No abstract

White clover (Trifolium repens L.), red clover (Trifolium pratense L.), and lucerne (Medicago sativa L.) were grown in the glasshouse on a soil known to be low in available boron (B). 6 rates of B and 3 rates of lime in factorial combination were applied. B deficiency symptoms developed in all 3 species and these are described. Dry matter responses to B were greater for red clover and lucerne than for white clover. Critical B concentration ranges in plant material of 13-16, 15-18, and 17-18 ppm were established for white clover, red clover, and lucerne respectively. Lime had little effect on DM yield but reduced B concentration in the plants in early cuts.

Cobalt chelate (Co EDTA) and cobalt sulphate(CoS0 4 ) , appliedin liquidand solidforms, were compared as sources of cobalt (Co) for topdressing pastureata sitelocatedwithinapaddock~e r~grazing lambs r~sponded to vitamin B 12 mjecuon.The two matenals were equallyeffective in increasing pasture Co concentration but the effects from both lasted only about 100 days. Rate of application of bothmaterialsaffectedthemaximum pastureCoconcentration obtainedbutdidnotgreatly influencethe duration of the response.There was a small advantageat first from the liquid form but it did not persist. It is concludedthat Co EDTA is no better than CoS0 4 and because of its high relative cost it cannot be recommended for topdressing pastures.Thereis a needfora slow-release sourceof Co that willmaintainpastureCoconcentration at an adequate level for lambs for much of the grazing season but until such materialbecomesavailablea recommendation on a more effectiveuse of CoSO is made.

Six rates of boron (B) were applied to 2 white clovers (Trifolium repens L.), alsike clover (Trifolium hybridum L.), 3 red clovers (Trifolium pratense L.), and lucerne (Medicago sativa L.) in the glasshouse on a soil which was known to be low in available B. None of the 7 cultivars produced seed without added B, and red clovers also did not produce seed at low B rates. Maximum seed yields and the amount of B required to produce them were higher for red clovers and lucerne than for white and alsike clovers. The increase in seed yield of lucerne from B application was due entirely to an increase in the number of flowers formed and setting seed. In contrast, increases in white clover seed yields were due entirely to increases in the number of seeds per flower. For red clovers, increases in both the number of flowers and seeds per flower contributed to increased seed yields. It is concluded that B application may be beneficial in areas such as Marlborough and Canterbury for commercial herbage legume seed crops.

Two field trials comparing rates and times of application of borax to lucerne were conducted for 4 years on yellow-brown pumice soils in the Taupo area. Boron deficiency symptoms occurred at one site every year, but only when there was a prolonged dry period. Borax applications prevented boron deficiency symptoms and resulted in dry matter yield increases of 9-43% for individual cuts and an average annual increase of 1530 kglha (14%) over the 4 years. No response occurred at the other site where the soil contained a higher level of available boron. Annual rates of application greater than 11.2 kglha of borax increased the boron concentration of the lucerne at both sites but did not increase yields. Time of application also had no effect on yield. A single application of 22.4 kglha of borax at the start of the trial was as effective throughout the 4 years as repeated annual applications. This rate, applied with the spring topdressing every fourth or fifth year, is recommended to prevent boron deficiency and maintain yields of lucerne hay on the pumice soils in the Taupo area. INTRODUCTIONBoron is required in only small amounts by plants, but brassicas, lucerne, and some fruits and vegetables have a higher requirement than many other plants.