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  • Malkiat Singh Duhra

Soil, Trees and Ecosystem

The soil of North-West India (Punjab, Haryana, and western UP) has degraded due to intensive and monoculture cultivation of crops, specifically growing wheat and rice, over large areas since 1970. Carbon content of top soil in this region is 0.05%, while healthy soil is expected to have 2% carbon content. During the 1940s and 1950s, there were a large number of trees even in cultivated areas. Land consolidation during the 1950s -1960s and intensive cultivation after 1965 resulted in the cutting of trees at a large scale. These two factors (tree cutting and intensive cultivation) degraded the soil. Now, it is very urgent to take necessary steps to improve soil health by growing leguminous crops, reducing the area of rice and wheat, and planting trees to overcome problems like the depletion of soil, pollution and lowering down the water table to a dangerous level. Agricultural scientists and the government have been advocating crop diversification to save ground water. Farmers don’t seem to be keen to shifting to other crops unless they are given assured markets and granted prices for their produce. The government should purchase all crops at minimum support price (MSP), as is done in case of rice and wheat.

Trees stabilize and prevent soil erosion, increase aeration and water infiltration, while adding nutrients to the soil. Soils with higher organic matter content supplied by trees reduce the need for the use of fertilizers to produce crops. Pesticide and fertilizer use contribute to local air and water pollution, which can lead to a range of human health issues. Additionally, reducing their use results in fewer pollutants reaching and contaminating the water and lower crop production costs for farmers.

Soil health describes the sustained capacity of soil to function as a living ecosystem, supporting plant, animal and human life. Soil contains billions of bacteria, fungi, and other microbes that are vital to soil fertility and ecosystem functioning. Overall, soil health plays a key role in determining agricultural productivity, environmental resilience and ecosystem susceptibility. This is due to an ability of soil to store, cycle and transform nutrients, as well as providing a medium in which plant roots can become established. Additionally, soil aids in rain, snowmelt and irrigation control, while filtering water and trapping any harmful pollutants that could go on to contaminate local water bodies.

Since land productivity is largely determined by soil health, land that has degraded is made up of soil with low biodiversity. Fertility soil can take hundreds of years to form and can become easily eroded where biodiversity is low, reducing its ability to support crops and store water and carbon, and resulting in the release of additional carbon emissions into the atmosphere. It is estimated that 2 to 5 million hectares of arable land is lost to soil erosion annually and it’s estimated that if this extent of land degradation continues, we will see a 30% reduction in food production by 2040. Restoring soil biodiversity not only increases agricultural productivity but also has the potential to trigger at least half of the emission reductions required to limit the global average temperature increase to below 2 C above pre-industrial levels, set out in the Paris agreement.

Trees Maintain and Optimize Soil Health:

Forests contribute to the formation of soil by laying down roots that aid in the weathering of rock material, while adding foliage and encroaching soil in place. Adding organic content in the form of foliage allows the soil to hold more water, with every 1% increase holding a further 60,000 litres per acre. Furthermore, roots of trees improve the soil structure by acting as underground water channels, while root growth breaks up soil, creating the space required for increased aeration and drainage. Trees attract and maintain large populations of microorganisms that live in the soil, through supplying additional organic matter, encouraging maximum soil biodiversity. Carbon sugars are produced via the roots and obtained by microorganisms that supply trees with nutrients in return. The mutually beneficial relationship improves the soil quality since the more microorganisms that live in the soil, the more fertile the soil becomes.

The rate at which erosion occurs is largely down to the amount of tree and plant cover in a given area. This vegetation offers defence against wind and rain. Ground cover and the leaf litter layer beneath forest canopies act as ideal protection against soil erosion. Where vegetation has been removed, soil erosion becomes accelerated and the likeliness of flooding increases. Some type of trees can enrich the soil with additional nutrients. Leguminous tree roots have the ability to add nitrogen to the soil via root nodules, supporting the growth surrounding plants. Meanwhile eucalyptus and jack pine tree species releases substances from their roots that increase the availability of phosphorus in the soil. These fertilizer trees are being integrated with crop land across the globe due to their capacity to improve degraded soil conditions caused by continuous crop cycles that prevent the landscape from recovering.

Trees offer the soil protection from extreme sunlight exposure. This is specially important in hot climates where soil microorganisms risk becoming dormant or drying out, resulting in infertile soil. Trees also ensure a more consistent supply of water to the soil by regulating rainfall, slowing down the rate runoff in dry conditions while sheltering the soil from heavy rainfall, thus reducing erosion. Some species of trees provide a habitat for bacteria and fungi in their root structure. These organisms perform nitrogen fixation, which is a significant factor in soil fertility. Trees also recycle nutrients by pulling them up from deeper layers of the ground and bringing them up to the surface through the decomposition of leaf and plant litter to for soil organic matter. Trees increase evaporation (water is lost to the atmosphere) and enhance infiltration capacity where the water stays in the ground. Trees reduce the amount of storm water runoff, which reduces erosion and pollution in our waterways and may reduce the effects of flooding. Many species of wildlife depend on trees for habitat. Trees provide food, protection, and a home for many birds and animals. The soil shade and organic materials under trees help hold moisture so it can be absorbed and replenish ground water levels. Trees allow more water to percolate to reach groundwater and it can also provide a cooling effect and prevent evaporation.

In India, farmers have to plough the fields many times to destroy weeds. No-till results in more organic matter in soil and less erosion, which means more fertility, less fertilizer, and higher yields. Ploughing reduces a farm’s long term productivity by exposing the organic matter-rich top soil to the surface. This create fluctuations in soil moisture and temperature, which soil organisms cannot handle. Tilling also reduces the pores in the soil, which would otherwise have allowed water to infiltrate the soil and recharge groundwater. The number of earthworms per square meter varied between 119 in ploughed land and 160 in non-till land. Earthworms play important roles in adding nutrients to soil. Tilling also effects certain fungi in soil that form beneficial symbiotic relations with plants; receiving sugars from plants and supplying them with nutrients such as phosphorus and nitrogen.

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