Excessive N fertilization of crops is considered by producers as an insurance against yield losses in Pakistan. High nitrate content sewer water for irrigating crops is common in Pakistan. Increasing nitrate concentration in vegetables, soil and drinking is a public health concern.
Nitrate by itself is non-toxic, however, its metabolites are related to Gastric cancer , Methaemoglobinaemia (blue babies syndrome in infants and elderly people), and blocking of iodide uptake (neuro-transmitter). The USEPA has set a standard for 10 ppm nitrate in drinking water.
Thus, a reduction of nitrate pollution in plant-soil-water ecosystems is highly desirable. The present study was conducted to evaluate the extent of nitrate pollution in vegetable-soil-water ecosystems of Punjab, Pakistan
Data collection Collection of vegetables Summer and winter vegetables were collected from all 35 districts in Punjab, Pakistan. In each district, 9 markets and agricultural fields were selected to collect: Carrot, Eggplant, Okra, Onion, Potato, Radish, Spinach, Squash, Tomato, and Turnip. Total number of vegetables = 35 x 9 x 2 = 630
Sample collection points from different localities in Punjab, Pakistan
Data collection…... Collection of soil samples Soil samples were randomly collected from all 35 districts. In each district, 4 soil samples were collected at 0 - 15, 15 - 30, 30 - 60, 60 - 90 , and 90 - 120 cm depth. Total number of soil samples = 35 x 4 x 5 => 700
Data collection.... Collection of water Water samples were randomly collected from all 35 districts in summer and winter. In each district, 20 samples of 5 different types of water samples were collected.
Data collection..... The water samples collected from Water & Sanitation Authority = Deep well water (~ 400 ft) Medium Depth Pump = Medium well water (~ 200 ft) Shallow Depth Pump = Shallow well water (~ 100 ft) Tube-well = Water collected from rural areas (~ 300 ft) Bottled water = As standard Total number of samples = 35 x 2 x 20 => 1400
Sample analysis Vegetables were analyzed for N itrate, phosphorus, potassium, iron, manganese, zinc, copper and boron content Soils were analyzed for N itrate, pH, organic matter, Ec, phosphorus, potassium, iron, manganese, zinc, copper and boron content
Sample analysis………. Water samples were analyzed for Nitrate, pH, Ec, bi-carbonate, carbonate, residual sodium carbonates, sodium absorption ratio, chloride, sulfate, calcium/magnesium, sodium, phosphorus, potassium, iron, manganese, zinc, copper and boron content
Data organization and statistical analyses Vegetable, soil and water data were organized and a number of suitable predictor variables were created for multi-variate statistics . The variables were: Division - Different locations Population density - High, medium and low Season - Summer and winter Types of water Types of vegetables Agricultural intensity - High, moderate, and low Sewer water use - High, moderate, and low Types of soil, and soil depth
Data organization and statistical analyses…. Multi-variate statistics were performed as follows: Mean and standard error of mean Analysis of variance Repeated analysis Duncan multiple range test (DMRT) To evaluate predictor variables Simple and interactive effects on nitrate pollution of vegetables, soil and water samples
Nitrate concentration of drinking water sources in different divisions (cities)
Seasonal variation in nitrate concentration of drinking water sources
Nitrate pollution of drinking water sources as influenced by agricultural activities
Nitrate pollution of drinking water sources as influenced by sewer water-use
Nitrate pollution of drinking water sources as influenced by soil texture
Conclusions Greater Ag-intensity and sewer water use for irrigation significantly increased nitrate pollution. Among the winter vegetables, nitrate accumulation was highest (> 5000 ppm ) in radish/spinach and lowest (<1000 ppm ) in potatoes. Among the summer vegetables, nitrate accumulation was highest (~ 2000 ppm ) in eggplant and lowest (<1000 ppm ) in tomatoes.
Conclusions….. Averaged across soils, wide-spread nitrate accumulation was found at 2 - 3 feet deep The nitrate pollution was more pronounced in Sandy Clay Loam than other soils
Conclusions….. Except deep well, nitrate pollution was more abundant in medium, shallow and tube-well water The medium, shallow and tube-well drinking water sources were easily affected by agricultural intensity, and sewer water use for irrigating crops