Fei TENG, Huizhe CHEN, Yanhua ZENG, Xueqing CAI, Defeng ZHU

State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou 310006, China

In the last few years, with the significant rise in farmers’ income, it is no longer suitable to plant rice artificially, especially for the late transplanting rice, because it would require more labors to finish the job, which leads to a continuous decline in the plantation of late transplanting rice from accounting for 71% of the total rice land to the current 40%. Statistics suggested that the yield of two-seasonal rice was 57% higher than oneseason rice[1]. Therefore, it is of great significance for the increasing yield in China to stabilize and increase twoseasonal rice plantation area and to promote two-seasonal rice plantation technology[2].

Currently, there are many problems in the late transplanting rice,such as high sowing density, poor seedlings quality, and less elastic seedling age[3-5].In the southern China,especially in the lower reaches of Yangtze River, it has become one outstanding problem that the late transplanting rice is not suitable for plantation. Because the temperature during the seedling period of late transplanting rice is high, and the seedling grows rapidly. The seedling age often is no more than 18, while there is about one month in which both the early rice and the late rice are growing. Therefore, it is common to see the transplanting of late rice. 36 days after sowing, the seedlings and roots deteriorate, and the ratio of sugar to nitrogen declines significantly.The seedling is long and slender,and is not suitable for mechanical plantation[6]. Studies found that the yield decreases rapidly after transplanting seedlings and the yield decreases with the rising of transplanted seedlings[7-8]. However, the current studies often focus on one species,and there are little studies on the influences of late transplanting ages on different species. In order to fully un-derstand the influences of different transplanting ages on the growth and yield of rice, we studied four different species and observed their growth and yield, and defined the features of late transplanting rice, which can provide theoretical references to promote the development of rice planting technology.

Materials and Methods

Materials and plant methods

The experiment was carried out in the China National Rice Research Institute in 2013. The soil texture was sticky and fertile. The annual average temperature was 16 ℃, and the precipitation was 1 388 mm. The sunshine hours were about 1 763 h and there were 231 frostless days.Table 1 showed the test species and related features, both as late rice. We planted seedlings on July 1 and used mud to cultivate seedlings. The seedling board that was prepared three days before sowing plants was 1.5 m wide,while the ditch was 0.4 m wide. There were two rows of seedlings in the seedling disk that was 58 cm long and 28 cm wide. The disk bottom was closely related to the seedling bed.We selected and dried seedlings before putting seedlings into water. We accelerated germination and the sowing amount was 80 g per disk.

Experiment design

The tested species were sowed on July 1. The 10-day-old seedlings were the first period and there were five periods in general. The seedlings were transplanted every fifth day. The longest seedling period was 30 days.

The row spacing was 30 cm, and the plant spacing was 14 cm. There were two branches in each bundle.The fertilizer and water treatment was consistent with diseases and insect pests treatment, and the base fertilizer,tillering fertilizer and panicle fertilizer were applied at a proportion of 5:3:2. The tillering fertilizer was applied within one week of mechanical plantation. Phosphate fertilizer was all applied as basic fertilizer. We adopted the intermittent irrigation method for rice plantation.

Determination project and method Growth period and tillering dynamics We recorded the growth of different species in various growth periods,from sowing period,transplanting period,earing period,flowering period and maturing period. After transplanting seedlings, we selected three representative places, and evaluated the number of earing.

Seedlings quality We chose 20 strains of seedlings for each treatment before transplanting. We measured the seedling height,the root length and the number of roots. The seedlings were parched at 80 ℃.

The quality of dry matter and the leaf areas We selected three rice strains for different treatments during the earing period and flowering period.We measured the green leaves on the plants with the LI-3000A leaf area meter produced by LI-COR Company.We put the leaves,stems and ears into different bags and then dried them at 80 ℃.

Table 1 Tested species

Table 2 Comparison on the quality of different transplanted seedling ages

The yield and its composition We looked into the number of effective ears in each treatment, and calculated the average number of ears in each strain. We chose three representative plants to measure the number of particles in each ear, the fertility rate and the particles weight.We measured the regional yield by calculating the standard moisture.

Data treatment and analyses

SAS software and Excel software are used for analysis. The variation analysis used LSD multiple comparison method.

Results and Analyses

The seedlings of different ages

We studied the quality of seedlings of different ages and found that the strain height of the first three patches of plants increased significantly, while the last two patches roseslowly. Mechanical plantation required the transplanting of seedlings, and the stain height was between 12 and 20 cm[9-11]. Therefore, the planting results would be influenced if the plants were transplanted 20 days later. According to the root length and the root number of ten-day-old seedlings were notably smaller than other seedlings, which suggested that the roots of early transplanted seedlings were poor, and the seedling result was not ideal.Comparing the dry weight of the upper seedlings,we found that the dry weight of the aerial part of “Yongyou No.8”gradually enlarged, and there were significant differences between plants.The dry weight of “Xiushui 03” increased dramatically along with the rise in the seedling ages.Therefore,as the transplanted seedlings grew older,the accumulated efficiency of dry matter gradually declined, and were affected by plants of the last three stages.

Table 3 Influences of different transplanting seedlings on the rice growth d

Comparing the growth of seedlings of different ages

Table 3 compared the growth of seedlings of different ages. We found that the older transplanted rice seedlings were,the longer earing days lasted, which suggested that it was difficult for the rice that is thermalresponse to achieve full heading, and the planting risks were large. There were little differences in the full-heading period of the rice that was sensitive to light. According to the number of days between earing days to the maturing days, the milking phase of the rice that was photo-response tended to rise, as the transplanted rice got older, while the milking phase of the rice that was thermal-response was likely to be longer. Therefore, it had been observed that the growth of rice that was thermal-response was greatly influenced by the seedling ages. The long transplanted seedlings ages led to the delaying of growth period, and thus the seedlings in the milking phase would also suffer. On the contrary, the rice that was photo-response would not be greatly influenced by the seedling ages.

Table 4 Yield and component factors of plants at different transplanting seedling ages

The quality of dry matter at different periods

Fig.1 compared the accumulation of dry matter during the jointing phase,the full heading phase,and the maturing phase. In the early period of growth, as the seedlings grow elder,the growing period for seedlings shortened, which would lead to malnutrition. The processed dry mattergradually accumulated with the prolonging of field plantation.According to the dray matter quality during the full heading phase, the differences between seedlings of divergent ages narrowed down as dry matter quality continued declining. As we can see from the dry matter quality during the final mature phase, the dry matter of 15-day-old seedlings that were thermal-response were more than 10 days of treatment, while the rice that was photo-response still declined. Generally speaking, the dry matter quality during the nutritional period varied significantly,and the differences of plants during the growth period were small,which suggested that the late transplanting produced significant impacts on the nutrition accumulation of late rice seedlings. The nutrition accumulation was not proportional to the seedling ages.

Yield and its component factors

Table 4 compared the rice yield of different seedling ages. As the age of transplanted seedlings increased, the yield of rice that was photo-response varied little,and by comparing the yield of two species that was sensitive to temperature, the yield of Tianyouhuazhan had decreased notably since the 20thday, while the yield of Hyou 518 had started to decline since the 25thday, which suggested that the yield of rice that was thermal-response was greatly influenced by the transplanting ages. When we analyzed the yield composition of different treatments, each species showed regular differences in the aspect of effective earing number and fertility rate. As for the number of effective earing, the species that was thermal-response at the last two periods was less than that of the first three treatments.The fertility rate of Tianyouhuazhan started to decline since the 25thday, and the fertility rate of Hyou518 descended since the 30thday, which indicated the late transplanting rice was considerably affected by the fertility of late rice that was sensitive to temperature. The fertility rate of 30-day-seedling of Yongyou 8 fell rapidly,while the difference of the fifth Xiushui 03 fertility rate was insignificant. Therefore, the age of transplanted seedlings had significant influences on the yield of late rice.The primary reason for the reduction of yield was that the late transplanting rice led to a decline in the number of effective earing and a decrease of fertility rate.

Conclusions and Discussion

The current mechanical planting requires transplanting medium and small seedlings, while it is common to see late seedling because of seasonal changes. In order to enhance the quality of mechanical transplanting of late rice, and to stabilize the rice production, it is necessary to define the influence of late transplanting seedlings on its growth and yield.

Because of different selected materials and regional environment, the study results were not the same. Because the species in most experiments was uniform, it was difficult to study the influences of late transplanting seedlings on the growth and yield of late rice.As we can see from the yield,most mathematics scholars found that with the delay of seedling ages, the yield of mechanical plantation of rice tended to decline[12-14]. Some other scholars believed that the yield of mechanical plantation first rose and then declined[15]. This study result proved that with the delay of transplanting days and increase of seedling ages, the yield of transplanted seedlings was little, and the transplanted seedlings of late maturing species were no more than 30 days.Studies found that influences of late transplanting rice were significant to the number of effective earing and fertility rate. With the increase in the transplanted seedling ages,the fertility of each species tended to decline. Besides, it is widely acknowledged that the seedlings of late transplanted plants were weak,and the root activity was poor[7,16-18]. This study proved that too early or too late of transplanted seedlings were detrimental to mechanical plantation, which was the same as previous studies.

The growing phase is an essential study object of this experiment. Studies found that the age of transplanted seedlings exerted significant influences on the late rice that was thermal-response, and had small influences on the late rice that was photoresponse. As the seedling age grew older, the thermal-response rice delayed in different degrees during the full heading period and maturing period,and it was easy to suffer from cold temperature until milking. The growing period of photo-response species was barely affected by the seedling ages,so the growth period did not delay.The comparison of dry matter quality at different phases indicated that the dry matter accumulation was seriously affected by seedling age.The dry matter quality of thermal-response rice increased rapidly,while the dry matter of photo-response rice tended to decline gradually. The optimal transplanting seedling age was 15 days of thermalresponse rice, while photo-response rice was 20 days. The thermal-response rice should be selected as early maturing varieties,while the photo-response rice could be selected as late maturing varieties for high yield.

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