Contents & Foreword, Characterizing And ... - IRRI books

Table 3. Phosphorus fertilizer recommendationsfor lowland rice grown in Java based on soil Pstatus as determined by 25% HCl extraction(Hermanto 1995).Extractable P Recommended P rate(mg kg –1 ) (kg ha –1 )176 10 every fourth seasonsoil P was increased. In 1998, the fourth edition of lowland maps for Java and theouter islands was digitized by CSAR.The definition of low, medium, and high soil P was derived from P responsivenessfield trials conducted throughout the lowlands of Java (Table 3). The lack ofresponse to P fertilizer was demonstrated in 18 and 15 trials conducted by Sri Adiningsih(unpublished) over the 1987-88 wet season and 1988 dry season, respectively. Ricegrown in the wet season responded to P at only seven sites and rice grown in the dryseason responded at only two sites. The significant yield increases tended to be small(0.5 t ha –1 ) in terms of actual grain yields. Trials with rice on experimental farmslocated at Muara in West Java and Ngale in East Java in the wet and dry seasons alsoproduced no response to P applications (Miyake et al 1984).The fourth edition (Widjaja-Adhi and Sri Adiningsih, personal communication)of lowland soil maps for Java (scale 1:500,000) showed that most of the lowlandsof Java were classified as having medium to high soil P status (Fig. 1). Thedominance of medium to high P status is because the lowlands have received P fertilizerin excess of that required for rice crops for many years. Over the past 30 years, Phas been applied to irrigated and rainfed lowland rice fields at an average of 20 kg Pha –1 crop –1 . Subsequently, extractable soil P has increased as P has accumulated in thesoil and P fertilizer requirements in 1999 are low (Table 2). Mapping data and resultsfrom lowland rice trials indicate that P fertilizer need only be applied to most lowlandrice in Java at rates equivalent to the amount of P removed in the grain. High-yieldingrice cultivars may produce between 5 and 8 t grain ha –1 (Hermanto 1995); thus, Pfertilizer needs to be applied at between 12.5 and 20 kg ha –1 crop –1 to avoid removingP from the soil. However, most lowland areas in Java can be cropped for severalseasons without a depletion of soil P resulting in a decline in grain yield.Soil P maps (1:500,000) of the lowland areas of Lampung also show that largeareas have a high soil P status (Fig. 2), which has been extensively developed foragricultural use through the transmigration programs. However, using the same classificationsystem, other provinces such as South Sumatra are mainly classified ashaving low to medium soil P status (Table 2). Lowland regions on most of the otherislands that have been mapped are deemed to have low to medium soil P status. Exceptionsare the soils of Bali and Lombok (Fig. 3), which have medium to high soil Pbecause the islands are volcanic.174 Clough et al