Response of dent corn and sweet corn [Zea mays] to two different forms of Co-situs application methods of controlled release fertilizer in upland field of a volcanic ash soil

Summary Polyolefin coated fertilizer as a new type of controlled release fertilizer (CRF) has began to be used in upland crops in Japan due to its high N recovery rate and environmental friendly characteristics under humid climate. The objective of this paper lies in investigating the response and adaptability of dent corn ( Zea mays L. var. indentata Sturt.) and sweet corn (Zea mays L. var. saccharata Sturt.) to two forms of co-situs application methods (co-situs band application and co-situs spot application) of CRF in upland field of a volcanic ash soil (Alic Pachi Mellanudand) under humid climate conditions. The results obtained showed that, compared to the conventional side-band application of urea, for sweet corn and dent corn, in co-situs spot application of LP70 (polyolefin coated urea, 70 day type), the mean germination percentage at each sowing point greatly decreased by 66.7% and 50%, respectively ; In co-situs band application of LP70, the germination percentage decreased by 26.7% and l0.0%, respectively ; under the condition of co-situs band application of urea, nearly all the seeds of two corns did not germinate and the germinating power was inhibited completely ; The weather conditions with less rainfall and higher temperatures at the germination stage probably increased tendency of poor germination under the co-situs application conditions ; Co-situs spot application of LP70 further retarded seedling development, but such retardation was not obvious at the late growing period because of good water conditions, and in this treatment, the grain yield of both corns as well as the uptake amount of N, P, K decreased significantly, too, but there were no significant difference for harvest index and nitrogen harvest index as compared with control, suggesting that poor germination and less plant number is the main reason for significant decrease of yield and nutrients uptake. Based on the above results, it is therefore recommended that the co-situs application of CRF especially the co-situs spot application would not be applied in sweet com production, and the co-situs band application of CRF is ideal fertilization method for dent corn production under upland conditions without irrigation in humid area.