eChapter Name: Methods for Soil Analysis
9789389907117
eBook Name: A HANDBOOK OF SOIL-PLANT-WATER-FERTILIZER AND MANURE ANALYSIS
by M.V. Durai
Introduction
Soil is the main source of nutrients for the plants. Soil also provides support for plant growth in various ways. Knowledge about soil health and its maintenance is critical to sustaining crop productivity. The health of soils can be assessed by the quality and stand of the crops grown on them. However, this is a general assessment made by the farmers. A scientific assessment is possible through detailed physical, chemical and biological analysis of the soils. Essential plant nutrients such as N, P, K, Ca, Mg and S are called macronutrients, while Fe, Zn, Cu, Mo, Mn, B and Cl are called micronutrients. It is necessary to assess the capacity of a soil to supply nutrients in order to supply the remaining amounts of needed plant nutrients (total crop requirement - soil supply). Thus, soil testing laboratories are considered nerve centres for nutrient management in crop production systems and plantation forestry.
Soils may have large amounts of nutrient reserves in them. All or a part of these reserves may not be of any use to crops because they may not be in plant-available form. For the purpose of estimation or analysis of plant-available soil nutrients, such methods are to be used that have been tested/verified for the correlation of nutrients extracted and their plant availability. This book describes internationally accepted and widely used methods. Apart from nutrients, soil pH estimation is also critical in the assessment of soil health. Generally, plants prefer soils that are close to either side of neutrality. However, there are acid- loving plants and also plants that can withstand high soil alkalinity. Hence, good yields and economic returns from farming are possible in acid and alkali soils. With proper amendments, still higher yields can be obtained in acid and alkali soils. Soil pH also has a considerable influence on the activity of soil micro-flora and on the availability of soil nutrients to crops. It is also important to estimate physical properties such as soil texture, structure, bulk density, soil colour, water content and soil temperature.