The Effect of Different Weed Control Managements on Yield and Yield Components of Three Rice Cultivars

 Rice (Oryza sativa L.) is one of the world’s most important food crops. Currently, more than one third of the human population relies on rice for their daily sustenance. Rice is predominantly grown by transplanting seedlings into puddled (conventional wet-tillage) soil and kept flooded for most part of the growing season. The puddled soil ensures good crop establishment, weed control with standing water, and reduces deep-percolation losses. However, the conventional method of rice crop establishment requires a large amount of water, labour, and energy, which are gradually becoming scarce and more expensive. Thus, reducing the profitability and sustainability of puddled transplanted rice. Dry direct seeded rice has shown promise under several ecologies and production systems to overcome these challenges, and is considered as potential alternative to puddled transplanted rice. Weed infestation in direct-seeded rice fields remains the single largest constraint limiting their productivity. An effective early weed management tactic is imperative for any direct-seeded rice production technology aiming at achieving higher productivity and profitability.

 In order to investigate the effect of different weed managements on yield and yield components of rice in the direct crop system, an experiment was conducted in 2020 on farms located in Babolsar (Behnamir). The experiment was performed as a factorial based on randomized complete block design with three replications. Experimental factors include rice cultivars (Shiroudi, Khazar and Hashemi) as well as other treatments including weed control by increasing the competitiveness of rice seeds by coating and weed management at five levels including coating the seeds with CaCl2 and KCl, weeding, chemical control (Council active) and control  (no weeding).

 Weed management by coating rice seeds with calcium chloride, potassium chloride, chemical control and weeding was reduced 26, 26, 23 and 63% dry weight of broadleaf weeds and 14, 27, 9 and 36% dry weight of narrow leaf weeds, respectively, compared to control treatment. The maximum emergence percentage in Shiroudi cultivar with 99, 97 and 95% was obtained under weeding, coating the seeds with CaCl2 and KCl treatment, respectively. Also, the highest emergence rate was observed under the management of weeding and coating of potassium and calcium chloride seeds. Seed coating with CaCl2 and KCl substantially improved the stand establishment under drought and well-watered conditions owing to early completion of pre-germination metabolic activities during priming. In general, the results of mean comparison showed that weed management improved rice height compared to the control treatment. The results of this study attributed the increase in height to the effect of pretreatment on increasing the rate of emergence and better establishment of seedlings due to better plant use of related resources. The results showed that the maximum number of seeds per panicles with 137 were obtained in Khazar cultivar. The highest number of seeds per panicles with 127, 124 and 122 seeds was under weeding management and coating with CaCl2 and KCl, respectively. The results of cultivar effect showed that the maximum 1000-seed weight with 23.83 g was observed in Shiroudi cultivar. Also, 1000-seed weight in Khazar and Hashemi cultivars were 22.1 and 21.09 g, respectively. The reason for the increase in the number of 1000-seed weight in Shiroudi cultivar can be attributed to the genetic potential and physiological quality of this cultivar. Also, the results of weed management effect showed that coating rice seeds with calcium chloride and potassium chloride, chemical control and weeding increased 14, 26, 4 and 33% of grain yield and 4, 14, 2 and 18% of biological yield compared to control treatment, respectively. Improved yield by seed coating in direct seeded rice might be the result of enhanced dry matter partitioning toward the panicles that resulted in improved kernel yield.

 According to the results of this study, seed coating treatments with CaCl2 and KCl in rice cultivars can increase rice yield by improving seedling characteristics. Therefore, farmers can be advised to use a simple and inexpensive crop management method to pretreated seeds with CaCl2 and KCl.