GRAZING INTENSITY AND SOIL NITROGEN ACCUMULATION

The balance between the litter and animal excreta pathways was varied by imposing a range of sheep grazing intensities on a dryland ryegrass-white clover pasture for 3 years. In contrast to laxly grazed treatments, hard grazed treatments lost soil carbon and nitrogen. Greatest overall losses occurred in the driest year, and lowest losses occurred in years of greatest pasture growth. The importance of allowing some litter cycling, by avoiding continual hard grazing is discussed. Keywords: N-fixation, soil nitrogen, grazing, carbon, balance, litter, pasture.</jats:p

WHAT IS THE MAKE-UP OF A DRYLAND PASTURE?

Summer grazing managements, spelling, set-stocking, fast or slow rotations and topping or no topping, did not influence herbage growth in autumn of Nui ryegrass pasture. The cause of pasture deterioration on dryland, previously suggested to be through summer overgrazing, now seems more likely to be an effect of autumn overgrazing, particularly if pastures have been attacked by Argentine stem weevil and drought is continuing from summer. Low nitrogen fertility through often low fixation of nitrogen by clover, uncertainty of response of pasture to nitrogen fertiliser in cool season, and the effects from overgrazing, cause an extreme limitation in autumn-winter feed supply for stock in drought years. Feeding of silage in summer-autumn is advocated as a positive approach to this situation. On sunny aspects of dry hill country, buildup of dead herbage through summer considerably reduces the quality of the subsequent cool season growth of grass in the herbage mass. Several attempts to establish oversown grasses for improved cool season yield have not been successful. Dry hill grassland thus provides a considerable challenge to effect much improvement beyond manipulating the quality of the existing vegetation by grazing management. Keywords: Dryland pasture, grazing management, fertility, herbage quality</jats:p

Environmental and agronomic constraints in dryland pasture and choice of species

Hawkes Bay in the north down to North Otago, the duration and intensity of summer drought is unpredictab!e and variable. Within this region, winter temperatures are generally high enough to allow slow growth of pasture but summer drought can completely halt growth in most years, particularly on the commonly found shallow free draining soils. On these soils, moisture stress can develop very quickly because of the limited available soil water. Nearer the foothills, rainfall is greater and severe moisture stress less common. On sunny aspects in hill country however soils are commonly below wilting point for over six months of the year.</jats:p

AUTUMN NITROGEN FERTILISER IN A DRYLAND SHEEP SYSTEM

Applying 50 kg N/ha to dryland ryegrass-white clover pasture in autumn in each of four years resulted in an increased carrying capacity over the control for the last two years of 137 kg liveweight per ha at minimum in December, with an early spring peak of 211 kg extra liveweight per ha. Despite higher stocking rates on N-treated pastures in the later years. feed on offer at grazing was greater from early winter until the onset of severe drought, typically 8 months later. This improved level of feeding lifted ewe bodyweights post lambing by at least 4 kg. These higher ewe body weights were associated with significantly higher birth weights of twin lambs. Daily growth rates of these lambs. in a flock averagmg better than 175% lambing, were in excess of 260 g/head when ewe bodyweights were over 60 kg post lambing. Keywords: Nitrogen fertiliser, sheep grazing, lamb growth rates</jats:p

Effect of ryegrass containing the endophyte (Acremonium lolii), on the performance of associated white clover and subsequent crops

Ryegrass seed lines with (+E) and without (-E) the fungal endophyte Acremonium lolii were sown with white clover. Fewer clover seedlings survived under +E ryegrasses irrespective of whether the plots were mown or grazed. The dominant contrast was an inverse competitive relationship between grass yield and clover seedling survival. A further component unexplained by effects of defoliation or competition is interpreted as an allelopathic effect. Two pot trials, using wheat, were established to determine it there was any residual effect of +E wards on following crops. Wheat grown in soil with a history of +E or-E ryegrass with clover produced higher yields from the-E than the +E soil. However, wheat grown on soil from previously clover-free pastures showed no difference between +E and -E. Residual effects on wheat crops are therefore interpreted as being related to lower nitrogen fertility, as a result of reduced clover growth in +E pastures. Keywords: Ryegrass, endophyte, white clover. competition, vigour. allelopathy, soil nitrogen, wheat yield, Acremonium lolii</jats:p

Response of irrigated lucerne to defoliation and nitrogen fertiliser

A 3-year-old stand of lucerne (Medicago media Per.) cv. 'Wairau' was spray irrigated and subjected to three defoliation frequencies from spring to autumn, after which all plots received a common management. Nitrogen fertiliser was applied to half the plots after each defoliation. Total dry-matter yields calculated for a 12-month period were 24.0 and 28.2 tonnes DM/ha, and herbage N yields for control plots and those receiving N were 730 and 860 kg/ha respectively when the lucerne was defoliated at first flower. The highest mean growth rates (150 kg DM ha/day) occurred in midsummer, coinciding with maximum temperatures and radiation. Maximum response to N fertiliser also occurred at this time. Nitrogen fertiliser depressed spring lucerne yields. Defoliation management did not affect short-term N yields, but frequent defoliation reduced dry-matter yields and allowed extensive weed invasion. Nitrogen fertiliser did not affect weed yields