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Understanding changes in soil organic C (SOC) and total soil N (TSN) is important for evaluating C fluxes and optimizing N management. We evaluated long-term SOC and TSN changes under dryland rotations for historical stubble-mulch (HSM) and graded terrace (GT) plots on a clay loam soil in Bushland, TX. Compared with adjacent grassland with no history of cultivation, stored SOC in the surface 0.30 m of HSM declined by 41% after 86 yr of cultivation, with half of the estimated changes occurring during the first 20 yr. In the HSM plots under a winter wheat (Triticum aestivum L.)-fallow rotation, SOC and TSN (0.0-0.152 m) were significantly greater with decreasing tillage intensity (P < 0.05) in 1977 for treatments imposed in 1941. On GT plots under a winter wheat-sorghum [Sorghum bicolor (L.) Moench]-fallow rotation, SOC and TSN storage under no-till were not significantly (P = 0.396 and P = 0.261, respectively) different from stubble- mulch tillage 30 yr after treatments were imposed in 1984. Calculated export of N in wheat and sorghum grain from 1927 to 2013 from GT (1.6 Mg ha-1) accounted for 80% of the difference between TSN in grassland and GT plots. From 1927 to 1960, TSN decline exceeded N in exported grain by 1.2 Mg ha-1 and may explain present-day accumulation of NO3-N at 1 to 6 m in the unsaturated zone. Since 1966, crops have probably been assimilating NO3-N located deeper in the soil profile to supplement N requirements. [ABSTRACT FROM AUTHOR]

Examines carbon and nitrogen conservation in dryland tillage and cropping systems. Accumulation of crop residues near the soil surface in no-till; Limitation of soil disturbance with stubble mulch; Increase of microbial activity with the redistribution of residues; Improvement of soil productivity with frequent cropping and use of crops.

Water conservation often is limited by soil conditions that cause runoff, even from small rainstorms. This study evaluated the influence of tillage-induced aggregates on infiltration into Pullman soil (Torrertic Paleustoll). Tillage methods were PLOW (plowing and disking), ROTO (rotary), SWEEP (sweep), or NOTILL (no-tillage). Aggregate sizes were <0.42, 0.42-0.84, 0.84-2.0, 2.0-6.4, and 6.4-18.3 mm. Rainwater was applied until runoff and percolation became constant. Final infiltration (If) rates differed due to tillage, aggregate size, and interaction effects, but maximum difference was only 8.1 mm h-1, suggesting that If rate differences have little significance from a water conservation viewpoint during intense, short-duration rainstorms that occur in semiarid regions. Cumulative infiltration (Ic) apparently is of greater significance; it was greatest for large aggregates. The PLOW treatment resulted in most large aggregates and presumably would result in greatest Ic. However, under field conditions, Ic was similar for PLOW and SWEEP treatments. For the SWEEP treatment, tillage undercut the surface and retained more residues, thus negating the advantage of larger, but apparently less stable, aggregates with the PLOW treatment with respect to Ic. [ABSTRACT FROM AUTHOR]

Soil and water conserving practices must be used to sustain dryland crop production in semiarid regions. In this 1994 study, we evaluated the effects of different cropping system and tillage method treatments on surface residue cover, organic matter content, aggregation, and water infiltration for a soil used for grain sorghum [Sorghum bicolor (L.) Moench] production in the United States Southern Great Plains from 1982 to 1994. Cropping systems were continuous sorghum (CS) and winter wheat (Triticum aestivum L.)— fallow—grain sorghum—fallow (designated WSF) and tillage methods were no‐tillage (NT) and stubble mulch tillage (SMT). Treatments were CS‐NT, CS‐SMT, WSF‐NT, and WSF‐SMT. Surface residue cover before planting sorghum was >70% with CS‐NT and WSF‐NT, 29% with CS‐SMT, and 12% with WSF‐SMT. Surface cover after planting was =50% with both NT treatments, whereas amounts with other treatments were similar to those before planting. Soil organic matter contents (0‐ to 10‐cm depth) were greater on CS than on WSF plots, but were not affected by tillage method in either cropping system. Water stable aggregation (0‐ to 2‐cm depth) was greater with SMT than with NT in both cropping systems, but differences between cropping systems were not significant. Dry aggregates were smaller with NT than with SMT. Water infiltration was or tended to be greater on CS than on WSF plots, apparently because the WSF plots contained more water when infiltration was measured. Infiltration was not affected by tillage method, apparently because the greater amount of surface residues on NT plots counteracted the less water stable aggregates and smaller dry aggregates that had potential for reducing infiltration on the NT plots. This study indicates that no cropping system‐tillage method combination treatment had a consistently beneficial or detrimental effect on soil conditions. In conclusion, both cropping systems (CS and WSF) and both tillage methods (NT and SMT) are suitable for conserving soil and water resources and, therefore, for sustaining dryland crop production in the semiarid United States Southern Great Plains. [ABSTRACT FROM PUBLISHER]

The specific yield of the Ogallala formation, a water table aquifer, was determined with a neutron moisture meter. An access tube penetrated a 12-foot section of the aquifer. This section was saturated by recharging water to the aquifer and then dewatered by pumping for 11 days. The specific yield of the aquifer was calculated from neutron moisture measurements made at saturation after most gravity drainage had occurred. The average specific yield for 25 measurements made at ½-foot intervals was 052. This value compares favorably with the specific yields determined by tracer techniques and laboratory analysis of cores. However, the specific yield determined by the neutron method was 50% greater than the specific yield determined by pumping tests. [ABSTRACT FROM AUTHOR]