Procedures for Soil Analysis

Procedures for soil analysis

To detect possible nutritional deficiencies in culture, can be used three methods of analysis:

Visual inspection of the culture to check for signs of deficiencies. This method only reports critical gaps once and sometimes the damage symptoms observed may be unreliable. Chlorosis, for example, may be the result of a low nitrogen, a supply of a nematode, a saline soil or dry, of a disease (viral) or other problems not related to levels of soil nutrition .

· Analysis of soil. Measure soil nutrient levels and other characteristics. Farmers rely on these tests to determine lime and fertilizer needs of crops.

· Analysis of plant tissue. They measure only nutrient levels in the tissues of the plant. This type of analysis to detect possible deficiencies not found in the soil analysis.

Of the three methods described, the soil analysis is the most important for most crops, especially for a year. You can have a soil test at the beginning of the season to allow the farmer to provide the nutrients necessary before sowing or planting. It is important to perform soil tests to determine the amount of each nutrient that is available for plant growth. From the results of the analysis of the soil, the farmer can decide how much fertilizer should be applied to achieve a sufficient level.

There are three stages to perform soil analysis:

· Sampling of soil. The farmer removed and soil samples sent to a testing center.

· Analysis of the soil. The laboratory performs a test soil sample and concludes with a recommendation to the farmer.

· Preparation of a plan of fertilization. The farmer acts according to the recommendation given by the analysis center.

SOIL SAMPLING

The results of the analysis of a soil depends on the quality of the sample collected by the farmer at the center of analysis. So then sets out the recommendations to follow in taking soil samples for physico-chemical analysis:

Frequency of Analysis

The frequency of soil analysis depends on the harvest and how it has grown. For most crops, collecting samples every two or three years should be sufficient. Intensive crops such as fruits or vegetables require an annual sampling and greenhouse crops make their analysis more often. Analysis should be performed before sowing or planting.

Any change in harvesting practices should be preceded by a soil test analysis. For example, if a farmer intends to change from normal tillage to a conservation should be done a soil test before the first year. A farmer growing that changes must also perform a soil test before the new crop.

Sampling sites and number of subsamples

The property should be divided into homogeneous sampling plots in color, texture, and crop treatments. The number of samples depends on the variability or heterogeneity of the plot. The estimate is the more accurate the larger the number of subsamples. So guidance is considered appropriate to take from 15 to 40 samples in each plot, making a zig-zag and putting all the samples in a common fund. There should be no sample representing a larger area of ​​4 hectares. It is advisable to take 10 to 20 sub-samples for plots between 5000 and 10000 m2.

Depth of sampling

Depends on the type of crop, but usually always recommended discarding the first 5 cm of topsoil. For most crops just take samples from the first 20-40 cm of soil. In the case of crops of grass and meadows recommended sampling depth is 5 to 10 cm. On the other hand, in those deep-rooted crops and fruit sampling is recommended at a depth of 30 to 60 cm.

Sampling Procedure

For the sampling tubes or augers are used for soil sampling. You can also use a shovel. For this we have to make a V-shaped hole, cut a piece of 1.5 cm from the wall of the hole and remove most of the sample with the blade. Each soil sample should include all soil sampling depth.

Once the sampling is recommended to mix all the samples together to obtain a homogeneous soil mixture. Take about 1 kg of this mixture, let it air dry and sent to the lab for analysis, specifying the most of the plot data.

Sampling in greenhouses

The fertilization program for cultivation in greenhouses is very different from that used for field crops. Generally, farmers depend mainly on extensive reserves of soil nutrients such as organic nitrogen or potassium interchangeably. However, intensive greenhouse crops are often used substrates to which nutrients are supplied through fertilizer complex plans, this way you have total control over the nutritional status of the plant.

To carry out sampling in these crops will be taken as an example the methodology used in vegetable crops in sand and drip irrigation. To do this, choose a point 10-15 cm from the trunk of the plant and in the direction of the line portagoteros. Discard the layer of sand and compost and prick up to the average depth of the roots (10 cm). This sampler will use a half-round rod or a small hoe. The important thing is to remove the soil throughout the drilling and in the same amount. The amount of soil removed (150-200 g) should be similar at all sampling points (subsamples). Avoid sampling in the bands and corridors as well as the 4-5 meters next to them.

AN? SOIL ANALYSIS

There are two methods for analysis of soil samples collected. The oldest method uses chemical reactions that produce color changes. The exact color depends on the amount of minerals available in the soil. For the analysis of pH, the color depends on soil pH.

These simple chemical tests are very easy to make but are unreliable. Therefore, these assays based on the comparison of colors have been replaced by laboratory tests using modern equipment such as pH meter and spectrophotometer. These devices measure a fast and accurate amounts of minerals in the soil samples.

However, laboratory results are reliable only if they are validated in soils similar to those of sampling. That is, trials should be based on studies on fertilization and soil nutrient levels in soil-like sample.

Usually in a soil analysis performed the following tests:

· Determination of texture by mechanical analysis of the sample screening.

· Measurement of soil organic matter.

· Determination of pH levels through the use of pH meters.

· Measurement of soluble phosphorus or available (free phosphorus for plant growth) by washing the sample with an acid solution and subsequent analysis in a spectrophotometer.

· Measurement of exchangeable potassium.

Today there are many relatively inexpensive electronic devices (digital pocket pH meters, conductivity meters and nutrients, etc) which allow at lot faster and on time trials on crops that require constant monitoring of soil nutrient status (horticultural crops nurseries, etc.)..

AN? ANALYSIS OF PLANT TISSUE

The analysis of plant tissue in combination with soil give a fuller picture of the nutritional status of the plant. In the analysis of tissue analysis is performed only plant nutrients rather than soil nutrients. These tests are useful in determining possible nutritional problems related to micronutrient deficiency, more difficult to determine on the ground.

With the plant tissue analysis can distinguish between physiological disorders caused by nutritional deficiencies of other diseases caused by fungi, bacteria or viruses. In addition, these studies allow to know the phenomena of competition between the different elements that prevent the absorption of nutrients.

Nutrient levels vary considerably in different plant tissues or at different ages. So before analysis is important to determine the portion of the plant used and the required growth stage.

Sampling of plant material for analysis is an operation that is in relation to the analysis pursued, and is always subordinate to the discretion and good sense of the operator. However, the analysis of plant material should always be representative, so that it is statistically significant.

Input this approach, we can distinguish two options for sampling:

1) Sampling of parts or whole plant.

2) Sampling of leaves for leaf analysis.

In both cases the plot should be divided into units of sampling. In this case the sampling unit is a group of plants that are visually similar, have the same force, the same development is in the same soil type, and that they practice the same cultural techniques. The plants sampled must be representative of the sampling unit.

When the terrain looks like, the sampling unit should represent no more than:

Greenhouses: 3000 m2.

Irrigation: 10000 m2.

Extensive: 25000 m2.

If any zones are clearly different from the rest of the crop but very small, it is advisable not to sample it. In any case, the sample must be accompanied by the corresponding report as receiving laboratory criteria.

The following sets out a number of general rules on the collection and transport of plant tissue for analysis, although the modes of action will depend on the crop:

• Use bags or other containers of paper (avoid plastic).

· If parts or whole plant sampled need to be taken 20 or 30 plants, taking care that are in the same stage of development and having the same morphological characteristics.

· In the sampling of leaves for leaf analysis, always take the leaves for union with the stem, so that the laboratory receives all its leaf petiole. The leaf samples will be the first fully developed, with blade and petiole (be the 4 th, 5 th or 6 th start counting from the apex).

· The best time for leaf sampling is in the early hours of the morning.

· The number of leaves is to make more relevant to the representativeness of the sample with the amount of material required for analysis, the latter being very small. Because it is considered valid the same criteria as for soil sampling, ie 10 to 20 sheets, taking over the smaller leaves them and vice versa.

· Do not take delivery in the laboratory more than is strictly necessary, avoiding direct sunlight. If the shipment is made late is convenient to put the samples in a refrigerator to slow down its metabolic activity.

· If you have to wait several days before sending samples to the laboratory, it is interesting to wash them with a nonionic detergent, citric acid type, to avoid the results of the analysis the influence of potential contamination. After washing, rinsed with distilled water and dried in the sun.

Do not forget the correct labeling of the samples to avoid confusion.

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