Grain yield of aerobic rice as influenced by seed rate and row spacing in aerobic situation under changed climate

Aerobic rice system is the method of cultivation, where the rice crop is established by direct seeding in un-puddle field. The grain yield of aerobic rice in aerobic situation realized by the farmers is still lower. Among many factors, seed rate and row spacing influence the grain yield of aerobic rice crop. The present investigation was carriedout to study the influence of seed rates and row spacing on grain yield of aerobic rice in aerobic situation, and field experiment was conducted at Rice Research Station, Bankura, West Bengal, India during kharif season of 2011 and 2012. The experimental results exhibited that the highest grain yield (3.40, 3.49 and 3.42 t ha-1 during kharif 2011, kharif 2012 and in pooled value, respectively) was recorded from treatment S2, where seed rate was 30 kg ha-1. Among the different row spacing, the maximum grain yield of 3.47, 3.45 and 3.46 t ha-1 during kharif season of 2011 and 2012 and on pooled basis was obtained with the treatment R1 i.e. 20 cm row spacing. The treatment combination of S2 (seed rate @ 30 kg ha-1) and R1 (20 cm row spacing) recorded the highest grain yield (4.01 t ha-1) of aerobic rice. It was established that the seed rate @ 30 kg ha-1 and 20 cm row spacing was promising for realizing best grain yield of aerobic rice in aerobic condition. It is an important eco-safety tool for tackling the climate change scenario.

Potential of crude extract and isolated compounds from golden beard grass (Chrysopogon serrulatus) for control of sprangletop (Leptochloa chinensis) in aerobic rice systems

Extraction and fractionation of the culm plus leaves of Chrysopogon serrulatus Trin. produce three major compounds, dibutyl phthalate (DBP), diphenylamine, 4,4′-dioctyl and simiarenol, which potentially act as allelochemicals or phytotoxic compounds. The effects of these compounds were examined using Leptochloa chinensis (L.) Nees as the bioassay species. The isolated compounds showed different degrees of inhibitory effects against L. chinensis. Of the three, DBP was the most potent and was able to inhibit L. chinensis germination by >70% at 500 mg L–1, followed by simiarenol and diphenylamine, 4,4′-dioctyl with inhibition values ranging from 40 to 52%. Under aerobic conditions, DBP at 2.4 kg a.i. ha–1 reduced the emergence and shoot fresh weight of L. chinensis by >50%, with negligible effect on root and shoot growth of aerobic rice seedlings, suggesting this as the most suitable rate and compound to control L. chinensis without injuring rice seedlings. At an application on the day of sowing rice seed, across DBP rates, reduction in root and shoot height of rice plants was evident when assessed 14 days after DBP treatment. However, rice plants become less susceptible with increasing growth stage. The findings suggest that DBP has potential to be developed as a pre-emergence, soil-applied natural herbicide for control of L. chinensis in aerobic rice system.