Soil testing for better crop production

Dr Linthoi Watham *

Soil testing refers to one or more of a wide variety of soil analysis conducted for one of several possible reasons but the most widely conducted soil tests are those done to estimate the plant available concentrations of plant nutrients, in order to determine fertilizer recommendations in agriculture.

In agriculture, a soil test commonly refers to the analysis of a soil sample to determine nutrient content, composition and other characteristics such as the acidity or pH level.

It determines fertility or the expected growth potential of the soil which indicates nutrient deficiencies, potential toxicities from excessive fertility and inhibitions from the presence of non-essential trace minerals. It measure soil nutrients that are expected to become more plant available. They do not measure the total amounts of nutrients in the soil.

Soil testing is a useful tool for making recommendations for the application of fertilizers to the crop. Soil test results can be viewed in three categories

1. Low or Yes a fertilizer addition will likely increase growth and yield.
2. High or no a fertilizer addition will not likely increase growth or yield.
3. Intermediate or maybe a fertilizer addition may increase growth or yield.

Most soil test values do not vary greatly from year to year. However, soil and environmental conditions cause fluctuations in measurements such as pH and nitrate nitrogen. Drastic changes in test values year to year may indicate an unrepresentative soil sample or a laboratory error.

Objectives of soil testing

Soil testing is multipurpose in nature. It aims at
1. Grouping soils into classes relative to the levels of nutrients for suggesting fertilizer practices.
2. Predicting the probability of getting profitable responses.
3. Helping to evaluate soil productivity, and
4. Determining specific soil conditions, like alkali, salinity and acidity which limits the crop yield.

Phases of soil testing

Soil testing is a programme that may be divided into four phases
1. Collecting the soil samples
2. Extracting and determining the available nutrients
3. Calibrating and interpreting the analytical results
4. Making the fertilizer recommendations

Soil sampling

To obtain a meaningful and accurate soil test results, it is important to collect soil samples from the correct depth and from multiple locations within a field.

Soil sample are typically collected using hand probes, hand augers, spades, shovels or vehicle mounted hydraulic probes or augers. Unless they are the only option, avoid shovels and spades because they are designed to obtain the same amount of soil from each depth and location, possibly biasing results. Tools should be cleaned between fields and stored away from fertilizers to prevent contamination.

Sampling time : Ideally, soil sampling occurs yearly in the spring to best estimate growing season nutrient availability, however due to time constraints and soil conditions, it may be more practical to sample soil in the fall or winter.

Collection of soil samples from the field

A farm or field to be sampled is given a general inspection, and a diagram prepared showing the different fields, the drainage pattern, and the main kinds of soil such as upland or bottomland. Make a transverse over each area to be sampled separately taking a core or slice of the plow layer at intervals of 15 to 20 steps and compositing them together in a bag. 10 to 30 well distributed cores or sliced are composited for each sample.

Preparation of soil samples

1. Drying
2. Grinding
3. Sieving
4. Mixing
5. Partitioning
6. Weighing
7. Storing

Conclusion : The farmers find it extremely difficult to know proper type of fertilizer which would match the soil. In order to give farmers a service leading to better and more economic use of fertilizers and better soil management practices for increasing agricultural production.

Efficient use of fertilizers is a major factor in any programme designed to bring about an economic increase in agricultural production.