Tillage timing to improve soil water storage in Mediterranean long fallow

Authors: Wuest, Stewart; SCHILLINGER, WILLIAM - Washington State University

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2022
Publication Date: 7/20/2022
Citation: Wuest, S.B., Schillinger, W.F. 2022. Tillage timing to improve soil water storage in Mediterranean long fallow. Agricultural Water Management. 272. Article 107835. https://doi.org/10.1016/j.agwat.2022.107835.
DOI: https://doi.org/10.1016/j.agwat.2022.107835

Interpretive Summary: Creation of a dry soil mulch to maintain near-surface moisture in dry environments is an ancient practice that is still used in many regions of the world for timely establishment of crops after long fallow. Before availability of herbicides, the first tillage during fallow was timed to kill weeds, but now the optimum timing for tillage depends only on the interplay of evaporation and infiltration of rain. The goal is to maximize total root zone water storage and seed-zone water at planting time. Our objective was to measure the effect of delaying soil mulch creation progressively later in the spring and summer on weed-free fallow for winter wheat in the Pacific Northwest. Over a period of six years and a total of 12 site-years, different tillage timings were compared to an untilled treatment. Soil water was measured at seeding time in the seed zone and total root zone. Seed-zone water and total stored water produced by different tillage timings was surprisingly constant, with few statistically significant or substantial differences. On average, only 2% of water was lost in the top meter of soil over an 80-day period. Responses to late spring rain was obvious, and tillage near the end of June often produced maximum soil water content. This is much later than standard practice, which can provide for better weed control and reduced total tillage.

Technical Abstract: Creation of a dry soil mulch to maintain near-surface moisture in dry environments is an ancient practice that is still used in many regions of the world for timely establishment of crops after long fallow. Before availability of herbicides, the first tillage during fallow was timed to kill weeds, but now the optimum timing for tillage depends only on the interplay of evaporation and infiltration of rain. The goal is to maximize total root zone water storage and seed-zone water at seeding time. Our objective was to measure the effect of delaying soil mulch creation progressively later in the spring and summer on weed-free fallow for winter wheat (Triticum aestivum L.) in the Mediterranean inland Pacific Northwest drylands of the United States. Over a period of six years and a total of 12 site-years, four to seven tillage timings were compared to an untilled treatment. Soil water was measured at seeding time in the seed zone and total root zone. Seed-zone water and total stored water produced by different tillage timings was surprisingly constant, with few statistically significant or substantial differences. On average, only 2% of stored water was lost in the top 1.0 m of soil over 80 days during the hot, dry period towards the end of fallow. Responses to late spring rain could be seen, and tillage near the end of June (early summer) often produced maximum soil water content.