BORON DEFICIENCY IN LUCERNE STANDS

Press, Volume CXIV, Issue 33442, 25 January 1974, Page 22

BORON DEFICIENCY IN LUCERNE STANDS

Last November and December a number of inquiries were received about poor or stunted growth of lucerne stands.

In many cases these were ■ three to four-year-old stands I which had given good hay crops the year before, but had not even produced enough growth for one cut I following the dry spring. Samples were taken of plants and soil and sent to the Ministry of Agriculture’s plant diagnostic service at Lincoln, and to the soil testing laboratory at Invermay, near Dunedin. The results from the plant samples indicated boron | deficiency, and the soil

samples showed medium to low fertility levels with pH levels of 5.8 to 5.9. Boron is essential in the symbiotic relationship between legumes, particularly lucerne, and the nodule bacteria living on their roots. In lucerne, mild deficiency of boron affects the setting and yield of seed, while plant growth and appearance may be normal. At a more severe deficiency level, growth is stunted, young leaves are yellow and sometimes have red tints, and growing plants may be dwarfed ordying. In New Zealand,; boron deficiency is wide-1 spread in turnips and! swedes, moderately wide-? spread in lucerne and rare in pasture.

Diverse symptoms of boron deficiency are pro- 1 duced in different crops.! Most farmers are familiar’ with the condition in’ turnips and swedes of! brown heart, sometimes called Raan. Other boron, deficiency conditions include’ heart-rot of beets and! mangels and corky pit of! apples. Boron deficiency! also affects most tree fruits,; tobacco, celery, cauliflower, , kales and even hops. Lime can cause a reduction in boron levels, but, these effects are usually, short-lived, unless excess lime is applied. Water shortage increases the likelihood of boron deficiency. It is often encountered on dry. sandy or gravelly soils, and these include the Lismore soils found over large areas i of Canterbury.

Most of the boron in the soil is found as a highly insoluble mineral, tourmaline, which becomes available only very slowly through weathering. The boron available to plants is? released mainly from organic forms, such as plant material breaking down. On arid soils, other boron forms (borates) also contribute to the supply. In humid climates, available, .boron is concentrated in the top horizon of the soil. This is thought to be an important reason why boron deficiency in >. long-term crops such as lucerne, pastures and even apples is more severe in dry summers than in moist ones. Use of the nutrients in the top layer of the soil is impossible through lack of moisture.

Lucerne is very responsive to boron application when it has been deficient.

Care must be taken when applying borax top-dressing to a seedbed, as excessive quantities can affect seed germination. The usual rates are 22.4 kilograms of borax per hectare, or when incorporated in super, 250 kilograms per hectare of borated superphosphate should be used. This is 9.1 kilograms per acre and 100 kilograms per acre respectively for those who have not yet converted their paddock areas to hectares, and who have to buy their fertilisers in metrics.

If applying to a seedbed,! top-dress with borax or; borated super a few days] before the seed is sown to; avoid injury to germinating’ seedlings. 22.4 kilograms per hectare is a maximum rate of borax to apply under dryland conditions,'as excess boron can lead to collapse of leaves of white clover and other plants. The dead leaves assume a whitish or bleached appearance. -Also, do not use borated fertilisers on grain crops, as it may lead to whitening of the young shoots, and subsequent possible depression of yield. Under irrigation on better soils where hay is being made and fed elsewhere rates of up to I 45 kilograms per hectare! may be used. The fertiliser equivalent! in 7500 kilograms per hec-; tare of lucerne hay, which! is the approximate yield of dry matter from a dryland, stand on a Lismore-Eyre I soil type, is as follows: 2.5 cwt per acre muriate ofi potash (potassium), 1.5 cwt per acre lime (calcium). 2! cwt per acre superphosphate (phosphorus and sulphur), 0.6 cwt per acre serpentine (magnesium), and 0.2 cwt borax (boron). However, if the hay is fed back on to the stand, and the paddock is grazed after the first cut, most of these nutrients will be returned, along with a fair “dollop” of nitrogen.

However, the message is i clear: If lucerne stands are being taken for hay, a good: check should be kept on fertility levels through soiltesting. This will enable; production to be kept at its highest level at a time when' all feed is important. _■

The writer of the accompanying article is A. G. Leith, farm advisory officer, Ministry of Agriculture and Fisheries, Rangiora.