The new agri-am process for ammoniation: Stack-ammoniation of mature forages using ammonium salts

V. C. Mason, J. E. Cook, T. Smith, J. W. Siviter, A. S. Keene and R. D. Hartley
Animal and Grassland Research Institute
Hurley, Nr Maidenhead, SL6 5LR, Berkshire, UK

Summary
Introduction
Conclusions
References

Summary

In many regions of the world access to anhydrous or aqueous ammonia is limited and attempts to employ urea as a precursor for upgrading purposes have often produced disappointing results.

To alleviate this situation an attempt was made to exploit the ammonia in both volatile and stable ammonium salts, reacting these compounds with a stoichiometric excess of quicklime or slaked lime in the presence or absence of added water in laboratory studies. Because of their instability, ammonium 'carbonate' (ie. carbamate/bicarbonate) and ammonium bicarbonate effectively upgraded straws when heated with the straw in Kilner jars in the absence of lime, with or without added water, at 90°C for 15 h. Ammonium sulphate, in contrast, produced a similar response only when heated with quicklime or slaked lime in the presence of water. When these treatments were conducted at 20°C for 35 days the volatile salts and the ammonium sulphate were only effective when treated with lime and water.

The findings for mixtures of ammonium 'carbonate' or sulphate with quicklime and water were then corroborated in sheep studies, using stack treatments of grass hay. Further work with cattle confirmed the effectivity of the ammonium sulphate-quicklime mixture in the stack technique.

It was concluded that these processes can provide a means of ammoniation for farm treatments, and it is suggested that the composition of the chemical residue can be manipulated through choice of salts and alkalis to provide a mineral supplement for animal feeds or a fertilizer for soil improvement.

Introduction

The process of ammoniation is widely used to increase the digestibility of organic matter and the nitrogen content of cereal and grass straws (Sundstol and Coxworth, 1984). Unfortunately, in many regions of the world access to anhydrous or aqueous ammonia is limited and attempts to employ urea as a precursor of ammonia for upgrading purposes have often produced disappointing results (Mason and Owen, 1985).

A potential source of ammonia, currently unexploited, is that available in ammonium fertilizers and other ammonium salts. Some of these chemicals are volatile, but ammonia can be released from the more stable compounds by reaction with a stoichiometric excess of such alkalis as quicklime, slaked lime or caustic soda. The objective of the present work was to examine the feasibility of exploiting this principle to upgrade mature forages by the oven and stack methods.

In vitro studies

In a preliminary study, a factorial experiment was designed to compare five sources of ammonia (aqueous ammonia, anhydrous ammonia, ammonium 'carbonate' (i.e., a mixture of carbamate and bicarbonate), ammonium bicarbonate and ammonium sulphate) under laboratory conditions. For this, samples of chopped barley straw (cv Sonja) were treated in Kilner jars with ammonia (35 g/kg straw DM) released from these chemicals by volatilization and/or by reaction with a stoichiometric excess of quicklime or slaked lime in the presence or absence of added water. In all cases the chemicals and added water were placed or mixed in a small glass vial within the Kilner jar, so that only gases or water vapour could come into direct contact with the straw. Half the jars for all treatments were then stored at 20°C for 5 weeks simulating a stack treatment, the remainder being held at 90° C for 15 h to simulate an oven treatment.

Tables 1 and 2 present estimates of in vitro organic matter digestibility for processes occurring in the absence or presence of added water, respectively. In the absence of water, heating the volatile salts to 90°C for 15 h gave improvements in digestibility which were similar or slightly inferior to those obtained with the positive ammonia controls, but under these conditions ammonium sulphate treatment gave little or no improvement. In contrast, at 20° C prolonged storage of straw in the presence of the potentially volatile salts gave responses which were no more effective than those achieved with ammonium sulphate. Furthermore, the results achieved with anhydrous ammonia (not reported in Table 1) tended to be inferior to those obtained with aqueous ammonia. The effect of lime was inconsistent.

Table 1. Upgrading barley straw using different ammonia sources* (no added water) (OMD in vitro: g/kg).

		NH3 source
		No NH3	Aq. NH3	(NH4)2CO3a	NH4HCO3b	(NH4)2SO4
90°C	-	329	432	376	411	303
15 h	CaO	364	458	408	401	324
	ca(OH)2	319	432	435	420	349
20°C	-	315	433	339	338	322
35 d	CaO	325	426	349	323	325
	Ca(OH)2	301	455	379	362	350

* Rates: per kg straw DM: 0 g H₂O; 35 g NH₃; 0, 70 g CaO or 92.5 g Ca(OH)₂.
a. (NH₄)2CO₃ = carbamate/bicarbonate mixture.
b. Lime and water rates doubled. SED = 23.5.

Table 2. Upgrading barley straw (cv. Sonja) using different ammonia sources* (water added) (OMD in vitro: g/kg).

		NH3 source
		No NH3	Aq. NH3	(NH4)2CO3a	NH4HCO3b	(NH4)2SO4
90°C	-	283	442	467	418	327
15 h	CaO	294	427	450	453	438
	Ca(OH)2	296	434	449	443	442
20°C	-	311	440	374	362	344
35 d	CaO	332	479	431	453	464
	Ca(OH)2	324	466	406	478	473

* Rates: per kg straw DM: 120 g H₂O; 35 g NH₃, 0, 70 g CaO or 92.5 g Ca(OH)₂.
a. (NH₄) 2CO₃ = carbamate/bicarbonate mixture.
b. Lime and water rates doubled.
SED = 23.5.

In the presence of added water (Table 2), the situation changed, ammonium sulphate giving efficient upgrading when mixed with quicklime or slaked lime and kept under simulated stack or oven conditions. Moreover, at 20°C the 'carbonate' and bicarbonate treatments gave satisfactory improvements when lime was included in the process. Anhydrous ammonia and aqueous ammonia gave similar responses under these conditions. The results clearly indicate the potential use of both volatile and non-volatile ammonium salts for upgrading straw.

Sheep studies

These principles were also examined in in vivo digestibility studies with sheep and cattle. For the sheep trials (Table 3), baled perennial ryegrass hay (cv Cropper) of medium quality (1.5% N) was chopped and fed, untreated, or subsequent to ammoniation by one of four techniques. In the first, 440 kg hay DM were treated with anhydrous ammonia (35 g NH₃/kg hay DM: 90°C for 15 h) in a purpose-built, insulated An-Stra-Verter oven, the ammonia being provided from an external pressure tank (conventional oven technique). The second approach used the same oven, but an attempt was made to produce the ammonia in situ by treating a mixture of 58.6 kg fertilizer grade ammonium sulphate and 33 kg quicklime with 60 kg water in a trough, placed in the bottom of the oven prior to heating (experimental oven technique). The third and fourth techniques were stack methods in which similar principles were applied to treat 465 kg hay DM with ammonia (35 g/kg DM). In these, dry mixtures of 63 kg ammonium sulphate fertilizer and 33 kg quicklime or 44 kg ammonium 'carbonate' (i.e., 310 g NH₃/kg DM) and 33 kg quicklime were treated with 60 and 50 kg water, respectively, in metal troughs placed close to the stack under the plastic sheeting. With both stack methods ammoniation proceeded at ambient temperature over 8 weeks during July and August, 1984. The hays were then fed ad libitum to sheep in a conventional digestibility-intake study.

As shown in Table 3, the two stack methods improved the digestibility of organic matter almost as efficiently as did the conventional oven-ammonia method. However, intakes for these treatments by sheep were inferior to those for the conventional oven method though superior to those for the control. In contrast, the experimental oven technique gave poor results.

Table 3. Upgrading perennial ryegrass (cv Cropper) hay by ammoniation for sheep.*

Method:	Untreated	Oven-NH3	Oven-NH3	Stack-NH3	Stack-NH3	SED
N-Source:	-	Anh. NH3	(NH4)2SO4	(NH4)2CO3+	(NH4)2SO4
OMD, g/kg	636	690	619	671	680	10.0
OMI, g/kg LW	18.4	22.4	18.9	21.2	20.2	1.14
DOMI, g/kg LW	11.7	15.5	11.7	14.2	13.8	0.69
N retn. g/d	0.93	3.75	1.52	3.67	3.77	0.56

* All animals received supplement containing 1.4 g soybean meal, 0.5 g min/vit mix and 0.1 g Na₂SO₄ kg/LW.

+ Ammonium carbamate/bicarbonate mixture.

Cattle studies

For the cattle studies (Table 4), baled winter barley straw was fed untreated, or subsequent to upgrading by one of three techniques. In the first, 500 g straw DM were treated with anhydrous ammonia (35 g/kg DM) by the conventional An-Stra-Verter oven method, discussed above. The second was a stack method similar to those used in the sheep studies, but differing by treating a mixture of 66 kg ammonium sulphate fertilizer and 35 kg quicklime with 60 kg water to generate maximally 17 kg ammonia to upgrade 500 kg straw DM. In the third approach, straw was treated with sodium hydroxide (50 g/kg straw DM) using a J F Straw Processor, and then ensiled. The digestibility trial involved four British Friesian steers (c. 248 kg LW) tethered in individual standings. These were given each of the four straws (2.8 kg/d) according to a randomised latin square sequence, each fed together with rolled barley (1.8 kg/d) and fishmeal (0.2 kg/d) in diets designed to satisfy 1.3 times the maintenance energy requirement. The untreated and NaOH-treated straw diets were further supplemented with 40 g urea/d to equalize the nitrogen intake. Water was available at all times. Each trial consisted of a 21 day preliminary and a 5 day collection period.

Table 4 shows that in this experiment, where intakes were standardized, the stack method gave an improvement in digestibility which was very similar to that achieved with the conventional ammonia oven method. In the case of organic matter, this improvement was also close to that obtained with the J F ensilage system. In view of the high content of concentrate feeds in these diets, the improvements achieved were satisfactory.

Table 4. Upgrading winter barley straw (cv. Igri) for cattle.*

Method:	Untreated	Oven-NH3	Stack-NH3	Silo-JF	SED
Chemical:	-a	Anh. NH3	(NH4)2SO4	NaOHa
OMD, g/kg	668	725	722	730	7.4
DMD, g/kg	639	669	670	705	10.9

* Ration: 2.8 kg straw, 1.8 kg rolled barley, 0.2 kg fishmeal (1.3 x M).
a. Supplement: 40 g urea.

Conclusions

In general, these experiments demonstrate that ammonium salts, including fertilizers, can be used as a source of ammonia for upgrading. The troughs used as reaction vessels in the stack treatments were rather inefficient since they provided no means for mixing the residues subsequent to the addition of water. This meant that ammonia produced in the base of each trough had difficulty in escaping to the surface of the residue. Clearly, the question of the structure of a simple reaction vessel which will permit the free movement of ammonia remains to be solved, as does the optimal ratio of chemical mixture to water.

A promising feature of this approach is that different ammonium salts (including urea hydrolysates) and alkalis may be used to generate ammonia and they may also be used in complex combinations. We have successfully tested a mixture of ammonium sulphate, all-ammonium hydrogen orthophosphate, quicklime and sodium hydroxide for this purpose in laboratory studies. Thus, the efficiency and rate of ammonia release can be altered, and the composition of the residue may be changed so that the latter can ultimately serve as a mineral supplement or lick for animals or as a fertilizer for soils. This may be used to reduce the effective cost of the ammonia treatment.

References

Sundstol F and Coxworth E M, 1984. Ammonia treatment. In: Straw and other fibrous by-products as feed. Eds. F Sundstol and E Owen. Elsevier Science Publishers, Amsterdam.

Mason V C and Owen E, 1985. Urea versus ammonia for upgrading graminaceous materials. Paper presented to ARNAB Workshop, Alexandria, Egypt, October 1985.