Behavior and environmental bioactivity on weeds herbicide residual applied on straw cane sugar in different soil water conditions

Abstract

This work will evaluate leaching in soil and efficacy on controlling weeds by amicarbazone, imazapic, sulfentrazone and tebuthiuron when applied on sugar cane straw and submitted to different periods of drought. Three experiments will be conducted. The first will be on leaching and will use two different methodologies, bioassays and high efficiency liquid chromatography (HPLC), following the 4 x 2 experimental design with four repetitions, that will be adopted for each of the methodologies isolated, with four periods of drought and two quantities of straw. This factor will be adopted for amicarbazone (800 i.a. ha-1); imazapic (210 i.a. ha-1), sulfentrazone (800 i.a. ha-1) and tebuthiuron (900 i.a. ha-1) individually. Herbicides will be applied on the top of the soil columns mounted in PVC tubes with 0 and 10 t ha -1 of straw. These treatments will be submitted to four different drought periods (0, 30, 60 and 90 days after treatment application). To evaluate the leaching through the methodology of HPLC, after a simulated rain of 30 mm will be performed the extraction and quantification of herbicides. For the treatments that will constitute the bioassay, will be performed the sowing of Cucumis sativus (bioindicator), will be held evaluations of fitoxicity by 7, 14, 21 and 28 DAS, and by 28 DAS will be also determined dry mass, height and leaf area of plants. In the second experiment, the experimental unit shall consist of a recipient that will pack an amount of straw equivalent to 10 t ha - 1. Collecting facilities will be attached to these recipients with the objective of storing water with residual herbicide. After the assembly of these structures, will be applied the herbicides amicarbazone (800 i.a. ha-1); imazapic (210 i.a. ha-1), sulfentrazone (800 i.a. ha-1) and tebuthiuron (900 i.a. ha-1), and elapsed periods of drought equivalent to 0, 30, 60 and 90 DAT will be simulated a rain of 30 mm. After this rain, when the straw is dry, the water contained in the collecting facilities will be taken for analysis by high efficiency liquid chromatography system. The third experiment will be conducted in the greenhouse and will examine the effectiveness of weed control, and will follow the factor 4 x 4 x 2 with four repetitions, with four periods of drought, four weed species and two quantities of straw, and this factor will be adopted for each of the four herbicides individually. Vessels with a capacity of 20 L will be filled with soil and on its surface amounts of straw equivalent to 0 and 10 t ha - 1. In the sequence will be applied amicarbazone (800 i.a. ha-1); imazapic (210 i.a. ha-1), sulfentrazone (800 i.a. ha-1) and tebuthiuron (900 i.a. ha-1). After the application of the herbicides, treatments will undergo four periods of drought (0, 30, 60 and 90 DAT). Promptly after these periods, will be simulated a rain of 30 mm, and in sequence, when straw is dry, it will be carefully removed and will be planted the weeds Merremia aegypitia (L.) urban; Mucuna Aterrima Piper & Tracy; Ricinus communis L.; Momordica charantia L.. The control of these weeds will be evaluated by 7, 14, 21, 28, 35, 60 and 90 days after sowing weeds (DAS) and by 90 DAS, the plants are cut close to the ground, checking the dry mass of the shoots. (AU)