"Mere desh ki dharti sona ugle, ugle heere moti..." the popular 1967 Bollywood song comparing India's nutrient-rich soil to gold, diamonds and pearls might now be a thing of the past, especially in Tamil Nadu, Gujarat and the desert state of Rajasthan.

Farmers in these three states have devoted over half of their land to growing thirsty crops, including rice, wheat, and onion. These crops not only drink up more water but suck up even more nutrients.

A six-month investigation into understanding the impact of growing water-guzzling crops revealed that the top three states primarily growing water-intensive crops have depleted groundwater levels and soil nutrition, adding to the cost of health.

Soil samples collected from Tamil Nadu, Gujarat and Rajasthan were found to be severely lacking both macro and micronutrients, especially nitrogen, potassium, iron and sulphur. One in five samples reported sulphur deficiency compared to one in 10 in states focusing on non-water-intensive crops.

Not just this, nearly nine in 10 soil samples in the top three states growing water-intensive staple food crops showed nitrogen deficiency.

The absence of nutrients in the soil results in less nutritious food crops which in turn have a domino effect on your health. While you may eat vegetables and fruits thinking they are rich in essential proteins, vitamins and minerals, they might be lacking all or some of them because of the depleted soil.

In this three-part series, we explore the impact of cultivating water-guzzling crops on groundwater use, soil health, and potentially human well-being. In the first part of the three-part series, we explored the impact on groundwater. It can be read here. In this second part, we look at the health of the soil and the food grown on it.

States dependent on water-intensive crops have poorer soil health

A comparison of states growing water-intensive crops versus those growing non-water-intensive crops reveals a striking difference in soil health. The top three states - Tamil Nadu, Gujarat and Rajasthan - with the highest area share devoted to water-intensive crops have significantly lower levels of essential nutrients in soil compared to those growing non-water-intensive crops - Jharkhand, Odisha and Tripura. Here are the key findings:

• On average, nine in 10 soil samples in water-intensive crop-growing states were reported to have non-optimal nitrogen, a key nutrient for plants. Whereas, this figure was six in 10 in non-water-intensive crop-growing states.
• Similar levels of phosphorus deficiency were reported in two groups of states - 28.03 per cent in water-intensive crop growing states compared to 24.68 per cent in non-water-intensive crop growing states.
• States with a larger proportion of area under cultivation for water-intensive crops have twice the levels of potassium deficiency than states primarily growing non-water-intensive crops.

• Sulphur deficiency was almost twice (20.60 per cent) as prevalent in states growing water-intensive crops compared to those focusing on non-water-intensive crops (11.09 per cent).
• Iron deficiency was significantly higher in water-intensive crop states, with a 36 percentage point difference compared to non-water-intensive crop states, where iron deficiency levels were much lower.

"Intensive irrigation leads to soil salinisation, compaction and erosion, nutrient leaching, reduced microbial activity and waterlogging. Poor soil health leads to reduced crop yields, low-quality produce, and increased costs for farmers and low farm income," explains Dr Ashok Kumar, an agronomist, at the FAO.

Staple or non-staple, water-guzzling crops leave soil undernourished

Growing staple foods that require a lot of water appears to be even worse for the soil than growing other types of water-intensive crops.

Farmers in Tamil Nadu have devoted over half of their land under cultivation to water-intensive staple crops like rice, potatoes and millet. Farmers in Madhya Pradesh and Punjab have dedicated nearly half of their land to other water-guzzling staples.

On the other hand, Goa has the highest share of area under cultivation dedicated to water-intensive non-staple crops, using just over half of its agricultural land to grow crops like sweet potatoes, walnuts, nutmeg and oilseeds. Gujarat and Rajasthan follow with about a quarter of their land under cultivation for non-staple crops such as bananas, berries, nutmeg, and pepper.

The crop profile has a large influence on their current soil health.

Soil in the top three states growing water-intensive staple food crops was found to be more deficient in nitrogen and sulphur than those growing water-intensive non-staple crops. Nearly nine out of 10 soil samples showed nitrogen deficiency. Whereas, about one in four samples showed sulphur deficiency, as per the Soil Health Card 2023-24.

"When we give excess water to the soil, there is a chance of nutrient leaching and loss of nutrients, particularly mobile nutrients like nitrogen," explains Dr Ashok Kumar Patra, the 2022 Glinka World Soil Prize Winner. "Nitrogen is highly dynamic in the soil. Additionally, sandy soil has low nutrient retention," adds Dr Patra, an Emeritus Scientist & Former Director of ICAR-Indian Institute of Soil Science, Bhopal.

But these states fare slightly better on other key nutrients with a marginal difference in the proportion of soil samples reporting phosphorus, potassium and zinc deficiency. For instance, three in 10 samples showed phosphorous deficiency as compared to four in 10 samples from non-staple food crop growing states.

Similarly, 35 per cent of soil samples in states growing water-intensive staple crops showed zinc deficiency, which is lower than the 40 per cent in states growing water-intensive non-staple crops.

The chain reaction set off by water-intensive farming that leaches key nutrients from soil

Soil health depends on its physical, biological and chemical properties. Nitrogen, an element often washed away in the irrigation of thirsty plants, is key for soil fertility. This also impacts other key elements critical to soil health.

Soil in the top three states with the highest area under water-intensive crops was found to be extremely deficient in nitrogen, according to the Soil Health Card 2023-24.

99 per cent of the soil samples tested in Tamil Nadu and Rajasthan were found to have either low or high nitrogen levels. In Gujarat, eight in 10 soil samples reported non-optimal nitrogen.

"Nitrogen is present in both biological and mineral forms. At any time, if you have excess nitrogen somewhere, except biological, it escapes into the atmosphere as ammonia and gas," explains Ajai Pachori, Joint Director, Agriculture (Chemistry), Government of Rajasthan. He adds, "Secondly, mineral nitrogen, which we provide through fertilizer, can leach because of excessive water usage. It can leach beyond the roots and pollute water."

Denitrification is another process that causes nitrogen loss in waterlogged soil. "As water moves downward through the soil, nitrate easily travels with it, often sinking below the plant root zone. While phosphorus doesn't leach as much, other nutrients like sulphur, calcium, and magnesium are more likely to move downward with the water. Excessive irrigation can carry dissolved metals deeper into the soil as well."

Mr Pachori recommends that one-third of the nitrogen requirement should come from organic material in the form of farmyard manure and compost. Three-fourth of the nitrogen requirement should be met by fertilisers - either urea or ammonium sulphate or DAP (Diammonium Phosphate).

However, as Dr Pachori said, farmers are using DAP more than required.

On average, eight in 10 samples in the three states had non-optimal potassium in the soil.

Nearly one-third of the soil samples in Tamil Nadu have non-optimal phosphorus. Four in 10 soil samples in Gujarat and one in 10 in Rajasthan had non-optimal phosphorus.

"States using more water for irrigation give higher yields and take up more nutrients from the soil," explains Dr Ashok Kumar Patra, 2022 Glinka World Soil Prize winner. "But if farmers don't add an equal amount of nutrients to the soil, there will be a nutrient deficiency," adds Dr Patra, an Emeritus Scientist & Former Director of ICAR-Indian Institute of Soil Science, Bhopal.

Excessive irrigation can lead to loss of nutrients from the soil, leaving it less fertile.

Since the soil in his field has a light texture, Kala Khan, a farmer residing in the Alwar district of Rajasthan has applied fertiliser like DAP and urea to fulfill the phosphorus and nitrogen requirements. Fellow farmer Bijendra Kumar often adds more urea to compensate for the water shortfall.

"A rise in the quantity of phosphorous results in micronutrient (zinc and iron) deficiency in soil. Phosphorous and zinc and iron have an antagonistic effect," Dr Pachori said.

Excessive DAP dries up the soil, reduces water-holding capacity, makes soil alkaline and destroys micro-organisms and bacteria in the soil, added SP Yadav, Agriculture Research Officer, Soil Testing Laboratory, Alwar, Rajasthan.

The three top water-intensive crop growing states have mixed results. In Rajasthan, over half of the soil samples showed deficiencies in both iron and zinc, while 8 per cent also displayed a lack of sulphur.

On the other hand, in Gujarat, one-fifth of the soil samples were found deficient in sulphur. 29 per cent of the soil samples had iron deficiency while 37 per cent had zinc deficiency.

One-third of the soil samples in Tamil Nadu reported sulphur deficiency. 40-45 per cent of the sample had iron and zinc deficiency, as per the Soil Health Card 2023-24.

Five years ago, Rajasthan's soil was more deficient in zinc. Now it is iron deficient. "It is because our department supplies zinc. Farmers too shell out some money and buy zinc supplements," said Mr Yadav.

The consequences of poor soil on plant health

Lack of soil nutrients directly impacts plant growth - both in terms of quality and quantity. Micronutrients iron and zinc act as catalysts and support various metabolic activities. "Iron and zinc deficiency in soil can lead to retarded growth, less production, and low quality of produce," said Ajai Pachori, Joint Director, Agriculture (Chemistry), Government of Rajasthan.

Zinc also helps plants in an uptake of nutrients like calcium and chlorophyll formation.

Sulphur, another micronutrient, aids in the growth of oilseeds and pulses. Sulphur deficiency in the soil can lead to protein deficiency in pulses, said SP Yadav.

"Let's say you grow pulses on soil lacking sulphur. The harvested crop will look like a regular pulse; when cooked, it will appear and taste like any other. However, it won't meet your protein needs, as the sulphur deficiency in the soil has caused it to lack essential protein," he explained.

Nitrogen, a macronutrient, plays a key role in plant germination. "The plant's body, which develops from the seed, is composed of nitrogen. The main role of nitrogen is to increase greenery, and plant growth," adds Mr Yadav.

Phosphorus, a co-macronutrient, helps develop roots and grain formation.

The job of potassium is to increase production quality and protect crops from diseases and pests.

"Soil health manifests directly with micronutrient deficiencies within the food items, which could be cereals, pulses, fruits and vegetables, etc," explains Dr Rajiv Tandon, Consultant Paediatrician and Executive Director, The Health Continuum. He adds, "And that eventually leads to the same low levels of minerals and vitamins in the people who eat that particular food item."

Restoring soil health

The bottom line is that states growing water-intensive crops have bad soil health. Thirsty crops take up more nutrients than less thirsty crops and vice versa. Therefore, sustainable farming practices play a vital role in maintaining and improving soil health.

Farmers are being taught to use fertilisers judiciously and apply farmyard manure to maintain soil health. Mr Yadav explained, "Farmers often have livestock, but don't utilize their manure effectively. Typically, it's spread on the soil, where it's exposed to pollution and extreme heat, causing it to dry out. When it rains, the nutrients are washed away, and the manure doesn't decompose properly, limiting its potential benefits. However, by digging a pit to store the manure, soil retains moisture throughout the year. Microorganisms can break it down more efficiently, transforming it into valuable vermicompost. This process enhances the soil's physical, chemical, and biological properties."

There is a synergy between water and nutrients, opines Dr Ashok Kumar from FAO. "Crop rotation, such as alternating cereals with legumes, can enrich the soil with nitrogen for future crops. Similarly, rotating water-intensive crops with deep-rooted crops can help break compacted soil layers formed by the cultivation of water-intensive crops. On the other hand, shallow-rooted crops help prevent soil erosion. This will enhance soil structure and improve soil infiltration and retention," he adds.

As farmers dig deeper to irrigate their fields, they encounter saline water that isn't ideal for crops. "When saline water accumulates in the topsoil, it leads to soil salinity, which hampers germination. Let's say a seed germinates regardless of salinity, the plant's growth will be retarded. The roots won't develop properly, which affects the flowering and fruiting stages," added Mr Yadav.

To restore soil health, Dr Ashok Kumar suggests adopting sustainable irrigation practices such as micro-irrigation, monitoring soil moisture levels, and implementing crop rotation and diversification to maintain soil health.

"There are many ways to restore soil health in areas affected by intensive irrigation such as no-till farming, adding organic matter, planting cover crops, crop rotation, bioremediation and integrated nutrient management," he adds.

The article is part two of a three-part series on the impact of growing water-guzzling crops on groundwater, soil nutrition and health. In the first part, we looked at the depleting groundwater. It can be read here.

In the third part, we explore the link between soil nutrition and human health. Read the part three here.

Methodology:

This data story looks at the impact of growing water-intensive crops on groundwater, soil health and human health.

To begin with, the author looked at the "Mekonnen, M.M. and Hoekstra, A.Y. (2010) The green, blue and grey water footprint of crops and derived crop products" report to identify water-intensive crops in states across India. The author considered only blue water footprint data to know how much groundwater is being used to irrigate a crop, in a state. If a state uses more blue water than the national average to grow a certain crop, then the author considered the crop "water-intensive" in that state.

The author also looked at the "Area, Production & Yield - Reports" from 2013-2023 to calculate the proportion of area under cultivation of water-intensive or non-water-intensive crops in each state. The area, production and yield reports were taken from the official website of the Directorate of Economics and Statistics, Department of Agriculture and Farmers Welfare, Ministry of Agriculture & Farmers Welfare.

Following this methodology, the author identified three states with the highest proportion of area under cultivation for water-intensive crops and three states with the highest proportion of area under cultivation for non-water-intensive crops. They then looked at Soil Health Card data (2023-24) by the Ministry of Agriculture and Farmers Welfare. They focused on the status of macronutrients (N, P, K) and micronutrients (S, Fe, Zn) in the soil to see if the soil in states growing water-intensive crops is more deficient in essential nutrients.

The author also looked at the National Family Health Survey (NFHS-5) data specifically for the six states and analysed data for key health indicators - malnutrition and anaemia among children under five and women.

All supporting data and analysis can be accessed here.

The author travelled to Alwar district in Rajasthan and met farmers in different villages to understand their challenges.

(Reporting for this story was supported by the Environmental Data Journalism Academy- a program of Internews' Earth Journalism Network and Thibi.)