Investigating the dynamics and distribution of soil phosphorus (P) fractions can provide a basis for enhancing P utilization by crops.  Four treatments from a 29-year long-term experiment in black soil with maize cropping were involved in this study: no fertilizer (CK), inorganic nitrogen and potassium (NK), inorganic nitrogen, phosphorus, and potassium (NPK), and NPK plus manure (NPKM).  We analyzed soil P fractions in different soil layers using a modified Hedley sequential method.  The long-term NPKM treatment significantly increased total P by 0.6–1.6 times in the different soil layers.  The Olsen-P concentration far exceeded the environmental threshold for soil Olsen-P (50.6 mg kg^–1) in the NPKM treatment in the 0–60 cm soil profile.  Moreover, the concentrations and proportion of labile and partially labile inorganic P (Pi) fractions (i.e., NaHCO₃-extracted Pi, NaOH-extracted Pi, and dilute HCl-extracted Pi) to the sum of all P fractions (Pt) in the 0–60 cm soil profile were higher in the NPKM treatment than in the NPK treatment, indicating that manure could promote the transformation of non-labile into more labile forms of P in soil, possibly by manure reducing P fixation by soil particles.  Soil organic matter, Mehlich-3 extractable iron (Fe), and organic-bound aluminum were increased by fertilization, and were the main factors influencing the differences in the P fractions in the 0–20 cm soil layer.  Soil mineral components, i.e., free Fe oxide and CaCO₃, were the main factors influencing the P fractions in the subsoil.  The soil P transformation process varied with soil layer and fertilization.  Application of manure fertilizer can increase the labile (Olsen) P concentrations of the various soil layers, and thus should reduce the mineral P fertilizer requirement for crop growth and reduce potential environmental damage

Although returning crop residue to fields is a recommended measure for improving soil carbon (C) stocks in agroecosystems, the response of newly formed soil C (NFC) to the integrated supply of residue and nutrients and the microbial mechanisms have not been fully understood. Therefore, an 84-day incubation experiment was conducted to ascertain the microbial mechanisms that underpin the NFC response to inputs of residue and nitrogen (N), phosphorus (P), and sulfur (S) in two black soils. The results showed that adding residue alone accelerated microbial nutrient mining, which was supported by decreases of 8–16% in the ratios of C:N and C:P enzyme activities (relative to soils with nutrient inputs). The NFC amounts increased from 1155.9 to 1722.4 mg kg⁻¹ soil in Gongzhuling and increased from 725.1 to 1067.5 mg kg⁻¹ soil in Hailun as the levels of nutrient supplementation increased. Boosted regression tree analysis suggested that β-glucosidase (BG), acid phosphatase (AP), microbial biomass C (MBC), and Acidobacteria accounted for 27.8, 18.5, 14.7, and 8.1%, respectively, of the NFC in Gongzhuling and accounted for 25.9, 29.5, 10.1, and 13.9%, respectively, of the NFC in Hailun. Path analysis determined that Acidobacteria positively influenced NFC both directly and indirectly by regulating BG, AP, and MBC, in which MBC acquisition was regulated more by AP. The intensity of NFC was lower in Hailun soil than in Gongzhuling soil and was directly affected by AP, thereby indicating the importance of soil status (e.g., SOC and pH) in determining NFC. Overall, our results reveal the response of NFC to supplementation by N, P, and S, which depends on Acidobacteria and Proteobacteria, and their investment in BG and AP in residue-amended soil.

Understanding the characteristics and influences of various factors on phosphorus (P) fractions is of significance for promoting the efficiency of soil P.  Based on long-term experiments on black soil, fluvo-aquic soil, and loess soil, which belong to Phaeozems, Cambisols, and Anthrosols in the World Reference Base for Soil Resources (WRB), respectively, five fertilization practices were selected and divided into three groups: no P fertilizer (CK/NK), balanced fertilizer (NPK/NPKS), and manure plus mineral fertilizer (NPKM).  Soil inorganic P (Pi) fractions and soil properties were analyzed to investigate the characteristics of the Pi fractions and the relationships between Pi fractions and various soil properties.  The results showed that the proportion of Ca₁₀-P in the sum of total Pi fractions was the highest in the three soils, accounting for 33.5% in black soil, 48.8% in fluvo-aquic soil, and 44.8% in loess soil.  Long-term fertilization practices resulted in periodic changes in soil Pi accumulation or depletion.  For black soil and fluvo-aquic soil, the Pi accumulation was higher in the late period (10–20 years) of fertilization than in the early period (0–10 years) under NPK/NPKS and NPKM, whereas the opposite result was found in loess soil.  The Pi accumulation occurred in all Pi fractions in black soil; mainly in Ca₈-P, Fe-P, and Ca₁₀-P in fluvo-aquic soil; and in Ca₂-P, Ca₈-P, and O-P in loess soil.  Under CK/NK, the soil Pi was depleted mainly in the early period in each of the three soils.  In addition to the labile Pi (Ca₂-P) and moderately labile Pi (Ca₈-P, Fe-P, Al-P), the Ca₁₀-P in black soil and fluvo-aquic soil and O-P in loess soil could also be used by crops.  Redundancy analysis showed that soil properties explained more than 90% of the variation in the Pi fractions in each soil, and the explanatory percentages of soil organic matter (SOM) were 43.6% in black soil, 74.6% in fluvo-aquic, and 38.2% in loess soil.  Consequently, decisions regarding the application of P fertilizer should consider the accumulation rate and the variations in Pi fractions driven by soil properties in non-acidic soils.

Soil productivity (SP) without external fertilization influence is an important indicator for the capacity of a soil to support crop yield. However, there have been difficulties in estimating values of SPs for soils after various long-term field treatments because the treatment without external fertilization is used but is depleted in soil nutrients, leading to erroneous estimation. The objectives of this study were to estimate the change of SP across different cropping seasons using pot experiments, and to evaluate the steady SP value (which is defined by the basal contribution of soil itself to crop yield) after various longterm fertilization treatments in soils at different geographical locations. The pot experiments were conducted in Jinxian of Jiangxi Province with paddy soil, Zhengzhou of Henan Province with fluvo-aquic soil, and Gongzhuling of Jilin Province with black soils, China. Soils were collected after long-term field fertilization treatments of no fertilizer (control; CK-F), chemical fertilizer (NPK-F), and combined chemical fertilizer with manure (NPKM-F). The soils received either no fertilizer (F0) or chemical fertilizer (F1) for 3–6 cropping seasons in pots, which include CK-P (control; no fertilizer from long-term field experiments for pot experiments), NPK-P (chemical fertilizer from long-term field experiments for pot experiments), and NPKM-P (combined chemical and organic fertilizers from long-term field experiments for pot experiments). The yield data were used to calculate SP values. The initial SP values were high, but decreased rapidly until a relatively steady SP was achieved at or after about three cropping seasons for paddy and fluvo-aquic soils. The steady SP values in the third cropping season from CK-P, NPK-P, and NPKM-P treatments were 37.7, 44.1, and 50.0% in the paddy soil, 34.2, 38.1, and 50.0% in the fluvo-aquic soil, with the highest value observed in the NPKM-P treatment for all soils. However, further research is required in the black soils to incorporate more than three cropping seasons. The partial least squares path mode (PLS-PM) showed that total N (nitrogen) and C/N ratio (the ratio of soil organic carbon and total N) had positive effects on the steady SP for all three soils. These findings confirm the significance of the incorporation of manure for attaining high soil productivity. Regulation of the soil C/N ratio was the other main factor for steady SP through fertilization management.

Black soil is one of the most precious soil resources on earth because it has abundant carbon stocks and a relatively high production capacity.  However, decreasing organic matter after land reclamation, and the effects of long-term inputs of organic carbon have made it less fertile black soil in Northeast China.  Straw return could be an effective method for improving soil organic carbon (SOC) sequestration in black soils.  The objective of this study was to evaluate whether straw return effectively increases SOC sequestration.  Long-term field experiments were conducted at three sites in Northeast China with varying latitudes and SOC densities.  Study plots were subjected to three treatments: no fertilization (CK); inorganic fertilization (NPK); and NPK plus straw return (NPKS).  The results showed that the SOC stocks resulting from NPKS treatment were 4.0 and 5.7% higher than those from NPK treatment at two sites, but straw return did not significantly affect the SOC stocks at the third site.  Furthermore, at higher SOC densities, the NPKS treatment resulted in significantly higher soil carbon sequestration rates (CSR) than the NPK treatment.  The equilibrium value of the CSR for the NPKS treatment equated to cultivation times of 17, 11, and 8 years at the different sites.  Straw return did not significantly increase the SOC stocks in regions with low SOC densities, but did enhance the C pool in regions with high SOC densities.  These results show that there is strong regional variation in the effects of straw return on the SOC stocks in black soil in Northeast China.  Additional cultivations and fertilization practices should be used when straw return is considered as an approach for the long-term improvement of the soil organic carbon pool.

Ecological engineering involves the use of plants to promote establishment, survival and efficiency of natural enemies in agricultural systems.  Some plant species may be hosts or provide resources to some pest species.  We assessed the risks and benefits of sesame (Sesamum indicum L.), as a nectar source for seven economically important Lepidopteran pest and four parasitoid species in a range of vegetable crop systems.  Our results showed that the mean longevities of arthropod parasitoids Pteromalus puparum (L.), Encarsia sophia (Girault & Dodd) and male Microplitis tuberculifer (Wesmael) were significantly extended when fed on sesame flowers compared to the water control.  Sesame flowers had no effect on adult longevities and fecundities of six out of the seven Lepidoptera pest species tested except Plutella xyllostella (L.) females laid more eggs when fed on sesame flowers.  It is likely that the increased fecundity is due to accessibility to nectar at the bottom of corolla because of their smaller body sizes.  Our findings provide a first step towards better understanding of the risks and benefits of using sesame to implement ecological engineering for the management of vegetable pests.

The combined use of chemical and organic fertilizers is considered a good method to sustain high crop yield and enhance soil organic carbon (SOC), but it is still unclear when and to what extent chemical fertilizers could be replaced by organic fertilizers.  We selected a long-term soil fertility experiment in Gongzhuling, Northeast China Plain to examine the temporal dynamics of crop yield and SOC in response to chemical nitrogen, phosphorus, and potassium (NPK) fertilizers and manure, applied both individually and in combination, over the course of three decades (1980–2010).  We aimed to test 1) which fertilizer application is the best for increasing both maize yield and SOC in this region, and 2) whether chemical fertilizers can be replaced by manure to maintain high maize yield and enhance SOC, and if so, when this replacement should be implemented.  We observed that NPK fertilizers induced a considerable increase in maize yield in the first 12 years after the initiation of the experiment, but manure addition did not.  In the following years, the addition of both NPK fertilizers and manure led to an increase in maize yield.  SOC increased considerably in treatments with manure but remained the same or even declined with NPK treatments.  The increase in maize yield induced by NPK fertilizers alone declined greatly with increasing SOC, whereas the combination of NPK and manure resulted in high maize yield and a remarkable improvement in SOC stock.  Based on these results we suggested that NPK fertilizers could be at least partially replaced by manure to sustain high maize yield after SOC stock has reached 41.96 Mg C ha^–1 in the Northeast China Plain and highly recommend the combined application of chemical fertilizers and manure (i.e., 60 Mg ha^–1).