Slow-Release Urea Prills Developed Using Organic and Inorganic Blends in Fluidized Bed Coater and Their Effect on Spinach Productivity

The application of urea-based fertilizers in developing countries has gained significant momentum over time. urea usage is to meet demand and supply gap of food resources as world population is increasing at a fast pace. urea contains largest content of nitrogen (46%) among all the solid nitrogenous fertilizers. However, main drawback of urea is its higher dissolution rate. After soil application, most of urea nitrogen is lost through a leaching, runoff, nitrification-denitrification and ammonia volatilization. To tackle urea related environmental pollution, development of slow-release urea fertilizer is a need of the hour and this would also increase product use efficiency in terms of crop productivity and its N uptake. We studied the usage of polymeric materials in combination with inorganic substances like sulfur and plaster of Paris as effective and biodegradable coating substances for urea prills. For coating on urea prills, fluidized bed coater was used whereas paraffin wax and molasses were used as binding agents. The urea was coated with four different formulations, i.e., C-1: PVA 5% + plaster of Paris 10% + sulfur 5% + paraffin wax 2%, C-2: PVA 5% + starch 10% + sulfur 5% + paraffin wax 2%, C-3: gelatin 5% + plaster of Paris 10% + sulfur 5% + paraffin wax 2% and C-4: PVA 5% + starch 10% + sulfur 5% + paraffin wax 2.5% + molasses 2.5%. Each formulation along with uncoated urea prills (C-0) were evaluated for characterization and N release kinetics. All the formulations along with uncoated urea were applied to spinach crop in pot experiment. A control (No N: untreated) was also kept. Spinach biomass yield and N uptake were determined. The formulation C-1 yielded highest urea-N release efficiency and spinach N uptake of6.87% and 1.93 g N/pot, respectively. Themodified Schwarz and Sinclair formula gave the excellent representation of release of nutrient-N from coated urea prills. It is concluded that coating urea prills with organic and inorganic blends is better option to slow down N release kinetics and improve spinach productivity. Therefore, by using coated fertilizers, farmers can improve agro-environmental value of urea, worldwide.

A Comparison of Co-Current and Counter-Current Modes of Operation in Urea Prilling Tower

In this paper, a model for urea prilling tower with co-current flow of cooling air and urea prills (particles) is presented. The process is modelled by simultaneous solution of the differential equations for hydrodynamics, heat and mass transfer between the air and prills. The process variables such as temperature, absolute and relative humidity of air along the height of the tower were obtained from this model. Temperature and moisture distribution of urea prills and their radial and vertical velocities were also calculated. The results of the present model were compared with the counter-current operation model available in the literature. The simulation results show that heat transfer performance for co-current operation is significantly less than that of the counter-current scenario. This is more pronounced for small prills, i.e. 1.0 mm than that of the large prills. The advantage of the model is that it can be used to investigate influence of operating parameters on efficiency of the co-current process. This also helps us to set the process control strategies for design and quality control purposes of the process.

EFFECT OF SELENATE VS. SELENITE FORMS OF SELENIUM IN INCREASING THE SELENIUM CONCENTRATION IN FORAGES AND CEREALS

A greenhouse study was conducted on a fine sandy loam to determine the effect of adding different sources of Se on the Se concentration of forages and cereals. The three sources of Se were: NH4NO3 prills containing (i) 1.20% Se as sodium selenate, (ii) 1.02% Se as sodium selenite and (iii) urea prills containing 1.00% Se as sodium selenite. Application of 20 g Se ha−1 as sodium selenate (source i) produced Se concentrations of 1.02 and 1.05 mg kg−1 in timothy and 1.04 and 0.55 mg kg−1 in alfalfa in the two cuts, respectively, and 0.78 mg kg−1 in barley grain. This application rate of Se in the form of selenite resulted in 0.07–0.09 mg Se kg−1 in the two forages and barley grain. At similar application rates of Se, the ammonium nitrate doped with sodium selenate produced about 5–18 times more Se in the forages and barley than when doped with sodium selenite. Overall no significant difference was found in the plant Se concentration between ammonium nitrate or urea prills as the carrier for selenite. Key words: Sodium selenate and selenite doped NH4NO3, greenhouse, Se in forages and cereals

RESPONSE OF WINTER WHEAT TO FALL-APPLIED LARGE UREA GRANULES WITH DICYANDIAMIDE

Three field experiments were undertaken over a 2-yr period to compare the response of winter wheat to fall-applied large urea granules containing a nitrification inhibitor (dicyandiamide, DCD) with that of commercial urea granules (prills) applied as a top dressing in the spring. The objective was to determine the effectiveness of large urea granules coupled with DCD in conserving N when applied at planting or one month after planting. Granules of 1, 2 and 3 g urea as well as 2 g urea + DCD were compared with commercial urea prills at an application rate of 80 kg N ha−1. Large urea granules, as compared with fall-incorporated commercial urea prills, were effective in conserving N over the winter period especially when applied 1 mo after planting and resulted in yields and apparent N recovery similar to those with top dressed commercial prills applied in the spring. Incorporation of DCD into 2-g granules (50 or 100 g kg−1 urea) further increased the conservation of N fertilizer as reflected by higher yields and greater apparent fertilizer N recovery. Uptake of 15N from 2-g urea granules decreased with distance from the granule. However, plants furthest from spaced large granules were able apparently to obtain sufficient N to reach the yield potential dictated by the weather and soil conditions. Yield and N recovery data indicated that N conservation increased with increasing granule size. Crop response and fertilizer N availability decreased as depth of placement exceeded 10 cm. Placement between the 5 and 10 cm depths appeared to maximize fertilizer N availability. It was concluded that a combination of large urea granules and a nitrification inhibitor (such as DCD) can effectively conserve fall-applied N and result in yield responses and N uptake by winter wheat similar to that with commercial urea prills applied as a top dressing in the spring. Key words: Time of application, yield, 15N recovery, apparent fertilizer N recovery