Right pH level: Rich soil

It doesn’t mean anything to most people. But pH is most important in farming. Many farmers would not know what it’s all about but they can see and feel its effects on their harvests. Crops vary in their need for pH but the right level — medium, neutral or low — could spell a windfall. On the other hand, incorrect levels make for production malaise like low yield, crop failure, more expenses, low incomes and, eventually, a barren soil.

Understanding pH and knowing what to do can help a lot in avoiding these harvest disruptions. The H stands for hydrogen which is an essential part of every acid which is present in the water we drink. The letter p taken from the word potential is a mathematical symbol used to translate into simple values acid or alkaline levels in the soil. The neutral point is 7 which is the pH level of pure water.

Explains Dr. Perfecto Evangelista, division chief, Soil and Water Resources Research of the Department of Agriculture’s Bureau of Soils and Water Management (BSWM): In the case of soil, a pH level above the neutral pH7 means a chalky, alkaline soil. Below that point, the soil tends towards acidity, and some soils, especially those abused by excessive fertilization, can have a low pH4.

"This level of acidity," he explains, "cannot be tolerated by vegetables, herbs, and fruits of commercial value. When such a very low pH level occurs in the soil, the land becomes unproductive and turns into a wasteland. In acidic soils, hydrogen combines with the ions of fine clay particles and decomposing matter to neutralize their beneficial effects on plants."

There are several ways to determine the pH level of the soil in a farmer’s field. The more precise ones are the highly sophisticated laboratories maintained by the Bureau of Soils and Water Management across the regions of the country listed in this article.

BSWM laboratory analysis functions include: soil analysis (chemical, salinity/alkalinity, physical analysis and soil test kit; water analysis (salinity/alkalinity); plant tissue analysis: fertilizer analysis; and microbial analysis.

Moreover, there are also inexpensive chemical soil test kits but under non-laboratory controlled conditions, the results are somewhat complex and difficult to interpret. The simplest and most convenient ones which can be used right in the field are the self-powered electronic soil pH meters with highly sensitive electrode probe that is simply pushed into the soil at the root zone of the plants to a depth of 10 to 14 centimeters for a graduated pointer reading of pH from 3.5 to 9.0.

Once the soil is found to have the correct pH for the specific plant, its is advisable to check the pH together with other elements such as NPK before and after every cropping so that immediate corrective measures can be taken. This is necessary because the nature of soil itself and application of fertilizers, sometimes, tend toward the acid. Water washes calcium and other cations downward more quickly on garden-type soil-sandy soil, in particular – so that the soil cannot hold its alkalinity and or lime easily. Plants, also, dispense with the calcium from the soil as they grow. (As humus in the soil rots and micro-organisms get to work, acids are produced.)

To increase the pH level, lime or calcium hydroxide is added. To reduce it, decomposing organic matter like compost, peat or chemicals such as sulphate of ammonia or flowers of sulphur are added.

There are three main types of lime: ground limestone, hydrated lime and burnt lime. Ground limestone is slower-acting but is easier to handle. Burnt lime is the quickest acting but must be handled with extra care. One part burnt lime, 1-1/2 parts hydrated lime and 2 parts ground lime make a good liming mix. Hydrated lime may take effect in two or three months. Ground chalk or limestone may take up to six months.

For general liming applications and small pH adjustments, apply from 500 kilograms to 1000 kg of ground limestone or ground chalk per hectare. It is important to remember that it’s best to allow at least one month to pass between adding lime and applying fertilizer. Avoid adding lime at the same time as compost, animal manure or superphosphate to prevent loss of nitrogen or ammonia gas in the atmosphere.

While lime stimulates the availability of plant nutrients, the soil should not be limed automatically because the large amounts of equally important plant nutrients become increasingly "locked up" or ineffective above pH7.

There are several benefits of liming which will help ensure productivity of the farm:

• Reduces acidity and increase pH;

• Binds the fine particles of clay into larger particles for better aeration and soil drainage;

• Helps to retain moisture and plant nutrients in sandy soils;

• Supplies the plants with food calcium;

• Makes nitrogen available by stimulating micro-organisms that help decompose organic matter;

• Helps increase worm population, particularly at pH range 6.0 to 6.5;

• Serves as protection against some plant diseases such as club root in brassicas and leaf crops like cabbages, lettuce and mustard; too, it is disliked by some pests, slugs, leather jackets and wire worms that harm the plants.