Evaluation of Controlled Release Fertilizer on Bulb Yield, Nutrient Content, and Storage Quality of Overwintering Intermediate-Day Onions

Abstract

Controlled release fertilizer (CRF) can delay its availability for plant uptake and increase fertilizer use efficiency, which might be useful for overwintering onion (Allium cepa L.) which has a growing season of 7 to 8 months. The study was performed to evaluate the effect of CRF on bulb yield, nutrient content, and storage quality of intermediate-day onions in onion growers’ fields during the 2013/2014 and 2014/2015 growing seasons. The formulation of CRF used was 18N-3.1P-7.5K, and as an N source, 50% polymer-coated urea-N and 50% urea-N plus diammonium phosphate-N were blended. Treatments included CRF 25%, CRF 50%, CRF 100%, or CRF 150% based on the soil test recommended N rate. Separated NPK fertilizers of single application (NPK once), three-split application (NPK 3-split) and non-fertilized plot were checks. Soil NO3-N content in all CRF treatments and NPK once peaked at 133 days after transplanting. Marketable bulb yields for NPK once and CRF 150% was 66.12 Mg ha-1 and 65.67 Mg ha-1, respectively, on a 2-year average, which were not significantly greater than CRF 50%, CRF 100%, and NPK 3-split. Most nutrient uptakes in the bulb were not different among all treatments except for no fertilization. Apparent nutrient recovery of CRF 25% was 32.5% in N, 20.9% in P, and 76.1% in K on a 2-year average, approximately twice that of CRF 100%. Total flavonoids content was higher in CRF 25% than in other treatments. The 50% reduced CRF rate based on the soil test recommended N rate should satisfy crop demand of available nutrients when electric conductivity was more than 1.5 dS m-1 and organic matter was 35 g kg-1 in preplant soil.Comparison of bulb yield characteristics of onion as affected by application rates of controlled release fertilizer (CRF) and application methods of NPK fertilizer. Treatments Marketable yield (Mg ha-1) Unmarketable yield (Mg ha-1) Stand reduction (%) Large† Medium Small Total 2013/2014 CRF 25%‡ 52.98 ns§ 27.48 ns 1.26 ns 81.73 ns 1.29 ns 2.8 ns CRF 50% 62.67 22.44 0.67 85.79 0.69 2.3 CRF 100% 67.81 19.62 0.45 87.87 0.94 4.6 CRF 150% 68.31 22.00 0.58 90.89 0.55 1.9 NPK once 69.16 18.81 1.49 89.47 1.21 2.8 NPK 3-split 68.08 19.13 0.50 87.71 0.80 5.1 No fertilization 60.71 22.08 1.49 84.29 0.56 5.6 2014/2015 CRF 25% 3.28 ns 24.41 ns 10.37 b 38.07 ns 0.80 ns 7.90 ab CRF 50% 2.87 29.07 8.96 b 40.89 0.48 8.94 a CRF 100% 2.10 22.69 10.28 b 35.07 0.97 8.31 a CRF 150% 3.16 27.14 10.14 b 40.44 0.72 6.30 ab NPK once 4.43 28.24 10.10 b 42.77 1.02 6.83 ab NPK 3-split 2.33 28.68 10.88 b 41.88 0.68 4.88 b No fertilization 0.67 14.92 17.18 a 32.78 0.33 7.17 ab F-test Year (Y) ** ns ** ** ns ns Fertilizer (F) ns ns ** ns ns ** Y × F ns ns ** ns ns ns †Size categories in bulb diameter: large (≥8.0 cm), medium (≥6.0 and <8.0 cm), small (≥4.0 and <6.0 cm), and cull (<4.0 cm).‡CRF 25%, 50%, 100% and 150% rates based on soil test recommended N rate; NPK once = single application of N, P and K with 100% rate based on soil test recommended N, P and K rate; NPK 3-split = basal and 2-split applications of N, P and K.§Fisher’s protected least significant difference (p ≤ 0.05). ns, *, **: not significant or significant at p ≤ 0.05, p ≤ 0.01.