Elements of Site Selection for Fruit Crops

Elevation

Elevation can be looked at two ways, as the elevation within a certain location (high point vs. low point) or as the absolute elevation (feet above sea level).  Since Mississippi does not have mountainous regions, we are most concerned with the relative elevation within a certain location.  Planting a fruit crop on or near the highest point on any given location will promote better air and water drainage.  Both of these factors can seriously inhibit plant growth and productivity.  Air drainage is essential in times of frost and freeze, because cold air is heavier than warm air, thus it settles in low elevation spots.  Water drainage is also important because standing water will limit the oxygen available to the plant root system.   Many fruit crops are susceptible to damage from short-term flooding, especially stone fruits like peaches.  Some fruiting plants, like pecans, can tolerate standing water for short periods of time, but it can limit their growth.

Slope

The slope of a site refers to the degree of inclination of the land. A slight to moderate slope can be beneficial because it accelerates cold air drainage. Generally, the steeper the slope, the faster cold air moves downhill, assuming there are no barriers to air movement. Air drainage for spring frost protection is important.  Trees or other native vegetation that slow or stop air drainage should be removed during site preparation. Steep slopes, however, can create problems. Machinery is difficult if not dangerous to operate on steep slopes, and the potential for soil erosion is increased. Soil erosion is responsible for an average loss of 2 to 8 tons of soil per acre each year in some states. Every attempt must be made to minimize that loss. Slopes with greater than approximately 15 percent (a 15-foot drop in elevation for each 100-foot horizontal displacement) should be avoided. Consult the local Soil Conservation Service office for advice on erosion control measures.

Aspect

The aspect of a slope refers to the compass direction toward which the slope faces (north, south, east, or west). Eastern, northern, and northeastern slopes are probably superior to other aspects. Often, however, other factors such as the presence of woods, steep slopes, and exposed rocks dictate that another aspect must be used. The preference for eastern and northern aspects relates to heat load differences between various slopes. Southern and western exposures are hotter than eastern and northern exposures. Southern exposures warm earlier in the spring and can slightly advance bud break compared to northern slopes. The consequence of advanced bud break is increased potential for frost damage. Southern aspects can also lead to more extensive trunk warming on sunny winter days than on northern slopes. The consequences could be reduced cold resistance and subsequent cold injury. Bark splitting and trunk injury to the southwest sides of fruit trees is occasionally observed and is related to trunk warming on sunny winter days with subsequent, rapid cooling. Southern and western aspects can also be expected to be hotter during the summer than northern and eastern aspects. Eastern aspects also have an advantage over western aspects because the eastern slopes are exposed to the sun first. Plants on an eastern slope will dry (from dew or rain) sooner than those on a western slope, potentially reducing disease problems.

Previous Crop History

The previous crop history of a proposed fruit planting is very important.  Some chemicals used in agriculture have long periods of persistence in the soil; thereby potentially having the undesired effect of damaging new plants.  Another issue is root rot diseases.  This is especially a problem when other woody plant species, like oaks, were on the site prior to planting.  Cleared sites that previously had woody plant species on them should be left fallow for at least 1 year and preferably 3 to 5 years.  Often fungal root diseases are must have a host to live on in order to survive.  Once a tree is removed, the root system will slowly decompose rendering it unsuitable for continued survival of the pathogen.  In certain soils, nematodes may cause problems.  This is especially true of sandy soils.  If in doubt, have the soil tested for nematodes before planting.

 

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