Water and Land as Shared Resources for Agriculture and Aquaculture: Insights from Asia

Effects of organic fertilizers produced from fish pond sediment on growth performances and yield of Malabar and Amaranthus vegetables

The increasing intensification of aquaculture production requires the development of strategies to reduce its environmental impacts such as the pollution caused by the discharge of nutrient-rich sediments into local water bodies. This research was undertaken to investigate and evaluate the effect of using organic fertilizers produced from the pond sludge of freshwater snakehead fish (Channa striata) composted with organic amendments of peanut shells and coir fiber on growth performance indices and yields of Malabar spinach (Basella alba L.) and Amaranthus cruentus (Amaranthus L.) vegetables in the dry and wet seasons. An organic fertilizer quality experiment showed that the richest nutrient contents of the produced organic fertilizer were achieved when using 30% sludge mixed with 70% organic amendments (50% peanut shells + 50% coir fiber). This was selected and used for a vegetable cultivation experiment. For the reference treatment, only chemical fertilizer was applied, while in the other four treatments, 25, 50, 75, and 100% of the chemical fertilizer were substituted with the organic fertilizer. A 25–50% reduction in the chemical fertilizer application resulted in better growth performance indices and final yields than the other treatments, including the reference treatment, for both crops. The highest yields of Malabar spinach and Amaranthus cruentus vegetables were found in Treatment 3 (50% chemical fertilizer combined with 50% organic fertilizer), followed by Treatment 2 (25% organic fertilizer combined with 75% inorganic fertilizer) (P < 0.05). The results show that the reuse of sludge from snakehead fish ponds mixed with agricultural by-products as organic fertilizer for vegetables not only improves vegetable productivity but also reduces the costs of chemical fertilizer and decreases environmental pollution.

Quantifying spatio-temporal variation in aquaculture production areas in Satkhira, Bangladesh using geospatial and social survey

Despite Bangladesh being one of the leading countries in aquaculture food production worldwide, there is a considerable lack of updated scientific information about aquaculture activities in remote sites, making it difficult to manage sustainably. This study explored the use of geospatial and field data to monitor spatio-temporal changes in aquaculture production sites in the Satkhira district from 2017-2019. We used Shuttle Radar Topographic Mission digital elevation model (SRTM DEM) to locate aquaculture ponds based on the terrain elevation and slope. Radar backscatter information from the Sentinel-1 satellite, and different water indices derived from Sentinel-2 were used to assess the spatio-temporal extents of aquaculture areas. An image segmentation algorithm was applied to detect aquaculture ponds based on backscattering intensity, size and shape characteristics. Our results show that the highest number of aquaculture ponds were observed in January, with a size of more than 30,000 ha. Object-based image classification of Sentinel-1 data showed an overall accuracy above 80%. The key factors responsible for the variation in aquaculture were investigated using field surveys. We noticed that despite a significant number of aquaculture ponds in the study area, shrimp production and export are decreasing because of a lack of infrastructure, poor governance, and lack of awareness in the local communities. The result of this study can provide in-depth information about aquaculture areas, which is vital for policymakers and environmental administrators for successful aquaculture management in Satkhira, Bangladesh and other countries with similar issues.

Blue-green water utilization in rice-fish cultivation towards sustainable food production

Integrated rice-fish culture is a competitive alternative to rice monoculture for environmental sustainability and food productivity. Compared to rice monoculture, rearing fish in rice field ecosystems could increase food (rice and fish) production from this coculture. Moreover, the water productivity of rice-fish coculture is considerably higher than that of rice monoculture, because of double cropping. Despite these benefits, rice-fish coculture has not yet been broadly practiced. One of the potential challenges for the wider adoption of rice-fish coculture is water management. There are two forms of water involved in rice-fish cultivation: (1) blue water-surface and groundwater, and (2) green water-soil water from rainfall. The aim of this article is to focus on key factors determining the adoption of rice-fish cultivation through the effective utilization of blue-green water. We suggest that the efficient application of blue and green water in rice-fish coculture could help confronting water scarcity, reducing water footprint, and increasing water productivity.

Research on Expansion Characteristics of Aquaculture Ponds and Variations in Ecosystem Service Value from the Perspective of Protecting Cultivated Lands: A Case Study of Liyang City, China

In the context of global food insecurity, a large amount of cultivated land in China has been occupied by aquaculture ponds, leading to a series of variations in the ecological environment. The Chinese government pays close attention to the problem. In order to achieve sustainable development and ensure the safety of China’s cultivated land, the paper uses Liyang City as an example to discuss the spatial characteristics of the expansion of aquaculture ponds through occupying cultivated lands and analyzes the variations in ecosystem service value and cultivated land function. The conclusions are as follows: (1) 2073.24 hectares of cultivated lands were occupied for expanding aquaculture ponds in Liyang from 2009 to 2019, and there was a small number of new aquaculture ponds in the ecological protection area, which shows that the aquaculture ponds in Liyang City are at the stage of disorderly expansion; (2) the total value of ecosystem services increased by 1.43%; supply and support services values decreased, but the increase in regulation and cultural services values was sufficient to more than compensate for the mentioned losses; and (3) the expansion of aquaculture ponds leads to a decrease in the carbon storage of cultivated land, which in turn has negative impacts such as an increase in atmospheric carbon concentration.

Reuse and recycle: Integrating aquaculture and agricultural systems to increase production and reduce nutrient pollution

Integrated agriculture and aquaculture systems (IAAS) allow nutrients, energy, and water to flow throughout the components of the system, increasing the efficiency with which inputs are converted to food. Yet effectively designing an IAAS requires understanding how nutrients accumulate and alter the system's productivity. Here we developed a mechanistic model for nitrogen transport and utilization and parameterized it using the IAAS in He'eia, Hawai'i. Of note, we modeled tidal influence, which extends existing IAAS models that often assume aquaculture in tank enclosures. We simulated the impact of nitrogen loading from three possible land use scenarios across agriculture and development priorities on the productivity of the fishpond downstream. We projected that organic nitrogen and nitrate concentrations parallel the successive increases in nitrogen loading across management strategies. Autotroph and fish densities were predicted to follow similar trends in response to increased nitrogen availability, causing fish harvests to increase from the current land use (25 kg/ha) to the restored agriculture (35 kg/ha) and urban (50 kg/ha) alternatives. While fish harvests were predicted to be highest in the urban scenario, modeled caloric production in the restored scenario from agriculture and aquaculture would sustain 235 people (4.3 people/ha) in the He'eia IAAS, 16 and 125 times more than the current or urban land uses, respectively. Restoring diversified agriculture was also predicted to retain a larger proportion of nitrogen inputs (0.43) than urbanizing the region (0.30), which would reduce nitrogen export to the adjacent Kāne'ohe Bay. Several state variables were notably sensitive to tidal flux rates, highlighting the importance of incorporating tidal dynamics into a coastal IAAS model. This model provides valuable insights for the management of existing coastal IAAS and design of new IAAS in coastal regions to improve the sustainability of future food systems.