Control of manganese deficiency in sugar beet by placement of a manganated compound fertilizer

In Finland, manganese deficiency in sugar beet has traditionally been controlled by spraying the foliage with manganese sulphate. According to field experiments, placement of an acid compound fertilizer seems to provide a new possibility of controlling manganese deficiency of sugar beet in heavily limed fields. In 1-year experiments carried out in 1984—1985 in seven fields which showed slight symptoms of manganese deficiency, conversion from top dressing to the placement techniquealone increased the availability of soil manganese to sugar beet. The availability was, however, best safeguarded only when manganese (0.7 %) was added to acid compound fertilizer and applied by the placement technique. Placement of manganese (25 —30 kg/ha MnS04; Mn 26 %) together with acid compound fertilizer increased the root yield by 2.0 tons (+ 7%) per hectare in average compared to placement ofmanganese-freecompound fertilizer. The new method of application did not have a significant effect on the quality of sugar beet. Index words; manganese fertilization, fertilizer reaction, band applied manganese


Introduction
Manganese, a nutrient that plants need minimal quantities of, has been a well-known plant nutrient for over 60 years (McHargue 1922).According to some studies, a sugar beet yield of 35 tons/hectare only contains 2000 g of manganese in average, including the tops (Draycott 1972).
In Finland, the sugar beet soils normally contain much more manganese than a crop needs, but unfortunately most of the manga- nese is not in a plant-available form (Mäntylähti 1981, Sperlingsson 1982).Like other plants, sugar beet can only make use of man- ganese in the form Mn 2+ either as such (Cheng and Ouellette 1971) or small quantities of organic complex compounds of man- ganese (Garcia and Sanchez de La Puente  1977).
The quantity of plant-available manganese is affected by several external factors; avail- able manganese can take an inavailable form or vice versa.This is a typical equilibrium re- action that can be illustrated by the following oxidation-reduction equation (Scheffer and  SCHACHTSCHABEL 1976): (inavailable manganese available manganese) According to the above equation, the quantity of manganese available to plants can be controlled by the acidity and the redox-potential of the soil.
In Finland, the cultivated soil is naturally acid.In sugar beet cultivation these soils re- quire heavy liming, because sugar beet grows well in neutral soil.Liming decreases the acid- ity of the soil, but makes manganese partly inavailable to plants.Heavy liming can cause manganese deficiency which is in fact a very common situation in Finland.Fertilizers that increase soil acidity counter- act liming.These fertilizers release manganese for the use of plants (Solovjev and Golubev   1978).The usefulness of this information is, however, only theoretical, because acidifica- tion of the whole growth bed by fertilizers would be very expensive.The soil pH can, however, be lowered locally.For instance, by mixing a granulated fertilizer in the tilled soil layer, acidification takes place in the soil con- tiguous to the fertilizer granules (Slotta 1981).But because of the high buffer capacity of the soil this is only of minor significance to the plant.A better result is achieved by placing the fertilizer in rows beside the seed row.This depresses the pH around the fertil- izer row to the extent that a remarkable amount of manganese becomes available to plants (Voth 1978, Voth and Christenson   1980, Walsh and McDonnel 1957).In heav- ily limed soils the availability of manganese to sugar beet can be further increased by ad- dition of manganese sulphate in the acid NPK fertilizer (Voth 1978, Voth and Christenson  1980).
In Finland, manganese deficiency in sugar beet is usually controlled by spraying the fo- liage with manganese sulphate (10 kg/ha dis- solved in 300 1 of water) when clear symptoms of manganese deficiency (varicoloured foliage) are observed in late June or early July.Spraying may be repeated after I -2 1 -2 weeks, if nec- essary.
Leaf application is, however, in many re- spects insufficient for the control of manga- nese deficiency.When the plants are small it is difficult to combat manganese deficiency, most of the mixture being wasted because of the small area of the foliage (Hale, Watson   and Hull 1946).Apart from that, spraying is mostly carried out after symptoms of deficien- cy have been observed.Thus the effect is bound to remain scanty (Draycott and Far-  ley 1973).The sugar beet may have suffered from latent manganese deficiency for a longer period of time before appearance of symptoms.The effect of spraying remains scanty also because there is no internal, between-leaf transfer of manganese (Henkens and Jong- man 1965).The new leaves developing after spraying may suffer at least from latent man- ganese deficiency.
Addition of manganese fertilizer in the soil also involves some problems, because manganese rapidly becomes inavailable to plants when mixed into a well limed and tilled soil.Top dressing requires relatively high quantities of manganese with regard to the benefit achieved (Draycott and Farley 1973).
It seems that the fertilizer placement tech- nique together with acid compound fertilizers would offer a new possibility of economical control of manganese deficiency in sugar beet  (Voth 1978, Voth and Christenson 1980,  Walsh and McDonnel 1957).The fertilizer placement technique is increasingly being used in Finland and there is an acid (pH 5.5) fer- tilizer on the market specifically designed for sugar beet, a sodium containing compound fertilizer (NPKNaB; 13-6-8.5-6-0.2).Kemira Ltd. kindly enough produced a small quantity of this fertilizer with a manganese content of 0.7 % for the present study.

Materials and methods
The new idea was tested in seven heavily limed old sugar beet fields in 1984-1985.The experiments were carried out in fields which have previously shown symptoms of manganese deficiency (Table 1).
Each experiment consisted of six treatments in quadruplicate: 1. Top dressing (900 kg/ha Na-containing compound fertilizer) The experimental plots consisted of 7 rows, 12 meters each, three midmost rows being harvested (20 row meters).
The sugar beet was drilled directly to stand (distance between seeds 15 cm).The top dres- sing plots were fertilized manually before the last tilling.In the placement plots the fertiliz- er was applied to each row separately, near the seed row (about 3 cm deeper than the seed row and 6 cm aside of it) after the last tilling, using a sugar beet fertilizer-seeder.
Spraying with manganese sulphate was carried out immediately after appearance of symptoms of deficiency in the foliage.In 1984, spraying was done in early July and in 1985 in mid-July because of the later seeding period.In each plot the symptoms of deficien- cy were evaluated visually and samples of ma- ture leaves were taken 10-14 days after spraying.An ash extract was made of dried and ground plant tops.The percentage of manganese in the extract was determined by atomic absorption spectrophotometry.

Results
Because of the relatively small number of field studies, no correlation could be pointed between the concentrations of manganese in the soil and plants.In the following, only me- ans of the seven experiments are evaluated.
Effect on the quantity and quality of the crop The average root yield, percentage of sugar and concentration of impurities of beets are presented in  the test factors have affected much more the quantity than the quality of the crop.
Spraying of manganese sulphate did not have a statistically significant effect on the quantity of the crop.The difference between treatments 1 and 3 show the effect of foliage fertilizing when the main nutrients have been applied by top dressing.In such instances fo- liage fertilizing has resulted in a minor, stat- istically insignificant decrease in the beet yield (-O.l tons/ha).The difference between treat- ments 2 and 4 shows the effect of foliage fer- tilization when the main nutrients have been applied by the fertilizer placement technique.The foliage fertilizer is responsible for a small increase in root yield ( + 0.9 tons/ha), which cannot be shown statistical significance, how- ever.
It is interesting to observe that compared to top dressing the fertilizer placement tech- nique significantly increases the yield only when foliage fertilizer has also been applied.The results indicate an interaction between the fertilizer placement technique and foliage fer- tilization.
In the present study, manganese had a strong effect on the sugar beet root yield when manganese was added to NPK fertilizer ap- plied by the fertilizer placement technique.The manganese fertilization is responsible for the difference between treatments 2 and 6, the increase in the yield being statistically significant ( + 2.otons/ha, + 7 %).Top dressing with Mn-containing compound fertilizer has not had any effect.

Effect on symptoms of manganese deficiency and manganese concentration in plant tops
The fertilizer placement technique most prominently decreased the symptoms of man- ganese deficiency (Table 3).Foliage fertiliza- tion only slightly decreased the symptoms.There was no considerable difference between placement of manganese-containing NPK fer- tilizer and the conventional NPK fertilizer in favour of the former.
The manganese concentrations in the tops increased by 1.9-fold compared to the control (treatment 1) when the fertilizer placement technique was applied.Placement of manganese-containing compound fertilizer most prominently affected the manganese concent- rations in the tops.Manganese concentrations increased by2.5-fold (Table 3).

Discussion
The results of the present study clearly indicate that even in Finland manganese defici- ency may decrease the sugar beet root yield.Manganese fertilization is necessary especially when symptoms of manganese deficiency are present.Crops exhibiting slight manganese deficiency responded to manganese probably better than expected (Draycott and Farley  1973).The results do not exclude the possibility of latent deficiency causing losses in the beet yield (Sperlingsson 1982).Therefore, in the future, tests should be conducted both on fields with no symptoms and on heavily limed fields with apparent symptoms.Some reports suggest that foliage fertiliza- tion should also have shown the effect of manganese fertilization under these circumstances (Draycott and Farley 1973, Draycott and   Farley 1976).This was, however, not the case, probably because foliage fertilization was applied only once, and possibly too late (Farley and Draycott 1978).
The results of the study further indicate that manganese would best be available to sugar beet when manganese-containing NPK fertil- izer is placed to each row separately (Voth   and Christenson 1980).This would ensure sufficient availability of manganese to sugar beet throughout the growing period.The man- ganese inside the fertilizer row was somewhat protected against the oxidizing reactions of the soil.

Table I .
Soil characteristics.

Table 2 .
The results indicate that

Table 2 .
Effect of the treatments on the quantity and quality of sugar beet yield.

Table 3 .
Effect of the treatmentson symptoms of manganese deficiency and manganese concentration of tops.