Organic material combined with inorganic fertilizer has been shown to greatly improve crop yield and maintain soil fertility globally. However, it remains unclear if crop yield and soil fertility can be sustained in the long term under the combined application of organic and inorganic fertilizers. Three long-term field trials were conducted to investigate the effects of organic amendments on the grain sustainable yield index (SYI), soil fertility index (SFI) and nutrient balance in maize–wheat cropping systems of central and southern China during 1991–2019. Five treatments were included in the trials: 1) no fertilization (control); 2) balanced mineral fertilization (NPK); 3) NPK plus manure (NPKM); 4) high dose of NPK plus manure (1.5NPKM); and 5) NPK plus crop straw (NPKS). Over time, the grain yields of wheat and maize showed an increasing trend in all four fertilization treatments at the Yangling (YL) and Zhengzhou (ZZ) locations, while they declined at Qiyang (QY). The grain yield in the NPKM and 1.5NPKM treatments gradually exceeded that of the NPK and NPKS treatments at the QY site. The largest SYI was recorded in the NPKM treatment across the three sites, suggesting that inorganic fertilizer combined with manure can effectively improve crop yield sustainability. Higher SYI values were recorded at the YL and ZZ sites than at the QY site, possibly because the soil was more acid at QY. The key factors affecting grain yield were soil available phosphorus (AP) and available potassium (AK) at the YL and ZZ sites, and pH and AP at the QY site. All fertilization treatments resulted in soil N and P surpluses at the three sites, but soil K surpluses were recorded only at the QY site. The SFI was greater in the 1.5NPKM, NPKM and NPKS treatments than in the NPK treatment by 13.3–40.0 and 16.4–63.6% at the YL and ZZ sites, respectively, and was significantly higher in the NPKM and 1.5NPKM treatments than in the NPK and NPKS treatments at the QY site. A significant, positive linear relationship was found between SFI and crop yield, and SYI and nutrient balance, indicating that grain yield and its sustainability significantly increased with increasing soil fertility. The apparent N, P and K balances positively affected SFI. This study suggests that the appropriate amount of manure mixed with mineral NPK fertilizer is beneficial to the development of sustainable agriculture, which effectively increases the crop yield and yield sustainability by improving soil fertility.
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The decomposition, nutrient release characteristics and driving factors of straw under different C/N ratio were studied based on coal mining area, so as to provide as theoretical basis for the full utilization of straw resources and reclaimed soil fertility improvement.
Air-dried maize straw and wheat straw were cut into 2 mm pieces and were selected for decomposition experiment of a coal mining reclamation area in Shanxi Province. Two C/N ratio levels of 25 and 10 were designed in maize straw and wheat straw by supplementing urea, taking no nitrogen application that C/N ratio levels was 52 and 74 as the control. All the straws (8 g in organic carbon) were put into a nylon mesh bag (0.38 µm aperture), and horizontally buried into 15 cm deep of soil. On the 12, 23, 55, 218, 281 and 365 days after buried, samples were collected from the bags to analyze the dynamic of the dry matter residue and nutrient (carbon, nitrogen, phosphorus and potassium).
During the first 55 days, the adjusting the C/N on 25 with the application N was the best way to accelerate the decomposition of maize straw. Meanwhile, the adjusting the C/N on 10 was the best way to accelerate the decomposition of wheat straw. Application N could significantly promote the release of carbon and phosphorus from maize straw during the first 55 days. Application N could significantly accelerate the release of carbon, nitrogen and phosphorus from wheat straw, but had no significant effect on the release of potassium. The thermal equation of straw decomposition and nitrogen and potassium release was better than the temporal equation, and phosphorus release from straw was not suitable for the exponential decay equation. When the accumulated temperature was 4 600 ℃, the average release rates of carbon, nitrogen, phosphorus and potassium from straw were 49.2%, 39.5%, 40.8% and 90.3%, respectively; When the accumulated temperature reached 1 125 ℃, more than 85% the potassium of straw was released. The decomposition of straw was mainly influenced by the temperature, organic carbon, lignin and hemicellulose.
Application N could accelerate the decomposition of maize straw and the release of carbon and phosphorus in the early stage, which could significantly accelerate the wheat straw decomposition and the release of carbon, nitrogen and phosphorus too. Temperature could better reflect the process of straw decomposition and nitrogen, potassium release than time, the decomposition of straw was mainly regulated by the temperature, organic carbon, lignin and hemicellulose. Therefore, combined with the hydrothermal conditions in the coal mining area, the straw with an appropriate amount of urea should be returned to the field in the right time to improve the content of nitrogen, phosphorus and potassium of the reclaimed soil.
The main controlling factors of soil fertility and temporal and spatial evolution characteristics in typical county of cinnamon soil region were investigated, so as to provide the basis for scientific management of nutrients and soil fertilization.
Based on the data of soil fertility, including soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), available potassium (AK) and pH, at Shouyang County in 1983, 2007 and 2017, the Nemerow index method was used to calculate the comprehensive index of soil fertility, the random forest method was used to explore the main controlling factors of soil fertility, and the combined method of GIS and geostatistics was used to determine the temporal and spatial variability characteristics and the distribution patterns of the comprehensive index of soil fertility and its main factors.
(1) The overall level of cultivated land soil fertility showed an upward trend in Shouyang County during the past 34 years, and the comprehensive index of soil fertility increased by 0.26, which changed from 1.16 to 1.42. The changes of soil fertility index were characterized by stages. From 1983 to 2007, the average annual increases of SOM, TN and AK were 0.09 g·kg-1, 0.0021 g·kg-1 and 1.61 mg·kg-1, respectively, while the changes of AP were not significant. From 2007 to 2017, SOM, TN and AP increased significantly, with the average annual increases of 0.25 g·kg-1, 0.01 g·kg-1 and 0.31 mg·kg-1, respectively, while the changes of AK were not significant. (2) The analysis results of the random forest model showed that, the main controlling factors of soil fertility were TN and SOM in 1983, with the importance of 75.3% and 17.8%, respectively. In 2007, the main controlling factors of soil fertility became AK, AP and TN, with the importance of 31.8%, 27.1% and 26.8%, respectively. In 2017, the main controlling factors were TN, AK and AP, and the importance for the three factors were 31.8%, 27.1% and 26.8%, respectively. (3) There were certain spatial differences in the main controlling factors of soil fertility. From 1983 to 2007, SOM increased in the whole county; TN decreased in the northwest and central regions, but increased in other regions; AP decreased in the north regions, but increased in the south regions; AK increased in the whole county. From 2007 to 2017, SOM increased fast in the southeast regions but slow in other regions; TN decreased in the middle regions but increased in other regions; AP decreased in the east regions, but increased in other regions; AK decreased in the east and west regions, but increased in the central region.
After 34 years, the cultivated land soil fertility of Shouyang County has been improved, and SOM, TN, AP and AK were the main controlling factors affecting the soil fertility variability. SOM, TN and AP increased fast in the south regions, while AK increased fast in the east regions. It was suggested that the whole Shouyang County still needed to increase the application of nitrogen fertilizer moderately, especially in the central region, and stabilize the application of phosphate fertilizer, while control the application of potassium fertilizer in the future.
The combined application of organic manure and chemical fertilizers is an effective way to enhance soil organic carbon (SOC) sequestration through its influences on organic carbon (OC) input and the stability of SOC fractions. However, there is limited information on the carbon sequestration efficiency (CSE) of chemically separated SOC fractions and its response to OC input under long-term fertilization regimes, especially at different sites. This study used three long-term fertilization experiments in Gongzhuling, Zhengzhou and Qiyang spanning 20 years to compare the stocks and CSE in four different OC fractions (very labile OC, labile OC, less labile OC, and non-labile OC) and their relationships with annual OC input. Three treatments of no fertilization (CK), chemical nitrogen, phosphorous, and potassium fertilizers (NPK), and chemical NPK combined with manure (NPKM) were employed. The results showed that compared with CK, NPKM resulted in enhanced SOC stocks and sequestration rates as well as CSE levels of all fractions irrespective of experimental site. Specifically for the very labile and non-labile OC fractions, NPKM significantly increased the SOC stocks by 43 and 83%, 77 and 86%, and 73 and 82% in Gongzhuling, Qiyang, and Zhengzhou relative to CK, respectively. However, the greatest changes in SOC stock relative to the initial value were associated with non-labile OC fractions in Gongzhuling, Zhengzhou, and Qiyang, which reached 6.65, 7.16, and 7.35 Mg ha–1 under NPKM. Similarly, the highest CSE was noted for non-labile OC fractions under NPKM followed sequentially by the very labile OC, labile OC, and less-labile OC fractions, however a CSE of 8.56% in the non-labile OC fraction for Gongzhuling was higher than the values of 6.10 and 4.61% in Zhengzhou and Qiyang, respectively. In addition, the CSE for the passive pool (very labile+labile OC fractions) was higher than the active pool (less-labile+non-labile OC fractions), with the highest value in Gongzhuling. The redundancy analysis revealed that the CSEs of fractions and pools were negatively influenced by annual OC input, mean annual precipitation and temperature, but positively influenced by the initial SOC and total nitrogen contents. This suggests that differential stability of sequestered OC is further governed by indigenous site characteristics and variable amounts of annual OC input.
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Rational nitrogen (N) application can greatly increase rice (Oryza sativa L.) yield. However, excessive N input can lead not only to low N use efficiency (NUE) but also to severe environmental pollution. Reducing N application rate with a higher planting density (RNHD) is recommended to maintain rice yield and improve NUE. The effects of RNHD on fertilizer N fate and rice root growth traits remain unclear. We accordingly conducted a two-year field experiment to investigate the influence of RNHD on rice yield, fertilizer 15N fate, and root growth in a double-rice cropping system in China. In comparison with the conventional practice of high N application with sparse planting, RNHD resulted in similar yield and biomass production as well as plant N uptake. RNHD increased agronomic NUEs by 23.3%–31.9% (P < 0.05) and N recovery efficiency by 17.4%–24.1% (P < 0.05). RNHD increased fertilizer 15N recovery rate by 14.5%–34.7% (P < 0.05), but reduced 15N retention rate by 9.2%–12.0% (P < 0.05). Although a reduced N rate led to significantly reduced root length, surface area, volume, and biomass, these root traits were significantly increased by higher planting density. RNHD did not affect these root morphological traits and reduced activities of nitrate reductase (NR) and glutamine synthetase (GS) only at tillering stage. Plant N uptake was significantly positively correlated with these root traits, but not correlated with NR and GS activities. Together, these findings show that reducing N application with dense planting can lead to high plant N uptake by maintaining rice root growth and thus increase NUE.
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