Soil Health Card, Soil Sampling, Soil Testing, Interpretation and Recommendation

Introduction

The Government of India had commenced the Soil Health Card (SHC) Scheme in February 2015 to assist soil health by means of balanced fertilization for sustainable agriculture. Soil Health Card is a field specific comprehensive report of soil fertility status and other important soil parameters that influence crop productivity. It is close to a physician’s prescription, where the health status of the soil is provided and suggestions are made to the farmers accordingly. Details in a Soil Health Card includes 12 important parameters such as pH, electrical conductivity (EC), organic carbon, macro–nutrients like N, P and K, secondary nutrients like sulphur and micronutrients such as zinc, iron, manganese, copper and boron.

Soil sampling and processing

Soil sampling is perhaps the most crucial step for any analysis. Since a very small portion of the huge soil mass of a field is used for analysis, it becomes essential to get a truly representative soil sample from it. For collecting a representative soil sample, due consideration must be given to the following tips.

1. A field can be treated as a single sampling unit if it is considerably uniform. Generally, an area not exceeding 0.5 ha is taken as one sampling unit.

2. Recently fertilized plots, bunds, channels, marshy tracts, and areas near trees, wells, compost piles or other non-representative locations must be carefully circumvented during sampling.

3. An area of about 2–3 metres on the edge of all the sides of the field should be left in large fields.

4. Larger areas may be divided into suitable number of smaller homogenous units for better representation.

Size of the soil sample

The amount of soil to be collected for each composite sample depends on the type of analysis. For soil fertility evaluation about 250 g soil is to be collected; but for complete physico–chemical analysis and pedological studies about 1500 g soil is to be collected.

Soil sampling procedure

For making composite sample, collect small portions of soil up to the desired depth (0-15 cm or more) by means of suitable sampling tools from 15 to 20 well distributed locations, moving in zigzag manner from each individual sampling site after scrapping off the surface litter, if any, without removing soil. From fields having standing crops in row, draw samples in between the rows.Mix together the soil collected from all the locations within one field very thoroughly by hand on a clean piece of cloth or polythene sheet or clean cemented floor. Reduce the bulk to about 500 g by quarteringprocess. For this, spread the entire soil mass, divide into four quarters, discard two opposite ones and remix the remaining two. Repeat this process until about 500 g soil is left.

Depth of sampling

The penetration of plant roots into the soil is principal consideration in deciding the depth of sampling. Therefore, the following factors should be kept in mind while sampling.

1. For cereals, vegetables and other seasonal crops the samples should be drawn from 0–15 cm (plough layer or furrow slice).

2. For deep rooted crops or longer duration crops like sugarcane or under dry farming conditions, samples should be collected from different depths depending on the requirements of individual situations.

3. For plantation crops or fruit trees, composite sample from 0–30, 30–60 and 60–90 cm depths should be made from 4–5 pits dug in about 0.5 ha field. For pedological studies the samples are taken up to a depth of 180 cm or deeper.

Sampling tools

Sample can be drawn with the help of (i) soil tube (tube auger) (ii) screw type auger (iii) post-hole auger (iv) kassi or phawda (spade) or (v) khurpi.

For sampling of soft and moist soil, a tube auger, spade or khurpi is an appropriate tool. A screw type of auger is more convenient on hard or dry soil while the post-hole auger is useful for sampling excessively wet area like rice fields. If a spade or khurpi is used, a “V” shaped cut may be first made up to plough layer (upto 15 cm) and about 2 cm uniformly thick slice is taken out from one clean side. Tube auger attached to a long extension rod is convenient for sampling from lower depths of a soft soil.

Drying

Wet soil samples cannot be stored due to the change in the chemical nature of some inorganic and organic materials. On drying, ferrous (Fe+2) iron changes to ferric (Fe+3) ion. Wet soil samples are generally dried in the shade at room temperature, processed and stored. For determination of some elements and compounds such as ammonium (NH4+) and nitrate (NO3–) nitrogen, exchangeable potassium, acid extractable phosphorus and ferrous iron, fresh samples from the field without any drying are needed and the results are expressed on oven dry basis. For this, a small amount of sample is dried in an oven at about 105 oC for 2 hours for estimation of moisture percentage and oven dry weight of the sample is taken for analysis.

Information sheet to be sent to the laboratory along with soil samples

[NOTE:Cropping history include year, crops grown, fertilizers applied and yield].

1. If the Soil is Acidic (< 6.5 pH): The soil acidity can be minimized with the use of liming materials such as CaO, Ca (OH)2, CaCO3, CaCO3. MgCO3 and Basic slag. Lime recommendations are generally made on the basis of a 6–8 inches depth (The roots of most field crops penetrate upto 6 inches or 15 cm depth of soil. The roots of some field crops penetrate more depth i.e., 9 inches or 23 cm. For 9 inches, increase the quantity of lime by at least 50% of the quantity that is recommended for 6 inches). Apply all the lime before cultivation. Mix it thoroughly in the soil at the depth of cultivation (15 cm). For high rate of lime, two split applications are desirable, broadcasting one half at one time followed by disking and ploughing and then application of second half of lime and repeating the disking and ploughing. The sub–soil acidity can be rectified by applying lime at deeper depths with large tillage equipment. For better outcomes, lime should be applied 3 to 6 months before seeding. The frequency of application depends upon texture of soil. For coarse textured soil, light and frequent applications are essential whereas for fine textured soil limited application is preferred. Hence, there is every possibility of overliming for the coarse textured soil or soil which has low organic matter. Overliming is detrimental. It induces the deficiency of some nutrient elements, viz., P, K and micronutrients other than Mo. By liming, the soil pH is raised to a desired value (e.g., 6.8). After few years the raised pH tends to come down to its initial pH, as the Ca and Mg are removed from soil by crops or by leaching particularly in humid regions resulting in the reduction of percentage base saturation. Recommend the regular application of small amount of lime at an interval of 1–2 years to maintain the raised soil pH. This is prominent for arable soils (or coarse textured soils) in humid regions. If both surface and sub–surface soils are strongly acidic, suggest the deep incorporation of lime to a depth about 1 foot (30 cm).

[NOTE: If the farmer can not procure lime, recommend the cultivation of crops that have lower lime requirement. Recommend the use of hand gloves and covering of nose with a piece of cloth during handling these liming materials].

Ag–Lime

Application of lime on field

Table 1. The time period needed for completion of reaction of the liming materials

[NOTE: The burnt lime or quick lime or unslaked lime (CaO) and hydrated lime or slaked lime or builders’ lime (CaOH)2 are corrosive. They injure seeds and seedlings, if they come in contact. So, these should be rolled out well before planting to prevent injury to germinating seeds. They take few weeks for reaction in soils. If surface and sub–surface soils are strongly acidic recommend the deep incorporation of lime to a depth of about 1 foot (30 cm)].

Table 2. Calcium carbonate equivalent (or) Neutralizing value (%)

[NOTE:Calcium carbonate equivalent is defined as the acid neutralizing capacity of a liming material expressed as a weight percentage of CaCO3. From above table, we can assume, Ca(OH)2 will neutralize 1.35 times as much acid as the same weight of CaCO3].

Table 3. Relationship between soil SMP–buffer pH and lime requirement values to achieve desired pH of the soil

2. If the Soil is Sodic (> 8.5 pH) : a) As a first step ensure proper land levelling b) Leach out of the excess salts from the sodic soil by ponding with irrigation or rain water for a period of 10 days prior to gypsum application after proper land levelling. This can be fulfilled most efficiently during summer. This step will ensure leaching of soluble salts and soluble carbonates, if any c) Apply gypsum dose (calculated on the basis of soil test), evenly–broadcast and mix thoroughly with the top 10 cm of the soil d) Again apply heavy irrigation and keep the water (this water should have low SAR values) ponded for about 15 days to promote leaching out the salts and other reaction products out of the root zone e) After complete drainage of water and attaining field capacity conditions, grow green manure particularly Dhaincha after conventional tillage. After about 45–50 days, incorporate Dhaincha into the soil 2–3 days before the rice transplanting f) In the next rabi season, wheat can be grown as the second crop to get the economic returns.

[NOTE 1: Based on relative tolerance of crops, their reclaiming effect on soil and economic returns, it has been observed that Sesbania–rice–wheat is the best cropping pattern in a highly sodic soil and this cropping pattern should be followed in first 4 to 5 years of reclamation. When pH of the surface soil reduces in the range of 8.5 to 9, other moderate and less tolerant crops can be included in the cropping sequence viz. mustard, sugarcane, barley and cotton. Then the other crops which are sensitive to sodicity, can be grown profitably after that period].

[NOTE 2: Because of its high solubility in water, calcium chloride is the most readily available source of soluble calcium but it has rarely been used for reclamation because of its high cost. Similarly iron and aluminium sulphates are usually too costly and are seldom used for any large-scale improvement of sodic soils. Large–scale use of sulphuric acid for improving sodic soils is generally not recommended because of handling and application difficulties associated with the large volumes of these acids at the field level].

[NOTE 3: Gypsum is normally broadcasted and then incorporated into the soil by disking or ploughing as it is more effective in the removal of exchangeable sodium than when applied on the soil surface. Also mixing limited quantities of gypsum in shallower depths is more beneficial than mixing it with deeper depths. Deeper-mixing exposes gypsum to react with Na2CO3 of the soil resulting in lesser reduction in exchangeable sodium percentage throughout the depth. This can decrease the seed germination rate and consequently the crop yield. In shallow mixing, soluble carbonates move down with the wetting front without reacting with applied gypsum. For improving sodic soils with hardpans or dense clay subsoil layers, deep ploughing (up to 100 cm) has been found to be a desirable practice. Improvement in crop yields as a result of deep ploughing occurs because of enhanced water intake rates and depth of penetration. This practice results in the doubling of the effective available water holding capacity of the subsoil layers].

[NOTE 4: Sodic soils are generally low in organic matter. Addition of organic materials and crop residues in the soil helps in improving and maintaining soil structure, preventing erosion, and supplying essential plant nutrients besides reclaiming the sodic soils. Organic materials and the plant roots help in enhancing the biological activity in the soil. Organic amendments on decomposition increase the partial pressure of CO2 and produce organic acids. These processes help in increasing electrolyte concentration, mobilizing Ca through enhancing the solubility of soil calcite (CaCO3), lowering pH and ESP of the soil. Most commonly used organic amendments are crop residues, FYM, green manure, poultry manure etc].

[NOTE 5: Generally, application of organic materials together with inorganic amendments is cost–effective, hastens the reclamation process and increases the crop yields; thus, their combined use should be encouraged. Application of 20 t FYM ha–1 combined with gypsum gives higher crop yields than the gypsum applied alone].

Table 1. Estimated efficiencies for various materials used to reclaim sodic/alkali soils compare to Gypsum

[NOTE 1. The quantities of ameliorant are based on 100% pure materials. If material is not 100% pure, necessary corrections must be applied. If mine Gypsum is only 70% pure, the quantity to be added will be 1 x 100/70 = 1.43 tonnes instead of 1 tonne].

[NOTE 2. Hundred per cent oxidation is assumed of materials like sulphur or pyrite in order to be as effective as soluble calcium compounds. In practice, however, this does not happen; thus, their effectiveness is much lower].

Table 2. Relative tolerance of crops to soil sodicity

[NOTE:*Relative yields are 50% of the potential of the given crops in the respective sodicity ranges].

3. If the Soil is Saline [EC > 4.0 dS m–1]: Salinity problems are caused from the accumulation of soluble salts in the root zone. These excess salts reduce the plant growth and vigor by altering water uptake and causing ion–specific toxicities or imbalances. Establishing good drainage is generally the cure for these problems, but salinity problems are often more complex. Proper management procedures, combined with periodic soil tests, are needed to prolong the productivity of salt affected soils. Saline soils cannot be reclaimed by chemical amendments, conditioners or fertilizers. A field can only be reclaimed by removing salts from the plant root zone. In some cases, selecting salt–tolerant crops may be needed in addition to managing soils.

Continuous or intermittent ponding with sufficient quantity of water is the most common method used for leaching the salts out of the root zone. The efficiency of this method also varies with the texture of the soil; it will be more in coarse textured soils compared to fine textured soils. Lower water holding capacity of coarse textured soils leads to higher pore volumes of displacing water while low intake rate of fine textured soils leads to larger fraction of water to be wasted as runoff or as evaporation from stagnant water at the soil surface. The basin furrow method of leaching is considered to be more efficient than ponding methods. Water in this method, is allowed to meander back and forth across the field through adjacent sets of furrows. The quantity of water required is much less than that needed for ponding method of leaching.

The efficiency of leaching method mainly depends upon how uniformly the water is applied in the field. Therefore, proper land levelling is a very important step before initiation of the leaching process. Variations in micro–relief within the field lead to the differential salinity build up; enhanced salinity in raised areas and relatively lower salinity in depressions presumably due to more leaching. In general, depth of water to be used for leaching should be equivalent to the depth of the soil to be reclaimed. As a thumb rule, passing of 1 m leaching water per meter soil depth under continuous ponding removes 80% of the soluble salts from the soil.

[NOTE 1: There must be drainage to reclaim a sodic, saline, or saline–sodic soil. Make sure you have adequate drainage. Without adequate drainage, proper reclamation of any salt-affected soil cannot be achieved on a long–term basis. Salt affected soil problems do not develop overnight, it takes years for salts to accumulate enough to reduce crop growth and/or water infiltration. Reclamation can take just as long].

[NOTE 2: Deep ploughing and sub–soiling methods mechanically break the impermeable layer, cemented sub–soil layer or hardpan in the soil profile at some depth to enhance the infiltration and transportation of salts dissolved in water to deeper soil layers. Deep ploughing has been shown to benefit water penetration, aeration and plant growth in the poorly–structured soils].

What is drainage and how we can improve it ?

Drainage is the unconstrained downward movement of water beyond the crop root zone. It is the ability to move water through and out of the root zone. Hardpans, bedrock, and shallow water tables impede drainage. Signs of poor drainage include surface ponding, slow infiltration, or a soil that remains wet for prolonged periods of time. Digging within and below the root zone can specify where a drainage problem exists. In most of the cases, poor drainage can be improved by breaking up a hardpan with deep tillage. If drainage is impeded by a shallow water table or bedrock, artificial drainage must be installed or another use for the land might need to be considered.

Saline soil

Table 1. Salinity scale

Table2. Relative tolerance of certain crops / plants to salty soil

Table 3. Factors for converting various salinity units to deci Siemens per meter

NOTE: 1. For soil solutions having EC ranging from 0.1 to 5.0 dSm–1.

a) TDS [Total dissolved solids (mg L–1)] = EC (dS m–1) x 640.

b) Sum of soluble cations or anions [mmol (+ or -) L–1] = EC (dS m–1) x 10.

2. For soil solutions having EC ranging from 3 to 30 dS m–1.

OP (Osmotic potential in bars) = EC (dS m–1) x (–0.36).

NOTE: 1 dS m–1 = 1 mmho cm–1 = 1000 μmho cm–1.

1 mg L–1 = 1 ppm.

Mg L–1 = milligrams per liter.

ppm = parts per million.

dS m–1 = deci Siemens per meter at 25 °C.

mmho cm–1 = millimhos per centimeter at 25 °C.

μmho cm–1 = micromhos per centimeter at 25 °C.

Table 4. General recommended doses of micronutrient fertilizers

Table 5. Salt affected soils

NOTE: EC (Electrical Conductivity) values in above table are mentioned in dS m–1.

ESP (Exchangeable Sodium Percentage).

SAR (Sodium Adsorption Ratio).

Table 6. Current status of nutrient use efficiency (NUE) of agricultural ecosystem

Table7. Fertilizer recommendations

CONCLUSION:

1. The recommendations are for the high yielding varieties of wheat, rice and maize. For horticultural crops, vegetables and flowering plants the concerned specialist of State Dept. or Division of Fruits and Horticulture Technology / Vegetable Crops / Floriculture of that particular institution may be consulted for specific recommendations.

2. Sample number ---------------- is Alkali soil may be treated with Gypsum @ -------------- tons ha–1 followed by leaching with good quality irrigation water and sample number ---------------- is Saline soil may be leached with good quality irrigation water without Gypsum before fertilizer/manure application.

Facts for the Students

1. When compared to calcium, high sodium concentrations raise the zeta potential of the soil exchange complex, which repels clay particles from one another and causes soil colloids to disperse. This is a typical property of alkali/sodic soils.
   

2. The main effect of high concentration of soluble salts on plants in a saline soil is osmotic stress. The semi–permeable membrane of plant roots permits water to pass but rejects most of the salts. Osmotically it becomes difficult for the roots to extract water from saline solutions and thus, plants growing in saline soils appear water stressed. At times, these soil conditions are known as ‘wet drought’ conditions because of physiological unavailability of water to plants.
   

3. Rainfall in arid and semi–arid regions is not sufficient to leach down the salts to the deeper layers of soil. Coupled with it, high evaporation in these areas results in the accumulation of large amount of salts in the root zone. Accumulation of salts has been found to increase with increase in dryness of the area.
   

4. The degree of soil acidity or alkalinity, expressed as pH, is a master variable that affects a wide range of soil chemical and biological properties.
   

5. A base is a substance that combines with H+ ions, while an acid is a substance that releases H+ ions. The anions OH– and HCO3– are strong bases because they react with H+ to form the weak acids, H2O and H2CO3, respectively.
   

6. Ammonium ions (NH4+) from organic matter or from most fertilizers are subject to microbial oxidation that converts the N to nitrate ions (NO3–). The reaction with oxygen, termed nitrification, releases two H+ ions for each NH4+ ion oxidized.
   

7. The cations in the soil solution and on the exchange complex are mainly Ca2+, Mg2+, K+, and Na+. These cations are nonhydrolyzing and so do not produce acid (H+) upon reacting with water as Al3+ or Fe3+ do. However, they generally do not produce OH− ions either. Rather, their effect in water is neutral, and soils dominated by them have a pH about 7 unless certain anions are present in the soil solution. The basic hydroxyl (OH−) generating anions are principally carbonate (CO32−) and bicarbonate (HCO3−). These anions originate from the dissolution of such minerals as calcite (CaCO3) or from the dissociation of carbonic acid (H2CO3).
   

8. Pure water is a poor conductor of electricity, but conductivity increases as more and more salt is dissolved in the water. Thus, the EC of the soil solution gives us an indirect measurement of the salt content.
   

9. The pH of saline soils is usually below 8.5. Because soluble salts help prevent dispersion of soil colloids, plant growth on saline soils is not generally constrained by poor infiltration, aggregate stability, or aeration. In many cases, the evaporation of water creates a white salt crust on the soil surface, which accounts for the name white alkali that was previously used to designate saline soils.
   

10. The pH values of sodic soils generally exceed 8.5, rising to 10 or higher in some cases. These extreme pH levels are largely due to the fact that sodium carbonate is much more (100 times) soluble than calcium or magnesium carbonate and so maintains high concentrations of CO32− and HCO3− in the soil solution.
    

11. The extremely high pH levels in sodic soils may cause the soil organic matter to disperse and/or dissolve. The dispersed and dissolved humus moves upward in the capillary water flow and, when the water evaporates, can give the soil surface a black colour. The name black alkali was previously used to describe these soils.
    

12. Soluble salts lower the osmotic potential of the soil water, making it more difficult for roots to remove water from the soil. For established plants (and soil bacteria), this condition requires the expenditure of more energy on osmotic adjustments–accumulating organic and inorganic solutes to lower the osmotic potential inside the cells to counteract the low osmotic potential of the soil solution outside. The lost energy results in reduced growth. For annual crops, the lowered osmotic potential can result in more frequent wilting and reduced water uptake from the soil profile. Plants are most susceptible to salt damage in the early stages of growth. Salinity may delay, or even prevent, the germination of seeds. Young seedlings may be killed by saline conditions that older plants of the same species could tolerate. The radicle (root precursor) of a germinating seed appears to be particularly sensitive to salinity. As young root cells encounter a soil solution high in salts, they may lose water by osmosis to the more concentrated soil solution. The cells then collapse. The same can happen to the tender young stems of certain seedlings.
    

13. Flocculation is important because water moves through large pores and plant roots grow mainly in pore space. Dispersed clays plug the soil pores and impede water movement and soil drainage.
    

14. Cations bring together negatively charged clay particles to flocculate soil clays. Sodium (Na+) is a much poorer flocculator than Ca2+ and Mg2+ because it has less charge and because its ionic size in water is much larger.
    

15. Relative to Na+, Ca+2 has 43 times greater flocculating power and Mg+2 has 27 times greater flocculating power.
    

16. The selection of the critical value for ECe 4 dS m−1 to distinguish a saline soil from non–saline soil is based on the expected salt damage to crops. At this level, the yield of many crops is restricted. At ECe values between 2 and 4 dS m−1, the growth of only sensitive crops is affected. Below ECe value of 2 dS m−1, the effect of salinity is negligibly small. Use of ESP value of 15 is arbitrary since no sharp changes in soil properties have been observed as the proportion of Na+ ions on the exchange complex is increased. The U. S. Salinity Laboratory has used, from history and experience, the ESP value of 15 as a boundary limit to distinguish sodic from the non–sodic soils.
    

17. Based on Indian experience, saline and sodic soils are distinguished on the basis of preponderance of chlorides and sulphates over that of sodium. If Na+ /(Cl− + SO4−2) ratio is less than 1 and pH of the saturated soil paste (pHs) is less than 8.2, the soil is designated as saline and if ratio of Na+ /( Cl− + SO4−2) is more than 1.0 and pHs is more than 8.2, soil is defined as the sodic.
    

18. Globally, more than 800 million hectares (Mha) of land are estimated to be salt–affected (FAO 2008). These soils cover a range of soils defined as saline, saline–sodic and sodic. According to the estimates of the Central Soil Salinity Research Institute (CSSRI), Karnal (Haryana) salt affected soils occupy about 10 Mha.
    

19. According to one estimate (Mandal et al. 2010), an area of 6.74 Mha in India suffers from salt accumulation out of which 3.78 Mha are sodic while 2.96 Mha are saline soils.
    

20. The states of Gujarat (2.20 Mha) and Uttar Pradesh (1.37 Mha) in India have the largest area under salt-affected soils.

Facts about liming materials and liming

1. Dolomite is unique in that there are two carbonates present, so half of the molecular weight is used to determine calcium carbonate equivalent.
   

2. Calcium carbonate (CaCO3), or calcite and calcium-magnesium carbonate [CaMg(CO3)2], or dolomite, are the most common liming materials and generally referred to as Ag-lime.
   

3. Calcium oxide (CaO) is the only material to which the term lime may be correctly applied. CaO also known as unslaked lime, burnt lime, or quick lime, CaO is white powder, shipped in paper bags because of its caustic properties. It is manufactured by heating CaCO3 in a furnace, driving off CO2. CaO is most effective of all liming materials. When unusually rapid results are required, either CaO or Ca(OH)2 should be used. Because of high reactivity with water, avoid contact with skin, eyes, and lungs.
   

4. Calcium hydroxide, or slaked lime, hydrated lime, or builders’ lime, is a white powder and difficult to handle. Neutralizing of acid occurs rapidly. Slaked lime is prepared by hydrating CaO and has a high CCE.
   

5. The effectiveness of liming materials also depends on their particle size distribution of fineness, because the reaction rate depends on the surface area in contact with the soil. CaO and Ca(OH)2 are powders with the smallest particle size, but limestone needs to be crushed to reduce the particle size. Sieve size or mesh is the number of openings per inch. A 60–mesh sieve has 60 openings per inch. A particle passing 60–mesh sieve would have a diameter, 0.0098 in. (<0.25 mm).
   

6. Decreasing the particle size fraction of liming material decreases the lime rate required to raise soil pH, or increases the effectiveness of a given lime material. For example, a 100–mesh lime material (100% efficient) requires only 1 t/a to increase the soil pH to 7.0, whereas a 50–mesh sieve lime material (40% efficient) requires 2 t/a.
   

7. Surface lime applications without mixing in the soil are not immediately effective in increasing soil pH below the surface 0–2 in. depth. It was observed that 10 or more years were required for surface applied lime without incorporation to raise soil pH at a depth of 6 in.
   

8. For rotations with legumes and other crops with higher optimum pH ranges, lime should be applied 3–6 months before seeding.

REFERENCES

1. Basak, R. K. (2017). Soil Testing and Recommendation A Text Book. Kalyani Publishers, Ludhiana.
   

2. Choudhary, O. P. and Kharche, V. K. (2018). Soil salinity and sodicity. Soil science: an introduction, 12, 353-384.

3. FAO (2008). FAO Land and Plant Nutrition Management Service. Available at http://www.fao.org/ ag/agl/agll/spush.
   

4. Havlin, J. L., Tisdale, S. L., Nelson, W. L. and Beaton, J. D. (2018). Soil Fertility and Fertilizers. Pearson India Education Services Pvt. Ltd.
   

5. Mandal, A. K., Sharma, R. C., Singh, G. and Dagar, J. C. (2010) Computerized database of salt affected soils in India. Technical Bulletin, CSSRI/Karnal/2/2010. pp. 28.
   

6. Meena, V. S., Meena, S. K., Verma, J. P., Kumar, A., Aeron, A., Mishra, P. K., Bisht, J. K., Pattanayak, A., Naveed, M. and Dotaniya, M. L. (2017). Plant beneficial rhizospheric microorganism (PBRM) strategies to improve nutrients use efficiency: a review. Ecological Engineering, 107, pp.8-32.
   

7. Mahapatra, P., Rout, K. K., Agarwal, B. K. and Sarkar, A. K. (2019). Determination of forms of soil acidity and its lime requirement. Soil Analysis. Indian Society of Soil Science, New Delhi, pp. 377-386.
   

8. Saha, A. K. (2014). Methods of Physical and Chemical Analysis. Kalyani Publishers, Ludhiana.
   

9. Sarkar, D. K. (2019). Soil Plant Water Analysis Theory and Practice. BS Publications, A unit of BSP Books Pvt. Ltd, Hyderabad.
   

10. Sehgal, J. (2018). A Text Book of Pedology. Kalyani Publishers, Ludhiana.
    

11. Singh. D., Chhonkar, P. K. and Dwivedi, B. S. (2010). Manual on Soil, Plant and Water Analysis. Westville Publishing House, New Delhi.
    

12. Tan, K. H. (2010). Principles of Soil Chemistry. CRC Press Taylor & Francis Group, Boca Raton, London, New York.
    

13. Trivedi, A. and Dutta, A. (2020). Soil health cards: limitations and ways to fix the loopholes.
    

14. Weil, R. R. and Brady, N. C. (2017). The Nature and Properties of Soils. Pearson Education Limited.
    

Authors:

Eetela Sathyanarayana

Mandla Rajashekhar

Jurukuntla Bharghavi

Suddakanti Saranya

Manchala Santhosh Kumar

Banda Rajashekar

Saideep Thallapally

Jatoth Veeranna

Ashish Rai

Bekkam Rakesh