Abstract
Three-year late season field experiment was conducted between 2011 and 2013 on the irrigated lowland experimental field at Edozhigi (9o04N, 6o7E) in the Southern Guinea savannah ecological zone of Nigeria, to determine the effects of different water depths and seedling rates on weed control, yield and yield components of lowland rice. The trial was laid out using a split plot design with six water depths (5 cm, 10 cm, 15 cm, 20 cm, saturated soil and continuous flow of water at 3 cm depth) as the main plots while seedling rates of 2, 4, and 6) per stand constituted the sub-plots. The treatments were replicated three times. The results indicated that the growth of weed species was significantly affected as water depth increased while rice yield was significantly enhanced as water depth increased to 20 cm. The 20 cm water depth gave weed control efficiency (WCE) of 57.6, 94.1 and 93.3% at 60 days after transplanting (DAT) in 2011, 2012 and 2013 respectively which was about 87% better than that obtained from saturated plots. At water depths of 10 and 20 cm, the growth of grasses and sedges were reduced by 60 and 100% respectively, while saturated and continuous flow of water encouraged their growth. Water depths of 10, 15 and 20 cm gave grain yield of 5052, 4700 and 4066 kg ha-1 which were 84, 85 and 85.5% higher than yields obtained from saturated plot in 2011, 2012 and 2013 respectively. Transplanting of 4 to 6 seedlings significantly suppressed weed growth and enhanced rice grain yield than 2 seedlings per stand. It is therefore concluded that maintaining water depths of 15 and 20 cm and seedling rates of 4 and 6 significantly suppressed weed growth and enhanced rice yield.
Highlights
The major impediment to the cultivation of rice is the heavy weed infestation which competes with the crop to such an extent that the crop gets smothered by the weeds
The 20 cm water depth gave weed control efficiency (WCE) of 57.6, 94.1 and 93.3% at 60 days after transplanting (DAT) in 2011, 2012 and 2013 respectively which was about 87% better than that obtained from saturated plots
The higher percentage weed control efficiency recorded in 20 cm water depth and six seedlings /stand could be ascribed to inability of some weed seeds to germinate under anaerobic condition created by impounded water and suppression of already germinated weed seedlings
Summary
The major impediment to the cultivation of rice is the heavy weed infestation which competes with the crop to such an extent that the crop gets smothered by the weeds. The weeds share plant nutrients but transpire a lot of valuable conserved water from the soil. The weeds serve as alternative hosts for certain diseases and pests. Weed infestation can interfere with operations at harvest and significantly increase harvesting and drying costs. Weed competition is the most important yield reducing factor followed by drought, blast, soil acidity and general soil infertility (Johnson et al, 1997). Pandey (2009) reported that weeds are at present the major biotic constraint to increased rice production worldwide. Weeds constitute a big constraint to the production of rice in Nigeria. Ukwungwu and Abo (2004) reported that weeds constitute the greatest bottleneck to increased yield and quality of rice in Nigeria
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