POTENTIAL FOR USE OF CONTROLLED RELEASE FERTILIZERS IN AGRICULTURE: PRESENT AND FUTURE

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1 POTENTIAL FOR USE OF CONTROLLED RELEASE FERTILIZERS IN AGRICULTURE: PRESENT AND FUTURE Connie K. Kohut, Lenz Haderlein, Dale Marantz Agrium Inc., R.E.Dowbenko, Redwater, AB, Canada ABSTRACT Controlled release fertilizers (CRF) are fertilizers that release nutrients in a controlled manner in order to match the nutrient demand uptake of a crop. These products have the potential to improve fertilizer use efficiency, increase crop yield and quality and minimize potential losses to the environment. Their use in agricultural crops has been limited primarily because of cost, but also because the advantages of CRF have not been consistently demonstrated for a variety of crops and conditions. Field trials comparing coated and uncoated urea in Western Canadian crops have been conducted for a number of years. Results show that controlled release urea is effective in reducing seedling fertilizer damage and maintaining yields in cases where seed placed urea damage occurs. Coated urea may also be capable of outperforming banded urea through an increase in nitrogen use efficiency. INTRODUCTION Fertilizers may contribute significantly towards environmental degradation, particularly in intensive agricultural systems, because the recovery or use efficiency of nutrients by crops is relatively low. For example, it is estimated that N use efficiency for cereal production worldwide is only 33% (Raun and Johnson, 1999). Much of the N not used by the crop is presumed to be lost to the environment through soil denitrification, runoff, volatilization, leaching and gaseous plant emissions. This has resulted in growing concerns about issues such as drinking water contamination, eutrophication and greenhouse gas emissions. In addition, the economics of inefficient fertilizer use must be taken into consideration. There has been and will continue to be an increasing demand for techniques which increase fertilizer use efficiencies and reduce losses from soil-plant systems. Controlled release fertilizers are designed to slowly release nutrients at a rate which matches the demand of the plant to which it has been applied in order to maximize fertilizer use efficiency and minimize potential losses to the environment. Increased nutrient use efficiency may also increase the yield and quality of crops, thus providing an economic benefit for growers. Another advantage of CRF in many cropping systems is the reduction in fertilizer induced seedling damage. Although starter fertilizer placed with the seed has provided a consistent benefit in most cropping systems, recommended application rates are very low because there is an inherent risk of seedling damage from the fertilizer due to a high salt index or ammonia volatilization. Controlled and slow release fertilizers can generally be classified into three types: inorganic compounds of low solubility, low solubility organic N-compounds and coated water soluble fertilizers. The first two categories have limited potential for agricultural use because their rate of nutrient release is difficult to 1

2 predict, depending upon factors such as soil type, moisture content, and history of previous usage. Development of polymer coated fertilizers in the last two decades offers the most promise for future widespread use in agriculture because they can be designed to release nutrients in a manner which closely matches plant demand. The polymers used are generally very durable and show consistent release rates that are predictable with temperature. The rate of nutrient release can be changed by manipulating properties of the polymer coating. Despite continuing technological developments and commercial availability, the use of CRF in agriculture is very limited, accounting for less than 1% of worldwide fertilizer consumption. The main reason for this is cost; CRF may range between 3 and 8 times the cost of a corresponding standard fertilizer. Current usage of CRF is limited primarily to non-agricultural markets such as lawn and turfgrass. The exception to this is Japan, where CRF are widely used on agricultural crops such as rice and vegetables (Shaviv and Mikkelsen, 1993). There is therefore an enormous potential for the increased use of CRF in agriculture in North America and Europe if the cost of production can be reduced and advantages such as increased nutrient recovery, improved crop yield and quality and reduced environmental impacts can be consistently demonstrated. Controlled release fertilizers can be expected to be adopted most rapidly in locations where N losses are large (such as high rainfall areas or sandy soils), in crops where in-season N applications are common, and in crops with a shallow rooting system. There have been a limited number of published studies which investigate the value of CRF on large acreage agricultural crops, but those that exist generally indicate that there is significant value in using CRF under most conditions. Howard and Oosterhuis (1997) found that N fertilizer application rates on cotton could be reduced by 40% if controlled release rather than conventional fertilizers were used. Trials using polymer coated urea on winter wheat indicated that there was a 20% yield increase compared to grower s standard practice; research on potatoes, onions and garlic has also shown a general increase in yield and quality when using CRF (Tindall and Detrick, 1999). In Western Canada, it has been found that on barley, fall application of polymer coated urea resulted in decreased nitrate accumulation and fertilizer N loss, while spring application resulted in increased crop N uptake (Nyborg et al., 1993). The objective of this paper is to outline some of the results obtained when testing controlled release urea (CRU) in Western Canadian field crops. The objectives of the experiments were to compare CRU to seed-placed and banded urea and determine if CRU can reduce or eliminate fertilizer seed placed damage, and increase crop yields. FIELD TRIALS Seed-Placed Urea A shift towards direct seeding and reduced tillage systems in Western Canada requires that most or all fertilizer must be applied in a single pass at the time of seeding. Placing N fertilizers such as urea with the seed can damage emerging seedlings or prevent them from germinating because of toxic ammonia release (Bremner and Kromeier, 1989). Strategies to reduce ammonia toxicity in direct seeding systems include physical separation of seed and fertilizer using side or midrow banding, increasing the spread of seed and fertilizer through the opener, or using urea with modified properties. Urease 2

3 inhibitors have been used with some success to reduce seedling damage from seed-placed urea (Pauly et al., 1996). Alternatively, a polymer coated urea should slow urea release to the soil and thus reduce ammonia volatilization within the seed row. In 1998 and 1999, 19 small plot field trials were established in Alberta and Saskatchewan to measure the yield response of wheat, barley and canola to seed placed nitrogen fertilizers. The experiments were established as two-factor randomized blocks with four replicates. Nitrogen treatments were: banded urea (below seeding depth), seed-placed urea, seedplaced controlled release urea (CRU) and a CRU/urea blend. Treatments were applied across four rates of N: 25, 50, 75 and 100 kg ha -1. Significant plant stand reduction (p=0.05) from seed-placed urea compared to side-banding was observed at 12 of 20 sites. In all cases where damage occurred, CRU was as effective as side-banding in preventing seedling damage and stand reduction. The mean grain yields at each site averaged across 4 rates of applied N are shown in Table 1. Table 1. Mean grain yield (kg ha -1 ) at each site averaged across 4 rates of applied N. Site Crop Seed-placed Banded CRU LSD Effect* urea (0.05) 1998 Delmas Canola ** Didsbury Canola ** Marwayne Canola NS Ellerslie Canola NS Wainwright ** Hussar ** Sedgewick NS Battleford ** Delisle ** 1999 Ellerslie AB Barley ** Carstairs AB Canola ** Elk PointAB Canola NS Hafford SK Canola NS Kinley SK Canola NS Naicam SK Canola ** Sedgewick AB Canola NS Athabasca AB ** Battleford SK NS Humboldt SK ** * - Effect indicates a yield difference between SPU and other treatments at a given site. ** - indicates significance at the 0.05 level of probability 3

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5 CRU vs. uncoated urea A series of small plot field experiments were conducted from 1987 to 1999 to determine the effectiveness of banded CRU in increasing yields of spring-seeded cereal crops compared to conventional uncoated urea (Figure 1). Figure 1. Mean grain yield (kg ha -1 ) of cereal crops using banded urea and CRU Banded Urea Banded CRU B A 5000 Grain Yield (kg ha -1 ) kg N ha -1 B A 72 kg N ha -1 B A W. Vauxhall 1987 Gwynne 1987 Lethbridge 1987 Redwater 1991 Lacombe 1991 Barley Ellerslie 1999 The results indicate that over a number of years, there has been a variable response to CRU. We speculate that significant yield responses to CRU are only found in years and locations where appreciable N losses occur. In cases where the N losses are minimal, CRU and banded treatments should provide similar yields, as long as the N from the CRU is released early enough for the crop to utilize it. In Western Canada, leaching is not normally considered a major factor in N losses, but under high precipitation and in fine textured soils, denitrification of conventional urea may be an important factor. CONCLUSIONS Plant stand and yield response data have shown the effectiveness of CRU in reducing seedling toxicity and maintaining yields when compared to seed-placed urea in large acreage crops commonly grown in Western Canada. Controlled release urea was shown to be as effective as side-banding in maintaining plant stands and yield at all 13 sites where seed-placed damage was noted. Polymer coated urea may 5

6 also be capable of outperforming banded urea through an increase in N use efficiency, particularly when there is a strong crop response to added N and climatic and soil conditions result in increased N losses from the rooting zone. The cost of CRU is probably the greatest hurdle limiting its implementation in this and other agricultural markets. Increased acceptance of CRF in agriculture will be dependent upon the consistent demonstration of the agronomic and environmental advantages and continued technological advances which reduce the cost of CRF production and improve the nutrient release characteristics to match that of the crop. REFERENCES Bremner, J. M. and M. J. Krogmeier Evidence that the adverse effect of urea fertilizer on seed germination in soil is due to ammonia formed through hydrolysis of urea by soil urease. Proc. Natl. Acad. Sci. USA. 86: Howard, D.D. and D.M. Oosterhuis Programmed soil fertilizer release to meet crop nitrogen and potassium requirements. p. 576 in Proc. Beltwide Cotton Conferences, Jan. 6-10, New Orleans, LA. Pauly, D. G., M. Nutting and R. Dowbenko Using a urease inhibitor, N-butyl thiophosphoric triamide (NBPT) for seed-placing nitrogen with wheat, barley and canola. p In Soils and Crops '96. University of Saskatchewan, Saskatoon SK. Feb 22 and Nyborg, M., E.D. Solberg and M. Zhang Polymer-coated urea in the field: mineralization, nitrification, and barley yield and nitrogen uptake. The Dahlia Greidinger Memorial International Workshop on Controlled/Slow Release Fertilizers, Technion-Israel Institute of Technology, Haifa, Israel, March 7-12, Raun, W.R. and G.V. Johnson Improving nitrogen use efficiency for cereal production. Agron. J. 91: Shaviv, A. and R.L. Mikkelsen Controlled-release fertilizers to increase efficiency of nutrient use and minimize environmental degradation - a review. Fertilizer Res. 35: Tindall, T.A. and J. Detrick Controlled released fertilizer application and use in production agriculture. pp in Western Canada Agronomy Workshop, Brandon MB, July 7-9,