28th Ambassadorship, Month 3, Report 1

Month: May

Free report

Topic: Detrimental Effect of High Input Agriculture

1. Land/soil related problems

a. Soil degradation

Soil degradation refers to decline tin the productive capacity of land due to decline in soil quality caused through processed induced mainly by human activities. It is a global problem. The Global Assessment of the Status of Human-induced soil Degradation (GLASOD) was the first worldwide comparative analysis focusing specifically on soil degradation. Worldwide around 1.96. Billion ha are affected by human induced soil degradation, mainly caused by water and wind erosion (1094 and 548 million ha respectively). Chemical degradation accounted for 240 million ha, mainly nutrient decline (136 million ha) and salinization (77 million ha), physical degradation occurred on 83 million ha, mainly as a result of compaction, sealing and crusting. The processes leading to soil degradation are generally triggered by excessive pressure on land to meet the competing demands of growing population for food, fodder, fibre and fuel. Therefore, the direct causes for soil degradation are unsustainable land use and inappropriate land management. The most common direct causes include:

• Deforestation of fragile lands

• Over cutting and grazing of vegetation

• Extension of cultivation on to lands of low capability/potential

• Improper crop rotations

• Unbalanced fertilizer use

• Non-adoption of soil conservation practices

• Inadequacies in planning and management of irrigation resources

• Overdraft of groundwater in excess of capacity to recharge

The strategies for improving soil quality and sustainability include skilled management, crop rotation, soil and water conservation, conservation tillage integrated nutrient management, integrated water management, integrated pest management and integrated ( crop & livestock system) farming systems etc.

b. Deforestation:

Deforestation refers to the transfer of forest land to non-forest uses and includes all land where the forest cover has been stripped off and the land converted to such uses as permanent cultivation, shifting cultivation, human settlements, mining, reservoirs etc. Deforestation continues to threaten and erode the area under forest cover in several countries of the World. The underlying causes of deforestation are rooted in a complex web of social, economic and institutional problems. They include:

• The combined effects of poverty, skewed land distribution, and rising population pressure

• Increased demand for tropical timber and Agricultural products, and

• International debt obligations, which can lead developing countries to accelerate the pace of forest exploitation in order to earn needed foreign exchange.

Deforestation, together with over grazing, is modifying the climate, and accelerating the erosion of biodiversity, which in turn posing the threat to ecological sustainability and food security.

c. Accelerated soil erosion

Agricultural productivity depends largely on the topsoil (up to 20 cm thickness), as it serves many functions such as support for rooting, supply of plant nutrients, storage and release of soil moisture etc. The loss of the topsoil usually instigated by the activities of man, termed as accelerated soil erosion, is the most serious form of land degradation.

Some erosion, however, takes place through natural processes slowly but some natural processes of decay and regeneration replace this loss. A balance is maintained between soil loss and soil formation, but when vegetation is stripped away, as in deforestation and shifting cultivation, the soil becomes vulnerable to damage by wind and water and the slow rate of natural erosion is accelerated. Along with the eroded topsoil, three major plant nutrients viz., Nitrogen, phosphorus, and potassium ranging from 4.4 to 8.4 tonnes per ha are also lost. Crop yields are reduced by erosion through less supply of plant nutrients, shallow depth of soil, poor structure, surface sealing and crusting, which leads to reduced water infiltration and poor seedling establishment , In addition to this on-site effects, the off-site effects of erosion are also of serious concern for the sustainability of Agricultural productivity.

d. Siltation of reservoirs

 Siltation of reservoirs is the major off-site effect of soil erosion by water. The process of deposition of soil particles carried by water is called sedimentation or siltation. Sedimentation or siltation is both a serious and growing problem, but its severity varies from one reservoir to another. Usually, every reservoir is provided with certain storage capacity to accommodate for the natural sedimentation rate, which capacity is called its dead storage. Sediment accumulation is not controlled in most of the reservoirs and they are irreversibly getting filled with sediment and constitute the most non-sustainable water resource system in Nepal today. These increased rates of siltation are adversely affecting capacity of the reservoirs to sustain the gains in productivity achieved over the past decades. In addition to the drastic reduction in life of the projects involving huge investments, these accelerated rates of siltation of reservoirs and other water storage sites are causing floods that effect life and property quite often.

2. Irrigation related problems

a. Rise in water table

A feature common to many irrigation commands of surface water projects is excess recharge over discharge of groundwater, leading to rise in water table. The irrigation command areas are recharged not only by rainfall infiltration, but also by seepage from reservoirs, canals, distributaries and field channels, and return circulation of irrigation water. The rise in groundwater table ultimately leads to waterlogging, salinization & alkalization in irrigation commands.

b. Water logging Presence of excess water in or near the root zone or standing water above the soil surface for any substantial period of time known as water logging. Water logging is said to occur when the water table rises to within the root zone of crops. The water table, which is considered harmful would depend upon the type of crop, soil type and water quality. The actual depth of water table, when it starts affecting the crop yield adversely, may from zero for rice to about 1.5m for other crops.

c. Salinization & Alkalization

The most well understood problem is of salinization and alkalization of soils. The problem is increasing at an alarming rate in the canal-irrigated areas through increase in water table, poor water management practices and lack of drainage. The rate of increase of the problem is fast in the black soil regions of heavy texture, with serious drainage problem. The vast irrigation development without drainage, adequate field channels and water management technology has seriously reduced the effectiveness of irrigation system and aggravated the problem of salinity, alkalinity and water logging. Excessive amounts of soluble salts, mainly Cl and SO4 of Na, Ca and Mg limit optimal crop growth due to direct toxic effects of salts and increased osmotic stress which physiologically inhibits the availability of soil water.

d. Over exploitation of groundwater:

In many arid and hard rock areas, overdraft and associated quality problems are increasingly emerging. The over draft of groundwater has resulted in:

• Failure of shallow wells,

• Shortage of water supplies

• Deepening of wells

• Increased pumping lights and pumping costs

• Increased energy requirements

• Sea water ingress in coastal areas

• Increased inland salinity in groundwater

• Land subsidence due to compression of the aquifers

Although groundwater is a renewable resource, it is not inexhaustible. If groundwater supplies are to be maintained perennially, the recharge must balance discharge. However, all that recharged is not necessarily recoverable. The groundwater withdrawal must be limited to safe yield, which is defined as the amount of water that can be withdrawn annually from a groundwater basin without producing an undesired result. While the permissive sustained yield is the maximum rate at which water can be economically and legally withdrawn perennially from a specified source, without bringing about some undesired result. It is always less than natural recharge and in limited by physical or other constraints