| Crop management practices have significant effects on plant growth and yield formation in rice. As compared with single season rice, double season rice increases grain yield through the increase in harvest area, it is considered as one effective way to addressing food security issue. However, grain yield of double season rice is significantly affected by various management practices, such as seedling age. To determine the effects of different crop management practices on growth and yield formation of double season rice, field experiments were conducted at Dajin, Hubei Province, China(29°51′ N115°33′ E) in early and late seasons of 2013 and 2014.The experiment was arranged in a split-split plot design with seedling ages as main plots, transplanting density and seeding rate as sub and sub-sub plots, respectively. The objectives of this study are to investigate the effects of various crop management practices on rice growth, examine if seeding rate and transplanting density treatments could alleviate the negative effects of prolonged seedling age in double season rice, and determine the effect of seeding age, transplanting density and seeding rate on rice yield and yield components. The results are as follows:Plant growth was significantly changed due to the variation in seedling age. Stem height of main stem was lower than of tiller stems at prolonged seedling age treatment, and both of which were significantly lower than that at normal seedling age treatment. Panicle height at normal seedling age treatment was 14.1 and 35.6 % higher than that of main and tiller stems at prolonged seedling age treatment, respectively. Compared to normal seedling age treatment, leaf area index(LAI), specific leaf weight(SLW), crop growth rate(CGR), dry matter production and translocation were all reduced at prolonged seedling age treatment. At PI, LAI at normal seedling age treatment was 117.4% higher than at prolonged seedling age treatment. There was no significant difference between the two seedling age treatments at heading(HD). CGR at normal seedling age treatment was 124.7, 18.6 and 9.0 % higher than at prolonged seedling age treatment from seeding to PI, seeding to HD and seeding to maturity, respectively. The amount of preanthesis dry matter transported to grain during grain filling was 308.8% higher at normal seedling age treatment than at prolonged seedling age treatment.Among the three transplanting density treatment, T2 had highest LAI and CGR than T1 and T3. No significant differences were found in biomass production and translocation during grain filling. Low seeding rate treatment had relatively higher LAI and CGR, but similar SLW, biomass production and translocation compared with high seeding rate treatment.1. Seedling age treatment significantly affected the heading dynamics. At prolonged seedling age treatment, premature heading occurred in the main stems. There were two phases of heading for main and tiller stems, respectively at prolonged seedling age treatment. Compared to normal seedling age treatment, heading of main stems at prolonged seedling age treatment started 5 and 10 days earlier in early and late season rice, respectively; heading of tiller stems started 6 and 11 days later. Transplanting density treatment had no effect on the date of premature heading, but affected number of main stems bearing premature heading panicles. Premature-heading panicles at T2 treatment were around two folds of at T1 and T3 treatments. Low seeding rate treatment could delay the occurrence of premature heading in the main stems.2. Compared with normal seedling age treatment, grain yield decreased by 9.3% due to the lower biomass(7.0 %) and grain weight(7.9%) at prolonged seedling age treatment. The reduction in biomass at prolonged seedling age treatment may be caused by the decrease of plant height; the lower grain weight might be due to the occurrence of premature heading. Among the three transplanting density, grain yield at T2 was 3.2 and 10.8% higher than T1 and T3, respectively. The yield advantage at T2 resulted from more panicles m-2, which was 12.7 and 32.8% higher at T2 than T1 and T3, respectively. Grain yield at S2 was 2.7% higher than at S1 because number of spikelets m-2 at S2 was 1.5% higher.In conclusion, among the three agricultural treatments, seedling age had the largest effect on growth and yield formation in double season rice in our study. Prolonged seedling age treatment lead to a decrease in seedling quality, a reduction in growth and dry matter production, premature heading and yield loss. Transplanting density and seeding rate treatments could not alleviate the negative effects from prolonged seedling age treatment. Therefore, proper seedling age is vital in achieving high and stable grain yield in double season rice in central China. |
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