Farmers face several problems in adoption of direct seeding rice (DSR) such as weeds, panicle sterility, diseases and insects’ pests, lodging and stagnant yield. Each of them is described as follows:
The major problem of adopting direct seeded rice particularly in dry field is weed infestation. DSR seedlings have disadvantage over transplanting rice seedlings as weeds suppress the rice seedlings at initial stages. But in transplanted rice, early weeds which are much harmful easily controlled by flooding. In worldwide, an estimated 50 species of weed cause major loss in production. The weed flora also changes in DSR as farmers adopting this advanced method of planting. Some species such as barnyard grass and Asian sprangleotop become more prevailing in recent years. Such species were not common when DSR introduced first time into world. This system also favor flat sedge and water plant in Australia and USA and lindernia spp in Asia. Weeds infestation are major hurdle in adopting DSR in Pakistan. Weed species such as climbing dayflower, rice flat sedge, purple nut sedge and prominently horse-purslane increased significantly in DSR. Severe weeds infestation occurs in DSR than transplanting rice because rapid growth rate of weeds at initial stages of rice ultimately reduce the growth of rice and there is no flooding condition to reduce the weed growth. In DSR compounds such as phenoxy and sulfonylurea are major herbicides used to control broad leaved weeds and sedges. Such weeds are becoming resistant to herbicides due to their use every year. Recent evidences that weeds i.e. dwarf clover, thwaites, and globe fingerush become resistant to phenooxy herbicides so research should be made on weed tolerance.
Diseases and insect pests
Among the susceptible diseases, rice blast is most overwhelming in both direct and aerobic rice. Water scarcity is the favorable condition to induce rice blast. The important trait considered in breeding programs is rice blast. DSR favors the rice blast as there is no water film and this technology spreads the disease. Studies show that several processes such as germination, spore liberation and infection in rice blast epidemics are effected by the water supply level. Management of water supply controls the microclimate especially dew deposition, which alters the lifecycle of the pathogen and influence the crop physiology therefore susceptibility of host is also affected. But the risk of insects to damage the crop is reduced in DSR while a yellow orange leaf virus, sheath blight, ragged stunt virus and dirty panicle have been perceived in DSR. When pattern of planting is shifted to DSR then root-nematodes also attacked the crop.
The most sensitive stage in rice is flowering during drought period. Both patterns of rice planting i.e. TPR and DSR are sensitive to deficiency of water. Rice grown in DSR have less moisture so in any type of shortage of water will reduce the time to anthesis resulting a panicle sterility. Water stress reduce the starch level and viability of pollens which increase the number of sterile spikelets.
The inability of vertical standing of crop is often observed in DSR as compared to TPR in the previous years. The thickness of sclerenchyma tissues gives the strength to the base of plant against lodging. Lodging tolerant varieties of rice have specific characteristics such as increase number of vascular bundles and also the peripheral portion. At harvesting stage DSR rice is more susceptible to lodging. There is a noticeable reduction in yield and quality of grain due to reduced rate of photosynthesis. Mechanical harvesting of such a crop is also difficult and create hindrance in working of harvester. So the proper stand of a crop is necessary to obtain a good yield.
Most of the observations show that yield is reduced in DSR but it is complicated to understand the reasons. The reduction in yield may be the combinations of different factors such as nutrient depletion, soil sickness, and effects of allelopathy, soil degradation and soil borne diseases. For example, plant autotoxicity is mostly observed in Brazil which reduce the yield and it is mostly occurred in dry seeded regions. Such decline in production occurs when continuously growing upland rice cultivars for more than two years.
Dr. Nadeem Akbar, Shakeel Ur Rehman, Dr. Shakeel Ahmad Anjum, Usman Nazir
Agro-biology Laboratory, Department of Agronomy, University of Agriculture, Faisalabad 38040, Pakistan