Soil materials were fractionated into 20 separates ranging from 4,760µ to < 2µ in diameter. These separates were packed into splash‐cups and exposed to simulated rainfall intensities of 2 to 12 cm/hr. Raindrops were 5.1 mm in diameter and fell 11.33 m onto the surface of soil materials. Soil particles detached from the surface by the raindrops were oven‐dried and weighted.The amount of detached soil particles from surfaces of all separates was linearly related to simulated rainfall intensity. Linearity was significant at the 0.01 level of probability, except for the coarsest and finest separates. Slope of the line is used to characterize the susceptibility of soil materials to detachment from the surface by raindrops. The slope is measured as milligrams of particles per cm3 of water hitting the surface of soil materials.Detachment of soil particles exposed to simulated rainfall increased from 2.2 mg/cm3 of water for separates 4,760–3,360µ in diameter to a maximum amount of 288 mg/cm3 of water for separates 210–149µ and 149–105µ in diameter. Then, the amount of detached particles decreased with decreasing diameter of particles. Detachment for < 2µ diameter particles was 11 mg/cm3 of water.High‐speed movies showed that splash of raindrops from surfaces of separates > 105µ in diameter consisted of much smaller water drops than from separates < 105µ in diameter. Splash from the surfaces of separates < 105µ in diameter exhibited a crown effect and then broke into smaller drops.
Experiments were conducted in controlled temperature cabinets to determine the factor that caused corn (Zea may L.) radicles to grow nearly straight down from the seed in a greenhouse experiment conducted during the summer, and horizontally in a second experiment conducted during the winter. The possibility of horizontal growth caused by atrazine residues in the soil of the second experiment was eliminated when this type of growth was observed in vermiculite as well. Nearly vertical growth was observed when radiant energy from a heat lamp was directed onto the soil surface. The possibility that the roots followed a temperature gradient was eliminated by demonstrating vertical growth toward as well as away from the radiant energy. The soil temperature at the seed was found to be the primary factor involved. The angle of radicle growth varied from 30° from the horizontal at 18 C to 61° from the horizontal at 36 C. The influence of soil temperature on the direction of radicle growth explains many observations on root growth from the literature. It appears that the direction of growth of the radicle as well as that of the seminal and nodal roots is controlled by soil temperature.
Sharpsburg silty clay loam was separated into 11 aggregate fractions with the following diameters: 9,250–4,760µ, 4,760–3,360µ, + … +, 297–210µ, and <210µ. Krilium solution was added to half of each aggregate fraction to make the aggregates more water‐stable. The aggregate fractions were packed into splash‐cups and exposed to simulated rainfall intensities from 2 to 12 cm/hr. Raindrops were 5.1 mm in diameter and fell 11.33 m onto the surface of soil materials. Splash of soil particles and aggregates was caught, oven‐dried, and weighed.The amount of detachment of aggregates was linearly related to the rainfall intensity.Detachment of non‐treated aggregates exposed to rainfall increased from 76 mg of particles per cm3 of water to a maximum amount of 172 mg/cm3 as the aggregate diameters decreased from 9,250–4,760µ to 2,360–1,680µ. Then, the amount of detachment decreased with decreasing diameter to aggregate to 78 mg/cm3 for aggregates < 210µ diameter.The addition of Krilium to aggregates reduced the amount of detachment of aggregates >420µ in diameter exposed to simulated rainfall. The amount of splash increased with decreasing diameter of Krilium treated aggregates until 297–210µ diameter was reached (138 mg/cm3), then it decreased (101 mg/cm3) for aggregates < 210µ diameter.
Deep profile sampling under different water and crop management systems revealed limited movement of N and none of P from the rooting profile of nonirrigated Nebraska soils. Leaching of N to the water table was apparent in most irrigated soils located on valley positions and in sandy soils of the uplands. Alfalfa (Medicago sativa L.), with its deep rooting system, was noted to be an effective scavenger of inorganic N that may have accumulated under prior annual crops.
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