EFFECTS OF SOIL TEXTURE AND SOIL SALINITY ON THE PLANT WATER RELATIONSHIP, GROWTH, YIELD AND WATER USE EFFICIENCY OF THE SOYBEAN CROP - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 25

• In the absence of salt stress, is soybean sensitive to the soil texture?

• In the presence of salt stress, is soybean tolerance to soil salinity modified by the soil

texture?

•

If so, how can the change in tolerance to salinity be interpreted in relationship to the
soil texture?

II- M ATERIALS AND M ETHODS

The study was conducted in Bari (southern Italy). The climate is characterised by hot dry
summers, with maximum air temperature sometimes higher than 40 C° and minimum relative
air humidity often less than 20%.

1- Crop

Soybean (Glycine max, Talon variety) was grown from 18 July 1995 until 16 October
1995. The crop was sown at a density of 45 seeds per lysimeter, reduced to 25 plants at the
two-leaf stage and 18 plants at harvest time because of successive samplings. Fertilising was
done at the rate of 250 kg P 2 O 5 /ha at 23 D.A.S.(Days After Sowing) before the second
irrigation and at the rate of 50 kg N/ha, divided over three dates at 27, 48 and 65 d.a.s, always
two days after irrigation.
The main phenological stages observed during the crop cycle were: plant emergence (12
D.A.S.), the beginning of anthesis (40 D.A.S.), the beginning of pod formation (52 D.A.S.)
and harvest (90 D.A.S.).

2- Set -Up

The set-up consisted in 30 cylindrical lysimeters of reinforced fibreglass with an internal
diameter of 1.2 m and a depth of 1.2 m. A layer of coarse sand and gravel, 0.10 m thick, was
overlaid by a repacked soil profile of 1 m. At the bottom of the lysimeter, a pipe serving as a
drainage outlet connected the lysimeter to a drainage reservoir. A 15 lysimeter block was
filled with loam, and a second block with clay. Table 1 presents the physical properties of the
soil after the lysimeters were filled.
The set-up was covered at a height of 4 m by a sheet of transparent plastic. This sheeting
excluded any rain, but also attenuated solar radiation by up to 10 %.
The lysimeters were irrigated with three different qualities of water: the control treatment
with fresh water (C) containing 3.7 meq Cl/l and an electrical conductivity (EC) of 1.1 dS/m,
and two saline treatments (15 and 30) containing 15 and 30 meq Cl/l and an EC of 2.3 and 3.6
dS/m respectively, obtained by adding equivalent amounts of NaCl and CaCl 2 to fresh water.
For each water quality, five lysimeters were available. Table 2 presents the chemical
composition of the waters.