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How to take care of your fruit tree orchard

By George Mbakaya

Clement Kotonya, jack fruit farmer at his orchard in Imbo, Homa Bay county. Fruit trees grow and produce in one place for 15 to 50 years or more. [Denish Ochieng, Standard]

“What venture can I start that will guarantee me good yields in future and a solid retirement plan?” a friend recently asked me. There are many options, but I can place my bet on fruit trees.

Fruit trees grow and produce in one place for 15 to 50 years or more. By the time they are in bearing, they have extensive root systems that extend outward from the trunk and downward several feet if the soil is well drained.

For healthy fruit trees, good soil-management practices require that soil fertility is maintained, water penetrates readily and is not lost by runoff.

Also key is soil structure that is not unduly injured and that conditions favour growth and fruitfulness of the trees decade to decade.

Important aspects of the soil

The soil pH (whether a soil is acid or alkaline) is an important property. It affects the availability of nutrients and the activity of microbes and other tiny creatures in the soil. In general, the best soil pH for citrus trees is between 5.5 and 6.5. If the pH falls below 5.0, aluminum toxicity and manganese toxicity often occur in citrus roots. A low pH also causes a deficiency of nutrients such as calcium, magnesium, and phosphorus (which are easily fixed by soil particles), and molybdenum.

Get the pH right

Fruit trees growing in soils with a pH higher than 7.5, often suffer from a deficiency of micronutrients such as iron, manganese, copper and zinc.

A foliar spray of fertiliser can be applied to supplement the micronutrients. In addition, ammonium sulphate can be applied as a nitrogen source and sulphur to modify the soil pH to 6.5. The techniques used to apply sulphur can be the same as those used to apply lime.

To correct the pH, liming with limestone or dolomite is recommended. Farmers should also avoid applying too much ammonium, in the form of nitrogen fertilisers such as urea or ammonium sulphate. This is because there is a danger of making the soil more acidic. In orchards where the soil pH is below 5.0, liming materials should be applied after the fruit is harvested. They should be incorporated into the soil at a depth of at least 15 - 30 cm, since lime has poor mobility in the soil.

Mixing manure or compost

Mixing manure or compost with the lime materials is recommended. This helps to keep the soil aerated, and avoids compaction. Chemical fertilisers should not be applied at the same time as lime, since this would reduce the fertiliser efficiency of the nitrogen. Inorganic fertilisers may also be applied separately, a month after applying the lime materials.

Routine soil monitoring of soil pH is needed to determine whether there is a need for lime materials. Growers should not apply lime unless it is needed.

Applying lime aimlessly is not only wasteful, but micronutrient deficiencies may occur if growers apply too much lime. For this reason, annual lime applications should be discontinued when the soil pH has been modified to more than 6.0.

Orchard management can also include green manures, which act as a source of organic matter. Common green manure crops in orchards include legumes such as perennial peanut and beans. Grass cover and mulches can effectively reduce soil erosion and runoff, and subsequently increase the infiltration rate of water.

In spite of the labour cost needed to keep the area around the trunks of trees weeded, grass cover is a good technique for orchards, especially in sloping land or mountainous areas. If the orchard is sown in grass, the amount of nitrogen fertiliser should be increased by 20-30 per cent in the first few years, to allow for grass growth. Good soil management should include regular soil analysis to determine nutrient deficiency. Before planting, send the soil samples to the laboratories for analysis. Evaluate the results with the experts to determine the correction needed.

[The writer is an expert on sustainable agriculture and agricultural solutions]

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