Delayed Transplanting of Aged Rice Seedlings Causes the Yield Reduction in Farmer's Field

Four year experiments were conducted to find out the causes of yield reduction of farmer’s field of Nepal from 2011 to 2014. Randomised complete block design with three replications were used to compare twelve rice genotypes with Khumal-4 as a standard check. One set of genotypes were transplanted in the last week of June and the other set was transplanted two weeks delayed as summer season rice. Results showed that rice different parameters like grain yield, plant height, panicle length, days to heading and days to maturity were found significant (p<0.05). Plant height, panicle length and fertile grain per plant were also found significant in early transplanted rice than delayed transplanted rice. Delayed transplanted aged rice seedlings took shorter days to flower and mature than early transplanted rice. On an average, 38.44% decrease in yield was found from early to delayed transplanted rice from 2011 to 2014. Similarly, grain yield of early transplanted rice was found higher than delayed transplanted rice in all the year. The reason could be that too early and too late transplanting could not fulfill the required temperature and photoperiod for rice crop. Late transplant of aged rice seedlings are severe to cold and effect plant growth and yield. Thus the yield reduction of farmer’s field can be minimised by transplanting rice in appropriate time with recommended package of practices.


Introduction
Quality seeds, irrigation and fertilizers are prerequisite materials for harvesting higher productivity from a crop. Though farmer's supply quality seeds, fertilizers and irrigation in time and grow rice in well managed way, they found difficulty to get its potential yield in countries like Nepal. Agricultural scientists and policy makers have also reported the yield reduction in farmer's field which might be due to farmer's poor field management, less use of fertilizers, lack of high yielding fertilizer responsive variety, unavailability of irrigation facility in time and lack of trained farmers (NARC, 1997). Earlier scientists have reported that late transplanting cause yield reduction and reduce total biomass of the crop (Santhi et al, 1998).
Yield is the end result of interaction between genetic constitutions of a plant and environment under which it grows. Among environmental factors, climate plays an important role in getting high yield. The highest yield can be harvested with earliest planting (Kumar, 2001). Nielsen and Thomison (2003) also reported that delayed planting of corns shortens the available growing seasons. The reason could be that too early and too late transplanting could not fulfill the required temperature and photoperiod for rice crop. Late transplant are severe to cold and effect plant growth and yield (Bashir et al, 2010). Akram et al. (2007) reported that yield and yield parameters like number of tillers, grains per panicle, plant height, 1000 grain weight and sterility of different rice varieties were significantly affected by transplanting dates. Similarly, Gangwar and Sharma (1997) also observed more number of panicles in early transplanting than in late transplanting. This was due to the fact that rice genotypes planted earlier had longer period for their vegetative growth compared to those sown later. But Nazir (1994) reported that earlier transplanting in rice causes lower number of grains per panicle due to grain sterility because of high temperature at the time of grain maturation. Transplanting at its optimum time reduces grain sterility. The overall results of the present investigations lead us to the conclusion that there is a significant effect of transplanting dates on the yield, yield components and days taken to 100% flowering of rice genotypes even 08FAN10 and Khumal-4 were common in 2013 and 2014. Soil of the experimental plot was silty-clay loam with pH 6.5 to 6.7 tested before transplanting. Recommended dose of fertilizers @80:30:30 kg/ha NPK were applied. Full dose of phosphorus and potassium and half dose of nitrogen were applied as basal. 1/4 th part of nitrogen was applied at 30 days i.e. at tillering stage after 1 st weeding and the remaining 1/4 th part at booting stage after 2 nd manual weeding. A total of 4m x 3m net plot area with a plant spacing of 20cm x 15cm was used for transplanting. One seedling per hill was transplanted in both early and delayed transplanting. Rice early transplanting was done in last week of June when seedlings were 25-28 days old but delayed transplanting was done at 1 st week of July when seedlings became 38-40 days old in all years of 2011, 2012, 2013 and 2014.

Data collection and analysis
Observations and data records of all the traits were made based on Standard Evaluation System for Rice (IRRI, 2002). Rice different parameters such as days to heading, days to maturity, panicle length, plant height, fertile grain number per panicle and grain yield per hectare were taken. Days to heading and days to maturity were taken when each plot was 80% flowered and matured respectively. Average plant height and panicle length were taken from five plant of each plot before grain full physiological maturity. Grain yield per hectare were taken at 12% moisture content. Statistical analysis was done by using MSTAT and GenStat program.

Days to heading
Statistically significant difference in days to heading were found for both early and delayed transplanting in 2011 to 2013 and non significant in 2014 (p<0.05) (Figure 1). The average days to 80% rice heading was 84 and 111 days for early and delayed transplanting in 2011, 107 and 121 days in 2012, 113 and 121 days in 2013, and 106 and 127 days in 2014 (Table 2; Table 3; Table 4; Table 5). Longest days to heading were obtained from NR   (Table 2; Table 3; Table 4; Table 5). Longest days to maturity were recorded from NR  (Table 2; Table 3; Table 4; Table 5).

Plant height
Significant difference in plant heights were found for both early and delayed transplanting in 2011 to 2013 and non significant difference in 2014 respectively (Table 2; Table 3; Table 4; Table 5

Panicle length
Significant difference in panicle length was obtained from both early and delayed transplanting in 2011 to 2013 and non significant difference in 2014 for arly and delayed transplanting ( Table 2; Table 3; Table 4; Table 5

Number of fertile grain per plant
Fertile grain number per plant is a direct attributes of yield. Significant difference were found in number of kernel per panicle of early and delayed transplanting in 2011, 2012, 2013 and non significant difference in 2014 (p<0.05) ( Table 2; Table 3; Table 4; Table 5  This result is similar to the findings of Vandana et al. (1994) who reported that dry matter accumulation in leaves The average reduction in panicle length was found from early to delayed transplanted crop was 5.92% from 2011 to 2014. Highest reduction (8.79%) was obtained in 2011 and lowest (2.73%) in 2013. Similarly, mean difference in panicle length were 2.5 cm, 1.7 cm, 0.7 cm and 1.5 cm from 2011 to 2014 respectively (Figure 4). Reduction in panicle length in delayed transplanting from the early one may be due to lack of full photosynthesis during its growing period, inability of roots to absorb minerals from soil. This result reveals the findings of Hussain et al (2005) and Shah (2001) who reported that maximum number of panicle was produced by line transplanted method in early transplanting. This might be due to adaptation with climate, well adopted root system and well adopted leaf structure and canopy having optimum light absorption, nutrients uptake and synthesis of more carbohydrates.
Average increase in fertile grain number per plant was 21.51% from delayed to early transplanting from 2011 to 2014. Maximum increase was 46.2% in 2012 but there was decrease in fertile grain number by 6.6% from early to delayed transplanting in 2013. The difference in fertile grain number was 14, 67, -8 and 53 from 2011 to 2014 respectively ( Figure 4). These results resembles to the findings of Akram et al. (2007) and Kameswara and Jackson (1997) who reported that number of kernels per panicle were significantly affected as sowing date is delayed. Awan et al. (2011) also reported that reasons for low yield and less grain number are use of imbalance inputs at improper time, transplanting of aged rice nursery and imbalanced use of fertilizer etc. However these results are contrary to that of Habibullah et al. (2007) (Figure 3). These results supports the findings of Hwang et al (1998) who reported that paddy yields deteriorated as planting date was delayed. Shah (2005) also reported that June 15 seeding recorded significantly the highest paddy yield and decreased with the delay in planting time. In the same way, Iqbal et al (2008) reported that the highest yield was obtained when the rice crop was sown earlier in the season. Similarly, according to Baloch et al. (2006) among planting dates, June 20 th planted crop gave highest paddy yield. Somato et al. (1961) concluded that early transplanting of seedlings resulted in higher yield of grain than late transplanting. This concept is further supported by Khan and Baloch (1970) and Pirzada et al. (1962) who revealed that sowing of nursery in the month of April and transplanting in June produced the highest yields which reveals the results of Bali and Uppal (1995) who concluded that rice crop transplanted on 10 th July gave 9.4 to 17.9 % higher grain yield than 30 th July transplanting due to higher root density, NPK uptake and head rice recovery. Khakwani et al. (2006) also suggested that highest paddy yields are obtained in early transplanting. The reason could be that this might be due genotype genetic superiority, appropriate temperature for growth and development, nutrients absorption, proper root system of the genotype and proper time of transplanting which leads to provide optimum duration for seed filling.

Conclusion
On an average 38.44% decrease in yield was found from early to delayed transplanted rice from 2011 to 2014. Comparison of different parameters of rice from 2011 to 2014 showed that late transplanted aged rice seedlings had always lower yield than early transplanted rice which might be due to aged seedlings, improper root growth and development causing less absorption of nutrients from soil, shorter duration of photosynthesis during grain filling period and cold during grain maturation time. So this might be the possible reason to have high yields in earlier transplanting. Climate change and irratic rainfall pattern has pushed away the planting time of rice. Labor scarcity and delay in monsoon also causes delay in transplanting. Thus farmer's field have lower yield because of delayed transplanting of aged rice seedlings. The yield reduction of farmer's field can be minimised by transplanting rice in appropriate time with recommended package of practices.