本研究通过84天的室内培养试验来揭示秸秆和养分（氮(N)、磷(P)和硫(S)）联合供应下土壤新碳生成的潜在微生物机制。结果表明，与对照土壤相比，单独添加秸秆刺激微生物进行养分开采，这与C:N和C:P酶活的比例降低了8-16%相吻合。随着养分补充水平的增提高，公主岭土壤新碳生成量从1155.9增加到1722.4 mg kg^-1，海伦土壤则从725.1增加到1067.5 mg kg^-1。回归树分析表明β-葡萄糖苷酶（BG）、酸性磷酸酶（AP）、微生物量碳（MBC）和酸杆菌对公主岭新碳生成的相对影响分别为27.8、18.5、14.7和8.1%；对海伦新碳生成的相对影响分别为25.9、29.5、10.1和13.9%。路径分析表明酸杆菌通过调节BG、AP和MBC直接或间接对土壤新碳生成产生积极影响，其中MBC的获取更多受到AP的调节。海伦土壤的新碳生成强度低于公主岭土壤，并且海伦土壤的新碳生成与AP活性直接相关，表明土壤属性（例如SOC和pH值）对土壤新碳生成的重要性。综上，本研究揭示了添加秸秆的土壤中新碳生成与NPS养分补充的响应关系，且土壤新碳生成主要依赖于酸杆菌和变形菌的生长代谢及对BG和AP的调控。

土壤微生物生物量氮（MBN）在土壤中包含了最大比例的生物活性氮（N），是土壤氮循环的重要参与者。农业活动（例如作物轮作和单作）极大地影响了农业生态系统中的MBN。但是，目前农业生态系统中作物轮作和单作对MBN影响的研究极其缺乏。因此，本文基于203个已发表的文献进行整合分析（Meta 分析），以量化在合成氮肥施用下轮作和单作系统对MBN的影响。本研究发现，作物轮作显著提高了MBN的响应比（RR），并在旱地轮作条件下达到最高水平。然而，旱地作物单作并没有改变MBN的响应比，但是，水稻单作中MBN的响应比有所增加。作物轮作和单作系统之间的差异可能是由于不同的种植管理方式、氮素添加的方式、添加量和施肥年限所致。与作物单作系统相比，作物轮作对土壤总氮（TN）的增加幅度更大，对土壤pH的降低幅度较小。MBN的RR与矿质N的RR仅在作物轮作系统中正相关，MBN的RR与土壤pH的RR仅在单作系统中正相关。随机森林和结构方程模型的结果表明，MBN变化的主要驱动因素在作物轮作系统中是土壤矿质N和TN，在单作系统中是土壤pH。总之，本研究表明，轮作由于改善了土壤氮源，可以作为提高MBN的有效途径，从而提高MBN对由于大量施用化学氮肥导致的低pH的抵抗力。

高谷物日粮诱导的亚急性瘤胃酸中毒（SARA）会损害反刍动物的瘤胃上皮屏障功能，但SARA是否会持续性损害瘤胃上皮屏障的形态结构和功能还尚不清楚。本研究旨在以泌乳山羊为动物模型，研究SARA是否对瘤胃上皮的形态结构、通透性及参与上皮屏障功能的关键基因表达具有持续性影响。选取12只安装有永久性瘤胃瘘管的泌乳中期奶山羊，随机分为对照组（Ctrl，n=4）和SARA组（n=8），对照组试验动物饲喂NFC/NDF比为1.40的基础饲粮，SARA组依次饲喂NFC/NDF比为1.40、1.79、2.31和3.23四种饲粮诱导试验动物发生SARA。SARA诱导成功后从SARA组中随机选取4只患病动物让其自由采食混合粗饲料4周使其恢复，即post-SARA组。采用pH值监测系统连续监测瘤胃pH值以判定SARA的严重程度。采集瘤胃腹囊上皮组织，利用透射电镜、尤斯灌流室、PCR和Western blot等先进技术检测瘤胃上皮的形态结构和功能。结果表明：与对照组相比，（1）SARA组瘤胃上皮乳头长度、宽度、表面积和角质层厚度显著增加(P<0.05)，棘基层厚度和上皮总厚度则显著降低(P<0.05)。post-SARA组这些参数则趋向于恢复到对照组水平(P>0.05)。同时透射电镜结果显示，SARA减少了瘤胃上皮紧密连接数量，加宽了上皮细胞之间的间隙。（2）SARA组和post-SARA组瘤胃上皮短路电流（Isc）、组织导电性（Gt）以及辣根过物氧化酶（HRP）通过瘤胃上皮的流速均显著增加(P<0.05)，这表明SARA可引起瘤胃上皮通透性持续升高，进而导致其屏障功能长期受损。（3）SARA组和post-SARA组瘤胃上皮紧密连接蛋白CLDN1, OCLN and ZO-1的mRNA和蛋白表达量均极显著下调(P<0.01)。由此可见，SARA可导致瘤胃上皮屏障结构和功能持续受损，这与瘤胃上皮紧密连接蛋白表达下调密切相关，而且瘤胃上皮屏障功能的恢复滞后于形态结构的恢复。

The concentration of soil Olsen-P is rapidly increasing in many parts of China, where P budget (P input minus P output) is the main factor influencing soil Olsen-P.  Understanding the relationship between soil Olsen-P and P budget is useful in estimating soil Olsen-P content and conducting P management strategies.  To address this, a long-term experiment (1991–2011) was performed on a fluvo-aquic soil in Beijing, China, where seven fertilization treatments were used to study the response of soil Olsen-P to P budget.  The results showed that the relationship between the decrease in soil Olsen-P and P deficit could be simulated by a simple linear model.  In treatments without P fertilization (CK, N, and NK), soil Olsen-P decreased by 2.4, 1.9, and 1.4 mg kg^–1 for every 100 kg ha^–1 of P deficit, respectively.  Under conditions of P addition, the relationship between the increase in soil Olsen-P and P surplus could be divided into two stages.  When P surplus was lower than the range of 729–884 kg ha^–1, soil Olsen-P fluctuated over the course of the experimental period with chemical fertilizers (NP and NPK), and increased by 5.0 and 2.0 mg kg^–1, respectively, when treated with chemical fertilizers combined with manure (NPKM and 1.5NPKM) for every 100 kg ha^–1 of P surplus.  When P surplus was higher than the range of 729–884 kg ha^–1, soil Olsen-P increased by 49.0 and 37.0 mg kg^–1 in NPKM and 1.5NPKM treatments, respectively, for every 100 kg ha^–1 P surplus.  The relationship between the increase in soil Olsen-P and P surplus could be simulated by two-segment linear models.  The cumulative P budget at the turning point was defined as the “storage threshold” of a fluvo-aquic soil in Beijing, and the storage thresholds under NPKM and 1.5NPKM were 729 and 884 kg ha^–1 P for more adsorption sites.  According to the critical soil P values (CPVs) and the relationship between soil Olsen-P and P budget, the quantity of P fertilizers for winter wheat could be increased and that of summer maize could be decreased based on the results of treatments in chemical fertilization.  Additionally, when chemical fertilizers are combined with manures (NPKM and 1.5NPKM), it could take approximately 9–11 years for soil Olsen-P to decrease to the critical soil P values of crops grown in the absence of P fertilizer. 

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.

Food shortages arise more frequently owing to unpredictable crop yield losses caused by biotic and abiotic stresses.  With advances in molecular biology and marker technology, a new era of molecular breeding has emerged that has greatly accelerated the pace of plant breeding.  High-throughput genotyping technology and phenotyping platforms have enabled large-scale marker-trait association analysis, such as genome-wide association studies, to precisely dissect the genetic architecture of plant traits.  Large-scale mapping of agronomically important quantitative trait loci, gene cloning and characterization, mining of elite alleles/haplotypes, exploitation of natural variations, and genomic selection have paved the way towards genomics-assisted breeding (GAB).  With the availability of more and more informative genomic datasets, GAB would become a promising technique to expedite the breeding cycle for crop improvement.  

Nitrogen (N) loss from fertilization in agricultural fields has an unavoidable negative impact on the environment and a better
understanding of the major pathways can assist in developing the best management practices. The aim of this study was
to evaluate the fate of N fertilizers applied to acidic red soil (Ferralic Cambisol) after 19 years of mineral (synthetic) and
manure fertilizer treatments under a cropping system with wheat-maize rotations. Five field treatments were examined:
control (CK), chemical nitrogen and potash fertilizer (NK), chemical nitrogen and phosphorus fertilizer (NP), chemical nitrogen,
phosphorus and potash fertilizer (NPK) and the NPK with manure (NPKM, 70% N from manure). Based on the soil
total N storage change in 0–100 cm depth, ammonia (NH3) volatilization, nitrous oxide (N₂O) emission, N plant uptake, and
the potential N leaching loss were estimated using a mass balance approach. In contrast to the NPKM, all mineral fertilizer
treatments (NK, NP and NPK) showed increased nitrate (NO₃^–-N) concentration with increasing soil depth, indicating higher
leaching potential. However, total NH3 volatilization loss was much higher in the NPKM (19.7%) than other mineral fertilizer
treatments (≤4.2%). The N₂O emissions were generally low (0.2–0.9%, the highest from the NPKM). Total gaseous loss
accounted for 1.7, 3.3, 5.1, and 21.9% for NK, NP, NPK, and NPKM treatments, respectively. Estimated N leaching loss
from the NPKM was only about 5% of the losses from mineral fertilizer treatments. All data demonstrated that manure
incorporation improved soil productivity, increased yield, and reduced potential leaching, but with significantly higher NH₃
volatilization, which could be reduced by improving the application method. This study confirms that manure incorporation is an essential strategy in N fertilization management in upland red soil cropping system.

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).

The phytohormone auxin plays a central role in coordinating plant growth and development. GH3 is one of the three gene families that respond rapidly during auxin stimulation. Here, we report the identification and characterization of the GH3 gene family in maize. A total of 12 GH3 genes were identified, which are not evenly distributed over the 10 maize chromosomes. Maize GH3 protein sequences share a conserved domain which occupies nearly the entire protein. Diversified cis-elements were found in promoters of maize GH3 genes. In this study, the 12 maize GH3 proteins were primarily classified into two phylogenetic groups, similar to the 13 rice GH3 proteins, while 9 of the 19 Arabidopsis GH3 proteins were observed in the third phylogenetic group. Microarray analysis showed that expression of maize GH3 genes is temporally and spatially modulated. Additionally, maize GH3 genes displayed variable changes at transcript level upon pathogen infection. Results presented here provide insight into the diversification and evolution of GH3 proteins, and lay a foundation for the functional characterization of these GH3 genes in future, especially for elucidating the mechanisms of GH3-mediated pathogenesis.

In order to reveal the impact of various fertilization strategies on carbon (C) and nitrogen (N) accumulation and allocation in corn (Zea mays L.), corn was grown in the fields where continuous fertilization management had been lasted about 18 years at two sites located in Central and Northeast China (Zhengzhou and Gongzhuling), and biomass C and N contents in different organs of corn at harvest were analyzed. The fertilization treatments included non-fertilizer (control), chemical fertilizers of either nitrogen (N), or nitrogen and phosphorus (NP), or phosphorus and potassium (PK), or nitrogen, phosphorus and potassium (NPK), NPK plus manure (NPKM), 150% of the NPKM (1.5NPKM), and NPK plus straw (NPKS). The results showed that accumulated C in aboveground ranged from 2 550–5 630 kg ha–1 in the control treatment to 9 300–9 610 kg ha–1 in the NPKM treatment, of which 57–67% and 43–50% were allocated in the non-grain organs, respectively. Accumulated N in aboveground ranged from 44.8–55.2 kg ha–1 in the control treatment to 211–222 kg ha–1 in the NPKM treatment, of which 35–48% and 33–44% were allocated in the non-grain parts, respectively. C allocated to stem and leaf for the PK treatment was 65 and 49% higher than that for the NPKM treatment at the both sites, respectively, while N allocated to the organs for the PK treatment was 18 and 6% higher than that for the NPKM treatment, respectively. This study demonstrated that responses of C and N allocation in corn to fertilization strategies were different, and C allocation was more sensitive to fertilization treatments than N allocation in the area.

The improvement of soil productivity depends on a rational input of water and nutrients, optimal field management, and the increase of basic soil productivity (BSP). In this study, BSP is defined as the productive capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local field management. Based on 19-yr data of the long-term agronomic experiments (1989–2008) on a fluvo-aquic soil in Zhengzhou, Henan Province, China, the decision support system for agrotechnology transfer (DSSAT ver. 4.0) crop growth model was used to simulate yields by BSP of winter wheat (Triticum aestivium L.) and summer maize (Zea mays L.) to examine the relationship between BSP and soil organic carbon (SOC) under long-term fertilization. Five treatments were included: (1) no fertilization (control), (2) nitrogen, phosphorus and potassium fertilizers (NPK), (3) NPK plus manure (NPKM), (4) 1.5 times of NPKM (1.5NPKM), and (5) NPK plus straw (NPKS). After 19 yr of treatments, the SOC stock increased 16.7, 44.2, 69.9, and 25.2% under the NPK, NPKM, 1.5NPKM, and NPKS, respectively, compared to the initial value. Among various nutrient factors affecting contribution percentage of BSP to winter wheat and summer maize, SOC was a major affecting factor for BSP in the fluvo-aquic soil. There were significant positive correlations between SOC stock and yields by BSP of winter wheat and summer maize (P<0.01), and yields by BSP of winter wheat and summer maize increased 154 and 132 kg ha–1 when SOC stock increased 1 t C ha–1. Thus, increased SOC accumulation is a crucial way for increasing BSP in fluvo-aquic soil. The manure or straw combined application with chemical fertilizers significantly enhanced BSP compared to the application of chemical fertilizers alone.

Carbon sequestration in agricultural soils is a complex process controlled by farming practices, climate and some other environment factors. Since purple soils are unique in China and used as the main cropland in Sichuan Basin of China, it is of great importance to study and understand the impacts of different fertilizer amendments on soil organic carbon (SOC) changes with time. A research was carried out to investigate the relationship between soil carbon sequestration and organic carbon input as affected by different fertilizer treatments at two long-term rice-based cropping system experiments set up in early 1980s. Each experiment consisted of six identical treatments, including (1) no fertilizer (CK), (2) nitrogen and phosphorus fertilizers (NP), (3) nitrogen, phosphorus and potassium fertilizers (NPK), (4) fresh pig manure (M), (5) nitrogen and phosphorus fertilizers plus manure (MNP), and (6) nitrogen, phosphorus and potassium fertilizers plus manure (MNPK). The results showed that annual harvestable carbon biomass was the highest in the treatment of MNPK, followed by MNP and NPK, then M and NP, and the lowest in CK. Most of fertilizer treatments resulted in a significant gain in SOC ranging from 6.48 to 29.13% compared with the CK, and raised soil carbon sequestration rate to 0.10–0.53 t ha–1 yr−1. Especially, addition of manure on the basis of mineral fertilizers was very conducive to SOC maintenance in this soil. SOC content and soil carbon sequestration rate under balanced fertilizer treatments (NPK and MNPK) in the calcareous purple soil (Suining) were higher than that in the acid purple soil (Leshan). But carbon conversion rate at Leshan was 11.00%, almost 1.5 times of that (7.80%) at Suining. Significant linear correlations between soil carbon sequestration and carbon input were observed at both sites, signifying that the purple soil was not carbon-saturated and still had considerable potential to sequestrate more carbon.

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 associated soil organic carbon (SOC) and total nitrogen (TN) content in loess soil. A 21-yr long-term experiment was performed, in which soil management regimes include cropland abandonment (Abandonment), bare fallow (Fallow) and wheat-fallow cropping (Cropping). Under Cropping, the following nutrient treatments were employed: control (CK, no nutrient input), nitrogen only (N), nitrogen and potassium (NK), phosphorus and potassium (PK), NP, NPK, and manure (M) plus NPK (MNPK). Results demonstrated that Abandonment significantly increased the content of soil macro-aggregates (>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.

Soil organic carbon (SOC) and soil Olsen-P are key soil fertility indexes but information on their relationships is limited particularly under long-term fertilization. We investigated the relationships between SOC and the percentage of soil Olsen-P to total P (PSOPTP) under six different 15-yr (1990-2004) long-term fertilizations at two cropping systems in northern China. These fertilization treatments were (1) unfertilized control (control); (2) chemical nitrogen (N); (3) N plus chemical P (NP); (4) NP plus chemical potassium (NPK); (5) NPK plus animal manure (NPKM) and (6) high NPKM (hNPKM). Compared with their initial values in 1989 at both sites, during the 11th to 15th fertilization years annual mean SOC contents were significantly increased by 39.4-47.0% and 58.9-93.9% at Gongzhuling, Jilin Province, and Urumqi, Xinjiang, China, under the two NPKM fertilizations, respectively, while no significant changes under the no-P or chemical P fertilization. During the 11th to 15th fertilization years, annual mean PSOPTP was respectively increased by 2.6-4.2 and 5.8-14.1 times over the initial values under the two chemical P fertilizations and the two NPKM fertilizations, but was unchanged in their initial levels under the two no-P fertilizations at both sites. Over the 15-yr long-term fertilization SOC significantly positively correlated with PSOPTP (r2=0.55-0.79, P<0.01). We concluded that the combination of chemical P plus manure is an effective way to promote SOC accumulation and the percentage of soil Olsen-P to total P at the two mono-cropping system sites in northern China.

Soil organic carbon (SOC), soil microbial biomass carbon (SMBC) and SMBC quotient (SMBC/SOC, qSMBC) are key indexes of soil biological fertility because of the relationship to soil nutrition supply capacity. Yet it remains unknown how these three indexes change, which limits our understanding about how soil respond to different fertilization practices. Based on a 22-yr (1990-2011) long-term fertilization experiment in northwest China, we investigated the dynamics of SMBC and qSMBC during the growing period of winter wheat, the relationships between the SMBC, qSMBC, soil organic carbon (SOC) concentrations, the carbon input and grain yield of wheat as well. Fertilization treatments were 1) nonfertilization (control); 2) chemical nitrogen plus phosphate plus potassium (NPK); 3) NPK plus animal manure (NPKM); 4) double NPKM (hNPKM) and 5) NPK plus straw (NPKS). Results showed that the SMBC and qSMBC were significantly different among returning, jointing, flowering and harvest stages of wheat under long-term fertilization. And the largest values were observed in the flowering stage. Values for SMBC and qSMBC ranged from 37.5 to 106.0 mg kg-1 and 0.41 to 0.61%, respectively. The mean value rank of SMBC during the whole growing period of wheat was hNPKM>NPKM>NPKS>CK>NPK. But there were no statistically significant differences between hNPKM and NPKM, or between CK and NPK. The order for qSMBC was NPKS>NPKM>CK>hNPKM>NPK. These results indicated that NPKS significantly increased the ratio of SMBC to SOC, i.e., qSMBC, compared with NPK fertilizer or other two NPKM fertilizations. Significant linear relationships were observed between the annual carbon input and SOC (P<0.01) or SMBC (P<0.05), and between the relative grain yield of wheat and the SOC content as well (P<0.05). But the qSMBC was not correlated with the annual carbon input. It is thus obvious that the combination of manure, straw with mineral fertilizer may be benefit to increase SOC and improve soil quality than using only mineral fertilizer.

Alfalfa (Medicago sativa L.) is an important forage crop in the world and it is of great significance for the improvement of its salt tolerance. To improve salt tolerance in alfalfa, a rice ascorbate peroxidase gene (OsAPX2) was introduced into alfalfa using Agrobacterium tumefaciens-mediated transformation with marker gene bar. The different T-DNA insertions in T1 transgenic alfalfa were identified by Southern hybridization. Three independent T2 transgenic lines were selected for stress analysis and the results showed that all of them were salt tolerant compared with wild-type plants. The transgenic plants had low levels of H2O2, malondialdehyde and relative electrical conductivity under salt and drought stresses. Moreover, the contents of chlorophyll and proline, and APX activity were high in transgenic plants under salt and drought stresses. Taken together, the overexpression of OsAPX2 enhances salt tolerance in alfalfa through scavenging reactive oxygen species.

Long-term fertilization experiment provides the platform for understanding the proton budgets in nitrogen transformations of agricultural ecosystems. We analyzed the historical (1990-2005) observations on four agricultural long-term experiments in China (Changping, Chongqing, Gongzhuling and Qiyang) under four different fertilizations, i.e., no-fertilizer (control), sole chemical nitrogen fertilizer (FN), sole chemical phosphorous and potassium fertilizers (FPK) and chemical nitrogen, phosphorous and potassium fertilizers (FNPK). The significant decline in topsoil pH was caused not only by chemical N fertilization (0.29 and 0.89 ΔpH at Gongzhuling and Qiyang, respectively) but also by chemical PK fertilization (0.59 ΔpH at Gongzhuling). The enhancement of available nutrients in the topsoil due to long-term direct nutrients supply with chemical fertilizers was in the descending order of available P (168-599%)>available K (16-189%)>available N (9-33%). The relative rate of soil pH decline was lower under long-term judicious chemical fertilization (-0.036-0.034 ΔpH yr-1) than that under long-term sole N or PK fertilization (0.016-0.086 ΔpH yr-1). Long-term judicious chemical fertilization with N, P and K elements decreases the nutritional limitation to normal crop growth, under which more N output was distributed in biomass removal rather than the loss via nitrate leaching. We concluded that the N distribution percentage of nitrate leaching to biomass removal might be a suitable indicator to the sensitivity of agricultural ecosystems to acid inputs.

Soil physical properties are important indicators of the potential for agricultural production. Our objective was to evaluate the effects of long-term inputs of green manures on physical properties of a reddish paddy soil (Fe-Typic Hapli-Stagnic Anthrosols) under a double cropping system. The common cropping pattern before the study was early-late rice-fallow (winter). The field treatments included rice-rice-fallow (R-R-WF), rice-rice-rape (R-R-RP), rice-rice-Chinese milk vetch (RR- MV), and rice-rice-ryegrass (R-R-RG). The rape, Chinese milk vetch and ryegrass were all incorporated as green manures 15 d before early rice transplanting during the following year. The soil bulk density in all green manure treatments was significantly reduced compared with the winter fallow treatment. Soil porosity with green manure applications was significantly higher than that under the winter fallow. The green manure treatments had higher 0.25-5 mm water stable aggregates and aggregates stabilities in the plow layer (0-15 cm depth) compared with the fallow treatment. The mean weight diameter (MWD) and normalized mean weight diameter (NMWD) of aggregates in the green manure treatment were larger than that with the winter fallow. Soil given green manure retained both a higher water holding capacity in the plow layer soil, and a larger volume of moisture at all matric potentials (-10, -33 and -100 kPa). We conclude that the management of double-rice fields in southern central China should be encouraged to use green manures along with chemical fertilizers to increase SOC content, improve soil physical properties and soil fertility.

Agricultural production plays an important role in affecting atmospheric nitrous oxide (N2O) concentrations. Field measurements were conducted in Dalian City, Liaoning Province in Northeast China from two consecutive years (2009 and 2010) to estimate N2O emissions from a spring maize field, a main cropping system across the Chinese agricultural regions. The observed flux data in conjunction with the local climate, soil and management information were utilized to test a process-based model, DeNitrification-DeComposition (DNDC), for its applicability for the cropping system. The validated DNDC was then used for exploring strategies to reduce N2O emissions from the target field. The results showed that the major N2O pulse emissions occurred with duration of about 3-5 d after fertilizer application in both years 2009 and 2010, which on average accounted for about 60% of the total N2O emissions each year. Rainfall and fertilizer application were the major factors influencing the N2O emissions from spring maize field. The average N2O fluxes from the CK (control plot, without fertilization) and FP (traditional chemical N fertilizer) treatments were 23.1 and 60.6 μg m-2 h-1 in 2009, respectively, and 21.5 and 64.3 μg m-2 h-1 in 2010, respectively. The emission factors (EFs) of the applied N fertilizer (270 kg N ha-1) as N2ON were 0.62% in 2009 and 0.77% in 2010, respectively. The comparison of modeled daily N2O emission fluxes against observations indicated that the DNDC model had a good performance even if without adjusting the internal parameters. The modeled results showed that management practices such as no-till, changing timing or rate of fertilizer application, increasing residue incorporation, and other technically applicable measures could effectively reduce N2O emissions from the tested fields. Our study indicated that avoiding application of N fertilizers at heavy rainfall events or splitting the fertilizer into more applications would be the most feasible approaches to reduce N2O emissions from spring maize production in Northeast China.