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Tillage alters the soil environment and microbial communities responsible for decomposition and nutrient cycling. This study aimed to evaluate the effects of tillage intensity (minimum vs. conventional) on the soil chemical and microbial properties of a winter wheat (Triticum aestivum L.)-fallow rotation in the low-precipitation zone of the Pacific Northwest. Soils collected for 2 yr at two depths from both crop phases (wheat and fallow) were analyzed for pH, nutrient availability, total C and N, fungal and bacterial gene abundance, and enzyme activity related to C, P, and N cycling. All soil variables excluding soil pH were significantly greater in the top 10 cm of the soil. Except for pH and nitrate, all were greater in 2016 than in 2017. Across the full rotation, tillage did not affect any measured parameter. Instead, crop phase influenced several soil chemical properties and arylamidase activity, although the effects were not consistent across depth. Fungal abundance was influenced by tillage intensity but only in the top depth under wheat, indicating a phase-specific effect rather than a change persisting across the entire rotation. Soil enzymes were strongly related to total C, total N, and phosphate across the two soil depths, but effects were inconsistent between depths and across phases. Overall, crop phase and year were stronger drivers of soil chemical and microbial properties than tillage intensity. Short-term (<4 yr) tillage intensification does not have a strong influence on the nutrient cycling capacity of soil, although fungal numbers may decline in the Acropped phase.

Interest in soil organic carbon (SOC) levels is focused on both soil quality and sequestering carbon from the atmosphere. Farmers have developed minimum tillage systems and no-till systems. This study carefully measured SOC at three sites where long-term, randomized, replicated studies compared minimum tillage and no-till rotations in the low-precipitation inland Pacific Northwest, USA. To overcome seasonal, annual, and rotational effects, a soil sample was taken from each plot monthly for three years. The top 250 kg m-2 dry soil mass (representing the 0- to 20-cm depth) from each core was analyzed for SOC. Averages of monthly samples revealed the tilled treatment had 7.21 g kg-1 of SOC compared to 7.04 for the no-till treatment (p < 0.004). Examining variation month-to-month, 93% of sample variation was due to sample date, and 7% due to blocks (replications) within sites. Of 77 individual site-by-date samples, only six produced significant t-tests (p < 0.05) but SOC differences were 46–31 in favor of tillage and those 46 had larger differences. Power calculations estimated 34–100 samples would be required to detect a relative difference of 5% given the data's standard deviation. Soil water and soil temperature to 30 cm was measured at the time of sampling, and while no-till more often had greater water, temperature differences were inconsistent. We conclude that no-till did not result in more soil carbon in these systems and judicious tillage is an option for sustainable production. • Measurements over three years revealed significantly more C with tillage. • Variance in measurements was due to date of sampling, not spatial variability. • Surface soil moisture tended to be greater in no-till, except during fallow. • Soil temperatures were not consistently greater or less with no-till. [ABSTRACT FROM AUTHOR]

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. • Tillage during fallow reduced both evaporation and infiltration of water. • Tillage improved seed-zone water at the end of arid fallow. • Delayed tillage facilitated soil storage of rain. • Peak seeding-time moisture at 21 cm was most often experienced with tillage in June. [ABSTRACT FROM AUTHOR]

A 2-yr winter wheat (Triticum aestivum L.)-fallow rotation continues to be the most common cropping system in much of the US. Pacific Northwest. The sustainability of soils in the region depends on our ability to halt or greatly reduce wind and water erosion. An incomplete understanding of how tilled summer fallow preserves seed-zone moisture for timely fall crop establishment has slowed efforts to optimize tillage techniques for creating profitable and erosion- resistant systems. This 2-yr study created a series of soil mulches at two sites representing major soils in the region. It was found that timing and depth of mulch creation had consistent effects at all four site-years. Tillage performed in mid-June to depths of 10 and 15 cm preserved up to 0.01 kg kg-1 greater water content than no or 5-cm tillage, an amount of water that can make substantial differences in the germination of winter wheat. The later or shallower tillage treatments produced water contents similar to zero tillage below the 15-cm depth. Temperature profiles at 1-cm resolution demonstrated different shapes under different mulch treatments, which may prove useful in making quick mulch performance comparisons in the field. To optimize the timing and depth of summer fallow tilage, it will be necessary to characterize spring water storage plus the potential for end-of-summer water storage for each soil type. [ABSTRACT FROM AUTHOR]

Abstract: Reduced tillage methods for field crop production result in less disruption of soil structure and often increased amounts of crop residue maintained on the soil surface. The combination of these two factors produces increased surface soil aggregation. This study was conducted in the field and within pots to determine whether surface residue by itself improves soil aggregation within a short period of time. The soil was a silt loam loess deposit in the Pacific Northwest, USA, where summers are hot and dry, and most precipitation (420mm) is received during the mild winters. Two pot studies were conducted over winter, one under a shelter with controlled irrigations (183mm), and the other outdoors receiving natural precipitation (77mm). In both pot studies 640gm−2 wheat (Triticum aestivum L.) residue was either placed on the surface of the soil or thoroughly mixed into the soil. The field study was conducted on plots where, for the past 7 years, wheat crop residues were either incorporated through chisel/disk tillage or removed before tillage and replaced on the surface after tillage. The field study included plots where wheat was grown with no tillage. In the pots, there was no significant effect due to residue treatment on aggregate mean weight diameter, measured monthly for 4 winter months. This was true despite dissolved organic carbon being leached from the surface residue. In the 7-year-old field plots, replacing residues on the surface resulted in slightly greater mean weight diameter of aggregates at 5–10cm depth compared to the mixed residue treatment. The no-till plots had significantly greater mean weight diameter at 0–5cm depth than either tilled treatment. Our conclusion is that surface residue by itself failed to increase aggregation of tilled surface soil within the first rainy season after tillage. [Copyright &y& Elsevier]