The nitrate and nitrite contents in cereals, pulses, vegetables and canal water used for irrigation were determined in samples collected from the Agricultural Research Stations of the four provinces of Pakistan. Nitrate concentrations in cereal grains were generally low (90 to 316 ppm). Two varieties of rice obtained from the Swat Research Center NWFP were found to contain maximum accumulation of nitrates(upto 2780 ppm). Results of province-wise comparison indicated that all means of nitrite contents were statistically non-significant.
The nitrate and nitrite values of common pulses varieties grown in Pakistilfl ranged from 72 to 209 and 3 to 11 ppm respectively.
The vegetables were found to contain maximum accumulation of nitrates and nitrites (110 to 6490 and 10 to 47 ppm respectively). Ritter gourd, radish, spinach and sugar beet were the major accumulator of nitrates and nitrites. The nitrate and nitrite contents of okra, potatoes, turnip and carrot vegetables showed significant differences in their mean values. Reduction of nitrate into nitrite in vegetables was comparatively more than in cereals and pulses.
The nitrate and nitrite contents of canal water used for irrigation had the highest concentration in NWFP province (72 ± 8 and 15± 3) ppm.
The field experiments were conducted on wheat and vegetable crops (winter and summer season) to study the effect of application of nitrogenous fertilizer on the accumulation of nitrates and nitrites. 1 he soil used was analysed for total nitrogen, nitrates, nitrites, organic matter, saturation (%), soil pH, available potassium and phosphorus before and after the cultivation of crops.
The nitrate and nitrite contents did not vary significantly in seeds of different sets on the application of the fertilizer at different stages of crop growth.
Results of field experiments in wooden crates at varying rates of nitrogen fertilizer in vegetable crops indicated significant differences in their nitrate and nitrite contents. High doses of fertilizer tended to increase the accumulation of nitrates and nitrites.