**1. Introduction**

Owing to the coupled impact of traditional farming practices and inherent inefficiency of nutrient uptake by crops (up to 60%), there is an inevitable release of drainage water (35–60% of surface irrigation water) rich in nutrients [1]. For example, in a watershed (190,000 ha) in Western Australia, facing high nutrient fluxes, phosphorous losses are measured to be 140 tonnes per annum (tpa) that is twice its target. It is expected to rise to 1300 tpa in the next 100 years if current practices continue [2]. In another study on the North China Plain, the recovery of fertilizer N by the crop at the conventional N fertilizer rate (300 KgNha−1) was approximately 25%, while 30–50% of the applied N was lost [3].

In order to avoid exacerbating the water crisis and to prevent food shortages, an advantageous strategy is the conservation and reuse of agricultural drainage (and the dissolved nutrients) before it ends up in freshwater system [4]. Reusing drainage water and nutrients emanating from one farm in another farm, before they enter the water system, can have huge environmental as well as economic benefits. In particular, reuse reduces the amount of freshwater extracted from the environment, thus lowering its diversion from sensitive ecosystems. In regions where irrigation water supplies are limited, drainage water can be used to supplement them [5, 6]. In addition, agricultural drainage reuse can benefit the farmers (or any stakeholders) by saving cost on not using fresh irrigation water and fertilizer inputs.

The only concern about drainage water reuse is whether or not the water is safe for reuse, that is, does not contain high concentration of salts and pesticides. Highly saline water cannot be used for salt-sensitive crops. However, it can successfully be used for salt-tolerant crops, trees, fodder, and natural wetland and even for salt-sensitive crops at later growth stages [4, 7]. Conjunctive use of saline water with freshwater increases the suitability of drainage water. With regard to pesticides, in areas where strong environmental safeguards exist for pesticide usage, there is little risk associated with the reuse of surface runoff or tail water drainage [7–9]. Hence, drainage water can safely be used if appropriate considerations are taken into account.

Drainage water and dissolved nutrients have been globally utilized for crops and greenhouses. In some intensive farming areas, farmers have begun to test their groundwater for nitrate concentrations and therefore change their nutrient budgets accordingly [10]. In another case, reapplication of N-rich runoff waters provided more than the annual nutrient requirements for that land [11]. In one study, reuse of saline water for salt-tolerant forages has been investigated under varying salinity-level treatments (between 15 and 25 dS/m). For this experiment, sand tanks were used in a greenhouse. Almost all forages showed promise with regard to biomass production, whereas wheatgrass, Bermuda-grass, and paspalum performed particularly well [12].

Some work in local drainage reuse is reported for hydroponic systems maintained in a greenhouse (in which plants are grown in water instead of soil). In one application, high-quality tomato was grown with drainage reuse [13]. During seedling stage, fresh nutrients were supplied with irrigation of which 20–30% overflowed as drainage. At the final stage of ripening, the preserved drainage was reused with no wastage being drained out from the greenhouse. In a similar work based on greenhouses in Australia, drainage reuse was used for growing cucumber and tomato [14]. The study was aimed at investigating the use of drainage water of the greenhouse to increase water and nutrient use efficiency and reduce the environmental impact. Flow meters were installed to gauge the volumes of water applied to the crops. Water samples were taken five times a day for inflows and outflows, and were analyzed for pH, salinity, and concentrations of nutrients. The results indicated 33% reduction in freshwater usage for irrigation. Furthermore, it was determined that drainage water collected from the greenhouse contained 59% of applied N and 25% of applied P. These studies, though small scale and based on local drainage reuse, are very encouraging.

Existing work though promising is based on spatially and temporally limited manual sampling of soils and waters and on hypothetical guesses as to the processes involved in the N cycling. Furthermore, various resource constraints and farmer's concerns regarding real time availability of information on volumes, timings, and quality of discharges that will be delivered to the farms [15, 16] restricts wide

*Water Sustainability through Drainage Reuse in Agriculture – A Case for Collaborative Wireless... DOI: http://dx.doi.org/10.5772/intechopen.106486*

adoption of this mechanism in agriculture. Despite tremendous promise of the benefits of drainage water reuse and technological advancements, implementation of an intelligent and autonomous management mechanism has not kept pace with the deteriorating water situation. Some of the reasons as outlined in a detailed study [17] are as follows: (i) insufficient awareness of available technology, (ii) unavailability of soil, weather, and crop data, (iii) inappropriate model selection which inadequately capture the system details, and (iv) gap between decision makers and scientists. The integration of useful and relevant scientific information is necessary and critical to enabling informed decision making for drainage reuse or disposal [18]. Recent adoption of WSNs in agriculture and hydrology presents huge promise for improving water management, and the next section discusses the applications of WSNs for water quality monitoring and agriculture and identifies huge opportunities available with real time, dense, and remote data availability.

This chapter presents the architecture of water quality management using collaborative monitoring (WQMCM), which uses existing networked farms and water systems and low-complexity predictive models to enable real-time drainage water management [19–21]. The functional overview of the WQMCM framework with the design of a modified drainage network is discussed.

#### **2. Function overview of WQMCM**

WQMCM is an integrated control and management strategy, which requires that individually targeted monitoring units or local networks, representing different stakeholders in a catchment, for example, a farm, should be able to share information with each other about runoff, drainage, or nutrient fluxes. These events may be intense but are short-lived and so information sharing becomes important as they may be very fast, and so may normally be missed with the usual sampling rate. Allowing event information to be transmitted across multiple networks as they are detected will allow prediction of when the repercussions of that event might be seen downstream, allowing other stakeholder networks in the vicinity to adjust their monitoring and management strategy. This will include taking decisions about reusing or disposing the drainages, or increasing their sample rate to catch transient events. As emphasized in the literature, drainage reuse strategy reduces the overall stress of nutrient losses to the water system and provides economic benefit as well by reducing fertilizer usage. The proposed framework enables stakeholders to manage and benefit from this reutilization by sharing information about their availability and presence. Such a de-centralized approach comprising autonomous networks presents a flexible methodology where independent networks, in addition to local monitoring objectives, seek to opportunistically utilize neighboring events.

To demonstrate the mechanism of the proposed framework with respect to agricultural drainage reuse, a modified drainage network is designed. **Figure 1** illustrates an example irrigation and drainage system in which various farms and drainage regions are linked with each other through water flow paths. The figure shows an additional bay, drainage reuse bay, linked with individual farm's irrigation and drainage bay to implement the drainage reuse mechanism. Each farm would have the option to either use drainage from another farm or fresh irrigation water for irrigation. As mentioned earlier, the WQMCM framework aims to combine local individual networks into an integrated mechanism; therefore, it is assumed that these farms are monitored by individual networks with local application objectives. These

objectives are to facilitate farming decisions with regard to, for example, irrigation or pesticides scheduling by monitoring microclimate (soil moisture, crop cover, and soil temperature) of the field. For implementing the framework, an additional network on the water system, the drainage reuse bay in this case, is required to monitor drainage and nutrient contributions by each farm. As shown in **Figure 1**, individual sensors in the drainage network are deployed at the outlet of each farm to monitor its drainage outflow. Other nodes monitor base flow in the drainage bay. This network will be either deployed by an official governing body working toward maintaining water quality or by local farmers for a collaborative cause.

These networks, under the proposed WQMCM framework, share information about the start of a daily event with each other, for example, an irrigation event in a farm or high pollutant drainage discharge from drainage bay. When event information is received from a farm network (e.g., farm A), the drainage network node associated with that farm uses on-node predictive models to forecast the values for expected drainage and nutrient dynamics as a result of that event. The forecasting of

#### **Figure 1.**

*A modified drainage network design to implement drainage reuse for the WQMCM framework.*

#### *Water Sustainability through Drainage Reuse in Agriculture – A Case for Collaborative Wireless... DOI: http://dx.doi.org/10.5772/intechopen.106486*

drainage dynamics is undertaken by the drainage network for the following reasons. Firstly, because drainage network links all the farms and the stream networks, it is ideal to have the drainage network disseminate the predicted information about drainage to all the other farms and stream network for reuse, treatment, or disposal. Secondly, the main drainage bay could be distantly located from the drainage ditch of a farm; hence, volumes of actual drainage outflows received by a drainage bay from a farm may change owing to evapotranspiration and absorption during its transport. Additionally, running predictive models is a computational overhead, which should naturally be taken up by the network responsible for decision making.

**Figure 2** illustrates the format of information shared by a farm and the parameters predicted by a drainage network. The shared event information packet from a farm includes network and event details. To identify a network, information such as network id, type, and location is included. Network type is related to whether it is a farm, drainage, or a stream network, which helps filter out received messages. For instance, a farm network may only want to receive information from drainage or stream network, or a drainage network may only be interested in information coming from farms for obvious reasons. Network location filters out geographically dislocated networks or the ones located downstream, which are unlikely to impact upstream networks. Further to that, event detail in the information packet includes event depth/volume, event duration, fertilizer quantity applied. Any additional event information will be governed by the requirements of a predictive model, which is discussed in the next chapter. As far as the predicted parameters for expected drainage are concerned, as discussed in chapter 1, the relevant information necessary to implement a proactive monitoring and management system is drainage depth/ volume (*Q*), fertilizer loads in the drainage (*TON*), start time (*t*1), and duration (*t*d) of the drainage.

Predicted values of drainage and nutrient dynamics by the sensor node are transmitted to the gateway of drainage network, from where it is relayed to the neighboring farm and stream networks. The farm networks (e.g., farm B) uses the predicted information and local decision support model to decide whether to reuse the drainage or not, and transmit a reuse acknowledgement to the drainage network. In the former case in which network B intends to reuse the drainage, the drainage water, once available from farm A, is allowed to drain into the drainage reuse bay (through a control pump) instead of the main drainage bay. From the reuse bay, the drainage is then pumped into the irrigation bay of farm B. In case none of the networks send reuse

#### **Figure 2.**

*Parameters related to upcoming event shared by neighbor networks and the predicted variables for the resulting drainage event.*

acknowledgements, the drainage would be drained into the main drainage bay. The stream network can then decide, based on the predicted values for nutrients, whether to divert the flow in case of high-nutrient outflows or to otherwise allow it to enter the stream.
