SOIL AND WATER QUALITY FOR AGRICULTURE By ZEESHAN AKRAM SOIL CHEMIST Fatima Sugar Research and Development Center – Fatima Group

What is Soil ? The unconsolidated material or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants.

SOIL FERTILITY The ability of a soil to support satisfactory plant growth Ensures nutrient and water supplies Provides pleasent conditions for root growth, development and harvesting of potential yield.

Soil Quality Soil quality is the capacity of soils within landscapes to sustain biological productivity, maintain environmental quality, and promote plant and animal health Protecting soil quality like protecting air quality and water quality should be fundamental goal of our Nation’s Environmental Policy Poor Good

Soil Analysis The standard techniques are employed for analysis of soil. These techniques are mainly based on potentiometry, electrical conductance, atomic absorption spectrophotometery, flame photometry. Results are expressed in units acceptable in national and international literature.

Method of Soil Sampling Divide the field into different blocks on the basis of soil variability. Samples are collected from each block with soil auger from different depths. For the field crops samples are collected from the depth of 0–15 & 15-30 cm Samples are collected in zigzag pattern across the field. For the orchards samples are collected up to the depth of 150 cm. The samples should be taken under the crown of trees. Put the samples in polythene bags labeled as under: - Farmer’s name - Block No. - Depth

Precautions for Soil Sample Collection Samples should not be taken: Along the water channel, roadside, pathway and boundaries Under the tree shade Close to the heaps (manure) Areas where the plant population is not uniform Areas where domestic refuse are thrown Places in the field where fertilizers are dumped Sampling in low lying area.

Methods of soil Analysis

SOIL REACTION (pH): pH (paste) Remarks Soil pH is the most important parameter which indicates soil reaction and ultimately affects availability of many soil nutrients to plants. In classifying soils for their reaction, they are categorized in three distinct groups; acid, neutral and alkaline. The pH value is determined potentiometrically using combination electrode. The pH value of soil paste can be interpreted as following: pH (paste) Remarks 7.00 - 7.50 Soil contains no alkaline earth carbonates. 7.51 - 8.50 Alkaline, some quantity of bicarbonate is present. ESP may or may not exceed15. > 8.51 Alkali, carbonate is dominant anion and ESP may exceed 15.

Soil pH 14 Acidic Zone Alkaline Zone pH Range

SOIL SODICITY (SAR) EC (dS m-1) SAR Remaks Sodium adsorption ratio (SAR) of soil extracts and irrigation waters indicates relative activity of sodium ions in exchange reactions with soil. SAR = Na / (SQR ((Ca + Mg) / 2)) The ionic concentrations are in milliequivalent per liter. The criteria being used to classify the soils according to salt type and amount is as under: EC (dS m-1) SAR Remaks < 4 <13 Non Saline - non Sodic soils > 4 <13 Saline soils < 4 >13 Sodic soils > 4 >13 Saline - Sodic soils

SOIL ORGANIC MATTER Organic Matter (%) Remarks Soil sample is treated with potassium dichromate in presence of sulfuric acid and excess of chromate (not reduced) is determined with standard ferrous sulphate (Walkley and Black method). Organic Matter (%) Remarks < 0.86 Poor 0.86 - 1.29 Satisfactory >1.29 Adequate

Nitrogen Distillation Unit

SOIL PHOSPHORUS The Olsen method is used which is standard method for soils of arid and semi-arid regions. Phosphorus is extracted with 0.5-M sodium bicarbonate solution buffered at pH 8.5. Phosphorus is extracted with 1:20 ratio (soil: extractant) for thirty minutes and P is estimated spectrometrically at 880 nm after developing a blue colour by ammonium molybdate and ascorbic acid. The soil P indices are as follows: Phosphorus Rating Remarks (mg / kg -Soil) < 3.5 Very low The yield would be less than 50%,potential without P application. 3.6 - 7.0 Low Optimum yields of all crops can not be obtained without P application. 7.1 - 14.0 Medium All crops need P application. 14.1 - 21.0 Adequate High P requiring crops need P application. > 21.0 High P is recommended for soil fertility maintenance or to balance N:P ratio.

SOIL POTASSIUM The method used for the assessment of soil K status is comprised of 1 N ammonium acetate extraction with 1:20 ratio (soil: extractant). The shaking time is thirty minutes and K is estimated on flame photometer. Fertilizer recommendations are made on the basis of soil K indices, which are as follow: Potassium Rating Remarks (mg /kg soil) < 40 Very low The yield would be less than 50% potential without K application. 41 – 80 Low Optimum yields of all crops can not be obtained without K application. 81 – 180 Medium All crops need K application.. 181 – 280 Adequate High K requiring crops need K application.. > 280 High No need of K application to all crops but K fertilizer is recommended to balance its mining.

Flame photometer Analysis

SOIL MICRONUTRIENTS Micronutrient Deficiency limit (mg / kg soil) Zinc (Zn), copper (Cu), iron (Fe) and manganese (Mn) are determined by extracting with diethylene triamine penta acetic acid (DTPA). The extractant is buffered at pH 7.3. The concentrations of Zn, Cu, Fe and Mn are determined on atomic absorption spectrophotometer using air-acetylene flame and appropriate standards for calibration. The critical levels for DTPA extractable micro-nutrients are as follows: - Micronutrient Deficiency limit (mg / kg soil) Zn < 1.0 (1.5 – Rice Only) Cu < 0.2 Fe < 4.5 Mn < 1.0 B (0.1 Normality HCl, extractant) <0.6

Atomic Spectroscopy Analysis

Soil Fertility Criteria OM (%) Class Soil-P (ppm) Soil-K (ppm) <0.86 Poor < 7 Low 0-80 0.86 – 1.29 Satisfactory 7-14 Medium 81-180 > 1.29 Adequate 15-21 >180 >21 Contd….

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