Influence of the level and duration of infestation of crops on rice yield
Authors: Dudchenko V. , Palamarchuk D. , Dovbush O. , Tsilynko L. , Palamarchuk A. 
Published: January 2022

Goal. Determine the effect of the number and duration of the period of presence of weeds in rice crops on the level of yield.
Methods. We used general approaches to the study of the phytosanitary state of agrocenoses: herbological, laboratory-field, calculated, mathematical-statistical. Weed exposure studies were performed at 10, 20 and 30 pieces of chicken millet/1 m2, competition period — 20, 40, 80 days, and before harvest. Option of pure sowing, as well as all types of weeds without weeding and without treatments. Weeds were recorded at the same time as other pests at the same sites at the appropriate times. The number of weeds by species and their total number were counted, and their height, phase of development and biomass were determined. During the growing season, the increase in raw weed mass and rice yield were determined. The size of the experimental and accounting area is 1 m2, rice variety Ukraine 96.
Results. The most competitive species for nutrients and light on rice crops are representatives of the genus Echinochloa. There are different data regarding the decrease in rice yield from the number of weeds and the duration of their competition in crops. In the literature there are references that the level of infestation with chicken millet in the amount of 30—40 plants per 1 m2 reduces the yield by 10—15%, an increase in the number to 200 or more plants per 1 m2 leads to a decrease in yield by 50 % or more. In 2016—2018 In the experiment, the number of weeds was formed, which is the most competitive in obtaining a harvest of rice on the territory of Ukraine — chicken millet (ELH 10 pcs/m2). Studies of the influence of weediness were carried out at the number of 10, 20 and 30 pcs/1 m2, the competition period was 20, 40, 80 days and before harvesting, as well as the option of clean sowing. It was found that the yield of rice is negatively affected by both the number of weeds and the duration of infestation (competition). The dependence of the weight of rice grain on the weight of weeds was studied without the formation of the number, that is, all that were present in the sowing from the moment of germination in different periods (20, 40, 80 days) and before harvesting.
Conclusions. Rice yield losses were determined with different numbers of chicken millet and different duration of joint growth, peculiarities of growth and development of chicken millet under competitive conditions, general soil contamination in rice paddies. The minimum losses in comparison with clean crops are 5.8 %, provided that the number of chicken millet is 10 pcs/m2, and the duration of the competition is only 20 days. With the number of 10 pcs/m2, 20, 30 pcs/m2 of chicken millet, and their competition before harvesting, the losses are — 68.7%, 81.4% and 73.9%, respectively, in comparison with clean crops. An increase in weed weight is directly proportional to a decrease in grain weight. A reliable strong relationship was established between an increase in the mass of weeds and the mass of grain r = –0.901.