Ação dos herbicidas alachlor e diuron sobre a atividade microbiana do solo, emergência de plântulas e crescimento da mamoneira anã cultivada no Recôncavo Sul Baiano

Abstract

The objective of this study was to evaluate the influence of the herbicides alachlor and diuron on soil microbial activity, seedling emergence and growth of the castor bean dwarf (EBDA MPB01), grown in a Typic distrocoeso of Recôncavo. Two experiments were conducted at the Experimental Center of Agricultural Sciences, Environmental and Biological Sciences of Federal University of Bahia Recôncavo in Cruz das Almas-BA: 1 year (sown in November 2007) and two years (sown in November 2008) in a randomized block design with five treatments (control: zero dose; alachlor L.ha 5-1; alachlor L.ha 7-1; diuron 2.4 L.ha-1; diuron 4.0-L.ha 1) and four replications. After conventional tillage, herbicides were applied pre-emergence, one day before planting of castor bean dwarf variety of MPB 01, spaced 1.0 m x 0.5 m. The NPK was made in the pit, and the day of planting according to soil analysis and recommendation for mamoneira.O nitrogen was fractionated. The parameters were: final seedling emergence, speed of emergence and soil microbial activity. The experiment was irrigated when necessário.Realizou-way analysis of variance and Tukey test at 5% for years 1 and 2, separately or together (1 + year2 years), the parameters for the index of germination speed and percentage of emergency. In the case of microbial activity were adjusted cumulative curves of each treatment for years 1 and 2, separately. Assessments of plant growth began 21 days after emergence, at fortnightly intervals until the end of the cycle. Dried pasta plant in its various fractions (roots, leaves, stems, seeds and clusters) were obtained after remaining in a forced ventilation oven at a temperature of 65 º C + 5 º C until constant weight. The dry mass of curls and final seed was obtained at harvest. The treatment means were subjected to analysis of variance and, in the case of doses, it was also the regression. Models were fitted to polynomial equations and the mean test used for variables was the Scott-Knott 5. Was computed to dry mass (g plant-¹) and leaf area (dm2) as the basis for determining the physiological indices: absolute growth rate, relative growth rate, leaf area ratio, net assimilation rate, area index leaf growth rate and culture. It was concluded that: the herbicides alachlor and diuron, stimulate soil microbial activity and alachlor affect the speed and the final emergence of seedlings of castor bean dwarf MPB01; yields obtained were below the estimate for EBDA MPB01 cultivar of dwarfvariety castor bean, lthough there was no negative influence of herbicides on the vegetative parts or yield of castor bean, which recommends further studies in the Bahia region Recôncavo; all physiological indices of castor bean cultivar EBDA MPB01 showed growth trends typical of this culture, not being affected by the herbicides alachlor and diuron.