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HOR 100

SOIL MANAGEMENT PRACTICES AFTER PLANTING
After planting, the soil should be carefully managed so that it remains in good condition suitable to the needs of the crop with least expenses. This involves maintenance of the physical condition of the soil, its moisture and nutrient content. A good system of soil cultivation should ensure:
   Weed control and saving in moisture and nutrients
   Very little disturbance to soil and preventing soil erosion
   Reduced cost of cultivation
The soil management practices undertaken after planting include the following:
Clean culture
Involves regular ploughing and removal of weeds. Has many disadvantages
   Frequent cultivation depletes humus rapidly leading to the depletion of nutrients
   Causes injury to roots
   Hard pan is created in the soil
   Causes more soil erosion
These defects can be minimized by avoiding deep and frequent cultivation and avoiding cultivation when the soil is too wet.
Mulching
Crop residues like straw, stalks, leaves, sawdust, polythene films are spread in the tree basins and in inter spaces between trees. Main objectives of mulching are:
 To conserve soil moisture
 To control the weed growth
 Keeps soil cool in day; warm at night hours
 Reduces surface run-off
 Adds humus to the soil
 Prevents soil erosion
 Fruits are protected and kept clean since they fall on the mulches
 It allows the absorption of more rain water
 It reduces irrigation frequency.
Disadvantages of mulching
 Dry materials used as mulches encourage the risk of fire
 Thick mulches may act as places for mice and rodents to live and multiply. These may cause damage to tree trunks and roots by eating the bark and burrowing to the land.
 Mulching localizes roots on the moist topsoil surface instead of allowing deep penetration. This will result in lodging due to lack of anchorage

INTERCROPPING

In young widely spaced crops, there is a long period of time when there is extensive ground area between planting points which require attention. The main crop should be clean weeded upto 1 m. radius and the rest of the area used for intercrops. Intercrops are used for the following reasons:
·         To maximize on land use
·         To nurse the main crop e.g. through modification of the climate, thereby helping the main crop to establish better. For example, tall growing temporary trees such as bananas can be used to shade main fruit species when they are still young.
·         To conserve the soils through protection from raindrop impact and direct sunlight.
The following problems are usually encountered in an intercrop/cover crop situation:
·         Competition for resources with the main crop
·         Host of diseases/pests of main crop
·         Makes mechanization difficult
CONSERVATION AGRICULTURE
Conservation Agriculture (CA) is an approach to managing agro-ecosystems for improved and sustained productivity, increased profits and food security while preserving and enhancing the resource base and the environment. CA is characterized by three related principles, namely:
q   Continuous minimum mechanical soil disturbance.
q  Permanent organic soil cover.
q  Crop rotation
In conservation agriculture, minimum or zero tillage is practiced. Minimum tillage refers to a reduction of tillage operations to a minimum possible to ensure good seedbed, rapid germination and favourable growth conditions. Tillage is reduced by omitting operations which do not give much benefit compared to the cost. Zero tillage refers to placement of the seed onto the soil without soil preparation. It is an extreme form of minimum tillage. Primary tillage is completely avoided and secondary tillage is restricted to land preparation in the row zone only. In zero tillage, there is direct sowing of the seed directly onto the soil without any disturbance of the soil.
Advantages of Conservation Agriculture
q   Improves soil structure
q   Protects the soil against erosion and nutrient losses by maintaining a permanent soil cover and minimizing soil disturbance.
q   Enhance soil organic matter levels and nutrient availability by utilizing the previous crop residues or growing green manure/cover crops keeping these residues as a surface mulch rather than burning.
q  Requires significantly less water use due to increased infiltration and enhanced water holding capacity from crop residues left on the soil surface.
q  Mulches also protect the soil surface from extreme temperatures and greatly reduce surface evaporation
q  Land under no-till is not cleared before planting and there is less weeding due to establishment of permanent soil cover
q  Soil nutrient supplies and cycling are enhanced by decomposition of crop residues at the soil surface
q  Soil fertility is built up over time under conservation agriculture, and fewer fertilizers are required to achieve optimal yields over time.
q  Insect pests and other disease causing organisms are held in check by an abundant and diverse community of beneficial soil organisms, including predatory wasps, spiders, nematodes, springtails, mites and beneficial bacteria and fungi, among other species.
q  The significant reduction in fossil fuel use under no-till agriculture results in fewer greenhouse gases being emitted into the atmosphere and cleaner air in general.
q   Reduced applications of agrochemicals under CA also significantly lessens pollution levels in air, soil and water. 
MINERAL NUTRITION
Fertilizer placement
Soil application
Applied to the soil and taken up by the roots. Less expensive and better suited for large application rates of the major nutrients and for pre-plant application. Applications by broadcasting, banding or top dressing
Circle banding: A furrow is cut, 20 cm wide and 30 cm deep, around the tree in a circle beneath the outer canopy
Strip band application. Parallel furrows are cut, 20 cm wide and 30 cm deep, between the rows of the trees. This method is suitable for old orchards, where the trees are more than 10 years old because of greater root spread.
Hole placement. Four or five holes are dug beneath the outer canopy of each tree. The holes should be 15-20 cm in diameter, and at least 30 cm deep.
Broadcasting: Fertilizer broadcast on the surface under the spread of the branches at least 15 cm from the trunk, since injury can occur if placed too close.
Foliar applications
Absorption of nutrients is very rapid, and plant’s response is evident in 1-2 days. However, application must be more frequent than soil application because of little residual effect. Used for applying nutrients immobile in soil (Fe and Zn) or those immobile in plants (Ca and B)
   Boron: applied to increase level at flowering 
   Calcium and Iron: applied at post-bloom to harvest period to increase level in the fruit.
   Application of macronutrients to quickly correct deficiency
Fertigation
Refers to application of soluble fertilizers through an irrigation system. In fertigation, a fertilizer concentrate is prepared and mixed in the tank. This fertilizer concentrate is sucked and mixed with the irrigation water at set ratios e.g. 1:100, 1:200. As the water and fertilizer mixes, the concentrate gets diluted and gets to the plant at acceptable levels.
Benefits over other fertilizing methods include:
q allows accurate and uniform application of nutrients at the right concentration in order to meet the actual nutritional requirement of the crop throughout the growing season
q Allows for change of the fertilizer program during the growing season in order to adjust for fruit, flower, leaf and root development.
q increases the efficiency of fertilizer application thereby reducing the amount of applied fertilizer and production costs
q lessens the potential of groundwater pollution caused by fertilizer leaching
q Saves on labor
q the supply of nutrients can be more carefully regulated and monitored.
q Crop foliage is kept dry thus avoiding leaf scorching and delaying the development of plant pathogens.
q Allows application of small concentrations of micronutrients which are otherwise very difficult to apply accurately to the soil by soil application
Phosphorus fertilization
Specific growth factors associated with phosphorus
         stimulate root development
         Increases stem strength and thickness allowing plants to withstand strong winds
         improves flower formation and seed production
         More uniform and earlier crop maturity
         increases resistance to plant diseases.
Deficiency symptoms
Phosphorus deficiency is difficult to diagnose. Crops usually display no obvious symptoms of phosphorus deficiency, other than a general stunting of the plant during early growth and dull-green or blue-green color. Plants become slender, with thin stems and fruit cluster development is poor. Red or purple color forms on the underside of the leaves, including the veins, delayed maturity and roots become brown and develop few lateral branches.
Soil pH and P
Soil pH is a measure of the concentration of hydrogen ions (H+) in the soil solution. The concentration of H+ ions in the soil solution determines whether the soil is acid, neutral or alkaline (basic). A pH of 7 is neutral, below 7 is acid and above 7 is alkaline (or basic). Plant nutrients are most available at a pH varying from 5.5 to 7.0. A soil containing a pH less than 5 is strongly acidic and injurious to plant growth. Similarly, pH above 7.5 is strongly alkaline and also injurious to growth.
Continuous use of fertilizers alters the soil pH.  Acid-forming fertilizers include fertilizers that  contain sulphur, fertilizers containing ½ the content as nitrogen and ⅓ the content as P. Examples are urea, DAP, ammonium phosphate, ammonium nitrate, ammonium sulphate and phosphoric acid. Increased acidity causes the following effects in crop production:
v  Increases the solubility of Fe, Al and Mn in the soil to a level which is toxic to plant growth
v  Causes nitrogen deficiency because the nitrogen-fixing bacteria will not thrive under acidic conditions.
v  Causes phosphorous deficiency due to conversion of P to insoluble forms. Under acid conditions, phosphorus reacts with iron or aluminium in the soil to form iron or aluminium phosphates which are of low solubility.
v  Causes Ca and Mg deficiency because the soluble forms in insufficient quantities
Low soil pH is remedied by liming with CaCO3, dolomite (Mg,CaCO3)2 or CaO. Liming removes the H+ from solution and raises the pH.
NITROGEN FERTILIZATION
Roles in plants
         An essential component of proteins, which make up the protoplasm and enzymes
         Nitrogen is also present as a part of nucleoprotein, amino acids, amines, amino sugar, polypeptides, chlorophyll and other organic compounds in plants.
         Needed for cell division and reproduction.
         Increases vegetative growth
         Plays a role in flowering, fruit set, fruit growth and fruit size
Deficiency symptoms
         New leaves are small, thin and light green in color.
         Mature green leaves slowly turn to irregular green and yellow pattern, become entirely yellow, and then are shed.
         Plants may appear nearly normal but are undersize.
         Plants have poor flowering and carry little or no fruit load. They are also highly erratic in bearing.
Nitrogen fertilizer sources
Urea, Calcium ammonium nitrate, Ammonium sulphate, Ammonium sulphate nitrate, Calcium nitrate, Potassium nitrate, Magnesium nitrate, Ammonium nitrate, Urea phosphate, Sodium nitrate, Nitric acid
Potassium
Physiological roles
         Maintenance of water turgor in leaves
         Regulates opening and closing of stomata
         Balances charge between negatively and positively charged ions within plant cells.
         Regulation of turgor pressure protect plant cells from disease invasion.
         Enzyme activation
         Protein synthesis
         Facilitates cell expansion
         Improves fruit color
         Improves resistance to strong winds and drought.
Potassium deficiency is likely to occur on sandy soils due to leaching. Lack of soil moisture also reduces K uptake. Supply to plants may be decreased by soils are very high in Ca and Mg or by heavy application of N.
Potassium deficiency
Moderately low K cause a general reduction in growth without visual deficiency symptoms. Presence of visual deficiency symptoms means that production has already been seriously impaired.
Potassium deficiency in leaves
         Fruits accumulate large amounts of K, so leaf symptoms are more likely and most severe as fruit approaches maturity during heavy crop years.
         Symptoms appear first on older leaves because K is mobile but may affect young leaves in severe cases.
         Deficiencies result initially in yellowing of tissue along leaf margins.
         The leaf margins later dry up completely while the inner parts of the leaves remain green
Deficiency effects on fruits
         Reduction in fruit size over time
         Premature shedding of fruit.
         The fruits have lower acid concentration hence low fruit quality
         Decreased yield
         Other deficiency effects
         Deficiency causes a reduction in the rate of photosynthesis leading to reduced production of carbohydrates.
         Increased susceptibility to disease outbreaks, drought and cold
Potassium fertilizer sources
         Potassium nitrate
         Potassium sulphate
         Potassium chloride (muriate of potash)
         Monopotassium phosphate
PRUNING AND TRAINING
Training is the practice of directing tree growth into a particular shape and form. Pruning is the removal of parts of a plant to correct or maintain the formed tree structure. Correct training and pruning are essential for early production, sustained high yields, optimum fruit quality and efficient management. Symptoms of unsatisfactory growth that suggest adjustments in the type and/or amount of pruning include the following:
   Failure to control pests or diseases may indicate that the trees are too high or too thick for good spray coverage.
   Poor fruit color may be due to shading or excessive vegetative vigor.
   Small fruits may be due to Low plant vigor
   Oversize fruit may be due to high vigor which is often a response to over pruning.
   Harvesting problems because the trees are too tall or too thick
   Low yields may be due to few bearing branches
Training and Pruning objectives
1. To control size of the plant. Unpruned avocado or mango trees can attain heights and widths of over 20 meters. Such trees bear fruits at the top of the canopy, making harvesting difficult.  The large sizes also make spraying difficult
2. To control the form of the tree with respect to the angle of branching. Remove narrow-angled branches and leave wide-angled branches which should be well spaced and distributed around the tree. Narrow angled branches are weak and tend to break under heavy fruit load. 
3. To open the center of the tree to light exposure
4. To facilitate air movement to the center of the tree. Opening the tree canopy permits adequate air movement through the tree, which promotes rapid drying to minimize disease infection and allows thorough pesticide penetration.
5. Improve health through removal of diseased, dead or damaged parts. This allows the plant’s energy to be channeled to productive branches.
6. Removal of suckers growing below the grafting point
7. To aid in establishment of transplants. Root and shoot pruning reduces transpiration shock and promotes successful plant establishment.
   Pruning of taproot encourages the development of fibrous root system
   Shoot pruning in seedlings conserves moisture by reducing the transpiration surface
8. To balance between shoot and fruit production. The main aim when pruning is to obtain a good crop of fruits rather than a tree with abundant lush but unproductive foliage. Unpruned trees tend to produce a large crop of small fruits often damaged by pests and diseases and much of the crop is out of reach at the top of the tree. Overpruned trees tend to produce light crops of large fruits. Pruning is therefore carried out to achieve a balance between shoot growth and fruit production.