Influence of Seasonal Variations and Photoperiodism on Growth Phases and Crop Cycles in Selected Rice (Oryza sativa) Genotypes Grown in Southern Nigeria

Aim: To investigate the influence of seasonal variations and photoperiodism on the growth phases and cropping cycles of selected rice genotypes in Nigeria

Study Design: The study was a 2 factor factorial experiment laid out in a randomized complete block design (RCBD) with three (3) replicates.

Place and Duration of Study: The trial studies was carried out in four locations, Adim, Assiga, Idomi and Ofodua in 2014 and 2015 crop growing seasons.

Methodology: The experiment for seasonal variation effect was carried out in the field while the experiment on photoperiodism effect was carried in the screen house at Adim. The experiment was a 2 factor experiment. Factor 1 was the rice genotypes which had 4 levels (FARO 44, FARO 12, FARO 15 and FARO 55) while factor 2 which was the different locations also had four levels (Adim, Assiga, Idomi and Ofodua). The experiments were laid out in a randomized complete block design (RCBD), replicated three times with intra and inter – row spacing of 15x15 cm. Plot size of 25 x20 m, was maintained with sampling area of 2 m2. For the natural day length, three seedlings were transplanted into the polyethylene bags containing about 5 kg of soil later thinned to two plants and fertilized with 1g of N, P2O5 and K2O because the initial soil analysis results showed low values of the soil nutrients. The soils were flooded throughout the growth of plants. The experiment for photoperiod was carried out at the World Bank Assisted Rice project in Adim in June, 2014. Three 7 - day old seedlings were transplanted to each polyethylene bag containing 5 kg of soil and fertilized with 2 g each of N, P2O5 and K2O. The plants were subjected to 8, 10, 12, 13, 14 16 and 24 h photoperiods, in a 24 h cycle. The experiment was terminated after 200 days. Their response to different photoperiod treatments were investigated with rice plants in polyethylene bags subjected to varying lengths under artificial light.

Results: High photoperiod - sensitive varieties, showed significant (p<0.05) difference in their maturation periods (crop cycle) when planted at different times (seasons) of the year. The results showed significant (p<0.05) differences in growth phases and crop cycles in the various genotypes as influenced by seasons and photoperiod. The results showed that total growth phase (BVP and PSP) was 86 d for FARO 44 and >130 d for FARO 15. The longest crop cycle of 249 d occurred when plantings were made in January – February with FARO 15 while shortest crop cycle of 78 d occurred when plantings were made in the October - November with FARO 44. In some of the photoperiod - sensitive varieties, exposure of the rice genotypes for 10 h yielded the shortest crop cycle and growth phases for FARO 44 while exposure of varieties to longer photoperiods of 24 h yielded the longest crop cycles for all the varieties when planted in the same month, of different years. These varieties would be unsuitable for planting during the off season (August to September). The results are discussed in light of photoperiod sensitivity of some rice varieties planted at different times of the year.

Conclusion: The results of the study have shown that growth phases and crop cycle of any rice variety is determined by the length of the vegetative reproductive and ripening phases. Since the duration of reproductive and ripening phases is very essential to the crop, it is the vegetative phase that differs and determines the crop cycle of the rice variety. In this test, the crop cycles of Faro 44 and Faro 12 did not vary much with different photoperiods. These test crop varieties (Faro 44 and Faro 12) contrast strongly with those of Faro 52 and Faro 15, in terms of the seasonal variations and photoperiodic screening. The study has been able to bridge the gap in knowledge on seasonal variations and photoperiodism and how these influence rice growth and production in this agro-ecology.