Soil nitrogen and organic carbon differences between no‐till and conventional tillage systems are often dramatic and well documented, but these differences between no‐till and stubble mulch tillage systems are more subtle. Our objective was to evaluate changes in soil inorganic N, organic N, organic C, surface soil moisture and grain yield on the southern High Plains as affected by stubble mulch and no‐till tillage systems from 1988 to 1992. The cropping system was a sorghum (Sorghum bicolor (L.) Moench)‐sorghum‐fallow‐wheat (Triticum aestivum L.) rotation conducted on a Pullman sandy clay loam (fine, mixed, thermic Torrertic Paleustoll) under dryland conditions near Clovis, NM. Tillage treatments were main plots and N fertilization treatments were subplots. Averaged over 5 yr and 37 sampling dates, the no‐till treatment had 2.0 mg kg−1 less inorganic N, 40 mg kg−1 more organic N, and 617 mg kg−1 more organic C than the stubble mulch treatment. Although differences between tillage systems were generally small, they were most noticeable during sorghum planting and development. No‐till unfertilized treatments often showed N deficiency symptoms during development. Nitrogen fertilization was more important than tillage system in determining sorghum and wheat yields in wet years. In dry years, N‐fertilized stubble mulch treatments had the lowest yields. Since conversion to either stubble mulch or no‐till in 1987, organic C levels under both systems have continually increased.

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Tillage or the lack of tillage affects infiltration and its variability across the field. To quantify infiltration characteristics of soil under no‐till and clean‐till furrow irrigated systems, a 3‐yr rotation of wheat (Tritium aestivum L.)‐sorghum [Sorghum bicolor (L.) Moench]‐fallow on a Pullman sandy clay loam soil (fine, mixed, thermic Torrentic Paleustoll) was initiated. Treatments were no‐till and clean‐till with or without wheel traffic. Soil water contents, water advance times down the furrow, wetted cross‐sectional area of flow, and cumulative furrow infiltration during three irrigations for each cropping event were determined. No‐till treatments conserved significantly more soil water (3.0 cm) during the fallow periods than clean‐till. Average water advance times to the end of the field were 301 and 175 min for no‐till and clean‐till, respectively. Wheel traffic significantly decreased advance times, by a factor of 1.98, during the initial irrigations at planting with no effect on subsequent irrigations. Wetted cross‐sectional area in no‐till furrows was significantly greater than in clean‐till during sorghum irrigations, averaging 0.0206 and 0.0093 m2, respectively. However, these factors did not contribute to a consistent increase in infiltration in the no‐till treatments. Grain yields for sorghum were significantly greater in no‐till than clean‐till: 4147 and 3584 kg ha−1, respectively, but clean‐till wheat yields (5414 kg ha−1) were significantly greater than no‐till yields (4657 kg ha−1). No‐till conserved more water during the fallow periods, but surface characteristics of planting wheat no‐till in sorghum residue may decrease uniformity over long furrows.

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