Effect of Long-Term Fertilization on Soil Productivity on the North China Plain

Pedosphere 25(3): 450–458, 2015 ISSN 1002-0160/CN 32-1315/P c 2015 Soil Science Society of China ⃝ Published by Elsevier B.V. and Science Press

Effect of Long-Term Fertilization on Soil Productivity on the North China Plain WANG Jing-Yan1,2 , YAN Xiao-Yuan2 and GONG Wei1,2,∗ 1 Sichuan

Provincial Key Laboratory of Ecological Forestry Engineering, Sichuan Agricultural University, Ya’an 625014 (China) Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China) 2 State

(Received July 7, 2014; revised December 6, 2014)

ABSTRACT Soil productivity is the ability of a soil, in its normal environment, to support plant growth and can be evaluated with respect to crop production in unfertilized soil within the agricultural ecosystem. Both soil productivity and fertilizer applications affect crop yields. A long-term experiment with a winter wheat-summer maize rotation was established in 1989 in a field of the Fengqiu State Key Agro-Ecological Experimental Station, a region typical of the North China Plain, including seven treatments: 1) a balanced application of NPK chemical fertilizers (NPK); 2) application of organic fertilizer (OM); 3) application of 50% organic fertilizer and 50% NPK chemical fertilizers (1/2OMN); 4) application of NP chemical fertilizers (NP); 5) application of PK chemical fertilizer (PK); 6) application of NK chemical fertilizers (NK); and 7) unfertilized control (CK). To investigate the effects of fertilization practices on soil productivity, further pot tests were conducted in 2007–2008 using soil samples from the different fertilization treatments of the long-term field experiment. The soil sample of each treatment of the long-term experiment was divided into three pots to grow wheat: with no fertilization (Potunf ), with balanced NPK fertilization (PotNPK ), and with the same fertilizer(s) of the long-term field experiment (Potori) . The fertilized soils of the field experiment used in all the pot tests showed a higher wheat grain yield and higher nutrient uptake levels than the unfertilized soil. Soil productivity of the treatments of the field experiment after 18 years of continuous fertilizer applications were ranked in the order of OM > 1/2OMN > NPK > NP > PK > NK > CK. The contribution of soil productivity of the different treatments of the field experiment to the wheat grain yield of Potori was 36.0%–76.7%, with the PK and NK treatments being higher than the OM, 1/2OMN, NPK, and NP treatments since the soil in this area was deficient in N and P and rich in K. Wheat grain yields of PotNPK were higher than those of Potori and Potunf . The N, P, and K use efficiencies were higher in PotNPK than Potori and significantly positively correlated with wheat grain yield. Soil organic matter could be a better predictor of soil productivity because it correlated more strongly than other nutrients with the wheat grain yield of Potunf . Wheat yields of PotNPK showed a similar trend to those of Potunf , indicating that soil productivity improvement was essential for a further increase in crop yield. The long-term applications of both organic and chemical fertilizers were capable of increasing soil productivity on the North China Plain, but the former was more effective than the latter. The balanced application of NPK chemical fertilizers not only increased soil productivity, but also largely increased crop yields, especially in soils with lower productivity. Thus, such an approach should be a feasible practice for the sustainable use of agricultural soils on the North China Plain, particularly when taking into account crop yields, labor costs, and the limited availability of organic fertilizers. Key Words: matter

balanced fertilization, chemical fertilizer, crop yield, soil fertility, nutrient use efficiency, organic fertilizer, soil organic

Citation: Wang, J. Y., Yan, X. Y. and Gong, W. 2015. Effect of long-term fertilization on soil productivity on the North China Plain. Pedosphere. 25(3): 450–458.

The North China Plain is one of the major grainproducing regions in China, with an area of 178 700 km2 , of which 88 500 km2 is farmland (Lin et al., 2000). It is a highly productive agricultural area with a main cropping system of winter wheat and summer maize, and is often referred to as “China’s breadbasket” (Shi, 2003). Insufficient farmland to cope with the overpopulation is a problem in China, and will continue to get worse during the course of the 21st century (Yang et al., 2003); thus, the sustainable use of agricultural soils in this area could be crucial in terms of China’s food se∗ Corresponding

author. E-mail: [email protected].

curity. The traditional organic agricultural methods of this region dating back thousands of years have been changing since the 1980s, with more chemical fertilizers and less organic fertilizers being applied due to increased accessibility to chemical fertilizers and rising labor costs (Wang and Lu, 1998). However, little information is available on the response of soil productivity to these changes in fertilization practices on the North China Plain. Soil organic matter (SOM) is a reservoir of carbon (C) in the biosphere as well as a reservoir of nutrients

FERTILIZATION EFFECT ON SOIL PRODUCTIVITY

in soil, and contains nearly all nutrients necessary for plant growth (Gong et al., 2008). The SOM in farmland soils has been recognized as an important indicator of soil productivity (Yang et al., 2003), and thus increasing SOM levels through farming practices is essential for improving soil productivity (Bhattacharyya et al., 2010). An overall increase in the SOM content has been found in China’s agricultural soils in the past 30 years by direct measurements, with the largest increase being in soils of the North China Plain (Yan et al., 2011). The results of previous long-term fertilization experiments have shown that both organic and chemical fertilizers are the likely reason for the increased SOM content and crop yields in this region since the 1980s (Gong et al., 2009; Zhang, H. M. et al., 2009). Gong et al. (2012) suggested that the resulting high crop yields lead to high crop inputs to soil in the form of residues and exudates, such that plant SOM derivation overwhelms SOM decomposition. The crop yield of each season in long-term experiments is the result of soil productivity and fertilizer application during the crop growing season. It is difficult to differentiate the effects of soil productivity and fertilizer application based on the crop yield data because both the soil productivity and fertilizer levels differ among the treatments of long-term experiments. To solve this problem, we conducted pot tests by growing wheat in soils from different fertilization treatments of a long-term field experiment, and investigated how soil productivity had been affected by 18 years of organic and chemical fertilizer application under a winter wheat-summer maize cropping system on the North China Plain. Our expectation was that the results would help in selecting optimal fertilization management practices for soil productivity improvement and the sustainable use of agricultural soils. MATERIALS AND METHODS Study area This study was conducted at the Fengqiu State Key Agro-Ecological Experimental Station, a region typical of the North China Plain (Gong et al., 2009), in Fengqiu County, Henan Province, China (35◦ 00′ N, 114◦ 24′ E), with a winter wheat-summer maize rotation, which is the main cropping system of the North China Plain. The 30-year mean annual temperature is 13.9 ◦ C, and the lowest and highest mean monthly temperatures are −1.0 ◦ C in January and 27.2 ◦ C in July, respectively. The mean annual precipitation is 615 mm, two-thirds of which falls between June and September.

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Long-term field experiment A long-term experiment was established in 1989 in a field of the study site. The field had been under a winter wheat-summer maize rotation for many years and, to achieve homogenous conditions, was not fertilized for three years before the start of the experiment in September 1989. The fertility of the soil, an Aquic Inceptisol (USDA Soil Taxonomy), was low: the 0–20 cm soil layer contained 4.42 g kg−1 organic C, 0.45 g kg−1 total N, 0.50 g kg−1 total P, 18.6 g kg−1 total K, 9.51 mg kg−1 inorganic N, 1.9 mg kg−1 available P (Olsen-P), and 78.8 mg kg−1 available K. The long-term field experiment included seven fertilization treatments with a winter wheat-summer maize rotation: 1) a balanced application of N, P, and K chemical fertilizers (150 kg N ha−1 + 32.7 kg P ha−1 + 124.5 kg K ha−1 for wheat and 150 kg N ha−1 + 26.2 kg P ha−1 + 124.5 kg K ha−1 for maize) (NPK); 2) application of organic fertilizer (equivalent to 150 kg N ha−1 ) with additional chemical fertilizers applied to make the total P and K input equal to that of the NPK treatment) (OM); 3) application of half the amounts of the chemical fertilizers applied in the NPK treatment and half the amounts of the organic and chemical fertilizers applied in the OM treatment (1/2OMN); 4) application of N and P chemical fertilizers (150 kg N ha−1 + 32.7 kg P ha−1 for wheat and 150 kg N ha−1 + 26.2 kg P ha−1 for maize) (NP); 5) application of P and K chemical fertilizers (32.7 kg P ha−1 + 124.5 kg K ha−1 for wheat and 26.2 kg P ha−1 + 124.5 kg K ha−1 for maize) (PK); 6) application of N and K chemical fertilizers (150 kg N ha−1 + 124.5 kg K ha−1 for both wheat and maize) (NK ); and 7) unfertilized control (CK). Each treatment had four replicates and the 28 plots each of 9.5 m × 5 m were arranged in a randomized block design (Gong et al., 2009). The above-ground biomass in each plot was removed, except the crop stubble after harvest of each crop. The N, P, and K chemical fertilizers used are urea, calcium superphosphate, and potassium sulfate, respectively. Urea, totaling 150 kg N ha−1 , is applied in two splits: for maize, two-fifths (60 kg N ha−1 ) as basal fertilizer and the remaining three-fifths (90 kg N ha−1 ) as supplemental fertilizer; for wheat, three-fifths (90 kg N ha−1 ) as basal fertilizer and the remaining two-fifths (60 kg N ha−1 ) as supplemental fertilizer. All P, K, and organic fertilizers were applied as basal fertilizers. The organic fertilizer was made from wheat straw, oil rapeseed cake, and cottonseed cake after composting. All basal fertilizers were evenly spread onto the soil sur-

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face by hand and immediately incorporated by tillage before sowing. Supplemental urea was surface-applied by hand and then incorporated into the plowed layer with 20 mm of irrigation water, generally in February for wheat and in July for maize. After each harvest, the crop yield was recorded on the basis of oven-dry weight for the different fertilization treatments of the long-term field experiment. Pot tests Pot tests were set up in October 2007 using soils from different fertilization treatments of the long-term field experiment. The top 20-cm soil was collected evenly from each of the 28 field plots (7 treatments in four replicates) of the long-term field experiment with a soil core sampler of 5 cm in diameter after harvest of the summer maize in 2007. Each soil sample was air-dried, passed through a 5-mm mesh, and cleaned manually of visible roots and organic residues before being mixed thoroughly and divided into three PVC pots with a diameter of 25 cm and height of 25 cm. The three pots each containing 5.5 kg (oven-dried weight) of soil from a same treatment of the long-term field experiment were unfertilized (Potunf ), fertilized with balanced NPK at the same rate (calculated on an area basis) as in the NPK treatment of the long-term field experiment (PotNPK ), or fertilized with organic and/or chemical fertilizer at the same rate(s) (calculated on an area basis) as the treatment in the long-term field experiment (Potori ). All the pots were buried randomly in a field neighboring that of the long-term field experiment. Soil moisture was adjusted to 60% field capacity before sowing. Twenty-five wheat seeds were sown evenly in each pot in mid-October 2007, and 15 seedlings of similar size were retained and the others removed 7 d after germination. Sampling and analysis At the time of the wheat harvest in June 2008, plants (including visible roots remaining in the soil) were collected from each pot, washed, and then dried in an oven at 65 ◦ C to a constant weight to obtain the wheat grain, straw (including stalk, leaf, and husk tissues) and root weights. The grain, straw, and root samples in each pot were ground to fine powders with a tissue grinder (Gong et al., 2012) and used for N, P, and K determination. Plant N, P, and K were determined by the micro-Kjeldahl method, ascorbic acidmolybdenum blue-colorimetric method, and flame photometric method, respectively, after digesting the plant samples with H2 SO4 -HClO4 (Lu, 1999).

The surface (0–20 cm) soils before the pot tests were determined for SOM (by the wet oxidation method with 133 mmol L−1 K2 Cr2 O7 at 170–180 ◦ C), total organic nitrogen (TON) (by the micro-Kjeldahl method), available N (by the alkaline hydrolysis diffusion method), available P (Olsen-P), available K (by flame photometry after extraction with 1 mol L−1 ammonium acetate), and pH (soil:water ratio of 1:2.5). All data were expressed on the basis of oven-dry weight. Calculations and statistical analysis The mean annual crop yields for 1990–2007 were calculated for the different fertilization treatments of the long-term field experiment. Nutrient (N, P, or K) uptake (mg pot−1 ) by wheat was calculated as the nutrient concentration multiplied by the wheat biomass. Because the soil from each treatment in the longterm field experiment was divided into three pots with application of no fertilizer, NPK fertilizers, and the same fertilizer as in the field experiment, the difference method could then be used to calculate nutrient (N, P, and K) use efficiency (NUE, %) using the following equation: NUE =

TUf − TUu × 100 FA

(1)

where TUf is total uptake of nutrient (N, P, or K) by wheat in PotNPK and Potori that received fertilizer (N, P, or K); TUu is the total uptake of nutrient (N, P, or K) by wheat in Potunf ; and FA is the amount of fertilizer (N, P, or K) applied in the pot. The wheat grain yield in Potunf can be considered as a relative indicator of soil productivity of the fertilization treatments in the long-term field experiment; therefore, the contributions of the soil productivity (ConSP , %) of the fertilization treatments in the long-term field experiment to wheat grain yield were calculated as follows: ConSP =

YCu × 100 YCo

(2)

where YCo and YCu are the wheat grain yield of Potori and Potunf , respectively. All data were expressed as means of four replicates. Statistical analysis was performed using the SPSS 16.0 software package for Windows. Statistically significant differences were identified using analysis of variance (ANOVA) and Tukey’s honestly significant difference (HSD) test. Relationships between wheat grain yield and soil chemical properties were examined by the Pearson’s correlation analysis.

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RESULTS Soil chemical properties before the pot tests Selected chemical properties of the soil samples taken from different fertilization treatments of the long-term field experiment were characterized before the pot tests as in Table I. Soil nutrient contents with long-term application of organic and chemical fertilizers were generally significantly (P < 0.05) higher than those of the control without fertilizer application. Mean annual crop yields of the long-term field experiment The mean annual crop yields from 1990 to 2007 of the different fertilization treatments of the long-term field experiment were summarized in Table I. The crop yields of all the long-term fertilization treatments except the NK treatment were significantly (P < 0.05) higher than those of the control without fertilizer. The PK and NK treatments, an unbalanced use of chemical fertilizers with long-term serious deficiency of N and P, respectively, had a significantly lower crop yield than the other fertilization treatments. Wheat grain yield All unfertilized soils from the fertilized treatments of the field experiment showed a higher wheat grain yield as compared with the unfertilized soil from the unfertilized control (Fig. 1a). The wheat grain yield was highest for the OM treatment, followed by the 1/2OMN treatment, and both were significantly higher

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than the NPK, NP, PK, and NK treatments. For the chemical fertilizer treatments, the balanced application of fertilizers (NPK) showed a significantly higher wheat grain yield than the unbalanced applications of fertilizers (NP, PK, and NK), which were ranked in the order of NP > PK > NK. The wheat grain yields for the OM, 1/2OMN, NPK, NP, PK, and NK treatments represented increases of 2 231.9%, 1 928.0%, 1 628.4%, 1 391.4%, 1 162.1%, and 7.8%, respectively, over the value for the CK treatment. In PotNPK , the wheat grain yields (Fig. 1b) showed a similar trend to those of Potunf (Fig. 1a), with no significant differences between the OM, 1/2OMN, NPK, NP, and PK treatments. The wheat grain yields for the OM, 1/2OMN, NPK, NP, PK, and NK treatments showed increases of 110.1%, 96.1%, 85.7%, 83.4%, 82.6%, and 11.9%, respectively, over that for the CK treatment. Furthermore, the wheat grain yields of PotNPK increased by 22.3%, 11.0%, 7.0%, 161.5%, 1 824.2%, and 2 316.8% for the OM, 1/2OMN, NP, PK, NK, and CK treatments, respectively, as compared with those of Potori . In Potori , the wheat grain yields for all fertilized treatments except NK were significantly higher than that for the CK treatment (Fig. 1c), being highest for the NPK treatment, followed by the 1/2OMN, OM, and NP treatments. No significant differences were found between the NPK, 1/2OMN, OM, and NP treatments and the PK and NK treatments had significantly lower wheat grain yields than the other fertilized treatments. The wheat grain yields for the OM, 1/2OMN, NPK, NP, PK, and NK treatments increased by

TABLE I Selected soil chemical properties before the pot experiment and the mean annual crop yields (from 1990 to 2007) of the different fertilization treatments of the long-term field experiment on the North China Plain Treatment of pH the long-term field experimenta) OM 1/2OMN NPK NP PK NK CK a) NPK

8.31±0.05b) cc) 8.34±0.04c 8.35±0.03bc 8.38±0.05bc 8.43±0.07bc 8.47±0.06b 8.64±0.08a

Organic matter

Total organic N

Available N

g 16.21±0.78a 12.34±0.96b 9.63±0.73c 8.98±0.78c 8.36±0.56cd 7.30±0.57d 6.75±0.62d

kg−1

Yield P

K kg−1

mg 0.853±0.050a 86.9±6.2a 19.6±1.6b 0.670±0.042b 65.4±2.6b 16.3±1.3bc 0.528±0.025c 50.7±2.2c 13.9±1.2c 0.498±0.030c 46.3±3.8cd 12.7±1.1c 0.468±0.032cd 42.7±1.2de 47.0±5.8a 0.413±0.015de 36.7±2.7ef 2.5±0.3d 0.390±0.029e 33.2±2.5f 2.3±0.2d

Wheat

Maize ha−1

kg 164.6±7.5cd 3436±69c 149.6±7.6d 4484±60b 166.1±5.5c 4609±29a 61.6±4.8e 4415±19b 251.0±10.8b 1078±38d 277.4±4.5a 594±11e 53.5±2.2e 568±32e

year−1 5994±39c 6811±60a 6922±71a 6544±71b 1481±55d 870±25e 766±55e

= balanced application of N, P, and K chemical fertilizers; OM = application of organic fertilizer with additional chemical fertilizers applied to make the total P and K input equal to that of the NPK treatment; 1/2OMN = application of half the amounts of the chemical fertilizers applied in the NPK treatment and half the amounts of the organic and chemical fertilizers applied in the OM treatment; NP = application of the same amounts of N and P fertilizers as the NPK treatment; PK = application of the same amounts of P and K fertilizers as the NPK treatment; NK = application of the same amounts of N and K fertilizers as the NPK treatment; CK = unfertilized control. b) Mean±standard deviation (n = 4). c) Values followed by the same letter(s) in the same column are not significantly different at P < 0.05.

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Fig. 1 Wheat biomass of the pot tests with no fertilization (a), balanced NPK (b), and the same fertilizer(s) as in the long-term field experiment (c) using soil from the different fertilization treatments of the long-term field experiment on the North China Plain. NPK = balanced application of N, P, and K chemical fertilizers; OM = application of organic fertilizer with additional chemical fertilizers applied to make the total P and K input equal to that of the NPK treatment; 1/2OMN = application of half the amounts of the chemical fertilizers applied in the NPK treatment and half the amounts of the organic fertilizer and chemical fertilizers applied in the OM treatment; NP = application of the same amounts of N and P fertilizers as the NPK treatment; PK = application of the same amounts of P and K fertilizers as the NPK treatment; NK = application of the same amounts of N and K fertilizers as the NPK treatment; CK = unfertilized control. Values are means of four replicates and bars with the same letter within each pot test are not significantly different at P < 0.05.

4 050.9%, 4 170.3%, 4 388.4%, 4 042.2%, 1 587.9%, and 40.5%, respectively, over that of the CK treatment. Contribution of soil productivity to wheat grain yield The contribution of soil productivity of the longterm OM, 1/2OMN, NPK, NP, PK, and NK treatments to wheat grain yields of Potori was 56.2%, 47.5%, 38.5%, 36.0%, 74.8%, and 76.7%, respectively. Nutrient uptake and use efficiency by wheat The trends for N, P, and K uptake, which was calculated as the nutrient concentration multiplied by the wheat biomass (Fig. 1), were inconsistent in Potori (Table II). Irrespective of nutrient type, the highest mean uptake was observed in PotNPK , followed by Potori , with the lowest in Potunf . Similar to nutrient uptake by wheat, the trends for N, P, and K use efficiency of PotNPK or Potori were also inconsistent (Table III). The nutrient use efficiency was 21.3%–41.6% (average 31.4%) and 1.1%–32.9% (average 18.4%) for N, 5.2%–25.0% (average 13.7%) and 6.0%–11.1% (average 8.6%) for P, and 11.2%– 17.5% (average 13.9%) and 0.8%–13.1% (average 6.9%) for K in PotNPK and Potori , respectively. Relationships of nutrient use efficiency and soil chemical properties with wheat yield Wheat grain yields of PotNPK and Potori were

significantly positively correlated with N (r = 0.824, P < 0.01), P (r = 0.683, P < 0.01), and K (r = 0.813, P < 0.01) use efficiency (Fig. 2). Table IV shows the relationships between the soil chemical properties before the pot experiment and wheat grain yields of Potunf . Wheat grain yield was significantly positively correlated with SOM, TON, available N, and available P. However, wheat grain yield was not significantly related to available K. The correlation coefficient of wheat grain yield with SOM was higher than those with other soil chemical properties. DISCUSSION Valuable information and convincing evidence can be obtained by long-term field fertilization experiments (Jiang et al., 2004). Numerous studies have shown that the long-term application of organic and chemical fertilizers alone or in combination can achieve higher crop yields (e.g., Campbell et al., 2001; Zhang, W. J. et al., 2009; Yan and Gong, 2010) and maintain soil fertility (e.g., Edwards and Lofty, 1982; Schjønning et al., 1994; Glendining et al., 1996; Blair et al., 2006; Purakayastha et al., 2008). However, some studies have found that soil fertility declines with continuous application of chemical fertilizers alone due to soil acidification and structural degradation (e.g., Malhi et al.,

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TABLE II Nutrient uptake by wheat of the pot tests with no fertilization (Potunf ), balanced NPK (PotNPK ), and the same fertilizer(s) as in the long-term field experiment (Potori ) using soil from the different fertilization treatments of the long-term field experiment on the North China Plain Treatment of the N uptake long-term field Potunf Experimenta) OM 1/2OMN NPK NP PK NK CK Mean

P uptake PotNPK

Potori

Potunf

K uptake PotNPK

Potori

Potunf

PotNPK

Potori

mg N pot−1 mg P pot−1 mg K pot−1 118.1±11.7b) ac) 389.0±55.6a 236.6±31.1b 14.0±2.0a 41.7±7.2ab 31.8±3.5a 65.3±13.1a 172.4±9.3a 127.7±15.8a 98.4±8.7b 350.2±45.9ab 240.0±12.5b 11.6±1.7ab 38.4±5.4abc 24.9±2.1b 48.4±7.9b 139.4±11.1b 103.4±5.5b 83.1±4.5c 325.4±24.3ab 325.4±14.5a 10.6±0.8b 27.0±3.1c 27.0±1.6b 37.3±3.9bc 114.8±10.0c 117.6±13.3ab 67.4±2.4d 295.4±14.5b 233.0±20.9b 7.5±0.6c 33.4±1.6bc 19.3±1.7c 23.1±2.1cd 117.6±13.3bc 46.0±3.0c 59.8±5.1d 365.7±43.3ab 91.3±5.8c 6.7±0.6c 47.0±10.5a 16.3±0.8c 34.5±4.2bc 116.9±9.1bc 44.1±5.8c 24.7±2.8e 187.4±24.7c 32.5±3.7d 1.0±0.1d 9.4±1.4d 0.9±0.1d 11.4±1.5d 85.0±4.3d 16.3±1.9d 19.5±1.9e 176.3±26.5c 19.5±1.9d 0.7±0.0d 9.6±1.3d 0.7±0.0d 9.4±2.0d 78.0±14.1d 9.4±2.0d 67.3 298.5 168.4 7.4 29.5 17.3 32.8 117.7 66.4

a) NPK

= balanced application of N, P, and K chemical fertilizers; OM = application of organic fertilizer with additional chemical fertilizers applied to make the total P and K input equal to that of the NPK treatment; 1/2OMN = application of half the amounts of the chemical fertilizers applied in the NPK treatment and half the amounts of the organic and chemical fertilizers applied in the OM treatment; NP = application of the same amounts of N and P fertilizers as the NPK treatment; PK = application of the same amounts of P and K fertilizers as the NPK treatment; NK = application of the same amounts of N and K fertilizers as the NPK treatment; CK = unfertilized control. b) Mean±standard deviation (n = 4). c) Values followed by the same letter(s) in the same column are not significantly different at P < 0.05.

TABLE III Wheat nutrient use efficiency of the pot tests with balanced NPK (PotNPK ) and the same fertilizer(s) as in the long-term field experiment (Potori ) using soil from the different fertilization treatments of the long-term field experiment on the North China Plain Treatment of the long-term field experimenta)

N use efficiency PotNPK

P use efficiency Potori

PotNPK

K use efficiency Potori

PotNPK

Potori

11.1±1.3a 8.3±2.3abc 10.2±1.4ab 7.3±0.8bc 6.0±0.5c – – 8.6

17.5±1.0a 14.9±2.6ab 13.1±2.4b 15.0±1.6ab 13.5±1.8ab 12.0±0.5b 11.2±2.2b 13.9

10.2±1.7ab 9.0±2.1b 13.1±2.4a – 1.6±0.4c 0.8±0.1c – 6.9

% OM 1/2OMN NPK NP PK NK CK Mean

36.8±7.6b) ac) 34.2±7.2a 32.9±2.2ab 31.0±3.1ab 41.6±6.0a 22.1±3.4b 21.3±3.3b 31.4

16.1±3.1c 19.2±2.7bc 32.9±2.2a 22.5±3.0b – 1.1±0.2d – 18.4

17.2±4.3b 16.7±3.5b 10.2±1.4bc 16.1±1.7b 25.0±6.4a 5.2±0.8c 5.5±0.8c 13.7

a) NPK

= balanced application of N, P, and K chemicall fertilizers; OM = application of organic fertilizer with additional chemical fertilizers applied to make the total P and K input equal to that of the NPK treatment; 1/2OMN = application of half the amounts of the chemical fertilizers applied in the NPK treatment and half the amounts of the organic and chemical fertilizers applied in the OM treatment; NP = application of the same amounts of N and P fertilizers as the NPK treatment; PK = application of the same amounts of P and K fertilizers as the NPK treatment; NK = application of the same amounts of N and K fertilizers as the NPK treatment; CK = unfertilized control. b) Mean±standard deviation (n = 4). c) Values followed by the same letter(s) in the same column are not significantly different at P < 0.05.

2000; Graham et al., 2002; Malhi et al., 2003). Such differences possibly result from different management practices and soil properties in the study sites before the experimental campaigns. Our study confirmed that the long-term application of organic and chemical fertilizers on the North China Plain can increase crop yields, soil productivity (Fig. 1) and soil nutrient contents (Table I). Long-term fertilization also led to a slight decrease in soil pH in our study, but such a decrease in soil pH might be more suitable for crop

growth since the original soil was alkaline. The measured wheat grain yields of PotNPK with balanced NPK fertilization, as in the original NPK treatment in the long-term field experiment, represented the response of wheat grain yield to the balanced application of N, P, and K chemical fertilizers under different soil productivities. The soils in Potori were fertilized in the same way as that of the long-term field experiment, and thus the wheat grain yields in this pot test represented the trend for the original treatments

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Fig. 2 Relationships of N (a), P (b), and K use efficiency (c) with the mean wheat grain yield of the pot tests with balanced NPK and with the same fertilizer(s) as in the long-term field experiment on the North China Plain. TABLE IV Correlation coefficients between soil chemical properties before the pot experiment and the wheat grain yield of the unfertilized pot test using soil from the different fertilization treatments of the long-term field experiment on the North China Plain Soil chemical propertya)

Wheat grain yield

SOM TON AN AP AK

0.849** 0.830** 0.833** 0.414* −0.074

*, **Significant at P < 0.05 and P < 0.01, respectively. a) SOM = soil organic matter; TON = total organic N; AN = available N; AP = available P; AK = available K.

of the long-term field experiment. The wheat grain yield in Potunf can be considered as a relative indicator of soil productivity; therefore, significant differences in soil productivity among the treatments were found after 18 years of field fertilization and long-term applications of organic and chemical fertilizers—both alone and in combination—were capable of increasing soil productivity (Fig. 1a). Because the different fertilization treatments of the long-term fertilization experiment resulted in differences in soil productivity, their soil productivity contributions to wheat grain yield were calculated. The contribution of soil productivity of the fertilization treatments of the long-term field experiment to the wheat grain yield of Potori was ranked in the order of NK > PK > OM > 1/2OMN > NPK > NP. The PK and NK treatments reflected an unbalanced use of chemical fertilizers with long-term serious deficiency of N and P, respectively, and both had a lower crop yield (Table I, Fig. 1c) and soil productivity (Fig. 1a), as compared to the other fertilization treatments, thus possessing the highest contribution

from soil productivity. The annual atmospheric inorganic N deposition ranges from 15 to 50 (average 27) kg N ha−1 year−1 on the North China Plain, and this may have partly mitigated N deficiency and improved crop growth of the PK treatment (Zhang, Y. et al., 2008; Gong et al., 2011), probably leading to the soil productivity in the PK treatment being higher than that in the NK treatment. Although the NP treatment also reflected an unbalanced use of chemical fertilizers, with no K applied for 19 years, it had higher crop yield and soil productivity than the PK and NK treatments since the soil itself was rich in K. Wheat grain yields in Potunf , PotNPK , and Potori using the soil samples from the fertilized treatments of the long-term field experiment increased by 7.8%– 2 231.9%, 11.9%–110.1%, and 40.5%–4 388.4%, respectively, as compared with those using the control soil (Fig. 1). This indicated that fertilizer and soil productivity in the fertilized treatments of the long-term field experiment largely affected the crop yield and increased the yield difference both in Potunf and Potori . However, PotNPK could obviously increase the crop yield, especially for the soil with lower productivity (i.e., CK, NK, and PK), and decrease the crop yield difference among the treatments even though they had significant differences in soil productivity. As compared with Potori , wheat grain yields in PotNPK increased by 7.0%–22.3% for the OM, 1/2OMN, and NP treatments, whereas the increases were as large as 161.5%– 2 316.8% for the PK, NK, and CK treatments. These results further indicated that the deficiency of soil N and P was an important limiting factor for increasing crop yield and soil productivity in the study area, crop yields could be largely increased as long as N and P fertilizers were properly applied, and higher and more

FERTILIZATION EFFECT ON SOIL PRODUCTIVITY

steady crop yields could be obtained by a balanced application of N, P, and K chemical fertilizers. The efficient use of nutrients in fertilizers applied could increase crop yield and reduce environmental pollution (Velthof et al., 1998). In the present study, the N, P, and K use efficiencies were 1.1%–41.6%, 5.2%–25.0%, and 0.8%–17.5%, respectively (Table III). The nutrient use efficiencies were higher in PotNPK than Potori , and significantly positively correlated with the wheat grain yield, indicating that a balanced application of N, P, and K chemical fertilizers was more efficient in increasing crop yield and nutrient uptake and use efficiency, as well as in reducing the fertilizer loss and residue in soil. Zhang, F. S. et al. (2008) reviewed the nutrient use efficiency of the major cereal crops of the North China Plain and reported that the estimates of N, P, and K use efficiency for wheat range from 0.3% to 89.9%, 1.7% to 31.1%, and 0.9% to 88.2%, respectively. The N, P, and K use efficiencies in this study were well within those ranges, except for the NK treatment, which had a serious deficiency of P and thus limited crop growth and K uptake. Soil organic matter is closely related to soil structural stability, hydraulic properties, water availability, cation exchange, buffer capacity, mineralizable nutrient supply, and hence crop productivity (Lal, 2002; Gwenzi et al., 2009; Mulvaney et al., 2009). The fertilized soils of the field experiment showed higher nutrient contents (Table I) and wheat grain yields (Fig. 1) in the pot tests as compared with the unfertilized control, and the wheat grain yield of Potunf was significantly positively correlated with SOM, TON, available N, and available P before the pot experiment, but not significantly correlated with available K (Table IV). The N and P deficiencies in the PK and NK treatments, respectively, limited the K uptake and led to higher K residue in soil, which in turn resulted in a higher level of available K. If the correlation calculation excluded the PK and NK treatments, a significant positive coefficient could be obtained between wheat grain yield and soil available K (r = 0.798, P < 0.01). The results indicated that soil productivity was significantly affected by fertilization practices and soil fertility. Furthermore, the wheat grain yield had a stronger relationship with SOM than the other soil nutrients (Table IV), suggesting that SOM could be a better predictor of soil productivity than other soil chemical properties. The SOM content in the croplands of the North China Plain is low compared with that of the other major agricultural regions in China (Pan, 1999). Thus, maintaining SOM through appropriate management is important for the sustainable use of agricultural soils in this area.

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CONCLUSIONS Long-term application of both organic and chemical fertilizers increased the wheat grain yield, soil productivity, and nutrient uptake. The organic fertilizer was more efficient in increasing soil productivity than the chemical fertilizers. The mean wheat grain yields and nutrient uptake of the pot tests were ranked in the order of PotNPK > Potori > Potunf . PotNPK showed higher mean nutrient use efficiencies compared to Potori . The wheat grain yield of Potunf was significantly correlated with SOM, TON, available N, and available P, and even with available K when the PK and NK treatments were excluded, suggesting that the crop yield of the unfertilized control was a useful index for evaluating changes in soil productivity induced by long-term fertilization practices. The soil productivityincreasing effect of fertilization was mainly due to the improvement of soil fertility. The soil N and P deficiencies were the important limiting factor for increasing crop yield and soil productivity in the study area; crop yield and soil productivity could be largely increased as long as N and P fertilizers were properly applied. The application of organic fertilizer was not the most feasible measure to increase crop yield, but was the most feasible measure to increase soil productivity. Meanwhile, a balanced use of chemical fertilizers could obtain the highest crop yields and increase soil productivity, and thus is an important approach to increase the sustainability of the cropping system on the North China Plain, especially when the availability of organic manure is limited. ACKNOWLEDGEMENT This research was supported by the Knowledge Innovation Program of Chinese Academy of Sciences (Nos. KZCX2-YW-312 and KZCX2-YW-406-2) and the National Natural Science Foundation of China (No. 40621001). REFERENCES Bhattacharyya, R., Prakash, V., Kundu, S., Srivastva, A. K., Gupta, H. S. and Mitra, S. 2010. Long term effects of fertilization on carbon and nitrogen sequestration and aggregate associated carbon and nitrogen in the Indian sub-Himalayas. Nutr. Cycl. Agroecosys. 86: 1–16. Blair, N., Faulkner, R. D., Till, A. R. and 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. Campbell, C. A., Selles, F., Lafond, G. P., Biederbeck, V. O. and Zentner, R. P. 2001. Tillage–fertilizer changes: Effect on some soil quality attributes under long-term crop rotations in a thin Black Chernozem. Can. J. Soil Sci. 81: 157–165.

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