Part 2 : SOIL CONSERVATION

Imprimer

The soil is a complex world where biotic elements interact with each other and with the abiotic elements of the soil environment. It is a shelter for billions of organisms and microorganisms. The physicochemical network is concentrated in the rhizosphere and the detritusphere (plant litter) that covers the soil surface. Respecting the balance of this dynamic universe is a determining factor in soil fertility. Soil disturbance by humans (plowing, chemical inputs, etc.) or natural factors (heat stress, drought) degrades or even destroys its quality. Soil conservation agriculture (SCA ), increasingly practiced by farmers, is a non-disruptive practice that aims to protect soil health. SCA is based on three pillars: direct seeding, diversification of crops in time and space, and maximum soil coverage with crop residues. Human interventions are limited to the strict minimum, such as the use of herbicides.

The ecological study of soils integrates the abiotic components,  rocks and minerals, with the its biology, represented by plants, animals and micro-organisms. It considers the soil as a habitat for both animals and plants that draw from it the nutrients necessary for their growth.

This holistic vision helps us to better understand that soil health can be fragile;  although possessing a certain resilience, soil can be damaged by  human interventions. The latter must be prudent and as non-disruptive as possible.

The soil is at risk of erosion, due to the wind and water runoff that deprive it of part of its inherent structure and  richness. It is up to us to protect the soil against these erosive forces. One question obsesses farmers: how can I protect my land against degradation? They know that their practices must be the least disruptive, that they must not turn the soil over or plow it deeply, since these actions may unbalance or destroy its fragile ecosystem. The lighter the human footprint, the better the soil will be.

Soil conservation agriculture is an excellent answer to the grand challenge in  agriculture: how to properly feed humanity without degrading the soil.

The cornerstone of soil conservation agriculture is the practice of direct seeding, a concept that is spreading worldwide. A very small furrow is dug in the ground to place the seeds in before covering them, and the previous crop’s residues are left as a protective mulch. Consequently, soils are ploughed less and less deeply, and the surface is covered to prevent its degradation through erosion.

Soil Conservation agriculture

Many practices on farms are classifed under SCA. One example is plowing fields across the land – along the contour – rather than down the slope to reduce runoff erosion. Another example is the practice of planting trees on slopes and at the end of fields, beside ditches and waterways. Trees and other vegetation act as a buffer zone to trap water, sediments and the nutrients contained in the runoff water, so they are retained on the land.

Ultimately, SCA achieves two important goals. The first goal is to stabilize the soil, keeping it in place, while retaining residues and other natural materials on the surface to keep the soil warm and moist, creating the optimal conditions for seed growth.

The second objective, not insignificant for farmers, of this non-intrusive practice is to reduce production costs, particularly in terms of energy and wear and tear on equipment. In addition to saving money, the farmer saves time because deep plowing is time-consuming.

Soil Conservation Agriculture is not the same as organic farming. The former is primarily concerned with soil stabilization, preserving its structure by using the appropriate farming equipment that can achieve this purpose. In contrast, organic farming  is primarily concerned with the growth of plants, their treatment, and  soil fertility management without any chemical agents. Thus, rather than resorting to fungicides and other pesticides, organic farming will seek to use the soil biology to bio-protect plants against pests. Weeds are generally controlled by mechanical tilling, and with mulch barriers (geotextile or natural materials). Organic farming, finally, only uses organic fertilizers, animal manure, compost and other recycled materials. The SCA can use these practices as well, but it does not impose any  prohibition  from managing weeds by chemical weeding.

The Degradation of Soil

Ultimately , climate change and human disturbance are leading to global and irreparable soil degradation. Thus, according to the FAO, the surface area of arable land per capita will decrease by 50% in the next 50 years. The current situation, according to the FAO, would not be very encouraging: 33% of soils would already be degraded while 24 billion tons of fertile land would be lost each year. I think we must be careful when reading the figures. The FAO prediction is based on two relatively unpredictable assumptions. The first assumes that the surface area of available arable land is an immutable given. The second assumes a correct assessment of the demographic evolution of the world population, which is somewhat risky. The FAO figures are certainly alarming but they are only an extrapolation of past increase in the population. I do not know what the world’s population will be in 50 years.

The predictions use large-scale models that cannot reflect the situation at the farm level. They include indicators that reflect the most pessimistic, worst-case scenarios. The value of such predictions is  as a warning signal that encourages farmers to take better care of their land.

In the same vein, some estimate that 50% of the world’s land is poor in nutrients. This figure seems excessive to me. Certainly, some soils can be poor in nutrients because of their inherent physical and chemical properties. There is good evidence that soil fertility can be easily enriched by a supplementary supply of fertilizers – whether these are commercial fertilizers or recycled organic materials – with biological nitrogen fixation by natural soil microorganisms also improving the soil fertility. Nutrient poverty is also often due to human failures or, more precisely, dysfunctions in the agricultural value chain. The market and/or the economic system can make access to fertilizers difficult in some regions of the world. This is the case in Africa where logistical failures force some ingenious minds to consider delivering small bags of fertilizers to farmers by drone.

Secondly, the FAO is alarmed by the loss of soil biodiversity . The billion bacteria contained in a gram of soil are said to be in continuous decline. Of course, on the one hand, erosion by wind and rain carries away the bacteria. But on the other hand, I note that farmers are very attentive to preserving the richness of their soil. They compensate for nutrient removal by the crops and nutrient losses through erosion by adding straw and residues to their land. Indian and Chinese farmers know this well, as they systematically resort to this practice, which encourages the multiplication of bacteria.

Third, many people are alarmed by the release of carbon into the air by agriculture. In the global soil profile to a depth of 1 meter, there is three times more carbon than the world’s atmosphere. Soil degradation is said to release carbon that adds to the CO₂ concentration in the air. In fact, the figures I know are more optimistic. Advances in good agriculture practices have made the land 20% greener than it was 30 or 40 years ago, which means that the amount of vegetation on Earth has increased, leading to more carbon sequestration by the soil. This is a very positive phenomenon.

Agriculture has made great strides. Farmers are encouraged to plant more crops, diversify crops, use cover crops for uncultivated plots, and use green manures on their cultivated lands. Cover crops stabilize the soil and sequester carbon.

In conclusion, despite some frightening figures, I remain optimistic. We have done a lot of work thhrough education and outreach that has made farmers aware of the importance of preserving the balance and richness of their land. Some farmers may prioritize profit over soil health. This is a short-term calculation. The vast majority of farmers know that only the proper conservation of their soil will ensure the financial sustainability of their farm, now and for the future generations.