Covering the floor with polyethylene liner
The influence on intergranular gas composition, insect infestation and grain losses of covering the platform floor with a polyethylene liner is given in Table 1.
TABLE 1 - Influence of covering the platform floor with a polyethylene liner (duration of storage 8-10 months)
|
Gas concentration (%) 3-4 months after covering |
Infestation1 |
Losses due to mould (%) |
Total grain losses (%) |
||
|
Liner |
O2 |
CO2 |
|||
|
Yes* |
2-6 |
8-12 |
Rare |
0.16 ± 0.1 |
0.32 ± 0.06 |
|
No** |
6-9 |
2-4 |
Yes |
0.13 ± 0.06 |
0.28 ± 0.06 |
* = data for 4 years; ** = data for 5 years.
1 Presence of adult insects in samples from the upper grain layers after covering with the PVC liner.
The data obtained over several years indicate that covering the floor with polyethylene significantly influences change in intergranular gas composition and also provides better control of insect infestations. It would not appear to have any serious influence on the amount of grain on the top of the platform damaged by mould or on total grain losses by the end of storage.
Duration of storage
The influence of the duration of storage on grain loss, infestation and grain germination is given in Table 2. This table shows that satisfactory insect control can be achieved for 1, 2 and 3 years of storage on a platform with a polyethylene covering over the floor. Grain germination remained very high (94-97%) even after 2 years of storage, and it was reduced to 88% only after 3 years of storage.
TABLE 2 - Influence of duration of storage on grain losses and other parameters (platform floor covered with a polyethylene liner)
|
Duration of grain storage (months) |
Platform capacity (t) |
Infestation1 |
Germination (%) |
Losses (%) |
|
|
Mould |
Total |
||||
|
8-10* |
2,500-4,000 |
Rare |
95-97 |
0.16 ± 0.1 |
0.32 ± 0.06 |
|
23 |
2,500 |
Rare |
94-98** |
0.22 |
0.52 |
|
34 |
4 000 |
Rare |
88 ± 1.6 |
0.66 |
0.96 |
* = data for 4 years; ** = viability.
1 Presence of adult insects in samples from the upper layers after opening the PVC liner.
TABLE 3 - Microflora and mycotoxins in barley samples of different degrees of deterioration at the end of a 10-month platform storage under a PVC liner
|
Parameter |
Threshold value for the occurrence of symptoms of mycotoxicosis to animals |
Sample A |
Sample B |
Sample C |
Sample D |
|
|
Taken from center of mould spot |
Taken 10-20 cm below mould spot |
Taken from grain surface free from any mould spot |
Taken 0.5 m below grain surface |
|||
|
Visible signs of mould deterioration |
Visible signs of mould deterioration |
High moisture grain (17% m.c.) |
Low moisture grain (12 % m.c.) |
|||
|
Very spoilt grain |
Less spoilt grain |
Sound grain |
Sound grain |
|||
|
Mycotoxines (ppb) |
||||||
|
|
T-2 |
200 |
0 |
0 |
0 |
0 |
|
|
Zearalenone |
200 |
760 |
260 |
0 |
0 |
|
|
Deoxynivalenol |
400 |
0 |
0 |
60 |
0 |
|
|
Fusarenon X |
400 |
0 |
0 |
0 |
0 |
|
|
Nivalenol |
200 |
0 |
0 |
350 |
0 |
|
|
Diacetoxyscirpenol |
400 |
0 |
0 |
0 |
0 |
|
|
Ochratoxin A |
100 |
1990 |
1570 |
0 |
0 |
|
|
Aflatoxin B1 |
20 |
0 |
0 |
0 |
0 |
|
Microflora (fungi number per g) |
||||||
|
Total fungi |
|
2.7 x 1010 |
5.7 x 109 |
2.2 x 106 |
1.6 x 106 |
|
|
|
Fusarium |
|
5.5 x 104 |
1.5 x 104 |
4.5 x 105 |
5.5 x 105 |
|
|
Alternaria |
|
9.2 x 107 |
4.2 x 107 |
1.2 x 104 |
0.7 x 104 |
|
|
Penicillium |
|
2.4 x 1010 |
5.5 x 109 |
1.7 x 106 |
1.1 x 106 |
|
|
Aspergillus |
|
3.2 x 108 |
9.7 x 107 |
9.7 x 104 |
4.7 x 104 |
|
|
F. graminearum |
|
Few |
Few |
3.7 x 105 |
3.8 x 105 |
|
|
F. colmorum |
|
Few |
Few |
0.7 x 105 |
1.7 x 105 |
|
|
F. moniliforme |
|
Few |
Few |
9.5 x 104 |
2.5 x 104 |
|
|
P. ochraceus |
|
2.4 x 1010 |
4.4 x 109 |
1.4 x 106 |
0.8 x 106 |
|
|
P. urticea |
|
3.1 x 109 |
7.2 x 108 |
0.2 x 106 |
0.2 x 106 |
|
|
Mucor |
|
Many |
Many |
Few |
Few |
On the other hand, the duration of storage had a significant influence on both mould losses and total loss. At the end of 3 years of storage, mould losses were four times greater than average mould losses after 1 year of storage. Similarly, total loss after 3 years of storage was three times greater than average loss after 1 year of storage.
Microflora and mycotoxins
The initial temperature of grain stored on platforms was between 30-37°C, whereas the lowest ambient air temperature during the winter season was 2-6°C. This resulted in the establishment of strong temperature gradients within the bulk which in turn caused convection currents, leading to transfer of moisture to the peak area of the bulk and therefore to mould deterioration of the grain in some spots at the apex of the bulk. These spots were 5-50 cm deep.
Two samples of very spoilt barley and spoilt barley taken from these mould spots at a depth of 0-20 cm and two samples of sound barley at 17% m.c. and 12% m.c., respectively, were analysed for mycotoxins and microflora. The results are given in Table 3. These results demonstrate that spoilt grain from the mould spots could be seriously contaminated by zearalenone (260-760 ppb) and ochratoxin (1,600-2,000 ppb). Spoilt grain was contaminated primarily by Alternaria, Penicillium, Aspergillus and Mucor fungi. The quantity of spoilt grain at these spots was very small, but the importance of carefully removing all spoilt grain from the bulk surface must be emphasised.
Analyses of samples "C" and "D" show that the grain stored on platforms actually remains free from mycotoxins and is suitable for animal consumption.
Total costs of platform erection and hermetic storage of 4,000 t grain
The fixed cost of building a concrete platform (75 m by 25 m), together with the costs of PVC and polyethylene and the current cost for storing 4,000 t of barley for 1, 2 and 3 years are all shown in Table 4. The total per-year cost for storing 1 t of barley for a period of 3 years is C£1.23.
Table 5 shows the losses that occurred in 1992 and 1995 during storage of local barley in the open. Grain was affected by rain, and a part of it was completely destroyed. In the years 1992 and 1995, 65,500 t of barley stored in the open were affected by rain and, based on the weighted average loss of 5.23%, some 3,425 t were completely destroyed. The economic loss was about C£387,100.
Table 6 shows the estimated monetary saving in losses to the 65,500 t of barley, which in 1992 and 1995 remained in the open unprotected against the rain, had they been placed in hermetic storage. The total fixed and running costs for 1 year's hermetic storage of 65,500 t of local barley on a concrete platform under PVC is estimated to be about C£152,000. The economic loss due to the lack of appropriate protection was about C£387,100. In addition, hermetic storage of grain on platforms under PVC successfully protects the grain against insect, bird and rodent attacks and also prevents its contamination by mycotoxins.
TABLE 4 - Costs of building a concrete platform and of hermetic storage of 4,000 t of barley under PVC liner
|
Costs |
Total cost |
Depreciation (years) |
Costs per 1 year storage (C£) |
Costs per 2 years storage (C£) |
Costs per 3 years storage (C£) | |
|
Fixed costs | ||||||
|
|
Building platform |
56,250 |
30 |
1,875 |
3,750 |
5,625 |
|
|
PVC sheet for covering grain |
10,990 |
7 |
1,570 |
3,140 |
4,710 |
|
|
Polyethylene liner for covering floor |
522 |
1 |
522 |
522 |
522 |
|
|
Total fixed costs |
|
|
2,967 |
7,412 |
10,857 |
|
Current costs | ||||||
|
|
Electricity to inload 3000 t |
75 |
|
75 |
75 |
75 |
|
|
Labour to inroad 3000 t and level grain surface |
1,711 |
|
1,711 |
1,711 |
1,711 |
|
|
Labour to cover grain and weld PVC sheet |
1,100 |
|
1,100 |
1,100 |
1,100 |
|
|
Labour to cover floor with polyethylene liner |
40 |
|
40 |
40 |
40 |
|
|
Labour to remove PVC sheet |
155 |
|
155 |
155 |
155 |
|
|
Labour to inload grain into trucks using a tractor |
800 |
|
800 |
800 |
800 |
|
|
Total current costs |
|
|
3,881 |
3,881 |
3,881 |
|
Total of fixed + current costs | ||||||
|
|
Total costs per 4,000 t |
|
|
7,848 |
11,293 |
14,738 |
|
|
Total costs per 4,000 t per year |
|
|
7,848 |
5,647 |
4,913 |
|
|
Total costs per t per year |
|
|
1.96 |
1.41 |
1.23 |
Platform 25 m wide, 75 m long, 7 m high; C£1 = US$2.1.
TABLE 5 - Barley loss due to rain during open storage after harvest (1992 and 1995)
|
Year |
Total quantity harvested (thousand t) |
Quantity affected by rain |
Quantity completely spoilt by rain |
Losses (completely spoilt grain), % |
Losses (completely spoilt grain, C£113/t) (C£ x 1,000) |
||
|
(thousand t) |
(%) |
(t) |
of total quantity |
of quantity affected by rain |
|||
|
1992 |
161.4 |
48.3 |
30.0 |
2,463 |
1.5 |
5.1 |
278 |
|
1995 |
122.6 |
17.2 |
14.0 |
1,011 |
0.8 |
5.9 |
114 |
|
Average of 1992 and 1995 |
142 |
32.8 |
25.8* |
1,737 |
1.2 |
5.23* |
196 |
* = weighted average.
TABLE 6 - Economic effectiveness of grain storage using the hermetic method on platforms under PVC liners
|
1-year hermetic storage of 65,500 t of barley under PVC |
C£ x 1,000 (C£ 1 = US$2.1) |
|
Total cost (fixed + current): 65,500 t x C£1.96/t/year |
128 |
|
Total losses alter 1-year hermetic storage: 65,500 t x 0.32% losses x C£ 113/t |
24 |
|
Total (cost + losses) |
152 |
|
Total losses due to deterioration by rain occurring in 1992 and 1995 during storage of 65,500 t of barley in the open 65,500 t x 5.23% losses x C£113/t |
387 |
