SOIL FERTILITY EVALUATION AND REMOTE SENSING GOWRI PRIYA GVHSS, VITHURA

SOIL FERTILITY EVLUATION

Optimum productivity of any cropping system depends on an adequate supply of plant nutrients. Continuous removal of nutrients by the harvested crop, without adequate replacement will increase the potential for future nutrient related plant stress and yield loss.

When the soil does not supply sufficient nutrients for normal plant development and optimum productivity, application of supplemental nutrients is required. The proper rate of plant nutrient application is determined based on the nutrient requirement of the crop and nutrient–supplying power of eth soil. Several diagnostic techniques are commonly employed to assess the fertility status of the soil, in order to determine specific nutrient stress and the quantity of nutrients needed to eliminate the stress. These diagnostic techniques are:

Nutrient deficiency symptoms of plants

 Analysis of tissue from plants growing on the particular soil.

Biological tests in which growth of either higher plants or certain micro-organisms is used as  a measure of soil fertility.

Soil analysis.

Nutrient deficiency symptoms of plants:-

If a plant is lacking in a particular nutrient, characteristic symptoms may appear. E.g., when N is deficient, the leaves of most plants become pale green or light yellow. The visual evaluation of nutrient stress by diagnosis of deficiency symptoms should be used only as a supplement to other diagnostic techniques like soil and plant analysis.

Precautions should be taken while interpreting nutrient-deficiency symptoms because:

The visual symptom may be caused by more than one nutrient. E.g., Yellowing symptom can be caused by deficiency of N and S.

Deficiency of one nutrient may be caused by the excess of another nutrient. E.g. Mn deficiency may be induced by adding large quantities of Fe.

It is often difficult to distinguish deficiency symptoms in the field from disease or insect damage.

A visual symptom may be caused by more than one factor. E.g., Purple of red colour of sugarcane can be caused by P deficiency, low soil temperature, insect damage to roots or N deficiency.

Hidden hunger

Hidden hunger is the situation in which the nutrient content in the plant is insufficient to give optimum crop production, but the plant shows no deficiency symptoms.

Disadvantage of the diagnostic technique based on nutrient deficiency symptoms is that visual symptoms appear only after the nutrient level in the plant has been reduced to such a level that the yield is affected severely.

Plant analysis:-

These are of 2 types:-

Tissue tests on fresh tissue in the field.

Tissue analysis in the laboratory

Plant tissue is analysed to determine the nutrient deficiencies before visual symptoms appear. Plant analyses are based on the assumption that the amount of a given nutrient in a plant is directly related to the availability of the nutrient in the soil.

Tissue tests:- rapid tests for the detection of nutrients in fresh tissue are useful for verifying or predicting nutrient deficiencies of growing plants.

The general methods are:-

Plant parts are chopped up and extracted with reagents. The intensity of the colour developed is used as a measure of the nutrient supply. 

Plant tissue is squeezed to transfer plant sap to filter paper and colour-developing reagent are added. The resulting colour is used as a measure of the nutrient content.

Eg.,of plant parts used for testing:-

Crop Nutrient tested Part used

Cotton N Petiole of first

P mature leaf near

K The top of plant.

Small grains N Lower stem

P

K

Corn N Base of stalk

P

K Midrib of leaf below ear

2. Total analysis:- It is performed on the whole plant or on plant parts. After sampling the plant material is dried, ground, and the nutrient content determined. In this, the contents of all essential and non-essential elements can be determined. The plant part selected is important and sampling guidelines are established for each crop.

DIAGNOSIS AND RECOMMENDATION INTEGRATED SYSTEM (DRIS)

DRIS is a system that identifies all the nutritional factors limiting crop production and, thus, increases the chance of obtaining high crop yields by improving fertilizer recommendations.

To develop a DRIS for a given crop, the following requirements must be fulfilled:

All factors having an effect on crop yield must be defined.

The relationship between these factors and yield must be described.

Calibrated norms must be established.

Recommendations suited to particular sets of conditions and based on correct use of these norms must be continually refined.

[For teachers’ information:-

Establishment of DRIS norms:-

Step 1:-A  survey is conducted to obtain the data required to establish  DRIS norms. A large number of sites where a particular crop is grown are selected at random in order to represent the whole production are of a country, state or district. At each site, plant and soil analysis for all essential nutrients are conducted. Other parameters likely to be related directly or indirectly to yield are also recorded. In addition, details of soil treatments (‘fertilizers, herbicides etc.) climatic conditions (rainfall etc.), cultural practices  and any other relevant types of information are recorded and stored in computer for ready access.

Step 2:-The entire population of observations is divided into 2 populations, viz., high yielders and low yielders, based on vigour, quality and yield. Each nutrient in the plant is expressed in as many ways as possible. For eg., the percentage of N in the dry matter, or ratios of N/P, N/K, or products N.P, N.K and so on, may be used. The mean of each ratio for each population is calculated. Each ratio that significantly discriminates between the high yielders and low yielders is retained as a useful diagnostic parameter. The mean values for each of these ratios then constitute the diagnostic norms.

Chlorophyll meters:-  A hand-held chlorophyll meter can measure the relative chlorophyll content of the leaf thereby providing an indication of the N status of the plant. 

Crop logging:- The crop log is a graphic record of the progress of a the crop and contains a series of chemical and physical measurements. These measurements indicate the general condition of the plants and suggest changes in management that are necessary to produce maximum yields.] 

BIOLOGICAL TESTS

1. Field tests:- Field experiments are essential to measure crop response to nutrients. When large number of field tests are conducted on soils that are well characterized, fertilizer recommendations based on these tests can be applied to other soils with similar characteristics. Field tests are expensive and time consuming, but they are valuable tools and are widely used by scientists. 

2. Laboratory and green house tests:- Simpler and more rapid laboratory / green house techniques utilize small quantities of soil to quantify the nutrient supplying power of a soil.

A. Neubauer seedling method- This technique is based on the uptake of nutrients by a large number of plants grown on a small amount of soil. The total nutrients removed by the plants are quantified and tables are established to give the minimum values of macro- and micro nutrients available for satisfactory yields of various crops.

B. Microbiological methods:- Certain microorganisms can indicate nutrient deficiency in soil depending on the amount of colony growth. These methods are simple, rapid, ad require less space.

3. Soil testing:…………………………………………………………………………………………………………………

REMOTE SENSING

Remote sensing is the collection and analysis of data on features of the earth’s surface. The information is achieved through cameras and other imaging systems mounted on aircraft or space vehicles. Satellite systems provide repetitive coverage of very large areas with good spatial resolution. Through satellite imaging it is feasible to monitor land cover changes, both natural and those resulting from human activities. Infra red aerial crop photography is a reliable means of monitoring crop production systems. Healthy green plants reflect large amounts of infra red light, whereas plants under stress caused by such factors as drought, nutrient deficiency, disease, weeds, and chemical spray damage do not reflect infra red light. Other crop management problems like inadequate drainage, poor crop stand establishment, and uneven applications of fertilizers and herbicides can be detected by this technique.

[Reference: Tisdale et al., Soil Fertility and Fertilizers, 1997, pp. 405-461]