STRATEGIES TO INCREASE WATER PRODUCTIVITY IN IRRIGATED RICE SYSTEMS: IS REDUCING WATER INPUTS THE KEY?

La crescita della domanda mondiale di cibo e l\u2019aumentata incidenza di situazioni di carenza idrica ha notevolmente accentuato l\u2019attenzione sulla risicoltura, data la sua importanza per la nutrizione umana e il suo contributo ai prelievi idrici per fini irrigui. Pi\uf9 del 75% della produzione mondiale di riso ha infatti luogo in risaie irrigate che utilizzano circa il 40% dell\u2019acqua destinata al settore agricolo. Alla luce di questo contesto (descritto nel Capitolo 1), la Tesi si pone l\u2019obiettivo di valutare diverse tecniche di gestione dell\u2019acqua in risaia come risposta alle crescenti pressioni sugli agricoltori che sono chiamati a massimizzare le produzioni, riducendo al contempo i volumi irrigui apportati. Il lavoro \ue8 articolato su tre principali aree di indagine tra loro interconnesse: (i) ruolo delle tecniche di monitoraggio nel favorire l\u2019analisi dei fattori che determinano l\u2019efficienza d\u2019uso dell\u2019acqua; (ii) valutazione di diverse strategie irrigue alla scala di risaia; (iii) studio delle variazioni dei fabbisogni irrigui distrettuali laddove la sommersione tradizionale fosse sostituita da tecniche di risparmio idrico su larga scala. Per quanto concerne il primo punto, l\u2019attivit\ue0 di Tesi ha contribuito allo sviluppo del prototipo di un innovativo sistema per il monitoraggio delle dinamiche dell\u2019acqua in camere di risaia soggette a diverse tecniche irrigue. Svariati sensori sono stati utilizzati in maniera integrata permettendo la misura di diversi processi con alta risoluzione temporale (Capitolo 2). In aggiunta alle tecniche di monitoraggio a terra, \ue8 stata valutata la possibilit\ue0 di impiego di dati da satellite per la valutazione dello sviluppo della vegetazione nel tempo e nello spazio, informazione necessaria per lo studio di processi legati allo sviluppo vegetativo (Capitolo 3). Alla scala di campo sono stati valutati i bilanci idrici e gli indici di uso dell\u2019acqua di tre diverse tecniche di gestione: semina in acqua e sommersione continua (pratica tradizionale), e due tecniche alternative che consistono nella semina interrata e sommersione ritardata e semina interrata e irrigazione intermittente. Se, da un alto, la sommersione ritardata ha determinato riduzioni del raccolto del 3% a fronte di risparmi idrici del 20%, l\u2019irrigazione intermittente ha visto riduzioni del raccolto pari a circa il 30% come contraltare a risparmi idrici dell\u2019ordine del 65%. I valori pi\uf9 alti per quanto riguarda l\u2019indice di produttivit\ue0 dell\u2019acqua sono stati ottenuti con riso irrigato ad intermittenza, tuttavia la sua sostenibilit\ue0 economica sarebbe da valutare attentamente, date le significative perdite di raccolto osservate. Inoltre, \ue8 stata riscontrata una significativa variabilit\ue0 nei fabbisogni irrigui dei trattamenti in sommersione, i quali hanno subito variazioni comprese tra il 40% e il 50% da un anno al successivo (variazione concentrate soprattutto all\u2019inizio della stagione). Prendendo come riferimento la sommersione tradizionale, si \ue8 riscontrato un dimezzamento dei volumi irrigui necessari che sono passati da circa 3000 mm a 1500 mm. Tali variazioni sono state avvalorate da un\u2019analisi statistica e sono state attribuite alla combinazione di diversi fattori quali la profondit\ue0 di falda all\u2019inizio della stagione e modificazioni a livello delle propriet\ue0 e della struttura del suolo. Successivamente, il potenziale risparmio idrico conseguente ad un abbandono della tecnica di sommersione \ue8 stato valutato alla scala di distretto irriguo (Capitolo 5). I fabbisogni irrigui delle diverse colture del distretto (riso sommerso, mais irriguo e pioppo irriguo) sono stati stimati lungo un periodo di 4 anni grazie all\u2019applicazione, in maniera distribuita, del modello idrologico SWAP e all\u2019uso di equazioni di bilancio di massa. Successivamente, \ue8 stata individuata una relazione empirica che lega la soggiacenza alla ricarica di falda (data dall\u2019acqua di percolazione dei campi irrigati). Per lo scenario di conversione a riso irrigato, si \ue8 prestata particolare attenzione al meccanismo di feedback che lega il livello di falda ai volumi irrigui necessari. L\u2019importanza di questo legame \ue8 stata messa in luce attraverso lo sviluppo di due casi di studio. Nel primo caso, il feedback \ue8 stato trascurato e la stima dei fabbisogni irrigui \ue8 fatta sulla base degli attuali livelli di falda. Nel secondo caso invece, la stima devi volumi irrigui necessari \ue8 fatta in funzione dall\u2019equilibrio soggiacenza-ricarica che verrebbe ad instaurarsi a seguito di una consistente variazione delle pratiche irrigue. Nello scenario senza feedback sono state stimate riduzioni dei fabbisogni irrigui dopo una conversione delle tecniche irrigue pari al 65%. Tali riduzioni sono state invece del 45% quando il meccanismo di feedback \ue8 stato considerato nell\u2019analisi. Tuttavia il mantenimento di un turno irriguo per il mais di 15 giorni si \ue8 rivelato non sufficiente per il soddisfacimento dei fabbisogni idrici della coltura a causa dell\u2019aumentata soggiacenza. Accorciare il turno irriguo del mais a 10 giorni ha determinato un\u2019ulteriore riduzione dei risparmi ottenibili con una completa conversione a riso irrigato ad intermittenza (riduzione dei fabbisogni irrigui distrettuali pari al 40%). Oltre ad aspetti strettamente legati ai volumi idrici, sono state inoltre investigate le dinamiche del carbonio organico disciolto in funzione delle diverse tecniche di gestione dell\u2019acqua (Capitolo 6). Lo studio ha evidenziato un legame molto forte tra il ciclo del carbonio organico disciolto e le condizioni riducenti indotte dalla continua saturazione del suolo. Infine \ue8 stato sviluppato un caso di studio per quantificare il ruolo della falda nella riduzione dei fabbisogni irrigui di colture irrigate ad intermittenza come il mais. I risultati hanno evidenziato un contributo della risalita capillare pari a circa il 50% del volume evapotraspirato dalla coltura in aree con bassa soggicanza di falda (Capitolo 7). In conclusione, nonostante la tendenza a voler proporre soluzioni di carattere generale al problema dell\u2019efficienza d\u2019uso dell\u2019acqua in agricoltura, le attivit\ue0 di ricerca proposte nella seguente Tesi hanno messo in luce come sia difficile stabilire se il risparmio idrico sia effettivamente un obiettivo da perseguire in qualsiasi contesto produttivo (Capitolo 8).In a context of increasing food demand and increasing risk of water scarcity, irrigated rice systems are receiving a specific attention because of the role of rice in food nutrition and because of the relevant share of water withdrawals required by rice farming. More than 75% of the global rice supply is in fact produced in lowland irrigated areas, which in turn require around 40% of the global water used for irrigation. Given this background (Chapter 1), the Thesis investigates the role of water management in irrigated rice system, in response to the compelling pressures on farmers to maximise crop production while reducing the amount of water used for irrigation purposes. Three interlinked focus areas have been evaluated: (i) the role of monitoring techniques in improving knowledge on processes driving water use in rice systems, (ii) field-scale evaluation of the performance of different water regimes, (iii) effects induced by a large adoption of water saving technologies on the irrigation requirements at the district scale. First, a prototype of an innovative integrated multi-sensor system was developed in order to monitor water dynamics in paddy fields under different water regimes. Several monitoring devices were effectively used in an combined way, enabling to measure different processes with a high temporal resolution (Chapter 2). In addition to on-ground devices, the opportunity offered by the use of remote sensed data to capture the spatio-temporal evolution of crop growth and study crop-related processes was investigated (Chapter 3). Focussing on the field scale (Chapter 4), water balances and water use indices of three rice water managements were compared: water seeding-continuous flooding (\u201ctraditional\u201d practice) and two alternative regimes being dry seeding-delayed flooding and dry seeding-intermittent irrigation. If delayed flooding determined average yield reductions by 3% against a decrease of water applications by 20%, the 65% reduction of water applications in intermittent irrigated rice was counterbalanced by yield losses close to 30%. Therefore, in spite of intermittent irrigation achieving the highest water productivity, the economic practicality of the method could be questioned. Moreover, the irrigation requirements of the flooded treatments were found to vary significantly between years, with variations by 40% to 50% (mostly occurred in the first part of the season). Taking as a reference the traditional flooding regime, irrigation requirements halved from 3,000 mm in the first season to 1,500 mm in the subsequent one. Variations were statically validated and they were attributed to a combination of abiotic and biotic factors including groundwater levels at the beginning of the season and soil-related aspects. Then, the extent of reductions in irrigation requirements when replacing traditional flooding with intermittent irrigation was investigated at the scale of an irrigation district (Chapter 5). Water requirements of the different crops (flooded rice, irrigated maize and irrigated poplars) were investigated over a 4-year period by the application of a distributed modelling approach (use of the SWAP model) and water balance equations. An empirical relationship between groundwater recharge (provided by percolation from irrigated fields) and the groundwater levels was thus identified. For the scenario of intermittent irrigated rice, a particular attention was paid to the role of the feedback between groundwater levels and irrigation applications. The importance of feedback effects was highlighted by developing a case study where groundwater is assumed invariant from the present state (no feedback) and a case study where the estimated irrigation requirements are congruent with the \u201cnew\u201d equilibrium state between groundwater levels and groundwater recharge. According to the estimates of the scenarios, irrigation withdrawals of the district decreased by around 65% when the feedback mechanism was neglected, while a reduction by 45% was observed when the feedback was accounted for. However, maintaining a 15-days turn for maize irrigation, like in the present state, was found to be inadequate for the full satisfaction of maize water requirements due to the decrease in the groundwater levels. Shortening the irrigation turn of maize to 10 days instead of 15 further decreased the estimate of the savings achievable with flush irrigated rice (reduction of irrigation requirements equal to 40%). In addition to implications on water balance terms, a specific attention was paid on the dynamics of dissolved organic carbon in relation to the water regime. Results of the study highlighted a strong link between the cycling of dissolved organic carbon and the reducing soil conditions resulting from field flooding (Chapter 6). Finally, the role of shallow groundwater table on the reduction of the irrigation requirements of lowland crops under intermittent irrigation was quantified via modelling simulations. Results showed a contribution of capillary rise up to 50% of the amount of water evapotranspirated by the crop (Chapter 7). In spite of the tendency to seek for general and global solutions, the research activities presented in the Thesis highlighted the difficulty to provide a univocal response to the question as to whether reductions of water consumptions in rice paddies should really represent the target to be reached regardless the specific context (Chapter 8)

Towards an integrated model to explain the factors affecting collaborative innovation processes – insights from the agrifood sector

This study explores the relevant factors to involve multiple actors who develop and implement new technologies to build sustainable agrifood systems. By examining 11 cases, we found that technological, organization, environmental, behavioural and interorganizational factors (all mentioned in current literature) as well as collaborative business models (not mentioned in current literature) affect such initiatives. Based on this, we propose an integrated model. The agrifood sector is one of the first sectors in which a collaborative transition unfolds. As other sectors are likely to undergo similar transitions in the near future, lessons learnt from the agrifood sector can guide these transitions

Laboratory determination of soil hydraulic conductivity for paddy soils: effects of different soil sample saturation methods

Saturated soil hydraulic conductivity (Ks) is a key factor in predicting vertical percolation fluxes, especially in paddy areas, where the peculiar agricultural practices adopted (especially flooding) lead to the formation of a dense and low permeable layer below the ploughed horizon. The core method, reproducing the Darcy\u2019s experiment over large undisturbed soil samples, is considered the reference method for Ks determination. To prepare soil samples for the analysis, two different soil saturation procedures can be adopted: vessel (AtmSat) and under-vacuum saturation (VacSat). A comparison between Ks values obtained by the core method after applying the two procedures is still missing in the literature, and is presented in this work. Five soil profiles were opened in three paddy fields located close to Pavia (Northern Italy) in the context of the WATPAD project (Fondazione Cariplo, grant n 2014-1260). In particular, five couples (replicates) of large undisturbed soil samples (H 15.0 cm, \uf8 14.6 cm) were collected from the less conductive layer (LCL) of each profile. Ks was determined by the core method after the saturation of soil samples with the two procedures (AtmSat and VacSat). To assess the reliability of the resulting Ks values, vertical percolation fluxes estimated by the Darcy\u2019s law (applied by considering lab-measured Ks) for the three paddy fields were compared to the same fluxes obtained as residual terms in the water balance equation applied to the fields. The main outcomes of the study, probably justified by the peculiar characteristics of the analysed soils (low-permeability layers of paddy soils), are the following: (1) the duration of flux experiments to reach the steady-state flux at which the convergence Ks value is obtained was generally very long (up to 25 days in the case of VacSat); (2) also the time needed to reach an evident trend in the measured flux was often long (even more than 20 hours); (3) AtmSat was found to provide reasonable results only for samples with a higher sand content, while, in case of low Ks, the underestimation was found to be up to 10 fold (probably because of air entrapment); (4) when vacuum was applied slowly, VacSat provided accurate estimations of Ks at the steady-state, while a fast vacuum application may produce a relevant hydraulic gradient within the core that can lead to damaging the sample; (5) when applying VacSat, the initial estimation of Ks was misleading (often more than 10 times higher than the convergence value), which can be explained by changes in the electrical diffuse layer (EDL) due to interactions between pore water and within-aggregate water, and/or to the release of biological gasses due to vacuum conditions; (6) in case of VacSat, pouring water under vacuum (instead of before the vacuum application) increased the time needed to reach the steady-state flux, but allowed a smoother convergence to the final Ks value and an earlier evidence of the trend. Due to the low number of samples analysed, outcomes need to be further investigated by considering a larger number of samples and other soil type

Water balance implications of switching from continuous submergence to flush irrigation in a rice-growing district

Studies conducted at the field scale report significant reductions in the irrigation requirements of ricewhen continuous submergence (CS) is replaced by less water-demanding regimes such as flush-irrigation(FI, i.e. intermittent irrigations of rice growing in non-submerged soils). However, the effects of theirextensive application in paddy areas with shallow groundwater is much less studied. We present a sce-nario analysis investigating the impacts on irrigation requirements induced by a shift from CS to FI inan irrigation district of Northern Italy where rice is the main crop, followed by maize and poplar. Thearea is characterised by a shallow water Table whose depth fluctuates between two meters (in winter)and less than 1 m (in summer). We applied a three-stage procedure, where we first analysed presentstate conditions using the SWAP (Soil, Water, Atmosphere, Plant) model to simulate irrigation deliver-ies and percolation fluxes. Then, we calibrated an empirical relationship between estimated percolationfluxes and measured depths to groundwater. Finally, we applied this relationship, in combination withthe SWAP model, to predict the variation of district irrigation requirements due to a widespread shiftfrom CS to FI. Results show that neglecting the feedback between groundwater recharge due to irrigationand groundwater depth led to overestimating the reduction of irrigation requirements of rice, whichdecreased from around 80% when no feedback was considered to around 60% when it was accountedfor. Moreover, increased groundwater depths resulted in higher irrigation requirements for maize withan estimated growth of more than 50% due to the need of shortening the irrigation turn. These resultsdemonstrate the importance of considering the impacts on the hydrological processes at larger scaleswhen planning the conversion of CS into more efficient field irrigation methods

Exploring scale-effects on water balance components and water use efficiency of toposequence rice fields in Northern Italy

Water use efficiencies (WUEs) between 20% and 60% are commonly reported for single rice paddies. When larger spatial domains are considered, higher WUE than minimum values observed for individual fields are expected due to water reuse. This study investigates scale-effects on water balances and WUEs of four adjacent rice fields located in Northern Italy and characterized by different elevations (A 45 B + C > D). Water balance terms for the paddies were quantified during the agricultural season 2015 through the integrated use of observational data and modelling procedures. Following a Darcy-based approach, percolation was distinguished from net seepage. Results showed net irrigation of about 2,700 and 2,050 mm for fields A and B, and around 640 and nearly 0 mm for C and D. WUE of A, B, C and D amounted, respectively, to 21, 28, 66 and >100%. Values for C and D were due to less permeable soils, to seepage fluxes providing extra water inputs and to the shallow groundwater level. When the group of paddies ACD was considered (B was not included since it was separated by a deep channel), net irrigation and WUE were found to reach 1,550 mm and 39%, confirming the important role of water reuses in paddy agro-ecosystems

Novel framework to improve water management adaptation under climate change scenarios

The impacts of projected climate change on freshwater resources are increasingly promoting the adoption of different approaches to water management, due to the likely occurrence of reduced water supplies and early-stage drought conditions in many river basins across Southern Europe. The traditional strategy to cope with water scarcity has largely relied on hard-path measures aimed at expanding the existing supply capacity by great investments in centralized, large-scale infrastructures such as dams and distribution systems. This approach is, however, becoming more and more unsustainable, giving way to effective soft-path solutions based on improved predictive capacities, optimal decision making and drought risk management. Given the need to ensure a more sustainable and efficient water management under current and projected scenarios, the study presents a novel decision-analytic framework to assist decision-makers in designing and assessing alternative soft-path measures in order to increase the adaptation of the system to a changing climate. The framework is being developed within the SO-WATCH project and it will be demonstrated on the Lake Como river basin (Italy) by implementing a four-stage procedure as follows: i) calibration and validation of a physical model comprising three sub-models simulating, respectively, the upstream catchment processes (TOPKAPI-ETH), the lake dynamics and water releases (DISTRILAKE) and the water balance in the irrigation system downstream the lake (IDRAGRA), ii) coupling of the hydrological model with a multi-agent systems model developed to reproduce human decisions and their effects on the system dynamics (e.g. dam operations and farmers practices), iii) definition and impact assessment of hydro-climatic and socio-technoeconomic scenarios supported by the calculation of drought indicators and iv) design and evaluation of soft-path measures to improve the efficiency of the water system. Preliminary results based on different climate change projections for the time period 2096-2100 (ensemble of different Global Climate Models, Regional Climate Models and Radiative Concentration Pathways as of the IPCC Fifth Assessment Report) reveal a general reduction of the lake inflows in spring and summer, with an increasing frequency of drought conditions under the business-as-usual scenario. In order to design the most effective soft-path measures, a newly developed index, the Transpiration Deficit Index (D-TDI), will be applied along with other commonly used indexes. D-TDI takes into account the transpiration deficit (i.e. difference between potential and actual transpiration) computed by the IDRAGRA model on a daily basis and cumulated over a selected time span and allows an effective identification of drought prone areas