Improvement of the field drying rate of lucerne (Medicago sativa L.) using potassium carbonate and mechanical conditioning

J. agric. Engng Res. (1989) 44, 311-316

Improvement of the Field Drying Rate of Lucerne (Medicago sativa L.) Using Potassium Carbonate and Mechanical Conditioning R. H. MEREDITH,* I. B. WARBOYSt The combination of potassium carbonate (K2CO3) and mechanical conditioning for improved drying of lucerne was tested in the field when weather was poor for field drying with low temperatures, high humidities and rainfall. K2CO3 produced little benefit when the treated crop was cut and left in a flat dense swath, but gave significant and substantial acceleration of drying when used with mechanical conditioning, saving 24 h over untreated crop to 100% moisture content (dry weight basis) and being the only treatment to cure field hay to 33% moisture content (dry weight basis) within 5 days of cutting. In addition, the combination reduced rewetting by rainfall and accelerated subsequent re-drying relative to either treatment alone. It is considered that the passage of crop through the conditioner improved distribution and penetration of K2CO3, and promoted more rapid moisture loss through the effective ventilation given by a loose swath structure.

1. Introduction Traditionally, the drying rate of lucerne (Medicago satioa L.) has been accelerated by mechanical treatments with "crimpers" or "crushers". Increases in drying rate are directly related to the severity of the treatment, but are accompanied by increasing dry matter (d.m.) losses 1 which offset the benefits of faster drying. Because of such problems, research has been carried out in Australia into chemical treatments that accelerate drying by disrupting plant mechanisms that act to conserve water in the growing plant which resist water loss during field wilting. Potassium carbonate (K2CO3) applied as a dilute aqueous solution, is one chemical that has been successfully used in laboratory and field trials T M A mixture of K2CO3, methyl esters (of long chain fatty acids), and a surfactant, when used in combination with mechanical conditioning has been examined and increases in drying rate of 40% above mechanical conditioning alone were reported, s'e The best results were obtained when using mowers equipped with roll-conditioners. In one case ~ the K2CO3 mixture eliminated the difference in drying rate between lightly and heavily crimped hay. A potential therefore exists for the drying benefits of severe mechanical treatments to be realized without the associated dry matter losses. As part of an experimental programme to examine the efficacy of K2CO3 as a desiccant for lucerne, a field trial was conducted using K2CO3 in combination with light mechanical conditioning, which abrades the crop surface and sets up a raised, well ventilated swath. It was considered that physical damage to the hydrophobic plant cuticle might assist the action of the chemical in reducing plant barriers to water loss and if accompanied by a well structured swath would enable fuller expression of these effects. * Bayer UK Ltd., Elm Farm Development Station, Great Green, Thurston, Bury St Edmunds, Suffolk IP31 3SJ, UK t Department of Agriculture, Wye College (University of London), Wye, Ashford, Kent TN25 5AH, UK Received 19 September 1988; accepted in revised form 29 August 1989

311 0021-8634/89/120311 + 06 $03.00/0

~ 1989The British Societyfor Research in Agricultural Engineering

312

IMPROVEMENT OF LUCERNE DRYING RATE

2. Experimental details

2.1. Equipment A rotary mower-conditioner, shown in Fig. 1, (The Field Fairer, JF Farm Machines Ltd., Hempsted Lane, Gloucester, UK) equipped with " Y " shaped metal conditioning fingers (A) was used to cut the crop. A push bar (B) and spray boom (C) were fitted to the mower-conditioner for application of chemical treatments. The push bar was set to deflect the crop canopy and enable the spray to cover the stems.

2.2. Experimental design and methods Experimental material was a second cut, 3-year-old stand of lucerne in early bloom. The estimated d.m. yield was 3.7 t/ha. T h e r e were four treatments in a randomized block design with four replicates. Discards (3-6m wide) were cut the day before the trial commenced to leave 16 experimental swaths of 26 x 2-4 m. Due to the difficulty of separating the conditioning unit from the mower-conditioner (Fig. 1) all treatments involving mechanical conditioning were cut first and then the unit (cover and rotors) was removed for tests without conditioning. With or without mechanical conditioning, sprayed plots were treated after unsprayed plots to minimize cross-contamination of K2CO 3. Based on previous findings, a'4 a rate of 10 kg K2CO 3 in 450 l/ha of water was chosen for spray treatments. Treatments were applied in the following order: (1) (2) (3) (4)

Mechanically conditioned only. Sprayed with K2CO3 and mechanically conditioned. Control, no treatments applied to cut crop. Sprayed with K2CO3 only.

The upper plate (D) of the conditioning unit was adjusted to allow generous clearance between it and the conditioning elements (A). This arrangement produced abrasion of the plant surface, but little structural damage and set up a "fluffy" well-ventilated swath. Control and K2CO3 only swaths were cut after removal of the conditioning unit (E) and the resultant swath structure was very fiat, compact and uniform. No post-cutting treatments were applied.

C\

Lr~

Mower"

"T"'I"

Condltionlng

~-I

unit

Fig. I. Schematic layout of mower-conditioner for applying potassium carbonate. A, "'Y"-shaped metal conditioning fingers; B, Push bar; C, Spray boom; D, Upper-conditioning plate

R. H. MEREDITH; I. B. WARBOYS

313

Cutting commenced at 10.00h and the first samples for moisture content (m.c.) determination were taken when all the plots had been cut 1-5 h later. Three samples were then taken daily at 09.00, 13.00 and 16.30h, except on days 6 and 7 when only one sample was taken per day, at 16.30 h on day 6 and 13.00 h on day 7. A b o u t 1 kg d.m. of swath was grab-sampled across its width, from the crop surface to the ground and divided into two roughly equal sub-samples which were placed in separate polythene bags. Markers were used to identify the last sampling position and consecutive samples were taken at 0-5 m intervals along the swath to avoid interference from the previous sampling. Material was weighed fresh, then dried at 100°C for 24 h and reweighed. The fresh and dry weights of samples were used to calculate % m.c. on a dry weight basis (d.b.). The calculated values of % m.c. were statistically compared by analysis of variance at each sample time.

3. Results

The results are presented in Tables 1 and 2 and Fig. 2. The drying curves (Fig. 2 ) show that the greatest drying rate was given by K2CO3 combined with mechanical conditioning, followed by mechanical conditioning alone, followed by K2CO3 alone and finally the control (no treatments) until rainfall on the fifth evening. From Table 1 it can be seen that K2CO 3 alone rarely caused a significant reduction in m.c. relative to the control over the first 5 days, but significant effects were produced on the 2 days after rainfall. On the other hand, although mechanical conditioning alone generally produced significant effects before rain it was less effective afterwards. The combination of both treatments produced the most convincing effect on drying, with highly significant reductions in % m.c. relative to the control which were maintained despite rainfall. The combined treatment was usually significantly drier than either individual treatment with the time taken to dry to 100% m.c. reduced by 24 h, relative to the control. Individual treatments were less effective, taking until the morning (mechanical conditioning alone) or midday (K2CO 3 alone), compared with late afternoon on day 4 Table 1 Moisture contents (% d.b.) of lucerne after treatment with KzCO 3 and/or mechanical conditioning, with summarized analyses of variance for the final reading of each day

Treatment means and significances

Day

Time, h

Control

1 2 3 4 5 6 7

0.0 29-0 53.0 77.0 101-0 125.0 145.5

403-8 209-0 134.5 93.5 73-8 137.1 87.0

Statistical information

K2CO3

Mechanical conditioning

K2CO3 and mechanical conditioning

s.e.d

% CV

401.9 NS 202.5 NS 128.8 NS 66-8*** 64-0 NS 115.5"** 66.8*

379-8** 186.9 NS 114.9 NS 62.5*** 55-1"* 127-6 NS 73.8 NS

380.9** 156-9"** 78-0*** 46.4*** 31.4"** 106-8"** 48-6***

7-11 11.77 10.85 3-92 5-56 5-14 7.49

3.6 12-5 19-0 11.7 19.8 8-4 21.7

Key to statistical abbreviations: Effect of treatment on moisture content relative to the control: NS = not significant; *p = <0-05; **p = <0.01; ***p = <0.001 s.e.d = standard error of the difference between means. Difference between means divided by s.e.d, for t-statistic on 21 degrees of freedom % CV = 100 x ~/(residual variance/grand mean)

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I M P R O V E M E N T OF L U C E R N E DRYING RATE

Table 2 Times taken, (h) to reach 100% m.c. (d.b.) for lucerne treated with potassium carbonate and/or mechanical conditioning

Treatment

Time, h

T/C

Control K2CO 3 Mechanical conditioning K2CO3/mechanical conditioning

77.0 73-5 70.0 53-0

1-00 0-95 0-91 0-69

All times were estimated from the first sample time at which the % m.c. fell below 100% m.c. (d.b.) T / C = ratio of treatment time to control time

0 o

Control K2CO 3

+

Mechanncal c o n d i t i o n i n g only

•

K2CO 3 and mechanical conditioning

30oi .fi "0 C~

2000 U tI

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100 II- ~

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..... 33

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120

Time after cutting, h Day 1

Day 2

I Day 3

I Day 4 I Day 5

Day 6

bay 7

Fig. 2. Drying curves of lucerne after treatment with K2C03 and~or mechanical conditioning

R. H. MEREDITH; I. B. WARBOYS

315

(control) (see Table 2). Only K2CO3 combined with mechanical conditioning enabled hay to be safely cured for baling (33% m.c.) before rainfall on day 5 (see Fig. 2). 4. D i s c u s s i o n

The weather conditions were not ideal for hay-making, with low temperatures, high humidity and low hours of sunshine (Table 3). However, these conditions commonly occur during field hay-making in the U K and are therefore probably the most appropriate conditions for field testing the K2CO 3 treatment. Laboratory investigations with this crop 8 in the U K have shown that K2CO 3 can greatly reduce plant barriers to water loss, producing drying periods 75% shorter than the control, to 33% m.c. H o w e v e r , under field conditions swath limitations to drying also play an important part in the drying process. 9 If the microclimate surrounding conditioned material does not maintain a diffusion gradient of water vapour from the plant surface to the surrounding air then drying cannot occur. This situation will occur towards the base of a swath where air currents cannot penetrate to remove water vapour. This could explain why there was little benefit to drying from using the chemical with the disc mower only, since this produced dense, fiat swaths. In the mechanically conditioned swaths, benefits from the chemical were substantial and significant. The mechanical conditioning could have interacted with K2CO3 in two ways to produce this large difference in effectiveness. First, the passage of the crop through the conditioning unit may have improved distribution of the chemical and its penetration of the plant cuticle. Secondly, mechanically conditioned swaths were much more exposed to the wind, with a less dense structure that allowed improved ventilation; since the physical damage to the crop appeared slight this could be the main benefit of using the mower-conditioner. Although data is limited, rainfall had an important effect on the relative efficacy of treatments. Before rain, the mechanical conditioning produced useful reductions in % m.c. and this was further improved by combining with K2CO3, although the chemical alone was not consistently effective. After rain, mechanically conditioned swaths suffered most from rewetting and efficacy was greatly reduced from this form of treatment. T h e n mechanical conditioning alone did not significantly reduce % m.c. relative to the control and K2CO3 with mechanical conditioning was not significantly different to K2CO 3 alone, although numerically the combined treatment remained the most effective. Subsequent drying was fastest from K2CO3 and mechanical conditioning with no significant difference between K2CO3 alone and mechanical conditioning alone. T h e r e f o r e results show a mutual benefit from combining mechanical conditioning and potassium carbonate treatments. Without rain, the mechanical treatment improved the effectiveness of K2CO3 and after rain K2CO 3 reduced the extent of rewetting and improved subsequent drying relative to the mechanical treatment alone. Table 3 Weather data during the trial

Day

Mean temperature, °C Min. temperature, °C Max. temperature, °C Run of wind, km/d Sun, h Relative humidity, % Rainfall, mm

1

2

3

4

5

6

7

14.2 9.6 15.6 93 0 95 0

14-7 12-8 22-1 129 6-1 82 0

16.1 14-0 22-8 103 7-0 85 0

20-9 11.0 24.6 235 7.2 57 0

18-4 13.5 19.8 283 9.7 67 3.3

14.4 12.8 17.2 174 1.1 92 2-3

14-3 13-2 19.8 108 2-2 80 0

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IMPROVEMENT

OF LUCERNE

DRYING

RATE

5. Conclusions

(1) The efficacy of K2CO3 and mechanical conditioning treatments was improved in combination. The benefits were accelerated drying, reduced rehydration after rainfall and improved re-drying, relative to the control and both treatments alone. (2) Although the volume requirements (450 l/ha) could pose logistical problems when applied at mowing, and the cost of the active ingredient is high (approximately £3/kg), i m p r o v e m e n t s in the efficacy of spray application such as the use of electrostatic sp~aying might increase the practical viability of the combined chemical and mechanical treatment. Acknowledgements

We thank JF Farm Machines Ltd for loan of equipment and the Ministry of Agriculture for a Studentship to enable this work to be carried out. References

1 Straub, R. J.; Bruhn, H. D. Evaluation of roll design in hay conditioning. Transactions of the American Society of Agricultural Engineers 1975, 18(2): 217-220 2 Tuilberg, J. N.; Angus, D. E. The effect of potassium carbonate solution on the drying of lucerne; 1. Laboratory studies. Journal of Agricultural Science UK 1978, 91:551-556 3 Tullberg, J. N.; Minson, D. J. The effect of potassium carbonate solution on the drying of lucerne; 2. Field studies. Journal of Agricultural Science UK 1978, 91:557-561 4 Crocker, G. J.; Lodge, G. M. Potassium carbonate speeds up lucerne haymaking. (Abstract) Agricultural Gazette of New South Wales 1981, 92(3): 33-36 s Rotz, C. A.; Thomas, J. W.; Herrington, D. A. Mechanical and chemical conditioning to speed alfalfa drying. (Abstract) Paper, American Society of Agricultural Engineering 1982, No. 82-1036, 15 pp e Rotz, C. A.; Sprott, D. J.; Thomas, J. W. Interaction of mechanical and chemical conditioning of alfalfa. Transactions of the American Society of Agricultural Engineers 1984, 27(4): 1009-1014 7 Thomas, J. W.; Johnson, T. R.; Wieghart, M. A.; Hansen, C. M.; Tesar, M. B.; Helsel, Z. Hastening hay drying. Proceedings of the XIV International Grassland Congress, held at Lexington, Kentucky, USA, 15-24 June 1981 (Smith J. A., Hays V. W., eds). Boulder, Colorado: Westview Press, 1983, pp. 645-648 8 Meredith, R. H. Improving the field drying rate of lucerne with particular reference to the application of potassium carbonate. PhD Thesis, Wye College, University of London, Ashford, Kent, 1987 9 Jones, L.; Harris, C. E. Plant and swath limits to drying. In: Forage Conservation in the 80"s (C. Thomas, ed.). Occasional Symposium No. 11, British Grassland Society, 1980, pp. 53-60