Phosphorus (P) is an essential limiting nutrient for crop growth and productivity in most agroforestry systems. The knowledge of how rubber-based agroforestry systems with different ages affect P availability underlying complex rhizosphere mechanisms is unavailable. 

In a study published in Geoderma, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) evaluated the short-term (seven years) impact of perennial legume cover crop on rhizosphere P dynamic and availability during the dry and wet seasons in two rubber-based agroforestry systems of different ages located on P-deficient soil in southwest China. 

By analyzing cover crop biomass and P content, as well as net rhizosphere changes in P-mobilizing capacity and P fractions, the researchers quantified the cumulative effects of cover crop on rhizosphere P availability. 

They found contrasting seasonal effects of perennial cover crop on rhizosphere P cycling after seven years of surface-placed residues of legume plant under no-till acidic soil in rubber-based agroforestry systems. 

Compared with respective monocultures, young agroforestry systems increased plant biomass and P stock in both seasons, but the mature ones decreased their levels, except for increased biomass and P stock of floor litter in the dry season.  

Furthermore, young and mature agroforestry systems decreased net rhizosphere Ca–P in the dry season and wet season respectively. Young agroforestry systems changed net rhizosphere P fractions, but the mature ones remained constant.  

"Our results suggest that rhizosphere P cycling and availability were more significant in young agroforestry systems. The biomass of the cover legume plant residue is more beneficial than other factors in controlling rhizosphere P cycling processes in rubber-based agroforestry system," said LIU Chenggang from XTBG.