[Effects of Different Equal N Substituting Proportions of Chemical Fertilizer with Organic Fertilizer on Soil Active Organic Carbon Components and Enzyme Activities in Rubber Plantation Field of Hainan， China].

The effect of organic fertilizer substituting chemical fertilizer on active soil organic carbon （SOC） composition and enzyme activity in rubber plantation soil of Hainan is still unclear. In this study， the 0-40 cm soil （10 cm per layer） in the rubber plantation fields of Hainan was taken as the research object， and a total of six fertilization treatments were set up： nitrogen-free control （CK）； chemical fertilizer （NPK）； and organic fertilizer substituting 25%， 50%， 75%， and 100% of chemical fertilizer （M25， M50， M75， and M100）. Soil physicochemical properties， five active SOC components [particulate organic carbon （POC）， light organic carbon （LFOC）， easily oxidized organic carbon （ROC）， dissolved organic carbon （DOC）， and microbial biomass carbon （MBC）] and four types of soil enzyme activities [β-1，4-glucosidase （BG）， β-1，4-N-acetylglucosaminidase （NAG）， L-leucine aminopeptidase （LAP）， and acid phosphatase （ACP）] were analyzed to seek the best substitution ratio of chemical fertilizer with organic fertilizer and provide theoretical basis for improving soil fertility in Hainan. The results showed that organic fertilizer substituting chemical fertilizer could increase soil pH. The bulk density in the 0-10 cm and 20-30 cm soil layers was the lowest in the M50 and M25 treatments， respectively. The total nitrogen （TN） content in the 0-40 cm soil layer in the M50 treatment was the highest， and SOC stock （SOCstock） was in the order of M50>M25>M75>M100>NPK>CK， ranging from 4.7-6.6 t·hm-2. The ROC was significantly higher under the four replacing treatments than that of the CK and NPK treatments in the 20-30 cm soil layer. The DOC under the M50， M75， and M100 treatments was significantly higher than that of the CK and NPK treatments in the 20-30 cm soil layer， and there was no significant difference among all of the replacing treatments. Only the M50 treatment had lower activities of BG， LAP， and ACP in the 0-10 cm soil layer than that in the 10-20 soil layer. Compared with those in the NPK treatment， the M50 treatment significantly decreased the activities of BG （-27.3%）， LAP （-21.3%）， and ACP （-23.2%） in the 0-10 cm soil layer， and the M25 treatment significantly reduced the activities of NAG （-34.0%） and LAP （-35.8%） in the 20-30 cm soil layer. Fertilization method and soil depth had significantly interactive effects on BG and ACP activities. In the 0-10 cm soil layer， the vector length （1.0） of the M50 treatment was significantly lower than that of the NPK treatment （1.2）. In the 30-40 cm soil layer， the vector length （1.1） of enzyme activity under the M25 treatment was significantly lower than that of the CK treatment （1.3）， indicating a weak microbial C restriction. The vector angle （VA） of enzyme activity under the six fertilization treatments was greater than 45°， indicating a strong microbial P restriction. In the 0-40 cm soil layer， the VA of enzyme activity （59.1°-62.0°） under the four replacing treatments was lower than those under the CK （62.1°） and NPK treatments （62.3°）. SOC was positively correlated with pH， TN， AP， AK， POC， LFOC， ROC， and DOC. SOC was negatively correlated with VA. VA was negatively correlated with AP （P<0.05）. With the respective of comprehensive evaluation， the M50 treatment had the best synergistic effect on soil physicochemical properties， active SOC components， and enzyme activity in the rubber plantation of Hainan and could be promoted in the rubber planting area of Hainan.