Assessing yield and water use efficiency of Capsicum annuum L. cultivated in a greenhouse under different irrigation strategies

Several methodologies and techniques are available for irrigation management in protected environments. Despite the cultivation of vegetables in the greenhouse is largely present in the northeastern region of Brazil, not many research has been aimed at supporting growers for accurate irrigation management.

The objective of this study is to evaluate yield and irrigation water use efficiency of Capsicum crop cultivated in a greenhouse under different methods to define the daily irrigation depth, based on the soil water status and the atmospheric evaporative demand. Moreover, two different strategies to apply the estimated irrigation depths (single or double daily application) were also examined.

The experiment was carried out in a greenhouse in the Federal Rural University of Pernambuco (UFRPE), northeastern of Brazil (8° 01’ 07” S and 34° 56’ 53” W, altitude 6.50 m). Based on a completely randomized design, the experimental units were distributed according to a 4 x 2 factorial scheme with eight replications, with a total of 64 experimental units. Four methods to estimate daily irrigation water requirement were evaluated: two based on soil sensors (soil water content sensors EC-5, SWS, and tensiometers, TS), whereas the other two were based on the atmospheric evaporative demand (weighing lysimeter, WL, and Piché evaporimeter, PE). Moreover, the daily irrigation depths were applied with a single watering (at 8:00 am) or split into two applications (the half at 8:00 am and the half at 4:30 pm). The commercial yield of the examined crop was calculated through the relationship between the weight of fresh fruit and the area occupied by the plant.

The statistical analysis showed that the water use efficiency, the total water volume applied and the commercial yield of capsicum were significantly influenced by the method used to estimate crop water requirement, as well as the irrigation strategies. The total irrigation depth applied during the entire crop cycle resulted in equal to 509 mm, 678 mm, 716 mm, and 790 mm for treatments with WL, PE, SWS, and TS, respectively. The seasonal applied irrigation depths corresponded to an average daily crop water requirement ranging, according to the treatments, from 5.4 to 8.3 mm day^-1; these values are consistent for the examined crop cultivated under protected conditions. The highest yields of commercial fruits were obtained in the treatments in which the highest irrigation depth (SWS and TS) was applied. On the other hand, the highest values of water use efficiency were obtained in those treatments in which the irrigation depth was defined based on SWS and WL. Splitting the estimated daily irrigation depth in two applications promoted greater commercial productivity and water use efficiency (10.73 t ha^-1 and 1.60 kg m^-3) compared to a single application (8.14 t ha^-1 and 1.22 kg m^-3), with an increase of both variables of about 31%. These results evidenced that splitting the daily irrigation depth is a promising strategy to increase water use efficiency for vegetable crops in protected environments.