- Email: [email protected]
Comparison of labour content of different methods of steam sterilizing glasshouse soils
-377
Comparison
of Labour Content of Different Methods of Steam Sterilizing Glasshouse Soils E. S.
DEVINE*
Investigations were made into the labour content of steam sterilizing glasshouse soils by Hoddesdon pipes used in hand and machine cultivated soil, the spike method and the mobile steaming grid method m machine cultivated soil. Measurements were recorded in time per unit area for each system. and the optimum size of equipment and bout area in relation to team size calculated.
1.
‘Treatments and procedure Investigations were made into the most suitable methods of steam sterilizing glasshouse xoils. as follows :+ A. Hoddesdon pipe system, using steel pipes 1 I ft long and 14 in bore dia, each pipe having 26 pairs of opposite holes of A in dia spaced 4.15 in apart. The pipes were located in the ground at a depth of 15 in and side by side at 15 in apart. Each pipe was closed at one end and steam fed in through a vertical pipe of the same bore joined rigidly to the other end. The pipes were placed in the glasshouse parallel in a longitudinal direction, burying each pipe successively so that the soil from one trench filled in the previous one. The pipes were fed with steam in units of 6 and when the second unit of 6 was in operation, the first set of pipes was being successively withdrawn into previously dug trenches. B. Steam injection on prepared soil by pressing spikes into it. The vertical pipes were 14 in long and each had four t in holes located at 90” to one another around the spike, and 2 in from the tip, pointed to facilitate entry into the soil. The spikes were fed with steam through 6 ft long horizontal pipes to which they were attached. Operation was across the house, moving along the house. C. Mobile steaming grid (“Jackson” automatic soil steaming system), having a grid ??H:~rvestinp
and Handlmy
Department,
N.I.A.E.
which is designed to move through the glasshouse soil at a predetermined depth and a winch, a small electrically operated unit of 0.25 hp, to pull the grid. The unit examined consisted of four steam pipes spaced 1 ft apart which lay horizontally on the floor of the area to be heated at the required depth (10 in). The grid was 7 ft long and was fitted with a pair of depth control rollers mounted at the top edge of the front. Its forward speed was regulated to 5 inimin to give a soil temperature of 210 “F and a steaming time of 17 min at any point.’ A 30 ft sheet of 250 G. polyethelene 54 in wide was attached to the rear of the grid. This provided insulation and reduced the loss of steam to proportions similar to that obtained when a sheet is used in the other methods. All measurements were made in commercial glasshouses from which the heating pipes had been removed. Following an analysis to establish correctness of procedure, rated time measurements were made on each element as it occurred in the cycle, using a stopwatch reading to & min. The basic time obtained for each element was normalized, relaxation allowances added and standard times calculated. Method A was applied either directly after cropping (Al) or following mechanical cultivation (A2) which, as in Methods B and C, consisted of subsoiling to 16 in, rotary cultivation to a depth of 9 in and ploughing.
278
DIFFERENT
METHODS
OF
STEAM
STERILIZING
GLASSHOUSt
SOII..S
TABLE I
Standard time for preparing an 11 ft long Hoddesdon pipe-
-
Element
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Basic time, min
Switch off steam valve Disconnect steam hose and pipe Couple up steam hose and pipe Move header Turn on steam Cover steaming pipes with plastic sheet Pull pipe fully back Measure space for next pipe Cover pipe with soil Dig base of trench with fork Check temperature
Frequency
0.170 0.245 0.175 O*lOO 0.100 0.730 0.376 0.128 3,864 0.699 0.140
1 for 1 1 1 for 1 for 1 for 1 1
6
6 6 6
1 1 1 for 6
Basic cycle time, min
R.A., P.
0.028 0.245 0.175 0.016 0.016 0.120 0.376 0.128 3.864 0.699 0.023
12.5 12.5 12.5 12.5 12.5 12.5 15 10 25 12.5 10
Standard lime, __~_
min .-._. _._.---
0.03 I 0,276 0.197 0.018 0.018 0.135 0.432 0.141 4.920 0.786 0,025
-
2. Results 2.1. Method A Total standard time to prepare one Hoddesdon pipe for operation is 6.979 man-min (Table I). Effective steaming area per pipe = 14.3 ft2. Time 6,979 per ft2 surface area = - 14.3 = 0.490 min. Time per ft2 to prepare soil for steaming, using a tractor unit is 0.042 man-min (subsoiling 0.010 min, ploughing 0.016 min, rotary cultivation 0.016 min). If element 2 is omitted for purposes of comparison, the time to bury manually a Hoddesdon pipe into prepared soil (Method A2) is 0.35 min/ft2, compared with 0.70 man-min, where pipes are dug into soil which has not been cultivated after cropping (Al), other activities accounting for 0.14 man-min/ft2 in both cases.
2.2. Method B Total standard time to prepare a spike for steaming = 1,356 man-min (Table II). Effective steaming area of 7 ft spike == 8.16 ft2. 1.356 Time per ft2 surface area = m = 0.166 min. Time to prick up surface = 0.052 man-min/fP. Total attention time = 0.218 man-min/ft2. Time to prepare soil = 0.042 min/ft2. 2.3. Method C The attention time when using a steaming grid is a variable, depending length and width of the house, and can lated from the data given in Table III, into consideration the soil preparation (O-042 man-min/ft2).
mobile on the be caltaking times
TABLE I1
Standard times for prepariag a spike pipe Element
1. Shut off steam 2. Disconnect steam pipe from spike 3. Re-connect steam pipe to Spike point 4. Move header 5. Switch on steam 6. Fit plastic sheet 7. Remove spike from soil 8. Cleaning holes in spike 9. Walk to new site and insert spike 10. Tap spike fully home
-
Basic time, min
Frequency
Basic cycle time, min
o-170 0.060
1 for 6
I
0.028 0.060
12) 12&
0.03 1 0.067
0.260 0.250 0.280 0.470 0.110 0.250 0.140 0.110
1 1 for 6 1 for 6 1 for 6 1 1 1 1
0.260 0.041 0.046 0.078 0.110 0.250 0.140 0,110
124 20 124 124 35 12) 35 20
0.292 0.049 0.052 0.087 0.148 0.281 0.217 0.132
--
R.A., %
Standard time, min
at next
-
E.
c.
IIf
Vlhk TABLE III Standard times for operating a mobile steam grid
-
Basic tin w, min
Basic cycle time, min 0.008
2. Turn off steam valve 3. Walk 1 pace
0.008 0.100 0.008
4. 5. 6. 7. 8.
Disconnect steam pipe Walk 1 pace with pipe Connect up steam pipe Walk 1 pace Turn on steam valve
0.460 0.013 0.570 0.008 0.100
Walk 1 pace Disconnect winch cable Move and re-locate winch Pass out 1 ft cable Connect up winch Adjust winch Walk 1 pace Clean out front. of grid Remove grid from soil Turn over grid Clean off grid Pull grid 1 ft Turn over grid Cover grid with soil
0.008 0.170 0.350 0.010 0.460 0.150 0.008
Element
1. Walk 1 pace
9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
0.100 0.008
1.720 0.008 0.130 0.312
0.312
0.420 0.980 0.450 0.210 0.014 0.770 6.160
23. Fit steaming sheet 24. Walk 1 pace 25. Hook in sheet _ --____-_ 26. Open trench for mobile grid, ftea
-~
0,460 0,013 0.570 O+lOS 0.100 __-.0.008 0.170 0.350 0.010 0.460 0.150 0.008 --. - -0.420 0.980 0.450 0,210 0,014 0.710 6.160 ___-_ - -_ I.720 0.008 0.130
Standard time, min
R.A., 9/,
10 10 10
0.009 o-1 10 0.009
15 15 15 10 10
0.529 0.015 0.655 o+IO9 0.110
10 IO 20 20 15 129 10
0.009 0.187 0.420 0.012 0.530 0.169 0.009
15 40 40 15 30 40 25
0.483 I.372 0.630 0.240 0.018 1.078 7.690
10 10 10
1.892 0.009 0.143
25
0.390
TABLE IV Comparisoa of l&our and times for a 300 x 60 ft (0.4 acre) glasshouse
Derails -
Steaming time, min _.__Work factor, min/ft” + 107; ~_ No. of men
24.75 ---__ 0.92 -__
I 2 -__
--___
SxT
1
Estimated ared per cycle, ft’, w
_~
C
53.8
24.75
23.10
0.58
0.29 -___ 1
2
/
85.8
Speed of grid 5 in per min 0.032 32.05 min cycle
I
I
1 79.65
1
/ 226
/
1200
_-
No. of cycles
(y-1
Labour requirement,
man-hours,
Tractor requirement,
man-hours
SxNxT
6. Total, man-hours
B
A2
Al ~--
209.7
15
251.6 -
172.4 13.0
87.01 13.0
9.60 13.00
251.6
185.4
100.0
22.60
-----
.____
280
3.
DIFFEREN
METHODS
Ol-
STEAM
SI‘t.RILILIN(i
Comparison of methods
Dimensions,
50 100 200 ______
= steaming time, ~==number of bouts T = number of men employed W = work factor. The combined attention and soil preparation time plus a 10% contingency allowance multiplied by the area of the house gives the total manhours for each method (Table IV). where S N
Area,
of
steaming
method
ft
/- 30 ’ 30 A 30
No. of cyle, ;I 8 ~~_~~__
Time. IrKlN-- mitr~f~ p
0.107 0.061 0.036 __.__~~ ~_
200 300
:
60 60
I5 I5
0.034 0.027
200 300
I 72 .< 72
18 18
0.033 0.026
Fig. I shows the effect of glasshouse area on labour requirement. The smallest area convenient for mechanical cultivation by a standard 4-wheel tractor is 4500 ftZ or 150 Y 30 ft. Methods B and C can be used in smaller houses following hand cultivation, but this reduces their overall advantage. The pipes used for steam sterilization are not always the correct length. The optimum length can be obtained from the bout area together
W
Efl>ct
3
TABLE V
SxNxT
I.
\011
The effect of house dimensions on the work factor of the mobile steaming grid
The above results show that the total labour requirement for steam sterilizing by the different methods in a 300 x 60 ft house was 0*840,0.530, O-260 and 0.069 man-min/fP for Methods Al, A2, B and C respectively. Moreover. A2 is 36.9 “/:, s; Al B is 50.9 So ,:I A2 B is 69.1 ;d --: A 1 C is 72.67;, -< B C is 86.6% K Al C is 91.67: c.: A2 From the above data and the known steaming times’ each method can be compared as in Table IV. The labour requirement for steaming is calculated from
Fig.
(;I.ASStIOI!St:
and
house
xl000 ft’ area
ON
lahorrr
requirement
I.
s.
I)1
3 I
VI\1
311
“I
50
150
100
200
200 Length Fix. 2.
of
250 house,
300
300
350
ft
Effect qf‘length qf house on the performonce
with the other known factors, i.e. width of pipes and number. For a spike pipe it is 7 ft; above this length the operator has to reach over the steamed soil too far to remove pipes. The greatest proportion of the labour of the mobile grid (Table V) is spent on its relocation and covering. Therefore the length of the glasshouse has only a limited influence on the overall time (f?,q. 2). The rate of work of the mobile grid investigated was low, due mainly to the low forward speed of 5 injmin, and the working depth was
250
of the mobile grid
limited by the design of the grid. Use of grids of 7 ft x 4 ft x 15 in used in tandem would increase the rate of steaming. Fig. 2. hortom. illustrates the effect of travel speed of a mobile grid on actual time spent steaming. 4.
Conclusions (a) The labour requirement of the mobile grid method is 86.6 and 72.6 % lower than that of Methods A2 and B respectively, that of B is 69.1 and 50.9”; lower than for AI and A2.
282
DIFFERENT
METHODS
(b) The mobile steaming grid method is mainly machine controlled with a low labour requirement at intervals, the others require constant operator attendance. (c) The time per ft” spent steaming in Methods Al, A2 and B are constant regardless of house size. In Method C the attention time decreases as the area to be steamed increases. (d) To obtain the greatest advantage in labour savings, a clear floor area and houses of dimensions of 150 x 30 ft or over are necessary.
OF
STEAM
STERILIZING
GLASSHOUSL
SOILS
Acknowledgements
The author wishes to thank the growers who co-operated in this work and who allowed all or part of their routines to be observed and measured. Valuable help was also received from Jackson’s Hesketh Bank, Lanes., the N.A.A.S. County Horticultural Officer for Lancashire and from members of Machine Utilization Section of N.I.A.E. REFERENCE ’
Morris, L. G. The steam sterilizing of soil-the applicaRep. 24, natn. Inst. tion of research to practice. agric. Engng, She, May 1954
Comparison
of Labour Content of Different Methods of Steam Sterilizing Glasshouse Soils E. S.
DEVINE*
Investigations were made into the labour content of steam sterilizing glasshouse soils by Hoddesdon pipes used in hand and machine cultivated soil, the spike method and the mobile steaming grid method m machine cultivated soil. Measurements were recorded in time per unit area for each system. and the optimum size of equipment and bout area in relation to team size calculated.
1.
‘Treatments and procedure Investigations were made into the most suitable methods of steam sterilizing glasshouse xoils. as follows :+ A. Hoddesdon pipe system, using steel pipes 1 I ft long and 14 in bore dia, each pipe having 26 pairs of opposite holes of A in dia spaced 4.15 in apart. The pipes were located in the ground at a depth of 15 in and side by side at 15 in apart. Each pipe was closed at one end and steam fed in through a vertical pipe of the same bore joined rigidly to the other end. The pipes were placed in the glasshouse parallel in a longitudinal direction, burying each pipe successively so that the soil from one trench filled in the previous one. The pipes were fed with steam in units of 6 and when the second unit of 6 was in operation, the first set of pipes was being successively withdrawn into previously dug trenches. B. Steam injection on prepared soil by pressing spikes into it. The vertical pipes were 14 in long and each had four t in holes located at 90” to one another around the spike, and 2 in from the tip, pointed to facilitate entry into the soil. The spikes were fed with steam through 6 ft long horizontal pipes to which they were attached. Operation was across the house, moving along the house. C. Mobile steaming grid (“Jackson” automatic soil steaming system), having a grid ??H:~rvestinp
and Handlmy
Department,
N.I.A.E.
which is designed to move through the glasshouse soil at a predetermined depth and a winch, a small electrically operated unit of 0.25 hp, to pull the grid. The unit examined consisted of four steam pipes spaced 1 ft apart which lay horizontally on the floor of the area to be heated at the required depth (10 in). The grid was 7 ft long and was fitted with a pair of depth control rollers mounted at the top edge of the front. Its forward speed was regulated to 5 inimin to give a soil temperature of 210 “F and a steaming time of 17 min at any point.’ A 30 ft sheet of 250 G. polyethelene 54 in wide was attached to the rear of the grid. This provided insulation and reduced the loss of steam to proportions similar to that obtained when a sheet is used in the other methods. All measurements were made in commercial glasshouses from which the heating pipes had been removed. Following an analysis to establish correctness of procedure, rated time measurements were made on each element as it occurred in the cycle, using a stopwatch reading to & min. The basic time obtained for each element was normalized, relaxation allowances added and standard times calculated. Method A was applied either directly after cropping (Al) or following mechanical cultivation (A2) which, as in Methods B and C, consisted of subsoiling to 16 in, rotary cultivation to a depth of 9 in and ploughing.
278
DIFFERENT
METHODS
OF
STEAM
STERILIZING
GLASSHOUSt
SOII..S
TABLE I
Standard time for preparing an 11 ft long Hoddesdon pipe-
-
Element
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Basic time, min
Switch off steam valve Disconnect steam hose and pipe Couple up steam hose and pipe Move header Turn on steam Cover steaming pipes with plastic sheet Pull pipe fully back Measure space for next pipe Cover pipe with soil Dig base of trench with fork Check temperature
Frequency
0.170 0.245 0.175 O*lOO 0.100 0.730 0.376 0.128 3,864 0.699 0.140
1 for 1 1 1 for 1 for 1 for 1 1
6
6 6 6
1 1 1 for 6
Basic cycle time, min
R.A., P.
0.028 0.245 0.175 0.016 0.016 0.120 0.376 0.128 3.864 0.699 0.023
12.5 12.5 12.5 12.5 12.5 12.5 15 10 25 12.5 10
Standard lime, __~_
min .-._. _._.---
0.03 I 0,276 0.197 0.018 0.018 0.135 0.432 0.141 4.920 0.786 0,025
-
2. Results 2.1. Method A Total standard time to prepare one Hoddesdon pipe for operation is 6.979 man-min (Table I). Effective steaming area per pipe = 14.3 ft2. Time 6,979 per ft2 surface area = - 14.3 = 0.490 min. Time per ft2 to prepare soil for steaming, using a tractor unit is 0.042 man-min (subsoiling 0.010 min, ploughing 0.016 min, rotary cultivation 0.016 min). If element 2 is omitted for purposes of comparison, the time to bury manually a Hoddesdon pipe into prepared soil (Method A2) is 0.35 min/ft2, compared with 0.70 man-min, where pipes are dug into soil which has not been cultivated after cropping (Al), other activities accounting for 0.14 man-min/ft2 in both cases.
2.2. Method B Total standard time to prepare a spike for steaming = 1,356 man-min (Table II). Effective steaming area of 7 ft spike == 8.16 ft2. 1.356 Time per ft2 surface area = m = 0.166 min. Time to prick up surface = 0.052 man-min/fP. Total attention time = 0.218 man-min/ft2. Time to prepare soil = 0.042 min/ft2. 2.3. Method C The attention time when using a steaming grid is a variable, depending length and width of the house, and can lated from the data given in Table III, into consideration the soil preparation (O-042 man-min/ft2).
mobile on the be caltaking times
TABLE I1
Standard times for prepariag a spike pipe Element
1. Shut off steam 2. Disconnect steam pipe from spike 3. Re-connect steam pipe to Spike point 4. Move header 5. Switch on steam 6. Fit plastic sheet 7. Remove spike from soil 8. Cleaning holes in spike 9. Walk to new site and insert spike 10. Tap spike fully home
-
Basic time, min
Frequency
Basic cycle time, min
o-170 0.060
1 for 6
I
0.028 0.060
12) 12&
0.03 1 0.067
0.260 0.250 0.280 0.470 0.110 0.250 0.140 0.110
1 1 for 6 1 for 6 1 for 6 1 1 1 1
0.260 0.041 0.046 0.078 0.110 0.250 0.140 0,110
124 20 124 124 35 12) 35 20
0.292 0.049 0.052 0.087 0.148 0.281 0.217 0.132
--
R.A., %
Standard time, min
at next
-
E.
c.
IIf
Vlhk TABLE III Standard times for operating a mobile steam grid
-
Basic tin w, min
Basic cycle time, min 0.008
2. Turn off steam valve 3. Walk 1 pace
0.008 0.100 0.008
4. 5. 6. 7. 8.
Disconnect steam pipe Walk 1 pace with pipe Connect up steam pipe Walk 1 pace Turn on steam valve
0.460 0.013 0.570 0.008 0.100
Walk 1 pace Disconnect winch cable Move and re-locate winch Pass out 1 ft cable Connect up winch Adjust winch Walk 1 pace Clean out front. of grid Remove grid from soil Turn over grid Clean off grid Pull grid 1 ft Turn over grid Cover grid with soil
0.008 0.170 0.350 0.010 0.460 0.150 0.008
Element
1. Walk 1 pace
9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
0.100 0.008
1.720 0.008 0.130 0.312
0.312
0.420 0.980 0.450 0.210 0.014 0.770 6.160
23. Fit steaming sheet 24. Walk 1 pace 25. Hook in sheet _ --____-_ 26. Open trench for mobile grid, ftea
-~
0,460 0,013 0.570 O+lOS 0.100 __-.0.008 0.170 0.350 0.010 0.460 0.150 0.008 --. - -0.420 0.980 0.450 0,210 0,014 0.710 6.160 ___-_ - -_ I.720 0.008 0.130
Standard time, min
R.A., 9/,
10 10 10
0.009 o-1 10 0.009
15 15 15 10 10
0.529 0.015 0.655 o+IO9 0.110
10 IO 20 20 15 129 10
0.009 0.187 0.420 0.012 0.530 0.169 0.009
15 40 40 15 30 40 25
0.483 I.372 0.630 0.240 0.018 1.078 7.690
10 10 10
1.892 0.009 0.143
25
0.390
TABLE IV Comparisoa of l&our and times for a 300 x 60 ft (0.4 acre) glasshouse
Derails -
Steaming time, min _.__Work factor, min/ft” + 107; ~_ No. of men
24.75 ---__ 0.92 -__
I 2 -__
--___
SxT
1
Estimated ared per cycle, ft’, w
_~
C
53.8
24.75
23.10
0.58
0.29 -___ 1
2
/
85.8
Speed of grid 5 in per min 0.032 32.05 min cycle
I
I
1 79.65
1
/ 226
/
1200
_-
No. of cycles
(y-1
Labour requirement,
man-hours,
Tractor requirement,
man-hours
SxNxT
6. Total, man-hours
B
A2
Al ~--
209.7
15
251.6 -
172.4 13.0
87.01 13.0
9.60 13.00
251.6
185.4
100.0
22.60
-----
.____
280
3.
DIFFEREN
METHODS
Ol-
STEAM
SI‘t.RILILIN(i
Comparison of methods
Dimensions,
50 100 200 ______
= steaming time, ~==number of bouts T = number of men employed W = work factor. The combined attention and soil preparation time plus a 10% contingency allowance multiplied by the area of the house gives the total manhours for each method (Table IV). where S N
Area,
of
steaming
method
ft
/- 30 ’ 30 A 30
No. of cyle, ;I 8 ~~_~~__
Time. IrKlN-- mitr~f~ p
0.107 0.061 0.036 __.__~~ ~_
200 300
:
60 60
I5 I5
0.034 0.027
200 300
I 72 .< 72
18 18
0.033 0.026
Fig. I shows the effect of glasshouse area on labour requirement. The smallest area convenient for mechanical cultivation by a standard 4-wheel tractor is 4500 ftZ or 150 Y 30 ft. Methods B and C can be used in smaller houses following hand cultivation, but this reduces their overall advantage. The pipes used for steam sterilization are not always the correct length. The optimum length can be obtained from the bout area together
W
Efl>ct
3
TABLE V
SxNxT
I.
\011
The effect of house dimensions on the work factor of the mobile steaming grid
The above results show that the total labour requirement for steam sterilizing by the different methods in a 300 x 60 ft house was 0*840,0.530, O-260 and 0.069 man-min/fP for Methods Al, A2, B and C respectively. Moreover. A2 is 36.9 “/:, s; Al B is 50.9 So ,:I A2 B is 69.1 ;d --: A 1 C is 72.67;, -< B C is 86.6% K Al C is 91.67: c.: A2 From the above data and the known steaming times’ each method can be compared as in Table IV. The labour requirement for steaming is calculated from
Fig.
(;I.ASStIOI!St:
and
house
xl000 ft’ area
ON
lahorrr
requirement
I.
s.
I)1
3 I
VI\1
311
“I
50
150
100
200
200 Length Fix. 2.
of
250 house,
300
300
350
ft
Effect qf‘length qf house on the performonce
with the other known factors, i.e. width of pipes and number. For a spike pipe it is 7 ft; above this length the operator has to reach over the steamed soil too far to remove pipes. The greatest proportion of the labour of the mobile grid (Table V) is spent on its relocation and covering. Therefore the length of the glasshouse has only a limited influence on the overall time (f?,q. 2). The rate of work of the mobile grid investigated was low, due mainly to the low forward speed of 5 injmin, and the working depth was
250
of the mobile grid
limited by the design of the grid. Use of grids of 7 ft x 4 ft x 15 in used in tandem would increase the rate of steaming. Fig. 2. hortom. illustrates the effect of travel speed of a mobile grid on actual time spent steaming. 4.
Conclusions (a) The labour requirement of the mobile grid method is 86.6 and 72.6 % lower than that of Methods A2 and B respectively, that of B is 69.1 and 50.9”; lower than for AI and A2.
282
DIFFERENT
METHODS
(b) The mobile steaming grid method is mainly machine controlled with a low labour requirement at intervals, the others require constant operator attendance. (c) The time per ft” spent steaming in Methods Al, A2 and B are constant regardless of house size. In Method C the attention time decreases as the area to be steamed increases. (d) To obtain the greatest advantage in labour savings, a clear floor area and houses of dimensions of 150 x 30 ft or over are necessary.
OF
STEAM
STERILIZING
GLASSHOUSL
SOILS
Acknowledgements
The author wishes to thank the growers who co-operated in this work and who allowed all or part of their routines to be observed and measured. Valuable help was also received from Jackson’s Hesketh Bank, Lanes., the N.A.A.S. County Horticultural Officer for Lancashire and from members of Machine Utilization Section of N.I.A.E. REFERENCE ’
Morris, L. G. The steam sterilizing of soil-the applicaRep. 24, natn. Inst. tion of research to practice. agric. Engng, She, May 1954