Molybdate Topdressing and Animal Health

New Zealand Journal of Agriculture, Volume 100, Issue 5, 16 May 1960, Page 419

Molybdate Topdressing and Animal Health

By

I. J. CUNNINGHAM,

Assistant Director-General, Department of Agriculture, Wellington'* 4 MOLYBDENUM is unquestionably a trace element of special interest in New Zealand, because some areas are deficient in it while other areas have too much. On the deficient areas molybdenum must be added as a fertiliser to grow good pastures or crops; on the excess areas there is so much molybdenum in the fodder that stock are poisoned. This excess may get into the grass because the soil is naturally high in molybdenum, or it may get there through careless or unnecessary use of molybdate fertilisers. Thus molybdenum has on the one hand possibilities of benefiting animal production by improving fodder production and on the other hand possibilities of doing harm by poisoning animals.

THE main purpose of this article is to describe the harmful effects of molybdenum on stock, and to show in what places and why molybdate fertilisers should not be used, but first, to make sure that the matter is kept in its proper perspective, the benefits which can result from the proper use of molybdenum are briefly described. Benefits of Molybdenum Molybdenum is an essential food for plants, though their requirements are very small. It is needed to convert nitrates into proteins and thus is necessary for plant growth. On soils that are deficient there will therefore be low production of pasture and low production of crops such as turnips and rape. The correct use of molybdate fertilisers on such deficient soils will greatly improve both pastures and crops. Molybdenum is also an essential food for the bacteria which grow in the nodules on the roots of legumes and which are responsible for taking nitrogen from the air and converting it to a form suitable for use by plants. Fixation of atmospheric nitrogen by clovers is very important in New Zealand grassland economy. Pastures depend in no small degree on the legume nodules to gather the nitrogen needed for growth. Clovers do not grow well on soil that is short of molybdenum and they respond spectacularly to suitable topdressing with molybdates. There is no doubt that proper use of molybdenum on deficient soils can improve clover growth, increase nitrogen supply for clover and for grasses growing in association, and

raise production of pastures and crops. In other words, molybdenum can in some districts greatly increase the supply of food for stock, and consequently enhance the stock-carrying capacity of the land. W. R. Lobb, Superintendent of the Department of Agriculture’s Winchmore Irrigation Research Station, has calculated just what this may mean on the sandstone and clay soils of the lowlands of Waitaki County. He estimates an increase of 60 per cent in stock carrying or a potential improvement of £500,000 annual gross farm income for that county alone. When the potential improvements of all the deficient areas of New Zealand are added, the total possible increase in primary production for the Dominion is likely to be very significant. Departmental Trials Obviously molybdenum is an important fertiliser which must be exploited to the full. Farmers can be well assured that its use in New Zealand is being most actively studied. The Farm Advisory Division of the Department of Agriculture is carrying out comprehensive experiments to learn where molybdates should be used. Experimental plots are laid down by farm advisory officers on known soil types, and regular observations are made of growth response to molybdate, with and without lime, phosphate, and sometimes other fertilisers. Some hundreds of trials have already been laid

down throughout the country and more are being laid down. Results from these experiments, superimposed on a background of knowledge previously obtained from chemical soil tests carried out at the Department’s Rukuhia Soil Research Station and from studies by other research groups, are quickly building up in broad outline the picture of molybdenum response in New Zealand. An article in the “Journal of Agriculture” for December 1953 by E. B. Davies and J. L. Grigg covers most of the existing knowledge. Responses in growth of pasture to molybdate topdressing have been observed in soils derived from greywacke and greywacke alluvium in Southland, Otago, Canterbury, Westland, and Nelson. Recently responses have been obtained on “pakihi” soils in west Nelson. In the North Island responses have occurred on soils derived from greywacke on the Rimutaka, Tararua, and Ruahine Ranges and on areas as far north as the Bay of Islands. Some sandstones just south of Auckland and in Northland are deficient in molybdenum, as also is Te Kopuru sand in Northland. Practically all soils of the steep country of North Auckland are molybdenum deficient. The interpretation is that it is desirable and economic to use molybdate fertilisers on these soils. Effect of Lime Some other studies of molybdenum in soil are of direct interest here. Only a proportion of soil molybdenum is available to plants. Availability is greater near a neutral reaction in soil and decreases as soils become more acid. Liming brings acid soils nearer to neutrality and therefore in certain circumstances will increase available molybdenum. Davies has noted that in some areas very high dressings of lime give unexpectedly high responses in pasture growth and he regards this as due to increases in molybdenum availability. In some places heavy liming may be as effective as applications of traces of molybdenum. This effect of lime has attracted considerable interest and has led to the belief or hope that molybdenum topdressing will replace liming. Therefore the relation of molybdate topdressing to a liming programme needs some further discussion. Lime is used to reduce soil acidity, to improve soil structure, to release some plant foods from the soil, to tie up certain substances harmful to plants, and to provide a plant food,

calcium. Incidentally, reducing acidity of soils may increase availability of molybdenum and thus produce an effect greater than would be expected from lime alone. In some quarters this possible secondary effect of liming on molybdenum supply is being mistaken for the whole effect of liming. It is hoped that the use of ounces of molybdenum per . acre will replace the cost and difficulty of applying hundredweights or tons of lime per acre. Obviously this will not be true in most cases, but in limited areas molybdenum can replace lime or reduce the amount of lime which must be used for pasture improvement. It is clear then that there are two very valuable and economically important results from using molybdate fertilisers: 1. To increase pasture and crop growth. 2. To replace some of the lime needed for pasture improvement. These results are, of course, obtained only where a molybdenum deficiency occurs. Danger of Excess Molybdenum The whole story has a strong appeal to the imagination of farmers. It is exciting to think that more grass can be made to grow by spreading something like a few handfuls of material over the whole farm. It has an appeal to the pocket as well. Also it is not uncommon in farming circles to attribute production failures to lack of a trace mineral, and molybdenum is a trace mineral which appears to do just the right things. The consequence is an urge to use molybdenum fertilisers at increasing rates and on any area irrespective of whether there is or is not a molybdenum deficiency. Unfortunately this brings in the other side of the picture. If molybdenum is used in excess or if it is used on land that. is already high in molybdenum, the harmful effect on stock may be very serious indeed. Poisonous effects from molybdenum have been observed in Britain, California, Florida, Ireland, Canada, and New Zealand. This article is confined to experience in this country. Role of Copper To make clear what happens it is necessary to explain first that molybdenum and copper are antagonistic to each other in the animal body. Molybdenum is poisonous, but within limits copper neutralises this poisoning. If copper in the food is low, a comparatively small amount of molybdenum is poisonous, but if copper is normal, the amount of molybdenum necessary to cause symptoms of poisoning is a great deal higher. The relative amounts of copper and molybdenum in the food are therefore predominantly important in determining the occurrence of molybdenum poisoning. An attempt is

made to illustrate this in Fig. 1. This illustrates four sets of circumstances, with the pasture copper shown as a clear column and alongside a black column representing the minimum amount of molybdenum which is poisonous in the same pasture. For a pasture with 10 parts per million (p.p.m.) of copper there must be 20 p.p.m. or more of moly b d e num to cause poisoning. For lower levels of copper the mini-

mum harmful level of molybdenum is lower. When pasture has 5 p.p.m. of copper, molybdenum is toxic at only about 7 p.p.m., and when pasture copper is 3 p.p.m. molybdenum is toxic at 3 p.p.m. These figures are not to be regarded as final, but as a general indication reached from field and experimental observations. ; Much of the knowledge of molybdenum poisoning in New Zealand relates to peat scours, which is caused by pasture the composition of which conforms to the two middle sets of symbols in Fig. 1. The copper in the grass is between 5 and 7 p.p.m. and molybdenum varies from 7 to 14 p.p.m., that is, just enough to be poisonous. The effect of this poisoning in stock is marked. Cattle scour severely and persistently in spring and sometimes in autumn. They lose condition and production falls. Young animals do not grow properly and bones are brittle and many have fractures from quite small knocks. The type of scouring is illustrated in Fig. 2. Proof that molybdenum is the cause of these symptoms follows from:

1. The occurrence of a seasonal variation of molybdenum content of the pasture with peak molybdenum content at seasons when scouring occurs. 2. The reproduction of symptoms by dosing molybdenum to cattle and by grazing cattle on pastures topdressed to reproduce the levels of copper and molybdenum that occur in natural cases. However, molybdenum poisoning is not confined to peat scours. Continuing investigations have shown that in cattle and sheep too much molybdenum in the diet will wash out stores of copper and produce a copper deficiency. An example of what happens in sheep is given in Fig. 3, which summarises the results with a group of 12 ewes kept on grass with copper content of around 10 p.p.m. and dosed regularly with molybdenum so that the molybdenum intake represented about 30 p.p.m. of the food eaten. The dosing started in October 1945 and continued until 1950. The thick black line is the average amount of copper in the ewes’ livers, measured on small pieces of liver removed at

different times. The steady drop in copper content of the ewes’ livers is clearly evident. The black stepped symbols indicate the copper contents in livers of new-born lambs; these are enclosed in a dotted column which shows the normal values for lambs’ livers at Wallaceville. Even in the early part of the experiment some of the new-born lambs from ewes dosed with molybdenum had low copper contents in their livers, and at the end of the experiment all such lambs had very low copper in the livers. The same train of events occurs with cattle. Ten yearling heifers were kept on pasture containing about 10 p.p.m. of copper. Five of these were dosed with molybdenum to give about 30 p.p.m. in the food. At the end of 81 weeks the untreated cattle had on the average 96 p.p.m. of copper in the dried liver, whereas the dosed cattle had only 10 p.p.m. of copper in the liver. Dosing with molybdenum had obviously greatly reduced the amount of copper in the livers of these cattle. Investigations have also shown that diseases resulting from copper depletion and associated with excessive molybdenum in the pasture occur on other soils beside peat soils. On Omihi soil and other soils in North Canterbury ataxia in lambs occurs and Merino sheep lose wool crimp. The pastures contain about 5 p.p.m. of copper and about 9 p.p.m. of molybdenum. On pumice soils between Lake Waikaremoana and Wairoa young cattle are copper deficient and unthrifty and show a marked loss of coat colour. The pastures have about 7 p.p.m. of copper and nearly 20 p.p.m. of molybdenum. A similar condition affects cattle in Raglan County. The appearance of the Wairoa cattle is illustrated in Fig. 4. All these circumstances show clearly that excess molybdenum is extremely dangerous to stock health. Great care must therefore be exercised when this element is used as a fertiliser. However, a warning to be careful is not by itself very helpful, and it is necessary to be specific about: 1. The areas where molybdenum content of pasture is so high that molybdate fertilisers should on no account be used. 2. The areas where copper in pasture is low, because in these areas increases of molybdenum in pasture are especially likely to be harmful. 3. The areas where molybdate topdressing produces an abnormally high response in molybdenum content of pasture. In such areas a small dressing might convert a safe pasture to a dangerous one. Some information on the first two points had already been accumulated, but this had to be expanded to give a reasonable cover of the Dominion. To do this quickly and with the facilities

available it was necessary to have some basis for generalisation, and for this soil type was selected. Samples of pasture were collected from all the main soil types in New Zealand in the spring of 1953, and were augmented in subsequent years, since spring is the season for maximum level of molybdenum in pasture. Analyses of these pastures for copper and molybdenum show which soils grow pastures high in molybdenum and which grow pastures low in copper.

The results of this work are discussed here. For measuring the response in pasture molybdenum to molybdate topdressing two methods were used, The fi rs t wa s to collect experience from a variety of topdressing trials w ith different rates of topdressing. The second was to obtain pasture samples f rO m trial plots laid down by farm advisory officers to measure response j n pasture growth rate to molybdate dressings. From each trial a sample

came from the untreated area, from the area topdressed with molybdate, and from the area topdressed with lime and molybdate. In assessing the results of surveys or of topdressing the following criteria are used to judge the relation to animal health. Copper Low: Below 5 p.p.m. Molybdenum— Normal: Below 3 p.p.m. Moderate: 3 to 10 p.p.m. (dangerous if copper low) High: Above 10 p.p.m. (potentially dangerous, even with normal copper) Pastures Moderate or High in Molybdenum Table 1 lists soils which grow pastures moderate or high in molybdenum without any additions of molybdate fertilisers. Soils which grow pastures containing more than 10 p.p.m. of molybdenum are emphasised by heavy type. Locations of the soils included in Table 1 are shown by the black patches in Fig. 5. The list is not final, as further work may modify it. On the North Island list soils derived from Taupo ash require comment. Only the areas of soil of these types near Wairoa are seriously high in molybdenum and on these areas stock disease has occurred. The main bulk of soils from Taupo ash produces a grass normal or moderate in molybdenum. The reason for this difference is a difference in origin of soils of close physical similarity. Not all farms on soils shown in Table 1 as moderate in molybdenum will have 3 or more p.p.m. in the pasture. Nevertheless these soils must be regarded as possibly dangerous and, except where it may be recommended in exceptional cases by farm advisory officers molybdenum should not be used. Quite obviously molybdate fertilisers should on no account be applied on any of the soils known to be high in molybdenum. Pastures Low in Copper Table 2 lists the soils that produce pastures low in copper, and the locations of these soils, with certain others consisting of peat, peat-pumice, or peat-sand mixtures which may be both high in molybdenum and low in copper, are shown in Fig. 6. Hukerenui silt loam requires some comment. Ataxia has occurred in lambs on this soil type. Though the copper content of the pasture was slightly above 5 p.p.m., the sample was of necessity taken from an area adjacent to copper topdressed land and could have received some copper contamination. For these reasons it was considered legitimate to include Hukerenui silt loam in Table 2 and Fig. 6.

TABLE I—SOILS THAT GROW PASTURE WITH MORE THAN NORMAL MOLYBDENUM N Normal M = Moderate H = High

Soil Number of Pasture Molybdenum *Soil name No. samples class p.p.m. North Island Manawatu set .. .. .. .. .. 1 25 N-M 1-6 Pakipaki coarse sandy loam *** ...... la 1 M 4 Tukituki set . . . . . . . . . . . . 1c 5 M 4-7 Kairanga set . . . . . . . . . . 2 16 N-M 1-7 ' Opiki complex . . . . . . . . . . 2b 3 M 3-8 tßotomahana sandy loam ■.. . . . . . . 3 6 M 4-8 tOtakiri gravel well drained phase .. . . 5a 2 N-M 1-4 Otakiri complex - . . .. . . . . . . 5c 2 M 3-4 Konoti clay loam . . . . . . . . . . 7b 4 M 4-6 Matapiro silt loam ** . . . . . . . . 8 4 N-M 1-7 Matapiro hill soils ** ........ 8H 1 M 5 Manawahe gravel . . . . .. .. . . 14d 3 N-M 2-4 Awakeri complex .. .. . . .. .. 15b 9 N-M 1-3 (Tuai coarse sand ***) . . .18 8 M-H 5-11 (Tuai hill soils ***) 18H 5 M-H 4-11 t(Tiniroto loamy sand ***) .. .. .. .. 18a 9 N-M 2-5 tfTihoi sand ***) .. .. .. .. 18b 4 M 3-7 (Tihoi-Opa complex ***) .. .. .. .. 18b 3 M 4 7 Rangipo sand .. .. .. .. .. 18?, 8 N-M 1-3 (Tiniroto sandy loam ***) .. .. .. ‘lBg 9 N-M 2-16 (....) sandy silt (Taumarunui district) .. ’,19 2 M 6.7 Ngaroma sandy silt .. .. .. .. 'l9 8 N-M 1-7 Ngaroma hill soils . . . . . . .. .. 1.9 H 3 N-M 2-7 Taumarunui hill soils . . . . . . . . 19aH 2 M 7-9 Manunui sandy silt . . . . . . . . 19d 3 N-M 2-3 Mamaku sandy silt . . . . . . . . 20 2 M 3 Waikoau sandy loam »*» . . . . . . . . 21 9 N-M 1-3 Waikoau hill soils *«* 2111 ' 7 N-M 1-8 Matawai sandy loam .. 22’ 5 M-H 5-12 Kourarau silt loam . . . . . . . . 25c 4 N-M 1-4 Wairama clay loam ........ 26 1 M 7 Wairama hill soils . . . . . . .. 26aH 3 N-M 2-5 Tutira sandy loam .. .. . . . . 49a, 7 N-M 1-6 Tutira hill soils .. .. . . . . . . 49aH I M 6 Whakatane gravelly sand .. .. .. .. 51a 7 N-M 1-3 Whangamata gravelly sandy loam .. .. .. 53 2 N-M 2-3 Kaipara clay .. .. .. . . .. 101 1 M 6 Waipu Clay .. .. .. .. .. lOld 3 N-M 1-5 fOtonga peaty loam .. .. .. .. 107 b 11 N-M 1-5 Ruakaka set . . . . . . . . . . 108 b 2 M 3-4 tßuakaka peat .. . . . . . . 109 2 M 3-4 fOne Tree Point peaty sand . . . . . . 109 b 3 N-M 1-4 Meanee-Fardon complex . . .. . . .. 11l 2 M 3-5 Takahiwai set .. .. .. .. .. 111 c 1 M 9 Ahuriri set .. .. .. .. 112 3 M-H 5-H Ahuriri set .. . . . . . . .. .. 112 a 1 M 7 Ahuriri stony sand .. .. .. .. 112 b 1 M 6 tTaihape silt loam .. .. .. .. .. 114 a 18 N-M 1-7 Turakina silt loam .. - .. .. .. .. 114 b - 11 N-M 1-7 Waitaha sandy loam .. .. .. .. 114 c 7 N-M 2-4 tMahoenui silt loam .. .. .. .. 115 15 N-M 1-9 Pahiatua silt loam .. .. .. .. 115 a 7 N-M 1-3 Hangaroa sandy loam .. .. .. .. 115 b 14 N-M i-H Waihua stony sandy loam . . . . .. 117 d 3 M-H 5-13 Unidentified peat soils from farms where peat scours occur . . . . . . .. . . M-H 4-16 South Island Harihari fine sandy loam ........ 2 M 4 tfHuihui sandy loam) .. .. .. .. 3 N-M 1-3 Kini peaty loam .......... 1 M 4 Motukarara Sandy loam weakly saline phase .. 4 N-M 1-5 t(Omihi silt loam) .. .. .. .. .. § M . 3-6 Waitapeka peaty silt loam .. .. .. 4 NM 1-4 Waikakahi complex silt loam .. .. .. 5 N-M 1-7 (Weka sandy loam) ........ 2 M . 4-7 Taitapu silt loam .. .. .. .. .. 4 N-M 1-3 it(. ■ • •) terrace soils associated with Onepunga soils 1 M 7

. Generally the soils listed grow pastures with less than 5 p.p.m. of copper, but there is some variation, as is indicated by the figures shown in Table 2, and in some North Island sands (sets 23 and 23b) many of the pasture samples have normal copper contents. The low copper is not necessarily enough on its own to cause stock disease, but it is so low that topdressing with molybdenum could well bring on trouble in animals. Clearly molybdate fertilisers cannot be used on any of these soils without risk. If molybdenum must be used to secure good pasture growth, copper fertilisers would have to be applied at the same time or copper cerate injections given to protect stock health. Responses to Molybdate Topdressing Pastures on different soils respond differently in molybdenum content to a topdressing with molybdate. This is illustrated in Table 3, which shows, for a variety of soils, the molybdenum content of pasture at different intervals after dressings of different amounts of ' molybdate. It is apparent from this table that pastures on different soils respond differently in molybdenum content to topdressings with molybdate. For example, 12 months after treatment with 4 oz per acre pastures on Kauru silt loam were six times as high in molybdenum .as untreated pastures from the same soil; and pastures on Lismore silt loam were only four times

as high as untreated pastures a few months after topdressing with 6 oz per acre. Pastures on Waiareka clay loam were no higher in molybdenum than untreated pastures 24 months after topdressing with 2| oz per acre, whereas pastures on Crownthorpe sandy loam were definitely higher 17 months after a similar treatment. Pastures on Heretaunga mottled silt loam had nearly 19 p.p.m. of molybdenum three months after a dressing of 8 oz of molybdate per acre, and pastures on Warepa soil at Invermay contained only 3.8 p.p.m.

from the same topdressing after the same interval. Some pastures reach a high level of molybdenum from comparatively small dressings of molybdate. Two ounces of molybdate per acre raised pastures on Heretaunga mottled silt loam to 6.9 p.p.m., and three dressings of 2 oz within two years raised sandy soils on Flock House to 11 p.p.m. This dressing of three lots of 2 oz in two years is higher than would ever be recommended, but not higher than might be applied by careless farmers. Table 3 thus shows two things. High or repeated dressings with molybdate will raise pasture molybdenum to dangerous levels, and responses on different soils are very different. Because of these different responses it was necessary to make measurements on a number of soil types to learn which are the soils on which abnormally high response in pasture molybdenum occurs after molybdate topdressing at usual rates (about 2| oz per acre). A content of less than 3 p.p.m. of molybdenum in pasture three months

after topdressing was regarded as a normal response. A content of 3 p.p.m. or more of molybdenum in pasture three months after topdressing was regarded as an abnormally high response. Information on. this— aspect, .. as already explained, was obtained by examining pasture samples from farm advisory officers’ trials. Results are shown in Tables 4 and 5 and are discussed under the two headings which follow. Pastures Showing Normal Responses Soils which grow pastures containing less than 3 p.p.m. of molybdenum

three months after topdressing are shown in Table 4. This table does not show where molybdate should be applied to obtain more grass or better crops on individual farms. This can only be decided after consultation with the local farm advisory officer. It does, however, indicate those soil types on which molybdenum can safely be used wherever it is profitable to do so. Pastures Showing Abnormally High Responses The first important point shown in Table 5 is that North Island soils respond more in molybdenum content of pasture to molybdate dressings than do South Island soils.

Seventeen soils in the North Island gave pastures with molybdenum content 3 p.p.m. or higher three months after topdressing. In the South Island one pasture from an area bordering Lake Ellesmere showed an abnormally high response and this was from a soil (Motukarara sandy loam) which produces high molybdenum pasture even without topdressing. A pasture molybdenum figure approaching 3 p.p.m. four months after molybdate application and a history of scouring in cattle which followed the topdressing but was apparently cured by copper suggested that a similar Lake Ellesmere soil (Taumutu shallow stony sand) should also be included in this group. The distribution of the 17 North Island soils in Table 5 is mapped in Fig. 7. The South Island soils are not mapped because they are included among the soils in Fig. 5. Of the 17 North Island ’ trials that gave a high response in molybdenum, four were in pastures that are low in copper. In these pastures a rise of molybdenum is more likely to be dangerous. On only one of the soils was the pasture growth so improved by molybdate topdressing that the farm advisory officer would recommend using molybdate fertiliser. This was Te Kopuru sand. But this is an important case, because copper in the pasture is very low. The molybdenum content of the pasture was 3.5 p.p.m. nine months after application of 2| oz of molybdate per acre and the copper was 3.1 p.p.m. On pasture of such composition copper deficiency and molybdenum poisoning could occur in grazing stock. On all the soil types in Table 5 molybdate fertilisers must be used with care. It appears that the 2 J oz per acre used in these trial plots is too high and that on these soil types and

indeed on the North Island generally a lower level should be used to guard against stock disease. For soil types

like Te Kopuru sand where low pasture copper accompanies high response to molybdate dressing the only safe procedure would be to combine a copper topdressing with a molybdate topdressing or to give stock copper cerate injections. On the basis of results discussed in this article it is possible to make specific comments on the use of molybdate fertilisers. 1. All the soil types listed in Table 1 and shown in Fig. 5 at present produce pastures above normal in molybdenum content. Topdressing with molybdate should be unnecessary and would further raise pasture molybdenum with possibility of harm to stock health. On these soils molybdates should not be used. 2. The soil types listed in Table 2 and shown in Fig. 6 produce pastures low in copper content. Topdressing with molybdate is likely to raise the molybdenum content of grass and a raised molybdenum content of grass with low copper is especially dangerous to stock. If

molybdate topdressing is necessary to improve pasture growth, copper topdressing at 5 lb of bluestone per acre should be applied at the same time to protect stock, or stock should be injected with copper cerates. 3. The soils listed in Table 5 and shown in Fig. 7 give abnormally high responses to a topdressing of 2| oz of molybdate per acre. Molybdate should not be used at this rate on these soils without concurrent use of copper. 4. The high response to molybdate dressings in a big proportion of the North Island trials (see Table 5 and discussion of it) suggests that 2J oz per acre is too high for the North Island. It is probable that a lower rate of topdressing would not produce sufficient increase in pasture molybdenum to cause any concern about stock health and yet would produce adequate growth responses in pasture. Responses in the South Island are not nearly as high and on most soils of that island a rate of topdressing with molybdate

higher than in the North Island could safely be used.

The lists of soils commented on in 1, 2, and 3 have been compiled from analyses made in the past five years. All the main soils have been covered, but a few of the less extensive soils may have been omitted. In future years these lists may be extended. Nevertheless the results so far obtained give some assistance in reaching a policy on the use of molybdate fertilisers. 5. The abnormally high responses on some soils to small rates of molybdate topdressing, and the marked response to higher single dressings or repeated dressings (Table 3) point very clearly to the need to adhere closely to recommended rates of molybdate. Molybdenum a Valuable Fertiliser Despite the discouraging outlook that these results might engender, they should not in any way be interpreted as suggesting that molybdate is unsafe where a deficiency exists. Molybdenum is a very valuable fertiliser and its correct use can be of great value. Careless and irresponsible use on the other hand can be harmful. This article shows where molybdates should not be used. Farm advisory officers in each district can, if necessary, give farmers information on the soil types on their farms and can tell them where molybdate should be used and the amount it is safe to use.

TABLE 2—SOILS THAT GROW PASTURES OF LOW COPPER CONTENT

North Island South Island Copper in Copper in Soil pasture .„ pasture .. .. -•-Soil name p.p.m. •Soil name No. . p p.m. « (Cheviot silt loam) .. 2.8 Rotomahana sandy loam 3 4.1 - 11.0 Ey re soils including Tarawera gravel .. 5 3.7 - 9.0 shallow and stony silt Qtakiri gravel well „ „ „ „ loam .. ■.. .. 3.8 - 8.1 drained phase . . 5a 3.9- 4.6 (Glasnevin shallow Awaken set . . . . 15 4.0 - 5.8 sandy loam ) .. .. .5 - 7.0 Taupo sand . . . . 18 3.9 - 8.9 (....) silt loam (Hawar(Timroto loamy sand den district) .... 4.8 ***) • • •• ■ • !8a 4.7 9.0 (Huihui sandy loam) .. 4.1- 6.3 (Tihoi sand) . . . . 18b 4.2 - 6.3 Hororata stony silt loam Mohaka sandy loam .. 21a 3.1 - 11.0 an d shallow loam .. 4.6 - 7.7 Patea sand . . . . 23 3.6 - 10.4 Lismore soils (shallow Whananaki sand . . 23b 4.1 - 12.0 and stony silt loam) 4.2 - 6.2 Marsden sand . . . . 23c 2.8 - 8.0 Mayfield silt loam . . 4.5 - 9.5 Red Hill set ... . . 24a 2.8 Mapua clay formation .. 4.3 - 4.5 Purimu hill soils . . 31dH 4.8 Oamaru complex . . 3.7 - 5.0 tHukerenui silt loam .. 46bH 5.1 Omaka gravelly loam 4.0 - 9.3 Wharekohe silt loam . . 47 4.5 - 8.6 (Omihi silt loam) . . 4.3 - 7.3 Te Kopuru sand . . 47d & 47dH 1.1 - 4.9 (Onepunga gravelly loam Whakatane gravelly ***) ~ ~ , . 4.3 . 6.2 sandy loam .. .. 51 3.2- 6.6 (....) terrace soils asOtonga peaty loam . . 107 b 3.9 - 10.2 sociated with OneRuakaka peat .. .. 108 b 1.7- 8.5 punga soils .. .. 2-57 Ruakaka peat .. ..109 1.7- 8.5 (....) clay and sandy One Tree Point peaty loam (Ohai district) 4.7 - 7.7 sand .. .. .. 109 b 1.7-10.9 Opuha hill soils .. 3.4- 4.7 Pukeokahu silt loam .. 113 b 4.5 Otanomomo peat . . ■ ' 3.7 Taihape silt loam . . 114 a 4.4 - 10.8 Temuka silt loam . . 4.8 - 9.5 Mahoenui silt loam . . 115 4.7 - 14.0 Waimea clay loam . . 4.8 - 9.5 Pohangina sandy loam 118 a 4.8 - Warepa silt loam . . 4.4 -15 4 Unidentified peats where (Weka clay and sandy peat scours occur .. 1.7-10.2 loam) .. .. 3.9- 5.7 * See footnotes Table 1. t See text page 424.

TABLE 4—SOILS WHICH GROW PASTURE WITH LESS THAN 3 p.p.m. OF MOLYBDENUM THREE MONTHS AFTER TOPDRESSING (COPPER ABOVE 5 p.p.m.)

Soil name Soil No. . North Island Waipunga set (except Pakipaki district) .. .. .. .. la Motatau clay .. .. .. .. Ta Waipukurau sandy loam .. .. 9b ■ Tokomaru silt loam . . . . . . 13 Milson silt loam .. .. .. 13a Halcombe hill soils .. .. .. 13bH Korea set .. . . . . . . 24d Korea hill soils .. . . .. 24dH Wanstead clay loam .. .. .. 25a Mangatea hill soils . . . . .. 25H Mangaotaki hill soils . . . . .. 29aH Marua hill soils .. . . .. 35H (Judgeford hill soils ***) .. .. 35bH Tauwhare hill soils .. .. .. 44eH Waikare clay .. . . .. .. 45 Waikare hill soils .. . . .. 45H Maungatawhiri fine sandy loam .. 46d Maungatawhiri hill soils .. .. 46dH Hangawera hill soils .. . . .. 46eH Te Kuiti sandy loam .. . . .. 60a Aria silt loam .. .. . . .. 60b Te Akau set .. . . . . . . 61c Ohakune hill soils . . . . . .. 65H Westmere silt loam .. .. .. 66d New Plymouth hill soils . . . . 67bH Stratford sand .. .. .. .. 68 Levin silt loam . . . . . . . . 75 Takapau silt loam .. .. .. 76 (Belmont silt loam ***) .. . . 76aH Matamau hill soils .. . . . . 77bH Dannevirke silt loam .. . . .. 78b Tahuna clay loam .. .. .. 84c Churchill set .. . . . . . . 86a Pakotai clay .. .. .. .. 90C Kerikeri friable clay .. . . . . 96a Rahotu loam .. . . . . .. 100 b Kaitaia clay loam . . . . . . 101 b Bluff loam .. . . .. . . 113 Whangaehu set .. .. .. .. 114 Whangamomona complex .. .. 116 Makara stony loam .. . . . . 122 Moeatoa set .. .. .... 122 a Ruahine set . . . . .... 124 Kaweka sandy loam .. .. .. 125

South Island (Aparima silt loam ***) Ashley silt loam (Blackstone stony loam ***) (....) hill soils (Collins district) Chertsey shallow silt loam Claremont silt loam Clydevale silt loam Hokitika gravelly sandy loam Glenroy silt loam easy rolling phase Jordan silt loam (Kaiwere Hill soils ***) (Kaiwere silt loam ***) (Karitane silt loam ***) Lyndhurst silt loam (Mokotua silt loam ***) Opuha silt loam Oxford silt loam Paparua stony sandy loam Barrhill silt loam (Ranfurly stony loam ***) Ruapuna very stony silt loam Wakanui silt loam (Takahe loam ***) Tasman silt loam (Tautuka silt loam ***) (Te Houka silt loam ***) Timaru silt loam Waimakariri silt loam Wangaeoa stony sandy loam and clay loam (Wharetoa silt loam ***) * See footnote Table 1.

TABLE S—SOILS GIVING PASTURE WITH 3 p.p.m. OR MORE OF MOLYBDENUM THREE MONTHS AFTER TOPDRESSING WITH MOLYBDATE

*Soil name Soil No. North Island Esk sand . . . . .. . . lb Tarawera gravel .. .. .. 5 Rissington set .. .. . . .. llcH Marton loam .. .. . . .. 13c Ohinepanea sand . . . . .. 14c Patea sand . . . . . . .. 23 Marsden set . . . . .. . . 23c Atua silt loam . . . . . . . . 29 Te Kopuru sand .. . . .. 47d Whakatane gravelly sand . . . . 51a Te Kulti silt loam . . . . . . 60 Hauturu silt loam .. . . .. 62cH Ohakune silt loam .. .. .. 65 New Plymouth brown loam . . . . 67 Pongakawa peaty loam . .. .. 107 f Moumahaki sandy loam . . . . 117 Te Ranga set . . . . . . . . 122 b South Island

Shorter Conference at Ruakura This Year

THE 1960 Ruakura Farmers’ Conference at the Department of Agriculture’s Ruakura Animal Research Station will be held from 14 to 16 June. This year’s conference is one day fewer than past conferences. The usual day of papers for all farmers has been deleted and the programme has been adjusted to give more general interest over the whole conference, and particularly to the field day. The first day will be devoted to papers and discussion of interest mainly to sheep farmers; the second day will be a field day, for all farmers, at Ruakura and at the Whatawhata Hill Country Research Station; and the third day will comprise papers and discussion for dairy farmers. About 1,000 farmers now attend the lectures in the conference hall at Ruakura, and the well organised field day is particularly popular; it attracted some 6,000 spectators last year.

* Revision by Wallaceville Animal Research Station of original work by Dr Cunningham when he was Superintendent at Wallaceville.

Footnotes to Table 1 * For North Island samples the soil names are those in Soil Bureau Bulletin No. 5, except where more detailed surveys have provided names which are indicated ***. Where Such surveys are not yet published the names are enclosed in brackets. In all cases the soil set number from Soil Bureau Bulletin No. 5 is shown for reference. The general Soil Map of the South Island has not yet been published and soil names are taken from district surveys. Where the surveys are not yet published the names are enclosed in brackets. (....) indicates that a soil name has not yet been allotted, and in such cases the texture is given and the district of origin shown in brackets after the texture. ** Pastures from these soils on one farm in Valley Rd. district, Hastings, have much higher molybdenum content than the same series in other districts. Though no physical differences occur, the soil molybdenum is higher for this soil type than in other areas. t Some samples low in copper have also been taken from areas of these soil types. t Spring sample only: Numerous others from same farm throughout the season.

Motukarara sandy loam Taumutu shallow stony sand * See footnote Table 1. See text on this page.

Soil Topdressing Molybdenum p.p.m. in dry grass Rate/acre Months since application Untreated Topdressed Peat .. Sand at Flock House .. Crownthorpe sandy loam Kaura silt loam ., . . Waiareka clay loam . . Lismore silt loam Heretaunga mottled silt loam i (Wallaceville) .. . . .. -1 VVarepa silt loam (Invermay) .. | 5 oz once 14 lb once 2 oz three times 2J oz once 4 oz once I 2j oz once 6 oz once 1 oz once 2 oz once 4 oz once 8 oz once : 1 oz once 2 oz once Warepa silt loam (Invermay) .. | 4 oz once 5 oz once 14 lb once 2 oz three times 21 oz once 4 oz once I 2| oz once 6 oz once 1 oz once 2 oz, once 4 oz once 8 oz once 1 oz once 2 oz once 4 oz once 8 oz once 14 14 24 since first 17 12 24 1 3 2-3 2-3 Less than 0.5 1.2 Less than 1 Less than 1 0.5 1.4 1.4 1.4 1.4 1.0 1.0 1.0 1.0 27 300 11 2.0 6 Less than 1 2 4.3 6.9 12.2 18.6 1.4 1.1 2.6 3.8

TABLE 3—EFFECT OF TOPDRESSING WITH MOLYBDATE ON MOLYBDENUM CONTENT OF PASTURE