Abstract
Heavy N losses are always associated with urea fertilizer application therefore, improving its efficiency is crucial to reduce economic and environmental losses related with its application. The viable approach to reduce the N losses from the surface applied urea is to coat it with sulfur, urease inhibitor and other biodegradable materials. Field experiment were conducted to investigate the impact of super and urease coated urea on growth, yield, yield components and N uptake in maize under calcareous soil conditions of Khyber Pakhtunkhwa (KPK) during 2011-12. The experiment was conducted in a randomized complete block design (RCBD) with 4 replications each. Urea coated with urease (agrotain) and nitrification inhibitors (super urea) were applied at 90 kg and 120 kg N ha -1 in 2 or 3 splits. The fertilizer treatments were applied at sowing, after 30 and 60 days of sowing (DAS), respectively. The results showed that inhibitors treated urea significantly improved the growth, yield and yield components of maize crop over granular urea and control treatment. Super urea shows its superiority over agrotain in terms of increased yield. Inhibitors application at 90 kg N ha -1 has pronounced effect than 120 kg N ha -1 . Three splits of coated urea performed better than 2 splits. The highest improvement of 38.06% in grain yield and 45.13% in total N uptake was obtained in treatment receiving super urea at 90 kg N ha -1 compared with granular urea at 90 kg N ha -1 . Agrotain treated urea at 90 kg N ha -1 gave the next highest improvement of 30.55% in grain yield and 38.87% in total N uptake than granular urea and control plots at 90 kg N ha -1 . These results suggest that the combined use of urease + nitrification inhibitors
Highlights
Urea has been shown to have lower N use efficiency in many cropping systems compared to other N fertilizers, meaning that a large percentage of the applied fertilizer N is not being used for productive purposes and is essentially lost [1]
Agrotain is quickly converted in soil to its more effective oxygen analogue N-(nbutyl) phosphoric triamide (NBPT), which forms a tridentate ligand with the urease enzyme, slowing urea hydrolysis, reducing NH3 volatilization from surface applied urea, and increasing N uptake and yield in a range of crops
The results obtained on the effect of urease and nitrification inhibitors on yield and N uptake of maize are presented and discussed as under: Yield Components: The results obtained on plant height, ear length, number of ears plant-1, number of rows ear-1, number of grains rows-1, number of grains ear-1 and 100 grain as influenced by N inhibitors and split application of urea are reported in Table 2 and 3
Summary
Urea has been shown to have lower N use efficiency in many cropping systems compared to other N fertilizers, meaning that a large percentage of the applied fertilizer N is not being used for productive purposes and is essentially lost [1]. Urea is quickly hydrolyzed within 1 to 2 days by soil urease to NH4+, hydroxyl (OH-) and carbonate (CO32-) ions, leading to a high pH and very high concentrations of NH4+ around the urea. This NH4+ reaches equilibrium with dissolved NH3. A. Laboratory Analysis: Total mineral N in soil samples was determined by the steam distillation method as given in Mulvaney [6]. Total N in soil and plant samples was determined by Kjeldhal method as described in Bremner [7]. Least significant difference (LSD) at 5% probability level was employed upon obtaining significant Fvalues between treatment means
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