Is the crop evapotranspiration rate a good surrogate for the recommended irrigation rate?

Numerous methodologies and technologies of varying levels sophistication for irrigation rate determination have been developed over the years to address limited water availability optimize productivity. Crop evapotranspiration is currently evaluated mostly according FAO56 approach, which has augmented in recent with remote sensing correlated plant indices. When no other information available, does give an indication optimal some circumstances. However, many circumstances discussed this short communication, replenishing soil crop either substantially overestimates or underestimates optimal, physiological (agronomical/economical) rate. Consequently, note raises doubts opens a discussion about extensive reliance on (potential actual) recommending (irrigation dose/irrigation amount). Il été développé nombreuses méthodologies et de différents niveaux pour déterminer le taux d'irrigation au fil des ans faire face à la disponibilité limitée l'eau optimiser productivité l'eau. Aujourd'hui, l'évapotranspiration d'un couvert est évaluée principalement selon l'approche FAO56, qui renforcée ces dernières années par télédétection d'indices végétaux corrélatifs. Quand aucune autre n'est disponible, d'évapotranspiration donne une du dans certaines circonstances. Cependant, autres circonstances évoquées cette brève fait reconstituer sol surestime ou sous-estime considérablement physiologique (agronomique/économique). Par conséquent, permet douter ouvre sur que évalué (potentiel réel) largement utilisé recommander un (dose d'irrigation/quantité d'irrigation). The word ‘optimal’ ‘optimal irrigation’ (or ‘recommended’ ‘recommended irrigation’) can several meanings. Physiologically, may perhaps be related (Ir) that results maximum photosynthesis biomass production. Agronomically, yields at harvest time, economically, one maximizes profits grower corresponds another objective function accounts for, example, also reduced environmental harms. Long-term data sets daily Ir are used determining peak requirements designing system capacity, current short-term estimates needed day-to-day scheduling. Seasonal required mainly regional national resources management (at resolution present discussion, most arguments partly interchangeable apply both seasonal [ET] rates). Three general control strategies (Romero al., 2012): (1) open loop (no control) measurements modify inputs decisions taken priori based heuristics, expert knowledge model system; (2) feed forward (a particular open-loop case) known estimated values future disturbances compensate their effects advance (3) feedback using consequences previous actions from relevant sensors calculate next action. In context dose/application depth), these as follows: calendar scheduling given, previously determined, tables (/charts) (Fessehazion 2014; Hill & Allen, 1996); coefficients real-time meteorological evaluating potential (Allen 1998, Pereira 2021a, 2021b; approach) proxy status indicators (Campbell 1982; Eldeiry 2016; Goldhamer Fereres, 2001; Jimenez 2020; Jones, 2004; Möller 2007; Naor, 2006). Over years, hybrids main three proposed (Kassing McCarthy 2013). For decades, approach 1998) Penman–Monteith equation (Monteith, 1965) reference (ET0) coefficient (Kc) characterizes targeted served worldwide standard actual by researchers, extension workers irrigators. This being continuously updated new types (Pereira 2015, 2021b). evaluate rates aid remotely sensed (and soil-adjusted) indices (Glenn 2011; Hunsaker 2003; Rozenstein 2018; Serra 2016), lysimeter studies (Evett López-Urrea Ohana-Levi Okechukwu Mbajiorgu, 2020) developed. purpose communication neither comprehensive review nor manual determine Its raise following content not provide information, it merely aims reminding us the, slightly forgotten, fundamentals implications recommended different Major problems (Equation 1) are: It extremely difficult impractical Dp, Cr ?SW components field 2012; Green Clothier, 1999; Noory 2021) (as opposed high-priced weighing lysimeters; Evett 2020); ETa, obviously dependent vary Ir, is, manipulating will affect (usually same direction) start indefinite, converging, iterative process; nothing indicates what respect ‘optimal’. question asked whether such assumed steady-state conditions 2) indeed prevail close Dp small compared ETa (to further Section 5 below). motivation (ETa), rate, probably stems high correlations between economic (relative potential) (de Wit, 1958; Doorenbos Kassam, 1979; Steduto 2012). Nevertheless, given day, constrained conditions, proportional ET0, account responses various crops climatic (grass alfalfa) (characterized e.g., grapevine 2020, who showed ET0 was strongest predictor ETc). Additionally, transferability adjustment local challenging 2015). subject under note. here FAO56's otherwise (ETc) (ETa) good surrogate (Ir = ? ET). An obvious is: If we do ability accurately assess LR Ief, why so important put much effort into assessing Equation (10)'s ‘required net rate’ (Ir)? words, there benefit more accurate than balance dictate (LR). addressing criteria optimizations outlined introduction, especially third, economical one, ratio varies two extreme scenarios. close-to-steady-state (on time scale) circumstances, even if intentional salt leaching operated, deep percolation (Dp, substantial cannot disregarded (Kanety Sperling, Transpiration root uptake (almost completely) stop night, while continues flow downwards, driven gravitational capillary forces. morning, when transpiration resume, only fraction volume flows back upwards due action but against Mind addition resistance conduct emitter roots, plant–atmosphere constitutes resistance, series resistance. Thus, increasing increase decreasing increments, ETa/Ir upon level out enough determined solely (Figure 1c). Unavoidable excessive beneficial maintaining content, low solution salinity proper nutrient concentrations fertigation practiced. Regarding aspects, solute course, desirable. With debate note, clear independent (Ir); reasonable agronomic range rates, factors increases Obviously, limit exceed ETc because solar energy (sometimes horizontal advective flux) limits evaporation. contrasting above 5.1 scenario) likely systems able use available held fine-texture holding capacity. Namely, negligible (Dp) smaller comparison (Kukal Irmak, Kurtzman, 2021; Stone 1996). Sometimes (unfortunately percentage arable land globally) shallow ground present, intensifies importance source roots: first, direct effect groundwater rise towards roots (Cr), second, phreatic surface (water table) reduce rainfall) efficiency (supplemental) 2a,b). without (indicative yield rain-fed cultivation). Then, still exceeds it, > whereas lower high, < Ir. means that, reasonably assuming continuous relationship, 2c). Similar concern raised 2, ‘optimal’? 1), higher evapotranspiration, 2), questionable efforts research practice always justified. Good status, (less negative) tissues, phenological (growth) stages assure vigour, adequate satisfactory restraining vegetative growth inducing formation reproductive, edible organs often require stress. Moreover, generally, where scarce sensible wastefully effectively irrigating larger areas stressing less critical stages), ‘deficit (Fereres Soriano, Lopez 2017; Rodrigues Pereira, 2009; Sepaskhah Akbari, 2005). single, generic strategy scheduled along seasons crops. mentioned above, (clayey) soils possess buffering variation storage roots) response manipulation rates. take few days improve exceeding weeks induce stress longer takes dry internal drainage slower infiltration. These shifts, shorter wetting drying, constitute reason different-than-evapotranspiration ? ETa). author expresses his gratitude editor-in-chief, Prof. Jiusheng Li, reviewers constructive comments. No available.