Dinâmica da comunidade de plantas daninhas e variabilidade espacial de atributos do solo no cultivo de cacaueiro no semiárido

Abstract

Cocoa cultivation is normally restricted to humid tropical regions. However, due to the occurrence of diseases that are difficult to control, there is a tendency for crops to migrate to drier regions of the tropics in order to escape the main phytosanitary problems. At the same time, these new crops have adopted technologies that are not normally used in traditional regions. However, there are several factors that can negatively affect cocoa productivity, considering this new production model, such as the occurrence of weeds and soil fertility. Thus, the aim of this study was to identify the dynamics and spatial variability of the weed community and the variation of soil attributes in an area withcocoaplants cultivated in full sun in a region with semiarid climate. Weed collection was carried out in fourperiods with an interval of approximately sixmonths, in plots consisting of eight cocoa clones, in a randomized block design with threereplications. For the evaluation of soil attributes, the design was randomized blocks in split plots, with three replications. The plots consisted of eight cocoa clones and the subplots corresponded to threeevaluation times. Each collected point was georeferenced, to demarcate the study area and prepare weed distribution maps and soil fertility maps using geostatistical tools. From the identification and counting of the species, the phytosociological variables were calculated. Composite soil samples were collected in each plot at depths of 0-0.2 and 0.2-0.4 m. In addition to descriptive and faunal analysis of the weed community and multivariate analysis of soil attributes, spatial variability was also determined. For this, the theory of regionalized variables was considered, which has different methods for analyzing spatial variation, and one of them is the semivariogram. Then, the prediction of each attribute in non-sampled areas was performed through interpolations through the use of kriging, represented in contour maps. The correlation between the phytosociological variables and the soil attributes was carried out only at the coincident evaluation times, using the R software. The weed community found in cocoa plants cultivated in full sun in the semiarid region is composed of species mostly belonging to the families Poaceae, Euphorbiaceae and Amaranthaceae. Eleusine indica has a higher index of importance and coverage value in most periods evaluated during cacao growth. The studied area has a weed community with medium diversity and a tendency to unbalance. The species E. indica is the most important in the weed community. The periodswith the greatest similarity in weed composition were December/2017 and July/2018. There is spatial variability of soil physical attributes and spatial and temporal variability of fertility attributes in the cocoa crop under full sun in a semiarid climate region. Fertilizer recommendations and cultural practices can be made regionally based on the generated spatial variability maps.