Automatically controlled deficit irrigation of lettuce in “organic potponics”

David Da Cunha Valença,Camila Ferreira De Pinho,Daniel Fonseca De Carvalho,Fernanda Reinert,Ricardo Antunes Azevedo,Leonardo Oliveira Medici

doi:10.1590/1678-992x-2016-0331

David Da Cunha Valença, Camila Ferreira De Pinho + Show 4 more

Open Access

https://doi.org/10.1590/1678-992x-2016-0331

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Abstract

Concerns with water crisis involve all sectors of society and irrigated agriculture remains the main water consumer. This study evaluated an agricultural production system for lettuce cultivation in greenhouse, “organic potponics”, to economize water and manure use, using a Simplified Irrigation Controller (SIC), based on soil matric potential monitoring. Five irrigation volumes were evaluated in pots with 4.8 L, fertilized with 200 g of vermicompost. One of the volumes was controlled with the SIC. The other volumes represented 130, 80, 60 and 33 % of that controlled by the SIC and all treatments received water at the same time. Shoot fresh weight, head diameter and stomatal conductance (gs) increased linearly with irrigation volumes. For shoot dry weight, number of leaves and water use efficiency (WUE), the regression was quadratic with maximum values at 126, 114 and 83 %, respectively. Leaf relative water content did not show variation among treatments and changes in some fluorescence parameters (Reo/RC, Sm, N and φR0) were much more remarkable to drought compared with the FV/ FM ratio, one of the most commonly used stress indicators. The data indicated a tradeoff between WUE and plant growth thus the economic values of water and lettuce should be taken into account to indicate the best SIC irrigation volume. Organic potponics is promising and should be further improved to save on water, labor and fertilizer use.

Highlights

The economy in water and nutrients for plant cultivation will depend on the efficiency of the sensorbased controllers for irrigation to avoid either drainage or drought, which causes waste of water or growth limitation, respectively (Cia et al, 2012; Boaretto et al, 2014; Medici et al, 2014)
Agronomic traits The application of different irrigation volumes induced a linear shoot fresh weight gain and the same behavior happened to the diameter of lettuce heads, while for shoot dry weight and leaf number, the quadratic regression model revealed significance by the analysis of variance (Table 1)
Soil moisture Soil moisture data (Table 1) obtained in this study for the volume of 100 % Simplified Irrigation Controller (SIC) adjusted to 6 kPa were between the values presented for the tensions of 3 and 9 kPa obtained with the use of SIC in the production of Figure 2 − The effect of different volumes of applied irrigation water using SIC on chlorophyll content measured on the 15th day after transplanting

Summary

Introduction

The economy in water and nutrients for plant cultivation will depend on the efficiency of the sensorbased controllers for irrigation to avoid either drainage or drought, which causes waste of water or growth limitation, respectively (Cia et al, 2012; Boaretto et al, 2014; Medici et al, 2014). The lack of such controllers at a low cost and ready to be used in commercial conditions may explain why precise irrigation is rarely used for growing plants in pots, as most use timers or manual control (Montesano et al, 2016). The organic potponics irrigation delivers water only, using SIC, while solid manure is directly applied to the substrate in the pots

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