Abstract
Ischaemum rugosum is a competitive weed in direct-seeded rice systems. Developing integrated weed management strategies that promote the suppression of weeds by crop density, cultivar selection, and nutrition requires better understanding of the extent to which rice interferes with the growth of this weed and how it responds to resource limitation due to rice interference. The growth of I. rugosum was studied when grown with four rice seeding rates (0, 25, 50, and 100 kg ha−1) and four nitrogen (N) rates (0, 50, 100, and 150 kg ha−1). Compared to the weed plants grown alone, weed tiller number was reduced by 63–80%, leaf number by 68–77%, leaf area by 69–77%, leaf biomass by 72–84%, and inflorescence biomass by 81–93% at the rice seeding rates of 25–100 kg ha−1. All these parameters increased with increasing rates of N from 0 to 150 kg ha−1. At weed maturity, I. rugosum plants were 100% taller than rice at 0 kg N ha−1, whereas, with added N, the weeds were only 50% taller than rice. Weed biomass increased by 82–160%, whereas rice biomass increased by 92–229%, with the application of 50–150 kg N ha−1. Added N favored rice biomass production more than it did the weed. Rice interference reduced the height and biomass of I. rugosum, but did not suppress its growth completely. I. rugosum showed the ability to reduce the effects of rice interference by increasing leaf area, leaf weight ratio, and specific leaf area, and by decreasing the root-shoot weight ratio in comparison to the weed plants grown alone. The results suggest that rice crop interference alone may reduce I. rugosum growth but may not provide complete control of this weed. The need for integrated weed management practices to effectively control this weed species is highlighted.
Highlights
Majority of the people living in Asia consume rice as their staple food and 90% of the world’s rice is produced and consumed in Asia
The height of I. rugosum was significantly affected by increasing the seed rates from 25 to 100 kg ha21, and plants grown alone were taller than plants grown with rice (Figures 2a and b)
Increase in rice seeding rates increased specific leaf area (SLA), leaf area ratio (LAR), and leaf weight ratio (LWR) and reduced root to shoot weight ratio (RSWR), whereas all these ratios declined with increase in N rate
Summary
Majority of the people living in Asia consume rice as their staple food and 90% of the world’s rice is produced and consumed in Asia. The major rice establishment method is manual transplanting of seedlings. This method is more laborious and requires more water [1]. Shortage of labour and water compels researchers and growers to develop alternative methods of crop establishment, such as dry-seeded rice (DSR). Acceptance of DSR is increasing among farmers in South and Southeast Asian countries. DSR is a resource-conserving technology compared with puddled transplanted rice, except that it is prone to heavy weed infestation [1]. Manual hand weeding is very expensive, time-consuming, and, sometimes, it is not feasible. Non-judicious use of herbicides, is linked with the evolution of herbicide resistance in weeds and concerns over soil and environmental pollution [3,4]
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