Xueyun Yang

Soil organic carbon sequestration in upland soils of northern China under variable fertilizer management and climate change scenarios

We determined the historical change in soil organic carbon (SOC) stocks from long-term field trials that represent major soil types and climatic conditions of northern China. Soil carbon and general circulation models were validated using these field trial data sets. We then applied these models to predict future change in SOC stocks to 2100 using two net primary production (NPP) scenarios (i.e., current NPP or 1% year−1 NPP increase). The conversion rate of plant residues to SOC was higher in single-cropping sites than in double-cropping sites. The prediction of future SOC sequestration potential indicated that these soils will be a net source of carbon dioxide (CO2) under no fertilizer inputs. Even when inorganic nutrients were applied, the additional carbon input from increased plant residues could not meet the depletion of SOC in parts of northern China. Manure or straw application could however improve the SOC sequestration potential at all sites. The SOC sequestration potential in northern China was estimated to be −4.3 to 18.2 t C ha−1 by 2100. The effect of projected climate change on the annual rate of SOC change did not differ significantly between climate scenarios. The average annual rate of SOC change under current and increased NPP scenarios (at 850 ppm CO2) was approximately 0.136 t C ha−1 yr−1 in northern China. These findings highlight the need to maintain, and where possible increase, organic carbon inputs into these farming systems which are rapidly becoming inorganic fertilizer intensive.

Long-term combined application of manure and NPK fertilizers influenced nitrogen retention and stabilization of organic C in Loess soil

AimsOur aims were to: (1) compare the immobilization of NH4+-N by clay minerals and microbial biomass in soils with different fertilization history and (2) evaluate the effects of available C and N addition on the stabilization of soil organic carbon (SOC) in anthropogenic Lou soils.MethodsHere we used three soil treatments, i.e., (a) no fertilizer (NF), (b) inorganic NPK fertilizers (F), and (c) manure plus inorganic NPK fertilizers (MF) from an 18-year old field trial located in the south Loess Plateau, China. Two short-term incubation experiments were used to assess the impact of adding available nitrogen (NH4+-N) and C (glucose) on NH4+ fixation by clay minerals, and the decomposition of SOC in these soils.ResultsThe NH4+ fixed by clay minerals in the MF soils (3.8% of added N) was significantly (P < 0.05) lower than that in the NF, and F soils (14.1%, and 9.5% of added N). The decomposition rate of SOC in the MF soil (3.3%) during the incubation was significantly (P < 0.05) lower than in the NF, and F soils (4.4%, and 4.2%). Addition of NH4+-N significantly (P < 0.05) increased the decomposition of SOC in different soil treatments, and the MF soil also had lower decomposition rate than the NF, and F soils.ConclusionWe concluded that long-term combined application of manure and NPK fertilizers reduces the NH4+ fixation by clay minerals and improves the stabilization of organic C in soil.

Effect of Long-Term Potassium Fertilization on Crop Yield and Potassium Efficiency and Balance Under Wheat-Maize Rotation in China

Abstract Sustainable potassium (K) management at different soil sites requires understanding the relationships between crop productivity and long-term K fertilizations on a regional or national scale. We analyzed responses of grain yield of wheat (Triticum aestivum L.) and maize (Zea mays L.), K efficiency, and partial balance (difference between K input through fertilizer and K output in the aboveground biomass) during 15- (1990-2005) or 18-year (1990-2008) K fertilizations at five distinctive agroecological zones across China. Compared to the inorganic nitrogen (N) and phosphorus (P) fertilization, the inorganic NPK fertilization significantly increased grain yields of wheat (21%) and maize (16%-72%) at Qiyang and Changping, where soils have low exchangeable and non-exchangeable K contents, but not at Urumqi, Yangling and Zhengzhou, where soils have a high exchangeable and non-exchangeable K and/or low N/K ratio in crop plants. Compared to the inorganic NPK fertilization, the inorganic NPK (30% N) and organic manure (70% N) fertilization (NPKM) increased grain yields of wheat (14%-40%) and maize (9%-61%) at four sites, but not at Zhengzhou. For a productivity of wheat at 2-5 t ha−1 or maize at 3-6 t ha−1, 13-26 or 9-17 kg K ha−1 were required to produce 1.0 t wheat or maize. The NP fertilization resulted in the lowest negative partial K balance and accumulated 52 kg K ha−1 year−1 less than the NPK fertilization, which accumulated 28 kg ha−1 year−1 less K than the NPKM fertilization. A re-evaluation of the site-specific fertilization effects on N/K ratio in crop plants and soil K accumulation under current NPK and NPKM fertilization is urgently needed to increase both crop yield and K use efficiency at different agroecological zones across China.

Contributions of wheat and maize residues to soil organic carbon under long-term rotation in north China

Soil organic carbon (SOC) dynamics in agro-ecosystem is largely influenced by cropping. However, quantifying the contributions of various crops has been lacking. Here we employed a stable isotopic approach to evaluate the contributions of wheat and maize residues to SOC at three long-term experimental sites in north China. Soil samples were collected from 0–20, 20–40, 40–60, 60–80 and 80–100 cm after 13 and 20 years of wheat-maize rotation, and SOC and its stable 13C composition were determined. Our data showed that the δ13C value of SOC varied, on average, from −22.1‰ in the 0–20 cm to −21.5‰ in the 80–100 cm. Carbon input through maize residues ranged from 35% to 68% whereas the contribution of maize residues to SOC (0–40 cm) ranged from 28% to 40%. Our analyses suggested that the retention coefficient was in the range of 8.0–13.6% for maize residues and 16.5–28.5% for wheat residues. The two-fold higher retention coefficient of wheat versus maize residues was due to the differences in the quality of residues and probably also in the temperature during the growing season. Our study highlighted the importance of crop management on carbon sequestration in agricultural lands.

Trends of Yield and Soil Fertility in a Long-Term Wheat-Maize System

The sustainability of the wheat-maize rotation is important to Chinas food security. Intensive cropping without recycling crop residues or other organic inputs results in the loss of soil organic matter (SOM) and nutrients, and is assumed to be non-sustainable. We evaluated the effects of nine different treatments on yields, nitrogen use efficiency, P and K balances, and soil fertility in a wheat-maize rotation system (1991–2010) on silt clay loam in Shaanxi, China. The treatments involved the application of recommended dose of nitrogen (N), nitrogen and phosphorus (NP), nitrogen and potassium (NK), phosphorus and potassium (PK), combined NPK, wheat or maize straw (S) with NPK (SNPK), or dairy manure (M) with NPK (M1NPK and M2NPK), along with an un-treated control treatment (CK). The mean yields of wheat and maize ranged from 992 and 2 235 kg ha−1 under CK to 5 962 and 6 894 kg ha−1 under M2NPK treatment, respectively. Treatments in which either N or P was omitted (N, NK and PK) gave significantly lower crop yields than those in which both were applied. The crop yields obtained under NP, NPK and SNPK treatments were statistically identical, as were those obtained under SNPK and MNPK. However, M2NPK gave a significant higher wheat yield than NP, and MNPK gave significant higher maize yield than both NP and NPK. Wheat yields increased significantly (by 86 to 155 kg ha−1 yr−1) in treatments where NP was applied, but maize yields did not. In general, the nitrogen use efficiency of wheat was the highest under the NP and NPK treatments; for maize, it was the highest under MNPK treatment. The P balance was highly positive under MNPK treatment, increasing by 136 to 213 kg ha−1 annually. While the K balance was negative in most treatments, ranging from 31 to 217 kg ha−1 yr−1, levels of soil available K remained unchanged or increased over the 20 yr. SOM levels increased significantly in all treatments. Overall, the results indicated that combinations of organic manure and inorganic nitrogen, or returning straw with NP is likely to improve soil fertility, increasing the yields achievable with wheat-maize system in a way which is environmentally and agronomically beneficial on the tested soil.

Three-decade long fertilization-induced soil organic carbon sequestration depends on edaphic characteristics in six typical croplands

Fertilizations affect soil organic carbon (SOC) content but the relative influences of the edaphic and climate factors on SOC storage are rarely studied across wide spatiotemporal scales. This study synthesized long-term datasets of fertilization experiments in six typical Chinese croplands, and calculated annual C input from crops and manure amendments, changes in SOC storage (ΔSOC) and C sequestration efficiency (i.e. the percentage of soil C change per unit of C input, hereafter referred as CSE) in 0–20 cm soil over three decades. Three fertilization treatments include no fertilization (CK), chemical nitrogen, phosphorus and potassium fertilizers (NPK) and combined chemical fertilizers and manure (NPKM). Results showed significant fertilization effects on C input and ΔSOC (NPKM>NPK>CK), and significantly higher CSE in Qiyang at Hunan than Zhengzhou at Henan and Heihe at Heilongjiang. The variance partitioning analysis (VPA) showed more variance of CSE can be explained by edaphic factors (up to 39.7%) than other factors. Furthermore, soil available N content and pH were identified as the major soil properties explaining CSE variance. This study demonstrated key controls of soil fertility factors on SOC sequestration and informs the need to develop strategic soil management plan to promote soil carbon sequestration under long-term intensive fertilization.

Soil aggregation and aggregate associated organic carbon and total nitrogen under long-term contrasting soil management regimes in loess soil

Abstract This study investigated the effects of three contrasting soil management regimes and different nutrient treatments on the distribution of water-stable aggregates (>2, 1–2, 0.5–1, 0.25–0.5, and 0.25 mm) and mean weight diameter (MWD) at 0–10 and 10–20 cm soil horizons compared with Cropping, whereas Fallow yielded lower values of above two parameters. Abandonment increased SOC and TN contents in all aggregate sizes by 17–62% and 6–60%, respectively, at 0–10 cm soil layer compared with Cropping. Conversely, Fallow decreased SOC and TN contents in all aggregates by 7–27% and 7–25%, respectively. Nevertheless, the three soil management regimes presented similar SOC contents in all aggregates at 10–20 cm soil horizon. Only Cropping showed higher TN content in >0.5 mm aggregates than the two other regimes. Consequently, Abandonment enhanced the partitioning proportions of SOC and TN in >1 mm macro-aggregates, and Fallow promoted these proportions in micro-aggregates compared with Cropping. Under Cropping, long-term fertilization did not affect the distribution of aggregates and MWD values compared with those under CK, except for NPK treatment. Fertilizer treatments enhanced SOC and TN contents in aggregates at all tested soil depths. However, fertilization did not affect the partitioning proportions of SOC and TN contents in all aggregates compared with CK. Comprehensive results showed that different soil management regimes generated varied patterns of SOC and TN sequestration in loess soil. Abandonment enhanced soil aggregation and sequestered high amounts of SOC and TN in macro-aggregates. Long-term amendment of organic manure integrated with NPK maintained soil aggregate stability and improved SOC and TN sequestration in all aggregates in loess soil subjected to dryland farming.

Microbial Properties of a Loess Soil as Affected by Various Nutrient Management Practices in the Loess Plateau of China

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons.

Effects of Long-Term Inorganic and Organic Fertilization on Soil Micronutrient Status

Soil micronutrients were studied on loess soil with an 18-year long-term experiment. The results indicated that total soil iron and copper contents were similar under all treatments, but total soil manganese and zinc contents were significantly greater at the surface soil in the fertilized plots than in the controls, and total manganese contents were significantly greater in the whole soil profile under manure plus inorganic fertilizers than under controls. Generally, application of inorganic fertilizers had no effects on available soil micronutrient contents. The straw plus inorganic fertilizers significantly increased available manganese content at surface soil and available iron in subsurface soils. However, manure plus inorganic fertilizers significantly augmented soil-available iron contents throughout the profile, and raised available manganese, copper, and zinc contents, respectively, at surface soil relative to controls. The results suggest that long-term input of organic amendments alter the properties of soil and increase its plant-available micronutrient contents.

Soil aggregation and aggregating agents as affected by long term contrasting management of an Anthrosol

Soil aggregation was studied in a 21-year experiment conducted on an Anthrosol. The soil management regimes consisted of cropland abandonment, bare fallow without vegetation and cropping system. The cropping system was combined with the following nutrient management treatments: control (CONTROL, no nutrient input); nitrogen, phosphorus and potassium (NPK); straw plus NPK (SNPK); and manure (M) plus NPK (MNPK). Compared with the CONTROL treatment, the abandonment treatment significantly increased the formation of large soil macroaggregates (>2 mm) and consequently improved the stability of aggregates in the surface soil layer due to enhancement of hyphal length and of soil organic matter content. However, in response to long-term bare fallow treatment aggregate stability was low, as were the levels of aggregating agents. Long term fertilization significantly redistributed macroaggregates; this could be mainly ascribed to soil organic matter contributing to the formation of 0.5–2 mm classes of aggregates and a decrease in the formation of the >2 mm class of aggregates, especially in the MNPK treatment. Overall, hyphae represented a major aggregating agent in both of the systems tested, while soil organic compounds played significantly different roles in stabilizing aggregates in Anthrosol when the cropping system and the soil management regimes were compared.