The hydraulic conductivity versus soil‐water content relation for different soil depths was measured in the field for three soil profiles. The soils varied in physical properties from homogeneous to heterogeneous with depth and from loamy sand to silty clay in surface soil texture. Hydraulic conductivity values calculated from drainage data taken during different time intervals compared favorably with each other and showed no measurable hysteresis. The soil‐water flux at various soil depths with and without evaporation at the soil surface was measured. The rate at which water drained from each of the profiles was predicted using Darcy's equation and some simplifying assumptions. The agreement between theoretical and measured results is discussed in terms of soil heterogeneity with depth.

Agricultural sustainability in the USA's west‐central Great Plains depends on efficient use of water—the primary yield‐limiting factor in the region. With perennially water‐short status, the efficient capture and storage of precipitation in soil, and the yield responsiveness of crops to water, are emphasized. Our objective was to quantify grain sorghum [Sorghum bicolor (L.) Moench] and winter wheat (Triticum aestivum L.) yield responses to stored soil water and precipitation by using data gleaned from research conducted from 1973 to 2004 near Tribune, KS on Ulysses silt loam (fine‐silty, mixed, superactive, mesic Aridic Haplustolls) and Richfield silt loam (fine, smectitic, mesic Aridic Argiustolls) soils. Soil water content was measured gravimetrically to the 183‐cm depth at crop emergence. Grain yield was related to available soil water at emergence (ASWe) (increased 221 kg ha−1 cm−1 in sorghum and 98 kg ha−1 cm−1 in wheat). Grain yield was also related to in‐season precipitation (ISP) (increased 164 kg ha−1 cm−1 in sorghum and 83 kg ha−1 cm−1 in wheat). From response‐surface analyses, 63% (sorghum) and 70% (wheat) of variations in grain yield were explained by variations in ASWe and ISP. In data sorted by tillage, yield response to water supply (WS) was greater with no‐till than with conventional tillage in both crops (184 vs. 129 kg ha−1 cm−1 in sorghum; 138 vs. 86 kg ha−1 cm−1 in wheat). This finding supports the concept that less tillage and more residue lead to more efficient use during the growing season of ASWe and ISP.

Compaction can be a problem in some no‐till (NT) soils, but accumulation of soil organic C (SOC) with time may reduce the soil's susceptibility to compaction. Relationships between SOC and soil maximum bulk density (BDmax), equivalent to maximum soil compactibility, have not been well documented, particularly in NT systems. We assessed near‐surface BDmax using the Proctor test under long‐term (>19 yr) moldboard plow (MP), conventional tillage (CT), reduced tillage (RT), and NT conditions in the central Great Plains and determined its relationships with SOC, particle size distribution, and Atterberg consistency limits. The experiments were located on silt loam soils at Hays and Tribune, KS, and loam soils at Akron, CO, and Sidney, NE. The near‐surface BDmax of the MP soil was higher than that of the NT soil by 13% at Sidney, while the near‐surface BDmax of the CT was higher than that of the NT soil by about 6% at Akron, Hays, and Tribune. Critical water content (CWC) for BDmax in the NT soil was higher than in the CT and MP soils except at Tribune. The BDmax decreased with increase in CWC (r = ‐0.91). The soil liquid limit was higher for NT than for MP by 82% at Sidney, and it was higher than for CT by 14, 9, and 31% at Akron, Hays, and Tribune, respectively. The SOC concentration in NT soil was higher than in MP by 60% at Akron and 76% at Sidney, and it was higher than in CT soil by 82% at Hays. The BDmax decreased (r = −0.64) and the CWC increased (r = 0.60) with an increase in SOC concentration. Across all soils, SOC concentration was a sensitive predictor of BDmax and CWC. This regional study showed that NT management‐induced increase in SOC improves the soil's ability to resist compaction.

Root depth and distribution in the field were correlated with easily measurable above‐ground morphological paranfeters of soybeans (Glycine max L. Merr. ‘Williams’) at specific physiological stages. Previous research on soybean rooting depth and distribution was conducted with pots or field soil containing a barrier limiting full expression of root development. Other studies sampled a limited numberof times in a barrier free soil.We investigated soybean root depth and distribution under irrigated and nonirrigated conditions in a deep barrier‐free Muir silt loam soll profile. Irrigated plots received a total of 28 cm of water in three furrow applications. We measured plant height and dry weight, root depth, root distribution, and leaf area index each time roots were sampled. Each soil increment sampled (75 cm wide, 7.5 on thick, and in 15 cm increments to the 180 cm depth) was soaked and roots washed free of soil using a 35‐mesh screen. We used neutron moderation and gravimetric sampling to obtain soil water measurements.Soybean roots reached the 160 cm depth in both irrigated and nonirrigated plots. Root depth increased faster than plant height. At physiological maturity, 67% of the soybeans' root dry matter was in the 0–15 cm layer and 89% in the 0‐90 cm layer of the irrigated soil compared with 51% in the 0‐15 cm layer and 83% in the 0–90 can layer of nonirrigated soil.A quick estimate of rooting depth after six node stage (V3) in nonirrigated soybeans, based on our work, would be twice the top height. With irrigated soybeans, root depth would be twice top height from V3 until pod development began (R5.5) and 1.4 ✕ top height thereafter. The coefficient of determination (R2) for root depth vs. plant height was 0.994 and 0.987 for irrigated and nonirrigated soybeans, respectively.

The extent to which tillage systems modify the near‐surface soil aggregate properties affecting soil's susceptibility to erosion by water and wind is not well understood. We hypothesized that an increase in soil organic carbon (SOC) content with conservation tillage systems, particularly no‐till (NT), may improve near‐surface soil aggregate properties that influence soil erodibility. This regional study assessed changes in aggregate resistance to raindrops, dry aggregate wettability, and dry aggregate stability as well as their relationships with changes in SOC content. Four long‐term (>19 yr) tillage systems including moldboard plow (MP), conventional till (CT), reduced till (RT), and NT were chosen across the central Great Plains at Hays and Tribune, KS, Akron, CO, and Sidney, NE. The kinetic energy (KE) of raindrops required to disintegrate 4.75‐ to 8‐mm aggregates from NT soils equilibrated at −0.03 and −155 MPa matric potential was between two and seven times greater than that required for MP and CT soils in the 0‐ to 2‐cm depth in all soils. At the same depth, the water drop penetration time (WDPT) in aggregates from NT soils was four times greater at Akron and Hays and seven times greater at Sidney and Tribune compared with that in plowed soils. Aggregates from NT soils were more stable under rain and less wettable than those from plowed soils particularly in the surface 0 to 5 cm, but RT had lesser beneficial effects than NT management. The SOC content increased with NT over MP and CT and explained 35% of the variability across soils in aggregate wettability and 28% of the variability in resistance to raindrops in the 0‐ to 2‐cm depth. Aggregate wettability explained 47% of the variability across soils in KE of raindrops required for the disintegration of aggregates. No‐till management did not affect dry aggregate‐size distribution and stability except at Akron where mean weight diameter (MWD) in RT and NT was 50% lower than in MP management in the 0‐ to 2‐cm depth. Aggregates in MP and CT soils were either stronger or equally strong when dry but less stable when wet than in NT soils. Overall, NT farming enhanced near‐surface aggregate properties affecting erosion by water but had small or no effects on dry aggregate stability.

To help make decisions on shifting of crop species in water management strategies, information is needed on comparative water use characteristics of the principal row crops. The objective of this study was to compare the water use characteristics of six row crops grown in a replicated and randomized field experiment. Crops were corn (Zea mays L.), grain sorghum (Sorghum bicolor (L.) Moench), pearl millet (Pennisetum americanum (L.) Leeke), pinto bean (Phaseolus vulgaris L.), soybean (Glycine max (L.) Merr.), and sunflower (Helianthus annuus L.). Crops were grown near Manhattan, KS, on Muir silt loam (Cumulic Haplustoll) in 1981 and on Eudora silt loam (JFiuventic Hapludoll) in 1982, and near Tribune, KS, on Ulysses silt loam (Aridic Haplustoll) in both 1981 and 1982.Soil water content was determined to the 3.1-m soil profile depth by the neutron attenuation method. Measured evapotranspiration (ET) was calculated as the sum of soil water depletion, rainfall, and irrigation. Reference ET was calculated by using the original Jensen-Haise equation. The maximum value of measured ET /reference ET was greater for sunflower (1.35) than for the other five crops (ranged from 1.05 to 1.15). The mean daily water use rate of sunflower (6.1 mm d-1 ) was 22% greater than the mean of the other five crops (5.0 mm d-1 ). The mean dry matter water use efficiency was 17.5 Mg ba-• m-• for the group of C 3 crops (pinto bean, soybean, and sunflower) and 33.3 Mg ba-• m-• for the group of C 4 crops (corn, grain sorghum, and pearl millet). Sunflower depleted significantly more water from deeper soil depths (0.99-1.60 m) than the other five crops at Manhattan in 1981 and 1982. Our findings consistently showed that sunflower bad a greater daily water use rate than the other five crops.

No abstract

Diverse crop rotations sustain crop productivity by increasing crop water productivity and improving soil structure. Th e objective of this study was to compare two 4-yr winter wheat (Triticum aestivum L.) and grain sorghum (Sorghum bicolor L.) rotations in terms of grain yield, available soil water, and water productivity along with continuous winter wheat. A fi eld study was conducted from 1996 through 2015 on a deep silt loam soil near Tribune, KS. Th e study consisted of three crop rotations: continuous annual wheat (WW), wheat-wheat-sorghumfallow (WWSF), and wheat-sorghum-sorghum-fallow (WSSF). Grain yield, biomass, water productivity, and soil water were all greater for sorghum aft er wheat compared with sorghum aft er sorghum. Similarly, grain yield, biomass, water productivity, and soil water were all greater for wheat aft er fallow compared with wheat aft er wheat. Th e yield of the second wheat crop was 80% of the fi rst wheat crop in WWSF, whereas the yield of a second sorghum was only 63% of the fi rst sorghum crop in WSSF. Th e average crop water productivity (7 kg ha -1 mm -1 ) of the WSSF rotation was greater than the other rotations. On average, the WSSF system produced 2.05 Mg ha -1 yr -1 wheat equivalent yield (WEY), which was similar to the 1.96 Mg ha -1 yr -1 WEY from the WWSF rotation and greater than WW, which produced 1.53 Mg ha -1 yr -1 of wheat grain. A WSF rotation would have produced 2.0 Mg ha -1 yr -1 WEY, so the 4-yr rotations were not more productive than a 3-yr WSF rotation.