| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Dep. of Plant Nutrition, China Agricultural Univ., Beijing, 100094, P. R. China
b Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078, USA
c Institute of Plant Nutrition, Univ. of Hohenheim, 70593 Stuttgart, Germany
* Corresponding author (chenxp{at}cau.edu.cn)
Received for publication May 23, 2005.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Abbreviations: ANOVA, analysis of variance • NUE, nitrogen-use efficiency • PASWC, plant-available soil water content • TDR, time domain reflectometry
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Excessive N fertilization may result in low NUE and potentially exerts more pressure on the environment. Nitrogen-use efficiency maybe defined as follows: NUE = (N uptake of N fertilization treatment – N uptake of no N treatment)/N fertilizer rate). A 15N experiment showed the recovery of fertilizer N by crops where conventional fertilization rates (300 kg N ha–1 for each crop) were used was approximately 25%, and that 30 to 50% of the applied N was lost in the winter wheat–summer maize rotation system on the North China Plain (Pan, 2001). Large amounts of fertilizer N loss to the environment could cause a serious environmental problem such as groundwater NO3 contamination (Zhang et al., 1996; Chen et al., 2000). In spite of this concern, N leaching has always been ignored as a main N loss pathway in the North China Plain because of low precipitation and high transpiration. Conversely, ammonia (NH3) volatilization has been considered the major pathway of N losses in this system due to high soil pH and the form of N fertilizer commonly applied (urea and NH4HCO3). Recently, investigations have shown good relationships exist between high NO3 concentration in the groundwater and high N fertilization in the North China Plain (Chen et al., 2000; Gao et al., 1999). There are numerous reports of severe NO3 accumulation from other parts of the world when fertilizer N was applied at higher quantity than crop requirements (Roth and Fox, 1990; Karlen et al., 1998; Elmi et al., 2000; Andraski et al., 2000). In the North China Plain, the rates of N fertilizer applied to winter wheat and summer maize were much higher than the crop N demand (Gao et al., 1999), therefore large amounts of NO3 accumulated in soil profiles (Ju et al., 2004; Liu et al., 2003). Hence, the importance of N leaching in the fate of N fertilizer should be reconsidered to better protect water quality.
Researchers have shown that the N rate for winter wheat can be reduced to <180 kg N ha–1 without any risk of yield decrease when yield response curve method or soil NO3 testing was used (Chen et al., 2004; Jia et al., 2001). Recently, an improved Nmin method which considers the synchronization of crop N demand and soil N supply, was developed and demonstrated great potential for improved NUE and minimized loss (Chen et al., 2001, 2005). However, the N loss of the optimized N fertilization technique needs to be compared with N loss due to the conventional N management practice. The objectives of this research were: (i) to investigate whether soil NO3 movement out of the effective root zone is a main pathway of N losses in the winter wheat–summer maize rotation system over a 4-yr study period, and (ii) to evaluate the potential of reducing N losses by the optimized N fertilization using an improved Nmin method in the winter wheat–summer maize rotation system in the North China Plain.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
A winter wheat–summer maize rotation system was used for the study, which involved planting and harvesting of two crops (wheat and maize) per year from 1999 to 2003. The eight successive crops were grown on the same plots over the 4-yr period. Winter wheat (var. Jingdong 8) was planted in mid-October with a row spacing of 15 cm and a seeding rate of 300 kg ha–1 and harvested at mid-June the following year. After winter wheat harvest, summer maize (var. Jingkeng 114 in 2000–2002, and Nonghua 103 in 2003) was planted with a row spacing of 70 cm and a seeding rate of 37.5 kg ha–1and harvested in early October each year. The experimental design was a randomized complete block with four replications and the plot size was 15 by 20 m.
Three N treatments, no N as a control, conventional N fertilization and optimized N fertilization, were used in the experiment. The conventional N fertilization treatment represents a typical farmer's practice in most high-yielding areas of the North China Plain. The conventional N fertilization treatment received 150 kg N ha–1 (NH4HCO3) at planting (incorporation after broadcasting) and another 150 kg N ha–1 (urea) as top-dress at shooting stage (broadcast followed by irrigation) for winter wheat; The conventional N fertilization treatment for summer maize received 100 kg N ha–1 (NH4HCO3) as first top-dressing fertilizer at three-leaf stage (banded in the 3–5 cm deep furrow with subsequent cover with soil in 2000 or broadcast followed by irrigation in 2001–2003) and another 200 kg N ha–1 (urea) as second top-dressing at 10-extended leaf stage (broadcast before rain in 2000 and broadcast followed by irrigation in 2001–2003).
The rate and time of N fertilization in the optimized N fertilization treatment was based on an improved Nmin method, which considered the synchronization of crop N demand and soil N supply (Chen et al., 2001, 2005). The plant N demand at three different growth periods included both shoot and root N demand as shown in Fig. 1 . In the first year (1999/2000), for winter wheat, the Nmin target value from regreening to shooting was 120 kg N ha–1 and from shooting to harvest was 125 kg N ha–1. In the years of 2000/2001, 2001/2002, and 2002/2003, the Nmin target value from regreening to shooting was adjusted to 90 kg N ha–1 and the Nmin target value from shooting to harvest was adjusted to 110 kg ha–1. The target values for summer maize and all years were 30 kg N ha–1 from sowing to three leaf stage, 90 kg N ha–1 from three leaf stage to 10 leaf stage and 110 kg N ha–1 from 10 leaf stage to harvest. Nmin target values were dependent on target yield (6 t ha–1 for each crop in this study) (Chen et al., 2001, 2005). The soil mineral N (Nmin = NH4–N + NO3–N) in the effective root depth changed with roots development. Soil samples (five cores from each plot) were taken from 0 to 30 cm for the first growth period, 0 to 60 cm for the second growth period, and 0 to 90 cm for the third growth period at the beginning of the periods and were measured for Nmin. The rate of N applied for each growth period was equal to the differences between the target N demand and the measured soil Nmin. After each crop harvest, soil samples in 0 to 90 cm were taken and analyzed for soil Nmin. Five 90-cm deep soil cores were taken from each plot, separated into 0- to 30-cm, 30- to 60-cm, and 60- to 90-cm depths. For evaluation of a possible NO3 movement to deeper soil layer, 90- to 200-cm soil samples were taken at the same time and separated into 90- to 120-cm, 120- to 150-cm, and 150- to 200-cm depths. All soil samples were sieved to pass a 2.0-mm screen, mixed, and extracted with 0.01 M CaCl2 solution. Extracted samples were analyzed for ammonium (NH4)–N and NO3–N using Continuous Flow Analysis (TRAACS 2000 system, Bran and Luebbe, Norderstedt, Germany). Soil water content was also determined at the same time of mineral N extraction. Table 1 shows the amount and time of applied N fertilizer in the optimized N fertilization treatment.
|
|
|
Aboveground biomass was measured manually on all plots. For winter wheat final harvest, three separate areas (each 3 m2) in the middle of each winter wheat plot were harvested to determine fresh grain yield. Grain and straw samples were for oven-dried at 60°C till weight constancy for the determination of dry matter. For summer maize final harvest, 39.2 m2 (seven rows, 8-m length) in the middle of each summer maize plots with N fertilizer application and 16.8 m2 (three rows, 8-m length) in the middle of each summer maize plots without N fertilizer application were harvested to determine fresh cob and stover yield. Six subsamples were randomly selected from the harvested summer maize plants and the stover and cob were separated and weighed. Whole cob and stover fraction samples were oven-dried at 60°C till weight constancy for the determination of dry matter weight. Subsamples of grain and stover were analyzed for N content by the Kjedahl method (Bremner, 1996). The wheat straw and maize stover were removed from the plots at each harvest and straw and stover were included in the calculation of N uptake. The differences among the treatments were determined using analysis of variance (ANOVA). Statistical analyses were performed using DUNCAN procedures of the SAS software package (SAS Institute, 1996).
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
|
Soil NH4–N in 0- to 90-cm profile in the conventional N fertilization treatments ranged from 3 to 36 kg ha–1 and did not change with time during the successive crop seasons. It was the same as that of the no N treatment (2–34 kg ha–1) and the optimized N treatments (3–32 kg ha–1).
Accumulation of Nitrate-Nitrogen in 0- to 200-cm Soils
No obvious accumulation of NO3–N was found in the 90- to 200-cm soil layer for the conventional N fertilization treatment right after the wheat harvest of the first growing season (winter wheat 1999/2000) (Fig. 4
). But after second crop (summer maize 2000) harvest, high accumulation of soil NO3–N was observed in the 90- to 200-cm soil layer for the conventional N fertilization treatment. Soil NO3–N accumulation in the 150- to 200-cm soil layer was found in the third crop (winter wheat 2000/2001) season. High accumulation of soil NO3–N occurred in 90- to 200-cm soil layer in the fourth, sixth, and eight crop seasons (summer maize 2001, 2002, and 2003). The increased amounts of soil NO3–N in the 90- to 200-cm layer (in the four summer maize crop seasons were 209, 60, 256, and 47 kg ha–1, respectively) equal to 90- to 200-cm soil NO3–N after harvest minus 90- to 200-cm NO3–N before sowing in each summer maize crop season (Fig. 4). In contrast, the amount of precipitation in these four summer maize growth seasons were 339, 214, 342, and 235 mm, respectively (Table 2). The amount of precipitation seems to be related to soil NO3 movement in the soil profile.
|
Nitrogen Balance
Soil N supplying capacity significantly decreased over time in this experiment for both the continuous no N fertilizer application and the optimized N fertilization treatment (Table 3). The N uptake by crops in the no N treatment was 187, 149, 122, and 97 kg ha–1, for each of the four experimental years (each year had two crops). The total N uptake by eight crops in the no N treatments (555 kg N ha–1), was contributed by 47 kg N ha–1 soil Nmin, and other unknown sources (508 kg N ha–1), probably from soil N mineralization and N deposition.
|
For the optimized N fertilization treatment, the total amount of N fertilizer applied in the successive eight crops was only 511 kg N ha–1, while the total N uptake was 1041 kg N ha–1, therefore the NUE was 95.1% (Table 3). This high rate of NUE is probably due to the utilization of elevated levels of residual N in the soil. Considering the contribution of soil N mineralization and N deposition (508 kg N ha–1) and soil Nmin (original soil Nmin minus final soil Nmin = 69 kg N ha–1), the total N losses was only 47 kg N ha–1, which could be separated as –10, 95, 0, and –38 into the each experimental year (Table 3).
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
It is accepted by many that N leaching is not an important pathway of N losses in the winter wheat–summer maize rotation system in the North China Plain because of low precipitation and high transpiration (Zhu and Wen, 1992). However, there is increasing evidence showing NO3 leaching occurring in low-rainfall regions under certain circumstances (Strong, 1995). Such leaching occurs episodically during extraordinarily wet periods (Campbell et al., 1984). The continuous 4-yr observation in this experiment showed that elevated concentrations of soil NO3–N were found in the 90- to 200-cm layer for the conventional N fertilization treatment, especially after the summer maize season. The increased levels of soil NO3–N in 90- to 200-cm layer during summer maize season in the four experimental years were 209, 60, 256, and 47 kg N ha–1, respectively. Researchers have shown that a very small portion of the total N taken up by maize occurs at soil depths >90 cm (Huang et al., 1996; Zhang, 2004). The total accumulation of 572 kg N ha–1 accounts for 37% of the overall N losses. Therefore, soil NO3–N movement to deeper soil layers (out of the crop rooting depth) should be considered an important pathway of N losses in this winter wheat–summer maize rotation system.
The movement of NO3 out of the root zone depends on the soil hydraulic properties, the amount of irrigation and/or precipitation, the amount of N applied, the form of N in the fertilizer and the time of application (Cameira et al., 2003). In our study, excessive N fertilization caused extremely large amounts of NO3 to accumulate in soil profiles after harvest. There are numerous reports on severe NO3 accumulation when fertilizer N was applied at higher quantity than crop requirements (Roth and Fox, 1990; Karlen et al., 1998; Elmi et al., 2000; Andraski et al., 2000). In the North China Plain, the rates of N fertilizer applied to winter wheat and summer maize were much higher than the crop N demand (Gao et al., 1999), therefore large amounts of NO3 accumulate in soil profiles of farmers' fields as well as in experimental fields (Ju et al., 2004; Liu et al., 2003). This not only wastes valuable resources but also poses more threat to groundwater quality in the region.
Nitrate movement depends much on water movement below the rooting depth of the crops. Higher water supply than the crop requirement (by rain and/or irrigation) is a very simple indicator for leaching potential. Commonly, irrigated land has a high potential for NO3 leaching, especially in combination with high N fertilizer application rates (Diez et al., 2000). In our experiment, the amount of soil NO3–N accumulation in 90- to 200-cm layer during winter wheat season did not increase significantly in four experimental years because the amount and time of irrigation were controlled well by soil water content testing. However, heavy rainfall events always happened in summer in the North China Plain. For instance, in these four experimental years, the precipitation in summer maize season was 339, 214, 342, and 235 mm, respectively, while the total amount for each experimental year were 416, 336, 475, and 436 mm, respectively. This explains the accumulation of soil NO3–N in 90- to 200-cm layer during the summer maize season. Hence, assessing NO3 movement considering only the winter wheat season is unjustified. This continuous field experiment also showed a good relationship between precipitation and increased soil NO3–N accumulation in 90- to 200-cm layer during summer maize season. The precipitations were 339 and 342 mm while the increased amounts of soil NO3–N accumulation in 90- to 200-cm layer were 209 and 257 kg N ha–1 following the summer maize seasons of 2000 and 2002. On the other hand, the precipitations were only 214 and 235 mm while the increased amounts of soil NO3–N accumulation in 90- to 200-cm layer were 60 and 47 kg N ha–1 for the other two summer seasons. Thus, in our study, excessive N fertilization combined with elevated precipitation during the summer maize season resulted in increased leaching of N.
Reduction of the applied N fertilizer rate to an optimized rate can reduce soil NO3 leaching (Power et al., 2000; Sogbedji et al., 2000; Diez et al., 2000; Guillard et al., 1999). Optimized N fertilization usually involves applying N fertilizer in split applications to match crops needs (Ottman and Pope, 2000). Nitrogen-use efficiency has been shown to be the greatest with split N application (Alcoz et al., 1993; Ayoub et al., 1995), and such split applications will presumably lower the potential for NO3 leaching. In this study, an improved Nmin method, which considered the synchronization of crop N demand and soil N supply was used for the optimized N fertilization treatment. The results of our study indicate that soil NO3–N in the root zone under conditions of optimized N fertilization was maintained at a relatively low level as compared with the conventional N fertilization treatment. However, the optimized N fertilization treatment did not reduce yield with the exception of summer maize yield in 2003 when a higher-yielding maize variety was used without changing the target N supply value. The optimized N fertilization treatment dramatically decreased soil NO3–N movement to deeper soil layers.
This continuous 4-yr experiment showed that the soil-available N supply from the mineralization of organic-bound N decreased with time, and the rate of N fertilizer in the optimized N fertilization treatments increased gradually. Therefore, the reduced amount of N fertilizer at the beginning of the experiment can not be maintained for a long time without impacting yields. The question is how much the potential ability of reducing N fertilizer in the optimized N fertilization system is in a long period. According to Engels and Kuhlmann (1993), in the optimum N treatment, the N mineralization and immobilization will finally reach a balance point. It means N supply will be equal to the N removal by crops if the N losses by fertilizer application can be controlled well and N deposition can be ignored. In the case of the middle-yield area (approximately 6 t ha–1 target yield for winter wheat as well as for summer maize) in the North China Plain, rough calculations show that the optimized N rate should be about 180 kg ha–1 for each crop of winter wheat–summer maize rotation system under the condition of no straw return and no organic fertilizer application. Comparing this strategy with farmers' current practices shows that approximately 40% of N fertilizer can be saved over the first few years.
|
ACKNOWLEDGMENTS |
|---|
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  P. He, S. Li, J. Jin, H. Wang, C. Li, Y. Wang, and R. Cui Performance of an Optimized Nutrient Management System for Double-Cropped Wheat-Maize Rotations in North-Central China Agron. J., November 1, 2009; 101(6): 1489 - 1496. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Li, Y. Miao, F. Zhang, Z. Cui, R. Li, X. Chen, H. Zhang, J. Schroder, W. R. Raun, and L. Jia In-Season Optical Sensing Improves Nitrogen-Use Efficiency for Winter Wheat Soil Sci. Soc. Am. J., July 14, 2009; 73(5): 1566 - 1574. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 X.-T. Ju, G.-X. Xing, X.-P. Chen, S.-L. Zhang, L.-J. Zhang, X.-J. Liu, Z.-L. Cui, B. Yin, P. Christie, Z.-L. Zhu, et al. From the Cover: Reducing environmental risk by improving N management in intensive Chinese agricultural systems PNAS, March 3, 2009; 106(9): 3041 - 3046. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Wan, X. Ju, J. Ingwersen, U. Schwarz, C. F. Stange, F. Zhang, and T. Streck Gross Nitrogen Transformations and Related Nitrous Oxide Emissions in an Intensively Used Calcareous Soil Soil Sci. Soc. Am. J., January 21, 2009; 73(1): 102 - 112. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Cui, F. Zhang, Z. Dou, M. Yuxin, Q. Sun, X. Chen, J. Li, Y. Ye, Z. Yang, Q. Zhang, et al. Regional Evaluation of Critical Nitrogen Concentrations in Winter Wheat Production of the North China Plain Agron. J., January 8, 2009; 101(1): 159 - 166. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Cui, X. Chen, Y. Miao, F. Li, F. Zhang, J. Li, Y. Ye, Z. Yang, Q. Zhang, and C. Liu On-Farm Evaluation of Winter Wheat Yield Response to Residual Soil Nitrate-N in North China Plain Agron. J., October 21, 2008; 100(6): 1527 - 1534. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Z. Cui, X. Chen, Y. Miao, F. Zhang, Q. Sun, J. Schroder, H. Zhang, J. Li, L. Shi, J. Xu, et al. On-Farm Evaluation of the Improved Soil Nmin-based Nitrogen Management for Summer Maize in North China Plain Agron. J., May 7, 2008; 100(3): 517 - 525. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Binder, S. Graeff, J. Link, W. Claupein, M. Liu, M. Dai, and P. Wang Model-Based Approach to Quantify Production Potentials of Summer Maize and Spring Maize in the North China Plain Agron. J., May 7, 2008; 100(3): 862 - 873. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Crop Science | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
