Yield sustainability, carbon sequestration and nutrients balance (Research Paper Sample)
Sustainable crop production in China as well as in the world is needed to feed the ever-growing world population. Improvement in the field managing technologies has accounted a significant contribution to increase the crop productivity (Deryng et al., 2011; Doltra et al., 2019). In China, during 1970-1990 the annual rice production was increased by 3.37% (FAO, 2008), mostly due to the cultivation of high yielding varieties and high consumption of chemical fertilizers (Tong et al., 2003; Yuan, 1996). However, yield growth rate was dropped by 0.6% per year from 1990 to 2006 (FAO, 2008). This might be further challenged by changes in global climate (Lobell and Asner, 2003; Peng et al., 2004) and scarcity of water resources (Van Nguyen and Ferrero, 2006). The fertilization approach is one of the best field management practices to achieve high crop yield. Chen et al., (2014) from 153 field studies found that manure addition increased crop yield by 8.5 to14.2 Mg ha 1 without increasing N input. In another study, based on 20 different field trials, Hijbeek et al., (2017) found that inorganic fertilization increased the yield of crop by 2.0 Mg ha−1 and yield did not increased significantly by manure application. It is clear that the mechanism of the yield response to different types of fertilization is not consistent. Therefore, to achieve sustainable and high yield of crop, it is essential to know the influence of long-term fertilization on crop productivity. Fertilizers application effects crop yield by changing soil chemical properties, such as soil pH and nutrient contents and C inputs.
Soil organic carbon (SOC) content is one of the main indexes of soil fertility (Hijbeek et al., 2017). The sequestration of SOC could be increased by the application of different fertilizers which provides high carbon inputs, such as manure application or incorporation of crop residue (Cai et al., 2015). Chemical fertilizers also influence the SOC sequestration by returning residues of crop to field such as roots and stubbles residues. For example, Zhang et al., (2012) found that inorganic fertilizers increased carbon inputs by 2.5 to 5.0 Mg ha-1 in southern China. In another study, compared with the winter fallow, the green manure rotation under double cropping system increased the SOC stock up to 24% (Yao et al., 2017). McDaniel et al., (2014) in their study, found that cover crops significantly increased rate of SOC sequestration as compared to no cover crops. However, the mechanism by which different fertilizers application influence the crop yield by changing SOC is not clear. Soil nutrients are main factors limiting crop yield. Therefore, high crop yield mainly depends on chemical fertilizer application rates. Though, lower than half amount of total inputs from chemical fertilizers efficiently used and did not showed surplus nutrient accumulation in soil (Galloway et al., 2008). Meanwhile, excessive use of chemical fertilizers not only increase air and water pollution (Lu and Tian, 2013; Peñuelas et al., 2012), but also degrading soil quality such as acidification (Lin et al., 2014).
Acidification of paddy soils has received significant attention due to its negative effects on soil fertility and crop production (Cai et al., 2015; Guo et al., 2010). One of the main reasons of soil acidity is the excessive rates of chemical fertilizer application (Zhu et al., 2018). However, China has achieved huge progress in attaining higher crop production, but most of the agricultural lands are still being affected by substantial acidification since 1980s (Guo et al., 2010). Addition of manure to the agricultural soils can improve not only SOC content but also can provide essential nutrients for plant uptake. Furthermore, after many years of manure application, its residual effects were observable, leading to availability of different nutrients for uptake by crop (Demelash et al., 2014). Application of manure to the cropland can reduce the soil acidity by improving soil pH due to alkalinity of manure (Mi et al., 2018; Rukshana et al., 2013). While, nitrification process can produce protons which may decrease soil pH (Xu et al., 2006).
The subtropical region of China is dominant with paddy soil under rice cultivation, playing a major role in national grain production (Hui-min et al., 2009). However, soil acidification is a major problem in this region that limits the plant growth (Cai et al., 2015). In paddy soil the pH in top soil decreased 0.13 units between 1980s and 2000s (Guo et al., 2010). Therefore, we made efforts to investigate the driving factors of manure, chemical fertilizers and soil properties that influence the sustainable crop production in acidic paddy soil.
Yield sustainability, carbon sequestration and nutrients balance under long-term combined application of manure and inorganic fertilizers in acidic paddy soil
Organic and inorganic fertilization management in intensive cropping system is important to achieve long-term high crop yield sustainability. We quantitatively investigated crop yield sustainability through soil fertility and nutrients balance in 34-years long-term experiment under double rice cropping system in acidic paddy soil. Seven treatments were selected: CK (no fertilization); NPK (Chemical nitrogen, phosphorus and potassium fertilizer); NPM (Chemical N, P and manure); NKM (Chemical N, K and manure); PKM (Chemical P, K and manure); NPKM (Chemical N, P, K and manure) and M (Manure). The rate of manure application was same in all treatments receiving manure. Results showed that crop yield and sustainability yield index under combined application of manure and chemical fertilizers were significantly higher than chemical fertilization and highest crop yield was under NPKM treatment. Long-term combined manure and chemical fertilization improved soil fertility as compared to CK and NPK. Soil C sequestration rates under NPM, NKM, PKM and NPKM treatments were increased, while decreased under CK and NPK over the fertilization years. The uptake of N, P and K was increased over the fertilization years in all treatments that were receiving manure, compared with CK and NPK. Apparent K balance was negative in all treatments. N balance (except CK and NPKM) and P balance (except CK) was positive in all fertilization treatments. P balance was exceeded the environmental risk threshold under combined application of chemical P fertilizer and manure. Boosted regression tree indicated that AN, SOC and TN were the most influencing factors of crop yield, accounted 36.5%, 17.8%, 13.4% of variations of relative yield, respectively. Path analysis showed that long-term fertilizer inputs increased soil nutrient contents and C input directly affected SOC. C input and soil pH indirectly influenced the relative crop yield. This study concluded that long-term combined application of manure and inorganic fertilizers increased crop yield sustainability, carbon sequestration rate compared to the inorganic fertilization. But long-term combined application of manure and inorganic phosphorus fertilizer enhanced the P balance. Therefore, rate of P inputs need to reduce under combined application of manure and inorganic P fertilizers in acidic paddy soil.
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