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University of Helsinki (2021)

Dew Collection and Mulching as Measures to Improve Water Balance in Dryland Agriculture

Tuure, Juuso

Titre : Dew Collection and Mulching as Measures to Improve Water Balance in Dryland Agriculture

Auteur : Tuure, Juuso

Université de soutenance : University of Helsinki,

Grade : Doctoral dissertation (article-based) / Doctoral Programme in Sustainable Use of Renewable Natural Resources 2021

Résumé partiel
Water scarcity is globally a key reason for crop yield losses. Difficulties in efficient utilization of the total available precipitation cause yield limitations and even total crop failure at rainfed dryland farms. This study assessed two potentially available measures to improve the water balance of dryland agriculture ; water recovery through passive dew collection and soil mulching with plant residue. Dew collection field experiments were conducted to evaluate the effectiveness of various plastic materials in dew collection in dryland conditions. The planar dew collectors were of the standard type : a 1 m2 surface tilted at 30◦ in respect to the horizontal. Dew yields were measured daily over a one-year period. The condensing surface temperatures and the meteorological conditions were monitored continuously, to calculate potential dew output. A laboratory method was prepared and tested for evaluating the attributes affecting dew condensation and droplet flow. The condensing surfaces were cooled below dewpoint by utilizing Peltier elements in controlled conditions. Dew yields measured in laboratory conditions were compared with calculated dew outputs, and with dew yields measured in field conditions. Dew occurred throughout the year, even through the dry seasons, and may be considered a small but reliable source of water. Annual dew yields were < 8% of the annual precipitation (322 mm). No significant differences were found between the tested materials. Clear skies, calm winds (0.5–2.5 m s-1), and conditions with dew point close to air temperature (Tdew ≈ Tair) favor dew condensation. Placement in the field affects the airflow characteristics at the condensing surfaces and ultimately the collected dew quantities, thus attention should be paid to the placement of the dew collectors in the field. Based on our results, a more comprehensive laboratory evaluation regime, with specific design and measurements of the airflow characteristics is needed to draw valid conclusions on the differences between the plastic foils. Mulching with plant residue was studied by measuring soil volumetric water content in vertical profiles in bare and plant residue-covered soil during a 100-day period. A one-dimensional model based on Richard’s equation was used to predict the effect of mulch over a two-year period. Compared with bare soil, mulching prolonged the time when continuously measured soil moisture content exceeded the water stress limit of maize. The predicted water-conserving effect increased with mulch thickness. However, plant residue mulch degrades naturally and the availability and competitive uses of plant residues may limit the thickness of the mulch layer. A mulch layer with a thickness of > 1 cm brought clear improvements to the soil moisture conditions and resilience against dry spells compared with bare soil.


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