Thirty-four different combinations of planter components (coulters, hoe openers, presswheels) and three commercially available planter units were compared under no-tillage conditions on five soil types, ranging from light- to heavy-textured clay, in the wheat belt of southern Queensland, Australia in the winter of 1981. Each combination was used to plant a single 10-m-long row of 100 seeds of "Songlen" wheat in a replicated randomized complete block trial. The germination rate of this wheat was determined at 92%. Comparisons of the relative performance of each treatment were based on the number of 14-day emergent seedlings (expressed as a percentage of the germination rate) and on seedling vigour at 28 days (determined by air dry vegetative mass, less roots).Planting combinations and units which manipulated the soil in the seed zone, creating a micro-seedbed, generally resulted in higher 14-day emergence (%) and 28-day seedling vigour (kg). These combinations involved the use of components such as a fluted coulter, a duckfoot tyne or a single-ribbed presswheel. Complete units such as John Deere's Powr-till, which also developed a micro-seedbed, provided the best results particularly on the heavier clays. Combinations which caused minimal disturbance did not generally perform well, with the exception of the triple disc unit on the light-textured soil.These results indicated that for heavier clay soils it is essential that no-till planters be able to create an adequate seed bed in the tilled zone. Units such as the Powr-till which can achieve this result can be quite expensive to purchase and maintain, indicating the need for a more conventional approach which has a similar ability to produce the seedbed. The results of this work indicate that suitable combinations of components (coulter, tyne, presswheel) can achieve this end.

On the uplands of the Darling Downs, runoff and erosion during summer fallows are a major problem. Interflow has been reported in tilled catchments in this area and might be controlled to reduce surface runoff and soil erosion. In view of the lack of data on interflow in tilled soils, this paper reports rates of interflow in a tilled soil for a range of stubble mulch rates, and describes the mechanisms of flow observed. Plots 22.5 × 4 m carrying surface mulches of 3,2,1 and 0.1 t ha −1 wheat stubble were prepared on a shallow black, cracking clay on 6% slope. The plots were pre-wet, and then simulated rain at 95 mm h −1 was applied (using a rainulator) for a 50-min test period. Perched water tables developed in the tilled layer and interflow was clearly visible flowing out beneath the collection gutter at the downslope end of the plot. Interflow rates were calculated from 1. (a) measurements of surface runoff on the rainulator plots at the end of the 50-min test periods; 2. (b) measurements of steady, deep infiltration rate for the site made using a rotating disc rainfall simulator. The interflow rates calculated for the rainulator plots were significantly related to stubble rates. Stubble appeared to increase interflow by reducing sediment loads in runoff water, thereby reducing the clogging of large voids in the tilled layer by sediment. Large, interconnected voids in the tilled layer must have been the major pathway for interflow.

For several years this laboratory and othersv" have been engaged in the study of stimulus coding in the auditory nervous system. A code may be considered simply as a language into which other languages may be translated.P We are interested here in the language that the nervous system uses in describing the external acoustic world. Sound stimuli initiate a series of events in the middle and inner ear. These events are translated into a series of spikelike discharges in the fibers of the auditory nerve. These fibers thus carry the entire auditory input to the brain. The discharges in these fibers follow the all-or-none law, so that presumably no information is