Uncoated Fertilizer Research Articles

New Straw Coating Material for Improving the Slow-Release Performance of Fertilizers.

In this work, we extracted cellulose from agricultural waste and produced a new straw coating material (ethyl cellulose, EC) through a series of modification operations. The slow-release properties of ethyl cellulose-coated urea (EU) and its absorption and utilization by plants were evaluated. The surface of EU can form a smooth and fine film, and the initial nutrient release rate is only 37.91% that of the uncoated fertilizer. Compared with common urea, the nitrogen of plants cultivated with EU increased by 17.69%, and the leached nitrogen decreased by 61.29%, indicating that EU can reduce nitrogen waste to the greatest extent and continuously supply nutrients to crops. Therefore, the application of EU could be a more practical, environmentally friendly, and sustainable alternative to nitrogen fertilizers.

Slow‐release fertilizers using lignin: Challenges and future prospects

AbstractLignin is an integral part of the plant cell wall and is the largest single source of aromatic carbon in the world, which makes it suitable for the production of feed, chemicals, fuels, and biomaterials. Total lignin production is greater than 50 million tons per annum; however, currently, less than 5% of the lignin is being valorized, and 95% is burnt to create steam and power. Burning aromatic carbons produces heat and power, making them low‐value materials. However, the macromolecules of lignin can be modified to use for several industrial applications, such as surfactants, paints, hydrogel, absorbents, and fertilizer. In this review, we provide a systematic and comprehensive summary of the last 10 years of the development of controlled release fertilizer (CRF) from lignin, which is a renewable material. Lignin‐based CRFs are green, environment friendly, and are considered efficient for agricultural use in place of urea and diammonium phosphate. Coating the fertilizer with lignin could increase fertilizer's 20–30 times slower release vis‐à‐vis uncoated fertilizer. However, the structure of lignin varies from one process to another process; it is therefore highly dependent upon the fractionation process and pulping methodologies adopted. A high degree of heterogeneity, complex structure, and low reactivity of the lignin results in an uneven coating, large surface porosity, and cracks in the coatings. The similarity of the lignin can be improved by chemical modifications in its molecule; however, any chemical processing increases the cost of slow‐release fertilizer. © 2023 Society of Industrial Chemistry and John Wiley & Sons Ltd.

Polymethyl methacrylate-g-carboxy-methylcellulose as an amphiphilic coating material for slow-release fertilizer

In the perspective of preparing coating material of water-soluble fertilizer with controlled and slow-release property, polymethyl methacrylate (PMMA) was grafted from carboxymethyl cellulose (CMC) through in-situ polymerization using potassium persulfate (KPS) as initiator. The prepared copolymers (PMMA-g-CMC) were fully characterized using Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic light scattering (DLS), X-Ray diffraction (XRD), Brunauer Emmett Teller (BET), Scanning electron microscopy (SEM) and mechanical tensile testing. The molecular weight (Mn) was also evaluated using the size exclusion chromatography (SEC). Next, conventional water-soluble diammonium phosphate (DAP) fertilizer was coated by the prepared copolymers using laboratory rotary drum. The coating effectiveness was evaluated in terms of its uniformity and thickness. The successfully coated nanomaterials significantly delay the release rate of nitrogen (N) and phosphorus (P) in water and soil, compared to their release using uncoated fertilizers. Finally, aerobic biodegradation of the coating agent was also demonstrated.

The Effect of Polyurethane Multilayer Coating on Nitrogen Release from Controlled Release Fertilizer

Nitrogen-based fertilizers are widely consumed to increase productivity since they play an essential role in plant growth. Common commercial fertilizers contain “mobile” nitrogens that can be easily transformed into other nitrogen compounds. The approach method to decrease nitrogen loss is called controlled-release fertilizer (CRF), which is done by modifying fertilizers with coating inhibitors such as polyurethane to provide surface resistance that inhibits nutrient release. Multilayer coating is one of the alternatives to minimize the risk of losing nitrogen content from granular fertilizer. This research will focus on the study of nitrogen release on the CRF modified by various polyurethane coating concentrations (6%, 8%, and 10%). The study was conducted by planting maize plants in a pot inside a greenhouse for nine weeks, followed by a nitrogen release test using a percolator. The morphology of final coating products was observed with scanning electron microscopy, while the mechanical properties and water content were measured with crushing strength test and water stability test. Three weeks after testing, polyurethane can reduce above 60% nitrogen release compared to uncoated fertilizer. After nine weeks since the maizes were planted, the nitrogen release will compare between inside the percolators’ simulation chambers and pot test to see the effect of polyurethane composition with nitrogen release pattern. The results show that the effective composition of polyurethane in CRF products is maximum at 8%w/w with nitrogen released above 75%. Keywords: controlled-release fertilizer, polyurethane multilayer coating, nitrogen release

Nitrogen fertilizer response of dry direct-seeded rice in rainfed lowlands of the Philippines

Dry direct-seeded rice (DDSR) is an adaptive practice used in rainfed lowlands of tropical Asia where insufficient rainfall at the onset of the wet season makes it difficult to successfully transplant rice seedlings. However, basic guidelines for nutrient management to support DDSR are lacking. Here, we evaluated crop growth and yield in DDSR with different N fertilizers (ammonium sulfate, urea, and coated compound fertilizer) applied at different timings. The total N rate was fixed at 100 kg ha−1. On-station trials were conducted at the International Rice Research Institute, in the Philippines, during the wet seasons of 2017 and 2018, and 17 on-farm trials were conducted in nine provinces in 2018 and 2019. In the on-station trials, ammonium sulfate did not increase yield compared with urea and coated compound fertilizer in either year. Application of N fertilizers at sowing promoted plant N uptake and early shoot growth, but the effect of the timing of N application on yield was not significant. The on-farm trials showed that a uniform N management recommendation is unlikely to be effective in DDSR. Yield increased significantly with coated compound fertilizer relative to the uncoated fertilizers in clay and silty clay soils, but not in other soil types. In general, flexible timing of the first application of N, ranging from 0 to 30 days after sowing, had no significant effect on yield, but the omission of N application at sowing reduced yield by 13–25% in two trials on sandy soils with a low nutrient-holding capacity.

Characteristics and preparation of oil-coated fertilizers: A review.

As the slow-release fertilizer, oil-coated fertilizer can not only slow down the nutrients loss, but also have outstanding advantages in controlling the nutrients release. Based on a large number of literature, this paper systematically investigated the composition, classification, properties and preparation of oil-coated fertilizers, summarizes the challenges faced by the oil-coated fertilizers and offers a few suggestions for the future research. Through literature research, some important conclusions were found: (1) Oil-coated fertilizers are generally composed of core fertilizers and coated oil layers, and some have active interlayers. (2) Vegetable oils has the characteristics of easy degradation, water resistance and impact resistance, and the nutrient release curves of vegetable oil coated fertilizer in soil and still water are "S" type. (3) The modified polyurethane exhibits good compatibility with urea, and can control the release of N in a long period of time, which is 30days longer than the N release life of ordinary polyurethane-coated fertilizers. (4) Oil-coated fertilizers can reduce the loss of N by slowing down the hydrolysis rate of urea and the nitrification from NH4+ to NO3-, which reduces the N2O release by 70-80% compared to the uncoated fertilizers. Moreover, the paper also proposes a new preparation method of oil-coated material.

Zinc Plus Biopolymer Coating Slows Nitrogen Release, Decreases Ammonia Volatilization from Urea and Improves Sunflower Productivity.

Currently, the global agriculture productivity is heavily relied on the use of chemical fertilizers. However, the low nutrient utilization efficiency (NUE) is the main obstacle for attaining higher crop productivity and reducing nutrients losses from these fertilizers to the environment. Coating fertilizer with micronutrients and biopolymer can offer an opportunity to overcome these fertilizers associated problems. Here, we coated urea with zinc sulphate (ZnS) and ZnS plus molasses (ZnSM) to control its N release, decrease the ammonia (NH3) volatilization and improve N utilization efficiency by sunflower. Morphological analysis confirmed a uniform coating layer formation of both formulations on urea granules. A slow release of N from ZnS and ZnSM was observed in water. After soil application, ZnSM decreased the NH3 emission by 38% compared to uncoated urea. Most of the soil parameters did not differ between ZnS and uncoated urea treatment. Microbial biomass N and Zn in ZnSM were 125 and 107% higher than uncoated urea, respectively. Soil mineral N in ZnSM was 21% higher than uncoated urea. Such controlled nutrient availability in the soil resulted in higher sunflower grain yield (53%), N (80%) and Zn (126%) uptakes from ZnSM than uncoated fertilizer. Hence, coating biopolymer with Zn on urea did not only increase the sunflower yield and N utilization efficiency but also meet the micronutrient Zn demand of sunflower. Therefore, coating urea with Zn plus biopolymer is recommended to fertilizer production companies for improving NUE, crop yield and reducing urea N losses to the environment in addition to fulfil crop micronutrient demand.

Cellulose nanocrystals-filled poly (vinyl alcohol) nanocomposites as waterborne coating materials of NPK fertilizer with slow release and water retention properties

Effective fertilizers management is essential for sustainable agricultural practices. One way to improve agronomic practices is by using slow-release fertilizers (SRF) that have shown interesting role in optimizing nutrients availability for plants growth. Considering the current ecological concerns, coated SRF using ecofriendly materials continue to attract great attention. In this context, novel waterborne and biodegradable coating nanocomposite formulations were elaborated from cellulose nanocrystals (CNC)-filled poly (vinyl alcohol) (PVA) for slow release NPK fertilizer with water retention property. CNC were extracted from hemp stalks using sulfuric acid hydrolysis process and their physico-chemical characteristics were investigated. CNC with various weight loadings (6, 10, 14.5 wt%) were incorporated into PVA polymer via solvent mixing method to produce viscous coating nanocomposite formulations with moderated shear viscosity. Uniform PVA@CNC coating microlayer was applied on the surface of NPK fertilizer granules in Wurster chamber of a fluidized bed dryer at controlled spraying and drying parameters. The nitrogen, phosphorus and potassium release profiles from coated NPK fertilizer were determined in water and soil. It was found that the coating materials extended the N-P-K nutrients release time from 3 days for uncoated fertilizer to 10 and 30 days for neat PVA- and CNC/PVA-coated fertilizer in soil medium, indicating the positive role of the presence of CNC in the PVA-based coatings. The morphology, coating rate and crushing strength of the as-prepared coated products were investigated in addition to their effect on water holding capacity and water retention of the soil. Enhanced crushing strength and water retention with a positive effect on the soil moisture were observed after coating NPK fertilizer, mainly with high CNC content (14.5 wt%). Therefore, these proposed nanocomposite coating materials showed a great potential for producing a new class of SRF with high nutrients use efficiency and water retention capacity, which could be beneficial to sustainable crop production.

Potassium Plus Biopolymer Coating Controls Nitrogen Dynamics of Urea in Soil and Increases Wheat Production

The low nitrogen utilization efficiency (NUE) of commercial fertilizers is one of the main hurdles in higher crop production and reduction of fertilizer N losses to the environment. However, interactions between most the macronutrients could have synergistic outcomes that affect crop NUE. The coating of urea with macronutrients and biopolymers may control N release and synergistically impact its crop NUE. In this study, urea was coated with 3% of different polymers, combined with 5% potassium iodide (KI) (i) Gum Arabica (GA + KI), (ii) polyvinyl alcohol (PVA + KI), and (iii) gelatin (Gelatin + KI) to control its N release, leaching, and increase of wheat NUE. Scanning electron microscopy, Fourier Transform Infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses confirmed the successful coating of all KI and biopolymer combinations on urea granules. All coating combinations slowed down urea release in water and reduced its leaching from the soil, but the highest reduction in both parameters was observed with the GA + KI treatment, compared to the uncoated urea. After soil application, GA + KI decreased urea leaching by 26% than the uncoated urea in lysimeter. In the field, soil mineral N remained significantly high with the GA + KI and PVA + KI treatments at the wheat tillering, booting, grain filling and maturity stages, compared to the uncoated urea. However, K content was only high (28%) with the GA + KI treatment at final harvest. Likewise, microbial biomass N was only high with GA + KI at grain filling (20%) and maturity stages (24%) than the uncoated urea. Such synchronized N availability led to high wheat grain yield (28%), N (56%) uptake, and apparent N recovery (130%) with the GA + KI treatment, compared to the uncoated fertilizer. The increment in NUE with GA + KI could be due to the synergistic effect of K on N availability; therefore, we observed higher wheat yield and N utilization efficiency with this treatment. Hence, urea coated with macronutrient (K) plus biopolymer is recommended to improve wheat yield, NUE, and for reduction of environmental N losses.

Novel water‐soluble polymer coatings controlNPKrelease rate, improve soil quality and maize productivity

AbstractWe investigated different combinations of polymers (5% each) (i) starch, gelatin (polymer coating; PC‐1), (ii) polyvinyl alcohol (PVA), gum Arabica (PC‐2), (iii) PVA, gelatin (PC‐3), (iv) starch, gum Arabica (PC‐4), (v) gelatin, gum Arabica (PC‐5), (vi) starch, PVA (PC‐6), for coating NPK (17, 17:17) in a fluidized bed granulator. Morphological characterization indicated a uniform coating of all formulations on NPK granules. A slow release of N (PC‐3), P (PC‐6), and K (PC‐3) was observed in water. In soil, high mineral N (63%), plant‐available P (72%), and K (24%) were observed in PC‐3, PC‐5, and PC‐6, respectively than uncoated fertilizer. Microbial biomass NPK was also higher in these treatment. This resulted in higher maize yield (66%), N (114%), P (164%), and K (137%) uptakes and apparent N (267%), P (196%), and K (358%) recoveries from applied fertilizer in these treatments. Among these, PC‐3 resulted in an increase of 115% shoot N, 169% P and 138% K uptakes and 268% apparent N, 206% P and 361% K recoveries than uncoated fertilizer. Hence, coating of NPK with this biodegradable polymer combination controlled N, P, and K release and synchronized these nutrients availabilities with maize nutrients demand therefore resulted in higher maize crop yield and nutrient utilization efficiencies.

Evaluation of a New Generation of Coated Fertilizers to Reduce the Leaching of Mineral Nutrients and Greenhouse Gas (N2O) Emissions

The increased use of fertilizers in agriculture and forest and horticulture nurseries contributes to the pollution of water resources and greenhouse gas emissions. The objective of this study is to evaluate a new generation of fertilizers coated with new biodegradable polymers in terms of physical quality, release kinetics, and their effect on reducing nitrate leaching and N2O emissions and compare them to uncoated fertilizers (Urea, monoammonium phosphate (MAP), and KCl) having the same mineral nutrient concentration. In a peat-based substrate, the release of mineral nutrients was similar in both types of fertilizer. Two hours after application, Urea released 34% more urea than Biodrix N, the difference disappearing after one day. The leaching of cumulative ammonium nitrogen after 20 days was reduced by 40% and 26% respectively by Aminaex and Biodrix N compared to Urea. In a peat-based substrate containing 30% (v/v) of compost, the cumulative nitrate leaching was reduced by 54% by Biodrix N and by 41% by Aminaex compared to Urea. The highest average N2O flux was observed on the first day for Urea, whereas for Aminaex and Biodrix N, N2O emissions increased on the third day, reaching a peak of efflux on day 10. A 10-day delay of the N2O efflux emissions and a longer period of emissions were observed in treatments containing Aminaex and Biodrix N compared to Urea. Cumulative N2O efflux was 142, 154, and 171 mg m−2, respectively, for Urea, Aminaex, and Biodrix N over a 20-day period. These new biodegradable polymer-coated nitrogen fertilizers can reduce mineral nutrient leaching in the event of heavy rainfall and lower maximum N2O emissions in comparison with conventional nitrogen sources.

Properties of Coated Controlled Release Diammonium Phosphate Fertilizers Prepared with the Use of Bio‐based Amino Oil

AbstractIn an effort to enhance the efficiency of fertilizer use and minimize their negative impact on the environment, a novel biomass‐based, functional controlled‐release fertilizer was used to improve nutrient use efficiency and increase crop production systems for more sustainable agriculture practices. Here, bio‐based amino‐oil (Priamine) mixtures were proposed as an outer coating with different layers for the control of phosphorus release from diammonium Phosphate (DAP). These hydrophobic coatings conferred excellent barrier properties and flexibility to coatings. The morphological characterization of the coated fertilizer was performed by scanning electronic microscopy (SEM), electronic diffraction X‐ray (EDX) and mapping, and revealed the formation of a cohesive film and a good adhesion between DAP fertilizer and coating film. The release rate of nutrients (phosphate) in water was investigated by UV–Vis spectrophotometer. The effect of coating thickness was investigated on release time and diffusion coefficient of phosphor release in distilled water. Release time increased with the coating thickness. The diffusion coefficient of nutrient release decreased with the coating thickness. Compared with uncoated granule which is totally solubilized after less than 2 hours, the P release profiles of the coated granules reached the equilibrium stage approximately after 98 and 126 hours when the DAP is coated with only Priamine single‐layer (1L) and double‐layer (2L), respectively. Moreover, the strategy adopted has successfully provided a very slow release and long‐term availability of nutrient sources with bio‐based coating oil compared to uncoated fertilizer (DAP) and therefore exhibited promising application for sustainable development of modern agriculture and circular economic.

Residual effect of KCl coated by polymeters incorporated in a corn crop

The use of polymer-coated potassium fertilizers may reduce the leaching of potassium (K) in the soil, increasing the availability of this nutrient to plants for a long period. In this context, the residual effect of doses and sources of potassium chloride (KCl) application on K nutrition, production components and corn grain yield in two sequential crops were investigated in this study. The experiment was conducted in a clayey Oxisol. The experiment was arranged in a randomized complete block design with four replicates in a 4 X 4 factorial scheme: four potassium doses (0, 40, 80 and 120 kg ha-1 of K2O ) and four KCl sources [uncoated fertilizer (conventional) and three sources of fertilizer coated with different polymers]. The KCl sources showed the same residual effect for most production components, leaf K content and corn grain yield in both crops. The increase of K fertilizer doses in the previous crop provided residual effect on the second-harvest corn crop, resulting in linear increase in leaf K content, weight of 100 grains and grain yield up to the dose of 77 kg ha-1, whit the use of any source of KCl.

Controlled release fertilizer based on starch chitosan encapsulation

Phosphor is the main component in a triple super phosphate (TSP) fertilizer which is needed by plants. However, phosphorus is very soluble in the water and makes it easily removed from the soil flowing into the river, and causing algae bloom problems. The solution for the problem is by using the fertilizer coated with starch-chitosan based material. The coated hydrogel bead fertilizer was expected to have a phosphorus controlled-released behaviour and retain the phosphor to be able to stay for a longer time in the soil. This research dealt with studying phosphorus releasing behaviour of starch-chitosan based fertilizer, water uptaking characteristic (swelling), and the morphology of the materials. The commercial granular fertilizer TSP was coated using starch-chitosan suspension. The coatings were conducted by spraying technique. The chitosan-starch mass ratio used were 100:0, 30:70, and 70:30, otherwise the starch percentages were made of 1%, 2%, and 3%. After coated by starch-chitosan suspension, the fertilizers were dried and used on the soil media. The soil which contained coated fertilizer was regularly watered and the phosphorus content was analyzed. The study showed that the water uptaking of the coated fertilizer was higher than that of the conventional uncoated fertilizer. The optimum condition of the chitosan-starch based coating was 30:70 and 2% of starch percentage. Furthermore, the higher chitosan content yielded the higher water uptaking capacity. This phenomenon is supported by the Scanning Electron Microscope (SEM) result. The coating fertilizer with higher chitosan content (ratio of 70:30, 2% starch) had more pores than that of lower chitosan content (ratio of 30:70, 1% starch).

Fortified fertilizer application in wheat (Triticum aestivum L.) grown under water stress condition

Abstract Water stress is a major threat against wheat growth. The effects of induced stress can be reduced after by fortified fertilizer treated by Plant Growth Promoting Bacteria (PGPB). With the objective to combat the water stress, two different experiments under net house and field condition were conducted. Three different states of fertilizer [F0: Control (no fertilizer application); F1: PGPB-coated fertilizer (urea and phosphorous) &F2: uncoated fertilizer (urea and phosphorous)]. In a pot experiment, wheat plants were applied fertilizer in raised and well-watered (60 percent of field capacity) and water stressed (40 percent of field capacity) conditions in soil filled pots. In experiment-II (field study), similar treatments of fertilizer were revised, but well-watered and water stress treatments/plots were irrigated for 60 seconds and 30 seconds respectively. At maturity plants were harvested and various morphological (number of tillers/plant, number of spikelet/spike, number of grains/spike, weight of grains, biological yield, economic yield and harvest index) and biochemical parameters (leaf nitrogen, phosphorous & potassium contents) of crop were recorded. Leaf chlorophyll and relative water contents of crop were also measured 60 days after sowing. In this study, it was demonstrated that the water stress adversely affected all the above mentioned parameters. The PGPB coated fertilizer application in wheat significantly increased (p<0.01 for pot and p<0.05 for field study) morphological and biochemical parameters in the presence and absence of water stress both under net house and field conditions. We can conclude from these findings that application of PGPB coated fertilizer is valuable strategy to mitigate the water stress impact on wheat with improved yield. Keywords: Coated fertilizer; Un-coated fertilizer; PGPB; Chlorophyll; Harvest inde http://dx.doi.org/10.19045/bspab.2019.80037

Hydrogel/clinoptilolite nanocomposite-coated fertilizer: swelling, water-retention and slow-release fertilizer properties

Preparation of a new core–shell slow-release fertilizer formulation was conducted through the coating of commercial NPK fertilizer with hydrogel/clinoptilolite (Hyd/CL) nanocomposite. The Hyd/CL nanocomposite was prepared from free radical polymerization of sodium alginate, acrylic acid, acrylamide, and clinoptilolite zeolite. The uniform coating on the surface of the fertilizer granules was verified by scanning electron microscopy. The swelling kinetics as well as the water-retention property and water absorption rate of the prepared samples was studied. Furthermore, the release of fertilizer from Hyd/CL nanocomposite-coated fertilizer granules into soil showed that the Hyd/CL nanocomposite layer around the fertilizer granules caused the system to liberate the nutrient in a more controlled manner (lower than 57 % of loaded fertilizer on the 30 days) than that with the uncoated fertilizer. The overall results eventually suggested that the hydrogel nanocomposite designed in this work can be used as a coating on granular fertilizer compounds for application in agriculture due to its water-retention and slow-release properties.

EVALUATION OF NITROGEN APPLICATION METHODS AND RATES WITH NUTRISPHERE-N ON SOIL NITRATE-NITROGEN IN SOUTHEASTERN COASTAL PLAINS

Nitrogen (N) application with Nutrisphere-N polymer may affect soil Nitrate-Nitrogen (NO3-N) movement in the soil. The objective was to evaluate two N application methods (all at planting and split application) and five N rates (0, 45, 90, 135 and 180 kg N ha-1) with Nutrisphere-N polymer on soil NO3-N in dryland corn (Zea mays L.) near Blackville, SC from 2010 to 2012. Soil samples were collected from the soil depth of 90 cm and divided into 15 cm increments following corn harvest. Compared to uncoated fertilizer, Nutrisphere-N improved NO3-N concentration by 29.8% with 180 kg N ha-1 in split applications at 0-15 cm depth and by 44.7% at 90 kg N ha-1 applied at planting at 15-30 cm depth. Soil NO3-N content increased with Nutrisphere-N by 26.2, 36.1, 28.0 and 17.3% at 45 kg, 90 kg, 135 kg and 180 kg N ha-1 in split applications at 15-30 cm depth, respectively. Nutrisphere-N improved soil NO3-N concentration by 40.1 and 31.6% at 90 kg and 135 kg ha-1 over uncoated treatment for N applied in split applications at 30-45 cm depth, respectively. Soil NO3-N content improved with Nutrisphere-N by 36.9% at 135 kg N ha-1 applied at planting, while NO3-N concentration improved by 33.9 and 34.9% at 135 kg and 180 kg N ha-1 with Nutrisphere-N applied in split applications at 45-60 cm depth, respectively. At 60-75 cm depth, Nutrisphere-N decreased soil NO3-N content by 22.0% at 180 kg N ha-1 applied at planting and increased content by 37.5 and 59.9% with split N applications of 90 kg and 135 kg ha-1, respectively. Soil NO3-N concentration increased with Nutrisphere-N by 30.6% over untreated fertilizer at 135 kg N ha-1 in split applications at 75-90 cm depth. Generally, N applications with Nutrisphere-N helped to reduce soil NO3-N losses.

Controlled-release P fertilizer concept evaluation using growth and P uptake of barley from three soils in greenhouse

Use of controlled-release P fertilizers to match the fertilizer P availability to crop requirement has potential for improvement of P uptake and crop production. Greenhouse experiments were conducted to evaluate the concept of controlled-release P fertilizer by using different coatings to regulate the release of P and to compare the growth and P uptake of barley (Hordeum vulgare L.) in three Alberta soils. Testing of different coatings in one experiment was followed by further evaluation of the promising treatments in two experiments. Commercial monoammonium phosphate (MAP) and diammonium phosphate (DAP) were coated with a polymer (thin-coated, 1.8% by weight or thick-coated, 2.2%) or enveloped in commercial packaging polyethylene film (shrink wrap, SW) with two, four or six pin-holes to control P release. Thin-coated treatment showed greater dry matter yield (DMY), P uptake (PU), net fertilizer P efficiency (NFPE) and net fertilizer releases efficiency of MAP compared to the uncoated, thick-coated or SW treatments in many cases. Coating of DAP did not consistently improve any of the above-mentioned parameters. In some cases, uncoated fertilizer had greater DMY, PU and NFPE than the polymer-coated treatments in early stages of crop growth (at the 13th, 26th, and 30th days), but coated treatments generally performed better during later stages of crop (at the 39th, 45th, 60th and 90th days). At 31.4 mg P pot-1 for example, thick-coated treatment had about 25% of its total PU during the 60th to 90th day, which resulted in greater spike yield accumulation in this treatment (8.4 g pot-1) compared to uncoated fertilizer (5.0 g pot-1). The P release rate was greater with thin-coated fertilizer than with thick-coated fertilizer during the 0 to 13th days (by 0.199 mg P kg-1d-1) and the 13th to 26th days (by 0.084 mg P kg-1d-1), but the opposite was true during the 26th to 39th days (by 0.112 mg P kg-1d-1) and the 39th to 52th days (by 0.064 mg P kg-1d-1). The polymer-coated, in particular the thin-coated, fertilizers delivered P in a manner that allowed the plants to use it more effectively than the uncoated MAP in several cases, which indicated a potential for improvement of fertilizer P efficiency and crop production. Key words: Barley growth, controlled-release P fertilizer, P uptake, yield

Evaluation of coated DAP and nimin coated urea on available P status of wetland rice soil

To evaluate the efficiency of coated DAP in rice variety ADT 36 (Short duration: 105-110 days in Kuruvai season) and Nimin coated urea in rice variety IR 20 (Medium duration: 130-135 days in late samba season), two field experiments were conducted on a low P available loamy sand soil (Udic Ustropept) at Agricultural Research Station, Bhavanisagar during the period 1997-98. Phosphorus was applied at levels 100, 80 and 60 per cent of recommended Pas coated and uncoated DAP and recommended dose of N was coated with Nimin. The treatments receiving coated DAP in first experiment, coated DAP along with Nimin coated urea in second experiment recorded the higher availability of P than uncoated fertilizers.

Nitrogen Source Affects Growth and Quality of Bougainvillea

Container-grown Bougainvillea Comm. Ex Juss. `Brasiliensis' were fertilized with ammonium sulfate, sodium nitrate, or ammonium sulfate plus sodium nitrate as N sources. Plants fertilized with sodium nitrate were stunted, extremely chlorotic, and produced few flowers compared to those receiving ammonium sulfate. In a second experiment bougainvilleas were fertilized with 12 different controlled-release or soluble ammonium, urea, or nitrate fertilizers as N sources. Plants grown with only nitrate N were chlorotic, stunted, and produced fewer flowers compared to those receiving N from urea or ammonium salts. High substrate pH, associated with nitrate fertilization, was believed to be a cause of the chlorosis, but possible toxicity symptoms (small necrotic lesions and premature leafdrop) were also observed on nitrate-treated plants. Plants receiving controlled-release urea or potassium nitrate were of higher quality than those receiving similar uncoated fertilizers.