Robust optimal diversion of agricultural drainage water from tea plantations to paddy fields during rice growing seasons and non-rice growing seasons

Abstract

We investigated seasonal water quality changes on different land uses in a small agricultural watershed dominated with rice and tea crops. Observed NO 3 -N in tea plantations and tea drainage channels was sufficiently high enough to cause downstream water pollution throughout the year. On contrary, significant NO 3 -N reductions were observed in abandoned and active paddy fields, and were highest in active paddy fields during rice growing seasons. Accordingly, a question is posed whether deliberately diverting NO 3 -N contaminated drainage water from tea plantations to paddy fields would be effective a strategy for reducing downstream water pollution. NO 3 -N ratios reduced in paddy fields are however neither distinct nor known in advance, and this uncertainty could consequently lead to further environmental risks like NO 3 -N leaching and production of greenhouse N 2 O gas. We assume that NO 3 -N reduction rates of paddy fields and drainage canals are constrained in an ellipsoidal set of uncertainty. A portfolio optimisation problem is formulated to determine optimal rates of diversion from tea drainage channel into paddy fields. The problem is numerically solved in robust optimisation approach by maximising minimum NO 3 -N reduced under uncertainty. An application demonstrated that robust approach allocates different optimal rates of diversion to hedge the risk of possible malfunctioning of NO 3 -N reduction processes. Overall worst-case NO 3 -N reduction is highest in rice growing season, due to increased drainage water allocations to active paddy fields. The robust optimisation approach has potential to support decision-making processes for reducing NO 3 -N pollution and water demand pressure on water resources, and cost of rice production thereof.

Effects of Stocking Density on the Growth Performance, Physiological Parameters, Antioxidant Status and Lipid Metabolism of Pelteobagrus fulvidraco in the Integrated Rice-Fish Farming System

“…The absorption capacity of rice to N and P is different at different rice growth stages [10]. During the tillering stage, rice displays a strong ability to assimilate N and P, effectively reducing the N and P load in water and soil [63][64][65]. Our study revealed that rice demands a substantial amount of N and P during the tillering stage to support its growth, resulting in a decrease in N and P content (30th August).…”

A multi-state Markov chain model for rainfall to be used in optimal operation of rainwater harvesting systems

“…The study area, which is referred to as the Imago area, has been established in Shiga Prefecture, Japan (Unami and Kawachi, 2005), and its location is shown in the satellite images (a) and (b) of Figure 1. As can be seen in the satellite image (c) of Figure 1, the Imago area extends over the Nunobiki hill with inland valleys, mostly covered by tea plantations and pastures on the ridges, forests in the slopes, and paddy fields in the valley bottoms (Mabaya et al, 2016). According to the local people's perception, the precipitation in the Imago area is anomalously less in comparison with the neighboring areas.…”

Effects of Different Stocking Densities on the Growth, Antioxidant Status, and Intestinal Bacterial Communities of Carp in the Rice–Fish Co-Culture System

“…Existing research demonstrates that for yellow catfish (Pelteobagrus fulvidraco), when density becomes excessively high, there is a noticeable decrease in weight gain, body length, and condition factor, whereas the feed conversion ratio and coefficient of variation increase [6]. In juvenile grass carp (Ctenopharyngodon idella), elevated densities are associated with slowed growth, reduced immunity, and decreased antioxidant capacities [7]. Additionally, high density adversely impacts the growth and digestive enzyme activity of juvenile crayfish (Procambarus clarkii), eliciting notable alteration in the content of proteins, fats, glucose, and urea nitrogen in response to the escalated farming density [8].…”