Figure 1.
Total root length of maize plants during the whole growth period in response to N fertilization in three consecutive years.
In 2007, the whole root system was excavated with a soil volume of 28 cm×35 cm and a depth of 40 cm. In 2008 and 2009, root systems were excavated within a soil volume of 28 cm×35 cm and a depth of 50 cm (2008) or 60 cm (2009) with 10 cm increments. The bars represent the standard error of the mean, n = 4. TDAT means N top dressing after tasseling. The total amount of N applied in TDAT treatment was 230 and 250 kg ha−1 in 2007 and 2008, respectively. TDBT means N top dressing before tasseling. The total amount of N applied in TDBT treatment was 395, 250 and 250 kg ha−1 in 2007, 2008 and 2009, respectively, and is the same in the following figures.
Figure 2.
Length of embryonic roots and different whorls (1st to 7th orders) of nodal roots of maize plants in response to N fertilization in 2007.
Arrows indicate the time of tasseling. Whole root systems were excavated with a soil volume of 28 cm×35 cm and a depth of 40 cm, and then separated into embryonic roots and different whorls of nodal roots. The bars represent the standard error of the mean, n = 4.
Figure 3.
Total root length of maize plants in each soil layer at different growth stages in response to N fertilization in 2008.
Root systems were excavated within a soil volume of 28 cm×35 cm and a depth of 50 cm with 10 cm increments. The bars represent the standard error of the mean, n = 4.
Figure 4.
Total root length of maize plants in each soil layer at different growth stages in response to N fertilization in 2009.
Roots were excavated within a soil volume of 28 cm×35 cm and a depth of 60 cm with 10 cm increments. The bars represent the standard error of the mean, n = 4.
Table 1.
Shoot dry matter accumulation (t/ha) in different growth periods, final shoot dry weight (DW) and grain yield (t/ha) of maize plants supplied with different N rates in three years.
Table 2.
Shoot N accumulation (kg/ha) in different growth periods and the final shoot N content of maize plants supplied with different N rates in three years.
Figure 5.
Soil mineral nitrogen (Nmin; NH4+-N+NO3−-N) in the 0–90 cm soil profile in response to N fertilization in 2007.
The soil samples were obtained using the soil auger method at the same time in each plant harvest. The bars represent the standard error of the mean, n = 4.
Figure 6.
Temporal and spatial distribution of soil mineral nitrogen (Nmin; NH4+-N+NO3−-N) in the 0–50 cm soil profile in response to N fertilization in 2008.
The soil samples were obtained by excavating soil layers within a soil volume of 28 cm×35 cm and a total depth of 50 cm with 10 cm increments at each time after shoot harvest. The bars represent the standard error of the mean, n = 4.
Figure 7.
Temporal and spatial distribution of soil mineral nitrogen (Nmin; NH4+-N+NO3−-N) in the 0–60 cm soil profile in response to N fertilization in 2009.
The soil samples were obtained by excavating soil layers within a soil volume of 28 cm×35 cm and a total depth of 60 cm with 10 cm increments at each time after shoot harvest. The bars represent the standard error of the mean, n = 4.
Table 3.
Ratio of DW and N uptake presilking and total accumulation in maize plants with different N treatments in 2007, 2008 and 2009.