MARCH: SILK
In March, mulberry trees in the Pearl River Delta start producing leaves, and farmers begin the first of eight harvests from March to December. The leaves go to special silkworm-rearing sheds nearby, where silkworm larvae continuously eat mulberry leaves for around forty days before they gain enough energy to metamorphose into moths. They start by winding a thin filament around themselves to form a cocoon and then transition from larvae to moths. The mature cocoons go to nearby mills that extract the filament to make yarn and start the silk-making process.
A similar process happens on Mulberry farms throughout China- the farmers foster the unique relationship between Bombyx Mori (silkworms) and white Mulberry. Unlike their inland peers, farmers in the Pearl River Delta practice a unique blend of agro-forestry and aquaculture where mulberry leaves are one of a diversity of outputs called the mulberry-dike, fish-pond system (Figure 1).
FISH SILK
The Pearl River Delta is a densely populated region in Eastern China where several large rivers converge into the Pacific. Historically, the economies of the villages in the Pearl River Delta focused on fishing- flooding and sulphuric soils made these lowlands hard to cultivate. By the 1300s, the delta became China’s main source of carp. To expand and control harvests, the Zhejiang people started damming and building dikes to create fishponds they could stock with cultivable land surrounding them.
Figure 1: An aerial view of the delta with ponds in grey and dikes in white. Source
A checkerboard of ponds with thin farmable land around them filled the delta (figure 1). First farmers planted lychee and longon on the dikes, the region was famous for growing them. But the thirsty fruit trees soon diminished the water table and farmers made more profit from mulberry trees and silkworm-rearing.
In the 1700s the Qing dynasty closed off all Chinese ports except Guaghzhou, the closest large city to the delta. The resulting high demand for mulberry caused most farmers to convert their dikes to mulberry and expand the system to nearby waterways and wetlands. Shunde, the city in the center of the delta, opened a filature (a factory that aggregates cocoons from farmers and unwinds the filament from the cocoons into skeins for weaving) late in that century to accommodate the mulberry boom.
ENERGY EXCHANGE
Although the farmers in the Pearl River Delta focus on mulberry on the dikes and carp in the ponds, the system thrives because of the diversity of crops and the careful exchange of resources. The delta is an example of a little to no-waste agriculture system– everything is cycled back into the system (figure 2).
Figure 2: The diverse components of the mulberry-dike, fish-pond system. Source.
In spring to early summer, farmers stock the rectangular ponds with carp fry. The ponds fill with river water from inlet channels. Before stocking the pond, they add compost from the farm to promote phytoplankton growth. Since fish are the main commodity in this system, the farmers focus on planting the dikes with crops that provide their carp with a balanced diet, along with the phytoplankton. Even the byproducts of crops, like mulberry that farmers can also profit from, go to the fish. Silkworm pupae are one of carp’s main food.
Before the mulberry produces leaves in March, farmers plant soybeans, mung beans, and peanuts amongst them. They increase available nitrogen in the soil and farmers can use them for their diet and fish food. The edges of the dikes have banana and other fruit trees to shade the ponds and harvest for food. In the early summer, farmers build trellises over the ponds from bamboo and grow melons and other ground crops on them to shade the ponds during the hot summers. Once the mulberry harvest finishes, farmers plant vegetables for their diet or selling in the local markets and grasses that carp eat. Farmers plant sugarcane every other year to let the soil recover from mulberry cultivation (figure 3).
Figure 3: farmers irrigating the mulberry and sugarcane using water from the ponds. Source.
After harvest, all annual plants are cycled back into either the ponds or soils as compost, and farmers dredge out the mud in the ponds to fertilize the plants and repair the dikes. Farmers also use the dredged mud to cover the floor of unused silkworm sheds and grow mushrooms.
Building off of thousands of years of tradition, the dike ponds are a self-reliant system where farmers can use knowledge of energy flows and balance to get the maximum output with no inputs. A system perfect for its densely populated surroundings that provides a market for and a labor force needed to process its diverse outputs.
At its peak in the 1980s, the Pearl River Delta produced 0.8% of China’s mulberry for silk. Over the last 25 years, mulberry cultivation in the delta has declined because the small producers can’t compete with bigger, more industrial mulberry farms. Now the mulberry-dike, fish-pond system is out of balance. Farmers have extended the fish ponds to maximize profits which has overloaded the carrying capacity of the ponds. Farmers get the maximum economic benefit from the pond-dike system when it is in balance, but bridging it from where it is now takes time, resources, and incentives. For now, silk from the delta has the same commodity price as silk from more conventional farms, making it a lower priority to carp for Pearl River Delta farmers.
NOTES
https://www.academia.edu/363917/An_energy_flow_model_of_the_mulberry_dike_carp_pond_farming_system_of_the_Zhujiang_Delta_Guangdong_Province_China?email_work_card=view-paper
https://www.mdpi.com/2073-445X/12/5/1066
https://www.sciencedirect.com/science/article/pii/S1875389212005263
https://www.sciencedirect.com/science/article/abs/pii/014362288390005X