MICROMORPHOLOGICAL CHARACTERISTICS OF ORGANIC SUBSTRATES AND THEIR RELATIONSHIP WITH WATER RETENTION AND ROOT GROWTH

Abstract

The study of micromorphology helps understanding the function of water and the physiological response of plant cultures in a substrate. This research evaluated the effect of micromorphology of mixtures of organic materials on water content and root growth of Chrysanthemum. The hypothesis was that a description of the micromorphology of proposed new substrates would help inferring water storage and movement, and consequently, root growth. Organic materials used were pine sawdust (AP), pine shavings (VP), henequen bagasse (BH), coconut coir dust (PC) and a control (peat:Agrolita™) substrate. Seven mixtures were evaluated, planting cuttings rooted in 1250 mL containers. In the mixtures, water potential (ψ), root volume (VR) and the dry weight of roots was determined (PSR); in the leaves, relative water content (CRA) and water use efficiency (UEA). The micromorphology and porosity were characterized with the description of thin sections. The results indicated that the shape and distribution of particle sizes, degree of decomposition of organic matter, type and size of pores had an influence on the water retention and movement in a substrate. The mixture of henequen bagasse and sawdust, in a ratio of 20:80 formed compound packing pores of 50 to 500 μm size, and surpassed the control mixture in water use efficiency, with no significant differences in water potential, relative water content or dry weight of roots. The combination of coconut coir dust and pine sawdust formed compound packing pores and micropores <50 μm that hindered water movement and affected root growth. In the 20PC:80VP mixture, 80% of the particles were >200 μm, with simple packing pores 80% of them with sizes between 200 and 500 μm that allow water percolation and a reduction in the water potential (ψ).