Agriculture Reference
In-Depth Information
Table 4 shows data for the same treatments regarding yield (Y), its components, and
seasonal evapotranspiration (ET). This table also includes the data on water use efficiency
calculated as the Y/ET relationship.
Table 4. Yield, its components, seasonal evapotranspiration (ET) and water use
efficiency (WUE) observed on the control treatments in loam and clay soils.
soil loam
clay
plant/m
2
18
a
18
a
n° pod/plant
44
a
41
a
n° grain/pod
2.6
b
2.7
a
1000-grain weight (g)
164
a
161
a
grain yield (g/ m
2
)
334
a
311
a
straw (g/m
2
)
261
a
257
a
seasonal ET (mm)
410
a
430
a
WUE (kg/m
3
)
0.81
a
0.72
a
The predawn leaf-water potential shows an increase, after each irrigation, and then
decreases during the irrigation interval. Differences in pre-dawn leaf-water potential between
the two soil types can be observed, but these differences do not show a clear trend. Soil
texture did not show a clear effect on the predawn leaf-water potential.
According to Mastrorilli et al. (1993), the soybean stomatal conductance is not affected
until the pre-dawn leaf-water potential exceeds the threshold of -0.4MPa. The two control
treatments had, therefore, optimal water conditions during the vegetative cycle, except for the
13 days between 30 and 43 DAS.
Between the emergence and the 55 DAS, the observed values per plant of leaf surface
and dry matter are perfectly identical in loam and clay soils. After that, the leaf surface and
the dry matter observed did not show a clear trend. Soil texture did not show a clear effect on
growth in leaf surface and dry matter either.
The values measured for loam and clay soils for yield in straw and grain are not
significantly different. The same can be observed, in general, for the yield components
measured for the two soil types.
In loam and clay soils, the measured seasonal evapotranspiration (ET) and the values
calculated for water use efficiency are not significantly different.
Van Hoorn et al. (2001) determined the nitrogen balance for control treatments in loam
and clay soils. This determination later allowed for the estimation of the quantity of organic
nitrogen (the sum of the nitrogen fixation and the nitrogen derived by the transformation of
organic matter). These quantities are equivalent to 23.5 and 21.2 g/m
2
in loam and clay soil
respectively. These values are very similar and represent 69% and 66% of the nitrogen
absorbed by the plants cultivated in loam and clay soil, respectively.
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