Core Ideas
Different growth stages of drip‐irrigated sugar beet can bear different water deficit level.
The canopy development stage is the most water‐sensitive period of the sugar beet.
Regulated deficit irrigation could increase beet yield and reduce the consumption of water resources in arid land.
ABSTRACT
The shortage of water resources promotes the development of water saving irrigation in arid land. Regulated deficit irrigation (RDI), as one of the water‐saving irrigation technologies through applying a certain amount of water stress to the crops to promote the distribution of the photosynthate of crops to the needs of the tissues and organs, can save water and may increase yield. Our study evaluated the effect of the RDI on the sugar beet (Beta vulgaris L. cv. Beta356). Seven irrigation treatments were applied based on the growth stages of sugar beet (canopy development, storage root development, and sugar accumulation) and water deficit levels (30, 50, and 70% of field capacity [FC]). The yield, quality, sugar yield, irrigation water use efficiency (IWUE), and agronomic physiological traits of sugar beet were evaluated. Moderate water deficit (50% of FC) during canopy development increased sugar yield by 27% compared with the control (70% of FC during the whole growth stages). Severe (30% of FC) water deficit increased sugar yield by 45% during storage root development, and by 55% during sugar accumulation. The RDI during canopy development and storage root development inhibited leaf growth but did not affect yield. Malondialdehyde content and relative conductivity increased significantly when soil water content dropped to the irrigation threshold levels (i.e., 30% and 50% of FC) before rehydration during canopy development. After rehydration, there were significant increases in peroxidase activity and proline content (indicators of antioxidant defense and osmotic stress). Our results indicated that RDI increased yield at 30% and 50% of FC during three growth stages (canopy development, storage root development, and sugar accumulation) of sugar beet, which reduced irrigation water requirements. RDI could be applied as a strategic action for crop sustainability and water saving in arid land.
The relationship between the leaf nitrogen content (LNC) and hyperspectral remote sensing imagery (HYP) was determined to construct an estimation model of the LNC of drip-irrigated sugar beets, aiming to provide supports for the in-time monitoring of sugar beet growth and nitrogen management in arid areas. In this study, a field hyperspectrometer was used to collect the leaf reflectance at the 350–2500 nm for each treatment on the 65th, 85th, 104th, 124th, and 140th day after emergence, and the LNC and leaf chlorophyll content (CHL) of sugar beets were also determined. The spectral characteristic parameters were selected to construct the vegetation indices. The LNC estimation model using HYP as the independent variable (HYP-LNC), and that using CHL and HYP as the independent variables (HYP-CHL-LNC), were compared. The results shows that the HYP-CHL-LNC models had a better linear relationship and a higher fitting accuracy than the HYP-LNC models.
Background: Limiting factors in photosynthesis includes stomatal limitations, mesophyll limitations, and biochemical limitations, and mesophyll limitations are the leading limiting factors in photosynthesis as shown by many studies. Mesophyll conductance (gm) exerts significant influences on the photosynthetic capacity of crops, playing a decisive role in mesophyll limitations. The limiting factors in photosynthesis for many crops under water deficit and rehydration conditions have been studied, but few studies of this kind on sugar beet can be found. Results: Our study aimed to analyze the dynamic changes of mesophyll limitations, stomatal limitations, and biochemical limitations by
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