Cropping Systems, Tillage and Crop Establishment

·  This topic is very hard to talk about since duckweed is only grown in water and it is the only flowering aquatic edible plant. However, I will try to give you an overview of how duckweed can be planted in a commercial way and the possibilities there are to integrate the crop with different edible crops and even animals in a circular and sustainable way.

     If we think about doing crop rotations with duckweed it might seem impossible since it grows in water while most of the other crops grow on soil. Nevertheless, as explained in last week's post there is a way to integrate duckweed in a farming system where many crops are grown. This model of agriculture is meant for farmers in developing countries. The residues of the crops grown in the land can be fed to the animals living on the farm. The residues from the animals can be converted into biogas by using a biodigester. The main production of the biodigester will be profited by the farmer while the residues of the biodigester, also known as digestate can be spread in the ponds and serve as a nutrient solution.

For duckweed cultivation, the farmer needs to mimic the natural condition in which the plants normally grow. (Skillicorn, Spira, Journey, & World Bank., 1993) This means they should have a constant supply of water with the necessary amount of nutrients. In Figure1 you can see that the water environment also needs to be protected against wind and flooding. This model can be implemented in almost any type of soil, except alkaline soils because they can increase the pH of the water and end up reducing plant growth. The plots need to have a moderate amount of water all year round, the water will not have a high evaporation rate because the crop will retain it. The depth of the water is also very important because they can influence the rate in which the water temperatures will change.

The nutrients are a key element for duckweed since the plant absorbs them and turns them into plant tissue. (Skillicorn et al., 1993) Apart from N,P,K the plant needs trace minerals to support rapid growth. In a hydroponic system in which duckweed grows, trace minerals play an important role.

Figure 1:file:///C:/Users/laura/Downloads/Duckweed_Aquaculture_A_New_Aquatic_Farming_System_%20(1).pdf

There are many interesting ways of combining duckweed with other crops. In countries like Bangladesh, bamboo is used as a wind buffer and to reduce high temperatures, since it can filter the excessive sunlight. Next to the crops, some cash crops or can be planted such as bananas or species like the ‘giant swamp taro’ which can be planted close to duckweed for shade and will also benefit from the nutrients that are available. Figure 2 can give an overview of possible intercropping with duckweed.

Figure2: file:///C:/Users/laura/Downloads/Duckweed_Aquaculture_A_New_Aquatic_Farming_System_%20(1).pdf

References:

Skillicorn, P., Spira, W., Journey, W., & World Bank. (1993). Duckweed aquaculture : a new aquatic farming system for developing countries. World Bank. Retrieved from https://www.researchgate.net/publication/242631709_Duckweed_Aquaculture_A_New_Aquatic_Farming_System_for_Developing_Countries