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Influences of Long-Term Fertilizer and Tillage Management on Soil Fertility of the North China Plain
Pedosphere 21(6): 813–820, 2011 ISSN 1002-0160/CN 32-1315/P c 2011 Soil Science Society of China Published by Elsevier B.V. and Science Press
Influences of Long-Term Fertilizer and Tillage Management on Soil Fertility of the North China Plain∗1 NIU Ling-An, HAO Jin-Min∗2 , ZHANG Bao-Zhong and NIU Xin-Sheng Quzhou Experimental Station, China Agricultural University, Quzhou 057250 (China) (Received May 15, 2011; revised September 24, 2011)
ABSTRACT In the North China Plain, fertilizer management and tillage practices have been changing rapidly during the last three decades; however, the influences of long-term fertilizer applications and tillage systems on fertility of salt-affected soils have not been well understood under a winter wheat (Triticum aestivum L.)-maize (Zea mays L.) annual double cropping system. A field experiment was established in 1985 on a Cambosol at the Quzhou Experimental Station, China Agricultural University, to investigate the responses of soil fertility to fertilizer and tillage practices. The experiment was established as an orthogonal design with nine treatments of different tillage methods and/or fertilizer applications. In October 2001, composite soil samples were collected from the 0–20 and 20–40 cm layers and analyzed for soil fertility indices. The results showed that after 17 years of nitrogen (N) and phosphorous (P) fertilizer and straw applications, soil organic matter (SOM) in the top layer was increased significantly from 7.00 to 9.30–13.14 g kg−1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg−1 in the 20–40 cm layer. Soil total N (TN) was increased significantly from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg−1 in the 0–20 and 20–40 cm layers, respectively, with N fertilizer application; however, there was no apparent effect of straw application on TN content. The amounts of soil total P (TP) and rapidly available P (RP) were increased significantly from 0.60 to 0.67–1.31 g kg−1 in the 0–20 cm layer and from 0.52 to 0.60–0.73 g kg−1 in the 20–40 cm layer with P fertilizer application, but were decreased with combined N and P fertilizer applications. The applications of N and P fertilizers significantly increased the crop yields, but decreased the rapidly available potassium (RK) in the soil. Straw return could only meet part of the crop potassium requirements. Our results also suggested that though some soil fertility parameters were maintained or enhanced under the long-term fertilizer and straw applications, careful soil quality monitoring was necessary as other nutrients could be depleted. Spreading straw on soil surface before tillage and leaving straw at soil surface without tillage were two advantageous practices to increase SOM accumulation in the surface layer. Plowing the soil broke aggregates and increased aeration of the soil, which led to enhanced organic matter mineralization. Key Words:
rapidly available K, rapidly available P, soil organic matter, straw return, total N
Citation: Niu, L. A., Hao, J. M., Zhang, B. Z. and Niu, X. S. 2011. Influences of long-term fertilizer and tillage management on soil fertility of the North China Plain. Pedosphere. 21(6): 813–820.
INTRODUCTION Improved nitrogen (N) and phosphorous (P) fertilizer management and straw application under different tillage systems can maintain or enhance longterm soil quality. This is particularly true for saltaffected soils that are vulnerable to degradation (Niu et al., 2003, 2005). Long-term fertilizer experiments are valuable for assessing yield trends and changes in nutrient dynamics and balances, predicting soil carrying capacity, and evaluating soil quality and sustain∗1 ∗2
ability. Trends in soil fertility have been reported in many short- (Marcote et al., 2001; Blaise et al., 2005) and long-term fertilizer experiments (Dalal and Mayer, 1986a; Albiach et al., 2000; Manna et al., 2005; Cai and Qin, 2006a, b; Hati et al., 2006; Masto et al., 2006; Ge et al., 2009). Frequent tillage may destroy soil organic matter (SOM) (Hernanz et al., 2002) and speed up the movement of SOM to deep soil layers (Shan et al., 2005). As an ecologically sound approach, conservation tillage usually shows advantages over conventional tillage pra-
Supported by the National Key Technology R & D Program of China (No. 2011BAD04B02). Corresponding author. E-mail: [email protected].
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ctices in improving soil quality and crop yields (Lal, 1989; Dick and Durkalski, 1997), and has the potential to conserve soil water and reduce soil erosion (Yang et al., 2003). No tillage generally favours the accumulation of SOM (Duiker and Beegle, 2006). With the adoption of conservation tillage, SOM content was increased in the 0–20 cm layer (Stockfisch et al., 1999; Wright et al., 2005) and a larger amount of soil organic carbon (SOC) was accumulated in the 0–10 cm layer (Yang and Kay, 2001). In the North China Plain, although a number of studies have been conducted on the changes of soil fertility under continuous cropping systems (Meng et al., 2005; Cai and Qin, 2006a, b; Yin and Cai, 2006; Chu et al., 2007; Wang et al., 2009), few studies have reported the influences of long-term N, P, and straw treatments under different tillage systems on a broad range of soil fertility indices such as SOM content, total nitrogen (TN), total phosphorous (TP), rapidly available P (RP), and rapidly available K (RK), particularly in salt-affected soils. Since the early 1980s, most of the salt-affected soils which had been damaged by drought, water logging, alkalization, salinization, and desertification in the lowland of the North China Plain had been reclaimed successfully (Shi and Xin, 1983). Nevertheless, crop productivity in this area is still low mainly because of low SOM content and N and P deficiencies. The primary objective of this study was to investigate the influences of long-term fertilization and tillage practices on a range of soil fertility indices of a reclaimed salt-affected soil. The influences of cropping practices on sustainability of the salt-affected soils of the North China Plain were also assessed. MATERIALS AND METHODS A field experiment was established in 1985 at the Quzhou Experimental Station of China Agricultural University (115◦ 1 E, 36◦ 51 N, 36 m above sea level), located in Quzhou County of Hebei Province.
With a warm-temperate monsoonal climate, the annual average precipitation at Quzhou is 515.8 mm, which is unevenly distributed in the year: 13.5% in spring (March–May), 65.7% in summer (June–August), 18.1% in autumn (September–November), and 2.8% in winter (December–January). The annual pan evaporation is about 1 837 mm. The shallow groundwater has a salt concentration of 5–11 g L−1 , mostly 5–7 g L−1 . There are two crops in a year: winter wheat (Triticum aestivum L.) from earlier October to the first week of June and maize (Zea mays L.) from the second week of June to the end of September. The soil there is a deep alluvial soil which is classified as a parasalic endorusti-ustic Cambosol in the Chinese Soil Taxonomy (Gong et al., 2007). It is characterized with a loamy texture, high salt content, and salt accumulation in soil profile. The basic soil properties were measured in 1984 and are listed in Table I. Drought, water logging, salinization, and low soil fertility are the major factors that limit crop productivity at the experimental site. The experiment, with an orthogonal design, had nine treatments with different tillage methods and fertilizer application rates (Table II). The tillage methods were: 1) minimum tillage (M), where the straw was spread over the field followed by tillage to 5 cm depth and sowing; 2) conventional tillage with straw incorporation (T1 ), where the straw was spread over the field followed by mouldboard plow to 30 cm depth and sowing; 3) conventional tillage with straw cover on soil surface (T2 ), where the straw was spread on the soil surface after mouldboard plow to 30 cm depth and sowing. There were three N rates, three P rates, and three straw rates (Table II). With three replications per treatment, the total number of field plots was 27. The N fertilizer was urea (460 g kg−1 N) and the P fertilizer was triple superphosphate (430 g kg−1 P2 O5 ). Of the total N fertilizer, 50% was applied to winter wheat, and another 50% to maize. For winter wheat, 30% of the total fertilizer N was applied at planting in earlier October, and 20% was broadcast
TABLE I Physical and chemical properties of the soil at the experimental site Soil depth cm 0–20 20–40
Texture
Silt loam Sandy loam
pH
7.8 7.8
Soil organic matter
Total nitrogen
7.00 4.00
g kg−1 0.37 0.22
Total phosphorus 0.60 0.52
Rapidly available phosphorus 9.9 3.2
Rapidly available potassium
mg kg−1 92.6 71.3
Salt content g kg−1 1.02 1.11
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TABLE II Tillage and fertilizer management of the experiment Treatment
Tillage methoda)
N fertilizer rate
P fertilizer rate −1
I II III IV V VI VII VIII IX
T1 T1 T1 T2 T2 T2 M M M
kg ha year 0 (P1 ) 75 (P2 ) 150 (P3 ) 75 (P2 ) 150 (P3 ) 0 (P1 ) 150 (P3 ) 0 (P1 ) 75 (P2 )
0 (N1 ) 112.5 (N2 ) 187.5 (N3 ) 0 (N1 ) 112.5 (N2 ) 187.5 (N3 ) 0 (N1 ) 112.5 (N2 ) 187.5 (N3 )
Straw rate
−1
0 2 250 4 500 4 500 0 2 250 2 250 4 500 0
(S1 ) (S2 ) (S3 ) (S3 ) (S1 ) (S2 ) (S2 ) (S3 ) (S1 )
a)
T1 = conventional tillage with straw incorporation; T2 = conventional tillage with straw cover on soil surface; M = minimum tillage.
at the soil surface in April, followed by surface irrigation. For maize, 30% and 20% of the N fertilizer was applied at sowing and at the 10- to 12-leaf stage, respectively. The P fertilizer was applied only to winter wheat annually at crop seeding. Generally, each crop was irrigated 3–4 times (705–825 m3 ha−1 each time) with groundwater. The salt content of the groundwater was about 0.75 g L−1 . The varieties of winter wheat and maize used in the study are shown in Table III.
the extraction with 0.5 mol L−1 NaHCO3 . Available K content in the soil was determined by flame emission spectrometry following the extraction with 1 mol L−1 neutral CH3 COONH4 (Westerman, 1990). The experimental results were analysed using the analysis of variance (ANOVA). The differences between treatments were evaluated using the least significant difference (LSD) multiple range test at P = 0.05 (Mead et al., 1983).
TABLE III
RESULTS AND DISCUSSION
Winter wheat (Triticum aestivum L.) and maize (Zea mays L.) varieties used during the experimental period Years
Winter wheat
Maize
1985–1989 1990–1994 1995–2001
Taishan 1 Jimai 23 Han 4564
Yedan 3 Yedan 13 Xiyu 3
In 2001, soil samples were collected from the 0–20 and 20–40 cm layers after maize harvest in October. The samples were air-dried and passed through a 0.25mm sieve for determination of SOM and total N. A sub-sample was passed through a 1-mm sieve for determination of available N, P, and K contents. Soil organic matter content was measured using an oxidative (potassium dichromate) method with 0.4 mol L−1 K2 Cr2 O7 -H2 SO4 solution and titrated with 0.2 mol L−1 FeSO4 . Soil total N content was measured by the Kjeldahl digestion technique, with Se powder and CuSO4 as catalysts. Soil total P was measured using NaOH fusion with the molybdate blue colorimetric method, and available P content was measured using the molybdate blue colorimetric method following
SOM content After 17 years of continuous tillage and fertilizer treatments, SOM contents were increased significantly, from 7.00 to 9.30–13.14 g kg−1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg−1 in the 20–40 cm layer (Table I; Fig. 1). The largest SOM content in the 0–20 cm layer, 13.14 g kg−1 , appeared in Treatment III, being significantly higher than those of Treatments I (10.03 g kg−1 ), IV (9.30 g kg−1 ), and VI (11.76 g kg−1 ). In the 20–40 cm layer, however, Treatment IV showed the largest SOM content (7.75 g kg−1 ), significantly higher than the other treatments except Treatment VIII. Application of N fertilizer, P fertilizer, and straw enhanced SOM accumulation. At the N fertilizer rates of 0, 112.5, and 187.5 kg ha−1 , the average SOM contents in the 0–20 cm layer were 10.39, 12.12, and 11.91 g kg−1 , respectively. At the P fertilizer rates of 0, 75, and 150 kg ha−1 , the average SOM contents were 11.20, 11.30, and 12.03 g kg−1 in 0–20 cm layer and 4.50, 5.37, and 6.42 g kg−1 in 20–40 cm layer, respectively. At
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Fig. 1 Soil organic matter (SOM) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
the straw rates of 0, 2 250, and 4 500 kg ha−1 , the average SOM contents were 11.06, 11.93, and 11.51 g kg−1 in the 0–20 cm layer and 5.96, 5.70, and 6.66 g kg−1 in the 20–40 cm layer, respectively. Clearly, the highest fertilizer rate did not always produce the highest SOM content, indicating that the SOM content did not respond linearly to fertilizer inputs (Suo, 2005; Xiao et al., 2009; Zhang et al., 2009). The three tillage practices showed different influences on SOM accumulation. Averaged over the different treatments, the SOM contents in the 0–20 cm layer were 11.89, 10.75, and 11.78 g kg−1 for the tillage methods T1 , T2 , and M, respectively. Therefore, spreading straw on soil surface before tillage (T1 ) and leaving straw on soil surface with minimum tillage (M) were advantageous to SOM accumulation in the surface layer. On the other hand, plowing the soil broke aggregates and increased soil aeration, which enhanced organic matter mineralization (Blevins et al., 1984; Dalal and Mayer, 1986b; Balldock and Kay, 1987; Cambardella and Elliot, 1993). In the 20–40 cm layer, the treatment with tillage to 30 cm depth, no N fertilizer, 75 kg ha−1 P fertilizer, and 4 500 kg ha−1 straw (Treatment IV) had the highest SOM content (7.75 g kg−1 ), indicating that under the experimental condition, tillage methods and straw rates interactively determined SOM accumulation in the deeper soil layer. While burying crop residues in the soil at tillage (e.g., Treatment III) or leaving crop residues permanently on soil surface (Treatment VIII) enhanced SOM accumulation in the surface layer (0–20 cm), leaving crop residues on soil surface after tillage
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and then incorporating them into soil with deep tillage before sowing the next crop (Treatment VI) was more beneficial to SOM buildup in the deeper layer (20–40 cm). Spreading straw over the field with minimum tillage seemed to have provided large amounts of nutrients for soil microorganisms in the topsoil, which accelerated straw decomposition and decreased the SOM content in the topsoil (0–20 cm). In the subsoil (20– 40 cm), there was minimum tillage disturbance and microorganisms received much less nutrients from the straw; therefore, SOM decomposition rate was relatively low and SOM content was high. Soil active organic matter fraction, expressed as the ratios of microbial biomass C or N to total soil C or N, respectively, appeared to be related to long-term tillage and fertilizer management. These ratios increased in proportion to increased organic inputs and reduced tillage or periods of fallow (Lundquist et al., 1999; Chu et al., 2007). Soil total N After 17 years of tillage and fertilizer treatments, mean content of soil TN was increased from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg−1 in the 0–20 and 20–40 cm layers, respectively (Fig. 2). In the 0–20 cm layer, the TN contents of Treatments III, IX, II, VIII, and I were 1.11, 1.07, 1.05, 1.04, and 0.94 g N kg−1 , respectively, significantly higher (P < 0.05) than that of Treatment IV (0.79 g kg−1 ). Averaged over the fertilizer treatments, the tillage methods M and T1 had the TN contents of 1.07 and 1.01 g N kg−1 in the 0–
Fig. 2 Soil total nitrogen (TN) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
FERTILIZER AND TILLAGE INFLUENCES ON SOIL FERTILITY
20 cm layer, respectively, significantly higher than that of the tillage method T2 (0.93 g kg−1 ), indicating that minimum tillage was favourable for soil N conservation. Similar results were also reported by L´ opez-Fando et al. (2007). This was because incorporated straw was susceptible to decomposition and transformation under the treatments with plowing. On the other hand, crop residues left on soil surface under minimum tillage were subject to less disturbance and therefore relatively low decomposition rate. Some N was also added to the soil from irrigation water and precipitation (Hu et al., 2000) and from the straw (Russell and Allan, 1973). In the subsoil layer (20–40 cm), TN content varied between 0.61 and 0.73 g kg−1 , and there were no significant differences (P < 0.05) among the treatments. The average TN contents for the treatments at N2 and N3 were 1.05 and 1.04 g N kg−1 , respectively, higher than that of the treatment at N1 (0.92 g N kg−1 ), indicating that fertilizer N enhanced TN accumulation. There were no significant differences in TN contents among the treatments with different P rates (P1 , P2 , and P3 ) and among the treatments with different straw rates (S1 , S2 , and S3 ). Therefore, P fertilizer and straw application did not contribute significantly to building up TN. Soil total P Soil TP contents were increased after 17 years of fertilizer and tillage treatments: from 0.60 to 0.67–1.31 g kg−1 in the 0–20 cm layer and from 0.52 to 0.60– 0.73 g kg−1 in the 20–40 cm layer (Fig. 3), which indicated that there were more P inputs from the fertilizer and straw than P removal by crop uptake and leaching.Treatments III and V had the TP contents of 1.05 and 1.09 g kg−1 , respectively, significantly higher (P < 0.05) than those of the other treatments (0.67– 0.89 g kg−1 ), indicating that combined N and P fertilizer application was the key for soil P buildup. It was interesting that Treatment VII, with the highest TP content (1.31 g P kg−1 ) but not the highest P input, had significantly higher (P < 0.05) TP than the rest treatments. Minimum tillage may improve soil TP storage (L´opez-Fando et al., 2007). In the 20–40 cm layer, the TP content in Treatment IV reached 0.73 g kg−1 , significantly higher (P < 0.05) than those of the other treatments (0.60–0.64 g kg−1 ) except Treatment VII (0.67 g kg−1 ). Some researchers (e.g., Nguyen et al., 2001) have reported residual P fertilizer accumulation mainly in surface soil layer. In
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Fig. 3 Soil total phosphorous (TP) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
our study, it appeared that with P buildup in the topsoil, the TP content in the 20–40 cm layer was also increased (Fig. 3), probably caused by leaching or mechanical mixing resulting from plowing. Soil rapidly available P Application of chemical P fertilizer increased RP storage in the topsoil layer (Fig. 4). For Treatments VII, V, and III, after 17 years, the RP contents in the 0–20 cm increased to 40.1, 30.3, and 24.4 mg kg−1 , respectively, significantly higher than those of the other treatments.
Fig. 4 Soil rapidly available phosphorous (RP) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
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TABLE IV Crop yields of winter wheat and maize in 2001 after 17 years of different tillage and fertilizer treatments Crop
Treatmenta) I
II
III
IV
V
VI
VII
VIII
IX
−1
kg ha Wheat 1 413.45 db) 6 893.55 b 7 504.05 a 2 001.00 c 7 320.45 ab 1 851.00 cd 1 017.45 d 1 791.00 cd 7 062.45 ab Maize 2 788.50 e 8 422.05 b 8 688.00 a 3 172.95 e 7 685.55 c 4 959.00 d 2 806.50 e 5 358.45 d 8 455.00 ab Total 4 201.95 e 15 315.60 b 16 192.05 a 5 173.95 d 15 006.00 b 6 810.00 c 3 823.95 e 7 149.45 c 15 517.50 ab a) b)
See Table II for details of each treatment. Values in a row followed by the same letter(s) are not significantly different at P < 0.05.
In the 20–40 cm layer, the RP content in 2001 ranged from 1.1 to 10.0 mg kg−1 . A significant increase from 1984 (3.2 mg kg−1 ) was recorded under Treatment IV. No significant RP differences existed among the other treatments. Soil rapidly available K In the past, it was often considered that soils on the North China Plain were rich in K and therefore RK in the soil could meet crop K demands. With increased application of chemical N and P fertilizers, however, the crop yield were improved steadily (Table IV) and the amount of RK removed from the soil was also increased. For the current study, the RK content in the 0–20 cm was 92.60 mg kg−1 in 1984, and was in the range of 82.1–103.2 mg kg−1 in 2001 (Fig. 5). Treatments V and IX, which received no straw application, had significantly lower RK contents than the other
Fig. 5 Soil rapidly available potassium (RK) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
treatments, indicating that returning crop straw into soil was the key to maintaining soil RK level. It was interesting that Treatment I, the treatment without straw application, showed significantly higher RK content than Treatments V and XI. This was explained by the fact that over the years, Treatment I had the lowest crop yield and therefore the least amount of K removal from the soil. On K-rich fluvo-aquic soils, the practice of no chemical K fertilizer and organic manure input for 5 years did not cause any threat to crop yield, but the RK content in the plow layer decreased at a rate of 3.8 mg kg−1 year−1 (Qin et al., 1998). CONCLUSIONS We investigated soil fertility changes as influenced by long-term tillage and fertilizer management practices under a winter wheat-maize annual double cropping system in the North China Plain. In the top soil layer (0–20 cm), the soil organic matter and total nitrogen contents were increased with N, P, and straw applications, but the highest fertilizer rates did not always produce the highest SOM content, indicating that the SOM content did not respond linearly to the fertilizer inputs. Both minimum tillage and conventional tillage with crop residue incorporation enhanced the soil organic matter and total nitrogen accumulation, plowing the soil enhanced organic matter mineralization, broke aggregates, and increased soil aeration. Fertilizer application also improved total N content in the 0–20 cm layer, but treatment differences were not different statistically. Phosphorous fertilizer application significantly increased soil total phosphorus and rapidly available phosphorus contents but nitrogen fertilizer, straw, and tillage system did not have apparent influence on the total phosphorus content. Straw cover after soil tillage plus a reasonable rate of P fertilizer (75 kg ha−1 ) improved P accumulation
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in the 20–40 cm layer. Increasing phosphorous fertilizer rates resulted in higher contents of rapidly available P. With increased N and P fertilizer rates and subsequent improvement in crop production, more rapidly available K was removed from the soil. Returning straw to soil was helpful to slow down the decrease of the rapidly available K, and wheat straw returning to soil was an effective measure to complement potassium. But other measures such as applying chemical K fertilizer were required to rebuild the available K pool in the North China Plain. In conclusion, the SOM, total N, and P may be maintained or increased by continuous applications of N and P fertilizers, other nutrients such as K may be gradually depleted if no chemical fertilizer or crop straw was supplied. This would consequently affect the long-term sustainability of crop production in the North China Plain. ACKNOWLEDGEMENT We are grateful to Prof. Hong Jie Di of Lincoln University, New Zealand, and Prof. Ren Tu-Sheng from China Agricultural University for their help in preparing the manuscript. REFERENCES Albiach, R., Canet, R., Pomares, F. and Ingelmo, F. 2000. Microbial biomass content and enzymatic activities after the application of organic amendments to a horticultural soil. Bioresour. Technol. 75(1): 43–48. Balldock, J. A. and Kay, B. D. 1987. Influence of cropping history and chemical treatments on the water-stable aggregation of a silt loam soil. Can. J. Soil Sci. 67(3): 501–511. Blaise, D., Singh, J. V., Bonde, A. N., Tekale, K. U. and Mayee, C. D. 2005. Effects of farmyard manure and fertilizers on yield, fibre quality and nutrient balance of rainfed cotton (Gossypium hirsutum). Bioresour. Technol. 96(3): 345–349. Blevins, R. L., Smith, M. S. and Thomas, G. W. 1984. Changes in soil properties under no-tillage. In Phillips, R. E. and Phillips, S. H. (eds.) No-Tillage Agriculture: Principles and Practices. Van Nostrand Reinhold, New York, USA. pp. 190–230. Cai, Z. C. and Qin, S. W. 2006a. Crop yield, N use efficiency and environment impact of a long-term fertilization experiment in a fluvo-aquic soil in North China. Acta Pedol. Sin. (in Chinese). 43(6): 885–891. Cai, Z. C. and Qin, S. W. 2006b. Diagnosis of balanced fertilization by N, P, K contents in grain and straw of wheat and maize. Plant Nutr. Fert. Sci. (in Chinese). 12(4): 473–478.
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820 L´ opez-Fando, C., Dorado, J. and Pardo, M. T. 2007. Effects of zone-tillage in rotation with no-tillage on soil properties and crop yields in a semi-arid soil from central Spain. Soil Till. Res. 95(1–2): 266–276. Lundquist, E. J., Jackson, L. E., Scow, K. M. and Hsu, C. 1999. Changes in microbial biomass and community composition, and soil carbon and nitrogen pools after incorporation of rye into three California agricultural soils. Soil Biol. Biochem. 31(2): 221–236. Manna, M. C., Swarup, A., Wanjari, R. H., Ravankar, H. N., Mishra, B., Saha, M. N., Singh, Y. V., Sahid, D. K. and Sarap, P. A. 2005. Long-term effect of fertilizer and manure application on soil organic carbon storage, soil quality and yield sustainability under sub-humid and semi-arid tropical India. Field Crop. Res. 93(2– 3): 264–280. Marcote, I., Hern´ andez, T., Garc´ıa, C. and Polo, A. 2001. Influence of one or two successive annual applications of organic fertilisers on the enzyme activity of a soil under barley cultivation. Bioresour. Technol. 79(2): 147–154. Masto, R. E., Chhonkar, P. K., Singh, D. and Patra, A. K. 2006. Changes in soil biological and biochemical characteristics in a long-term field trial on a sub-tropical inceptisol. Soil Biol. Biochem. 38: 1577–1582. Mead, R., Curnow, R. N., Hasted, A. M. and Currnow, R. M. 1983. Statistical Methods in Agriculture and Experimental Biology. Chapman and Hall, London. Meng, L., Ding, W. X., Cai, Z. C. and Qin, S. W. 2005. Storage of soil organic C and soil respiration as effected by long-term quantitative fertilization. Adv. Earth Sci. 20(6): 687–692 Nguyen, H., Schoenau, J. J., Van Rees, K. C. J., Nguyen, D. and Qian, P. 2001. Long-term nitrogen, phosphorus and potassium fertilization of cassava influences soil chemical properties in North Vietnam. Can. J. Soil Sci. 81(4): 481–488. Niu, L. A., Hao, J. M., Ding, Z. Y., Li, X. B., Niu, X. S. and Zhang, B. Z. 2005. Long-term fertilization effect on fertility of salt-affected soils. Pedosphere. 15(5): 669–675. Niu, L. A., Hao, J. M., Zhang, B. Z. and Niu, X. S. 2003. The changes of soil organic matter and fertilization system in the salt-affected area. J. Chin. Agr. Univ. (in Chinese). 8(supplement): 26–30. Qin, S. W., Gu, Y. C. and Zhu, Z. L. 1998. A preliminary report on long-term stationary experiment on fertility evolution of a fluvo-aquic soil and the effect of fertilization. Acta Pedol. Sin. (in Chinese). 35(3): 367–375.
L. A. NIU et al. Russell, E. J. and Alan, W. 1973. Soil Conditions and Plant Growth. 10th ed. Longmans Ltd., London. Shan, Y. H., Yang, L. Z., Yan, T. M. and Wang, J. G. 2005. Downward movement of phosphorus in paddy soil installed in large-scale monolith lysimeters. Agr. Ecosyst. Environ. 111(1–4): 270–278. Shi, Y. C. and Xin, D. H. 1983. Movement of Water and Salt in Soil and Comprehensive Control of Drought, Waterlogging, Salinity and Water in the Huang-HuaiHai Plain (in Chinese). Hebei People’s Publishing House, Shijiazhuang. Stockfisch, N., Forstreuter, T. and Ehlers, W. 1999. Ploughing effects on soil organic matter after twenty years of conservation tillage in Lower Saxony, Germany. Soil Till. Res. 52(1–2): 91–101. Suo, D. R. 2005. Combined fertilization of chemical and organic fertilizers in a long-term position experiment. Agr. Res. Arid Areas (in Chinese). 23(2): 71–75. Wang, J. H., Lin, X. G., Yin, R., Chu, H. Y., Chen, M. S., Dai, J. and Qin, S. W. 2009. Changes in soil humic acid, microbial biomass carbon and invertase activity in response to fertilization regimes in a long-term field experiment. Plant Nutr. Fert. Sci. 15(2): 352–357. Westerman, R. L. 1990. Soil Testing and Plant Analysis. 3ed. SSSA, Madison. Wright, A. L., Hons, F. M. and Matocha, J. E. 2005. Tillage impacts on microbial biomass and soil carbon and nitrogen dynamics of corn and cotton rotations. Appl. Soil Ecol. 29(1): 85–92. Xiao, W. W., Fan, X. H., Yang, L. Z. and Sun, B. 2009. Effects of long-term fertilization on organic nitrogen fractions and organic carbon in a fluvo-aquic soil. Acta Pedol. Sin. (in Chinese). 46(2): 274–280. Yang, X. M. and Kay, B. D. 2001. Rotation and tillage effects on soil organic carbon sequestration in a typic Hapludalf in Southern Ontario. Soil Till. Res. 59(3– 4): 107–114. Yang, X. M., Zhang, X. P., Deng, W. and Fang, H. J. 2003. Black soil degradation by rainfall erosion in Jilin, China. Land Degrad. Develop. 14(4): 409–420. Yin, Y. F. and Cai, Z. C. 2006. Effect of fertilization on equilibrium levels of organic carbon and capacities of soil stabilizing organic carbon for fluvo-aquic soil. Soils (in Chinese). 38(6): 745–749 Zhang, H. M., Wang, B. R., Xu, M. G. and Fan, T. L. 2009. Crop yield and soil responses to long-term fertilization on a red soil in southern China. Pedosphere. 19(2): 199–207.
Influences of Long-Term Fertilizer and Tillage Management on Soil Fertility of the North China Plain∗1 NIU Ling-An, HAO Jin-Min∗2 , ZHANG Bao-Zhong and NIU Xin-Sheng Quzhou Experimental Station, China Agricultural University, Quzhou 057250 (China) (Received May 15, 2011; revised September 24, 2011)
ABSTRACT In the North China Plain, fertilizer management and tillage practices have been changing rapidly during the last three decades; however, the influences of long-term fertilizer applications and tillage systems on fertility of salt-affected soils have not been well understood under a winter wheat (Triticum aestivum L.)-maize (Zea mays L.) annual double cropping system. A field experiment was established in 1985 on a Cambosol at the Quzhou Experimental Station, China Agricultural University, to investigate the responses of soil fertility to fertilizer and tillage practices. The experiment was established as an orthogonal design with nine treatments of different tillage methods and/or fertilizer applications. In October 2001, composite soil samples were collected from the 0–20 and 20–40 cm layers and analyzed for soil fertility indices. The results showed that after 17 years of nitrogen (N) and phosphorous (P) fertilizer and straw applications, soil organic matter (SOM) in the top layer was increased significantly from 7.00 to 9.30–13.14 g kg−1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg−1 in the 20–40 cm layer. Soil total N (TN) was increased significantly from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg−1 in the 0–20 and 20–40 cm layers, respectively, with N fertilizer application; however, there was no apparent effect of straw application on TN content. The amounts of soil total P (TP) and rapidly available P (RP) were increased significantly from 0.60 to 0.67–1.31 g kg−1 in the 0–20 cm layer and from 0.52 to 0.60–0.73 g kg−1 in the 20–40 cm layer with P fertilizer application, but were decreased with combined N and P fertilizer applications. The applications of N and P fertilizers significantly increased the crop yields, but decreased the rapidly available potassium (RK) in the soil. Straw return could only meet part of the crop potassium requirements. Our results also suggested that though some soil fertility parameters were maintained or enhanced under the long-term fertilizer and straw applications, careful soil quality monitoring was necessary as other nutrients could be depleted. Spreading straw on soil surface before tillage and leaving straw at soil surface without tillage were two advantageous practices to increase SOM accumulation in the surface layer. Plowing the soil broke aggregates and increased aeration of the soil, which led to enhanced organic matter mineralization. Key Words:
rapidly available K, rapidly available P, soil organic matter, straw return, total N
Citation: Niu, L. A., Hao, J. M., Zhang, B. Z. and Niu, X. S. 2011. Influences of long-term fertilizer and tillage management on soil fertility of the North China Plain. Pedosphere. 21(6): 813–820.
INTRODUCTION Improved nitrogen (N) and phosphorous (P) fertilizer management and straw application under different tillage systems can maintain or enhance longterm soil quality. This is particularly true for saltaffected soils that are vulnerable to degradation (Niu et al., 2003, 2005). Long-term fertilizer experiments are valuable for assessing yield trends and changes in nutrient dynamics and balances, predicting soil carrying capacity, and evaluating soil quality and sustain∗1 ∗2
ability. Trends in soil fertility have been reported in many short- (Marcote et al., 2001; Blaise et al., 2005) and long-term fertilizer experiments (Dalal and Mayer, 1986a; Albiach et al., 2000; Manna et al., 2005; Cai and Qin, 2006a, b; Hati et al., 2006; Masto et al., 2006; Ge et al., 2009). Frequent tillage may destroy soil organic matter (SOM) (Hernanz et al., 2002) and speed up the movement of SOM to deep soil layers (Shan et al., 2005). As an ecologically sound approach, conservation tillage usually shows advantages over conventional tillage pra-
Supported by the National Key Technology R & D Program of China (No. 2011BAD04B02). Corresponding author. E-mail: [email protected].
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ctices in improving soil quality and crop yields (Lal, 1989; Dick and Durkalski, 1997), and has the potential to conserve soil water and reduce soil erosion (Yang et al., 2003). No tillage generally favours the accumulation of SOM (Duiker and Beegle, 2006). With the adoption of conservation tillage, SOM content was increased in the 0–20 cm layer (Stockfisch et al., 1999; Wright et al., 2005) and a larger amount of soil organic carbon (SOC) was accumulated in the 0–10 cm layer (Yang and Kay, 2001). In the North China Plain, although a number of studies have been conducted on the changes of soil fertility under continuous cropping systems (Meng et al., 2005; Cai and Qin, 2006a, b; Yin and Cai, 2006; Chu et al., 2007; Wang et al., 2009), few studies have reported the influences of long-term N, P, and straw treatments under different tillage systems on a broad range of soil fertility indices such as SOM content, total nitrogen (TN), total phosphorous (TP), rapidly available P (RP), and rapidly available K (RK), particularly in salt-affected soils. Since the early 1980s, most of the salt-affected soils which had been damaged by drought, water logging, alkalization, salinization, and desertification in the lowland of the North China Plain had been reclaimed successfully (Shi and Xin, 1983). Nevertheless, crop productivity in this area is still low mainly because of low SOM content and N and P deficiencies. The primary objective of this study was to investigate the influences of long-term fertilization and tillage practices on a range of soil fertility indices of a reclaimed salt-affected soil. The influences of cropping practices on sustainability of the salt-affected soils of the North China Plain were also assessed. MATERIALS AND METHODS A field experiment was established in 1985 at the Quzhou Experimental Station of China Agricultural University (115◦ 1 E, 36◦ 51 N, 36 m above sea level), located in Quzhou County of Hebei Province.
With a warm-temperate monsoonal climate, the annual average precipitation at Quzhou is 515.8 mm, which is unevenly distributed in the year: 13.5% in spring (March–May), 65.7% in summer (June–August), 18.1% in autumn (September–November), and 2.8% in winter (December–January). The annual pan evaporation is about 1 837 mm. The shallow groundwater has a salt concentration of 5–11 g L−1 , mostly 5–7 g L−1 . There are two crops in a year: winter wheat (Triticum aestivum L.) from earlier October to the first week of June and maize (Zea mays L.) from the second week of June to the end of September. The soil there is a deep alluvial soil which is classified as a parasalic endorusti-ustic Cambosol in the Chinese Soil Taxonomy (Gong et al., 2007). It is characterized with a loamy texture, high salt content, and salt accumulation in soil profile. The basic soil properties were measured in 1984 and are listed in Table I. Drought, water logging, salinization, and low soil fertility are the major factors that limit crop productivity at the experimental site. The experiment, with an orthogonal design, had nine treatments with different tillage methods and fertilizer application rates (Table II). The tillage methods were: 1) minimum tillage (M), where the straw was spread over the field followed by tillage to 5 cm depth and sowing; 2) conventional tillage with straw incorporation (T1 ), where the straw was spread over the field followed by mouldboard plow to 30 cm depth and sowing; 3) conventional tillage with straw cover on soil surface (T2 ), where the straw was spread on the soil surface after mouldboard plow to 30 cm depth and sowing. There were three N rates, three P rates, and three straw rates (Table II). With three replications per treatment, the total number of field plots was 27. The N fertilizer was urea (460 g kg−1 N) and the P fertilizer was triple superphosphate (430 g kg−1 P2 O5 ). Of the total N fertilizer, 50% was applied to winter wheat, and another 50% to maize. For winter wheat, 30% of the total fertilizer N was applied at planting in earlier October, and 20% was broadcast
TABLE I Physical and chemical properties of the soil at the experimental site Soil depth cm 0–20 20–40
Texture
Silt loam Sandy loam
pH
7.8 7.8
Soil organic matter
Total nitrogen
7.00 4.00
g kg−1 0.37 0.22
Total phosphorus 0.60 0.52
Rapidly available phosphorus 9.9 3.2
Rapidly available potassium
mg kg−1 92.6 71.3
Salt content g kg−1 1.02 1.11
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TABLE II Tillage and fertilizer management of the experiment Treatment
Tillage methoda)
N fertilizer rate
P fertilizer rate −1
I II III IV V VI VII VIII IX
T1 T1 T1 T2 T2 T2 M M M
kg ha year 0 (P1 ) 75 (P2 ) 150 (P3 ) 75 (P2 ) 150 (P3 ) 0 (P1 ) 150 (P3 ) 0 (P1 ) 75 (P2 )
0 (N1 ) 112.5 (N2 ) 187.5 (N3 ) 0 (N1 ) 112.5 (N2 ) 187.5 (N3 ) 0 (N1 ) 112.5 (N2 ) 187.5 (N3 )
Straw rate
−1
0 2 250 4 500 4 500 0 2 250 2 250 4 500 0
(S1 ) (S2 ) (S3 ) (S3 ) (S1 ) (S2 ) (S2 ) (S3 ) (S1 )
a)
T1 = conventional tillage with straw incorporation; T2 = conventional tillage with straw cover on soil surface; M = minimum tillage.
at the soil surface in April, followed by surface irrigation. For maize, 30% and 20% of the N fertilizer was applied at sowing and at the 10- to 12-leaf stage, respectively. The P fertilizer was applied only to winter wheat annually at crop seeding. Generally, each crop was irrigated 3–4 times (705–825 m3 ha−1 each time) with groundwater. The salt content of the groundwater was about 0.75 g L−1 . The varieties of winter wheat and maize used in the study are shown in Table III.
the extraction with 0.5 mol L−1 NaHCO3 . Available K content in the soil was determined by flame emission spectrometry following the extraction with 1 mol L−1 neutral CH3 COONH4 (Westerman, 1990). The experimental results were analysed using the analysis of variance (ANOVA). The differences between treatments were evaluated using the least significant difference (LSD) multiple range test at P = 0.05 (Mead et al., 1983).
TABLE III
RESULTS AND DISCUSSION
Winter wheat (Triticum aestivum L.) and maize (Zea mays L.) varieties used during the experimental period Years
Winter wheat
Maize
1985–1989 1990–1994 1995–2001
Taishan 1 Jimai 23 Han 4564
Yedan 3 Yedan 13 Xiyu 3
In 2001, soil samples were collected from the 0–20 and 20–40 cm layers after maize harvest in October. The samples were air-dried and passed through a 0.25mm sieve for determination of SOM and total N. A sub-sample was passed through a 1-mm sieve for determination of available N, P, and K contents. Soil organic matter content was measured using an oxidative (potassium dichromate) method with 0.4 mol L−1 K2 Cr2 O7 -H2 SO4 solution and titrated with 0.2 mol L−1 FeSO4 . Soil total N content was measured by the Kjeldahl digestion technique, with Se powder and CuSO4 as catalysts. Soil total P was measured using NaOH fusion with the molybdate blue colorimetric method, and available P content was measured using the molybdate blue colorimetric method following
SOM content After 17 years of continuous tillage and fertilizer treatments, SOM contents were increased significantly, from 7.00 to 9.30–13.14 g kg−1 in the 0–20 cm layer and from 4.00 to 5.48–7.75 g kg−1 in the 20–40 cm layer (Table I; Fig. 1). The largest SOM content in the 0–20 cm layer, 13.14 g kg−1 , appeared in Treatment III, being significantly higher than those of Treatments I (10.03 g kg−1 ), IV (9.30 g kg−1 ), and VI (11.76 g kg−1 ). In the 20–40 cm layer, however, Treatment IV showed the largest SOM content (7.75 g kg−1 ), significantly higher than the other treatments except Treatment VIII. Application of N fertilizer, P fertilizer, and straw enhanced SOM accumulation. At the N fertilizer rates of 0, 112.5, and 187.5 kg ha−1 , the average SOM contents in the 0–20 cm layer were 10.39, 12.12, and 11.91 g kg−1 , respectively. At the P fertilizer rates of 0, 75, and 150 kg ha−1 , the average SOM contents were 11.20, 11.30, and 12.03 g kg−1 in 0–20 cm layer and 4.50, 5.37, and 6.42 g kg−1 in 20–40 cm layer, respectively. At
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Fig. 1 Soil organic matter (SOM) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
the straw rates of 0, 2 250, and 4 500 kg ha−1 , the average SOM contents were 11.06, 11.93, and 11.51 g kg−1 in the 0–20 cm layer and 5.96, 5.70, and 6.66 g kg−1 in the 20–40 cm layer, respectively. Clearly, the highest fertilizer rate did not always produce the highest SOM content, indicating that the SOM content did not respond linearly to fertilizer inputs (Suo, 2005; Xiao et al., 2009; Zhang et al., 2009). The three tillage practices showed different influences on SOM accumulation. Averaged over the different treatments, the SOM contents in the 0–20 cm layer were 11.89, 10.75, and 11.78 g kg−1 for the tillage methods T1 , T2 , and M, respectively. Therefore, spreading straw on soil surface before tillage (T1 ) and leaving straw on soil surface with minimum tillage (M) were advantageous to SOM accumulation in the surface layer. On the other hand, plowing the soil broke aggregates and increased soil aeration, which enhanced organic matter mineralization (Blevins et al., 1984; Dalal and Mayer, 1986b; Balldock and Kay, 1987; Cambardella and Elliot, 1993). In the 20–40 cm layer, the treatment with tillage to 30 cm depth, no N fertilizer, 75 kg ha−1 P fertilizer, and 4 500 kg ha−1 straw (Treatment IV) had the highest SOM content (7.75 g kg−1 ), indicating that under the experimental condition, tillage methods and straw rates interactively determined SOM accumulation in the deeper soil layer. While burying crop residues in the soil at tillage (e.g., Treatment III) or leaving crop residues permanently on soil surface (Treatment VIII) enhanced SOM accumulation in the surface layer (0–20 cm), leaving crop residues on soil surface after tillage
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and then incorporating them into soil with deep tillage before sowing the next crop (Treatment VI) was more beneficial to SOM buildup in the deeper layer (20–40 cm). Spreading straw over the field with minimum tillage seemed to have provided large amounts of nutrients for soil microorganisms in the topsoil, which accelerated straw decomposition and decreased the SOM content in the topsoil (0–20 cm). In the subsoil (20– 40 cm), there was minimum tillage disturbance and microorganisms received much less nutrients from the straw; therefore, SOM decomposition rate was relatively low and SOM content was high. Soil active organic matter fraction, expressed as the ratios of microbial biomass C or N to total soil C or N, respectively, appeared to be related to long-term tillage and fertilizer management. These ratios increased in proportion to increased organic inputs and reduced tillage or periods of fallow (Lundquist et al., 1999; Chu et al., 2007). Soil total N After 17 years of tillage and fertilizer treatments, mean content of soil TN was increased from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg−1 in the 0–20 and 20–40 cm layers, respectively (Fig. 2). In the 0–20 cm layer, the TN contents of Treatments III, IX, II, VIII, and I were 1.11, 1.07, 1.05, 1.04, and 0.94 g N kg−1 , respectively, significantly higher (P < 0.05) than that of Treatment IV (0.79 g kg−1 ). Averaged over the fertilizer treatments, the tillage methods M and T1 had the TN contents of 1.07 and 1.01 g N kg−1 in the 0–
Fig. 2 Soil total nitrogen (TN) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
FERTILIZER AND TILLAGE INFLUENCES ON SOIL FERTILITY
20 cm layer, respectively, significantly higher than that of the tillage method T2 (0.93 g kg−1 ), indicating that minimum tillage was favourable for soil N conservation. Similar results were also reported by L´ opez-Fando et al. (2007). This was because incorporated straw was susceptible to decomposition and transformation under the treatments with plowing. On the other hand, crop residues left on soil surface under minimum tillage were subject to less disturbance and therefore relatively low decomposition rate. Some N was also added to the soil from irrigation water and precipitation (Hu et al., 2000) and from the straw (Russell and Allan, 1973). In the subsoil layer (20–40 cm), TN content varied between 0.61 and 0.73 g kg−1 , and there were no significant differences (P < 0.05) among the treatments. The average TN contents for the treatments at N2 and N3 were 1.05 and 1.04 g N kg−1 , respectively, higher than that of the treatment at N1 (0.92 g N kg−1 ), indicating that fertilizer N enhanced TN accumulation. There were no significant differences in TN contents among the treatments with different P rates (P1 , P2 , and P3 ) and among the treatments with different straw rates (S1 , S2 , and S3 ). Therefore, P fertilizer and straw application did not contribute significantly to building up TN. Soil total P Soil TP contents were increased after 17 years of fertilizer and tillage treatments: from 0.60 to 0.67–1.31 g kg−1 in the 0–20 cm layer and from 0.52 to 0.60– 0.73 g kg−1 in the 20–40 cm layer (Fig. 3), which indicated that there were more P inputs from the fertilizer and straw than P removal by crop uptake and leaching.Treatments III and V had the TP contents of 1.05 and 1.09 g kg−1 , respectively, significantly higher (P < 0.05) than those of the other treatments (0.67– 0.89 g kg−1 ), indicating that combined N and P fertilizer application was the key for soil P buildup. It was interesting that Treatment VII, with the highest TP content (1.31 g P kg−1 ) but not the highest P input, had significantly higher (P < 0.05) TP than the rest treatments. Minimum tillage may improve soil TP storage (L´opez-Fando et al., 2007). In the 20–40 cm layer, the TP content in Treatment IV reached 0.73 g kg−1 , significantly higher (P < 0.05) than those of the other treatments (0.60–0.64 g kg−1 ) except Treatment VII (0.67 g kg−1 ). Some researchers (e.g., Nguyen et al., 2001) have reported residual P fertilizer accumulation mainly in surface soil layer. In
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Fig. 3 Soil total phosphorous (TP) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
our study, it appeared that with P buildup in the topsoil, the TP content in the 20–40 cm layer was also increased (Fig. 3), probably caused by leaching or mechanical mixing resulting from plowing. Soil rapidly available P Application of chemical P fertilizer increased RP storage in the topsoil layer (Fig. 4). For Treatments VII, V, and III, after 17 years, the RP contents in the 0–20 cm increased to 40.1, 30.3, and 24.4 mg kg−1 , respectively, significantly higher than those of the other treatments.
Fig. 4 Soil rapidly available phosphorous (RP) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
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TABLE IV Crop yields of winter wheat and maize in 2001 after 17 years of different tillage and fertilizer treatments Crop
Treatmenta) I
II
III
IV
V
VI
VII
VIII
IX
−1
kg ha Wheat 1 413.45 db) 6 893.55 b 7 504.05 a 2 001.00 c 7 320.45 ab 1 851.00 cd 1 017.45 d 1 791.00 cd 7 062.45 ab Maize 2 788.50 e 8 422.05 b 8 688.00 a 3 172.95 e 7 685.55 c 4 959.00 d 2 806.50 e 5 358.45 d 8 455.00 ab Total 4 201.95 e 15 315.60 b 16 192.05 a 5 173.95 d 15 006.00 b 6 810.00 c 3 823.95 e 7 149.45 c 15 517.50 ab a) b)
See Table II for details of each treatment. Values in a row followed by the same letter(s) are not significantly different at P < 0.05.
In the 20–40 cm layer, the RP content in 2001 ranged from 1.1 to 10.0 mg kg−1 . A significant increase from 1984 (3.2 mg kg−1 ) was recorded under Treatment IV. No significant RP differences existed among the other treatments. Soil rapidly available K In the past, it was often considered that soils on the North China Plain were rich in K and therefore RK in the soil could meet crop K demands. With increased application of chemical N and P fertilizers, however, the crop yield were improved steadily (Table IV) and the amount of RK removed from the soil was also increased. For the current study, the RK content in the 0–20 cm was 92.60 mg kg−1 in 1984, and was in the range of 82.1–103.2 mg kg−1 in 2001 (Fig. 5). Treatments V and IX, which received no straw application, had significantly lower RK contents than the other
Fig. 5 Soil rapidly available potassium (RK) contents in 2001 after 17 years of different tillage and fertilizer treatments. See Table II for details of each treatment. Bars with the same uppercase letter(s) and lowercase letter(s) indicate no significant difference at P < 0.05 in the 0–20 and 20–40 cm layers, respectively.
treatments, indicating that returning crop straw into soil was the key to maintaining soil RK level. It was interesting that Treatment I, the treatment without straw application, showed significantly higher RK content than Treatments V and XI. This was explained by the fact that over the years, Treatment I had the lowest crop yield and therefore the least amount of K removal from the soil. On K-rich fluvo-aquic soils, the practice of no chemical K fertilizer and organic manure input for 5 years did not cause any threat to crop yield, but the RK content in the plow layer decreased at a rate of 3.8 mg kg−1 year−1 (Qin et al., 1998). CONCLUSIONS We investigated soil fertility changes as influenced by long-term tillage and fertilizer management practices under a winter wheat-maize annual double cropping system in the North China Plain. In the top soil layer (0–20 cm), the soil organic matter and total nitrogen contents were increased with N, P, and straw applications, but the highest fertilizer rates did not always produce the highest SOM content, indicating that the SOM content did not respond linearly to the fertilizer inputs. Both minimum tillage and conventional tillage with crop residue incorporation enhanced the soil organic matter and total nitrogen accumulation, plowing the soil enhanced organic matter mineralization, broke aggregates, and increased soil aeration. Fertilizer application also improved total N content in the 0–20 cm layer, but treatment differences were not different statistically. Phosphorous fertilizer application significantly increased soil total phosphorus and rapidly available phosphorus contents but nitrogen fertilizer, straw, and tillage system did not have apparent influence on the total phosphorus content. Straw cover after soil tillage plus a reasonable rate of P fertilizer (75 kg ha−1 ) improved P accumulation
FERTILIZER AND TILLAGE INFLUENCES ON SOIL FERTILITY
in the 20–40 cm layer. Increasing phosphorous fertilizer rates resulted in higher contents of rapidly available P. With increased N and P fertilizer rates and subsequent improvement in crop production, more rapidly available K was removed from the soil. Returning straw to soil was helpful to slow down the decrease of the rapidly available K, and wheat straw returning to soil was an effective measure to complement potassium. But other measures such as applying chemical K fertilizer were required to rebuild the available K pool in the North China Plain. In conclusion, the SOM, total N, and P may be maintained or increased by continuous applications of N and P fertilizers, other nutrients such as K may be gradually depleted if no chemical fertilizer or crop straw was supplied. This would consequently affect the long-term sustainability of crop production in the North China Plain. ACKNOWLEDGEMENT We are grateful to Prof. Hong Jie Di of Lincoln University, New Zealand, and Prof. Ren Tu-Sheng from China Agricultural University for their help in preparing the manuscript. REFERENCES Albiach, R., Canet, R., Pomares, F. and Ingelmo, F. 2000. Microbial biomass content and enzymatic activities after the application of organic amendments to a horticultural soil. Bioresour. Technol. 75(1): 43–48. Balldock, J. A. and Kay, B. D. 1987. Influence of cropping history and chemical treatments on the water-stable aggregation of a silt loam soil. Can. J. Soil Sci. 67(3): 501–511. Blaise, D., Singh, J. V., Bonde, A. N., Tekale, K. U. and Mayee, C. D. 2005. Effects of farmyard manure and fertilizers on yield, fibre quality and nutrient balance of rainfed cotton (Gossypium hirsutum). Bioresour. Technol. 96(3): 345–349. Blevins, R. L., Smith, M. S. and Thomas, G. W. 1984. Changes in soil properties under no-tillage. In Phillips, R. E. and Phillips, S. H. (eds.) No-Tillage Agriculture: Principles and Practices. Van Nostrand Reinhold, New York, USA. pp. 190–230. Cai, Z. C. and Qin, S. W. 2006a. Crop yield, N use efficiency and environment impact of a long-term fertilization experiment in a fluvo-aquic soil in North China. Acta Pedol. Sin. (in Chinese). 43(6): 885–891. Cai, Z. C. and Qin, S. W. 2006b. Diagnosis of balanced fertilization by N, P, K contents in grain and straw of wheat and maize. Plant Nutr. Fert. Sci. (in Chinese). 12(4): 473–478.
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