Accumulated Impacts of Sulfur Spraying on Soil Nutrient Availability and Microbial Biomass in Rubber Plantations

Abstract

Sulfur spraying is a conventional prevention and control measure for rubber leaf diseases in the northern margin of tropical Southeast Asia. The aim of this study was to determine the long‐term (48 years) accumulated effects of sulfur spraying on some major soil microbial and nutrient properties in the area of rubber plantation. The results indicate a significant decrease in pH along the rubber chronosequence with yearly sulfur application. A negative effect of sulfur spraying on soil total sulfur content was also observed. Apart from that, soil microbial characteristics increased significantly, except for microbial biomass carbon. Soil nutrient bioavailability‐related characteristics showed a complex pattern of response to sulfur spraying, among which bio‐available ammonium nitrogen increased linearly, bio‐available nitrate nitrogen showed a trend resembling a large resting capital letter “S”, bio‐available phosphorus showed a contrary trend to nitrogen, a capital letter “S” resting the other direction, whereas bio‐available potassium had no response to sulfur spraying. Based on the comprehensive response indexes, soil microbial characteristics had a pulsing response to sulfur spraying accumulation and two critical turning points were sometime between the 23rd and 32nd year and between the 40th and 48th year. Soil nutrient bioavailability showed a volatile comprehensive pattern, but there was no significant difference during the chronosequence. There is need for control sulfur deposition frequency and dosage under the soil and environmental safety threshold in the diseases prevention and control in monoculture rubber plantation.