Material and Method

1. 2008 2010 Wheat plotRape plot Fig.3 The succeeding soybean growth at flowering stage in wheat or rape plots . AMF colonization rate(%) * ** Spore density (/g soil) ** ** ** ns * ** Soybean yield (g/m2) * Fig.4 Succeeding soybean yield from 2008 to 2010 after the cultivation winter crops. Fig.2 AMF colonization rate at flowering stage of succeeding soybean. Fig.1 AMF spore density at sowing of succeeding soybean. Effects of the Winter Crop on the Spore Density ofArbuscularMycorrhizal Fungi and the Growth of Succeeding Soybean Katsunori ISOBE*, Masao HIGO and Ryuichi ISHII College of Bioresource Sciences, Nihon University, Fujisawa Kanagawa 252-0880, Japan Arbuscular mycorrhizal fungi (AMF) improve the uptake of phosphate from soil through symbiotic associations with plant roots. The colonization in plant roots is necessary for the proliferating and new spore formation of AMF. When the non AMF host crops cultivated in winter, the density of AMF decreased. And if P fertilizer not applicant at the succeeding crop cultivation, the phosphorus lack probably occurred. In this experiment, we investigated that the effects of AMF host (wheat) or non host (rape) crop cultivation from autumn to spring on the AMF spore density and the succeeding soybean growth and yield. Table 1 Total P (mg/g) in soil at soybean sowing. Material and Method From autumn to spring, the wheat (Wheat plot) or rapeseed (Rape plot) were grown in experiment field of Nihon University from 2008 to 2010. And Fallow plot (no crops from autumn to spring) was prepared. From spring, soybean (cultivar;Enrei) plants were grown in all plots. In this period (from 2008 to 2010), phosphorus fertilizer did not applicant in all plots. Wheat (Triticum aestivum L.) and soybean (Glycine max Merr.) are the host plant of AMF, and rape (Brassica napus L.) is not host plant of that. The soil type of experiment field was volcanic ash soil. The phosphate absorption coefficient was very high (about 1800) and Bray Ⅱphosphate and total P content was very low (Table 1). The repetition number of this experiment was 3. After cultivation of winter crop, the spore density of AMF in field soil were analyzed. And the flowering stage of soybean, the colonization rate of AMF in soybean root were analyzed. At maturity stage of soybean, the yield of soybean analyzed in all plots. Result and Discussion The AMF spore density in soil of Rape plot decreased after cultivation winter crops in each year. On the other hand, the AMF spore density of wheat plot increased after the cultivation of wheat. Significant differences were found among the spore density of both plots in each year (Fig.1). This tendency was remarkable in Second (2009) and third year (2010). And the AMF colonization rate of succeeding soybean in wheat plot was higher than those in rape plot. But, No significant difference was found among the colonization rate of both plots in 2008, and significant difference were found in 2009 and 2010 (Fig. 2). The growth of succeeding soybean in each plot did not cleared in the first (2008) , and in the second (2009) and third (2010) year, those were cleared in each plot. Top dry weight, LAI and top P-absorption in wheat plot were higher than those of rape plot (Fig.3, Table 2). The succeeding soybean yield decreased second (2009) and third (2010) year. In first year, the succeeding soybean yield of rape plot was higher than that of wheat plot, on the other hand, in second and third year, the yield of wheat plot was higher than that of rape plot (Fig.4). In this experiment, P-fertilizer did not applicant in all plots. Phosphorus (P) content in soil decreased from first year to third year. And the P lack of soybean plants probably occurred in second and third year of rape plot. But, P lack did not occurred in wheat plot by the colonization of AMF. The colonized AMF in soybean roots of wheat plots uptaked P from soil and uptaked P by AMF transferred to host soybean plants in wheat plot. In conclusion, effective utilization of P in field soil by the large amount of fertilization in the past would be achieved by developing an appropriate combination with succeeding and subsequent crops due to utilization indigenous AMF. Table 2 Effects of winter crop on the growth of succeeding soybean. : Sporedensity at start