Soil-crop linkages and nurturing soil fertility

Detail

Soil is a living ecosystem

• Soil is not just dust. It is an ecosystem: a community of living things working together with their non-living surroundings.
• Living part: bacteria, fungi, earthworms and insects.

• Non-living part: minerals from broken-down rock, humus, water and air.

• Humus: the dark, decayed remains of plants and animals. It holds water and feeds nutrients to crops.

• Crops depend on soil as well as climate. The same rainfall gives different harvests on different soils.

Soil-crop linkages (Class 7, Fig. 1.10)

Soil	Main crops	Why it suits them
Alluvial (river-laid silt; Indo-Gangetic plain, deltas)	Wheat, rice	Fertile, deep and easy to plough. It is close to canals and rivers.
Black (regur; Deccan lava plateau)	Cotton	It holds moisture for a long time. That suits cotton, which grows over a long season.
Red (old crystalline rocks of the Peninsula)	Millets, groundnut, pulses	Light soil that is poor in nutrients. Crops that need little water grow well.
Laterite (high-rainfall hills: Western Ghats, North-East)	Tea, coffee, cashew	Heavy rain washes the soil, so it becomes acidic. Tree and plantation crops do well.
Desert (arid Rajasthan)	Bajra	Other crops grow only with irrigation.
Mountain (Himalaya)	Temperate fruits (apple, pear, plum)	Cool slopes and thin forest soils.

• Kerala grows rice and Punjab grows wheat. Three factors work together:
• Kerala: very heavy south-west monsoon rain plus wet coastal and deltaic soils → standing water in the fields → rice, a crop that needs a lot of water.
• Punjab: deep alluvium plus canal and tube-well irrigation plus a cool winter → rabi (winter-season) wheat.
• So soil alone does not decide the crop. Soil, rainfall and irrigation decide it together.

Nurturing the soil: traditional practices

• Crop rotation: growing different crops on the same field one after another, for example cereal → pulse → cereal. Each crop takes different nutrients, so the soil gets a rest.
• Multiple cropping: growing two or more crops on the same land in one year, or side by side. The ground stays covered, and the crops share the risk of failure.
• Organic manure:
• Cow dung: adds humus.
• Panchagavya: a mix of five cow products (dung, urine, milk, curd, ghee). It is sprayed or applied to boost soil microbes.
• Beejamrit: a seed treatment made from cow dung, cow urine and lime. It protects seeds from soil-borne disease.

Nurturing the soil: contemporary practices

• Terracing: cutting flat steps into hill slopes. Each step slows running water, so less soil is washed away.
• Afforestation: planting trees. Roots bind the soil, and leaf litter adds humus.
• Ploughing back crop residue: mixing stubble into the soil instead of burning it. This returns carbon and nutrients to the soil.
• Precise fertiliser application: giving each field only the nutrients it lacks, in the right amount and at the right time.
• Mulching: covering the soil surface with crop residue, leaves or plastic sheet.
• It keeps moisture in because less water evaporates.
• It blocks light, so fewer weeds grow.
• It keeps soil temperature even: cooler by day, warmer by night.
• It shields the soil from raindrops and wind, so less soil erodes.

Nitrogen fixation and the legume link

• Nitrogen fixation: the process of turning nitrogen gas from the air (N₂) into nitrogen compounds that plants can absorb.
• Rhizobium bacteria live in root nodules (small swellings on the roots) of legumes such as gram, lentil, arhar and moong.

• The bacteria take N₂ from the air → turn it into ammonia-based nitrogen → the plant uses it, and the leftover nitrogen stays in the soil for the next crop.

• How fertility is lost:

• Farmers dropped legumes from rice-wheat rotations (Punjab, Haryana, western Uttar Pradesh).
• Farmers also shortened fallows (periods when land is left uncropped to recover).
• With no natural nitrogen being added, the soil depends on urea, and its fertility runs down.

Soil organic carbon (SOC)

• Soil organic carbon: the carbon stored in decayed plant matter and microbe remains in the soil. It is the main part of humus.
• Many Indian soils have less than 0.5 per cent SOC. There are three causes:
• Heat: high temperatures speed up decay, so organic matter breaks down fast.
• Intensive tillage: frequent ploughing lets air into the soil, and the carbon is "burnt off" as CO₂.

• Stubble burning: residue is burnt (for example paddy straw in Punjab and Haryana) instead of being returned to the soil.

• Low SOC means the soil holds less water, has fewer microbes and makes poorer use of fertiliser.

Nutrient imbalance and hidden hunger of soils

• The ideal N:P:K ratio for Indian soils is 4:2:1. N is nitrogen, P is phosphorus and K is potassium. India's actual use leans heavily towards nitrogen because farmers rely on urea [4][5].
• Punjab is in the "very wide ratio" category, at more than 20:5:1 (2025-26 data) [4][5]. Haryana is also well above 4:2:1.
• Earlier picture: India's fertiliser use stood at 1.00 : 0.33 : 0.17, against a world average of 1.00 : 0.52 : 0.40 (FAO, 2000s). This imbalance began in the early Green Revolution years [6].
• "Nitrogen as a shovel":
• Heavy nitrogen makes crops grow fast.
• The fast-growing crop pulls other nutrients (P, K, S, Zn) out of the soil.

• So nitrogen "mines" the soil of its other nutrients [6].

• Nutrient depletion is reported in all 15 agro-climatic regions of India. Each year, crops remove 8–10 million tonnes more N + P₂O₅ + K₂O than farmers add (FAO estimate) [6].

• Micronutrient deficiency: micronutrients are elements that crops need in tiny amounts. Deficiency of sulphur and zinc is spreading in India, and boron deficiency is also common. Where zinc is short, crops respond poorly even to full N-P-K doses [6].
• Five decades of long-term fertiliser experiments under ICAR's All India Coordinated Research Project show the same result. Using only nitrogen fertiliser harms soil health and yields, and it leaves other major nutrients and micronutrients deficient [4][5].

Soil Health Card (SHC) scheme

• Launched: 19 February 2015 at Suratgarh (Sri Ganganagar district, Rajasthan).
• Aim: test every farm's soil and give crop-wise fertiliser advice that corrects unbalanced N:P:K use. Cards are renewed every two years.
• The 12 parameters [3]:

Group	Parameters
Macronutrients	N, P, K, S
Micronutrients	Zn, Fe, Cu, Mn, B
Physical/chemical	pH (acidity or alkalinity), EC (electrical conductivity: a measure of salt content), OC (organic carbon)

• Status now: since 2022-23, the scheme is a component of RKVY (Rashtriya Krishi Vikas Yojana) under the name "Soil Health & Fertility" [2].
• Scale:
• ₹1,706.18 crore released to states and UTs, and 8,272 soil-testing labs set up (February 2025) [2].

• Over 25 crore cards distributed (July 2025) [3].

• Related steps:

• Neem-coated urea was made mandatory in 2015. Its neem-oil coating releases nitrogen slowly, so the plant gets it as it needs it and less is wasted [4][5].
• Nano urea: nutrients are packed into very small particles that release slowly, so plants take them up better. A pilot project is running in 100 districts (2025-26) [4][5].
• Natural farming missions are covered in crops-agriculture-india.

The Green Revolution debate and Sikkim's organic path

• Costs of the Green Revolution (Class 7):
• The soil became poorer over time.

• Pesticides and fertilisers polluted soil and water.

• Sikkim:

• It banned chemical fertilisers and pesticides in 2014.
• It was declared India's first 100 per cent organic state in 2016.

• It shows that high-input farming can be replaced with organic manure and natural soil care.

• The debate: high yields and food security on one side, long-term soil health on the other. The middle path is balanced, need-based nutrient use, made possible by soil testing.

Prelims Hooks

• Soil-crop pairs: black → cotton; laterite → tea, coffee and cashew; red → millets, groundnut and pulses; desert → bajra; mountain → temperate fruits.
• Soil Health Card: launched 19 February 2015 at Suratgarh, Rajasthan (not Gujarat or Punjab).
• SHC parameters: the card tests 12, including S, Zn, Fe, Cu, Mn, B, pH, EC and OC. A common trap is "only N, P, K".
• SHC renewal: cards are renewed every 2 years. Since 2022-23 the scheme has been merged into RKVY as "Soil Health & Fertility" [2].
• Recommended N:P:K ratio = 4:2:1. Punjab's ratio is >20:5:1 [4].
• Nitrogen fixers: Rhizobium lives in the root nodules of legumes. Cereals such as rice and wheat do not have them.
• Mulching conserves moisture, suppresses weeds, moderates soil temperature and checks erosion. It does not add nitrogen directly.
• Sikkim: chemical ban in 2014; declared 100 per cent organic in 2016.
• Panchagavya = five cow products. Beejamrit = a seed treatment.
• Neem-coated urea (2015) slows nitrogen release and reduces the diversion of urea to non-farm uses.

Mains Points

• Causes of soil fertility decline (GS-III): nitrogen-heavy urea use (Punjab >20:5:1 against 4:2:1), legumes dropped from rice-wheat rotations, shorter fallows, stubble burning and intensive tillage. Together these give SOC below 0.5 per cent and spreading S, Zn and B deficiency [4][6].
• Policy response: a soil test leads to a crop-wise prescription. The Soil Health Card (more than 25 crore cards, 8,272 labs; 2025) is now merged into RKVY. Neem-coated urea and nano urea add to it. The weak points are lab quality, how many farmers follow the advice, and the urea subsidy that keeps nitrogen cheap [2][3][4].
• Distribution pattern (GS-I): crops follow soil plus climate plus irrigation. Examples are cotton on the black soils of the Deccan, plantations on Western Ghats laterite, and rice and wheat on the irrigated Indo-Gangetic alluvium (Kerala rice and Punjab wheat).
• Sustainable pathway: use traditional methods (rotation with legumes, organic manure, mulching) alongside precise fertiliser use. Sikkim's 100 per cent organic model (2016) is the test case, set against the Green Revolution's yield gains.