Intercropping hybrid poplar with soybean increases soil microbial biomass,mineral N supply and tree growth |
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| Authors: | David Rivest Alain Cogliastro Robert L Bradley Alain Olivier |
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| Institution: | 1.Département de Phytologie,Université Laval,Québec,Canada;2.Institut de Recherche en Biologie Végétale, Université de Montréal & Jardin Botanique de Montréal,Montréal,Canada;3.Département de Biologie,Université de Sherbrooke,Sherbrooke,Canada |
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| Abstract: | We hypothesized that tree-based intercropping in southwestern Québec, Canada, would stimulate soil microbial activity and
increase soil nutrient supply, thereby benefiting the growth of trees. Our experimental design comprised alternating rows
of hybrid poplar (Populus nigra L. × P. maximowiczii A. Henry) and high-value hardwood species spaced 8 m apart, between which two alley treatments were applied 5–6 years after
planting the trees. The first alley treatment consisted of a fertilized soybean (Glycine max (L.) Merr.) intercrop grown over two consecutive years, while the second consisted of repeatedly harrowing to minimize vegetation
in the alley. Tree rows were mulched with a 1.5 m wide polythene mulch. Microbial respiration and biomass, and mineral N concentrations
and mineralization rates were measured on five or six dates at 0, 2 and 5 m from hybrid poplar rows. On some of the sampling
dates, we found significantly higher soil microbial biomass, mineral N concentrations and nitrification rates, and a significantly
lower microbial metabolic quotient (qCO2), in the soybean intercropping than in the harrowing treatment. Over the 2 year period, hybrid poplar biomass increment and
N response efficiency (NRE) were significantly higher (51 and 47%, respectively) in the intercropping than in the harrowing
treatment. Microbial biomass and mineral N supply were significantly lower beneath the polyethylene mulch than in the alleys,
and we posit that this may stimulate the growth of tree roots into the alley. We conclude that soybean intercropping improves
nutrient turnover and supply for hybrid poplar trees, thereby increasing the land equivalent ratio (LER). |
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