Modelling current speed and carrying capacity in long-line blue mussel (Mytilus edulis) farms

The development of the mussel (Mytilus edulis) farming industry in Norway is based on suspended long‐line culture, and large areas of the coast are potentially suitable for farming. Norwegian fjords and coastal waters are regarded as oligotrophic environments in comparison with sites where most studies on mussel feeding on natural seston have been carried out. High mussel culture densities in oligotrophic water may cause seston depletion, resulting in low growth or tissue wasting due to reduced feeding and negative net energy balance. In this paper we present a carrying capacity model based on rate conditional processes, balanced against flushing and with emphasis on flow reduction as a function of farm design. The model is based on assumptions that friction forces are a function of geometric shape of the channel made up by the suspended mussel ropes as vertical boundaries and it quantifies carrying capacity according to information of farm length, space between long lines, seston concentration and background current speed and the relative importance of these factors. Estimates of how stocking density in mussel farming can be optimized in relation to the food supply (i.e. carrying capacity) are crucial to production management decisions, and the model may provide predictors for decisions regarding new site selection or expansion of existing operations.     

OSIRI: A simple decision-making tool for monitoring irrigation of small farms in heterogeneous environments

A new decision-making software tool for sprinkler or drip irrigation scheduling and monitoring, was developed at the request of small scale sugarcane (Saccharum spp.) farmers in Reunion Island (France) facing variable climate and soil conditions. Based on a simple water balance simulation model coupled with a comprehensive set of decisions rules, OSIRI was designed to provide farmers with targeted advices on discrete units of irrigation and for simulating scenarios of irrigation systems to optimize their performance. An optional procedure of direct adjustment by farmers and a system of controlled irrigation rationing are proposed. To meet the producer needs, the number of input parameters is adapted to the rather limited data availability, and the recommendation sheet is user-friendly oriented. Field data confirmed that OSIRI simulates very reasonably well actual evapotranspiration and drainage below the sugarcane root zone. Also, OSIRI allowed to save about 30% of irrigation delivery on a 140-day period as compared to the currently used crop water requirement method (respectively, 165 and 240 mm of water), without significant decrease in yield (respectively, 102 and 101 T ha⁻¹).