Soil pH is an expression of the degree of acidity or alkalinity of a soil. It influences plant nutrient availability. A very acidic soil (pH <5.0) typically has lower levels of nitrogen, phosphorus, calcium and magnesium available for plants and higher levels of availability of aluminium, iron and boron than soil with pH 7.0. At the other extreme, if the pH is too high, availability of iron, manganese, copper, zinc and especially phosphorus and boron may be low. A pH above 8.3 may indicate a significant level of exchangeable sodium.

The Table 2 shows the pH values in various soils and it shows the proportion, or percentage of the area in the study zones. Soil pH can be classified into 10 classes, the study region has a total of 8 kinds of soil pH ranges.

Extremely acid: If the soil has a pH value of 3.5 to 4.4, that soil can be considered as extremely acidic. This kind of soil is not suitable for any crops. In the study region 1.95 percent area have extremely acidic soil.

Soil pH or soil reaction is an indication of the acidity or alkalinity of soil and is measured in pH units. Soil pH is defined as the negative logarithm of the hydrogen ion concentration.

Figure 3

pH is simply a measure of how acidic or alkaline a substance is. Soil acidity or alkalinity (soil pH) is important because it identifies how easily plants can take up nutrients from the soil.

pH is a scale that chemists use to measure acidity. Values below 7 are considered acidic, values above 7 are alkaline (the opposite of acidic) and 7 is neutral, totally 23.43 percent of area having neutral pH value. Most plants can tolerate a wide pH range in solution culture, but they cannot tolerate a wide range of acidity in the soil. When soil acidity changes, the solubility of a number of metal ions also changes.

Under alkaline conditions, the solubility of minerals decreases to the point that nutrient deficiencies occur. Plant growth is, therefore, limited when there are deficiencies in iron, manganese, zinc, copper and boron. Phosphorus is also less available in alkaline soils and high levels of calcium may inhibit the uptake of potassium and magnesium. In the study region two kinds of alkaline soil can be find i.e., slight and moderate alkaline, some alkaline soils can be acidified using sulfur or acid forming fertilizers, but soils with free calcium carbonate cannot be easily acidified. It is often easier to manage the nutrient deficiencies that occur on alkaline soils than to acidify the soil.

Organic matter in soils and sediments is widely distributed over the earth’s surface occurring in almost all terrestrial and aquatic environments (Schnitzer, 1978). Soils and sediments contain a large variety of organic materials ranging from simple sugars and carbohydrates to the more complex proteins, fats, waxes and organic acids. Important characteristics of the organic matter include their ability to: form water-soluble and water insoluble complexes with metal ions and hydrous oxides; interact with clay minerals and bind particles together; absorption of both naturally-occurring and anthropogenically-introduced organic compounds; absorb and release plant nutrients; and hold water in the soil environment. As a result of these characteristics, the determination of total organic carbon is an essential part of any site characterization since its presence or absence can markedly influence how chemicals will react in the soil or sediment (Brain.A.Schumachre. 2002). SOC is one of the most important constituents of the soil due to its capacity to affect plant growth as both a source of energy and a trigger for nutrient availability through mineralization. SOC fractions in the active pool, previously described, are the main source of energy and nutrients for soil microorganisms. Humus participates in aggregate stability and nutrient and water holding capacity. Table 3 and Figure 5 show the organic carbon in the study area, organic carbon can be divided into three class i.e., low, medium and high. 10.39 percent of the area had low levels of the organic carbon, the maximum was covered by medium levels of organic carbon i.e., 62.39 percent, 27.23 percent of the area recorded high levels of organic carbon.

Figure 4

Phosphorus is highly mobile in plants, and when deficient, it may be translocated from old plant tissue to young, actively growing areas. Consequently, early vegetative responses to phosphorus are often observed. As a plant matures, phosphorus is translocated into the fruiting areas of the plant, where high-energy requirements are needed for the formation of seeds and fruit. The availability of phosphorus (P₂O₅, Kg/ha) in the soil can be classified into three classes i.e., low, medium and high. In the Hemavathi watershed 20.06% of area is having Low level of Phosphorus, 33.30% of area is having Medium and 46.62% of area having High level of Phosphorus. Phosphorus deficiencies late in the growing season affect both seed development and normal crop maturity. The percentage of the total amount of each nutrient taken up is higher for phosphorus late in the growing season than for either nitrogen or potassium.

Figure 5

Potassium is an essential plant nutrient and is required in large amounts for proper growth and reproduction of plants. Potassium is considered second only to nitrogen, when it comes to nutrients needed by plants, and is commonly considered as the “quality nutrient.” It affects the plant shape, size, color, taste and other measurements attributed to healthy produce. Plants absorb potassium in its ionic form, K+. Protein and starch synthesis in plants require potassium as well. Potassium is essential at almost every step of the protein synthesis. In starch synthesis, the enzyme responsible for the process is activated by potassium.

Figure 6

The availability of potassium in soil can also divided into three classes i.e., low, medium and high. In the study region is having 10.33% of Low level of Potassium, 27.73% of medium level and 61.92% of area is having High level of Potassium. Potassium is absorbed by plants in larger amounts than either magnesium or calcium; in fact, nitrogen is the only nutrient absorbed in larger amounts than potassium. Potassium is a vital component of numerous plant functions, including nutrient absorption, respiration, transpiration, and enzyme activity.