Viabilidad de la utilización de los indicadores de estado hídrico de la planta como herramienta para la programación del riego en nectarinos extra-tempranos

Abstract

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. El tema principal de la presente tesis doctoral es el estudio de la viabilidad de la utilización de los indicadores de estado hídrico del cultivo como herramienta para la programación de riego deficitario controlado de nectarinos tempranos. En esta línea se realizaron cinco ensayos: Utilidad del uso de las líneas de referencia de la fluctuaciones de diámetro de tronco y el potencia hídrico de tallo para la programación del riego de nectarino temprano Se realizó un estudio durante tres años en nectarino temprano (cv Flanoba). El objetivo fue estudiar líneas de referencia con las que estimar valores del potencial hídrico de tallo al mediodía (ΨT), tasa de crecimiento diaria de tronco (TCD) y máxima contracción diaria de tronco (MCD), en condiciones no limitantes de agua en el suelo a partir de diferentes variables meteorológicas. MCD presentó el mejor ajuste con el déficit de presión de vapor en el periodo comprendido entre las 11:00 y las 15:00 hora solar, periodo en el que la contracción del tronco era más rápida. Se discute el hecho de la baja correlación de MCD con ET0. Las ecuaciones eran diferentes para cada periodo fenológico pero estables en los tres años de estudio. Un nuevo enfoque para evaluar la sensibilidad de los indicadores de estado hídrico de la planta en nectarino temprano Se evaluó la sensibilidad de diferentes indicadores de estado hídrico de la planta (MCD, TCD, ΨT, conductancia estomática –Gs- y fotosíntesis neta –Pn-) durante la poscosecha de nectarinos tempranos (cv Viowhite). Se propuso un tratamiento control (TCTL), regado a 120% de la evapotranspiración del cultivo a fin de evitar condiciones limitantes de agua en el suelo, y un tratamiento deficitario (TD), regado al 50% de TCTL. Las mayores intensidades de señales (IS, relación de los valores de TD y TCTL) fueron alcanzadas por TCD, Gs y Pn (2.6, 3 y 2.9, respectivamente): Sin embargo, la sensibilidad (S) – calculada a partir de la relación entre IS y el coeficiente de variación (CV) de las medidas – fue mayor en ΨT y MCD (14 y 11.4 respectivamente) debido a que los CV fueron menores (11 y 14%, respectivamente). Un nuevo enfoque (S*) se propone para calcular la sensibilidad de los indicadores de estado hídrico de la planta, ya que el método estándar puede presentar valores altos de sensibilidad sin que dicho indicador presente diferencias entre tratamientos de riego. Establecimiento de un protocolo de programación del riego deficitario a partir de indicadores de estado hídrico de la planta en nectarino temprano El experimento realizado en nectarino temprano (cv Flanoba) se prolongó durante tres años (2009-2012). Se evaluaron diferentes metodologías de programación del riego llevadas a cabo en 3 tratamientos: un control (TCTL, regado sin condiciones limitantes de agua en el suelo); un tratamiento basado en la práctica habitual del agricultor (TFINC); y un tratamiento de riego deficitario controlado (TRDC), con el mismo riego que TCTL durante los periodos críticos del primer año y al 60% de TCTL durante la poscosecha de este mismo año. En los dos años posteriores, este tratamiento fue programado para mantener una IS de MCD con diferentes niveles de estrés (IS=1 durante los periodos críticos y IS =1.4 y 1.5 durante la poscosecha de 2010 y 2011, respectivamente). Los valores de IS obtenidos se ajustaron a los valores umbral durante gran parte del periodo de estudio. Los parámetros productivos no presentaron diferencias significativas entre tratamientos de riego. La disminución de agua aplicada en TRDC fue del 17, 15 y 37% respecto al riego aplicado en TCTL en los tres periodos de estudio. En contra, TFINC aplicó más agua (20 y 5% más que TCTL) durante los dos primeros años y un 10% menos que TCTL durante el tercer año. Las contracciones tempranas de diámetro de tronco son altamente sensibles al estrés hídrico de nectarinos La sensibilidad de diferentes indicadores de estado hídrico del cultivo fue evaluada durante dos años consecutivos. Los indicadores de estado hídrico estudiados fueron: ΨT, indicadores tradicionales derivados de las fluctuaciones de diámetro de tronco (MCD y TCD) y dos nuevos indicadores propuestos por primera vez en este trabajo (contracción temprana del tronco –EDS- y contracción tardía del tronco -LDS-). Las medidas se realizaron durante la poscosecha en un tratamiento control (TCTL, regado sin condiciones limitantes de agua en el suelo) y en un tratamiento de riego deficitario (TD, con déficit hídrico variable que promedió una reducción de riego de 37% respecto a TCTL). Los indicadores más sensibles fueron ΨT y EDS. IS fue mayor en EDS que en ΨT pero este último tenía CV menores. A diferencia de MCD, EDS presentó relaciones lineales con ΨT y mantuvo la sensibilidad al final del periodo de poscosecha. Efecto combinado del déficit hídrico y la carga productiva en nectarino temprano Durante tres años se evaluó el efecto del déficit hídrico y diferentes cargas productivas en el crecimiento vegetativo, el estado hídrico del cultivo, la producción y la calidad de la cosecha. Los parámetros productivos y de calidad no presentaron diferencias claras entre tratamientos de riego en ninguna de las cargas frutales estudiadas. Solamente la firmeza se vio reducida en TCTL cuando los niveles de carga frutal fueron bajos. Como era de esperar, TRDC presentó mayor eficiencia en el uso del agua (EUA) y menor crecimiento vegetativo. La relación entre la producción y el incremento anual de sección transversal de tronco se incrementó en TRDC respecto a los otros tratamientos conforme avanzaba el experimento, alcanzando diferencia del 53%. [ENG] This doctoral dissertation has been presented in the form of thesis by publication. The main topic of the present doctoral thesis is the study of the viability of the use of indicators of water status of the crop as a tool for the scheduling of regulated deficit irrigation of early nectarines. In this way, five trials were carried out: Feasibility of using trunk diameter fluctuation and stem water potential reference lines for irrigation scheduling of early nectarine trees A three-year experiment on early nectarine trees (cv. Flanoba) was carried out with the aim of studying the impact of environmental variables on the trunk diameter fluctuation parameters and the usefulness of the reference-lines derived from the relationship between different meteorological variables and plant water status indicators for sustainable irrigation scheduling. Plants were drip-irrigated and submitted to non-limiting soil water conditions. Measurements of stem water potential at midday (Ψstem), trunk daily growth rate (TGR) and maximum daily trunk shrinkage (MDS) were related with meteorological variables. MDS presented the best fitting line-regressions with both the average air temperature and vapour pressure deficit during the period 11.00–15.00 h solar time, since the most important fraction of trunk shrinkage occurred during that period of time, reaching 74% of MDS (on average over the three years studied), and sometimes 90%. Despite the continuous trunk growth of the trees during the experimental period and slight difference in crop load, inter-annual differences were not observed for the three reference lines obtained in any given year (fruit growth, early and late postharvest period). A new approach to ascertain the sensitivity to water stress of different plant water indicators in extra-early nectarine trees The sensitivity to water stress of different plant water indicators was evaluated during the late postharvest period of extra-early nectarine trees growing in a commercial orchard and submitted to two irrigation treatments: (i) a control (TC), irrigated at 120% of crop evapotranspiration, and (ii) a water deficit treatment (TD), irrigated at 50% of TC. The plant indicators studied were: MDS, TGR, Ψstem, leaf conductance (Gs); and net photosynthesis (Pn). Although the highest signal intensity (SI) values -the ratio of deficit irrigation treatment values to control values- were reached by TGR, Gs and Pn (2.6, 3 and 2.9, respectively), the sensitivity (S) values calculated as the ratio of SI to coefficient of variation (SI CV−1) were higher in Ψstem and MDS (14 and 11.4, respectively), since their CV values were the lowest (11 and 14%, respectively). A new approach (S*) is proposed to calculate the sensitivity of the plant water indicators, since the standard method can result in high sensitivity values without identifying differences between irrigation treatments. While S is more influenced by the CV values, S* would be influenced by both the SI and CV values. Implementing deficit irrigation scheduling through plant water stress indicators in early nectarine trees A three-year experiment on early nectarine (cv. Flanoba) trees was carried out with the aim of increasing water use efficiency through applying a sustained irrigation treatment. Experiments compared irrigation scheduling using conventional micrometeorology (110% of crop evapotranspiration, ETc) as a control treatment (TCTL), a treatment based on the normal practice of the farmer (TFINC) and a regulated deficit irrigation treatment (TRDI), which involved irrigating the crop at the same level as the control (TCTL) during the critical periods of the first year (second rapid fruit growth period and 2 months after harvest) and at 60% TCTL during postharvest. In the last two years (2010 and 2011), the irrigation was scheduled 20 to maintain SI of the maximum daily shrinkage of the trunk at different water stress levels depending on the phenological stage SI = 1.0 (non-water stress) and SI = 1.4 (moderate water stress). Most of the time that irrigation scheduling was based on MDS SI, this parameter varied only slightly around the pre-established threshold values. The information given by the stem diameter sensors and stem water potential (Ψstem) gave -1.5 MPa and MDS SI 1.5 as threshold values not to be exceeded during postharvest, since MDS and Ψstem SI values were only linear down to 1.5. The water saved amounted to 17, 15 and 37%of the amount used in the control in the three seasons, respectively. In contrast, the TFINC treatment applied more water (about 20 and 5% more than TCTL) during the first 2 years, and 10% less than TCTL during the third season. Early morning fluctuations in trunk diameter are highly sensitive to water stress in nectarine trees The sensitivity to water stress of different plant water status indicators was evaluated during two consecutive years in early nectarine trees. Measurements were made post-harvest and two irrigation treatments were applied: a control treatment (CTL), irrigated at 120 % of crop evapotranspiration, and a deficit irrigation treatment, that applied around 37 % less water than CTL during late postharvest. The plant water status indicators evaluated were Ψstem) and indices derived from trunk diameter fluctuations (MDS and TGR) and early daily shrinkage measured between 0900 and 1200 hours solar time (EDS), and late daily shrinkage (LDS) that occurred between 1200 hours solar time and the moment that minimum trunk diameter was reached (typically 1600 hours solar time). The most sensitive [highest ratio of signal intensity (SI) to noise] indices to water stress were Ψstem and EDS. The SI of EDS was greater than that of Ψstem, although with greater variability. EDS was a better index than MDS, with higher SI and similar variability. Although MDS was linearly related to Ψstem down to -1.5 MPa, it decreased thereafter with increasing water stress. In contrast, EDS was linearly related to Ψstem, although the slope of the regression decreased as the season progressed, as in the case of MDS. Further studies are needed to determine whether EDS is a sensitive index of water stress in a range of species. Combined effects of deficit irrigation and crop level on early nectarine trees A three-year long experiment was implemented in an early nectarine (cv. Flanoba) commercial orchard to evaluate the effects of deficit irrigation and different crop levels on vegetative growth, plant water status, and fruit yield and quality. Three irrigation treatments were assessed: (i) control, (TCTL); (ii) normal practice of the farmer (TFRM); and (iii) regulated deficit irrigation (TRDI). Besides, during the last two seasons, the interactions between TCTL and TRDI were studied at five different crop levels, which were obtained by controlling the distance between fruits left on the branches: from very low (16 cm between fruits) to very high (8 cm between fruits). Crop water use efficiency (WUE) of TRDI was higher than in TCTL and TFRM, increasing by around 25% in 2010 and 2011, and around 74% the final year. Interestingly, TFRM increased the WUE from the first year by more than 30%. The yield/annual increase in trunk-cross-sectional area (TCSA) ratio increased in TRDI with respect to the other treatments as the experiment progressed, reaching differences of 53%. Vegetative growth was clearly sensitive to deficit irrigation with a strong correlation between the increase in the water stress integral obtained by midday stem water potential (Ψstem) and the reduction in TSCA. In contrast, fruit production and quality were not affected by water deficit. As regards the interaction between crop level and water deficit, fruit firmness was the only fruit quality parameter studied that presented significant differences, the highest values corresponding to the fruits from TRDI trees and the lowest crop level.