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

The Centre for Soil and Agroclimate Research (CSAR) has been conducting a longtermproject on mapping of extractable soil P and K in lowlands since the late 1960s.Extensive mapping efforts have been restricted to soil P and K in lowlands becauselowland rice is the most economically important crop production system, and P and Kare the nutrients most likely to increase grain yields after nitrogen. The work at CSARhas resulted in complete extractable soil P and K maps for all the rice-cropping lowlandsof Java, Lampung in southern Sumatra, Bali, and Lombok. Some small uplandareas have also been mapped by CSAR for extractable soil P and K as part of landassessment processes conducted for the transmigration programs of the 1980s.Nutrient status maps produced solely by CSAR have not been published andhave therefore been largely inaccessible to researchers outside of Indonesia. Thischapter aims to introduce the evolution of extractable soil P and K mapping in Indonesiato the wider scientific community and demonstrate how the maps have beenused to improve P and K fertilizer recommendations. In conjunction with mappingexercises, many fertilizer response trials have been conducted, sometimes in the samelocation where soil samples were taken for mapping. Results from the field trialshave been used with the maps to create fertilizer recommendations for small regions.The review primarily examines the maps produced solely by CSAR but alsoincludes higher resolution maps produced by other institutions to highlight the limitationsof low-resolution mapping in improving fertilizer management. This review ofthe relationship between mapping and fertilizer recommendations is restricted to Javaand Lampung because these areas are the predominant ones for rice cropping andthey have high variability in P and K status relative to other mapped regions.The relationship between soil P status in the maps and P responsiveness of riceis exemplified through field trials including some trials conducted in 1998 in Lampung.Lampung was selected because the province has been mapped and it produces ricecrops that are responsive to P but not always as expected from soil P maps because ofP fixation. This is contrary to the situation in Java where rice crops have been overfertilized.As a result, rice is largely unresponsive to additional P and responsivenesstends to be closely related to expectations based on soil P mapping.Soils of Java and LampungSoil types are one of the elements of soil mapping that are used as a tool for producingfertilizer recommendations. The dominant soil types of Java and Sumatra differ; thus,the two regions need to be discussed separately (Table 1).Alluvials and Latosols are the main soil types in Java used for lowland ricecropping. Under native vegetation, lowland soils in Java are relatively rich in nutrientsbecause Java has a history of greater volcanic activity than the outer islands,especially eastern Indonesia (Amien 1997). The Latosols and Ultisols in the uplandsof Java have comparatively high native fertility and are highly weathered, acidic (pH4 to 5), low in most nutrients (Muljadi 1997), and susceptible to erosion even whenterraced (Amien 1997). However, with good fertilizer management, the uplands areproductive (Sri Adiningsih et al 1991).170 Clough et al