Dinâmica espaço-temporal da umidade do solo cultivado em dois sistemas de plantio de açaizeiro no nordeste paraense

Abstract

The açaizeiro (Euterpe oleracea Mart.) is a native palm of the Amazon biome, naturally occurring in lowland areas, with great extractive exploration and seasonal production concentrated in the period with the lowest rainfall in the region. With the growing demand for fruit pulp in national and international markets, there was an expansion of production to areas of terra firme, but there are still many gaps as to how the interaction with water dynamics occurs on terra soils. The aim was to evaluate the spatial and temporal variation of soil moisture content (θv) in two açaizeiro planting systems, monoculture and intercropped, to support the implantation of these crops in upland areas and to improve water management. The experiment was conducted in 2019 in a commercial açaizeiro plantation in Castanhal-PA, with an area of approximately 0.6 ha, implanted in two planting systems, monoculture and intercropped with the cupuaçuzeiro culture, under two irrigation levels of 0% and 100% of the reference evapotranspiration (ET0). Twelve puncture tensiometer batteries were implanted at five depths (0.1, 0.2, 0.3, 0.4 and 0.5 m) close to the açaizeiro clumps for monitoring soil tension in the different planting systems. The collections were performed daily from 7 to 8 am using a digital tensimeter and ruler, from April to December. Moistures were estimated using the adjusted model of Van Genuchten (1980) based on the retention curves of the studied depths. The mean values and standard deviations of θv were analyzed in the two cultivation systems with and without irrigation during the nine months of monitoring. The temporal stability of θv was analyzed by the relative difference and Spearman's correlation. Principal component multivariate analysis (PCA) was used to identify the associations of θv at different depths with physical properties, root density and climatic elements evaluated in the period. The resultsshow that the type of cultivation system with and without irrigation influences the spatial variability of θv, presenting greater variation in rainfed systems at all depths, responding to precipitation events, especially in the 0.1 to 0.3 m layers. The analysis of temporal stability identified the intercropped area as the most representative for the estimates of θv in the 0.1 to 0.4 m layers, with the 0.5 m layer being best represented in the monoculture, while the correlation matrix Spearman's, in general, identified instability of θv in all evaluated areas, even in irrigated areas. In the associations of θv and physical properties and root density, θv was not associated with any of the characteristics, while the association with climatic elements explained the variations that occurred during the analysis period. Therefore, variations in θv are influenced by climatic elements related to evapotranspiration, especially in the period identified as dry and in areas that do not receive irrigation, where all layers suffer great variation.