Influence of sowing dates on micro climatic indices
Plants respond to the climate where they are growing. Micro climate refers to the climatic conditions of a small, specific place, where conditions may differ from those of the larger surrounding space. Three main parameters to define a microclimate within a crop environment are temperature, humidity and sunshine hours
(Jagadish et al., 2017).
Different sowing dates significantly influenced the canopy temperature at all the growth stages of the crop (Fig 2). The highest values were recorded on 1
st April sown crop. During the entire crop growth period 1
st April received less stress condition as compared to the other sowing dates and this might be due to difference between ambient temperature and canopy temperature were in the range of 3 to 5.75
oC and among which the 1
st April sown recorded the lowest range (3 to 5.4
oC). The trend in the deviation of canopy temperature from ambient temperature indicated better. Therefore, 1
st April sown crop resulted higher in growth and yield attributing characters, this might be due to activation of some enzyme under favourable canopy temperature such as sucrose phosphate synthase, which helps in grain filling process and ultimately helps in increasing the yields.
Growing degree days were more in 1
st April sown crop (Fig 3), which means 1
st April sown absorbed more heat units than other sowing dates. This might be due to 1
st April sown crop received more number of degree days to complete its growing period. Due to delay in sowing from 15
th February to 1
st April, the heat units increased gradually throughout the growing period.
The morphological, physiological and yield parameters of rice have showed variation due to differed light intensity among the different date of sowing where 1
st April sown crop recorded high light intensity and thus lead to higher photosynthesis which helped in increasing the crop growth and yield (Fig 4).
Murty et al., (1976) amply demonstrated that the movement of photosynthates to aerial part was enhanced under lower light intensity but the available photo assimilates was low due to impaired photosynthesis under reduced light intensity. The high light resulted in grain filling by increasing the number of spikelets.
Soil moisture and temperature are the important climatic parameter for better growth of a crop. These two parameters are interrelated. At a very low soil temperature, moisture intake by crop stops. Soil moisture and temperature influence the germination of seeds. Excessively high amount is harmful to roots and extreme low amounts decrease nutrients uptake and also extreme low values influences the soil microbial population and rate of organic matter decomposition
(Yoshida et al., 2007). A very high soil temperature of more than 35
oC during tillering to panicle initiation would affect the grain filling process in addition to the grain setting process. A high soil temperature before the heading stage would significantly affect the grain filling
(Sato et al., 1973; Kobata et al., 2004). In rice, photo synthesis decreases when temperarture is more than 35
oC at the later ripening stage, while grain filling is insensitive to high root temperature. The adverse effect of extreme soil temperature during ripening on grain filling would be more prominent if the sink demand were large, as in the case of high spikelet numbers
(Sanoh et al., 2010). Results of this study revealed that 1
st April sown crop recorded higher productivity due to the favourable soil temperature (21-30
oC) during the growth period up to harvest of the crop (Fig 5, 6).
Influence of sowing dates and varieties on growth parameters
The growth parameters recorded periodically have showed variations due to different micro-climatic regimes and varieties. Plant height at all the growth stages was not influenced by different dates of sowing, however, 1
st April sown crop recorded higher values. High rainfall during the growth period on April 1
st sown crop during its vegetative growth might have increased the height. Among the varieties tested, highest plant height at all the growth stages was recorded in Inglongkiri which might be due to the genetic character of the variety (Table 1) as plant height depends on genetic makeup of a plant and environmental conditions. A similar findings was reported by
Asif et al., (2014), Ramachandra et al., (2015) and
Kannan et al., (2015). Leaf Area Index was recorded highest in 1
st April sown crop and sowing date significantly affected this physiological parameter.
Tiwari (2015), found that time of sowing in paddy crop is utmost importance due to variation in duration and climatic condition of the area.The leaf area index was also found to be significantly affected by different rice varieties. Highest LAI was observed in case of rice variety CR-Dhan 203. The variation in LAI among rice varieties might be due to the variation in genetical characteristics among the varieties (Table 1).
Influence of sowing date and varieties on yield attributes and yield
The yield attributes are the most important parameters of any crop which directly influence the crop yield. These yield attributes and yields are likely deviate up to considerable extent as a result of variability in the crop management practices for increased crop production.
The number of filled grains/panicle showed a better response with delay in sowing because in early sowing the plants might have suffered from unfavourable temperature which ultimately resulted in shedding of pollen; therefore, reduced the number of filled grains/panicle and ultimately the grain yield (Table 1). This might be attributed to better plant growth leading to significantly more number of filled grains/panicle and better partitioning of photosynthesis compared to other sowing dates. Moreover, due to favourable climatic condition such as optimum temperature (23 to 30
oC), average weekly rainfall (76.8 mm) might have resulted in higher uptake of nutrients as well as post photosynthetic contribution in respect to other sowing dates. Similar, findings were reported by
Khalifa 2009),
Dawadi and Chaudhary (2013),
Sidhu et al., (2014) and
Sivapalan (2014). Different rice varieties significantly affected the yield attributing characters of rice. Rice variety CR-Dhan 203 produced significantly higher number of grains/panicle which was followed by variety Inglongkiri and this is probably due to more effective tillers/m
2 and higher length of panicle exhibited by CR-Dhan 203 over rest of the varieties and also might be due to variation in genetical character of the variety. The significant differences in yield attributes among the rice varieties have also been reported by
Brar and Bhullar (2013),
Dawadi and Chaudhary (2013),
Ramachandra et al., (2015), Kumar et al., (2015) and
Tiwari (2015). The crop sown on 1
st April produced higher values in all the attributes and yield followed by 16
th March sown crop. This might be due to high light intensity amount in the micro-climatic regime. The variety CR-Dhan 203 resulted in highest grain yield. This might be due to the higher value of yield attributing characters and genetic yield potential of the rice variety in aerobic condition (Table 1).
Influence of dates of sowing and varieties on economic indices
Relatively late sowing positively influenced the yield and thereby net income in the experiment. Among the micro-climatic regimes, the 1
st April sown crop of aerobic rice gave the highest net income (Rs. 51755.36 /ha) and a B- C ratio (2.3) andthis might be due to higher yield. CR-Dhan 203 proved its superiority by giving highest net income (Rs. 46865.01/ha) and a B:C ratio (2.04) followed by Inglongkiri. This is attributed to net income in relation to the crop productivity and the gross income received. The increase in net income and benefit-cost ratio might be due to positive effect of the treatments on growth and yield attributes results in higher grain and straw yield (Table 1).
