Conserving soil moisture with mulches to maintain soil health and improve yield for vegetable production in Kansas

Abstract

Maintaining soil health for open field and high tunnel (HT) production of vegetables has become increasingly prioritized by growers in recent years. High tunnels (HT) are utilized by vegetable growers to extend the growing season and improve the yield and quality of crops. Meanwhile, the use of non-permeable polyethylene tarps has become popular for urban and small-scale vegetable farmers to manage weeds through occultation. Similar tarps could also be used as mulch, but little is known about how this will affect soil and crop productivity compared to other mulch types. This thesis aims to investigate how established and novel mulch types can help growers manage soil temperature, moisture, and health conditions across growing systems and climatic conditions and how these practices may affect the yield and quality of tomato and lettuce. Tomato and lettuce trials were conducted from 2022 to 2024 in HTs and open-field plots to determine the effect of various mulch treatments (bareground, black plastic film, black woven fabric, paper mulch, white silage tarp, and black silage tarp) on soil temperature, moisture, health, crop yield, and crop quality. Soil moisture and temperature were recorded throughout the growing seasons for both crops. Electrical conductivity (EC), bulk density, and respiration data were collected at termination of all trials to assess soil health. For tomato, harvesting occurred weekly to monitor yield. Texture and organoleptic quality were assessed from 3 harvests across the two years. In 2023, lettuce plants were harvested, and yield and quality data were collected. In the tomato trials, the application of black plastic mulch, fabric mulch, and black silage tarp was associated with higher average soil temperatures (23.7°C-28.9°C), compared to (22.4°C-26.8°C) under white tarp and paper mulch. In the fall lettuce trials, all mulch types retained soil heat in the early season (0.7°C-2.2°C) compared to bareground. The use of silage tarp maintained up to 21% more soil moisture than the bareground treatment for tomato. In the fall lettuce trials, all mulches were effective at managing moisture loss. Limited effects on soil health criteria were observed, though higher measurements of bulk density and EC may be associated with increases in soil moisture. This study indicates that mulch color and material affect soil temperatures and soil moisture in the summer, whereas in fall all mulches may reduce heat loss in the early period of the growing season and soil moisture (5-7%) in the late season. In the HT tomato trials, mulch had the greatest effects on yield during the early season, and the application of white silage tarp and plastic film mulch increased early marketable fruit yield by 58% compared to the bareground treatment. Mulch type had no significant effect on tomato or lettuce postharvest qualities that were assessed. Our data indicate that silage tarps may be an effective mulch, particularly for HT growers looking to conserve soil moisture and ultimately improve soil health, while maintaining yield. As growers address soil health concerns, it is likely that an integrated approach will need to be adopted that utilizes a combination of practices. The development of regional growing practices that ensure soil health and promote yield will be instrumental in supporting a growing population, and our study indicates that the use of mulches for vegetable production can contribute towards this goal.