Cover crop effects on spring soil water content and the implications for cover crop management in south coastal British Columbia
Soil water content in the spring is an important factor in making decisions on cultural operations. A 2-year study was conducted to determine the effects of fall planted cover crops on spring soil water content dynamics and to relate the water content to cover crop management in terms of field trafficability. Each year, cover crops were planted at two planting dates in the fall, late August and late September on a loamy, mixed, mesic Humaquept on the Fraser River delta, south coastal British Columbia. Treatments were bare (control), wheat, rye and spring barley. Soil samples were collected at approximately bi-weekly intervals beginning in early spring to determine soil water content. Plant samples were also obtained late in the spring to determine C:N ratio. Treatments affected soil water content differently at each sampling date. No differences in soil water content at depths 20�40 and 40�60 cm were observed. Critical soil water content value for trafficability was determined to be 0.32 kg kg-1. Cover crops attained critical C:N ratio of 31.7:1 when the soil water was still above the critical value. The results suggest that terminating the cover crop growth in the spring could best be done by either mowing or spraying the cover crops as opposed to incorporation in order to minimize compaction since the critical C:N ratio for net mineralization is achieved when the soil is still too wet.
Evaporation Measurements beneath Corn, Cotton, and Sunflower Canopies
The purposes of this investigation were to : develop a microlysimeter that would be representative of field conditions for measuring evaporation (E) from soil; separate evaporation and transpiration (T) estimates by concurrent measurements of ET and E from soil on a daily basis under irrigated cotton, corn and sunflower; and assess the interactions between the two ET components under the prevailing experimental conditions
Suppressed Light Emission of the Reaction Zone in Detonation
THE detonation of high explosives in water can be photographed with an open camera and a flash light as the explosive gases do not emit light. The method has been used1 to investigate the spread of shock waves and explosive gases, and to investigate the initiation by shock waves2. We have found that it can be used also in certain gases such as butane and propane. The method is not suitable, on the other hand, for explosives with two levels of detonation velocity in the case of low velocity. A great part of the reaction then occurs after the reaction zone has passed and the expanding explosive gases are very luminous even in water.