Cycling of potassium in a mature oil palm agroecosystem on an Oxisol in Malaysia

摘要

Oil palm is mainly grown on highly weathered Ultisols and Oxisols with low indigenous soil fertility. Usually, large amounts of fertilizers are applied to be able to sustain its production. This study was conducted to understand the K cycling in a mature oil palm agroecosystem on an Oxisol. Two representative 16-year old palms each from a fertilized and an unfertilized treatment in a NPK fertilizer response trial were sampled to determine the K contents in the various palm components. The K contents of other vegetation in the field and the soil were also determined. The K losses from fertilizer were estimated from annual rainfall at the experimental site based on reported models of run-off and leaching on similar soil and terrain. Results showed that the oil palm required 108 kg K ha~(-1) yr~(-1) and 245 kg K ha~(-1) yr~(-1) to produce fresh fruit bunches and leaves, respectively. Storage of K in the stem amounted to 96 kg K ha~(-1) yr~(-1). Thus, the oil palm needed about 484 kg K ha~(-1) yr~(-1), which included the K requirements (35 kg K ha~(-1) yr~(-1)) for male flowers and new roots. K losses through soil processes accounted for only 33 kg K ha~(-1) yr~(-1) while ground vegetation immobilized 5 kg K ha~(-1) yr~(-1). The infertile Oxisol soil could only meet about 10% of the K demand by the oil palm agroecosystem. The major components of K supply were applied K fertilizer (30% of K demand) and pruned oil palm leaves (23% of K demand). The other components of K supply were decayed male flowers, rain water and stemflow. This study shows that the oil palm is efficient in K cycling with minimal K losses to the environment provided excessive K fertilizer rate is not applied.