A variety of rubber agroforestry systems have been developed and are considered a sustainable practice to reduce competition for land and diversify farmers' income at the same time. However,  

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences conducted a study aiming to discern how the dynamics of soil P fractions are affected by two different stand ages (10- and 22-year-old, young and mature) and two management practices (mono- and intercropping) in rubber plantation systems. 

The researchers examined the seasonal, management and stand age effects on P fractions, acid phosphatase activity, microbial biomass P, other physical-chemical properties and litter and roots in four systems: 10-year-old rubber mono- (YM) and intercropping (YI) with N-fixing species (NFS), 22-year-old mono- (MM) and intercropping (MI) in Xishuangbanna, Southwestern China. 

They found that dynamics of P fractions and bioavailability differ with management and stand age. Most P fractions varied seasonally at different soil depths, with highest values in the fog-cool season (i.e. labile P at 5–60 cm, non-labile P, total inorganic P and organic P at 30–60 cm), while moderately labile P varied little over time. 

They further found that residual organic P acted as a buffering pool for labile P in highly weathered soil. Total P stock, to a certain extent, was reduced in YI, but increased in MI. In the long run, P pools cannot be compensated for traditional application of fertilizers, and thus litter conservation should be strengthened. 

The researchers thus concluded that mature rubber plantation intercropping with N-fixing species appears to be more effective than young stand for P pool sustainability and high system productivity. 

The study entitled "Phosphorous fractions in soils of rubber-based agroforestry systems: Influence of season, management and stand age" has been published online in Science of The Total Environment.