Analysis of lettuce evapotranspiration across soil water

Abstract

In this study, we evaluated the lettuce accumulated evapotranspiration (ET) across four levels of irrigation, using a nonlinear mixed‐effects model. The plants were grown in protected environments and monitored over 23 consecutive days. When the moisture of the substrate in the vessels reached 50% of their maximum retention capacity, the water levels were elevated according to four treatments: W 1 = 62.5 %, W 2 = 75.0 %, W 3 = 87.5 %, and W 4 = 100.0 %. The model appeared to provide a good fit to the data and showed that the estimates of the maximum amount of accumulated ET were similar for the three treatments with soil water deficit and lower for W 4. The results of the study supported the idea that optimization of the ET of lettuce plants could be achieved through irrigation with deficit, also indicating that the economical use of water was the most efficient way to boost agricultural production. Recommendations for resource managers The continued growth of the world population will result in a decrease of quality and availability of water and also an increase in demand for food. Therefore, sustainability will depend on high agricultural productivity with rational use of water. Considered the most efficient technology for boosting agricultural productivity, irrigation is also the largest water consumer in the world. With any kind of irrigation in the vegetable production area, the water intake for the plants must be treated with great caution. Both a lack or excess in water can decrease plant productivity. The amount of water available in the soil should be enough to maximize production. It is shown that high levels of irrigation are not necessary for this. It is important to balance the amount of irrigated water for an optimal level, in order that the production has its the production is maximized and valuable water resources are not wasted.

Modeling Accumulated Evapotranspiration Over Time

“…ϕ 1 is the inferior horizontal asymptote which gives the accumulated ET value when t !À∞. Biologically, this parameter does not have a consistent interpretation, but it is important in the fitting because it ensures the accumulated ET,in times close to zero, to be very small [2,3]. ϕ 2 is the superior horizontal asymptote and gives the accumulated ET value when t !…”

“…It is known that the production variables present a positive correlation with the amount of total evapotranspired water throughout the plants' life cycle. That is, the larger the total evapotranspiration water, the higher the values of the production variables [2,3]. Hence, the inflection point can indicate the proximity of the harvest day.…”

“…Studies in which the response variable is observed repeatedly throughout time in the experimental units are called longitudinal studies. This kind of work is common in agriculture when analyzing the increase or decrease of the response variable over time [2,3,[5][6][7][8].…”

“…Consider ET ij as the accumulated ET at the j situation, for plant i, with j ¼ 1, 2, ⋯,n i e i ¼ 1, 2, ⋯,N, where n i is the number of observations for the i-th plant and N is the total number of plants. The nonlinear 4PL mixed effect model can be expressed by [2,3] (3)…”

“…For these species, the accumulated ET over the plant cycle is directly related to its productivity. In other words, the greater the accumulated amount of evapotranspirated water, the greater the quantity of the production variables as shoot fresh and dry matter masses, number of leaves, and leaf area [2,3].…”