Treatments related to planting spacing were defined according to
the current recommendations of cotton crop productive system in
Mato Grosso, Brazil. Sowing was held on May 1, 2015, with IMA
5675B2RF cotton seeds and 8 plants per linear meter. Plant
densities, according to crop spacing, were, as follows: E0.4 -
225,000 plants ha-1
; E70 - 128,571 plants ha-1
and E100 - 90,000
plants ha-1
.
Soil profile moisture was continuously observed from 06/06/2015
using Diviner 2000®model (Sentek Pty Ltd, Australia) capacitance
probe, with readings at every 0.1 m. For moisture readings, nine
access tubes were installed, three for each planting spacing, at 1 m
deep in default random plots with intermediate irrigation (90% ETc)
in each spacing. Of the three access tubes for each spacing, one
was installed in the row-crop, and the other two between the lines
(on opposite sides). Soil moisture was a result of the average of the
three measuring points.
At 142 days after sowing, experiment harvesting was conducted,
and fruits and stems were separated. The collected material was
weighed and dried in an oven with forced air at 65°C for 72 h.
Subsequently, it was weighed to determine seed cotton and shoot
dry matter yield (stem + fruit). Thus, seed cotton (WUEY) and shoot
dry matter (WUEDM) water use efficiency for yield were calculated.
Efficiency was calculated through the ratio between the interest
variable and the total water amount supplied to the crop (rain +
precipitation).
Water use efficiency for yield and shoot dry matter variables were
statistically assessed through response surface analysis, using the
SigmaXL® 7.0 software tool to the maximum significance level of
5% for all statistical tests.