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Advantages of the integrated pig-biogas-vegetable greenhouse system in North China
Ecological Engineering 24 (2005) 177–185
Advantages of the integrated pig-biogas-vegetable greenhouse system in North China Xinshan Qia,b , Shuping Zhanga , Yuzhi Wanga , Renqing Wanga,∗ a
b
Institute of Ecology and Biodiversity, School of Life Sciences, Shandong University, 27 Shanda Nan Road, Jinan, Shandong 250100, China Shandong Provincial Environmental Inspection Station, 12 Zhi-jin-shi Street, Jinan, Shandong 250012, China Received 13 January 2004; received in revised form 30 September 2004; accepted 1 November 2004
Abstract An integrated pig-biogas-vegetable greenhouse system (PBVGS) was designed and studied in Laiwu, Shandong Province of North China from 2001 to 2002, where 20 groups of PBVGS and their corresponding controls were investigated. The PBVGS involves building a pigsty and a biogas digester in a vegetable greenhouse, putting pig dung into the biogas digester for fermentation, using the biogas for increasing illumination and air temperature in the greenhouse, and using the fermented waste as organic manure. The data indicate that the pig growth, biogas production and vegetable production were effectively improved in PBVGS, and that ecological, economic and social benefits were simultaneously achieved. The average annual net income of a standard PBVGS was 10,900 RMB, with an increase of 58.0% over its traditional non-integrated parts. It could use up 14,000 kg fresh pig dung and produce 10,000 kg organic manure one year for the improvement of soil fertility. The daily net weight increase for a pig in PBVGS averaged 0.82 kg, 227.6% higher than its controls. The average yield per hectare of cucumbers and tomatoes, increased by 18.4 and 17.8% over their controls, respectively. In addition, the biogas produced in the digester increased by 32.4% annually. Based on biogas fermentation, the PBVGS provides a fine ecological cycle from livestock feeding to vegetable production, resulting in a higher conversion efficiency in nutrient cycle and energy flow. © 2004 Published by Elsevier B.V. Keywords: Vegetable greenhouse; Pig feeding; Biogas fermentation; Integrated system; Ecological cycle
1. Introduction North China is located in temperate and warmtemperate zones, where it is too cold to farm in the ∗ Corresponding author. Tel.: +86 531 836 3573; fax: +86 531 856 5610. E-mail address: [email protected] (R. Wang).
0925-8574/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.ecoleng.2004.11.001
open air during wintertime. To increase the supply of vegetables in this area, many greenhouses were built during the last few decades (NSBC, 2002). However, the low temperature, lack of sunlight, insufficient carbon dioxide and destruction by pests constitute the main limiting factors of greenhouse production. Furthermore, the frequent application of chemical fertilizers and pesticides not only increases
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the cost, but also leads to a decline in vegetable quality. Traditional biogas fermentation techniques, especially using small household biogas digesters, have been quite sophisticated in China and were spread throughout South China (Deng, 2001). However, it was very difficult to transfer this methodology to North China, where the daily average air temperature during the winter is often below 10 ◦ C; under these conditions, the digester cannot operate normally. On the other hand, allowing livestock to wander and to feed in peasants’ small courtyards is still common in China (Zhang, 1990). Because the pigsties usually lack a roof, inadequate heat in the winter results in slow pig growth in addition to higher feedstuff costs. To solve the above problems, a new greenhouse integrated with pig feeding, biogas production and vegetable planting (PBVGS), was first designed and used in Liaoning Province, Northeast China in 1995. Later, it gradually spread to other regions of North China. In 2001, it was estimated that there were about 100,000 units of PBVGS in China (CREYEC, 2002). The original and common type of PBVGS was a semi-arcaded earth-log structure. In some regions with higher investment, it developed into steel-brick greenhouse structure with an auto-scrolling curtain and no poles, which could accommodate more pigs and had a larger planting area; In some regions, the livestock was not limited to pigs, cattle, chickens and other animals were also included; In a few locations, the pigsty or biogas digester was separated from the vegetable greenhouse, linked to each other through pipelines. To study the advantages of PBVGS over its traditional non-integrated parts, a case study was conducted in Laiwu, Shandong province, North China from 2001 to 2002. Laiwu District lies in the central mountainous area of Shandong Province. Its mean annual air temperature is 13.5 ◦ C, its annual precipitation is 802 mm, and it has an average of 2277 h of sunshine a year. In winter (from November to February), the monthly average air temperature generally varies from −3.0 to 5.4 ◦ C. Most farming activities have to stop during this period. In 2002, the total cultivated land of this city was 70,884 ha, averaging 0.08 ha for each farmer and 0.24 ha per farmer family. The PBVGS was first introduced into this district in 1997, and by 2002, there were about 610 PBVGS, covering an area of 33.3 ha.
Fig. 1. The design layout of a typical PBVGS pattern.
2. Material and methods 2.1. The design of PBVGS The concept of PBVGS was to plant vegetables, feed pigs and build a biogas digester in the same greenhouse, putting the pigs’ dung and urine into the digester for fermentation. The biogas could be used to increase the illumination and air temperature in the greenhouse, or be used as an energy resource for such things as food cooking and night lighting. In addition, CO2 from biogas burning, pig respiration and organic matter decomposition could enhance photosynthesis of vegetables. Once fully fermented in the digester, the residual dreg and liquor could be used as organic manure for the vegetables; the fermented liquor could also be used as pigs’ feedstuff. Thus, biogas production, manure accumulation, vegetable planting and livestock feeding were all accomplished, simultaneously, in the same greenhouse. The design layout of PBVGS is shown in Fig. 1. 2.1.1. Location The PBVGS was placed on the flat, highly fertile land that was exposed to the sun, easy to irrigate and to drain. 2.1.2. Greenhouse It represented a semi-arcaded earth-log structure, 8 m × 60 m long and covered with polythene film. Its earth-tamped back wall was 70 cm thick and 2 m high. There were many bamboo shores in the greenhouse; the highest back ones were 3.2 m high while the shortest front ones were 1.2 m. Tomatoes or cucumbers were planted in the greenhouse with an area of 450 m2 .
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2.1.3. Biogas digester The 10 m3 of cylindrical hydraulic digester was built at one end of the greenhouse according to the China’s construction standard of biogas digesters (CBCLG, 1985). The fermenting material from the pigsty, flowed into the fermentation room through an admission pipe; after several days of anaerobic fermentation, it was pushed into the drainage room by the high pressure in the biogas storage room. Finally, it was pumped out through a drainage pipe. The biogas in the storage room flowed out automatically into the peasants’ operation room or to the biogas lamps hung in the planted area, through a long conduit. 2.1.4. Pigsty The 12 m2 of pigsty was built just above the digester, in which 5–7 pigs were fed. Its partition wall that had two ventilation holes was built between the pig feeding area and the planted area. The upper hole, used for oxygen exchange, was 1.6 m from the ground, while the lower one (0.7 m high) was used for CO2 exchange. If needed, one or two ventilation windows were opened on the back wall, for air exchange. 2.2. The operation techniques of PBVGS 2.2.1. Management of the biogas digester Because the best ratio of carbon to nitrogen for fermentation materials is 20–30:1 while the fresh pig dung is only 13:1 (MOA/USDOE, 1998), some carbon-rich materials, such as minced stalks were put into the digester. To maintain 6–11% of reasonable fermentation concentration (the weight ratio of organic material to whole substance in the biogas digester, or a ratio of 400–500 kg fresh dung to 500–600 kg water), the pigs’ dung and urine were washed with some rationing water into the digester, in which the inoculating material accounted for 20–30% of the whole substance. To avoid acidification of the fermentation material and to adjust its pH to 6.8–7.4, limewater was added to the digester. More attention was paid to safety operation during the use of the biogas: the biogas transportation system was checked regularly to detect leakage, and the variation of the gas pressure was examined daily to avoid a dangerous over-pressure in the biogas digester.
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2.2.2. Use of the residual dreg, fermented liquor and biogas Before the vegetables were transplanted in the PBVGS, the diluted fermented residual dreg was applied 20–30 cm below the soil surface with a dosage of 37,500 kg ha−1 . The fermented liquor was applied three times to the soil surface in the vegetables’ early, medium and later growth period, respectively. In addition, it was also sprinkled on the vegetable leaves once a year during the vegetables’ fruit period. No additional chemical fertilizer was used in the PBVGS. The fully fermented liquor was also used as additive feedstuff of pigs. The clear liquor, which had been stored in the upper drainage room for about 1 month, was agitated with grain feedstuff at a ratio of 3:7 and then fed to the pigs. This means that 1–1.5 kg fermented liquor was given to a 15–50 kg pig per day and 1.5–2.5 kg was fed to a 50–100 kg pig. Pigs were fed three times daily. The biogas was used for cooking on a special stove. It was also transported to five biogas lamps, hung in the planted area, to increase light, air temperature and carbon dioxide. Except on cloudy days, the biogas lamps were lit twice in the morning and at noon, for 1 h each. 2.2.3. Prevention of the harmful gas pollution To prevent gas pollution from H2 S, SO2 , NO2 , NH3 , CO and C2 H4 , which were released by volatilization of dung, decomposition of organic wastes, burning of biogas and decomposition of plastic film, a partition wall was constructed between the pigsty and the planted area. Air ventilation was used to adjust the air temperature and humidity in the greenhouse at a moderate level. By dipping water drops formed on the plastic film with pH indicator papers, the harmful gases could be monitored regularly. Any pH value beyond 6.8–7.2 implied there were harmful gases accumulated in the greenhouse. 2.3. Research methods 2.3.1. Experimental design The experimental site lies at 117◦ 40 E longitude and ◦ 36 18 N latitude, 5 km south-east of Laiwu District. The experiment lasted from November 2001 to November 2002. Twenty groups of PBVGS and their corresponding controls were investigated simultaneously at
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Table 1 The experimental design of the PBVGS and its corresponding control Investigation date
PBVGS Size/number Air temperature (◦ C) Feedstuff consumption
Material input Fertilizer application
Control Size/number Air temperature (◦ C) Feedstuff consumption Material input Fertilizer
Pig production
Biogas production
Vegetable production
November 15, 2001– February 22, 2002
November 15, 2001– November 14, 2002
December 15, 2001– May 5, 2002
5–7 pigs −1 to 15 380 kg grain feedstuff and 150 kg fermented liquor for an average pig – –
A 10 m3 digester −1 to 35 –
450 m2 of planted area 1–20 –
840 kg pig dung (dry) –
– 1688 kg residual dreg and 900 kg fermented liquor (with three times of irrigation)
4–6 pigs
A 10 m3 digester
−10 to 12 470 kg grain feedstuff for an average pig – –
−12 to 35 –
An ordinary vegetable greenhouse −2 to 18 –
the same site, to compare the quantitative differences of pig, vegetable and biogas production. Soil fertility in all of the greenhouses was the same in the beginning of experiment. Its organic matter content 0–20 below soil surface was 1.2%, the total N was 0.078%, and the total P was 0.095%. The experimental designs for the PBVGS and its corresponding controls are shown in Table 1. In all the 20 groups of PBVGS, the same operational techniques were adopted as clarified above, among which 10 groups each were planted with tomatoes and 10 groups with cucumbers. The cucumbers were transplanted on November 10, 2001, with 65 cm distance between two adjacent rows and 28 cm distance between two adjacent vegetables in the same row; the tomatoes were transplanted on November 1, 2001, with 60 cm distance between two adjacent rows and 23 cm distance between two adjacent vegetables in the same row. Both cucumbers and tomatoes were irrigated 15 times during their growth period. A total of 95 pigs were fed for 100 days, each with the same feedstuff. The residual dreg
552 kg pig dung (dry) –
– 1125 kg ha−1 chemical application fertilizer and three times of irrigation
and fermented liquor were used as organic manure for the vegetables. Three traditional, non-integrated conditions were used as experimental controls: (a) 10 roof-less pigsties in the open air, each housing 4–6 pigs, 50 pigs were fed the same kind of grain feedstuff in the same period as in the PBVGS. (b) 10 household biogas digesters in the peasants’ open courtyards with the same type, same volume and same management measures as in the PBVGS. (c) Twenty ordinary greenhouses, 10 were planted with tomatoes and 10 with cucumbers. The vegetables were transplanted at the same time and in the same way, irrigated for the same times as in the PBVGS. During the experiment, 1125 kg ha−1 of carbamide was applied to the soil, but no fermented dreg and liquor were used. 2.3.2. Measuring methods and analytical techniques In order to monitor and adjust the microclimate in the greenhouse, the air temperature and moisture were
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measured and recorded daily, using a Louver-box Wetdry-bulb hygrothermograph (Wu and Fei, 1999). To determine the soil fertility, topsoil samples (to 20 cm depth) were collected from the experimental greenhouses on October 25, 2001, before the vegetables were transplanted, using a quincunx sampling and quartering dividing method. The organic matter of soil was analyzed, using the potassium dichromate reagent method, the total N using potassium dichromate–vitriol reagent method, and the total P using molybdenum–antimony colorimetry (ACCCSS, 1983). To compare the pigs’ weight, all of the piglets were weighed on November 15, 2001, to calculate the average weight of piglets in each group; after 100 days the pigs were weighed again, before they were sold. The daily feedstuff consumption in each group, including the fermented liquor used as additive feedstuff, was recorded during this period. The amount of dung and urine excreted by pigs was calculated according to the pig’s excrement constant (ATEET, 1986). The biogas volume produced by each biogas digester was measured from November 15, 2001 to November 14, 2002 using a gas flowmeter. The waterish fermented residual dreg was weighed before it was applied to the soil in PBVGS. To determine its dry weight, some dreg samples were collected. The sample was put in a porcelain evaporation pan which had a known weight before, and after dried in the oven at 103–105 ◦ C for 48 h, it was reweighed; The decreased weight of the pan represented the water weight in the dreg (Wu and Fei, 1999). Tomatoes and cucumbers were hand-harvested from the greenhouses at 2-day intervals from January 18 to May 5, 2002 and weighed for yield determination. Af-
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ter the vegetables were harvested on March 3, 2002, the samples were collected randomly and immediately sent to the laboratory to analyze the content of vitamin C. The vitamin C was measured using the fluorometry method (Wu and Fei, 1999) 2.3.3. Statistical analyses According to the measured data in the experiment, the least significant difference test was used to judge whether the production of PBVGS was significantly different from the traditional ways, using the software package STATISTICA for windows (StatSoft Inc., 1999). The T values were calculated on d.f. = n1 + n2 − 2 = 20+ 10 − 2 = 28 (pig and biogas), or d.f. = 10 + 10 − 2 = 18 (cucumber and tomato).
3. Results and analyses 3.1. Results The experimental results are listed in Tables 2–4, with the results of T significance tests of difference between the PBVGS and their corresponding controls. Compared to the pigs in roof-less pigsties, those in the PBVGS grew much faster but consumed less grain feedstuff (Table 2). The average weight of piglets in each group of PBVGS was approximately the same as in its controls at the beginning (P > 5%), but after 100 days’ feeding, the mean weight of pigs in PBVGS was 57.1 kg heavier than in the controls (P < 0.1%). The average consumption of grain feedstuff for a pig in the PBVGS was 89.9 kg less than the controls, which means it saved the farmer more than 100 RMB. One probable reason for the result is that the air temperature
Table 2 The average weight and feedstuff consumption of a pig in the 20 groups of PBVGS and their controls (kg per pig) Treatment
Pig’s weight
Feedstuff consumption
Piglet
Pig for sale
Net increase
Increase per day
Total consumption
Consumption per day
PBVGS Controls % Change t(28) value
30.8 30.6 0.65 0.351**
112.7 55.6 102.7 5.47***
81.9 25.0 227.6 5.25***
0.82 0.25 227.6 5.25***
380.2 470.1 −19.1 4.97***
3.8 4.7 −19.1 4.97***
∗∗ Represents a statistically insignificant difference between the PBVGS and the controls (P > 5%) using least significant difference test, t(28) < t(28)0.05 . ∗∗∗ Represents a statistically extremely significant difference between the PBVGS and the controls (P < 0.1%) using Least Significant Difference test, t(28) > t(28)0.001 .
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Table 3 Biogas production for an average digester in the 20 groups of PBVGS and their controls Treatment
PBVGS Controls % Change t(28) value
From 15 November 2001 to 22 February 2002
From 15 November 2001 to 14 November 2002
Operation days
Biogas produced (m3 )
Biogas by one unit of dry dung dry dung (m3 kg−1 )
Operation days
Biogas produced (m3 )
Biogas by one unit of (m3 kg−1 )
100 12 733 5.79***
108 6.4 1587 6.28***
0.450 0.222 102.7 4.36***
350 230 52.2 5.01***
450 340 32.4 5.62***
0.536 0.616 −13.0 2.42*
∗ Represents a statistically significant difference between the PBVGS and the controls (P < 5%) using least significant difference test, t(28) > t(28)0.05 . ∗∗∗ Represents a statistically extremely significant difference between the PBVGS and the controls (P < 0.1%) using least significant difference test, t(28) > t(28)0.001 .
(usually from −1 to 15 ◦ C) in the pigsties of PBVGS was warmer (averagely 12 ◦ C higher) in the winter than that in the roof-less pigsties; Another reason is that the pigs in PBVGS were fed with fermented liquor, which could not only accelerate the pigs’ growth but also save the consumption of grain feedstuff. Biogas production in the PBVGS was remarkably improved, especially in the winter (Table 3). The biogas digesters in PBVGS operated more days and produced more biogas than that in the household digesters (P < 0.1%). The biogas produced by one unit of dry dung in PBVGS was higher in the winter (P < 0.1%), but it was a bit lower in the whole year when compared to the controls (P < 5%). This is because the biogas production in the winter was comparatively inefficient, and it consumed much more pig dung but produced less biogas. A digester in PBVGS consumed 840 kg of dry pig dung for fermentation all the year, but it only consumed 552 kg of dry pig dung in the controls.
Data from Table 4 indicate that, not only the yield of cucumbers and tomatoes in PBVGS was greatly increased (P < 1%), but also the vitamin C content in vegetables was improved (P < 5%). One of the probable reasons is that the microclimate in PBVGS was improved by higher air temperature, more sufficient carbon dioxide and longer illumination. The air temperature of PBVGS in the winter was usually 2–3 ◦ C higher than that in the ordinary greenhouses. Another reason is the soil fertility of PBVGS was improved by applying the fermented residual dreg and liquor. On the other hand, the application of fermented dreg and liquor might have more benefits to the quality of vegetables when comparing to the use of chemical fertilizer. 3.2. The analysis of benefits 3.2.1. Economic benefits A standard PBVGS has an initial startup cost of about 12,000 RMB for the construction of greenhouse,
Table 4 The average yield and vitamin C content of vegetables in the 20 groups of PBVGS and their controls Treatment
PBVGS Controls % Change t(18) value
Cucumber
Tomato
Yield per group (kg)
Yield per hectare (kg)
Vitamin C content (mg kg−1 )
Yield per group (kg)
Yield per hectare (kg)
Vitamin C content (mg kg−1 )
8787 7421 18.4 3.56**
195270 164919 18.4 3.56**
146.5 125.6 16.6 2.65*
9688 8227 17.8 3.27**
215280 182820 17.8 3.27**
200.3 164.9 21.5 2.12*
∗ Represents a statistically significant difference between the PBVGS and the controls (P < 5%) using least significant difference test, t(18) > t(18)0.05 . ∗∗ Represents a statistically very significant difference between the PBVGS and the controls (P < 1%) using least significant difference test, t(18) > t(18)0.01 .
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biogas digester, management room and pigsty, with an average depreciation of 2100 RMB each year. The total production investment of PBVGS, including labor, materials, seeds and piglets, was 8000 RMB, saving the peasants 1350 RMB, including 100 RMB for coal, 150 RMB for electricity, 400 RMB for fertilizer and pesticides, and 700 RMB for feedstuff. Thus, the total annual cost for a standard PBVGS averaged approximately 10,100 RMB, the total production value (including pigs and vegetables) reached 21,000 RMB, and the total net income reached 10,900 RMB, which was 4000 RMB higher than that of both an ordinary greenhouse and a roof-less pigsty. 3.2.2. Ecological benefits First, the replacement of traditional pig breeding by PBVGS techniques was a great benefit to the pollution control. A standard PBVGS could use up 14,000 kg fresh dung and produce 10,000 kg of unharmful manure annually, which observably improved the local sanitation situation. Second, it effectively improved the soil fertility and reduced the pollution from chemical fertilizers and pesticides, and it provides a new way to produce pollution-free agricultural products. According to some relative studies (ATEET, 1986; Qi, 1996; Wang et al., 1999), the efficacy of organic manure applied to the soil of PBVGS, including 37,500 kg ha−1 of residual dreg and 20,000 kg ha−1 of fermented liquor, equals 622.0 kg of standard nitrogen, 148.8 kg of phosphorus and 782.0 kg of potassium. By sprinkling fermented liquor on the vegetable leaves, the disease and insect pests were also successfully controlled, allowing a decrease in the amount of pesticides. Thirdly, the PBVGS were also beneficial to the protection of local forest. One digester could produce 450 m3 of biogas each year, corresponding to 320–400 kg of standard coal or 643 kg of firewood (ATEET, 1986; MOA/USDOE, 1998). Its use in the farmers’ living energy successfully prevented trees from being cut in Laiwu District. 3.2.3. Social benefits The spread of PBVGS ensured a local supply of vegetables and meat in the winter, increased the peasants’ income, and improved the peasants’ living conditions. The lower cost and higher quality of agricultural products from PBVGS enhanced the competitive capability in current markets, promoted the adjustment of agricultural structure, and made good use of the surplus farm
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Fig. 2. Nutrient cycle and energy flow among the different components of the PBVGS.
labor in winter. As a new technique, it could speed the spread of scientific knowledge in rural areas. 3.3. The nutrient cycle and energy flow The present research reveals that a beneficial circle of the ecological system that closely linked vegetable planting, pig feeding and biogas producing was established with the effective use of nutrient materials, biological energy and solar energy (Fig. 2). Taking a standard PBVGS (with one 10 m3 digester, six pigs and 450 m2 of vegetables) and its corresponding non-integrated controls as an example, we calculate the main nutrient cycle and energy flow from November 15, 2001 to February 22, 2002 (Table 5). The former studies revealed that, in the winter of North China, the energy conversion ratio of pig growth to feedstuff consumption in the traditional roof-less pigsties is 6.0–12.5% (Zhang, 1990; Sun and Qi, 1993), and that of biogas output to pig dung input is 1.8–5.6% in the traditional household biogas digesters (CBCLG, 1985; MOA/USDOE, 1998; Deng, 2001). In this case study, the energy conversion ratio of pig growth to feedstuff averages 31.6% in PBVGS, which is much higher than the 7.8% of the control. About 55.4% of total pig dung energy is converted into biogas energy with the PBVGS, which is much higher than the 3.3% of the control. The conversion ratio of biogas output to dung input is 27.3% for the control of household biogas digester. In the PBVGS, nitrogen (N), phosphorus (P) and potassium (K), contained in the residual dreg and fermented liquor and used as organic manure of vegetables, account for 54.4%, 31.6 and 55.7% of the original
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Table 5 The nutrient content and energy value of different storage units in a standard PBVGS and its corresponding controls Items
Substance quantity (kg)
Energy value (×109 J)
Nitrogen (kg)
Phosphorus (kg)
Potassium (kg)
PBVGS (a) Pig production Feedstuff consumption Grain Fermented liquor Pig growth
3240 2280 (dry) 960 491
37.7 37.7 – 11.9
37.0 36.5 0.53 –
13.9 13.7 0.19 –
15.0 9.1 5.86 –
(b) Biogas production Pig excreta input Dung Urine Biogas output
2040 240 (dry) 1800 108 (m3 )
4.08 4.08 – 2.26
12.9 7.0 5.9 –
5.0 4.1 0.94 –
15.8 4.4 11.4 –
(c) Applied organic fertilizer Organic fertilizer 1322 Residual dreg 422 (dry) Fermented liquor 900
– –5.1 –0.50
1.2 3.3 5.5
8.8
Controls (a) Pig production Feedstuff consumption Pig growth
46.6 3.64
16.9 –
11.3 –
(b) Biogas production Pig dung input Biogas output
2820 (dry) 150 28.8 (dry) 6.4 (m3 )
0.49 0.134
5.6 1.0 0.18
45.1 – 0.84 –
0.49 –
0.53 –
Note: the conversion coefficients of nutrient and energy refer to the following references: ATEET (1986) and MOA/USDOE (1998).
nutrient substances in the pigs’ dung and urine, respectively.
vides a good way to make full use of organic wastes such as crop stalks and livestock excrements. 4.2. Discussion
4. Conclusions and discussion 4.1. Conclusions This experiment has shown that the PBVGS effectively improved the pigs’ growth, biogas production and vegetable production, and it has many advantages over its non-integrated parts. It successfully solved such problems existing in traditional production patterns as unstable biogas production, slow pig growth and limiting factors of greenhouses in the winter of North China. It organically combined vegetable planting, livestock feeding, and biogas fermentation techniques together, attaining a beneficial ecological cycle in a single greenhouse, as well as achieving considerable economic and social benefits. It had a higher efficiency of nutrient cycle and energy flow, and pro-
The reason for the PBVGS being successfully established and rapidly spreading in North China may be analyzed as follows: First, The PBVGS project has remarkable ecological, economic and social benefits. It is consistent with the government’s agriculture, environment and energy policy, and it wins the local government’s financial and technical approval in its spreading (Zhang et al., 1998; Wang et al., 1999). The management pattern of PBVGS accords with the Chinese present household contract responsibility system, which takes a family as the basic unit to rent land and sign contract with local government. Second, the PBVGS has many advantages in offering the peasants living energy, organic manure and high-quality products. It earns the peasants more money, and so it arouses the great enthusiasm by them. Thirdly, the development
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of PBVGS adapts to the present situation of natural resources in China. Currently in China, the average arable land per capita in the rural areas is only 0.14 ha, and a family’s courtyard usually occupies 0.033–0.1 ha (NSBC, 2002). The Chinese agriculture may adapt this system of family farming units and small-scattered farming areas for a long time. A PBVGS, occupying 0.048 ha land, can be built either in the field or in the courtyard, and it is reasonable for a family to manage and operate. Considering the characteristics of PBVGS, it is especially well suited for the area of temperate or warmtemperate zone such as in North China, but its advantages will become lost and finally disappear when it is spread in sub-torrid or torrid zone such as in South China. This paper is just a preliminary study on the original type of PBVGS with a semi-arcaded earthlog structure. Further research is required to demonstrate whether the new types of PBVGS have more advantages, what is the optimized combination of pigbreeding number, biogas digester volume and vegetable area, how much is the quantitative change of soil fertility after applying fermented residual dreg and liquor, how is the effect of fermented liquor on controlling vegetable disease and insect pests, and so on. Acknowledgements Supported by the National Scientific Fund Doctorate Program, No.: 20030422030. Our thanks to Prof. Robert Greenwood at the University of North California, USA and Prof. Harvey D. Blankespoor at Hope College, Michigan, USA, for their enthusiastic checking of the English. Thanks are also due to Mr. Feng Liu at the Texas A&M University, USA, for his valuable comments on improvements of the manuscript, and Ms. Cuiling Qi and Ms. Fengqin Wang at the Eco-
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agricultural Office of Laiwu, Shandong, China, for data collection.
References Agricultural Chemistry Committee of Chinese Soil Society (ACCCSS), 1983. The Regular Analysis Method of Agricultural Soil Chemistry. Science Press, Beijing, pp. 67–143. Agricultural Technology and Economy Editorial Team (ATEET), 1986. Agricultural Technology and Economy Handbook. China Agriculture Press, Beijing, pp. 79–291. Chinese Biogas Construction Leader Group (CBCLG), Chengdu Biogas Science Institute (CBSI), 1985. An Illustrated Handbook on the Standard Construction of Chinese Rural Household Biogas Digesters (GB4750-84). China Agriculture Press, Beijing, pp. 30–45. Chinese Rural Energy Yearbook Editorial Committee (CREYEC), 2002. Chinese Rural Energy Yearbook. China Agriculture Press, Beijing, pp. 105–135. Deng, K., 2001. Theory and Practice of Comprehensive Energy Construction in the Rural Area of China. China Environmental Science Press, Beijing, pp. 47–49, 152–160. MOA/USDOE Project Expert Team, 1998. Biomass Energy Conversion Technologies in China: Development and Evaluation. China Environmental Science Press, Beijing, pp. 56–66. National Statistic Bureau of China (NSBC), 2002. Agricultural Statistic Yearbook of China. China Agriculture Press, Beijing, pp. 10–50. Qi, X., 1996. A brief introduction of the utilization and techniques for agricultural organic wastes. Rural Eco-Environ. 12 (3), 50–53. StatSoft Inc., 1999. STATISTICA for Windows. Tulsa, OK. Sun, G., Qi, X., 1993. A study on the fine circle of eco-agriculture system and its mechanism of high yield and high benefit in Xishan village. Shandong Environ. 1993 (1), 31–33. Wang, Z., Ye, X., Li, Q., 1999. Chinese Ecological Agriculture and Intensive Farming Systems. China Environmental Science Press, pp. 53–66. Wu, B., Fei, L., 1999. Modern Technologies for Monitoring Environment. China Environmental Science Press, Beijing, pp. 263–274. Zhang, Z., 1990. Practical Pig-feeding Technology in China. Zhengzhou Henan Science and Technology Press, pp. 22–250. Zhang, Z., Deng, K., Ralph, O., 1998. Design for Market-oriented Development Strategy of Bioenergy Technologies in China. China Environmental Science Press, Beijing, pp. 74–104.
Advantages of the integrated pig-biogas-vegetable greenhouse system in North China Xinshan Qia,b , Shuping Zhanga , Yuzhi Wanga , Renqing Wanga,∗ a
b
Institute of Ecology and Biodiversity, School of Life Sciences, Shandong University, 27 Shanda Nan Road, Jinan, Shandong 250100, China Shandong Provincial Environmental Inspection Station, 12 Zhi-jin-shi Street, Jinan, Shandong 250012, China Received 13 January 2004; received in revised form 30 September 2004; accepted 1 November 2004
Abstract An integrated pig-biogas-vegetable greenhouse system (PBVGS) was designed and studied in Laiwu, Shandong Province of North China from 2001 to 2002, where 20 groups of PBVGS and their corresponding controls were investigated. The PBVGS involves building a pigsty and a biogas digester in a vegetable greenhouse, putting pig dung into the biogas digester for fermentation, using the biogas for increasing illumination and air temperature in the greenhouse, and using the fermented waste as organic manure. The data indicate that the pig growth, biogas production and vegetable production were effectively improved in PBVGS, and that ecological, economic and social benefits were simultaneously achieved. The average annual net income of a standard PBVGS was 10,900 RMB, with an increase of 58.0% over its traditional non-integrated parts. It could use up 14,000 kg fresh pig dung and produce 10,000 kg organic manure one year for the improvement of soil fertility. The daily net weight increase for a pig in PBVGS averaged 0.82 kg, 227.6% higher than its controls. The average yield per hectare of cucumbers and tomatoes, increased by 18.4 and 17.8% over their controls, respectively. In addition, the biogas produced in the digester increased by 32.4% annually. Based on biogas fermentation, the PBVGS provides a fine ecological cycle from livestock feeding to vegetable production, resulting in a higher conversion efficiency in nutrient cycle and energy flow. © 2004 Published by Elsevier B.V. Keywords: Vegetable greenhouse; Pig feeding; Biogas fermentation; Integrated system; Ecological cycle
1. Introduction North China is located in temperate and warmtemperate zones, where it is too cold to farm in the ∗ Corresponding author. Tel.: +86 531 836 3573; fax: +86 531 856 5610. E-mail address: [email protected] (R. Wang).
0925-8574/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.ecoleng.2004.11.001
open air during wintertime. To increase the supply of vegetables in this area, many greenhouses were built during the last few decades (NSBC, 2002). However, the low temperature, lack of sunlight, insufficient carbon dioxide and destruction by pests constitute the main limiting factors of greenhouse production. Furthermore, the frequent application of chemical fertilizers and pesticides not only increases
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the cost, but also leads to a decline in vegetable quality. Traditional biogas fermentation techniques, especially using small household biogas digesters, have been quite sophisticated in China and were spread throughout South China (Deng, 2001). However, it was very difficult to transfer this methodology to North China, where the daily average air temperature during the winter is often below 10 ◦ C; under these conditions, the digester cannot operate normally. On the other hand, allowing livestock to wander and to feed in peasants’ small courtyards is still common in China (Zhang, 1990). Because the pigsties usually lack a roof, inadequate heat in the winter results in slow pig growth in addition to higher feedstuff costs. To solve the above problems, a new greenhouse integrated with pig feeding, biogas production and vegetable planting (PBVGS), was first designed and used in Liaoning Province, Northeast China in 1995. Later, it gradually spread to other regions of North China. In 2001, it was estimated that there were about 100,000 units of PBVGS in China (CREYEC, 2002). The original and common type of PBVGS was a semi-arcaded earth-log structure. In some regions with higher investment, it developed into steel-brick greenhouse structure with an auto-scrolling curtain and no poles, which could accommodate more pigs and had a larger planting area; In some regions, the livestock was not limited to pigs, cattle, chickens and other animals were also included; In a few locations, the pigsty or biogas digester was separated from the vegetable greenhouse, linked to each other through pipelines. To study the advantages of PBVGS over its traditional non-integrated parts, a case study was conducted in Laiwu, Shandong province, North China from 2001 to 2002. Laiwu District lies in the central mountainous area of Shandong Province. Its mean annual air temperature is 13.5 ◦ C, its annual precipitation is 802 mm, and it has an average of 2277 h of sunshine a year. In winter (from November to February), the monthly average air temperature generally varies from −3.0 to 5.4 ◦ C. Most farming activities have to stop during this period. In 2002, the total cultivated land of this city was 70,884 ha, averaging 0.08 ha for each farmer and 0.24 ha per farmer family. The PBVGS was first introduced into this district in 1997, and by 2002, there were about 610 PBVGS, covering an area of 33.3 ha.
Fig. 1. The design layout of a typical PBVGS pattern.
2. Material and methods 2.1. The design of PBVGS The concept of PBVGS was to plant vegetables, feed pigs and build a biogas digester in the same greenhouse, putting the pigs’ dung and urine into the digester for fermentation. The biogas could be used to increase the illumination and air temperature in the greenhouse, or be used as an energy resource for such things as food cooking and night lighting. In addition, CO2 from biogas burning, pig respiration and organic matter decomposition could enhance photosynthesis of vegetables. Once fully fermented in the digester, the residual dreg and liquor could be used as organic manure for the vegetables; the fermented liquor could also be used as pigs’ feedstuff. Thus, biogas production, manure accumulation, vegetable planting and livestock feeding were all accomplished, simultaneously, in the same greenhouse. The design layout of PBVGS is shown in Fig. 1. 2.1.1. Location The PBVGS was placed on the flat, highly fertile land that was exposed to the sun, easy to irrigate and to drain. 2.1.2. Greenhouse It represented a semi-arcaded earth-log structure, 8 m × 60 m long and covered with polythene film. Its earth-tamped back wall was 70 cm thick and 2 m high. There were many bamboo shores in the greenhouse; the highest back ones were 3.2 m high while the shortest front ones were 1.2 m. Tomatoes or cucumbers were planted in the greenhouse with an area of 450 m2 .
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2.1.3. Biogas digester The 10 m3 of cylindrical hydraulic digester was built at one end of the greenhouse according to the China’s construction standard of biogas digesters (CBCLG, 1985). The fermenting material from the pigsty, flowed into the fermentation room through an admission pipe; after several days of anaerobic fermentation, it was pushed into the drainage room by the high pressure in the biogas storage room. Finally, it was pumped out through a drainage pipe. The biogas in the storage room flowed out automatically into the peasants’ operation room or to the biogas lamps hung in the planted area, through a long conduit. 2.1.4. Pigsty The 12 m2 of pigsty was built just above the digester, in which 5–7 pigs were fed. Its partition wall that had two ventilation holes was built between the pig feeding area and the planted area. The upper hole, used for oxygen exchange, was 1.6 m from the ground, while the lower one (0.7 m high) was used for CO2 exchange. If needed, one or two ventilation windows were opened on the back wall, for air exchange. 2.2. The operation techniques of PBVGS 2.2.1. Management of the biogas digester Because the best ratio of carbon to nitrogen for fermentation materials is 20–30:1 while the fresh pig dung is only 13:1 (MOA/USDOE, 1998), some carbon-rich materials, such as minced stalks were put into the digester. To maintain 6–11% of reasonable fermentation concentration (the weight ratio of organic material to whole substance in the biogas digester, or a ratio of 400–500 kg fresh dung to 500–600 kg water), the pigs’ dung and urine were washed with some rationing water into the digester, in which the inoculating material accounted for 20–30% of the whole substance. To avoid acidification of the fermentation material and to adjust its pH to 6.8–7.4, limewater was added to the digester. More attention was paid to safety operation during the use of the biogas: the biogas transportation system was checked regularly to detect leakage, and the variation of the gas pressure was examined daily to avoid a dangerous over-pressure in the biogas digester.
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2.2.2. Use of the residual dreg, fermented liquor and biogas Before the vegetables were transplanted in the PBVGS, the diluted fermented residual dreg was applied 20–30 cm below the soil surface with a dosage of 37,500 kg ha−1 . The fermented liquor was applied three times to the soil surface in the vegetables’ early, medium and later growth period, respectively. In addition, it was also sprinkled on the vegetable leaves once a year during the vegetables’ fruit period. No additional chemical fertilizer was used in the PBVGS. The fully fermented liquor was also used as additive feedstuff of pigs. The clear liquor, which had been stored in the upper drainage room for about 1 month, was agitated with grain feedstuff at a ratio of 3:7 and then fed to the pigs. This means that 1–1.5 kg fermented liquor was given to a 15–50 kg pig per day and 1.5–2.5 kg was fed to a 50–100 kg pig. Pigs were fed three times daily. The biogas was used for cooking on a special stove. It was also transported to five biogas lamps, hung in the planted area, to increase light, air temperature and carbon dioxide. Except on cloudy days, the biogas lamps were lit twice in the morning and at noon, for 1 h each. 2.2.3. Prevention of the harmful gas pollution To prevent gas pollution from H2 S, SO2 , NO2 , NH3 , CO and C2 H4 , which were released by volatilization of dung, decomposition of organic wastes, burning of biogas and decomposition of plastic film, a partition wall was constructed between the pigsty and the planted area. Air ventilation was used to adjust the air temperature and humidity in the greenhouse at a moderate level. By dipping water drops formed on the plastic film with pH indicator papers, the harmful gases could be monitored regularly. Any pH value beyond 6.8–7.2 implied there were harmful gases accumulated in the greenhouse. 2.3. Research methods 2.3.1. Experimental design The experimental site lies at 117◦ 40 E longitude and ◦ 36 18 N latitude, 5 km south-east of Laiwu District. The experiment lasted from November 2001 to November 2002. Twenty groups of PBVGS and their corresponding controls were investigated simultaneously at
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Table 1 The experimental design of the PBVGS and its corresponding control Investigation date
PBVGS Size/number Air temperature (◦ C) Feedstuff consumption
Material input Fertilizer application
Control Size/number Air temperature (◦ C) Feedstuff consumption Material input Fertilizer
Pig production
Biogas production
Vegetable production
November 15, 2001– February 22, 2002
November 15, 2001– November 14, 2002
December 15, 2001– May 5, 2002
5–7 pigs −1 to 15 380 kg grain feedstuff and 150 kg fermented liquor for an average pig – –
A 10 m3 digester −1 to 35 –
450 m2 of planted area 1–20 –
840 kg pig dung (dry) –
– 1688 kg residual dreg and 900 kg fermented liquor (with three times of irrigation)
4–6 pigs
A 10 m3 digester
−10 to 12 470 kg grain feedstuff for an average pig – –
−12 to 35 –
An ordinary vegetable greenhouse −2 to 18 –
the same site, to compare the quantitative differences of pig, vegetable and biogas production. Soil fertility in all of the greenhouses was the same in the beginning of experiment. Its organic matter content 0–20 below soil surface was 1.2%, the total N was 0.078%, and the total P was 0.095%. The experimental designs for the PBVGS and its corresponding controls are shown in Table 1. In all the 20 groups of PBVGS, the same operational techniques were adopted as clarified above, among which 10 groups each were planted with tomatoes and 10 groups with cucumbers. The cucumbers were transplanted on November 10, 2001, with 65 cm distance between two adjacent rows and 28 cm distance between two adjacent vegetables in the same row; the tomatoes were transplanted on November 1, 2001, with 60 cm distance between two adjacent rows and 23 cm distance between two adjacent vegetables in the same row. Both cucumbers and tomatoes were irrigated 15 times during their growth period. A total of 95 pigs were fed for 100 days, each with the same feedstuff. The residual dreg
552 kg pig dung (dry) –
– 1125 kg ha−1 chemical application fertilizer and three times of irrigation
and fermented liquor were used as organic manure for the vegetables. Three traditional, non-integrated conditions were used as experimental controls: (a) 10 roof-less pigsties in the open air, each housing 4–6 pigs, 50 pigs were fed the same kind of grain feedstuff in the same period as in the PBVGS. (b) 10 household biogas digesters in the peasants’ open courtyards with the same type, same volume and same management measures as in the PBVGS. (c) Twenty ordinary greenhouses, 10 were planted with tomatoes and 10 with cucumbers. The vegetables were transplanted at the same time and in the same way, irrigated for the same times as in the PBVGS. During the experiment, 1125 kg ha−1 of carbamide was applied to the soil, but no fermented dreg and liquor were used. 2.3.2. Measuring methods and analytical techniques In order to monitor and adjust the microclimate in the greenhouse, the air temperature and moisture were
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measured and recorded daily, using a Louver-box Wetdry-bulb hygrothermograph (Wu and Fei, 1999). To determine the soil fertility, topsoil samples (to 20 cm depth) were collected from the experimental greenhouses on October 25, 2001, before the vegetables were transplanted, using a quincunx sampling and quartering dividing method. The organic matter of soil was analyzed, using the potassium dichromate reagent method, the total N using potassium dichromate–vitriol reagent method, and the total P using molybdenum–antimony colorimetry (ACCCSS, 1983). To compare the pigs’ weight, all of the piglets were weighed on November 15, 2001, to calculate the average weight of piglets in each group; after 100 days the pigs were weighed again, before they were sold. The daily feedstuff consumption in each group, including the fermented liquor used as additive feedstuff, was recorded during this period. The amount of dung and urine excreted by pigs was calculated according to the pig’s excrement constant (ATEET, 1986). The biogas volume produced by each biogas digester was measured from November 15, 2001 to November 14, 2002 using a gas flowmeter. The waterish fermented residual dreg was weighed before it was applied to the soil in PBVGS. To determine its dry weight, some dreg samples were collected. The sample was put in a porcelain evaporation pan which had a known weight before, and after dried in the oven at 103–105 ◦ C for 48 h, it was reweighed; The decreased weight of the pan represented the water weight in the dreg (Wu and Fei, 1999). Tomatoes and cucumbers were hand-harvested from the greenhouses at 2-day intervals from January 18 to May 5, 2002 and weighed for yield determination. Af-
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ter the vegetables were harvested on March 3, 2002, the samples were collected randomly and immediately sent to the laboratory to analyze the content of vitamin C. The vitamin C was measured using the fluorometry method (Wu and Fei, 1999) 2.3.3. Statistical analyses According to the measured data in the experiment, the least significant difference test was used to judge whether the production of PBVGS was significantly different from the traditional ways, using the software package STATISTICA for windows (StatSoft Inc., 1999). The T values were calculated on d.f. = n1 + n2 − 2 = 20+ 10 − 2 = 28 (pig and biogas), or d.f. = 10 + 10 − 2 = 18 (cucumber and tomato).
3. Results and analyses 3.1. Results The experimental results are listed in Tables 2–4, with the results of T significance tests of difference between the PBVGS and their corresponding controls. Compared to the pigs in roof-less pigsties, those in the PBVGS grew much faster but consumed less grain feedstuff (Table 2). The average weight of piglets in each group of PBVGS was approximately the same as in its controls at the beginning (P > 5%), but after 100 days’ feeding, the mean weight of pigs in PBVGS was 57.1 kg heavier than in the controls (P < 0.1%). The average consumption of grain feedstuff for a pig in the PBVGS was 89.9 kg less than the controls, which means it saved the farmer more than 100 RMB. One probable reason for the result is that the air temperature
Table 2 The average weight and feedstuff consumption of a pig in the 20 groups of PBVGS and their controls (kg per pig) Treatment
Pig’s weight
Feedstuff consumption
Piglet
Pig for sale
Net increase
Increase per day
Total consumption
Consumption per day
PBVGS Controls % Change t(28) value
30.8 30.6 0.65 0.351**
112.7 55.6 102.7 5.47***
81.9 25.0 227.6 5.25***
0.82 0.25 227.6 5.25***
380.2 470.1 −19.1 4.97***
3.8 4.7 −19.1 4.97***
∗∗ Represents a statistically insignificant difference between the PBVGS and the controls (P > 5%) using least significant difference test, t(28) < t(28)0.05 . ∗∗∗ Represents a statistically extremely significant difference between the PBVGS and the controls (P < 0.1%) using Least Significant Difference test, t(28) > t(28)0.001 .
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Table 3 Biogas production for an average digester in the 20 groups of PBVGS and their controls Treatment
PBVGS Controls % Change t(28) value
From 15 November 2001 to 22 February 2002
From 15 November 2001 to 14 November 2002
Operation days
Biogas produced (m3 )
Biogas by one unit of dry dung dry dung (m3 kg−1 )
Operation days
Biogas produced (m3 )
Biogas by one unit of (m3 kg−1 )
100 12 733 5.79***
108 6.4 1587 6.28***
0.450 0.222 102.7 4.36***
350 230 52.2 5.01***
450 340 32.4 5.62***
0.536 0.616 −13.0 2.42*
∗ Represents a statistically significant difference between the PBVGS and the controls (P < 5%) using least significant difference test, t(28) > t(28)0.05 . ∗∗∗ Represents a statistically extremely significant difference between the PBVGS and the controls (P < 0.1%) using least significant difference test, t(28) > t(28)0.001 .
(usually from −1 to 15 ◦ C) in the pigsties of PBVGS was warmer (averagely 12 ◦ C higher) in the winter than that in the roof-less pigsties; Another reason is that the pigs in PBVGS were fed with fermented liquor, which could not only accelerate the pigs’ growth but also save the consumption of grain feedstuff. Biogas production in the PBVGS was remarkably improved, especially in the winter (Table 3). The biogas digesters in PBVGS operated more days and produced more biogas than that in the household digesters (P < 0.1%). The biogas produced by one unit of dry dung in PBVGS was higher in the winter (P < 0.1%), but it was a bit lower in the whole year when compared to the controls (P < 5%). This is because the biogas production in the winter was comparatively inefficient, and it consumed much more pig dung but produced less biogas. A digester in PBVGS consumed 840 kg of dry pig dung for fermentation all the year, but it only consumed 552 kg of dry pig dung in the controls.
Data from Table 4 indicate that, not only the yield of cucumbers and tomatoes in PBVGS was greatly increased (P < 1%), but also the vitamin C content in vegetables was improved (P < 5%). One of the probable reasons is that the microclimate in PBVGS was improved by higher air temperature, more sufficient carbon dioxide and longer illumination. The air temperature of PBVGS in the winter was usually 2–3 ◦ C higher than that in the ordinary greenhouses. Another reason is the soil fertility of PBVGS was improved by applying the fermented residual dreg and liquor. On the other hand, the application of fermented dreg and liquor might have more benefits to the quality of vegetables when comparing to the use of chemical fertilizer. 3.2. The analysis of benefits 3.2.1. Economic benefits A standard PBVGS has an initial startup cost of about 12,000 RMB for the construction of greenhouse,
Table 4 The average yield and vitamin C content of vegetables in the 20 groups of PBVGS and their controls Treatment
PBVGS Controls % Change t(18) value
Cucumber
Tomato
Yield per group (kg)
Yield per hectare (kg)
Vitamin C content (mg kg−1 )
Yield per group (kg)
Yield per hectare (kg)
Vitamin C content (mg kg−1 )
8787 7421 18.4 3.56**
195270 164919 18.4 3.56**
146.5 125.6 16.6 2.65*
9688 8227 17.8 3.27**
215280 182820 17.8 3.27**
200.3 164.9 21.5 2.12*
∗ Represents a statistically significant difference between the PBVGS and the controls (P < 5%) using least significant difference test, t(18) > t(18)0.05 . ∗∗ Represents a statistically very significant difference between the PBVGS and the controls (P < 1%) using least significant difference test, t(18) > t(18)0.01 .
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biogas digester, management room and pigsty, with an average depreciation of 2100 RMB each year. The total production investment of PBVGS, including labor, materials, seeds and piglets, was 8000 RMB, saving the peasants 1350 RMB, including 100 RMB for coal, 150 RMB for electricity, 400 RMB for fertilizer and pesticides, and 700 RMB for feedstuff. Thus, the total annual cost for a standard PBVGS averaged approximately 10,100 RMB, the total production value (including pigs and vegetables) reached 21,000 RMB, and the total net income reached 10,900 RMB, which was 4000 RMB higher than that of both an ordinary greenhouse and a roof-less pigsty. 3.2.2. Ecological benefits First, the replacement of traditional pig breeding by PBVGS techniques was a great benefit to the pollution control. A standard PBVGS could use up 14,000 kg fresh dung and produce 10,000 kg of unharmful manure annually, which observably improved the local sanitation situation. Second, it effectively improved the soil fertility and reduced the pollution from chemical fertilizers and pesticides, and it provides a new way to produce pollution-free agricultural products. According to some relative studies (ATEET, 1986; Qi, 1996; Wang et al., 1999), the efficacy of organic manure applied to the soil of PBVGS, including 37,500 kg ha−1 of residual dreg and 20,000 kg ha−1 of fermented liquor, equals 622.0 kg of standard nitrogen, 148.8 kg of phosphorus and 782.0 kg of potassium. By sprinkling fermented liquor on the vegetable leaves, the disease and insect pests were also successfully controlled, allowing a decrease in the amount of pesticides. Thirdly, the PBVGS were also beneficial to the protection of local forest. One digester could produce 450 m3 of biogas each year, corresponding to 320–400 kg of standard coal or 643 kg of firewood (ATEET, 1986; MOA/USDOE, 1998). Its use in the farmers’ living energy successfully prevented trees from being cut in Laiwu District. 3.2.3. Social benefits The spread of PBVGS ensured a local supply of vegetables and meat in the winter, increased the peasants’ income, and improved the peasants’ living conditions. The lower cost and higher quality of agricultural products from PBVGS enhanced the competitive capability in current markets, promoted the adjustment of agricultural structure, and made good use of the surplus farm
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Fig. 2. Nutrient cycle and energy flow among the different components of the PBVGS.
labor in winter. As a new technique, it could speed the spread of scientific knowledge in rural areas. 3.3. The nutrient cycle and energy flow The present research reveals that a beneficial circle of the ecological system that closely linked vegetable planting, pig feeding and biogas producing was established with the effective use of nutrient materials, biological energy and solar energy (Fig. 2). Taking a standard PBVGS (with one 10 m3 digester, six pigs and 450 m2 of vegetables) and its corresponding non-integrated controls as an example, we calculate the main nutrient cycle and energy flow from November 15, 2001 to February 22, 2002 (Table 5). The former studies revealed that, in the winter of North China, the energy conversion ratio of pig growth to feedstuff consumption in the traditional roof-less pigsties is 6.0–12.5% (Zhang, 1990; Sun and Qi, 1993), and that of biogas output to pig dung input is 1.8–5.6% in the traditional household biogas digesters (CBCLG, 1985; MOA/USDOE, 1998; Deng, 2001). In this case study, the energy conversion ratio of pig growth to feedstuff averages 31.6% in PBVGS, which is much higher than the 7.8% of the control. About 55.4% of total pig dung energy is converted into biogas energy with the PBVGS, which is much higher than the 3.3% of the control. The conversion ratio of biogas output to dung input is 27.3% for the control of household biogas digester. In the PBVGS, nitrogen (N), phosphorus (P) and potassium (K), contained in the residual dreg and fermented liquor and used as organic manure of vegetables, account for 54.4%, 31.6 and 55.7% of the original
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Table 5 The nutrient content and energy value of different storage units in a standard PBVGS and its corresponding controls Items
Substance quantity (kg)
Energy value (×109 J)
Nitrogen (kg)
Phosphorus (kg)
Potassium (kg)
PBVGS (a) Pig production Feedstuff consumption Grain Fermented liquor Pig growth
3240 2280 (dry) 960 491
37.7 37.7 – 11.9
37.0 36.5 0.53 –
13.9 13.7 0.19 –
15.0 9.1 5.86 –
(b) Biogas production Pig excreta input Dung Urine Biogas output
2040 240 (dry) 1800 108 (m3 )
4.08 4.08 – 2.26
12.9 7.0 5.9 –
5.0 4.1 0.94 –
15.8 4.4 11.4 –
(c) Applied organic fertilizer Organic fertilizer 1322 Residual dreg 422 (dry) Fermented liquor 900
– –5.1 –0.50
1.2 3.3 5.5
8.8
Controls (a) Pig production Feedstuff consumption Pig growth
46.6 3.64
16.9 –
11.3 –
(b) Biogas production Pig dung input Biogas output
2820 (dry) 150 28.8 (dry) 6.4 (m3 )
0.49 0.134
5.6 1.0 0.18
45.1 – 0.84 –
0.49 –
0.53 –
Note: the conversion coefficients of nutrient and energy refer to the following references: ATEET (1986) and MOA/USDOE (1998).
nutrient substances in the pigs’ dung and urine, respectively.
vides a good way to make full use of organic wastes such as crop stalks and livestock excrements. 4.2. Discussion
4. Conclusions and discussion 4.1. Conclusions This experiment has shown that the PBVGS effectively improved the pigs’ growth, biogas production and vegetable production, and it has many advantages over its non-integrated parts. It successfully solved such problems existing in traditional production patterns as unstable biogas production, slow pig growth and limiting factors of greenhouses in the winter of North China. It organically combined vegetable planting, livestock feeding, and biogas fermentation techniques together, attaining a beneficial ecological cycle in a single greenhouse, as well as achieving considerable economic and social benefits. It had a higher efficiency of nutrient cycle and energy flow, and pro-
The reason for the PBVGS being successfully established and rapidly spreading in North China may be analyzed as follows: First, The PBVGS project has remarkable ecological, economic and social benefits. It is consistent with the government’s agriculture, environment and energy policy, and it wins the local government’s financial and technical approval in its spreading (Zhang et al., 1998; Wang et al., 1999). The management pattern of PBVGS accords with the Chinese present household contract responsibility system, which takes a family as the basic unit to rent land and sign contract with local government. Second, the PBVGS has many advantages in offering the peasants living energy, organic manure and high-quality products. It earns the peasants more money, and so it arouses the great enthusiasm by them. Thirdly, the development
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of PBVGS adapts to the present situation of natural resources in China. Currently in China, the average arable land per capita in the rural areas is only 0.14 ha, and a family’s courtyard usually occupies 0.033–0.1 ha (NSBC, 2002). The Chinese agriculture may adapt this system of family farming units and small-scattered farming areas for a long time. A PBVGS, occupying 0.048 ha land, can be built either in the field or in the courtyard, and it is reasonable for a family to manage and operate. Considering the characteristics of PBVGS, it is especially well suited for the area of temperate or warmtemperate zone such as in North China, but its advantages will become lost and finally disappear when it is spread in sub-torrid or torrid zone such as in South China. This paper is just a preliminary study on the original type of PBVGS with a semi-arcaded earthlog structure. Further research is required to demonstrate whether the new types of PBVGS have more advantages, what is the optimized combination of pigbreeding number, biogas digester volume and vegetable area, how much is the quantitative change of soil fertility after applying fermented residual dreg and liquor, how is the effect of fermented liquor on controlling vegetable disease and insect pests, and so on. Acknowledgements Supported by the National Scientific Fund Doctorate Program, No.: 20030422030. Our thanks to Prof. Robert Greenwood at the University of North California, USA and Prof. Harvey D. Blankespoor at Hope College, Michigan, USA, for their enthusiastic checking of the English. Thanks are also due to Mr. Feng Liu at the Texas A&M University, USA, for his valuable comments on improvements of the manuscript, and Ms. Cuiling Qi and Ms. Fengqin Wang at the Eco-
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agricultural Office of Laiwu, Shandong, China, for data collection.
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