FAISALABAD (April 14 2009): The loss of organic matter is major concern for Pakistans croplands, as the organic matter plays an important role in the physical structure of soils and, more importantly, is a medium for biological processes. In a report on Irrigated Agriculture and Cropland, an ADB study says that the purely mineral content of soils contains nutrients that do not become available to plants until soil micro-organisms have processed them into usable forms.
Organic matter thus helps maintain the populations of beneficial micro-organisms. The `green revolution,` however, having provided farmers packages of seed, fertiliser, and water, has led them to neglect the use of organic manure, choosing instead to burn it as fuel. As a result, 96 percent of cropland in Punjab is deficient in organic matter content.
According to the ADB study, a recent assessment based on the aggregated findings of reconnaissance and detailed surveys of soil erosion by the Soil Survey of Pakistan suggests that the soil structure in Punjab and the North-West Frontier Province (NWFP) has not changed, while areas in Sindh and Balochistan have become prone to severe erosion between 1993 and 2003. Further research is, however, needed to validate these findings and determine their underlying causes.
The ADB study said that Pakistan depends heavily on irrigation agriculture, which accounts for more than 90 percent of its food and fibre, and also for most of its fodder production.
However, irrigation (based on perennial canal system) also contributes to several environmental problems. For instance, up to 30 percent of the canal command area becomes waterlogged after the monsoon season. The irrigation of crops with heavy water requirements (such as sugarcane and rice) deposits 20 million tons of river salts every year, and moves salts in the soil profile to the surface.
The resulting salinisation reduces crop yields, while the use of groundwater containing relatively high levels of dissolved salts leads to sodicity, especially in clayey soils, again reducing crop yields. Salinity has other ratchet effects. Farmers, especially in Sindh, use excessive amounts of water to flush away salts from soil surface and top horizons, but end up generating larger volumes of saline effluent for downstream ecosystems and users.
Irrigation efficiency in Pakistan is measured at around 35 percent. In other words, ADB report said, about two-thirds of the water diverted from rivers to canals, distributaries, and farmers fields is lost in conveyance, delivery, and application. Resultantly, there has been no improvement in crop productivity per unit of water use. The drainage of effluents from waterlogged and saline fields has damaged ecosystems, including downstream freshwater lakes.
It may be recalled that since the `green revolution` of the 1960s, Pakistans agriculture has become highly dependent on external inputs. The application of chemical fertilisers has doubled from 1.9 million ton to 3.8 million nutrient tons between 1991 and 2006. Since 2003, returns to per unit use of fertiliser have diminished except for last two years, showing an improved productivity (Figure 5).
The leaching of fertilisers from the soil has resulted in the eutrophication of natural water bodies and toxic algal blooms. Pakistan has no capacity to detect, analyse, and assess the risks of cyanobacteria-produced toxins.
High concentrations of nitrates in drinking water supplies can cause `blue baby` syndrome (the lowering of oxygen content in the blood, causing respiratory and digestive problems in new-borns). Pesticides are persistent and bio-accumulate in organisms, and the destruction of fish farms immediately downstream is only the first in a series.