Habilidade competitiva, períodos de interferência e nível de dano econômico de plantas daninhas na cultura da soja

Abstract

Weed competition in agricultural crops is one of the most important factors responsible for remarkable losses, what also occurs in soybean. The main weeds present in soybean fields include hairy fleabane, sourgrass, alexandergrass, crabgrass, tropical spiderwort and arrowleaf sida, among others, so knowing the competitive behavior of these plants against soybean is important to support adoption of control strategies that combine the agricultural sustainability with weed control excellence. This study aimed to study the competitive ability of alexandergrass and guanxuma in soybeans, their respective periods of interference (PI) and level of economic damage (NDE). Competitive skill work was carried out in a greenhouse in a completely randomized design with four replications. The competitors evaluated were the arrowleaf sida with the soybean cultivars BMX Ativa, DM 5958 RSF IPRO, Brasmax Elite and Nidera 5445 IPRO. The proportions of plants used (culture: weed) were 100: 0; 75:25; 50:50; 25:75 and 0: 100, which corresponded to 20: 0; 15: 5; 10:10; 5:15 and 0:20 pot-1 plants. The NDE studies were composed of the soybean cultivars NS 6909 IPRO, NA 5909 RG, DM 5958 RSF, Brasmax Elite IPRO, Brasmax Lança IPRO and SYN 13561 IPRO and densities of arrowleaf sida for each respective cultivar of 0, 2, 3, 4, 9, 15, 16, 23, 22 and 58; 0, 2, 3, 3, 6, 6, 10, 11, 18 and 47; 0, 3, 4, 7, 8, 10, 11, 13, 15 and 24; 0, 1, 4, 6, 12, 18, 19, 31, 44 and 50; 0, 4, 5, 6, 9, 13, 17, 20, 20 and 47; and 0, 2, 3, 5, 9, 11, 15, 18, 29 and 30 plants m-2). Brasmax Elite IPRO was used for the work of interference periods, with the treatments being separated into two interference models: in the “coexistence” group, soybeans lived with alexandergrass for periods of 0, 7, 14, 21, 28, 35 and 42 days after the emergency, as well as, throughout the cycle; in the control group, the culture was kept free from infestation for the same periods previously described. The variables evaluated were the morphophysiological of the crop and the weed for the study of interference. The competition between soybean cultivars in the presence of arrowleaf sida occurred regardless of the proportion of plants, causing reductions in all evaluated variables. It is noteworthy that there was competition for the same resources of the medium between soybean and arrowleaf sida. Some soybean cultivars were more competitive than others, demonstrating that there is genetic variability. The NDE values ranged from 0.55 to 0.95 plants m-2 for cultivars NS 6909 IPRO, NA 5909 RG and Brasmax Lança IPRO which showed greater competitiveness with arrowleaf sida. The lowest NDE values were 0.26 to 0.61 plants m-2, with the lowest competitiveness with arrowleaf sida. In experiments with the papuã competitor, the interference periods were established as, critical interference prevention period (PCPI), which comprises from 26 to 41 DAE; the period before interference (PAI) was 26 DAE, and the total period of interference prevention (PTPI) was 41 days. When soybeans are infested by arrowleaf sida and papuã there is a need to carry out the management of these species to avoid losses in grain productivity and consequently losses to the producer.