Wash. DC.

Begg, E. L. 1985. Identification and evaluation of soils. pp. 20-27 In D. E. Ramos (ed.) Walnut Orchard Management. Univ. Calif., Div. Agri. & Nat. Res., Pub. 21410.

Bey, C. F. 1980. Growth gains from moving black walnut provenances northward. J. For. 78(10):640-645.

Brison, F. R. 1978. Pecan Culture (2nd ed). Capital Printing, Austin, Texas.

Carter, W. T. 1931. Pecan soils of Texas. Proc. Nat. Pecan Assoc. 30:29-35.

Cathey, H. M.. 1990. USDA Plant Hardiness Zone Map. USDA-ARS Misc. Pub. 1475

Deneke, F. J., D. T. Funk, and C. Bey. 1980. Preliminary seed collection zones for black walnut. U.S. For. Serv. Northeastern area, NA-FB/M-4.

Gammon, Nathan Jr., R. H. Sharpe, and R. G. Leighty. 1956. Relationship between depth to heavy textured subsoil and drought injury to pecans. Proc. SE Pecan Growers Assoc. 49:37-43.

Harris, K. D. and C. G. Tauer. 1987. Variation among open pollinated provenances of pecan grown in an Oklahoma nursery. Oklahoma State University, Division of Agriculture Research Report P-892.

Hunter, J. H. 1955. Variations in the response of pecan trees to the drought of 1954. Proc. SE Pecan Growers Assoc. 48:6-9.

Hunter, J. H. and H. E. Hammar. 1961. Effects of different grades and rates of fertilizers applied to Schley pecan trees as influenced by other factors. Proc. SE Pecan Growers Assoc. 54:29-41.

Jacobs, H. S., and D. A. Whitney. 1971. Determine water quality for irrigation. Kansas State Univ. Coop. Ext. Serv. C-396.

Little, E. L. Jr. 1971. Atlas of United States Trees. Vol. 1.; Conifers and Important Hardwoods. USDA For. Serv. Misc. Pub. No. 1146.

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Longenecker, D. E., and P. J. Lyerly. 1974. Control of soluble salts in farming and gardening. Texas Agric. Exp. Sta. Bull. 874.

McCarthy, B. C. and W. A. Wistendahl. 1989. Distribution and replacement in a second-growth oak hickory forest of southeastern Ohio. Amer. Midl. Naturalist 119:156-164.

Nelson, R. O., W. A. Gustafson, and T. M. Morrissey. 1987. Northern pecan research- bud break, flowering, and fruiting data for 16 pecan clones. Ann. Rep. Northern Nut Growers Assoc. 78:117-118.

Ponder, F., Jr. 1981. Some guidelines for selecting black walnut planting sites. Ann. Rep. Northern Nut Growers Assoc. 72:112-117.

Pritchett, W. L. and R. F. Fisher. 1987. Properties and Management of Forest Soils. 2nd ed. John Wiley & Sons, New York. 494 pp.

Richards, L. A. (ed.) 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Agric. Handbook No. 60.

Skinner, J. J. 1924. Influence of soil type on the yield and quality of pecans. Agron. J. 16:51-57.

Skinner, J. J., E. D. Fowler, and A. O. Alben. 1938. Pecan soils of the gulf and southeastern states and maintenance of their fertility. USDA Circular No. 492.

Whitfield, M. S., Jr. 1980. Chemical character of water in the Red River alluvial aquifer, Louisiana. US Geological Survey. Water-Resources Investigations Open-file Report 80-1018.

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Univ. Calif., Div. Agri. & Nat. Res., Pub. 21410.

Woodroof, J. G., and N. C. Woodroof. 1929. Flowering and fruiting habit of the pecan. Proc. National Pecan Assoc. 28:128-136