adminTapuwa Mashangwa Agribusiness
NO project can be successful without adequate and proper planning. In agriculture soil tests are taken for granted as most farmers baselessly apply fertiliser. Firstly, no crop should be planted on any area without having done a soil test.
Fertilizer should never be applied without having taken a soil test of the area where the crop(s) will be planted. A fertiliser is a chemical or natural substance added to the soil to increase its fertility hence it is paramount to conduct a soil test to appropriately select and apply the corresponding fertilizer for that particular soil.
Fertilizer application and soil testing are inseparable processes.
The purpose of soil testing in high-yield farming is to determine the relative ability of a soil to supply crop nutrients during a particular growing season, to determine lime needs, and for diagnosing problems such as excessive salinity or alkalinity.
Soil testing is also used to guide nutrient management decisions related to manure and sludge application with the objective of maximizing economic/agronomic benefits while minimizing the potential for negative impacts on water quality.
Soil tests measure the relative nutrient status of soils and are used as a basis for profitable and environmentally responsible fertilizer application.
The accuracy of a soil test result is influenced by the laboratory analysis but may be influenced even more by the quality of the soil sample.
Sample collection is extremely important in the accuracy and repeatability of a soil test. Sample handling following collection is also important.
A soil sample, which does not represent the area being sampled will be misleading and result in over or under-application of fertiliser.
It is therefore very important to collect and handle soil samples properly.
The first basic principle of soil testing is that a field can be sampled in such a way that chemical analysis of the soil sample will accurately reflect the field’s true nutrient status.
This does not mean that all of the samples must, or will, show the same test results, but rather that the results must reflect true variations within the field.
Remember that the soil test recommendations for lime and fertilizer can never be more accurate than the accuracy of soil sampling.
Once the soil samples have been collected and prepared, the level of available nutrients in each sample must be determined.
Many chemical methods have been suggested and are being used for the measurement of essential plant nutrients. The criteria for chemical extracting and analysis of plant nutrients are that those processes must be rapid, accurate and reliable.
Most chemical extracting methods allow the extracting solution, which may consist of water, alkali, weak or strong acid or combinations of these chemicals, to react with the soil sample in a relatively short time.
The sample is then filtered and the solution analysed for the available nutrients.
In addition to extracting solutions, several other parameters of each soil test are important in determining the final number that is printed on a soil report for any one soil sample.
These parameters include: ratio of soil to extractant; shaking time, action and speed; method of expressing the results (e.g., lb/acre, ppm, index systems).
“Cut-off” levels for high test results and overall techniques used in the lab.
When interpreting soil test results, several things should be kept in mind.
The chances of getting a profitable response to fertilization are much greater on a soil that tests low in a given nutrient than on one that tests high.
This does not rule out the possibility of a profitable response from nutrient application at a high level of fertility or lack of a profitable response on soils of low fertility.
Soil tests are better at predicting the probability of a profitable response to nutrient application than predicting the actual quantity of nutrient that will be needed in any one year.
Soil testing in a low nutrient often will not yield as well as a soil testing at an optimum level no matter how much fertilizer is applied that year.
Interpretation of soil test results and recommendations often becomes a matter of how to improve the fertility status of soils testing less than optimum. How much will be needed to change the soil from low to medium or high in that element?
What will be the most economical level at which to maintain the nutrient status of the soil?
With top-level management practices, yields increase and the probability of a response at any given soil test likewise increases.
Wise use of soil testing incorporates a long-term approach to fertility management, in which site-specific soil test target levels are established for each field and nutrient management plans developed to reach and maintain the target levels.
The goal of soil testing is to help farmers achieve economical optimum yields while protecting the environment.
The basic philosophy of soil test fertilizer recommendations is: base them on soil test results; recommend that lower-testing soils be built up to higher test levels by adding extra fertilizer; apply maintenance amounts of plant nutrients to higher-testing soils to keep them there and to keep productivity high; and do not apply specific nutrients to soils testing very high in these nutrients.
Simple advice for higher productivity and greener profits!
l The writer is Engineer Tapuwa Justice Mashangwa, a young entrepreneur based in Bulawayo, founder and CEO of Emerald Agribusiness Consultancy. He can be contacted on +263739096418 or email: [email protected]
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