عنوان مقاله [English]
For some reasons, increasing poplar spacing in traditional poplar farming is not accepted by farmers. Scientific investigations has shown that for increasing wood quality, selection of optimum spacing, appropriate harvesting time, and cultivation of agricultural crops between tree rows, specially at early years would increase productivity and poplar cultivation area. Therefore, in this study populus nigra betulifolia seedlings were planted as randomized complete block design with three replicates and four mixed poplar and alfalfa treatments with tree spacing including 3X4, 3X6.66, 3X8, and 3X10 m also 2 control treatments namely sole (pure) alfalfa and pure trees (3X4m). Plot size was 1200 square meters. We investigated some important attributes during the years 1998-2008. Irrigation operation was done during the growing seasons. Ten distinctive growth attributes in conjunction with poplar and alfalfa were recorded on the treatments at different stages and suitable times during the study period. The data were analyzed using univariate and multivariate statistical methods. The study is aimed at evaluating the performance of poplar production intercrops with alfalfa. Results showed that the most amount of tree height growth belonged to mixed treatments including 3X4, 3X8 and 3X6.66 m with 159, 158 and 142 cm, respectively. Regarding the wood volume growth per hectare, the most amounts belonged to the same treatments with 18.4, 11.1 and 10.99 cubic meters, respectively. Also the most amount of dry weight production of alfalfa belonged to sole alfalfa, 3X10 and 3X8 m treatments with 7507, 4788 and 4265 kg per hectare, respectively. All of attribute amounts showing differences among treatments were significantly different at 5% level of probability. There was no significant difference among the spacing after 11 intercropping years for branch diameter and annual tree growth diameter. Meanwhile, for some attributes there were significant differences among years and interaction between treatments and years. As a final result, the suitable planting spacing of tree in Poplar/alfalfa intercropping system is 3X6.6 m according to the site conditions.