Cultivation of grains depletes the Cerrado’s water? On the contrary, it shows search

One of the goals of the Agricultural Sector Roadmap 1.5ºC, launched by agricultural commodity giants during Cop-27, last year, foresees, from 2025, a total boycott on the purchase of agricultural products from new areas of the Cerrado where there is conversion of land use. The biome covers 25% of the Brazilian territory, including much of the Midwest, the largest grain producing region in the country.

One of the recurrent justifications of those who defend this “freezing” of land use is that agriculture would contribute to an increase in water scarcity, with the risk of desertification in a region of predominantly sandy soils, with low water retention capacity. A narrative that does not hold up, according to researcher Lineu Rodrigues, Deputy Head of Research and Development at Embrapa Cerrados.

“Agriculture actually contributes to recycling good quality water. There is no relationship between agriculture and water scarcity or lack of water”, assures Rodrigues, who is a postdoctoral fellow in Irrigation Engineering and Water Management at the University of Nebraska.

A study by Rodrigues and Arnaldo José Cambraia Neto, a master’s student in Agricultural Engineering at the University of Viçosa, shows that if the entire Cerrado biome were converted to soy cultivation, the recharge of rainwater in groundwater would be 46.4% of the rainfall (against 46.3% of current levels). On the other hand, if the entire biome were to return to its native cover, predominantly of sparse shrub species, the recharge rate would be only 26%.

This does not mean that the entire Cerrado should give way to agriculture, points out Rodrigues, not least because of the importance of natural vegetation for the region’s biodiversity. What is not possible is to insist on the myth of agriculture as a predator of water resources.

The study by Rodrigues and Cambraia Neto – “Impact of land use and occupation on potential groundwater recharge in a hydrographic basin in the Brazilian Cerrado” – was published in the book “Groundwater: recent advances in interdisciplinary knowledge”, edited by the International Association of Water Resources (IWRA).

Understanding water cycling and how underground stocks are recharged is in line with a guideline from the United Nations Educational, Scientific and Cultural Organization (Unesco), which highlighted, in a 2022 report, that “in terms of climate adaptation , the ability of aquifer systems to store excess water can be exploited to improve year-round freshwater availability”.

Read below the interview of researcher Lineu Rodrigues to People’s Gazette.

Many people still associate agricultural activity as something that tends to deplete water resources. That makes sense?

First, the water in the world is constant, it doesn’t change, it cycles. It is part of the ecological cycle. So, there are places where the water presents this temporal and spatial variation. This place, which is the hydrographic basin, has the capacity to support the activities there. If economic activities grow a lot, regardless of whether it is agriculture, industry or a bank, there will be a lack of water. But it’s not that the water is running out. This is impossible, because water circulates, its quantity in nature is finite, but it is enormous, more than enough to meet the various uses. I’m talking about fresh water. And when we talk about groundwater, it’s another world to be explored. In this study, we evaluated precisely the recharge – which is important mainly for the water that appears in the dry period –, how this recharge behaved.

It is a classic mistake of your journalist friends, especially, to say that agriculture is drying up dams. In the Araguaia River, in Goiás, there is no period of water scarcity. What you have is an infrastructure problem. It rains a lot now and the water goes away, 85%, 86% goes to the sea. And we wanted to have more of this water up here. Agriculture actually contributes to recycling good quality water. There is no relationship between agriculture and water scarcity.

The Araguaia is a river that is the passion of Goiás, there are many people who live there as a tourist. Whoever has a house by the river – and that’s for whom a lot of money – any little thing they see, they go to court complaining. It’s classic conflict. And since there is agriculture, they blame agriculture. As well as Araguaia, there are several other regions. What we have to do, in terms of water resources, is to organize the rivers, manage water well, have a good infrastructure strategy. The dams are an excellent way to hold the water and later make the rivers permanent. We need to work on these issues. And define priority uses. I think producing food is a good use of water.

Your study compared two hypothetical situations. All Cerrado back to its native cover and all Cerrado cultivated with soy. Would the recharge of water in groundwater be greater with the cultivation of soybeans?

Yes, bigger. And this is important to be well explained. There are two types of water. Blue water and green water. Blue water is that water that is in the river, which is used for irrigation, for the urban center, for industry. And green water is water that rains and stays in the soil to be used by plants. Basically the native vegetation uses the bulk of this green water. And the native vegetation has a deep root system, I’m talking about six, seven meters of root. This root is using water, so the soil becomes drier and when it rains, the tendency of the rain is to recharge this soil profile. The water is trapped there.

In the case of agriculture, the system is shallower, and when it is still irrigated, the soil is generally wet. The rain comes and this water ends up infiltrating and going to the aquifers to recharge our rivers during the dry season. This is what happens in physical terms. Native vegetation, having a deeper root system, ends up using more water from the system when compared to an agricultural crop.

So in terms of replenishment, doesn’t agriculture steal water from the system?

No. There are two types of agriculture: rainfed agriculture, which depends heavily on green water, rainwater, and irrigated agriculture. In the irrigated area, when rainwater is lacking, you supplement it with river water, the blue water. So, agriculture, in fact, when it’s done well, mainly with good soil conservation work, it contributes to the hydrological cycle. There is no such competition, this stealing, this running out. If agriculture doesn’t use it, who will use it? The native vegetation. And if the native vegetation does not use it, who will? It will run out to sea.

And in the sea it will evaporate. 86% of the world’s rain is evaporated seawater. The water will evaporate, it will cycle anyway. Unless it’s in a glacier, where it can sit still for 2 million years, or in a deep aquifer, where it can sit still for ten thousand years.

In the Cerrado, from April it doesn’t rain anymore. But the rivers still have water. This water is from the aquifer, the result of recharge. Reload from where? Most of our agricultural areas

This greater recharge made possible by the crop compared to the native cover, it somehow contributes to the biome of the region?

Contribute yes. And it contributes 100% if it has increased recharge, if it has increased availability for the dry season. Because the water will seep in. Every practice you do that improves water infiltration into the soil increases recharge. And good agriculture is doing a good job of soil conservation that favors this water to infiltrate. Then the water seeps in. She makes a very slow horizontal movement. When it infiltrates then, it will move slowly horizontally and will reach the river in the dry season, when you need it.

Why don’t rivers in general dry up? Because there is water from the aquifer that is reaching the river. Because if it hadn’t, it would have ended, because it’s been raining less. Here in the Cerrado, where we did our studies, from April it doesn’t rain anymore. But the rivers still have water. This water is from an aquifer, the result of recharge. Reload from where? Most of our agricultural areas.

What about the criticism by some that Brazilian agriculture exports water in the form of grains?

This is the silliest speech I’ve seen. Whatever you do, the water will be returned with an inferior quality. Except in agriculture, which sometimes has an auxiliary quality and even manages to improve. There is no such thing as exporting water. The product that is produced here goes with a certain amount of water, but this water, after being consumed by animals or humans, is returned to the system. It is not a product that ends, it keeps cycling. This discussion of exporting water is fruitless in the management of water resources. If this water is not used, it goes to the sea. And the sea will take it to the world afterwards, by sea currents, and it will evaporate. A little water is also exported from there to here, via industrialized products, which required water there to produce. So what’s the balance? Is it positive? Is it negative? How does this impact the water management of a country? It is not something that can be randomly placed, it has to be supported and the connection shown.

Embrapa’s research has already demonstrated, over the years, that the soil of the Cerrado is naturally weaker. And that the producers built fertility harvest after harvest, with limestone, fertilizer, organic matter, green cover. So, can we say that agricultural work has contributed to the balance of the biome and enrichment of these soils?

Certainly, if you think about food production, the mathematical equation today does not complete without Brazil. Brazil is a fundamental part. Take Ukraine, which fought with Russia and the world went into crisis. If you take Brazil away, the world will die of hunger. And within the country, you have to think about the Cerrado. This region is strategic. These soils of ours did not produce anything in the 1970s. I’m talking about 30, 40, 50 years ago. They didn’t produce anything. And it was thanks to this soil reconstruction work, mainly with limestone and gypsum, correcting the acidity, which allowed us to have this strong agriculture, with well-preserved soils instead of degraded pastures. Today we have highly fertile soils in the Cerrado producing high quality pastures and every type of crop you can think of. And this greatly favors the water issue.

Where was this study done?

This study was carried out in the Cerrado biome (Buriti Vermelho hydrographic basin, in the Federal District), which represents 24% of our territory, and is the main agricultural frontier in Brazil. Due to the intensification of agriculture, often with irrigation, in some regions you end up increasing this dispute over water use. Therefore, we have to have alternatives to increase water availability, and for that it is necessary to understand the dynamics of groundwater.

We assessed land use and occupation changes in potential groundwater recharge in a Cerrado watershed. We used a model with the current situation, another with the situation of putting only soybeans in the biome, and a third with only native vegetation, to see what would happen with the issue of recharge. We observed that recharge in agricultural crops, as expected, retains 46.4% of the total rainfall, and when we talk about native vegetation, it is 26%. This is not bad, the native vegetation is important, because it takes this water and releases it back into the atmosphere. But in terms of recharge, thinking about the contribution to the aquifer, in the Cerrado region, where we did the study, the agricultural area ends up contributing more to the recharge than an area with native vegetation.