Pachic Haplustoll Research Articles

Eolian Influence on Development and Weathering of Some Soils of Point Reyes Peninsula, California

AbstractWind‐deposited sands have influenced characteristics of soils on Tomales Point at the northern end of Point Reyes Peninsula in California. The distribution of eolian materials, the interface between eolian and residual granitic parent materials, and mineral weathering were investigated in five pedons along a transect from near the edge of a wave‐cut bluff fronting on the Pacific Ocean to near the crest of a stabilized dune. Based upon distinct textural discontinuities, proportions of rounded and angular sands, organic carbon, and phyllosilicate species in silt and clay fractions, nonconforming zones of eolian materials over granitic residuum were clearly distinguished. The soils along the transect include members of coarseloamy, mixed, isomesic Pachic Haplustolls, coarse‐loamy, mixed, isomesic “Entic” Dystropepts, sandy, mixed, isomesic ustic Dystropepts, and mixed, isomesic Typic Ustipsamment families. A mineral weathering sequence involving the transformation biotite → vermiculite → smectite is evident within the buried granitic residuum along the transect.

Leaf and Canopy Temperatures of Pearl Millet Genotypes under Irrigated and Nonirrigated Conditions1

AbstractIt has been reported from previous research that leaf and canopy temperatures correlate with the level of water stress in a plant. If genotypes of a given species differ in their response to water stress, then leaf and canopy temperatures could serve as indices of their drought resistance. To test this hypothesis, 10 pearl millet (Penniserum americanum (L.) Leeke) genotypes differing in plant morphology were grown on a Eudora silt loam soil (fine silty, mixed, mesic, Pachic Haplustoll) under both irrigated and nonirrigated conditions. Leaf temperature (Tl), canopy temperature (Tc), canopy minus air temperature (Tc – Ta), leaf‐water potential (Ψl), leaf‐diffusion resistance (LDR), water use (WU), and crop yields were observed in both irrigated and nonirrigated treatments. Significant differences (P<0.05) were found in the grain yield, Tc, and Tc – Ta of genotypes, only in the irrigated treatment. Grain yield was negatively and significantly correlated with average afternoon Tc(r = −0.81) and average afternoon Tc – Ta(r = −0.78). Grain yield ratio (nonirrigated grain yield/irrigated grain yield) was positively and significantly correlated with average afternoon Tl(r = 0.64), average afternoon Tc(r = 0.64), and average afternoon Tc – Ta(r = 0.75). In the nonirrigated treatment, however, correlations of grain yield and grain yield ratio with various stress indices were nonsignificant. Average afternoon Tc and Tc – Ta was significantly correlated with average afternoon LDR only in the irrigated treatment. This study suggests that average afternoon Tc and Tc – Ta as observed in a nonstressed environment with an infrared thermometer could effectively be used as a technique to screen millet genotypes for their grain yield and grain‐yield stability (nonirrigated grain yield/irrigated grain yield).

Canopy Temperatures, Water Use, and Water Use Efficiency of Corn Genotypes1

AbstractIt is desirable to describe and characterize physiological properties of corn (Zea mays L.) genotypes that will permit a basis for selecting genotypes. The objective of this field study was to compare two hybrids (Mo17 ✕ B73, A619 ✕ A632) and their respective inbred parents under irrigated and nonirrigated conditions. Measurements of canopy temperature, stomatal diffusive resistance, xylem water potential, leaf area index, ear dry weight, and grain yield were determined. Water use was determined from neutron moderation measurements of the soil‐water profile. The soil was a fine silty, mixed mesic, Pachic Haplustoll that holds approximately 250 mm of plant available water.Hybrids had higher grain yield, water use, and water use efficiency than the inbred parents under both irrigated and nonirrigated conditions. Estimates of water use by both hybrids and inbreds were greater for irrigated than for nonirrigated treatments. Early ear dry weight appeared to be an indicator of final ear weight, and in this particular study, was an indicator of final grain weight. Canopy temperatures were cooler for hybrids than for the inbreds which is consistent with greater water use by the hybrids. Stomatal resistance and xylem water potential were not significantly different among genotypes.

Soybean Root Development and Soil Water Depletion1

AbstractWe conducted a field study to investigate soybean (Glycine max L. Merr., ‘Williams’) root growth and water depletion patterns. Field water depletion and rooting data are needed to assist in developing and refining models that consider root‐soil‐water interactions.Irrigated and nonirrigated soybeans were grown on a deep, barrier‐free, Muir silt loam soil (fine‐silty, mixed, mesic, Pachic Haplustoll). Soil water content, determined using neutron moderation (15‐ to 150‐cm profile), was used to calculate water depletion rates. Soil water content and desorption curves (obtained for each 15‐cm profile depth increment) were used to estimate soil water potential. Available soil water was estimated using —15 bars soil water potential as the lower limit of availability. We collected soil volumes (centered on the crop row) 76 cm wide, 7.6 cm thick, and 180 cm deep (sectioned to 15‐cm increments) and washed roots free using 35‐mesh screen.During the first half of our study, maximum root and water depletion depths were nearly equal. Later, water depletion tended to be about 15 cm deeper than root growth (possibly as a result of upward water movement into the water‐depleted root zone). Our data indicate that, as soybean root weight increased, there was a drying effect so available soil water and soil water potential decreased. Depletion effectiveness (defined as cm3 of water/g of root/day) was greatest with lower root weights, higher soil water potentials, and greater available soil water. Depletion effectiveness increased with depth in the soil profile; probably as a result of the roots being younger, in wetter soil, and less crowded. Our data indicate that a small portion of the root system can be responsible for much water uptake.

Irrigated and Nonirrigated Soybean, Corn, and Grain Sorghum Root Systems1

AbstractKnowledge of rooting patterns of various crops is important in designing irrigation systems and assessing water extraction capabilities. We investigated root depth and distribution under irrigated and nonirrigated conditions for soybeans [Glycine max (L.) Merr. ‘Williams’], corn [Zea mays (L.) ‘Prairie Valley 82S’], and grain sorghum [Sorghum bicolor (L.) Moench, ‘Pioneer 846’].Soil cores 6.7 cm in diam. were taken to 180 cm deep in the crop row, ¼ row, and ½ row (furrow) for each crop at physiological maturity. The cores were sectioned in 30‐cm increments and washed through 35‐mesh screen (0.73 mm opening), and the roots oven dried. The study soil was deep, barrier‐free, Muir silt loam (fine‐silty, mixed, mesic, Pachic Haplustoll).Approximately 71, 64, and 86% of the total root dry matter were in the upper 30 cm for irrigated soybeans, corn, and grain sorghum, respectively. Approximately 67, 39, and 79% of the total root dry matter were in the upper 30 cm for nonirrigated soybeans, corn, and grain sorghum, respectively. Only corn did not have roots in the 150 to 180‐cm zone. Seasonal water uses under irrigated conditions (neglecting water flux into or from the root zone) were 65 cm, 65 cm, and 53 cm in soybeans, corn, and grain sorghum, respectively. Seasonal water use was approximately 44 cm by each of the three crops under nonirrigated conditions.