Pueraria phaseoloides as a cover crop in agroforestry systems in the humid tropics: growth, nutrition and biological N2 fixation.

Analyse of the biomassa production and nutrition of pueraria as a cover crop grown in three different agroforestry systems (1- cupuacu, pupunha e seringueira; 2- cupuacu, pupunha, castanha-do-Para, urucu; and 3- cupuacu, seringueira, coco, citros) at two levels of fertilisation, and its potential to contribute to the N stocks of the cropping system by biological N2 fixation (NBF), in a Xanthic Farreasol in Manaus-AM (Brasil). With the exception of K, the nutrients stocks in pueraria litterwere more than twice as high as the nutrients applied by fertilisation. consequently, nutrient turnover of pueraria was an important process in the nutrient cycling of the fruit tree production system. The N in pueraria derived from biological N2 fixation estimated by 15N enrichment reached values from 9% to 45% and was higher throughout the wet than the dry season. Thus, 32-158 Kg N ha-1 of the biomass N were derived from atmospheric N2 exceeding the amounts of N added by fertilisation. The larger nutrient uptake and return through litter indicated a rapid nutrient cycling and plant-topsoil interface, thus reducing leaching and keeping nutrients available