Orchard Management (1+1)

SOIL MANAGEMENT

Introduction:

• Soil is one of the most important factors associated with the success or failure of fruit production.
• Most of the soil management practices in the orchard enhance nutrient and water supply needed for growth and production of fruit trees.
• This they do so by improving soil nutrient status, conserving soil moisture, altering of soil properties like soil pH and soil structure, maintaining soil organic matter contents and useful soil organism.

Nutrient uptake:

Sod culture and cover crops:

• Practice of establishing a complete sod cover on the orchard floor often cause a reduction in vigour and growth of the fruit plantations, which is commonly associated with reduced nutrient uptake, particularly the nitrogen.
• Fruit trees under permanent sod usually have lesser leaf nitrogen contents, particularly during mid to late growing season.
• In order to maintain soil fertility status, mowing down of sod should be done regularly, in addition to adequate nitrogen fertilization.
• Interestingly, nitrogen return to the orchard floor via sod clipping is estimated to be higher at 400-600 kg ha-1, and overall total soil nitrogen under sod is higher than over herbicides and clean cultivation.
• Sod cover also supplies high amounts of available nitrogen, however, it also uses large amount of the available nitrogen as it is mineralized and thus decreases its availability to the tree roots.
• On the contrary, sod culture usually increase leaf phosphorous concentration in apples.
• Elevated leaf phosphorus concentration may be due to an inverse relationship between phosphorus and nitrogen uptake or more mobility of phosphorus induced by mycorrhizal infection transferable from cover crops to the tree roots.
• Sod can also increase leaf potassium concentration and reduce leaf scorch symptoms typical of potassium deficiency.
• Potassium returns are high from sod clippings with annual estimates of 600 kg ha-1, for orchards under long term sod culture.
• Sod cover may increase soil and leaf calcium and magnesium contents and decrease leaching losses from the soil. However, if magnesium supply is inadequate, it may be associated with a sod-induced increase in leaf potassium.
• Sod may also decrease iron deficiency symptoms as observed elsewhere in apple.

Mulching:

Nitrogen:

• Organic mulches add significant amount of nitrogen to the soil and consequently improve soil fertility, which may cause long term beneficial effect to orchard nutrition.
• Decomposable mulches increase soil organic carbon contents and soil with a favourable C: N ratio expected to increase leaf nitrogen concentration as a result of increase in available soil nitrogen.
• In addition, mulches whether organic or inorganic, suppress the competition for nitrogen by under tree vegetation.

Phosphorus:

• Available phosphorus generally increases in orchard soil under decomposable mulches, especially seaweeds.
• Average water-extractable phosphorus has been estimated to be around 20 mg l-1 beneath the mowed grass mulching on the top of herbicide strip in comparison to 3 mg l-1 beneath sod between the rows.
• In spite of this, leaf phosphorus concentration is often reduced due to reduced under tree vegetation in mulched trees, apparently as a consequence of increased nitrogen uptake.

Potassium:

• Increased soil potassium availability as a consequence of mulching with hay and straw is generally noticed.
• This reflects large amount of potassium is added to the soil by many mulching materials; alternatively, improved potassium availability may also be due to reduced potassium fixation. Whatever the reason may be, more leaf potassium concentration as a consequence of organic mulching is most frequently observed.
• However, increased leaf potassium under mulching adversely affects leaf calcium and magnesium concentration, despite of increase in soil calcium and magnesium concentration.

Magnesium

• Magnesium deficiency in apple is more pronounced under mulch than sod.
• Organic nutrient content of soil and the kind of mulching material are also important consideration in interpreting such contradictory results.
• Conversely, mulching increases leaf boron concentration and thus may help to combat its deficiency (Plate 9.1).
• This may be related to the increase in warm water soluble boron under mulches.

(Source: ohioline.ag.ohio-stste.edu)
Plate 9.1: Symptoms of corky spots on Melrose apple

Cultivation:

• Cultivation often increases the availability of soil NO₃-N, especially relative to full ground cover.
• However, there is always seasonal variation in NO₃-N, which is associated with the extent and timing of weed and cover re-growth.
• Cultivation accelerate the mineralization of organic matter and increase NO₃-N availability, however total nitrogen tends to decline under cultivation.
• Cultivation improve leaf size and colour, leaf nitrogen concentration and availability of soil nitrogen.
• This may be due to mineralizing of nitrogen from the soil. However, cultivation may increase leaf nitrogen in the short term, but in the long term, it may not consistently increase leaf nitrogen.
• Cultivation may not have a major role in affecting the soil contents of other nutrients, however it affect leaf concentration of some of these.
• Different experimental reports suggest that leaf phosphorus and potassium increase and leaf calcium concentration decreases under cultivation.

Herbicides.

Nitrogen:

• Soils in orchard under herbicide weed control are richer in NO₃-N in comparison to grasses orchards, and its value in the former may be as high as 21 mg cm³ in the former compared to 10 mg cm³ of soil in the later during the mid summer.
• Effect of herbicides on leaf nitrogen content is variable. It may increase leaf nitrogen temporarily, due to removal of competition or may not affect leaf nitrogen concentration consistently.
• Variation of this effect in comparison to other practices such as cultivation and mulching may relate to variation in soil nitrogen mineralization potential and initial nitrogen status of the trees.
• Among different herbicides, simazine might affect nitrogen nutrition directly as it may increase leaf nitrogen concentration, but only in certain growing condition.
• Amitrole plus simazine herbicides can partially substitute nitrogen.

Phosphorus:

• Soils of untilled herbicidal strip accumulate greater quantities of phosphorus than under grassed alley, probably from the applied phosphorus.
• However, leaf phosphorous concentration is usually lower in trees under herbicidal strips than under grass.

Potassium:

• Potassium concentration normally does not vary considerably in the soils under herbicidal plots in comparison to phosphorus.
• However, vegetation control with herbicides generally causes a reduction of fruit trees leaf potassium concentration, which is occasionally accompanied by an increase in leaf magnesium.

Calcium and magnesium:

• Surface soils under herbicidal plot usually are much lower in exchangeable calcium and magnesium.
• This is related to the cycling of these cations by orchard floor vegetation since it is known that vegetation reduces leaching of these cations from the surface soil.
• Leaf calcium concentration however, varies with the type of herbicide.
• Higher leaf calcium concentration can be observed with Paraquat treatment, whereas a combination of Paraquat plus simazine has little effect.

Soil moisture and water uptake:

• The efficiency of orchard soil management method is generally judged by its ability to conserve soil moisture and make it available for use by the trees for growth and development.
• However, in certain circumstances, some soil treatments are given with the purpose of reducing, at least temporarily, water content of the soil.
• In water logged areas, sometimes soil is dried out in the fall for the purpose of hastening maturity, and in heavy compact soil tiling simply to provide better aeration may sometimes be profitable.
• In general, soil management aims at conserving soil moisture rather than dissipating it.

Sod culture and cover crops:

• Soil under permanent grass may begin to lose water 15-30 days earlier in the spring as comparison to the cultivated soil.
• Grasses in orchard require a large proportion of water for maintaining growth, and therefore in non-irrigated orchards this competition of water with fruit trees can become critical.
• The extent of soil moisture depletion varies with the vigour, rooting depth, and frequency of mowing of the orchard sod.
• Shallow rooted grasses such as Kentucky bluegrass (Poa pratenses L.) or annual blue grass (Poa annua L.) deplete less moisture from the orchard soil profile than deep rooted sods such as Landino clover (Trifolium repens L.) or S.23 perennial ryegrass (Lolium perenne L.).
• Competition of sod with fruit trees also modify the pattern of water depletion with more water being used from deeper in the profile.
• In summer, regular mowing of grasses is suggested to conserve moisture in soil by reducing water use by grasses.
• On the other hand, sod improves other physical properties as reflected by decrease in bulk density and increase in soil porosity.
• Decrease bulk density means an increase in total pore space available for root growth and increase in water holding capacity.
• Such changes are likely to increase earthworm populations.
• Such changes are expected to reduce surface moisture runoff and erosion and moisture conservation.

Mulching

• It is well recognized that conservation of soil moisture is the most significant advantage of mulching.
• This useful effect is more pronounced during the drying periods of May-June.
• The general improvement in soil moisture is likely a consequence of both improved infiltration capacity, particularly under hay, straw or pine needle mulch and reduced evaporation.
• However, the moisture conservation properties of organic mulches on a silt-clay soil may sometimes be undesirable; as such soils are likely to become susceptible to water logging in winter.

Cultivation

• Removal of weed and cover crop competition by cultivation increases soil moisture content relative to permanent orchard vegetation.
• However, moisture content of cultivated soil may not differ significantly from mulched soil, and may be less than herbicide-treated soil.
• Also, the moisture content of cultivated soils may show considerable seasonal variation depending upon the time of cultivation and cover crop or weed re-growth.

Herbicides

• In general, herbicide-treated orchard soils have a lower soil moisture deficit in comparison to grassed or cover cropped soil.