Soil Nitrate Accumulation in Response to Agricultural Activities.

Pakistani growers consider excessive N fertilization an insurance against yield losses. Moreover, indiscriminate use of high nitrate content sewer water for irrigating crops is common. Over time these two factors can lead to excessive nitrate accumulation in soil that can impact the environment. This study identified and evaluated nitrate accumulation at different soil depths in 35 districts of Punjab province, Pakistan. Soil samples were randomly collected at 0 - 15, 15 - 30, 30 - 60, 60 - 90, and 90 - 120 cm depth and analyzed for nitrate and other properties using standard methods. Agricultural soils in the densely populated rural areas were high in NO3 concentration (~ 16 mg kg-1) in both summer and winter. Extensive use of sewer water for irrigation (17 mg kg-1) caused a significantly greater NO3 accumulation than rainfed agriculture (11 mg kg-1).  Averaged across soils, wide-spread nitrate accumulation was found at 2 - 3 feet depths, and the accumulation was more pronounced in sandy soils. However, clayey soils (17 mg kg-1) had higher NO3 accumulation than sandy soils (12 mg kg-1).