Large Soil Cores Research Articles

A procedure for securing large and undisturbed soil cores for field simulation studies

Dynamic load is a technique which can be used to secure large pedons successfully in duplex profiles with massive clay B horizons. Data show that soil profiles obtained by this method have minimum change in soil physical properties including structure and compaction.

Transpirational, Leaf Area, Stomatal and Photosynthetic Responses to Gradually Induced Water Stress in Four Temperate Herbage Species

A series of physiological parameters was monitored under glasshouse conditions on micro-swards of four temperate herbage species. The micro-swards were grown on large soil cores so that the slow onset of water stress usually encountered in the field was simulated when water was withheld. Generally, water use per unit cover continued at a high rate even when water stress was causing considerable leaf death. Leaf diffusive conductance fell only gradually and did not reach minimum values until after much of herbage on the swards was dead. Stomatal closure in all species reduced water use per unit foliage cover by only 20-30%. Under increasing water stress, gross photosynthesis resembled stomatal conductances in remaining substantial (>50% of controls) even when relative water contents had fallen to below 80%. Both water use and gross photosynthesis were reduced more as a result of the reduced leaf area available for gaseous exchange than by the influence of stomatal action. Leaf moisture retention curves were similar for all species, there being a loss of c. 10% of relative water content per unit leaf water potential, down to drier than -5 MPa. It was concluded that the generally inferior herbage yields of white clover under dryland field conditions could be due in part to its relatively high leaf diffusive conductances when under water stress, while the better than average tall fescue yields under similar conditions may be attributed in part to its ability to roll its leaves tightly when water stress prevails.

Acetylene Reduction by Soil Cores of Maize and Sorghum in Brazil

Nitrogenase activity was measured by the C(2)H(2) reduction method in large soil cores (29 cm in diameter by 20 cm in depth) of maize (Zea mays) and sorghum (Sorghum vulgare). The activity was compared to that obtained by a method in which the roots were removed from the soil and assayed for nitrogenase activity after an overnight preincubation in 1% O(2). In a total of six experiments and 28 soil cores, the nitrogenase activity of the cores was an average of 14 times less than the activity of roots removed from the same cores and preincubated. Nitrogenase activity in the cores was very low and extrapolated to an average nitrogen fixation rate of 2.8 g of N/hectare per day. It was shown that inadequate gas exchange was not a reason for the lower activity in the soil cores, and the core method gave satisfactory results for nitrogenase activity of soybeans (Glycine max) and Paspalum notatum.

A Procedure for the Sampling and Testing of Large Soil Cores

AbstractThe significance of acquiring reliable data on the soil‐water characteristics of field soils is discussed in relation to the input requirements of computer‐based numerical models of the unsaturated flow process. A specification outlining the conditions to be fulfilled in sampling and testing a large soil core is then detailed. Equipment used in extracting a 40‐cm‐diam soil core is described together with relevant laboratory instrumentation.

SOILS

SummaryThe ability of the soil surface to accept continuous heavy rainfall is a critical factor in the prevention of accelerated erosion of tropical soils. The qualities required in the soil are complex, and are not easily inferred from simple laboratory measurements. A direct test has therefore been developed for this property. Large soil cores of undisturbed structure are brought to a standard moisture tension, and are subjected to heavy artificial rainfall of controlled drop‐size and intensity. The drainage tension is maintained at a constant value, and the rate of infiltration is measured. The apparatus is described in detail. Examples of results from a tropical rotation experiment are given, in comparison with porespace and percolation measurements.