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Abstract
SUMMARY AND CONCLUSION
The objective of the present study was to evaluate the effect of biuret in urea, as a nitrogen fertilizer on wheat and barley under calcareous soil condition, as affected by organic matter application. Also, the incubation of urea and biuret in soil was carried out, with or without organic matter to identify its decomposition products and, to better understand the results obtained from the pot experiments.
5.1. Pot Experiments
Two pot experiments were carried out in the seasons 2004 and 2005. Plastic pots were filled with 3 kg soil, and each pot has a 25.0 cm long, with a hole in the bottom. The pots were uniformly packed to a constant soil bulk density of about 1.3 ± 0.02 g/cm3, leaving a 3 cm of free upper space, for irrigation practices. Wheat (Triticum aestivum L.) and Barley (Hordeum vulgare L.) Cultivars are chosen for there experiments. Wheat and Barley seeds were sown at December, 1st 2004. The plants were thinned to four plants per pot, after 15 days from planting. Crystalline urea, with varying proportion of biuret, was mixed to prepare urea with different percents of biuret. These mixed urea were side banded; 1 ½ inches from plants in the seed bed, at a rate of 0.78 gm for wheat, and 0.45 gm for barley per pot in two equal doses . The first dose was after 15 days from planting, and the second was added after 45 from thinning. The experiment design was split plots with three replicates. The biuret treatments were in the main plots, and the organic matter was in subplots. The first factor (biuret) was applied at rates of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 % in one dose. The second factor (organic matter) was applied at with or without organic matter. For the organic treatment the pots were amended with Peat moss as a source of organic matter, at rate of 2% before 15 days from planting.
5.2. Incubation of biuret and Urea Experiments
The incubation laboratory experiment was conducted, to study the effect of Peat moss on the rate of biuret hydrolysis at 27º C. Plastic cups (36) were filled with 100 g of soil and amended with Peat moss at rate of 2%. Another set of cups left without Peat moss application. Biuret at rates of 0, 10, 20, 30, 40 and 50 mg N per 100 g soil were added. The treatments were replicated three times. The period of incubation was 14 days, and the soil moisture content was kept at the 70% of soil field capacity, by wetting the soil every two days. After incubation period, the soil systems were extracted with 2N KCL, and analyzed for NH4-N, NO3-N, NO2-N, urea-N and biuret-N. The total N before extraction, and the nonextractable N was calculated.
Another incubation experiment was conducted, to study the effect of Peat moss on the rate of urea hydrolysis. The same previous experiment was carried out, but using the urea instead of biuret, at rates of 0, 10, 20, 30, 40 and 50 mg N per 100 g soil. After incubation period, the soil systems were extracted, and analyzed for NH4-N, NO3-N, NO2-N and urea-N. Also, the total N before extraction, and the nonextracted N was calculated.