Recent Research Work

New Zealand Journal of Agriculture, Volume 91, Issue 3, 15 September 1955, Page 305

Recent Research Work

MINOR ELEMENTS

THE large improvement in fertility brought about by the use of ■ molybdenum on many soils has intensified the search for other minor-element deficiencies. The Extension Division of the Department of Agriculture has now in operation 15 mowing trials and 650 observational trials investigating molybdenum responses on pastures and 5 mowing trials and 160 observational trials to test responses from other minor elements on pastures.

MOLYBDENUM

A number of soils have been added to the list of soils responsive to molybdenum on the evidence of pasture topdressing trials. These include many hilly clay soils of North Auckland, some hill soils in the Wairarapa and Raglan and Kawhia Counties, soils derived from old sand dunes, some of the “pakihi” soils of the South Island, and a number of volcanic soils in the North and South Islands. It is becoming obvious from trial results that on the hill soils of the southern part of the North Island variations in molybdenum responses occur because of soil differences which are at present unmapped. Efforts are being made to define these unmapped differences of soils so that the trial results can be applied to the largest area possible. Other important information on molybdenum can be summarised as follows: — Two and a half ounces per acre of sodium molybdate may not be enough to obtain worthwhile responses on some soils, particularly on those derived wholly or in part from volcanic parent material and with a high clay content. Though in general the use of molybdenum is expected to reduce the rate at which lime needs to be applied, there are many soils on which quite heavy liming is essential before sodium molybdate applied at 2Joz. per acre will give beneficial results. Experiments on hill country near Palmerston North, however, are showing that 3cwt. of lime per acre combined with superphosphate and molybdenum- gives excellent results. As such light rates of lime can be applied by air, these findings are of considerable practical importance. Experiments are now being conducted to examine more closely the relationship between rates of molybdenum and rates of liming.

COPPER

Copper responses on pastures have been obtained in comprehensive minor element trials on a podzol derived from aeolian sand and on a mature podzol north of Auckland. Pastures on peat soils at the Department of Agriculture Rukuhia Soil Research Station have also shown responses to copper.

SULPHUR

. Sulphur deficiencies are now shown to be widespread, and the remedy for these deficiencies is of major importance to agriculture in New. Zealand. Gypsum, fine elemental sulphur, and superphosphate and its derivatives are suitable sulphur fertilisers. Most soils contain adequate amounts of sulphur in the organic fraction (humus) . This sulphur is thought to become available to plants only by action of bacteria which convert the unavailable organically bound sulphur into more simple inorganic sulphates. Districts in which prolonged dry weather reduces the activity of soil bacteria are the ones in which sulphur responses have been most prominent. These are Central and North Otago and parts of Canterbury. Sulphur deficiencies are also found on soils in which organic matter and hence total sulphur are very low, such as the soils derived from Tarawera ash and on new alluvial silt deposits. A considerable quantity of sulphur is received from salt spray by soils close to the sea.

ZINC

The only indications of zinc responses on pastures are on some recent soils derived from aeolian sand and on a peaty loam on fine, water-sorted pumice near Te Aroha. If it can be demonstrated that zinc deficiencies are common to a number of pumiceous peats, zinc salts would become a topdressing material of some importance to the Waikato. At present, however, there is no evidence that this is the case.

MANGANESE

Present experimental results indicate that manganese is not destined to play a large part in pasture fertilisation in New Zealand. There is a possibility, however, that it may be of some benefit in certain small areas such as the soils derived from volcanic ash ejected from Mt. Ngauruhoe.

MAGNESIUM

Magnesium may tend to have a slight but beneficial effect in reducing soil acidity to the benefit of pasture growth in trials on very acid soils. This appears to be so in a trial in the Marlborough Sounds. A good growth response, however, which can definitely be attributed to magnesium, has been recorded on a heavily limed soil near Palmerston, Otago.

VANADIUM AND TUNGSTEN

Nearly 30 trials are in progress for examining the roles of vanadium and tungsten in pasture production with and without the addition of molybdenum. Trials with tungsten were laid down because tungsten’s chemical behaviour is very similar to that of molybdenum. Vanadium was tried to find an explanation for the superiority of basic slag over other phosphatic fertilisers, which is a feature of certain soil types. Basic slag contains substantial amounts of vanadium. Good visual pasture responses to vanadium have been recorded in a few field experiments near Kaitaia on soils responsive to molybdenum. It is doubtful whether superphosphate plus vanadium has been better than superphosphate alone, but vanadium with molybdenum (at 2Joz. of sodium molybdate per acre) and superphosphate appeared in several instances better than molybdenum and superphosphate alone. These trials, however, so far give no reason to believe that true vanadium deficiency is occurring or that vanadium is essential to the growth of pastures. It is rather thought that vanadium may influence the availability of molybdenum. Further trials with rates of molybdenum and vanadium should clear this point. Tungsten has been included in a pasture measurement trial on a highly molybdenum responsive soil near Dunedin. In the absence of molybdenum it has improved pasture growth, but in the presence of applied molybdenum it has had no effect. So far, therefore, its role has been purely one of a molybdenum substitute.

—C. DURING