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Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain
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Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain Z.C. Yang a,b , N. Zhao a, *, F. Huang a , Y.Z. Lv a a b
College of Resources and Environment, China Agricultural University, Beijing 100193, PR China Institute of Agricultural Integrated Development, Beijing Academy of Agricultural and Forest Science, Beijing 100097, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 December 2013 Received in revised form 24 June 2014 Accepted 29 June 2014
The aim of the study is to analyze the effects of different fertilization of organic and inorganic fertilizers on soil organic carbon (SOC) sequestration and crop yields after a 22 years long-term field experiment. The crop yields and SOC were investigated from 1981 to 2003 in Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hebei Province, China. The dominant cropping systems are winter wheat–summer corn rotation. There were totally sixteen treatments applied to both wheat and corn seasons: inorganic fertilizers as main plots and corn stalks as subplots and the main plots and subplots all have four levels. The results revealed: after 22 years, mixed application of inorganic fertilizers and crop residuals, the SOC and crop yields substantially increased. Higher fertilizer application rates resulted in greater crop yields improvement. In 2002–2003, wheat and corn for the highest fertilizer inputs had the highest yield level, 6400 kg ha1 and 8600 kg ha1, respectively. However, the SOC decreased as the excessive inorganic fertilizer input and increased with the rising application of corn stalks. The treatment of the second-highest inorganic fertilizer and the highest corn stalks had the highest SOC concentration (8.64 g C kg1). Pearson correlation analysis shows that corn and winter wheat yields and the mineralization amount of SOC have significant correlation with SOC at p < 0.05 level. ã 2014 Elsevier B.V. All rights reserved.
Keywords: Wheat Corn stalks Long-term experiment Soil organic carbon sequestration Crop yields
1. Introduction The food security in China is very important because the large population and the better living standard need more food. The North China Plain (NCP) is one of the most important agricultural regions, where about 35 million ha of croplands are located and at least 14 million ha of land area is dominated by the cropping system of winter wheat–summer corn rotation (Liu et al., 2003). Winter wheat and summer corn cultivated on the NCP account for 48% and 59% of the country’s total, respectively (Liu and Mu, 1993). Therefore, the soil quality and crop yields of NCP have great implications for China’s food supply. Manure application to soil had been a common practice adopted at NCP for many centuries. It can enrich soil and hence ensure crop yields. But recently organic manure application has almost disappeared because the application of organic manure in arable cropping system is both labor-demanding and
* Corresponding author. Tel.: +86 1062731431. E-mail address: [email protected] (N. Zhao).
cost-inefficient. Another factor may be due to the increased use of inorganic fertilizers and biocides and consequential considerable increase of soil productivity in a relatively short time (Ellis and Wang, 1997). However, the application of inorganic fertilizer could reduce soil fertility and crop productivity in the long run (Yaduvanshi, 2001; Khan et al., 1986). Soil degradation is threatening food security (Oldeman et al., 1990), and will increase the emission of CO2. The rising level of carbon dioxide in the atmosphere is highly correlated with global warming. Therefore soil quality and its importance for sustainable agricultural development has received growing attention in recent years (Dumanski and Pieri, 2000; Zhang et al., 2003). Many researchers are concerned with the ways of addressing soil degradation to achieve a sustainable agriculture and CO2 abatement. Numerous researches had shown that manure applications can increase crop yields and soil organic matter (SOM), and improve the soil quality as well (Blair et al., 2006). As the rapid development of agricultural machinery, the practice of returning crop stalks to farm field has become one of the main sources of organic fertility required by cropland. Returning crop stalks like green manure can reduce soil erosion
http://dx.doi.org/10.1016/j.still.2014.06.011 0167-1987/ ã 2014 Elsevier B.V. All rights reserved.
Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011
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2.2. Soil sampling and chemical analyses
and ameliorate soil physical properties (MacRae and Mehuys, 1985; Smith et al., 1987), enhance SOM and fertility (Doran and Smith, 1987; Power, 1990), increase capacity of nutrient retention (Drinkwater et al., 1998; Dinnes et al., 2002), and decrease global warming potential (Robertson et al., 2000). This study was carried out based on the results of a long-term winter wheat–summer corn field experiment conducted from 1981 to 2003. The objectives of the study were (1) to assess effects of inorganic and corn stalks on yields and yield trends of both winter wheat and corn, (2) to monitor the changes in soil organic carbon (SOC) content under continuous winter wheat–corn cropping with different soil fertility management practices, and (3) to identify reasons for yields and SOC trends.
Soil samples were collected from the top soil layer (0–20 cm) of each plot once a year after the corn crop harvest, and then were air dried and subsequently ground to pass a 0.25 mm sieve. Soil organic matter was determined by a standard potassium dichromate digest method, and total N was measured with the Kjeldahl method. To determine the available P, soil samples were first extracted with HClO4-H2SO4 solution and 0.5 mol L1 NaHCO3 (pH 8.5), respectively. Subsequently, the Olsen P method was used. Available K was extracted with an ammonium acetate solution (NH4OAc, 1 mol L1) and then determined with a flame photometer.
2. Methods and materials
2.3. Incubation soil: C mineralization
2.1. Description of the long-term experiment
The samples for incubation were taken in October each year after corn harvest. Samples (10 g) of whole soil were incubated in triplicate in 500 mL glass jars. During the incubation, soil samples were wetted to field capacity. Small glass bottles were fitted within the jars containing 10 mL of 0.25 M NaOH to trap the CO2 evolved. Jars were sealed and stored in a dark room at 27 C. C evolution was determined by pipetting 5 mL of the C-containing NaOH, and autotitrating with 0.15 M HCl after precipitation of carbonates with 8 mL of 3 M BaCl2 (De Neve and Hofman, 2000).
The experiment was carried out at the Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hengshui (37420 N, 115 420 E, altitude of 31 m above sea level), Hebei Province, China from 1981 to 2003. The soil is alluvial soil (Soil taxonomy of USDA, 1999) with particle composition of sand 27.2%, silt 55.1%, and clay 17.7%. Selected soil properties were measured at the start of the experiment (in Table 1). The annual average precipitation was 411 mm with nearly all occurring between June and September (Fig. 1 in Supplementary data) and the annual average temperature was 12.5 C. The experiment utilized the split-plot design with inorganic fertilizers as main plots and corn stalks as subplots. The main plots and subplots all had four levels of treatments, which were expressed as A and B, respectively. So there were totally sixteen treatments with three replicates each treatment, which were set as (A1, A2, A3, A4)*(B1, B2, B3, B4). The four levels of main plots were: A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1). The larger the number attached to treatment appellations indicated a higher level of fertilizer input, either of inorganic or organic fertilizers. Phosphorous was applied as basal fertilizers once and for all prior to sowing of winter wheat in October. Nitrogen was divided into two halves, one for winter wheat and the other for summer corn. Half of the N that was allocated to winter wheat was applied as basal fertilizers just prior to its sowing, while the remaining half was top-dressed. All Nfertilizers that were allocated for corn were top-dressed. As for application method, basal fertilizers were applied before crop sowing and were mixed with soil by plowing, and top-dressing was applied to the soil surface before the tillage stage. Prior to the next round of planting, corn stalks were spread on the soil surface and incorporated into the soil through plowing with adequate irrigation that was applied during crop growth season. Winter wheat was grown at the end of October and harvested in early June, followed immediately by the sowing of corn in mid-June, which was harvested in mid-October. Winter wheat and summer corn required irrigation according to their specific water-demanding stages. To control growth-reducing factors, hand weeding and other plant protection measures were applied as needed.
2.4. Statistical analysis All ANOVA, regression, and multivariate analyses were conducted in SPSS 13.0. Treatments were analyzed by one-way ANOVA and significant differences between means were judged by Turkey's post-hoc tests. To determine the key factor (s) affecting yields and the quantitative relationships between them, stepwise multiple regression analysis was applied using the criteria of probability of p < 0.05 to accept. 3. Results and discussion 3.1. Wheat and corn yields and soil organic carbon content In order to assess the effects of inorganic and corn stalks organic nutrient sources on yields and yield trends of both winter wheat and corn, we selected the treatments of A1B1, A1B4, A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 to analyze. Yields in all treatments displayed similar changes, which increased overtime for A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 treatments, remained fairly steady for A1B1, A1B4 treatments, and decreased in some years (Fig. 1). Yields fluctuations were largest for A4B4 and smallest for A1B1. In 2002–2003, some treatments of wheat yield increased again and A4B4 treatment had the highest yield, that is, about 6400 kg ha1. For corn yield, A4B4 treatment also had the highest yield, about 8600 kg ha1. In the long run, the decrease in yields of both wheat and corn was the strongest with the A1B1 and A1B4. In both wheat and corn, yields of A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 were higher than those of A1B1, A1B4. The treatments of A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 substantially increased the yields of wheat and corn, especially from 1999 to 2000. So the response of wheat and corn to inorganic and organic fertilizers was distinct in the long term. By comparing the yield
Table 1 Characteristics of the 0–20 cm layers of the soil at the beginning of the experiment plot, Hengshui, China. Soil layer (cm)
Organic matter (g kg1)
Available N (g kg1)
Available P (mg kg1)
Bulk density (g cm3)
Field capacity (%)
Wilting coefficient (%)
pH
0–20
11.51
0.05
12
1.14
27.65
8.20
8.32
Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011
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7000
-1
Wheat yield (kg ha )
6000
A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
5000 4000 3000 2000 1000
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03
0
Year
-1 Corn yield (kg ha )
10000 9000
A1B1
A1B4
A2B1
A2B4
8000
A3B1
A3B4
A4B1
A4B4
7000 6000 5000 4000 3000 2000 1000
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03
0
Year Fig. 1. Winter wheat and corn yields during the 22 years field experiment at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1).
trends with precipitation trends (Fig. 1 in Supplementary data), we found that yields exhibited positive relationship with annual precipitation. For example, precipitation increased during 1982–1983, 1989–1990, 1993–1994, 1999–2000, the yields also had an increased trends in the same periods. SOC sequestration from fertilization application is a key pathway by sequestering CO2 in agriculture. The amount of SOC was related to the amount of plant residues that were returned to soil. Fertilization will affect the amount of SOC generated by crop residues left in the field after harvest (Gregorich and Drury, 1996). We examined the effects of long-term application of inorganic fertilizer (N and P), organic fertilizer, and combination of inorganic fertilizer and organic fertilizer on SOC dynamics. The SOC in different treatments had similar trends over time (Fig. 2). From 1984 to 1986, SOC showed a distinct declining trend over time. SOC under A1B1 declined rapidly in the first year until to the end of the experiment, albeit with a much slower rate. Overall reduction in SOC under A1B1 was 7.3% in the investigated 21 years. SOC under varying fertility treatments (A1B4, A2B1, A2B4, A3B1, A3B4, A4B1, and A4B4) all increased at the end of the experiment, suggesting that organic and inorganic
fertilizer can promote the accumulation of SOC and improve soil fertility in the long term (Dong et al., 2012). A3B4 had remarkably improved SOC which resulted in the highest SOC concentration (8.64 g C kg1). The average of yields over 1982–2003 was used to evaluate the long-term effects of inorganic and organic fertilizer. As observed in Fig. 3(a), the yields of both wheat and corn were higher followed by the application of more inorganic fertilizer and organic fertilizer. With the application of corn stalks, crop yields converged in both treatments, the difference between the A1, A2, A3, and A4 was obvious. However, for the same level of inorganic fertilizer, the yields increased with the application of more corn stalks, but the increasing rate was weak, suggesting that the inorganic fertilizer can increase the crop yields in a short time span. The corn yield was higher than wheat in all treatments except A4B1, suggesting that corn was more responsive to fertilization than wheat. A4B4 treatment produced the highest average yields (4351.5 kg ha1 and 4707.5 kg ha1), fertilization increased yields by 370% for wheat and by 75% for corn compared to A1B1. In sum, conjunctive application of inorganic and organic fertilizers can increase crop yields substantially (Nie et al., 2007; Singh et al., 2007).
Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011
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Soil organic carbon (g C kg-1 )
9 8.5
A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
8 7.5 7 6.5 6 5.5
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02
5
Year Fig. 2. Change in soil organic carbon content (0–20 cm) at sampling time after corn harvest at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1).
Fig. 3(b) also showed that all treatments of the applied fertilizers can increase SOC compared with A1B1 (Zhong et al., 2007; Masto et al., 2007), the effect became stronger as more inorganic and organic fertilizers were added. This means that the best way of enriching soil was the combination of inorganic and organic fertilizers (Malhi et al., 2006). Such combination can increase SOC very efficiently (Melero et al., 2006), indicating that fertilizers benefit the storage and accumulation of SOC in this long term experiment. For the treatment of A4B4, the SOC content was lower than that in A3B4, because more chemical fertilizers may inhibit the increase of SOC and hence lead to soil degradation.
(a) 5000
-1
Yields (kg ha )
4000
3000
2000
3.2. The effects of soil organic carbon content on crop yields
1000
0 A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
A3B4
A4B1
A4B4
Treatment
(b) 10 9
-1
Soil organic carbon (g kg )
8 7 6 5 4 3 2 1 0 A1B1
A1B4
A2B1
A2B4
A3B1
Treatment Fig. 3. Average of wheat and corn yields (a), SOC (b) in the different fertilizer treatments in the field experiment at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1). For Fig. 3(a), the white bars are the wheat yield and grey bars are the corn yield. The error bar is the standard deviation.
Analysis of variance across years was done to determine the effects of treatments (Gomez and Gomez, 1984). Grain yields of winter wheat and corn were recorded every year (1982–2003) from replicated treatments. The effects of corn stalks, inorganic fertilizer, soil organic carbon content, and the interaction between corn stalks and inorganic fertilizer on both winter wheat and corn yields were found significant (p < 0.05). In long-term experiments crop yields may be associated with such various factors as nutrients, cultivars, climate, soil types and management practices, and so on. Researchers had reported in recent years that soil organic matter was one of the most important factors in determining crop yields (Quiroga et al., 2006). Our research shows similar result. By Pearson correlation analysis of SPSS (Fig. 4), the corn yield had significant correlation with SOC at p < 0.05 level tow tailed (n = 240, r = 0.569), and the winter wheat yield had significant correlation with SOC at p < 0.05 level tow tailed (n = 240, r = 0.548). SOC increased with the rising in yields. It seems that SOC can increase crop yields, but there is some questions regarding the result: can the inorganic fertilizers increase SOC and increase crop yields at the same time? Is the increase of crop yields the only response to the application of inorganic fertilizer? What practices can be adopted to boost yields as a result of changes in soil organic matter content? SOC is an important nutrition sink for crops. The nutrients in SOC can be released by mineralizing, which afterwards can be used by crops to increase crop yields. The mineralization amount of SOC will be enhanced with the increase of SOC. Therefore, the mineralization amount of SOC is an important parameter in
Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011
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determining crop yields. Pearson correlation analysis found the mineralization amount of SOC had significant correlation with SOC (Fig. 5) and winter wheat yield (Fig. 6) at p < 0.05 level two tailed (n = 240, r = 0.601 and r = 0.583), but had low significant with corn yield (Fig. 6) at p < 0.05 level two tailed (n = 240, r = 0.419). This may be due to the fact that the mineralization amount of SOC was measured in October, after the harvest of corn. So the mineralization release nutrients for winter wheat and with more SOC being mineralized, winter wheat yield would rise further. But for corn, the nutrients released by mineralization became less, and hence the amount of SOC had lower correlation with corn yield than with winter wheat yield. Results of the correlation analyses from long-term experiments showed that crop yields will increase as the SOC increase, thus SOC was a very key factor in determining crop yields.
Wheat yield (t ha-1)
(a) 7.0
Total
6.0
Fit line for total 95% Confidence intervals
5.0 4.0 3.0 2.0 1.0
R2 linear = 0.548
0.0 5.0
6.0
7.0
8.0
9.0
Soil organic carbon (g kg-1)
4. Conclusion
(b) Total Fit line for total 95% Confidence intervals
10.0
Corn yield (t ha-1)
5
8.0 6.0 4.0 2.0
R2 linear = 0.569
0.0 5.0
6.0
7.0
8.0
9.0
Soil organic carbon (g kg-1) Fig. 4. Correlation of soil organic carbon and crop yields in the 21 years field experiment at Hengshui, China. Total refers to the total experiment data.
Significant differences in SOC and crop yields among different fertilization treatments were found in the study. Without fertilizer (A1B1), the SOC and crop yields will decline in a long-term experiment. The application of only corn stalks (A1B4) had a low efficiency in increasing SOC and crop yields. Combination of inorganic and organic fertilizer can substantially increase SOC and crop yields. The crop yields increased further with more fertilizer being added. Meanwhile, the treatment of A4B4 had the highest crop yields. However, SOC decreased with less inorganic fertilizers application and SOC increased with the addition of corn stalks. Fertilizer was an effective way of SOC storage. There was a trend that the crop yields had a relationship with SOC. More than twenty years of continuous winter wheat–summer corn rotation cultivation revealed a significant correlation at p < 0.05 level (tow tailed) between crop yields and SOC. The mineralization amount of SOC had a significant correlation at p < 0.05 level (tow tailed) with wheat yield which can confirm the result of crop yield related to SOC. North China Plain is one of the most important agricultural regions in China and the dominant cropping systems are winter
Soil organic carbon mineralization amount (g kg-1)
0.8
Total Fit line for total 95% Confidence intervals
0.7
0.6
0.5
0.4
0.3
0.2
R2 linear = 0.601 0.1 5.0
6.0
7.0
8.0
9.0
-1
Soil organic carbon (g kg ) Fig. 5. Correlation of SOC and mineralization amount of SOC in the 21 years field experiment at Hengshui, China. Total refers to the total experiment data.
Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011
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6.0
Wheat yield (t ha-1)
5.0
4.0
3.0
2.0
1.0
567 568 569 570 571 572 573 574 575 576 577 578 579
10.0
Total
Total
Fit line for total
Fit line for total
95% Confidence intervals
6.0
4.0
2.0
R2 linear = 0.583
R2 linear = 0.419
0.0
0.0 0.1
95% Confidence intervals
8.0
Corn yield (t ha-1)
7.0
0.2
0.3
0.4
0.5
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0.8
Mineralization count of soil organic carbon (g kg-1)
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Mineralization count of soil organic carbon (g kg-1)
Fig. 6. Correlation of mineralization amount and wheat and corn yields in the field experiment at Hengshui, China. Total refers to the total experiment data.
wheat–summer corn rotations. The combination of inorganic and corn stalks can replace the farmyard manure and green manure to fertilize soil and sustain crop yields. Acknowledgements This study was financed by the planning subject of “the twelfth five-year plan” in national science and technology for the rural development in China (2012BAD14B01-1) and special research of environmental nonprofit industry (2013467036). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.still.2014.06.011. References Blair, N., Faulkner, R.D., Till, A.R., Poulton, P.R., 2006. Long-term management impacts on soil C, N and physical fertility part I: broadbalk experiment. Soil Till. Res. 91, 30–38. De Neve, S., Hofman, G., 2000. Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues. Biol. Fertil. Soils 30, 544–549. Dinnes, D.L., Karlen, D.L., Jaynes, D.B., Kaspar, T.C., Hatfield, J.L., Colvin, T.S., Cambardella, C.A., 2002. Nitrogen management strategies to reduce nitrate leaching in tile-drainded midwestern soil. Agron. J. 94, 153–171. Dong, W.Y., Zhang, X.Y., Wang, H.M., Dai, X.Q., Sun, X.M., Qiu, W.W., Yang, F.T., 2012. Effect of different fertilizer application on the soil fertility of paddy soils in red soil region of Southern China. PLoS One 7, 1–9. Doran, J.W., Smith, M.S., 1987. Organic matter management and utilization of soil and fertilizer nutrients. In: Follett, et al. (Ed.), et al., Soil Fertility and Organic Matter as Critical Components of Production Systems. Spec. Pub. 9. SSSA, Madison, WI, pp. 53–72. Drinkwater, L.E., Wagoner, P., Sarrantonio, M., 1998. Legume-based cropping systems have reduced carbon and nitrogen losses. Nature 396, 262–265. Dumanski, J., Pieri, C., 2000. Land quality indicators: research plan. Agric. Ecosyst. Environ. 81, 93–102. Ellis, E.C., Wang, S.M., 1997. Sustainable traditional agriculture in the Tai Lake region of China. Agric. Ecosyst. Environ. 61, 177–192. Gomez, K.A., Gomez, A.A., 1984. Statistical Procedures for Agricultural Research. John Wiley & Sons, New Delhi.
Gregorich, E.G., Drury, C.F., 1996. Fertilizer increases corn yield and soil organic matter. Better Crops 80, 3–5. Khan, S.K., Mohanty, S.K., Chalam, A.B., 1986. Integrated management of organic manure and fertilizer for rice. J. Indian Soc. Soil Sci. 34, 505–509. Liu, X., Ju, X., Zhang, F., Pan, J., Christie, P., 2003. Nitrogen dynamics and budgets in a winter wheat-maize cropping systems in the North China Plain. Field Crop Res. 83, 111–124. Liu, X.H., Mu, Z.G., 1993. Cropping systems in Huanghuaihai region Cropping Systems in China. Agricultural Press of China, Beijing, pp. 388–407. MacRae, R.J., Mehuys, G.R., 1985. The effect of green manuring on the physical properties of temperate-area soils. Adv. Soil Sci. 3, 71–94. Malhi, S.S., Lemke, R., Wang, Z.H., Chhabra, B.S., 2006. Tillage, nitrogen and crop residue effects on crop yield, nutrient uptake, soil quality, and greenhouse gas emissions. Soil Till. Res. 90, 171–183. Masto, R.E., Chhonkar, P.K., Singh, D., Patra, A.K., 2007. Soil quality response to longterm nutrient and crop management on a semi-arid Inceptisol. Agric. Ecosyst. Environ. 118, 130–142. Nie, J., Zhou, J.M., Wang, H.Y., Chen, X.Q., Du, C.W., 2007. Effect of long-term rice straw return on soil glomalin, carbon and nitrogen. Pedosphere 17, 295–302. Oldeman, L.R., Hakkeling, R.T.A., Sombroek, W.G., 1990. World Map of Humaninduced Soil Degradation. ISRIC, Wageningen, The Netherlands UNEP, Nairobi. Power, J.F., 1990. Use of green manures in the Great Plains. In: Havlin, J.L., Jacobsen, J. S. (Eds.), Proceedings of the Great Plains Soil Fertility Conference, Denver, CO, 6– 7 March Kansas State University Manhattan, KS. , pp. 1–18. Quiroga, A., Funaro, D., Noellemeyer, E., Peinemann, N., 2006. Barley yield response to soil organic matter and texture in the Pampas of Argentina. Soil Till. Res. 90, 63–68. Melero, S., Ruiz, J.C., Herencia, J.F., Madejon, E., 2006. Chemical and biochemical properties in a silty loam soil under conventional and organic management. Soil Till. Res. 90, 162–170. Robertson, G.P., Paul, E.A., Harwood, R.R., 2000. Greenhouse gases in intensive agriculture: contributions of individual gases to the radioactive forcing of the atmosphere. Science 289, 1922–1925. Singh, G., Jalota, S.K., Singh, Y., 2007. Manuring and residue management effects on physical properties of a soil under the rice–wheat system in Punjab, India. Soil Till. Res. 94, 229–238. Smith, M.S., Frye, W.W., Varco, J.J., 1987. Legume winter cover crops. Adv. Soil Sci. 7, 95–139. Yaduvanshi, N.P.S., 2001. Effect of five years of rice–wheat cropping and NPK fertilizer use with and without organic and green manures on soil properties and crop yields in a reclaimed sodic soil. J. Indian Soc. Soil Sci. 49, 714–719. Zhang, F.S., Chen, X.P., Ma, W.Q., 2003. Discussion on fertilizer in an area of modern agriculture. Phosphate Compound Fertil. 18, 1–3. Zhong, W.H., Cai, Z.C., Zhang, H., 2007. Effects of long-term application of inorganic fertilizers on biochemical properties of a rice-planting red soil. Pedosphere 17, 419–428.
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Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain Z.C. Yang a,b , N. Zhao a, *, F. Huang a , Y.Z. Lv a a b
College of Resources and Environment, China Agricultural University, Beijing 100193, PR China Institute of Agricultural Integrated Development, Beijing Academy of Agricultural and Forest Science, Beijing 100097, PR China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 28 December 2013 Received in revised form 24 June 2014 Accepted 29 June 2014
The aim of the study is to analyze the effects of different fertilization of organic and inorganic fertilizers on soil organic carbon (SOC) sequestration and crop yields after a 22 years long-term field experiment. The crop yields and SOC were investigated from 1981 to 2003 in Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hebei Province, China. The dominant cropping systems are winter wheat–summer corn rotation. There were totally sixteen treatments applied to both wheat and corn seasons: inorganic fertilizers as main plots and corn stalks as subplots and the main plots and subplots all have four levels. The results revealed: after 22 years, mixed application of inorganic fertilizers and crop residuals, the SOC and crop yields substantially increased. Higher fertilizer application rates resulted in greater crop yields improvement. In 2002–2003, wheat and corn for the highest fertilizer inputs had the highest yield level, 6400 kg ha1 and 8600 kg ha1, respectively. However, the SOC decreased as the excessive inorganic fertilizer input and increased with the rising application of corn stalks. The treatment of the second-highest inorganic fertilizer and the highest corn stalks had the highest SOC concentration (8.64 g C kg1). Pearson correlation analysis shows that corn and winter wheat yields and the mineralization amount of SOC have significant correlation with SOC at p < 0.05 level. ã 2014 Elsevier B.V. All rights reserved.
Keywords: Wheat Corn stalks Long-term experiment Soil organic carbon sequestration Crop yields
1. Introduction The food security in China is very important because the large population and the better living standard need more food. The North China Plain (NCP) is one of the most important agricultural regions, where about 35 million ha of croplands are located and at least 14 million ha of land area is dominated by the cropping system of winter wheat–summer corn rotation (Liu et al., 2003). Winter wheat and summer corn cultivated on the NCP account for 48% and 59% of the country’s total, respectively (Liu and Mu, 1993). Therefore, the soil quality and crop yields of NCP have great implications for China’s food supply. Manure application to soil had been a common practice adopted at NCP for many centuries. It can enrich soil and hence ensure crop yields. But recently organic manure application has almost disappeared because the application of organic manure in arable cropping system is both labor-demanding and
* Corresponding author. Tel.: +86 1062731431. E-mail address: [email protected] (N. Zhao).
cost-inefficient. Another factor may be due to the increased use of inorganic fertilizers and biocides and consequential considerable increase of soil productivity in a relatively short time (Ellis and Wang, 1997). However, the application of inorganic fertilizer could reduce soil fertility and crop productivity in the long run (Yaduvanshi, 2001; Khan et al., 1986). Soil degradation is threatening food security (Oldeman et al., 1990), and will increase the emission of CO2. The rising level of carbon dioxide in the atmosphere is highly correlated with global warming. Therefore soil quality and its importance for sustainable agricultural development has received growing attention in recent years (Dumanski and Pieri, 2000; Zhang et al., 2003). Many researchers are concerned with the ways of addressing soil degradation to achieve a sustainable agriculture and CO2 abatement. Numerous researches had shown that manure applications can increase crop yields and soil organic matter (SOM), and improve the soil quality as well (Blair et al., 2006). As the rapid development of agricultural machinery, the practice of returning crop stalks to farm field has become one of the main sources of organic fertility required by cropland. Returning crop stalks like green manure can reduce soil erosion
http://dx.doi.org/10.1016/j.still.2014.06.011 0167-1987/ ã 2014 Elsevier B.V. All rights reserved.
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2.2. Soil sampling and chemical analyses
and ameliorate soil physical properties (MacRae and Mehuys, 1985; Smith et al., 1987), enhance SOM and fertility (Doran and Smith, 1987; Power, 1990), increase capacity of nutrient retention (Drinkwater et al., 1998; Dinnes et al., 2002), and decrease global warming potential (Robertson et al., 2000). This study was carried out based on the results of a long-term winter wheat–summer corn field experiment conducted from 1981 to 2003. The objectives of the study were (1) to assess effects of inorganic and corn stalks on yields and yield trends of both winter wheat and corn, (2) to monitor the changes in soil organic carbon (SOC) content under continuous winter wheat–corn cropping with different soil fertility management practices, and (3) to identify reasons for yields and SOC trends.
Soil samples were collected from the top soil layer (0–20 cm) of each plot once a year after the corn crop harvest, and then were air dried and subsequently ground to pass a 0.25 mm sieve. Soil organic matter was determined by a standard potassium dichromate digest method, and total N was measured with the Kjeldahl method. To determine the available P, soil samples were first extracted with HClO4-H2SO4 solution and 0.5 mol L1 NaHCO3 (pH 8.5), respectively. Subsequently, the Olsen P method was used. Available K was extracted with an ammonium acetate solution (NH4OAc, 1 mol L1) and then determined with a flame photometer.
2. Methods and materials
2.3. Incubation soil: C mineralization
2.1. Description of the long-term experiment
The samples for incubation were taken in October each year after corn harvest. Samples (10 g) of whole soil were incubated in triplicate in 500 mL glass jars. During the incubation, soil samples were wetted to field capacity. Small glass bottles were fitted within the jars containing 10 mL of 0.25 M NaOH to trap the CO2 evolved. Jars were sealed and stored in a dark room at 27 C. C evolution was determined by pipetting 5 mL of the C-containing NaOH, and autotitrating with 0.15 M HCl after precipitation of carbonates with 8 mL of 3 M BaCl2 (De Neve and Hofman, 2000).
The experiment was carried out at the Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hengshui (37420 N, 115 420 E, altitude of 31 m above sea level), Hebei Province, China from 1981 to 2003. The soil is alluvial soil (Soil taxonomy of USDA, 1999) with particle composition of sand 27.2%, silt 55.1%, and clay 17.7%. Selected soil properties were measured at the start of the experiment (in Table 1). The annual average precipitation was 411 mm with nearly all occurring between June and September (Fig. 1 in Supplementary data) and the annual average temperature was 12.5 C. The experiment utilized the split-plot design with inorganic fertilizers as main plots and corn stalks as subplots. The main plots and subplots all had four levels of treatments, which were expressed as A and B, respectively. So there were totally sixteen treatments with three replicates each treatment, which were set as (A1, A2, A3, A4)*(B1, B2, B3, B4). The four levels of main plots were: A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1). The larger the number attached to treatment appellations indicated a higher level of fertilizer input, either of inorganic or organic fertilizers. Phosphorous was applied as basal fertilizers once and for all prior to sowing of winter wheat in October. Nitrogen was divided into two halves, one for winter wheat and the other for summer corn. Half of the N that was allocated to winter wheat was applied as basal fertilizers just prior to its sowing, while the remaining half was top-dressed. All Nfertilizers that were allocated for corn were top-dressed. As for application method, basal fertilizers were applied before crop sowing and were mixed with soil by plowing, and top-dressing was applied to the soil surface before the tillage stage. Prior to the next round of planting, corn stalks were spread on the soil surface and incorporated into the soil through plowing with adequate irrigation that was applied during crop growth season. Winter wheat was grown at the end of October and harvested in early June, followed immediately by the sowing of corn in mid-June, which was harvested in mid-October. Winter wheat and summer corn required irrigation according to their specific water-demanding stages. To control growth-reducing factors, hand weeding and other plant protection measures were applied as needed.
2.4. Statistical analysis All ANOVA, regression, and multivariate analyses were conducted in SPSS 13.0. Treatments were analyzed by one-way ANOVA and significant differences between means were judged by Turkey's post-hoc tests. To determine the key factor (s) affecting yields and the quantitative relationships between them, stepwise multiple regression analysis was applied using the criteria of probability of p < 0.05 to accept. 3. Results and discussion 3.1. Wheat and corn yields and soil organic carbon content In order to assess the effects of inorganic and corn stalks organic nutrient sources on yields and yield trends of both winter wheat and corn, we selected the treatments of A1B1, A1B4, A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 to analyze. Yields in all treatments displayed similar changes, which increased overtime for A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 treatments, remained fairly steady for A1B1, A1B4 treatments, and decreased in some years (Fig. 1). Yields fluctuations were largest for A4B4 and smallest for A1B1. In 2002–2003, some treatments of wheat yield increased again and A4B4 treatment had the highest yield, that is, about 6400 kg ha1. For corn yield, A4B4 treatment also had the highest yield, about 8600 kg ha1. In the long run, the decrease in yields of both wheat and corn was the strongest with the A1B1 and A1B4. In both wheat and corn, yields of A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 were higher than those of A1B1, A1B4. The treatments of A2B1, A2B4, A3B1, A3B4, A4B1, A4B4 substantially increased the yields of wheat and corn, especially from 1999 to 2000. So the response of wheat and corn to inorganic and organic fertilizers was distinct in the long term. By comparing the yield
Table 1 Characteristics of the 0–20 cm layers of the soil at the beginning of the experiment plot, Hengshui, China. Soil layer (cm)
Organic matter (g kg1)
Available N (g kg1)
Available P (mg kg1)
Bulk density (g cm3)
Field capacity (%)
Wilting coefficient (%)
pH
0–20
11.51
0.05
12
1.14
27.65
8.20
8.32
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7000
-1
Wheat yield (kg ha )
6000
A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
5000 4000 3000 2000 1000
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03
0
Year
-1 Corn yield (kg ha )
10000 9000
A1B1
A1B4
A2B1
A2B4
8000
A3B1
A3B4
A4B1
A4B4
7000 6000 5000 4000 3000 2000 1000
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02 20 03
0
Year Fig. 1. Winter wheat and corn yields during the 22 years field experiment at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1).
trends with precipitation trends (Fig. 1 in Supplementary data), we found that yields exhibited positive relationship with annual precipitation. For example, precipitation increased during 1982–1983, 1989–1990, 1993–1994, 1999–2000, the yields also had an increased trends in the same periods. SOC sequestration from fertilization application is a key pathway by sequestering CO2 in agriculture. The amount of SOC was related to the amount of plant residues that were returned to soil. Fertilization will affect the amount of SOC generated by crop residues left in the field after harvest (Gregorich and Drury, 1996). We examined the effects of long-term application of inorganic fertilizer (N and P), organic fertilizer, and combination of inorganic fertilizer and organic fertilizer on SOC dynamics. The SOC in different treatments had similar trends over time (Fig. 2). From 1984 to 1986, SOC showed a distinct declining trend over time. SOC under A1B1 declined rapidly in the first year until to the end of the experiment, albeit with a much slower rate. Overall reduction in SOC under A1B1 was 7.3% in the investigated 21 years. SOC under varying fertility treatments (A1B4, A2B1, A2B4, A3B1, A3B4, A4B1, and A4B4) all increased at the end of the experiment, suggesting that organic and inorganic
fertilizer can promote the accumulation of SOC and improve soil fertility in the long term (Dong et al., 2012). A3B4 had remarkably improved SOC which resulted in the highest SOC concentration (8.64 g C kg1). The average of yields over 1982–2003 was used to evaluate the long-term effects of inorganic and organic fertilizer. As observed in Fig. 3(a), the yields of both wheat and corn were higher followed by the application of more inorganic fertilizer and organic fertilizer. With the application of corn stalks, crop yields converged in both treatments, the difference between the A1, A2, A3, and A4 was obvious. However, for the same level of inorganic fertilizer, the yields increased with the application of more corn stalks, but the increasing rate was weak, suggesting that the inorganic fertilizer can increase the crop yields in a short time span. The corn yield was higher than wheat in all treatments except A4B1, suggesting that corn was more responsive to fertilization than wheat. A4B4 treatment produced the highest average yields (4351.5 kg ha1 and 4707.5 kg ha1), fertilization increased yields by 370% for wheat and by 75% for corn compared to A1B1. In sum, conjunctive application of inorganic and organic fertilizers can increase crop yields substantially (Nie et al., 2007; Singh et al., 2007).
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Soil organic carbon (g C kg-1 )
9 8.5
A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
8 7.5 7 6.5 6 5.5
19 82 19 83 19 84 19 85 19 86 19 87 19 88 19 89 19 90 19 91 19 92 19 93 19 94 19 95 19 96 19 97 19 98 19 99 20 00 20 01 20 02
5
Year Fig. 2. Change in soil organic carbon content (0–20 cm) at sampling time after corn harvest at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1).
Fig. 3(b) also showed that all treatments of the applied fertilizers can increase SOC compared with A1B1 (Zhong et al., 2007; Masto et al., 2007), the effect became stronger as more inorganic and organic fertilizers were added. This means that the best way of enriching soil was the combination of inorganic and organic fertilizers (Malhi et al., 2006). Such combination can increase SOC very efficiently (Melero et al., 2006), indicating that fertilizers benefit the storage and accumulation of SOC in this long term experiment. For the treatment of A4B4, the SOC content was lower than that in A3B4, because more chemical fertilizers may inhibit the increase of SOC and hence lead to soil degradation.
(a) 5000
-1
Yields (kg ha )
4000
3000
2000
3.2. The effects of soil organic carbon content on crop yields
1000
0 A1B1
A1B4
A2B1
A2B4
A3B1
A3B4
A4B1
A4B4
A3B4
A4B1
A4B4
Treatment
(b) 10 9
-1
Soil organic carbon (g kg )
8 7 6 5 4 3 2 1 0 A1B1
A1B4
A2B1
A2B4
A3B1
Treatment Fig. 3. Average of wheat and corn yields (a), SOC (b) in the different fertilizer treatments in the field experiment at Hengshui, China. A1 (no fertilizer), A2 (N 90 kg ha1 and P2O5 60 kg ha1), A3 (N 180 kg ha1 and P2O5 120 kg ha1), A4 (N 360 kg ha1 and P2O5 240 kg ha1). The four levels of subplots were B1 (no fertilizer), B2 (corn stalks 2250 kg ha 1), B3 (corn stalks 4500 kg ha 1), B4 (corn stalks 9000 kg ha 1). For Fig. 3(a), the white bars are the wheat yield and grey bars are the corn yield. The error bar is the standard deviation.
Analysis of variance across years was done to determine the effects of treatments (Gomez and Gomez, 1984). Grain yields of winter wheat and corn were recorded every year (1982–2003) from replicated treatments. The effects of corn stalks, inorganic fertilizer, soil organic carbon content, and the interaction between corn stalks and inorganic fertilizer on both winter wheat and corn yields were found significant (p < 0.05). In long-term experiments crop yields may be associated with such various factors as nutrients, cultivars, climate, soil types and management practices, and so on. Researchers had reported in recent years that soil organic matter was one of the most important factors in determining crop yields (Quiroga et al., 2006). Our research shows similar result. By Pearson correlation analysis of SPSS (Fig. 4), the corn yield had significant correlation with SOC at p < 0.05 level tow tailed (n = 240, r = 0.569), and the winter wheat yield had significant correlation with SOC at p < 0.05 level tow tailed (n = 240, r = 0.548). SOC increased with the rising in yields. It seems that SOC can increase crop yields, but there is some questions regarding the result: can the inorganic fertilizers increase SOC and increase crop yields at the same time? Is the increase of crop yields the only response to the application of inorganic fertilizer? What practices can be adopted to boost yields as a result of changes in soil organic matter content? SOC is an important nutrition sink for crops. The nutrients in SOC can be released by mineralizing, which afterwards can be used by crops to increase crop yields. The mineralization amount of SOC will be enhanced with the increase of SOC. Therefore, the mineralization amount of SOC is an important parameter in
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determining crop yields. Pearson correlation analysis found the mineralization amount of SOC had significant correlation with SOC (Fig. 5) and winter wheat yield (Fig. 6) at p < 0.05 level two tailed (n = 240, r = 0.601 and r = 0.583), but had low significant with corn yield (Fig. 6) at p < 0.05 level two tailed (n = 240, r = 0.419). This may be due to the fact that the mineralization amount of SOC was measured in October, after the harvest of corn. So the mineralization release nutrients for winter wheat and with more SOC being mineralized, winter wheat yield would rise further. But for corn, the nutrients released by mineralization became less, and hence the amount of SOC had lower correlation with corn yield than with winter wheat yield. Results of the correlation analyses from long-term experiments showed that crop yields will increase as the SOC increase, thus SOC was a very key factor in determining crop yields.
Wheat yield (t ha-1)
(a) 7.0
Total
6.0
Fit line for total 95% Confidence intervals
5.0 4.0 3.0 2.0 1.0
R2 linear = 0.548
0.0 5.0
6.0
7.0
8.0
9.0
Soil organic carbon (g kg-1)
4. Conclusion
(b) Total Fit line for total 95% Confidence intervals
10.0
Corn yield (t ha-1)
5
8.0 6.0 4.0 2.0
R2 linear = 0.569
0.0 5.0
6.0
7.0
8.0
9.0
Soil organic carbon (g kg-1) Fig. 4. Correlation of soil organic carbon and crop yields in the 21 years field experiment at Hengshui, China. Total refers to the total experiment data.
Significant differences in SOC and crop yields among different fertilization treatments were found in the study. Without fertilizer (A1B1), the SOC and crop yields will decline in a long-term experiment. The application of only corn stalks (A1B4) had a low efficiency in increasing SOC and crop yields. Combination of inorganic and organic fertilizer can substantially increase SOC and crop yields. The crop yields increased further with more fertilizer being added. Meanwhile, the treatment of A4B4 had the highest crop yields. However, SOC decreased with less inorganic fertilizers application and SOC increased with the addition of corn stalks. Fertilizer was an effective way of SOC storage. There was a trend that the crop yields had a relationship with SOC. More than twenty years of continuous winter wheat–summer corn rotation cultivation revealed a significant correlation at p < 0.05 level (tow tailed) between crop yields and SOC. The mineralization amount of SOC had a significant correlation at p < 0.05 level (tow tailed) with wheat yield which can confirm the result of crop yield related to SOC. North China Plain is one of the most important agricultural regions in China and the dominant cropping systems are winter
Soil organic carbon mineralization amount (g kg-1)
0.8
Total Fit line for total 95% Confidence intervals
0.7
0.6
0.5
0.4
0.3
0.2
R2 linear = 0.601 0.1 5.0
6.0
7.0
8.0
9.0
-1
Soil organic carbon (g kg ) Fig. 5. Correlation of SOC and mineralization amount of SOC in the 21 years field experiment at Hengshui, China. Total refers to the total experiment data.
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6.0
Wheat yield (t ha-1)
5.0
4.0
3.0
2.0
1.0
567 568 569 570 571 572 573 574 575 576 577 578 579
10.0
Total
Total
Fit line for total
Fit line for total
95% Confidence intervals
6.0
4.0
2.0
R2 linear = 0.583
R2 linear = 0.419
0.0
0.0 0.1
95% Confidence intervals
8.0
Corn yield (t ha-1)
7.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Mineralization count of soil organic carbon (g kg-1)
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Mineralization count of soil organic carbon (g kg-1)
Fig. 6. Correlation of mineralization amount and wheat and corn yields in the field experiment at Hengshui, China. Total refers to the total experiment data.
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Please cite this article in press as: Yang, Z.C., et al., Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain. Soil Tillage Res. (2014), http://dx.doi.org/10.1016/j.still.2014.06.011