Temporal Changes in Soil Urease, Alkaline Phosphatase and Dehydrogenase Activity in Rainfed Wheat Field of Pakistan

Soil enzymes play a vital role in nutrient mineralization and their activity is an excellent sensor in predicting the capacity of nutrient supply to plants. Temporal changes in three soil enzymes activity (urease, alkaline phosphatase and dehydrogenase) in rainfed wheat were studies through field experiment conducted at the research farm of Pir Mehr Ali Shah Arid Agriculture University Rawalpindi, Pakistan. Wheat (Triticum aestivum L.) variety Chakwal-50 was grown with N and P combined fertilizer treatments as NP (100:80 kg ha) and 1⁄2 NP (50:40 kg ha), and CK (no fertilizer applied). Twelve experimental plots each of size 6 m × 6 m were prepared to accommodate three treatments each with four replications. The layout of the experimental plots in the field was according to Randomized Complete Block Design (RCBD). Soil samples were taken from each experimental plot at 0-15 cm depth on monthly basis from crop sowing up to the time of harvest and analyzed for soil urease, alkaline phosphatase and dehydrogenase activity, and for nitrate nitrogen and available phosphorus. The data collected were analyzed by two ways ANOVA to quantify the effect of fertilizer treatments and sampling timings on soil enzymes activity and nutrients availability. Results showed that enzymes activity increased from October (sowing time of crop) to November, followed by slight decline in December, thereafter maximum activity was observed during February and March (vigorous crop growth period) which again decreased up to May (crop maturity time). All the three enzymes showed strong positive relation with rainfall but weak relation with atmospheric temperature. Enzymes activity were positively related with P availability but negatively related with nitrate contents in the soil. It was found that the application of N and P fertilizers significantly (P<0.05) increased the activity of all three soil enzymes (urease, alkaline phosphatase and dehydrogenase) over control. A 75.5 % and 22.0 % higher alkaline phosphatase and dehydrogenase activity in NP treatment was found compared to that in the control,