Effects of sowing date on the growth characteristics of direct seeding rice

Taking three representative rice cultivars as test materials,a field experiment was conducted to study the matter production and yield formation of direct seeding rice under the conditions of different sowing dates.With the delay of sowing date,the grain yields of the three rice cultivars all decreased significantly,but the decrements varied.Under the delay of sowing date,the whole period of growth and development shortened notably,the growth dynamics of stems and tillers became not smooth and intensified as the sowing date further delayed,the leaf area index increased gradually at early growth stage but relatively declined at the middle and late growth stages,the photosynthetic potential at various growth stages displayed a declining trend,the dry matter accumulation increased at jointing stage but reduced at heading and maturity stages,the harvest index descended,and the population growth rate at various stages showed a significant decreasing trend.It was suggested that considering the suitable secure sowing date,the rice varieties favorable to promote in the study region would be the medium-maturing medium japonica and late-maturing medium japonica,and the early-maturing late japonica varieties could also be grown there.To attain high yield,all the rice cultivars should be sowed as early as the time for harvesting previous crop allows.Yet,from the view point of the security for reproduction,the medium-maturing medium japonica cultivars should be planted no later than June 30,the late-maturing medium japonica varieties no later than June 25,and the early-maturing late japonica varieties no later than June 20.