Influência do residual de Clomazone e Imazapir+Imazapique sobre o estabelecimento de forrageiras em áreas de terras baixas.

Abstract

Currently, producers need to adopt more efficient technologies for weed control, such as Clearfield (CL), which is tolerant to the chemical group of imidazolinones. Furthermore, pre-emergent herbicides are becoming indispensable and widely used by rice farmers. However, these herbicides can leave a long-lasting residual in the soil, which can even harm the development of other crops in rotation systems (carryover). The objective of this study was to evaluate the residual of the herbicides Clomazone and Imazapir+Imazapique, used in rice during the summer harvest due to the establishment of ryegrass, white clover and spontaneous vegetation pastures. The study was conducted in the experimental area of the Universidade Federal do Pampa (UNIPAMPA), in two stages: rice during the summer and forage during the winter. For both occasions, a randomized block design (RBD) with three replications was adopted. For irrigated rice, two cultivars were used, IRGA 424 RI and IRGA 431 CL. At the seedling formation (S3) and early tillering (V3) growth stages, herbicides were used as follows: 70 g p.c. ha-¹ Imazapir + Imazapique applied in S3, repeating the application in V3 (70 KIF); 1.2 L p.c. ha-¹ Clomazone + 140 g p.c. ha-¹ of Imazapir + Imazapique applied in V3 (120 GA + 140 KIF); 1.2 L p.c. ha-¹ Clomazone + 70 g p.c. ha-¹ of Imazapir + Imazapique applied in S3, applying another 70 g p.c. ha-¹ in V3 (120 GA + 70 KIF) and without herbicide application (ZERO HERB). The rice was managed according to the recommendations to express the maximum productive potential. In rice, the main production components were measured in order to promote uniformity of the plots for the implantation of forages. Manual sowing (broadcast) of forages occurred 98 days after the harvest of the rice crop (06/18/2024), considering Ryegrass, White Clover and the maintenance of the vegetation that emerged spontaneously. Thus, the experiment followed a 4 x 3 factorial arrangement, considering 4 herbicide residuals and 3 forages. At 50, 60, 70 and 80 DAS, a representative location was demarcated within the plots and the vegetation coverage rate was measured using the Canopeo application. After the coverage rate assessments, the green and dry mass of the aerial part and roots of all experimental units, taken from the same growth location as the coverage rate, was measured. There was an interaction between the Forage x Herbicide Residual factors for all studied variables. In general, we can observe higher values of the variables in ascending order where there was no herbicide application (ZERO HERB), in relation to 120 GA+140 KIF, this being the highest dose, followed by 120 GA+140 KIF, and 70 KIF, on some occasions, behaved the same as (ZERO HERB), but in most cases it harmed the establishment of plants, mainly clover and spontaneous vegetation, showing themselves to be very sensitive to herbicides, both in prepared soil and in fallow soil. The residual of herbicides applied to irrigated rice crops Gamit (Clomazone) and Kifix (Imazapir+Imazapique), harms the forage production of White Clover Trifolium repens, Ryegrass Lolium multiflorum and Spontaneous Vegetation in succession, both in soil prepared with agricultural mechanization and in fallow soil.