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

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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