Crop yield and soil carbon responses to tillage method changes in North China
Introduction
Achieving food security is an urgent, high-priority issue in China (Chen et al., 2011a). As a result, the continuous improvement of crop yield is a prominent goal in agricultural research. Mitigating and preventing further soil degradation due to erosion and soil organic carbon (SOC) loss are crucial for accomplishing this goal. Conservation tillage, which is generally defined as minimal soil disturbance resulting in a residue retention of at least 30% (Zhang et al., 2005), is becoming an economical and ecologically viable option for conserving energy and providing favorable soil conditions for sustainable crop production, soil carbon (C) sequestration, and efficient nitrogen fertilizer use (Mazzoncini et al., 2011, Chen et al., 2011b, Pramod et al., 2012). Currently, conservation tillage is used on 11% of the total global agricultural cropland (FAO, 2010). In China, the area under conservation tillage increased to 8.5 Mha in 2011, equivalent to 4.7% of the total agricultural cropland (Geng, 2012), and most of them use wheat-maize double cropping system in silt loam soils under temperate monsoon climates in the North China (Zhang et al., 2014).
Harrow tillage (HT), rotary tillage (RT) and no-tillage (NT) are frequently used to mitigate soil erosion and loss of SOC in North China (Zhang et al., 2005). However, after several successive years of these reduced tillage (i.e., only tilling to a depth less than 20 cm) or no-tillage systems, subsoil compaction at 15–30 cm depths appears to be increasing due to the increase of bulk density resulted by water infiltration and sowing and harvesting machineries (Kong et al., 2010, Wang et al., 2014). Furthermore, although adopting some form of conservation tillage is generally beneficial for increasing SOC levels and sequestering C in the topsoil (Ussiri and Lal, 2009, Martinez et al., 2013), the reduced incorporation of crop residues has been reported to increase subsoil bulk density and reduce crop root proliferation (Figuerola et al., 2012), thereby limiting water and nutrient availability (He et al., 2009) and resulting in reduced crop yields (Bhatia et al., 2010, Arvidsson et al., 2014). For example, many studies have demonstrated that decreases in crop yield in response to long-term NT adoption may be caused by reduced seed germination and emergence, lower early season soil temperatures, below-optimal plant populations, poorer weed control, delayed plant development and maturity, increased grain moisture content, and lower grain yield potential following adoption of NT (Toliver et al., 2012, Kovar et al., 1992, Fortin, 1993, Swan et al., 1994). Therefore, understanding the responses of SOC and crop yield to long-term conservation tillage is very important in China because achieving sustainable high yields and soil quality is a fundamental precondition for adopting conservation tillage.
Deep tillage (DT) to a depth more than 30 cm is an effective method to break up compacted subsoil layers and decrease soil bulk density (He et al., 2007, Hou et al., 2012). It has positive effects on soil structure, soil C sequestration, and crop yield in North China (Huang et al., 2006, Wang and Li, 2014, Xu et al., 2015). A previous study has demonstrated the bulk density was decreased by 8.7–11.8% and significant increased soil total porosity of the 10–40 cm layers after the long-term conservation tillage conversion to DT (Nie et al., 2015), which played an important role for the disruption of the compacted zone. However, the effects of tillage conversion on crop productivity and the SOC pool were unknown. Therefore, our objectives were to (1) quantify crop yield and SOC responses to 10-year HT, RT, and NT treatments and (2) determine how the conversion of these three conservation tillage methods to DT affected yield and SOC following the first 4 years after conversion to deep tillage.
Section snippets
Experimental site
The study site was located at Tai’an (North China, 36°09′N, 117°09′E), which typifies the soils and temperate continental monsoon climate of North China. The average annual precipitation and annual temperature were 710 mm and 13.8 °C, respectively, during the experiment. The soil is classified as Udolls according to the USDA Soil Taxonomy System (Soil Survey Staff, 1998). The soil texture is 40% sand, 44% silt and 16% clay. At the start of the experiment in 2002, the soil in the 0–30 cm layer had
Long-term conservation tillage effects on crop yield
Wheat and maize yields showed the largest decline with time under NT compared with the HT and RT treatments (Fig. 2a and b), although the HT and RT yields also generally decreased over time. The wheat yields under the HT, RT and NT treatments decreased by an average of 34, 31 and 52%, respectively, from 2005 to 2012. Maize yields showed similar declines, averaging 20, 16 and 24% decreases, respectively. The annual total yield of the wheat and maize production systems also decreased over the
Discussion
After the long-term adoption of NT, crop yield has been observed to decrease, remain unchanged, or increase only in the first several years in many regions (Powlson et al., 2014). Our study found that wheat and maize yields decreased in three conservation tillage treatments during 2005–2012, especially under the NT treatment, which produced the lowest annual yield. Similar trends have been reported in other studies (Soane et al., 2012, Gruber et al., 2012). However, many other studies have
Conclusions
In the present study, yield decreases were observed after the long-term use of 3 conservation tillage systems, including NT, HT, and RT. In addition, a negative effect of the RT treatment on soil C sequestration was observed, whereas the NT treatment was beneficial to C sequestration. The conversion of these long-term conservation tillage treatments to DT, i.e., NT-DT, HT-DT and RT-DT, resulted in significant improvements in the annual total yield of wheat and maize cropping system. Although
Acknowledgements
We appreciate the funding for this project awarded by the Natural Science Foundation of Shandong Province, China (ZR2015CQ007), the Youth Scientific Research Foundation of Shandong Academy of Agricultural Sciences (2015YQN37), the Special Research Funding for Public Benefit Industries (Agriculture) of China (201503121), and the National Science and Technology Research Projects of China (2012BAD14B07).
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