Is raising chickens under trees really ecological agriculture?
As an important form of mountain economy, raising chickens under trees has become a driving force for economic development in some places. The green food (eggs, meat) produced by raising chickens under trees is also admired by some people who favor ecological products and organic food.
However, most people do not know that while raising chickens under trees brings economic benefits to farmers, its impact on the soil beneath the trees, especially on the vegetation and soil of natural forest land, is also very serious. In mountain natural forest land, especially in some water conservation areas, raising chickens under trees must be done with great caution, and the size of the environmental carrying capacity and the ecological threshold must be fully considered.
Through the experimental forest farm located in Sidaohe Village, Baoshan Town, in the northern mountainous area of Huairou District, Beijing, we investigated the impact of different densities of raising chickens under trees on the soil, and found that high-density farming causes degradation of forest land vegetation and soil, thereby affecting the entire forest land ecosystem.
1050 chickens per hectare
Impact on soil stability
When 1050 chickens are raised per hectare, soil stability decreases by about 30% in about one month, by about 47% in 2 months, and by about 51.5% in 3 months. However, the decrease in the later period is smaller than in the earlier period.
Impact on soil infiltration rate
When 1050 chickens are raised per hectare, the soil infiltration rate at the initial stage of farming is 62.1%. After about 1 month, the soil infiltration rate decreases to 34.1%, a decrease of 28%, with a reduction rate of 45%; after 2 months of farming, the soil infiltration rate drops to 24.8%, a decrease of 37.3% within 2 months, with a reduction rate of 60%; continuing to farm until 83 days, the soil infiltration rate drops to 21.6%, a decrease of 40.5%, with a reduction rate of 65%. The infiltration rate declines quickly in the early stage of farming and slowly in the later stage, indicating that the infiltration rate tends to stabilize and the deterioration trend is curbed. This means that vegetation coverage is increasing, and that the consumption of plants by chicken feeding and the self-recovery of plants tend to balance.
Impact on soil nutrient cycling rate
At a farming density of 050 chickens per hectare, after 30 days of farming, the nutrient cycling rate decreases by 71%, vegetation is basically almost completely lost, and the ground surface is exposed in most places; after 60 days of farming, nutrient cycling decreases by 74%, a month-on-month decrease of 11%; after 83 days of farming, the nutrient cycling rate decreases by 84%. In the later stage of farming, plants in the experimental farming area are almost completely lost. The reduction proportion is greater than that of soil infiltration and soil stability. Soil nutrient cycling is closely related to vegetation, so this also shows that in the farming process, the most directly affected and most sensitively responding factor is vegetation, followed by soil infiltration capacity and stability.
750 chickens per hectare
Impact on soil stability
When 750 chickens are raised per hectare, soil stability decreases by about 6% in 1 month, by 12% in 2 months, and by 15% in 3 months. In the later stage of chicken farming, the bottoming-out range of soil stability decreases, possibly because in August and September, with high temperatures and abundant rainfall, plants grow luxuriantly and accumulate a large amount of biomass, so vegetation recovers somewhat in the later stage of farming, causing the decline in soil stability to slow.
Impact on soil infiltration rate
When 750 chickens are raised per hectare, the soil infiltration rate at the initial stage of farming is 60.6%. After 36 days of farming, the soil infiltration rate decreases by 4.4%, with a reduction rate of 7.3%; after 61 days of farming, the soil infiltration rate decreases by 8.3%, with a reduction rate of 13.7%; after 83 days of farming, the soil infiltration rate decreases by 12.4%, with a reduction rate of 20.5%.
Impact on soil nutrient cycling rate
When the farming density is increased to 750 chickens per hectare, after 30 days of chicken farming, the nutrient cycling rate decreases by 11.9%; after 60 days of farming, it decreases by 18%; when the farming time is increased to 82 days, the nutrient cycling rate decreases by 23.1%.
450 chickens per hectare
Impact on soil stability
When 450 chickens are raised per hectare, soil stability shows a steady downward trend during the nearly 3 months of chicken farming, with soil stability values decreasing by 3%, 7% and 4% respectively compared with the previous month. After 3 months, stability reaches its lowest at 69.6%, a decrease of 11.5% relative to 81.1% under free-range conditions, with a reduction rate of 14%.
Impact on soil infiltration rate
When the farming density is 450 chickens per hectare, the characteristics shown by the soil infiltration rate are clearly different from those at 1050 and 750 chickens per hectare. During the 3 months of farming, the soil infiltration rate at the initial stage of farming is 62.4%; after 36 days of farming it decreases by 5.9%, with a reduction rate of 9.5%; after 61 days of farming it decreases by 6.2%, with a reduction rate of 9.9%; after 83 days of farming, it drops to 51.9%, with a reduction rate of 17%.
Impact on soil nutrient cycling rate
When the farming density is increased to 450 chickens per hectare, after 30 days of chicken farming, the nutrient cycling rate decreases by 15%; after 60 days of chicken farming, the nutrient cycling rate decreases by 16%, a month-on-month decrease of less than 1%, which can be regarded as no obvious change, due to the vigorous plant growth in August and September; after 83 days of chicken farming, the nutrient cycling rate decreases by 27%, a month-on-month decrease of 13.5%.
150 chickens per hectare
Impact on soil stability
When the farming density is 150 chickens per hectare, soil stability shows no obvious change after chicken farming. In the later period, due to harm from natural enemies, the farming density was less than 150 chickens per hectare, and the soil showed even more clearly unchanged stability.
Impact on soil infiltration rate
When 150 chickens are raised per hectare, based on 3 monitoring checks of soil change characteristics, the soil infiltration rate shows no obvious change.
Impact on soil nutrient cycling rate
When the farming density is 150 chickens per hectare, the vegetation in the farming area shows no obvious change. After being eaten by chickens, plants recover in the season of vigorous plant vegetative growth. Mechanical damage to the soil surface layer is also not obvious. Therefore, the soil nutrient cycling rate calculated by the soil evaluation model SSA shows no change.
Excessive density will permanently affect forest land ecology
In short, the greater the farming density, the greater the amount of plants eaten by chickens, and the greater the vegetation loss. With high farming density, the mechanical damage by chickens to the ground surface is greater. In addition, chickens have the habit of dust bathing and making nests, which changes the surface structure, and soil crusting and vegetation coverage in the evaluation model decrease substantially. After raising chickens under trees, once the forest land vegetation and ground surface are affected, the soil infiltration rate changes. A decrease in soil infiltration rate means that the vegetation that intercepts and slows rainfall is reduced, and it also means that the characteristics of the soil surface have changed, and the ability of the soil to conserve and store surface water is reduced. To avoid changing the soil characteristics beneath the trees, the chicken farming density must be limited below a certain number. However, in actual practice, can this "maximum density" allow farmers to make a profit?
In addition to causing serious impacts on soil stability, soil infiltration rate and soil nutrient cycling, raising chickens under trees also has varying degrees of impact on plants and animals in the forest land environment, causing profound changes in the forest land environment.
The scratching and foraging behavior of chickens thoroughly disturbs the litter layer, reducing the population of soil animals and thereby changing the population structure. Because chicken feeding is selective, the composition and structure of vegetation change, and succession of plant communities is unavoidable. Changes in vegetation and soil will inevitably lead to changes in microorganisms.
High-density raising of chickens under trees is extremely damaging to vegetation, and further seriously affects the soil's nutrient cycling function. This impact is severe and long-lasting. Even if farming is stopped, the regenerated vegetation will differ greatly from the original vegetation. The original vegetation is mainly composed of perennial herbs and shrubs, while the secondary vegetation after high-density raising of chickens under trees is mainly composed of short-lived, annual herbs. How this vegetation change or the succession it forms will develop remains to be further observed.