Earthen pond-based floating beds for rice-fish co-culture as a novel concept for climate adaptation, water efficiency improvement, nitrogen and phosphorus management

Abstract

The current study was carried out to evaluate and investigate a unique rice/fish-polyculture as Integrated Aquaculture-Agriculture Systems (IAAS) model established in Egypt, using Earthen Pond-based Floating Bed (EPFB). This novel idea is intended to improve Water, Nitrogen, and Phosphorus Use Efficiency (WUE, NUE, and PUE, respectively). Three experiments were carried out in this investigation. The first and second experiments investigated the effects of rice planting density (20, 25, and 30 plant m2) and rice seed germination methods (Styrofoam Trays Technique, SFT; Directly Outside Germination method, DOG, and Outside Germination for 24 h, 24 h-OG) on rice characteristics, N-contents, P-contents, N-retention, and P-retention of different rice parts. While the third trial, which lasted 90 days, assessed the impact of the EPFB on rice production characteristics, fish growth performances, and nutrient utilization efficiency (N-, P-contents, and retentions) in comparison to Traditional Rice Cultivation (TRC). In terms of rice production characteristics, 30 plants m−2 had the highest significant (p ˂ 0.05) yield values. A density of 20 plants m−2 produced the highest N-contents and total dietary P-content values in rice stem and leaf, whereas a density of 30 plant m−2 produced the highest total dietary N-retention and P-content values. The SFT approach produced the most significant results in terms of rice production variables and total yield, with the EPFB surpassing the TRC in terms of rice production characteristics. TRC produced slightly more (4412.32 kg Fadden −1, 2.5%) than EPFB (4295.58 kg Fadden −1). The EPFB system demonstrated a cumulative improvement in apparent FCR values (1.15) when compared to the apparent average FCR (1.80) of the polyculture system (catfish and tilapia). In terms of nutrient utilization efficiency (N-content and retention), the EPFB exceeded the TRC with values of 41.49%, 61.16%, 32.39%, and 28.01%, respectively, in root N-content and retention, kernel N-retention, and total N-retention. TRC achieved higher P-contents and P-retentions contents (%) in all rice parts than the EPFB system. EPFB had a total N-retention gain of 70.22% (15.83% in Nile tilapia, 12.15% in catfish, and 42.23% in rice), and a total P-retention gain of 30.68% (7.48% in Nile tilapia, 7.38% in catfish, and 15.82% in rice). FBPS's net income, on the other hand, was 5.45 times that of TCR. In conclusion, fish culture coupled with rice has a low environmental impact since it avoids contaminated streams and recycles wastewater ponds after biological treatment with rice. By producing rice without the use of agrochemical fertilizers, the present unique EPFB idea as an integrated system model can positively boost biomass production, improve WUE, NUE, and PUE, and decrease climate impact.