Available soil water upper limit by modeling and direct determination in a greenhouse

Abstract

Pot capacity (PC) is a direct method of determining field capacity (FC) for experiments with plantings in pots. The objective of this study was to evaluate different laboratory methods to determine field capacity and compare them with the pot capacity method. The experimental design was completely randomized (CRD), with nine treatments (methods of obtaining FC) and four replications, totaling 36 experimental plots. The mean values of moisture contents in the FC of the nine methods were compared, being eight empirically obtained and one directly in the greenhouse, defined as a control treatment (PC). The relative accuracy (RA) for all treatments was determined in relation to the control treatment. The estimation of the upper limit of available water in the soil varies depending on the method, and a decreasing order of moisture levels can be observed at FC: FC-Lab4pts > FC-Labip > FC-Lab8pts > PC > FC-Lab6pts > FC-6KPa > FC-LabSWRC > FC-10KPa > FC-33KPa. The treatment FC-Lab6pts has the relative accuracy closest to 100% and can be a practical alternative to PC. The use of 4, 6, 8 or 10 points for modeling the SWRC does not interfere with the quality of the FC estimated by the Dexter inflection point method, which is much more efficient for experiments of this nature. The use of potentials -10 kPa and -33 kPa is not adequate to estimate FC in tests with pots in a greenhouse.

Biometric and morphological adjustments of Eugenia. dysenterica DC. seedlings in response to increased soil water deficit

“…In a previous study (Campos et al, 2019), the SWRC was determined in the laboratory, according to Klute (1986), and it was modeled using the Van Genuchten (1980) model, with Mualem restriction [m = 1 (1/n)], through the RETC software (Van Genuchten, Leij, & Yates 1991). The inflection point (IP) of the SWRC was used as the water content (ω -g g -1 ) at field capacity (FCIP), determined according to Dexter (2004) and Silva, Silva, Oliveira, Ferreira, and Serafim (2014), besides the matric potential (ΨmIP).…”

“…Comparisons of FC and PC estimation for our soil shows high correlation between them. More detail can be found in Campos et al (2019).…”

“…There were four replicates for each treatment. A fixed interval of 15% of the PC from one water treatment to another was established, assuming that the lowest assigned value (55% PC) was higher than the water content at the permanent wilting point (PWP), which was previously known through the determination of the soil water retention curve (SWRC) in a previous study (Campos et al, 2019). Each plot consisted of four polyethylene pots filled with 3.5 kg of soil and containing one cagaita tree plant per pot, totaling 40 experimental plots and 160 pots (sample units).…”