Soil organic carbon (SOC) sequestration is important for improving soil fertility of cropland and for the mitigation of greenhouse gas emissions to the atmosphere. The efficiency of SOC sequestration depends on the quantity and quality of the organic matter, soil type, and climate. Little is known about the SOC sequestration efficiency of organic amendments in Vertisols. Thus, we conducted the research based on 29 years (1982–2011) of long-term fertilization experiment with a no fertilizer control and five fertilization regimes: CK (control, no fertilizer), NPK (mineral NPK fertilizers alone), NPK+1/2W (mineral NPK fertilizers combined with half the amount of wheat straw), NPK+W (mineral NPK fertilizers combined with full the amount of wheat straw), NPK+PM (mineral NPK fertilizers combined with pig manure) and NPK+CM (mineral NPK fertilizers combined cattle manure). Total mean annual C inputs were 0.45, 1.55, 2.66, 3.71, 4.68 and 6.56 ton/ha/yr for CK, NPK, NPKW1/2, NPKW, NPKPM and NPKCM, respectively. Mean SOC sequestration rate was 0.20 ton/ha/yr in the NPK treatment, and 0.39, 0.50, 0.51 and 0.97 ton/ha/yr in the NPKW1/2, NPKW, NPKPM, and NPKCM treatments, respectively. A linear relationship was observed between annual C input and SOC sequestration rate (SOCsequestration rate = 0.16 Cinput –0.10, R = 0.95, P<0.01), suggesting a C sequestration efficiency of 16%. The Vertisol required an annual C input of 0.63 ton/ha/yr to maintain the initial SOC level. Moreover, the C sequestration efficiencies of wheat straw, pig manure and cattle manure were 17%, 11% and 17%, respectively. The results indicate that the Vertisol has a large potential to sequester SOC with a high efficiency, and applying cattle manure or wheat straw is a recommendable SOC sequestration practice in Vertisols.

Soil pH significantly impacts microbial activity and community assembly, which in turn determines the temperature sensitivity (Q₁₀) of soil respiration. Due to the high soil acidification in China, it is necessary to understand how soil acidification impacts Q₁₀. Here, the Q₁₀ of soil respiration was examined in a long-term field experiment (1982–present) with different soil pH caused by fertilization management. In this experiment, we selected treatments with neutral pH: (1) no crops and fertilization (CK); (2) crops without fertilization (NF); low pH with (3) crops with chemical fertilization (NPK); and (4) crops with chemical fertilization combined with wheat straw incorporation (WS). Under natural soil temperature changes, we observed that soil acidification lowered the Q₁₀ value of soil respiration. Considering only temperature changes, the Q₁₀ of soil respiration was strongly associated with microbial community composition, alpha diversity, and soil ammonium nitrogen. Considering the interaction between soil pH and temperature, warming strengthened the negative effect of soil pH on the Q₁₀ of soil respiration, and the pathway through which soil pH mediated Q₁₀ included not only microbial community composition, alpha diversity, and biomass but also the soil’s available phosphorus. This work enhanced our insights into the relationships between Q₁₀, temperature, and soil pH by identifying important microbial properties and key soil environmental factors.

Soil nutrients in deep soils are important for nutrient cycling and plant growth. Organic amendments have been widely used for enhancing soil health and crop yield. However, little is known about the effects of organic amendments on the vertical distributions of soil nutrients. Based on a 32-year long-term organic amendment experiment, the objective of this study was to evaluate changes in the vertical distribution of nutrients in a soybean–wheat system Vertisol. The results showed that NPK with manure or straw application significantly increased soil organic carbon (SOC), total N, total P, alkali-hydrolyzable N, available P and available K above the 40 cm soil layer. Variations in soil micronutrients primarily occurred above the 20 cm soil layer, and the highest contents were observed for NPKWS and NPKPM, respectively. Nevertheless, large amounts of NO₃⁻−N contents accumulated in the 120–200 cm depth with manure but not straw application, indicating a high potential risk of nitrate leaching in manure treatments. These findings suggested that the application of organic amendment (manure or straw) could be recommendable for improving soil nutrients along the soil profile. Straw incorporation could be used as an alternative option for sustainable agriculture in regions with inadequate manure resources or severe nitrate leaching.

To explore the effects of different fertilization regimes on soil organic matter (SOM) sequestration in a winter-soybean/corn rotation, a long-term field experiment was conducted in Anhui, China, from 1982 to 2011. There were six treatments, as follows: (1) no fertilizer input (CK); (2) mineral fertilizers input (NPK); (3) mineral fertilizers + 3,750 kg ha-1 wheat straw (WS/2-NPK); (4) mineral fertilizers + 7,500 kg ha-1 wheat straw (WS-NPK); (5) mineral fertilizers + 15,000 kg ha-1 composted farmyard manure (CNPK); and (6) mineral fertilizers + 30,000 kg ha-1 composted farmyard manure (DNPK). Mineral fertilizer applications combined with organic amendments improved soil physical properties. For the WS/2-NPK, WS-NPK, CNPK and DNPK treatments, the soil bulk density decreased more than 10%, while the air porosity and field water content increased more than 90% and 15%, compared with the values at the start of the experiment in 1982. Our results indicate that about two decades are needed for SOM to reach its saturation point in all treatments. The SOM sequestration rate was related to the fertilization regime. The average SOM sequestration rate in 1982-2005 was 0.27 g kg-1 yr-1 with NPK, 0.45 g kg-1 yr-1 with WS/2-NPK, 0.56 g kg-1 yr-1 with WS-NPK, 0.60 g kg-1 yr-1 with CNPK and 1.02 g kg-1 yr-1 with DNPK. Therefore, both the quantity and the quality of the organic amendment determine the SOM sequestration rate and SOM saturation level.