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Journal of soil science and plant nutrition

versión On-line ISSN 0718-9516

J. Soil Sci. Plant Nutr. v.10 n.4 Temuco  2010

http://dx.doi.org/10.4067/S0718-95162010000200005 

J. Soil Sci. Plant Nutr. 10 (4): 444 - 453 (2010)

 

EFFECT OF NITROGEN FERTILIZER AND MAIZE STRAW INCORPORATION ON NH4+15N AND N03 -15N ACCUMULATION IN BLACK SOIL OF NORTHEAST CHINA AMONG THREE CONSECUTIVE CROPPING CYCLES

 

Caiyan Lu1,2, Jian Ma1,2, Xin Chen1,2*, Xudong Zhang1, Yi Shi1,2, and Bin Huang2

1Key Laboratory of Terrestrial Ecological Process, Institute of Applied Ecology, ChineseAcademy of Sciences, Shenyang 110016, China.

2Key Laboratory of Pollution Ecology and Environmental Engineering, Institute of Applied Ecology, Chinese Academy of Sciences, Sheyang 110016, China. Corresponding author: chenxin@iae.ac.en


ABSTRACT

A pot experiment was conducted to evaluate the effect of nitrogen (N) fertilizer and maize straw incorporation on the accumulation of NH4+-15N and N03--15N in soil inorganic N pool among three consecutive cropping cycles, aimed to search for an effective N management practice to decrease superfluous accumulation of soil inorganic N and fertilizer N losses. The results showed that the amounts of soil NH4+-15N, N03-15N and inorganic 15N, and their percent to applied 15N-labeled fertilizer declined significantly with sampling time (p ≤ 0.001).Compared to low N application rate (44.64 mg N kg-1 soil), high N application rate (89.28 mg N kg-1 soil) enhanced significantly the amounts of soil NH4+-15N, N03--15N and inorganic 15N by 238.6%, 132.9% and 197.3%, respectively (p 0.001). In contrast, maize straw addition declined significantly the amounts of soil NH4+-15N and inorganic 15N by 21.4% and 16.1% compared to without maize straw (p ≤ 0.001). The results suggested that a combined application of chemical fertilizer and maize straw with a wide C/N ratio is an important means for reducing the superfluous accumulation of fertilizer N as soil inorganic N to subsequently lower its loss.

Keywords: N fertilizer, maize straw, NH4+-15N and N03--15N accumulation, Black soil


INTRODUCTION

Nitrogen (N) is one of the critical nutrients for crop production and is generally applied in large quantities in form of fertilizer to soils (Malhia et al, 2001; Murshedul et al, 2006; Singh et al, 2007; Kong et al, 2008). However, most plants only utilize less than one-half of fertilizer N applied, and the loss of fertilizer N was high (Zhu, 2000; Zhu and Chen, 2002). Nitrogen management in agro-ecosystems has been extensively studied due to its importance in improving crop yield and quality, and in mitigating the negative effects of fertilizer N losses such as nitrate contamination of groundwater, eutrophication of surface water, and greenhouse effect (Hillin and Hudak, 2003; De Paz and Ramos, 2004; Alam et al, 2006; Dambreville et al, 2008).

Soil exchangeable inorganic N is the common source of various N losses (Zhu, 2000), whereas the immobilization and release of fertilizer N in soil organic N and fixed NH4+ pools are important processes regulating fertilizer N transformation in soil, and play an important role in controlling soil N-potential supply (Mubarak et al, 2001; Macdonald et al, 2002; Elmaci et al, 2002; Lu et al, 2010). Therefore, a key challenge in minimizing loss of chemical fertilizer N is how to decrease the superfluous accumulation of soil exchangeable inorganic N, accelerate its transformation to other N forms (such as organic N and fixed NH4+), and synchronize the supply of available N with plant uptake during peak periods of crop N demand (Zhu, 2000; Lin et al, 2007). Understanding the accumulation of fertilizer N in soil inorganic N pool under different fertilization practices is of considerable importance in developing proper fertilization practice for minimizing fertilizer N loss while maximizing its use efficiency (Angas et al, 2006; Lu et al, 2008).

China consumes more than one quarter of total fertilizer N of the world (Li et al, 2007; Zhu et al, 2008). However, loss of fertilizer N in China is high (Zhu and Chen, 2002; Luo et al, 2006; Jing et al, 2007). Especially for Northeast China, which is famous for commercial crop production in China, decreasing fertilizer N loss and increasing its utilization efficiency is very important for sustainable development of agriculture in this region (Hu et al, 2007; Ma et al, 2007; Peng et al, 2007). Black soil (Hapli-Udic Isohumosols) is the main agricultural soil in Northeast China, but until now, researches focusing on the effects of different fertilization practices on the accumulation of soil inorganic N are still lacking. In this study, a pot experiment was conducted to examine the effect of N fertilizer and maize straw incorporation on the accumulation of NH4+-15N and N03--15N in the inorganic N pool of the black soil among three consecutive cropping cycles, aimed to search for an effective N management practice to decrease superfluous accumulation of soil inorganic N and fertilizer N loss.

 

MATERIALS AND METHODS

Study site

The study was conducted at the National Field Observation and Research Station of Shenyang Agro-ecosystems, a member of Chinese Ecosystem Research Network (CERN) established in 1987. This Station locates on the Lower Liao River Plain, with a humid and semi-humid continental monsoon climate of warm-temperate zone. Mean annual temperature is 7-8°C, with minimum and maximum mean monthly temperature in January (-13°C) and July (24°C), respectively. Mean active accumulated temperature (≤10°C) is 3300-3400°C. The total solar radiation is 5410-5600 kJ cm-2. The duration of frost-free season is 147-168 d. Mean annual precipitation is about 700 mm.

Experimental design

Black soil samples of 0-20 cm (Hapli-Udic Isohumosols) were collected from the Jilin Institute of Soil and Fertilizer, sieved through 5-mm, and adequately homogenized.

An outdoor pot experiment consecutively cropped with Chinese spring wheat (Triticum aestivum L. cv. Liaochun 9, from 8 April 2006 to 3 July 2006), buckwheat (Fagopyrum eaculentum moench. cv. Liaoqiao-2, from 10 July 2006 to1 Oct. 2006), and spring wheat (Triticum aestivum L. cv. Liaochun 9, from 3 April 2007 to 29 June 2007) was conducted. 6.5 kg of the soil was put into each pot with an outer diameter of 25 cm and a height of 15 cm, and each pot was sown with 15 spring wheat seeds or 8 buckwheat seeds. Six Treatments were set up, and each treatment had 20 pots and sampled for five times with four replicates at each sampling date.

During the experiment, soil moisture content was adjusted daily with deionized water to about 60% water holding capacity (WHC). The basic properties of the tested soil and fertilization treatments of outdoor pot experiment were given in Table 1 and Table 2.

Maize straw, concentrated superphosphate and potassium sulfate were applied as basal. Chemical N fertilizer was dissolved using de-ionized water and applied as top-dressing at the three tillering stage of the crops, i.e., on 9 May 2006, 25 July 2006, and 4 May 2007, respectively. Labeled (15NH4)2S04 (Shanghai Research Institute of Chemical Industry) with 50.12 atom% 15N was applied in the first cropping cycle, and non-labeled urea-N fertilizer was applied in the following two cropping cycles.

Sampling and analytical methods

Soil samples from the pots were collected on 19 May, 5 June, and 3 July 2006 (tillering anaphase, flowering, and ripening stage of spring wheat in the first cropping cycle), on 1 October 2006 (ripening stage of buckwheat in the second cropping cycle), and on 29 June 2007 (ripening stage of spring wheat in the third cropping cycle) by destructive sampling method. All fresh soil samples were sieved (<2 mm), and mixed homogeneously. About 100 g fresh subsamples were used to determine moisture content, soil NH4+-N and N03-N, and their atom% 15N.

Total carbon was measured using TOC-5000A automatic analyzer (Shimadzu Corporation, Japan). Total P and K were measured by sodium carbonate fusion and molybdenum antimony-ascorbic acid colorimetric method (Olsen and Sommers, 1982). Available P and K were determined by extraction method with sodium bicarbonate (Olsen et al., 1954) and ammonium acetate (Pratt, 1965), respectively. Soil mechanical composition and clay mineral composition was measured by pipette method and X-ray diffraction analysis, respectively (Whitting, 1965).

Total N was determined by the Kjeldahl method (Bremner and Mulvaney, 1982), inorganic N was measured by 2M KC1 extraction-MgO-Devarda alloy distillation method (Keeney and Nelson, 1982), and fixed NH4+ was determined by KOBr-KOH method (Silva and Bremner, 1966). Subsequently, atom% 15N in the acidified aqueous distillate was measured using a Finnigan Mat model 251 Isotope Ratio Mass Sepectrometer (USA). All the operation procedure was carried out from lower to higher atom% 15N to avoid cross-contamination.

Methods of calculation

The amount (mg N kg-1 soil) of soil NH4+-15N (CNH4), N03--15N (CN03) and inorganic 15N (Ci, and percent of soil NH4+-15N, N03--15N and inorganic 15N to applied 15N-labeled fertilizer (PNH4, PNO3 and Pi) was calculated according to the following formulas:

Where C is the amount (mg N kg-1 soil) of soil NH4+-N or N03--N and a is the atom% 15N of 15N-labeled fertilizer, b is the atom% 15N of treated soil NH4+-N or N03--N, c is the atom% 15N of background soil NH4+-N or N03--N, respectively.

where Cf is the amount of N-labeled fertilizer applied (mg N kg-1 soil), CNH4 and CNO3 is the amount (mg N kg-1 soil) of soil NH4+-15N and N03--15N.

Statistical analysis of data

Three-way Analysis of Variance (ANOVA) with SPSS 13.0 statistical package was conducted to detect effect of N fertilizer and maize straw incorporation on amount and distribution of NH4+-15N and N03--15N in soil inorganic N pool. Differences with a probability level of p ≤ 0.05 were considered significant.

 

RESULTS

Amounts of soil NH4+-15N and N03--15N

15N-labeled fertilizer existed in form of soil NH4+-15N and N03--15N in soil inorganic 15N pool. The amount of soil declined significantly with NH4-15N sampling time, and was significantly different between the treatments with the low and high N application rates (p 0.001, Table 3, Figure 1). Compared to the low N application rate, the high N application rate significantly increased the amount of soil NH4+-15N by 238.6% across three consecutive cropping cycles, and this effect was the largest in the flowering stage and then weakened with time (p 0.001, Table 3, Figure 1). In contrast, the application of maize straw significantly decreased the amount of soil NH4+-15N by 21.4% among the first cropping cycle, and this effect was the largest in the flowering stage and then weakened with time (p 0.001, Table 3, Figure 1).

 

The amount of soil N03-- N also significantly declined with sampling time (p 0.001, Table 3, Figure 1). Compared to the low N application rate, the high N application rate significantly increased the amount of soil N03--15N by 132.9% across three consecutive cropping cycles, and this increasing pattern weakened with time (p 0.001, Table 3, Figure 1). However, applying maize straw had no effects on the amount of soil N03--15N (p 0.05, Table 3, Figure 1). The change trend of soil inorganic 15N was the same with that of soil NH4+-15N (Table 3, Figure 1).

In soil inorganic 15N pool, the proportion of soil NH4+-15N accounting for inorganic 15N obviously decreased with sampling time, however, soil N03--15N accounting for inorganic 15N increased with sampling time (Figure 2). For example, the proportion of soil NH4+-15N accounting for inorganic 15N across four fertilization treatments was 78.54%, 68.77%, 33.48%, 11.08% and 12.46% on average at the five consecutive sampling dates, respectively, and that of soil N03--15N accounting for inorganic 15N was averagely 21.46%, 31.23%, 66.52%, 88.92% and 87.54%, respectively (Figure 2). The proportion of soil NH4+-15N was obviously higher than that of soil N03--15N at the tillering anaphase and flowering stage of the first cropping cycle, and vice versa in the ripening stage of three cropping cycles (Figure 2).

Distribution of 15N-labeled fertilizer in soil inorganic N pool

The percent of soil NH4+-15N to applied 15N-labeled fertilizer (Pmm) decreased significantly with sampling time (p 0.001, Table 4, Table 5). On 19 May 2006, the Pnh4 was averagely 11.12% across four fertilization treatments, and the corresponding proportions were 1.45%, 0.07% and 0.03% on 3 July, 1 October 2006 and 29 June 2007, respectively (Table 4). Compared to the low N application rate, the high N application rate remarkably elevated the Pnh4 by 69.1% across three consecutive cropping cycles, and this effect was the highest at the flowering stage and then weakened with time (p 0.001, Table 4, Table 5). In contrast, maize straw addition significantly lowered the Pmm by 19.6% in the tillering anaphase of the first cropping cycle, and this effect disappeared with sampling time, compared to those without maize straw addition (p 0.01, Table 4, Table 5).

The percent of soil N03--15N to applied 15N-labeled fertilizer (PN03) significantly decreased with sampling time (p 0.001, Table 4, Table 5). On 19 May 2006, the PN03 was averagely 2.90% across four fertilization treatments, and the corresponding proportions were 2.86%, 0.66% and 0.21% on 3 July, 1 October 2006 and 29 June 2007, respectively (Table 4). The high N application rate significantly increased the PN03 by 13.0% across three consecutive cropping cycles, compared to the low N application rate, and this increasing pattern weakened with time (p 0.05, Table 4, Table 5).

However, no significant effect from maize straw addition was observed in the PN03 (p 0.05, Table 4, Table 5).

The percent of soil inorganic 15N to applied 15N-labeled fertilizer (Pt) significantly decreased with sampling time (p 0.001, Table 4, Table 5). The highest P¡ was 14.01% in the tillering anaphase across four fertilization treatments. The change trend of P¡ was the same with PNH4 in different fertilization treatments (Table 4, Table 5).

 

DISCUSSION

Chemical N fertilizer existed in form of inorganic N. Thus it was expected that application of chemical N fertilizer enhanced the size of soil inorganic N pool. Our observation supported the above speculation that high N application rate significantly enhanced the amount of NH4+-15N and N03--15N in soil inorganic N pool (p 0.001, Table 2, Figure 1), and subsequently increased the loss of 15N-labeled fertilizer by 4.4% across three consecutive cropping cycles (Lu, unpublished). Angas et al. (2006) also found that soil mineral N increased with the increase of N fertilization rates, and applying more N than the crop needed elevated the superfluous accumulation of inorganic N and its loss.

In contrast, applying maize straw significantly declined the amount of soil NH4+-15N and inorganic 15N by 16.2% and 17.3%, and degraded the loss of 15N-labeled fertilizer by 12.4% in the tillering anaphase of the first cropping cycle among four fertilization treatments compared to those without maize straw addition. The results also showed that 14.8% loss of 15N-labeled fertilizer in the tillering anaphase accounted for 64.3% of the overall loss across three consecutive cropping cycles, which indicated that the loss of 15N-labeled fertilizer occurred mainly within 10 days after fertilization. A major reason for this was that low N application rate could meet the low N demand of spring wheat at the tillering stage, while high N application rate resulted in excessive N loss at the tillering stage. However, maize straw with a wide C/N ratio could provide plentiful carbon and energy sources to stimulate soil microbial activity, and accelerate the transformation of soil inorganic 15N into organic 15N (increasing the amount of soil organic 15N by 13.9%, and then decrease the loss percent of 15N-labeled fertilizer (Lu, unpublished, Gentile et al, 2009; Nayak et al, 2007; Chaves et al, 2006).

The amount of soil NH4+-15N was higher than that of soil N03--15N at the tillering anaphase and flowering stage, and then the trend was reversed at the ripening stages of three cropping cycles (Figure 1, 2), which suggested that the nitrification of soil NH4+-15N was low within 27 days after fertilization, and strengthened thereafter. The proportion of soil NH4+-15N accounting for inorganic 15N decreased with time, and that of soil N03--15N accounting for inorganic 15N increased with time, which further confirmed the above-mentioned results (Figure 2).

 

CONCLUSIONS

Our study indicated that high N application rate significantly enhanced the amount of soil NH4+-15N, N03--15N and inorganic 15N, compared to low N application rate. In contrast, maize straw with a wide C/N ratio is important in regulating the accumulation of NH4+-15N and N03--15N in soil inorganic N pool. Maize straw addition lowered the amounts of soil NH4+-15N, inorganic 15N, and their percent to applied 15N-labeled fertilizer, and then decreased the percent loss of 15N-labeled fertilizer. Thus, a combined application of chemical fertilizer and maize straw with a wide C/N ratio is an important means for reducing the superfluous accumulation of N fertilizer as soil inorganic N to subsequently lower its loss.

 

ACKNOWLEDGEMENTS

We thank Likai Zhou, Qi Li for providing help in English writing and statistical analysis. We thank Dewen Li, Zhaowei Zhang, Jun Wang, Xiaohua Xue for assistance in field sampling. We thank for the editor and anonymous reviewers for their helpful suggestions. This work was financially supported by National Nature Science Foundation of China (40535028) and Doctor Foundation of Liaoning province (20091090).

 

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