Soil Class, Mechanical Impedance and Irrigation: Impact on Physiological Performance in Green Dwarf Coconut

Abstract

The objective of this study was to assess the physiological aspects of young green dwarf coconut cultivated in greenhouse as a function of soil class and different compaction levels and moisture conditions. The experiment was carried out in a greenhouse, using a randomized complete block design with nine replications and with 32 treatments in a 2 × 4 × 4 factorial scheme, with two soil classes—Typic Kandiudult and Umbric Dystrochrept, four compaction levels and four soil moisture conditions. Leaf predawn water potential (Ψw), net photosynthetic (A), stomatal conductance (gs), transpiration rates (E) and growth traits were higher in coconut grown in Umbric Dystrochrept soil. Moreover, these plants showed the highest values of maximum quantum yield of photosystem II (Fv/Fm) and leaf ‘greenness' (SPAD reading) was higher, but only in the lowest soil moisture condition, when compared with Typic Kandiudult. Higher soil moisture led to a higher Ψw for both soil classes. Close relationship between SPAD reading and the increase in soil moisture as well as between Fv/Fm and the increase in soil moisture for coconuts grown in Typic Kandiudult soil was observed. Furthermore, good correlations were observed between Ψw and the increase in soil moisture in coconuts grown in both soil classes as well as between Fv/Fm and the increase in soil density in coconuts grown in Typic Kandiudult soil. Effects of soil compaction were not observed on other physiological variables. Overall, green dwarf coconut trees grown in Umbric Dystrochrept soil allowed the higher water storage, which may contribute to increases in circumference, plant height, leaf area and dry weight (leaves, stem and root) linked to high photosynthetic rates.