Decision support for optimised irrigation scheduling

The system, developed under the FLOW-AID (an FP6 project), is a farm level water management system of special value in situations where the water availability and quality is limited. This market-ready precision irrigation management system features new models, hardware and software. The hardware platform delivers a maintenance-free low cost dielectric tensiometer and several low-end irrigation or fertigation controllers for serving different situations. The software includes a complete, web based, Decision Support System (DSS) that consists of an expert planner for farm zoning (MOPECO) and a universal irrigation scheduler, based on crop-water stress models (UNIPI) and water and nutrient uptake calculations. The system, designed also to service greenhouse fertigation and hydroponics, is scalable from one to many zones. It consists of 1) a data gathering tool which uploads agronomic data, from monitored crops around the world, to a central web Data Base (DB), and 2) a web based Decision Support System (DSS). The DSS processes intelligently the data of the crop using Crop Response Models, Nutrient Uptake Models and Water Uptake Models. The central system returns over Internet to the low-end controller a command file containing water scheduling and nutrient supply guideline

Prospects in Agricultural Engineering in the Information Age - Technological Development for the Producer and the Consumer

Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is an Invited article from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 1 (1999): N. Sigrimis, Y. Hashimoto, A. Munack and J. De Baerdemaker. Prospects in Agricultural Engineering in the Information Age - Technological Development for the Producer and the Consumer

Enhancement of the intelligent leaf sensor

The maintenance of a suitable humidity environment in plant propagation chambers is a prerequisite for successful root growth of plant cuttings. This paper describes an innovative sensing method which has been developed to replace leaf sensors in plant propagation systems. Such chambers present critical situations for control because of the high humidity levels to be maintained, which makes direct sensing methods unsuitable. The new method is based on the fact that conditions of the microclimatic space are fully determined by the surrounding space, and implicitly relates the transfer phenomena between the two spaces through the selection of control parameters. The measured macroclimatic variables together with the identified control parameters provide an estimate of the moisture loss and determine the rate at which humidity should be supplied in the propagation chamber. An adaptive system guides the selection of control parameters on-line, in a process leading to optimal system performance. The system is performance driven, conducts real experiments on the site and uses a modified descent method to maximise performance. The performance surface was studied and a modification of the searching algorithm has improved the learning rate significantly

A new multirate sampled-data technique for adaptive pole positioning in linear systems

The adaptive pole placement problem for linear systems is solved using a new class of multirate controllers, called two-point multirate controllers. In such a type of controller, the control is constrained to a certain piecewise constant signal, while the controlled plant output is detected many times over a fundamental sampling period. On the basis of the proposed strategy, the original problem is reduced to an associate discrete pole placement problem, for which a fictitious static-state feedback controller is needed to be computed. This control strategy allows us to assign the poles of the sampled closed-loop system arbitrarily in desired locations, and does not make assumptions on the plant other than controllability and observability of the continuous and the sampled system, and known order. The controller determination relies on a closed-form formula, which can be thought as the extension of the Ackerman formula for multi-input/multi-output (MIMO) systems. Known indirect adaptive pole placement techniques require the solution of matrix polynomial Diophantine equations, which, in many cases, might yield an unstable controller. Moreover, the proposed adaptive scheme is readily applicable to non-minimum phase systems, and to systems which do not possess the parity interlacing property. Finally, persistency of excitation and, therefore, parameter convergence, of the continuous-time plant is provided without making assumptions either on the existence of specific convex sets in which the estimated parameters belong or on the coprimeness of the polynomials describing the ARMA model, or finally on the richeness of the reference signals, as compared to known adaptive pole placement schemes

What limits the application of wastewater and/or closed cycle in horticulture?

We determine the ¿optimal¿ management of a closed growing system with multiple sources of water, of price decreasing with quality. The management that balances marginal costs of water and fertilizers with marginal yield loss is determined. By using a number of yield response curves, in a couple of different cases (Holland and Mediterranean basin), we show that, with realistic prices both of resources and of produce, closed systems are financially viable only in two cases: 1. in regions with good water or 2. with high-value crops that offset the costs of ensuring good water (such as rain collection or desalinisation), so that there is no advantage for a grower to maintain a closed loop whenever the quality of irrigation water is poor. This means that a price structure of water resources that shifts the economic optimum towards poorer irrigation water has the consequence that the irrigation loop cannot be closed. In other words, there is no way that low-value crops using poor irrigation water may still be profitable under stricter environmental rules. We conclude that in view of the environmental impact, it would be advisable for irrigation and local authorities in horticultural areas either to provide good water at a relatively high price or to consider subsidizing investment costs of on-site desalinization plants, rather than stimulating use of poor quality water, or attempting to prevent pollution through unrealistic regulations. This means that local authorities, seriously planning to reduce agricultural pollution, should either provide incentives for growers to switch to less sensitive or more valuable combinations of crops, or contemplate developing other economic activities than agriculture