Monitoring long term soil fertility trends in the South African sugar industry using the FAS analytical database

The South African sugar industry greatly depends on soil and leaf analyses conducted by its Fertiliser Advisory Service (FAS) for identifying nutrient disorders in sugarcane. As the industry uses more than 200 000 tons of fer tiliser annually, it is important that trends in soil fertility and plant n utrient uptake are monitored to ensure that fertiliser practices are econom ically justified and in harmony with the environment. A database has been c omplied from the analyses of more than 200 000 soil and 70 000 leaf samples conducted since 1980. This has yielded valuable information on the effects of fertiliser use in different regions and on different soils. Results of changes in nutrient availability in different extension areas over a 15 yea r period are reported in relation to four bioclimatic regions, six soil par ent materials, the main cane varieties and also crop age. A significant tre nd towards increased acidification of soils derived from basement granite a nd Natal Group Sandstone parent materials has occurred in the rainfed coast al regions. This contrasts with the observed increase in soil alkalinity in the irrigated areas of Mpumalanga. There has been a steady build-up of soi l potassium in many areas, suggesting over application of this nutrient. Fu rther examples are given of the use of the database to improve the efficien cy of fertiliser use.