ABSTRACT
Summary Experiments over several years are summarized. Collectively, these experiments sought to improve the reliability of overdrilling techniques during growth periods of temperate swards. The studies sought first to identify the important physical requirements of seeds and seedlings in untilled soils, especially in unpredictably dry situations, and then to develop drilling machinery and techniques to fulfill these requirements more nearly than had hitherto been achieved in New Zealand. The studies first involved closely controlling and monitoring the drilling and seed-groove-covering procedures, the soil moisture status and mechanical properties, and postdrilling climates, using a tillage-bin technique. Cereal seeds were drilled into large undisturbed blocks of soil contained in steel bins, which were then placed in controlled-climate rooms for seedling emergence and groove microequipment studies. Subsequently, field trials with pasture and crop species sought to extrapolate these data to the variable oceanic climate and soil conditions of New Zealand. In drying soils, contrasting designs of groove openers and covering devices had less effect on seed germination than on subsurface seedling survival and emergence. The more traditional V- or U-shaped seed grooves consistently promoted less seedling survival (even when covered with loose soil) than grooves where soil disturbance was largely confined to a subsurface layer, with a narrow surface slit and an overlay of dead vegetative mulch. Two designs of drill openers, a bar-covering harrow, and several press-wheel designs were developed. The main effect that this improved equipment had was to improve the in-groove seedling habitat. An experimental chisel opener (with subsurface wings) and bar harrow combination significantly (P < 0.01) decreased the rate of loss to the atmosphere of in-groove humidity by 45% compared to a triple-disk opener and 16% compared to a hoe opener, both in association with the bar harrow. Press wheels operating on the seeds at the bases of the grooves before covering improved seedling responses for the triple-disk and hoe openers. A moderate correlation coefficient, r = 0.75, between the mean loss of in-groove humidity for 6 days and subsurface seedling survival was established across the three opener designs. Physical removal of a strip of the competing resident sward overlying the drilled grooves clearly contrasted with the desirability of retaining a mulch as a major component of the groove cover for moisture retention. A simultaneous band-spraying technique was evolved and tested, using paraquat (1,1'-dimethyl-4,4' bipyridinium ion) and/or glyphosate [N-(phosphonomethyl) glycine] applied in strips either ahead of or following the openers. Vigor of introduced species was related to the width and effectiveness of the herbicide bands.
