Nitrogen (N) plays a central role in modern agriculture. It is an essential nutrient and it is also the major
limiting nutrient in most agricultural soils growing non-leguminous crops. However, recovery of N in
cereal crops is usually 30-50% worldwide (Ladha et al., 2005). The percentage is often lower for paddy
rice (Oryza sativa L.) or for crops growing in high-rainfall or humid areas (Hauck, 1985). Low recovery
of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, and denitrification.
Improving N use efficiency (NUE) is desirable to improve crop yields, reduce cost of production, and
maintain environmental quality. One approach to increase NUE is to control the rate of N fertilizer
dissolution. Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of
uptake and utilization and optimum yield. Controlled-release fertilizers (CRF) and nitrification inhibitors
are potential sources for improving NUE in many crops (Shoji et al., 1991; Shaviv and Mikkelsen, 1993;
Shaviv, 2001; Trenkel, 2010).
The slow-release characteristics of CRF permit N uptake by plants according to their demand, and
reduce N leaching or denitrification losses. Polyolefin-coated fertilizer (POCF) is one of the CRFs
developed in Japan that shows highly controlled nutrient-release characterized by temperature. This
accurate nutrient control enables large amount of POCF to be placed with seeds or seedlings without salt
damage (Kanno et al., 1993; Kaneta et al., 1994). In order to distinguish the placement of large amounts
of POCF from seed-placement of small amount of soluble fertilizers, Shoji and Gandeza (1992) proposed
to name this method “co-situs” application. The central concept of co-situs application is to apply the
fertilizers at an intensive rooting zone with release patterns synchronized to the demand of the plant over
the entire growing season (Shoji and Kanno, 1994). The co-situs application of POCF has been carried out
for sustainable crop production in northeastern Japan.
It used to be common in Japan that a large amount of chemical fertilizer is applied to the paddy field by
broadcasting as basal application and then rice seedlings grown in the nursery boxes are transplanted using
mechanical transplanters. The recovery of the basal N applied by this conventional fertilization is low,
mostly less than 25% in northeastern Japan (Shoji and Mae, 1984). The strategy of co-situs application
was demonstrated in a paddy field at Akita Prefectural Agriculture Experiment Station, Ohgata, northeastern
Japan (Kaneta et al., 1994). Polyolefin-coated urea (POCU) was used in a no-till paddy rice cultivation by
transplanting the rice seedlings. All fertilizer N needed by rice for the entire growing season was applied
to nursery boxes using sigmoidal POCF (POCU-S100 which had a lag period of 30 days and release
duration of 70 days at 25°C). Rice seedlings were grown in 600g of POCU-S100 (240g N) applied nursery
boxes (size: 30 x 60 x 3 cm) without salt damage. Rice seedlings in 260 nursery boxes were transplanted
at a 30 x 15 cm spacing to a one-ha paddy field. This transplanting brought about 62 kg N ha-1 to the paddy
field because rice seedling roots held all fertilizer granules applied in the nursery boxes. Nursery boxapplied
POCU-S100 in a no-till transplanting paddy rice obtained a high correlation between the fertilizer-N
dissolution and fertilizer-derived N uptake (FDNU), and the very high fertilizer-N recovery using the 15N
tracer method, such as 87% of the dissolved N basis and 79% of the applied N basis in 1992. Compared
to the recovery of basal N applied by broadcasting soluble fertilizers, that of POCU was doubled by
broadcasting and almost tripled by co-situs placement in the paddy rice cultivation.
N release pattern, which includes soluble fertilizers with split-dressing and POCF with linear and
sigmoidal release, might strongly affect crop growth, yield and FDNU in the upland field under humid
condition. Several field experiments were conducted to determine (i) dent corn (Zea mays L.) N uptake
from split-dressed urea, co-situs applied POCU with linear (POCU-70) and sigmoidal (POCU-30+S60)
release using the 15N tracer method, (ii) N rate effect of single basal urea and two types of POCU (POCU-
30 and POCU-70) using the 15N tracer method, and (iii) effects of N supply pattern on the movement of inorganic N around the application site at the Kawatabi Experimental Station of Tohoku University,
northeastern Japan. Fertilizer-N recoveries of POCU with a sigmoidal release in 1994 and 1995 ranged
from 71 to 72% of the dissolved N basis, while those of POCU with a linear release and uncoated urea
were 60-63% and 40-57%, respectively (Kanno et al., 1997; Kanno, 2008). Synchrony of N supply with
crop demand using POCF improved NUE and reduced the N rate for target yield. Although N rate effect
of basal urea and two types of POCU on FDNU in 1996 and 1997 depended on yearly variations in climate
which related to the intensity of N leaching, the recovery of 150 kg N ha-1 uncoated urea, POCU-30 and
POCU-70 application were 49%, 61% and 63% in 1996 and 36%, 40% and 61% in 1997, respectively
(Kanno et al., 2006). Mean recovery rate significantly decreased from 52-36% with increasing N rate to
50-250 kg N ha-1 in 1997. Although the increase in N rate decreased the recovery rate, higher N recovery
rate of POCU-70 was sustained compared to those of uncoated urea and POCU-30. Due to microbial
transformations in most cultivated upland soils, mineral N source is likely to be oxidized to nitrate and
relatively high fractions of the applied N may potentially be leached or removed from the rooting zone
under humid condition. In this situation, N from POCF is expected to minimize or prevent nitrification or
nitrate leaching. Greater amount of soil inorganic N, which remained around the application site in the
middle to late growing season, increased fertilizer N uptake by dent corn in 1998 and 1999. The use of
POCU minimized the downward movement of soil inorganic N from the application site (Kanno et al.,
2000).