Growth conditions, plant material, crop management, and
experimental design
The trial was conducted in a greenhouse located at Paraje Águilas Bajas,
Santa María del Águila, Almería, Spain (36°47ʹ39″N 2°46ʹ32″W). The
greenhouse was composed of polycarbonate walls and a roof made of
trilaminated low-density polyethylene (LDPE) film (200 μm thickness)
with ~60% spectral transmittance in the
photosynthetically active radiation (PAR) region. The greenhouse was
unheated and passively ventilated with lateral side panels and flap roof
windows. It had an east-west orientation and a north-south crop row
alignment. The air temperature and relative humidity (RH) inside the
greenhouse were in the ranges of 12–32 °C and 50–70%, respectively.
Transplants of the sweet pepper (Capsicum annuum L.) hybrid
‘SV1204PB’ (Seminis, Montornés del Vallés, Barcelona, Spain) at the 4–5
true-leaf stage were planted in “Enarenado” sandy soil commonly used
in greenhouse production in Almería. The planting date was 19 July 2017
and the planting density was 2.0 m-2. The soil
composition was 13.5% (w/w) clay, 72.8% (w/w) sand, and 13.7% (w/w)
silt. Its pH was 7.52, its organic matter content was 0.71%, and its
total nitrogen, available phosphorus, and exchangeable potassium were
690 mg kg−1, 51.4 mg kg−1, and 321
mg kg−1, respectively. Aerial drip irrigation was
used. The in-line emitters were positioned at 0.30-m intervals and the
emitter flow rate was 3.4 L h-1. Preplant fertiliser
was broadcast at 90 kg·ha-1 P, 120
kg·ha-1 K, and 15 kg·ha-1 Mg and
incorporated into the soil. Additional fertiliser in the form of
K2SO4 (80 kg·ha-1 K)
was applied through the drip irrigation system. Nitrogen was applied via
fertigation in the form of 27% NH4NO3soluble fertiliser starting 10 d after transplanting until day 83. The
total N supply was split into ten weekly dressings. Powdery mildew
caused by Leveillula taurica was controlled by three foliar
applications of penconazole (Topas 10EC; Syngenta, Madrid, Spain) at the
label-recommended rate. Aphids and spider mites were controlled by one
foliar application each of imidacloprid (Confidor 200 SL; Bayer Crop
Science, Valencia, Spain) and fenpyroximate (Miro; Bayer Crop Science,
Valencia, Spain), respectively. Bumblebees promoted flower pollination.
Weeds were controlled by hand hoeing. The control and microbial-based
biostimulant treatments were compared in a randomised block design with
four replicates for a total of eight experimental plots. The
microbial-based biostimulants were applied through a drip irrigation
system. The first application was made at 15 d after transplanting (DAT)
(3 August 2017) at the rates of 1×10-6 spores
ha-1 Rhizoglomus irregularis BEG72 and
1×10-6 spores ha-1Funneliformis mosseae BEG234 in the form of 2.0 kg
ha-1 Team Horticola (Agrotecnologías Naturales, S.L.,
Tarragona, Spain) plus 1×1012 CFU
ha-1 Trichoderma koningii TK7 in the form of
1.0 kg ha-1 Condor Shield (Agrotecnologías Naturales,
S.L., Tarragona, Spain). The second treatment was applied 43 DAT (31
August 2017) at the rate of 5×1011 CFU
ha-1 Trichoderma koningii TK7 as 0.5 kg Condor
Shield (Agrotecnologías Naturales, S.L., Tarragona, Spain). Each
experimental plot was 30 m2 and contained 60 plants.