CHAPTER 9

The potassium of liquid manure

On Swiss pastures receiving regular applications of liquid manure (or Gülle), moreover, it was also noted that the sodium content of the grass frequently fell to the almost non-existent level of 0-02% in the dry matter: exactly as in the case of very heavy potassium fertilizer dressings. In the Herve region of Belgium, where very large quantities of liquid manure are used, minimum contents of 0-03% sodium ¹ and 0-05% magnesium ² in the dry matter are recorded with a potassium maximum of 4-3%.

Liquid manure causes more marked imbalances in grass than potassium fertilizers

Table 11 illustrates that the imbalances brought about in grass by dressings of potassium fertilizer, so-called "artificial" fertilizer,³ are equally the result of liquid manure application, a natural and organic fertilizer.

Table 11: Liquid manure can cause more marked mineral imbalances in grass than dressings of potassium fertilizers

These mineral imbalances are even more marked where liquid manure is applied, and as a result grass tetany is prevalent on pastures that have received heavy dressings, to the extent that farmers sometimes describe the condition as "liquid manure tetany".
This is no reason to abandon the use of either liquid manure or potassium fertilizers: the point is that they must be used properly.

Liquid manure is a fertilizer much too rich in potash

It is not surprising that the action of liquid manure is analogous to that of potassium fertilizers, for it is very rich in potassium and low in phosphoric acid. It is estimated that 1000 parts non-diluted liquid manure contains on the average:

	1-70 parts nitrogen (N)
	0-13 parts phosphoric acid (P2O5)
	4-70 parts potassium (K) or
	5-7 parts potash (K2O)

which corresponds to a compound fertilizer very unbalanced in composition:         (17-0 - 1-3 - 47-0)
But these are mean contents. The content of potassium per 1000 parts liquid manure can vary within the enormous range of 0-54 to 18-42 parts potash (K₂O), that is, in the proportion of 1 to 34.

Application of potassium fertilizer to the soil of a pasture considerably increases the potassium content of the urine

Leaving aside for the moment the question of liquid manure as a liquid fertilizer, let us turn our attention to urine itself applied immediately and directly to the soil by the grazing animal. It may be assumed that this urine applies, or more correctly returns, an average of 22 lb./acre [26 kg./ha.] ⁴ potash, which is an important annual dressing particularly as it is in the form of readily available potassium.
The return of potassium in the urine is particularly obvious where potassium fertilizers are applied annually and regularly to pastures. The enrichment of the soil with regard to potassium effects an immediate increase in the potassium content of the urine of the grazing animal. Indeed, any increase in the potassium in the ration results in a marked rise in the potassium content of the urine: the addition of potassium acetate to the ration of pigs can multiply by more than twenty the amount of potassium excreted daily in the urine.⁵ HORST, moreover, has established that the urine of cows fed on grass that had received heavy dressings of potassium fertilizer was twice as rich in potassium and twenty times poorer in sodium than that of cows consuming a herbage that had received no potassium fertilizer (Table 18 in chapter 23).

Upward spiral of potassium

Under the influence of very heavy annual dressings of potassium fertilizers (mineral or organic), therefore, there develops an ever-increasing excess of potassium in the pasture soil, the herbage and in the animal organism:

	Potassium accumulates in the pasture soil due to the fact that the greater part of the fertilizer potassium is returned through the medium of the urine.
	The potassium content of the herbage increases, with resulting mineral imbalances.6 Certain organs of the animal particularly the adrenal cortex, deteriorate.

In other words, the bio-cycle of the nutritive elements in the herbage is upset.
It is possible, moreover, that excessive rates of potassium fertilizer application to pastures do not always exert their depressant effect on the magnesium content of the blood serum of cows during the first few years of their use. The same may apply to experimental plots where the "with potash" and "without potash" results are reversed. In such cases the cumulative effects of potassium fertilizers on the soil, herbage and animal have either not materialized at all or only in part. Farming, however, is not carried on under the short-term conditions of some experiments and see the cumulative effects of the methods of management it employs, such as the use of potassium fertilizers, for example. The farmer finds himself faced with what might be called "the upward spiral of potassium". The greater part of the potassium in the grass (up to 95% when the latter is very rich in potassium) is returned almost immediately to the soil via the urine, with the result that very little potassium is removed from a pasture (for calculations, see chapter 10). As the amount of soil potassium removed by rainfall is also small, the result is an increasing accumulation of the element in the soil in forms of which little is known as yet. This cumulative effect is observed in the case of regular and excessive applications to pasture of potassium fertilizers as well as liquid manure. On certain farms in the Lower Rhineland where liquid manure was regularly applied to pasture, NAUMANN found that the soil contained 40-50 mg. K₂O per 100 gm. soil, whereas he was of the opinion that 20-30 mg. is the maximum.

Liquid manure as a nitrogenous fertilizer

Liquid manure is also a nitrogenous fertilizer, and the ammonia it contains seems to be particularly conducive to magnesium deficiency in grass, probably as a result of the formation in the soil of ammonia-magnesium compounds. Grass, which regularly receives liquid manure, has consequently, as has just been seen, extremely low or almost non-existent contents of magnesium (0-05%). Potassium fertilizers, on the other hand, hardly ever cause the magnesium contents of grass to fall to such low levels (see Table 4). Grass tetany brought about by liquid manure is therefore frequent, and particularly ruthless, although it is still often ignored.
The ammonia in liquid manure can likewise form ammonium-copper compounds with the copper in the soil and can thus, like nitrogenous fertilizers by a slow cumulative effect help to produce copper deficiencies. In addition, fermented organic liquids, as liquid manure, Gülle or town sewage water contain detectable quantities of hydrogen sulphide (H₂S) which form in the soil copper, iron and probably cobalt sulphides that are not assimilable by the plant.⁷ On farms where large quantities of liquid manure are spread regularly, therefore, the grass is frequently very low in copper (sometimes 2 - 3 p.p.m. in the dry matter).⁸

Addition of mineral salts to the liquid manure tank

These deficiencies in the composition of grass caused by repeated applications of liquid manure not only favour grass tetany but are generally dangerous for the health of the animal, especially its fertility.
If the imbalances in the grass attributable to liquid manure are to be reduced the liquid manure must be distributed as equally as possible over all the pastures involved in the management. Unfortunately this rule is rather difficult to apply in practice, pastures near the farm or in a topographically favourable position generally receiving almost all the liquid manure.
It must be noted, moreover, that even in the case of equal distribution pastures receive more liquid manure than they produce if there has been any "importation" of foodstuffs, such as happens, for example, when pigs are fattened on milk by-products from the farm and large quantities of concentrates, potatoes, etc., brought in from elsewhere.
An attempt must therefore be made to re-establish the mineral equilibrium of the grass by applying "compensatory" dressings of mineral elements to the soil. Such dressings can obviously be applied directly to the soil, but it seems simpler to use the medium of liquid manure as far as possible.⁹
It might be desirable in future to prepare a special fertilizer for the liquid manure tank. This would contain, per cu. ft. undiluted liquid manure, the mixture ¹⁰ detailed in Table 12.

Table 12: A mineral mixture to "improve" liquid manure and a fertilizer to "rectify" a soil that has received large quantities of liquid manure

The superphosphate unfortunately tends to fall to the bottom of the tank forming a hard mass,¹¹ which means that the tank must be stirred regularly. Should this present any difficulty, all these salts could be added, except the superphosphate, which would be put in just before the liquid manure, was pumped out of the tank, or even spread on the pasture itself ¹² (in which case basic slag could be used with equal advantage).
All this naturally involves considerable expense, and it is not easy to convince the farmer of the merits of spending his money in improving a fertilizer which, in his opinion, costs him nothing and has all the attributes of a "natural" fertilizer. What is expensive, however, and very expensive at that, is to be saddled with sick animals, particularly those suffering from tetany or sterility. It is of this that the farmer must be convinced, his attention being drawn to the defects in the composition of liquid manure and the consequences this may have for his stock. He will then willingly countenance the expense of fertilizers to "improve" it.
These fertilizers, moreover, will improve the flora of his pastures, so often debased by the use of liquid manure, and this in turn will mean an improvement in both the quality and quantity of his hay.

Improvement of soil deteriorating as the result of repeated liquid manure application

It must not be forgotten that large quantities of liquid manure applied over many years have created serious imbalances in the soil, which becomes overloaded with potassium and contains copper, iron and cobalt in non-available forms. The result is a particularly degenerate flora. For this reason it is wise, before taking regular steps to improve the liquid manure itself, to try (which is not easy) to remedy defects in the soil, which in turn will help to improve the botanical composition of the sward. In the author's opinion one single application of the fertilizers listed in the lower section of Table 12 will "rectify" the soil defects, but it will take three or four years before there is any very obvious improvement in the flora.

1. NAUMANN points out that on farms where liquid is distributed regularly the potassium : sodium ratio can reach high levels in hay as well as in the fresh grass. *

2. Figures as low as this are not the result of potassium alone. In the case of liquid manure these almost nil contents of magnesium are the result of the combined action of the potassium and ammonia in the liquid manure. *

3. So-called natural fertilizers are often far from being natural. It is not liquid manure that is natural, but urine. Like liquid manure, the other organic fertilizers, farmyard manure and compost, are prepared and manufactured by Man. Just as one speaks of "artificial mineral fertilizers", one is justified in describing liquid manure or farmyard manure as "artificial organic fertilizers". *

4. Assume that the stocking rate is 0-6 beasts per acre [1-5 per ha.], that each beast has a daily output of 3-28 gal. [15 litres] urine and that there are 200 grazing days in each year. The annual return would therefore be: 0-6 x 3-28 x 200 - 394 gal. per acre [1-5 x 15 x 200 = 4500 litres per ha.], or 1-82 m³ per acre [4-5 ml per ha.] which would supply between 1-2 x 1-82 [0-54 x 4-5] = 2-2 lb./acre [2-4 kg./ha.] and 40-52 x 1-82 [18-42 x 4-5] = 74 lb./acre [83 kg./ha.] potash, with a mean of 5-7 x 1-82 [5-7 x 4-5] = 22 lb./acre [26 kg./ha.] potash (K₂O).
   If we take a stocking density of 1-2 beasts/acre instead of 0-6, which is quite possible with rational grazing, the quantities of potash returned in the urine per acre of pasture will be doubled. *

5. 85 - 95% of the potassium in the ration is estimated to be excreted in the urine, 5 - 15% in the faeces and 3% in the perspiration. *

6. The effect of this return of excess potassium is even more accentuated by the fact that such urine returns only infinitesimal quantities of sodium compared with the normal. *

7. In a well-aerated soil the copper and iron sulphides; so formed are slowly oxidized to sulphates by the thiobacilli, with the result that the iron and copper once more become available to the plant. Unfortunately, liquid manure (and even more sewage water) reduces the aeration capacity of the soil and, in consequence, the "release" of the iron and copper of the sulphides. Stagnant water, moreover, also contains green and purple bacteria capable of utilizing the hydrogen of the hydrogen sulphide under anaerobic conditions. The extent to which these bacteria can develop in soils receiving regular applications of liquid manure or Gülle is still unknown. *

8. On many grassland farms it is customary to apply "blue vitriol" (copper sulphate) to the liquid manure tank. In so far as it is possible to know the real reasons behind a traditional farming method, it appears that this addition of vitriol reduces the "rotten egg" smell, that is, the smell of hydrogen sulphide. From the scientific point of view it appears that the copper sulphate forms with the ammonia a complex compound containing a cupric tetra-amine ion, from which the copper is precipitated in the form of copper sulphide insoluble by the hydrogen sulphide of the liquid manure.
       The farmer obviously does not suspect that, in neutralizing "the stinking gas", he is preventing the copper, iron and probably also the cobalt in his soil becoming available to the grass.
       One rather remarkable farmer was encountered by the author in the Styrian mountains (Austria). He added copper sulphate to his Gülle tank because a professor in Vienna had analysed his grass and found it to be low in copper. *

9. Especially in mountain regions where piping exists for spreading this liquid manure on pastures. *

10. The practice of adding "salt" to the liquid manure tank is not new. As one farmer explained: "My cows were devouring blocks of salt. It occurred to me that it would be easier to put the salt in the liquid manure tank so that it could 'climb' up in the grass and thus got itself down the cow's throat unaided." Incredible farmers' logic!
        Of course, the addition of sodium chloride to the liquid tank, like its use as a sodium "fertilizer", will remain limited so long as various taxes and duties continue to rnake its price prohibitive. *

11. To the author's knowledge sodium phosphate has not been experimented with, and might perhaps be of interest. *

12. In which case the advantage of superphosphate is lost, namely that by forming compounds with ammonia it reduces the nitrogen losses incurred when liquid manure is spread. *