Effects of Prilled Urea, Urea Briquettes and NPK Briquettes on the Growth, Yield and Nitrogen use Efficiency of BRRI Dhan48

Nitrogen is one of the most deficient plant nutrients in Bangladesh soils. The use nitrogenous fertilizer especially urea is a commonly used fertilizer for rice production but its efficiency very low about 30-40% under traditional broadcast method A field experiment was carried out in the Soil Science Field Laboratory of Bangladesh Agricultural University, Mymensingh during Aus rice growing season of 2014 to investigate the effects of prilled urea, urea briquettes and NPK briquettes on the growth, yield, and nitrogen use efficiency of BRRI dhan48. There were six treatments as T1 [check (N0P16K42], T2 [Urea briquette (one-3.4 g) (N52P16K42)], T3 (Urea briquette (one-2.7 g (N78P16K42)], T4 [NPK briquette (one-3.4g)(N51P13K32], T5 [Prilled urea (N78P16K42)] and T6 [NPK briquettes(two-2.4 g briquettes (N78P15K42)]. The experiment was laid out in a Randomized Complete Block Design (RCBD) with six treatments and four replications. Prilled urea was applied in two equal splits application; at 8 days after transplanting (DAT) and the second dose after 38 DAT, while for urea briquettes and NPK briquettes were deep placed (8-10 cm depth) at 8 DAT between four hills at alternate rows. Water samples were collected for every 7 consecutive days and analyzed for NH4-N. The results showed that the NH4-N concentration in floodwater reached to maximum on day 2 in PU treated plots and then decreased with time, while the urea briquettes and NPK briquettes treated plots slowly produced NH4-N over the growth period. The highest grain yield of 4.75 t ha-1 (69% over control) was obtained in the treatment T3 [Urea briquette (one-2.7g) (N78P16K42)]. The treatment T3 also produced the highest straw yield of 5.49 t ha-1. The maximum apparent N recovery and the maximum N use efficiency were found in the treatment T4 [NPK briquette (one-3.4g) (N51P13K32)]. It appeared that the deep placement of urea briquettes and NPK briquettes reduced N-losses and enhanced the recovery of applied N as well as N use efficiency in comparison with PU application.

Modeling of Urea Release from Briquettes Using Semi infinite and Shrinking Core Models

Briquetted urea is commonly used in wet agricultural soils since it has potential to reduce loss of urea occuring in the fields by various mechanisms. In the present study, commercially available uncoated urea briquettes were subjected to release in wet loam and wet silty clay soils, both maintained at 40% moisture, measured on dry basis. Adapted semi infinite model and developed shrinking core model predictions were compared with the experimentally determined concentration profiles and unreleased quantity of urea, respectively. Semi infinite model developed with the assumption of unchanging briquette size did not match well with experimental results. However, shrinking core model predicted the unreleased urea contents in briquettes reasonably well.

Agronomic performance of urea briquettes containing diammonium phosphate in rainfed transplanted rice on farmers' fields

Seventy-seven adaptive research trials were conducted, with the participation of local farmers, on their fields during the 1993 and 1994 wet seasons (southwest monsoon seasons) in the warm subhumid tropical zone on the west coast of India. The objective of the trials was to compare the agronomic and economic benefits of an improved management consisting of placing urea briquettes containing diammonium phosphate (UB–DAP) by hand (56 kg N/ha and 14 kg P/ha) after controlled transplanting using a modified 20×20 cm hill spacing with two other practices: (i) the current management system, consisting of random transplanting and two split applications of prilled urea (PU) and a basal application of single superphosphate (SSP) and (ii) the farmers' traditional management practices, involving random transplanting and broadcasting of fertilizers. In spite of marked variations in rainfall distribution patterns during the 1993 and 1994 seasons, the improved management using UB–DAP increased grain yields by 2·14 t/ha (89%) in 1993 and 1·23 t/ha (45%) in 1994 over traditional management practices and by 1·56 t/ha (52%) in 1993 and 0·83 t/ha (27%) in 1994 over the current management system. These additional yields were obtained at a 28–36% lower plant population density (25 hills/m2v. 35–39 hills/m2). The use of a modified 20×20 cm spacing could reduce by up to 50% the labour normally required for the conventional placement of UB by hand about 1 week after transplanting using the standard 20×20 cm spacing (8–10 workdays/ha). The estimated value: cost ratios for the improved management ranged from 4·9 (1994) to 8·6 (1993) and increased further when the savings in seed input were considered. Stochastic dominance analysis of the yield data suggests that the improved management of UB–DAP could be risk-free and therefore would be preferred over the other two managements by rice farmers and policy makers.

Rhizosphere soil nitrogenase (C2H2reduction) as influenced by the nitrogen management in intermediate deep water rice

SUMMARYIn a field experiment, the influence of different forms and methods of application of urea nitrogen on the rice rhizosphere soil nitrogenase was evaluated under simulated intermediate deep water situations. Nitrogenase was high when the soil received small amounts of nitrogen and phosphorus with a water level of 20–25 cm. Moreover, during and after the flash floods the nitrogenase activity was considerably increased. There was a significant reduction in the nitrogenase activity when the nitrogen was applied to the shallow water through urea briquettes, but when it was applied either behind the plough or between the rows, the activity was stimulated. Increased water level of about 50 cm for prolonged periods considerably reduced the nitrogenase activity. Results indicate that the method of application of urea nitrogen and the water level influenced the rhizosphere soil nitrogenase activity under intermediate deep water situations.