Assessing the Evaporation Method for Soil-Water Retention Curve Development and Comparison of Soil-Water Characteristics Across Different Tillage Practices in a Furrow-Irrigated Corn (Zea mays L.) System

Abstract

The thesis comprises three studies. The first study in this thesis (Chapter I) focused on a six-year corn field experiment to assess the influence of conservation agricultural practices on soil properties and their long-term effects on water-use efficiency and yield. Non-tillage management did not significantly reduce soil bulk density compared to conventional tillage, as no differences were observed between non-tillage and tillage systems throughout the 6-year experiment. There was no difference in total water-use efficiency among soil management practices in 2018, 2019, 2020, and 2021. Even though in one year of the study, a significant 24 kg ha-1 mm-1 improvement in water use efficiency was measured in the cover crop treatment, the no-till with cover crops system reduced corn yield by 1,500 kg ha-1 over the 6-year experiment compared to the no-tillage system alone. The study demonstrates that farmers can safely transition from a tillage-based management system to a no-till system without yield penalty or alternations in water use efficiency, although further research is needed to understand the observed yield penalty in the no-tillage with cover crops treatment. The second study in this thesis (Chapter II) compared the fine-textured blue tip Irrometer Miniature Low Tensiometer (MLT) to the HYPROP twin-miniature tensiometers. The goodness of fit of 1 and slopes of 1.01 and 1.04 kPa/kPa were measured in the saturated and below field capacity range, respectively, between the HYPROP mini-tensiometer average (HAVG) and the MLT. While there were some inconsistencies in the HAVG tensiometer readings below the field capacity range (4% deviation), this difference is minimal, as indicated by the low root mean square error (1.31 kPa) and standard error (0.004 kPa) of the slope, as well as the similarity of the slope to 1. Therefore, by using the model to adjust for this deviation measured between the methods in the dry range, the Irrometer MLT method can be considered a substitute for determining a retention curve over the MLT range and could serve as a useful alternative to the twin-miniature tensiometers in the HYPROP system. In the evaporation method, it is assumed that the soil core dries uniformly. In Chapter III, this assumption was tested by placing three Acclima™ Time Domain Reflectometer (TDR) sensors within a 250-cm3 core to assess the differences in soil moisture over time in Dewitt silt loam soil. A polynomial model (P \u3c 0.01) of y= 8.41 + (1.202*x) - (0.012*x2) with a goodness of fit of 0.99, was established between the weighted average volumetric water content and the volumetric water content measured by the HYPROP measured VWC. Model coefficients varied for the three sensors placements, suggesting that the core does not dry uniformly. Even though the sensors were not providing accurate estimates of water content due to their limitations, it was still possible to observe the drying pattern occurring from the edge to the center of the soil core