Soil Organic Carbon,Black Carbon,and Enzyme Activity Under Long-Term Fertilization

The present study aims to understand the effects of long-term fertilization on soil organic carbon (SOC), black carbon (BC), enzyme activity, and the relationships among these parameters. Paddy field was continuously fertilized over 30 yr with nine different fertilizer treatments including N, P, K, NP, NK, NPK, 2NPK (two-fold NPK), NPK+manure (NPKM), and CK (no fertilization), N, 90 kg urea-N ha⁻¹ yr⁻¹; P, 45 kg triple superphosphate-P₂O₅ ha⁻¹ yr⁻¹; K, 75 kg potassium chloride-K₂O ha⁻¹ yr⁻¹; and pig manure, 22 500 kg ha⁻¹ yr⁻¹. Soil samples were collected and determined for SOC, BC content, and enzyme activity. The results showed that the SOC in the NPKM treatment was significantly higher than those in the K, P, and CK treatments. The lowest SOC content was found in the CK treatment. SOC content was similar in the N, NP, NK, NPK, 2NPK, and NPKM treatments. There was no significant difference in BC content among different treatments. The BC-to-SOC ratios (BC/SOC) ranged from 0.50 to 0.63, suggesting that BC might originate from the same source. Regarding enzyme activity, NPK treatment had higher urease activity than NPKM treatment. The urease activity of NPKM treatment was significantly higher than that of 2NPK, NP, N, P, K, CK, and NPKM treatment which produced higher activities of acid phosphatase, catalase, and invertase than all other treatments. Our results indicated that long-term fertilization did not significantly affect BC content. Concurrent application of manure and mineral fertilizers increased SOC content and significantly enhanced soil enzyme activities. Correlation analysis showed that catalase activity was significantly associated with invertase activity, but SOC, BC, and enzyme activity levels were not significantly correlated with one another. No significant correlations were observed between BC and soil enzymes. It is unknown whether soil enzymes play a role in the decomposition of BC.     

Long-Term Manure Amendments Enhance Soil Aggregation and Carbon Saturation of Stable Pools in North China Plain

Organic amendment is considered as an effective way to increase soil organic carbon （SOC） stock in croplands. To better understand its potential for SOC sequestration, whether SOC saturation could be observed in an intensive agricultural ecosystem receiving long-term composted manure were examined. Different SOC pools were isolated by physical fractionation techniques ofa Cambisol soil under a long-term manure experiment with wheat-maize cropping in North China Plain. A field experiment was initiated in 1993, with 6 treatments including control （i.e., without fertilization）, chemical fertilizer only, low rate of traditional composted manure （7.5 t ha-h）, high rate of traditional composted manure （15 t ha-~）, low rate ofbio-composted manure （7.5 t ha-h） and high rate of bio-composted manure （15 t ha-h）. The results showed that consecutive （for up to 20 years） composted manure amendments significantly improved soil macro-aggregation, aggregate associated SOC concentration, and soil structure stability. In detail, SOC concentration in the sand-sized fraction （〉53 ~tm） continued to increase with manure application rate, while the silt （2-53 I.tm） and clay （〈2 ~tm） particles showed no further increase with greater C inputs, exhibiting the C saturation. Further physical separation of small macro-aggregates （250-2 000 tam） into subpools showed that the non-protected coarse particulate organic matter （cPOM, 〉250 pro） was the fraction in which SOC continued to increase with increasing manure application rate. In contrast, the chemical and physical protected C pools （i.e., micro-aggregates and silt-clay occluded in the small macro- aggregates） exhibited no additional C sequestration when the manure application rate was increased. It can be concluded that repeated manure amendments can increase soil macro-aggregation and lead to the increase in relatively stable C pools, showing hierarchical saturation behavior in the intensive cropping system of North China Plain.     

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

The sustainability of the wheat-maize rotation is important to China＇s 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 retuming 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.     

减氮覆膜下土壤有机碳组分含量的变化特征

【目的】明确长期优化施肥（减施氮肥）和减氮覆膜下土壤有机碳（SOC）与各组分有机碳含量特征及其对冬小麦籽粒产量的贡献,以期为黄土高原旱地土壤培肥和作物增产提供科学依据。【方法】依托山西省洪洞县7年定位试验,采集0—20 cm土层原状土样,利用连续物理分组方法进行分组,结合冗余分析,研究不同农田管理措施下冬小麦籽粒产量、SOC以及颗粒有机碳（POC）、矿质结合态有机碳（MOC）、轻组颗粒有机碳（Light-POC）和重组颗粒有机碳（Heavy-POC）含量特征,明确SOC含量与各组分有机碳含量的关系,量化其对冬小麦籽粒产量的贡献。试验共设农户施肥（FP）、测控施肥（MF）、垄膜沟播（RF）和平膜穴播（FH）4个处理。【结果】分析不同管理措施下冬小麦籽粒产量和SOC含量发现,FP处理的冬小麦平均产量最低,为3 070 kg·hm^-2,与FP相比,MF在减少氮肥用量的情况下并未造成小麦减产,而RF和FH可进一步显著提高小麦籽粒产量,增幅分别达到27.0%和46.4%;与试验初始（2012年）土壤相比,经连续7年采用不同管理措施后SOC含量均显著提高,提高幅度从小到大依次为11.8%（MF）、22.4%（RF）、25.5%（FP）和36.1%（FH）,即MF对试验地石灰性褐土SOC提升作用最小,但结合地膜覆盖会显著提升其培肥土壤的效果,FH对SOC含量提升的效果最佳。进一步分析不同处理下SOC组分的差异发现,与FP和MF相比,两种减氮覆膜措施不同程度提高了POC和Light-POC含量及Light-POC在SOC中的分配比例。结合SOC及其各组分有机碳含量与冬小麦籽粒产量的冗余分析、敏感性指数分析和SOC与各组分有机碳含量的相关性分析发现,各有机碳组分均以POC对小麦产量的贡献最大（达71.0%）并对SOC含量的变化和农田管理措施的响应最为敏感。因此,平膜穴播对作物产量和土壤肥力的提高主要是通过提高土壤有机碳中POC含量得以实现的。【结论】在减氮优化施肥的基础上进行平膜穴播,有利于提高黄土高原南部旱地褐土区土壤有机碳和活性有机碳含量,实现冬小麦可持续增产。     

Abundance and Community Composition of Ammonia-Oxidizers in Paddy Soil at Different Nitrogen Fertilizer Rates

Ammonia oxidation, the first and rate-limiting step of nitrification, is carried out by both ammonia-oxidizing bacteria （AOB） and ammonia-oxidizing archaea （AOA）. However, the relative importance of AOB and AOA to nitrification in terrestrial ecosystems is not well understood. The aim of this study was to investigate the effect of the nitrogen input amount on abundance and community composition of AOB and AOA in red paddy soil. Soil samples of 10-20 cm （root layer soil） and 0-5 cm （surface soil） depths were taken from a red paddy. Rice in the paddy was fertilized with different rates of N as urea of N1 （75 kg N ha＂ yr-1）, N2 （150 kg N ha~ yrl）, N3 （225 kg N ha1 yrl） and CK （without fertilizers） in 2009, 2010 and 2011. Abundance and community composition of ammonia oxidizers was analyzed by real-time PCR and denaturing gradient gel electrophoresis （DGGE） based on amoA （the unit A of ammonia monooxygenase） gene. Archaeal amoA copies in N3 and N2 were significantly （P〈0.05） higher than those in CK and N1 in root layer soil or in surface soil under tillering and heading stages of rice, while the enhancement in bacterial amoA gene copies with increasing of N fertilizer rates only took on in root layer soil. N availability and soil NO3--N content increased but soil NH4＋-N content didn＇t change with increasing of N fertilizer rates. Otherwise, the copy numbers of archaeal amoA gene were higher （P〈0.05） than those of bacterial amoA gene in root lary soil or in surface soil. Redundancy discriminate analysis based on DGGE bands showed that there were no obvious differs in composition of AOA or AOB communities in the field among different N fertilizer rates. Results of this study suggested that the abundance of ammonia-oxidizers had active response to N fertilizer rates and the response of AOA was more obvious than that of AOB. Similarity in the community composition of AOA or AOB among different N fertilizer rates indicate that the community composition of ammonia-oxidizers was relatively stable in the paddy soil at least in short term for three years.     

长期施肥下黑垆土有机碳变化特征及碳库组分差异

【目的】阐明长期施肥下土壤有机碳演变规律及碳库组分变化,揭示黄土旱塬土壤固碳效应及培肥模式。【方法】利用32年作物产量和土壤有机碳（SOC）数据分析土壤碳投入、固定及演变特征,采集2010年土样样品,通过物理分组方法得到砂粒、粗粉粒、细粉粒、粗黏粒、细黏粒及大团聚体和微团聚体,分析施肥对碳库组分的影响。【结果】试验中总碳投入从不施肥（CK）的8.10 t C?hm-2增加到秸秆还田（SNP）的69.40 t C?hm-2,耕层土壤SOC贮量施肥之间相差1.82倍,增施有机肥（M、MNP）SOC为21.76—24.04 t C?hm-2,SNP为16.01 t C?hm-2;土壤SOC贮量随碳输入量的增加而提高,有机碳固定率25.80%—36.05%,而秸秆还田只有8.20%;除长期不施肥处理仅靠根茬投入维持稳定的SOC水平外,其余所有肥料处理SOC均随试验年限延长而增加,SNP、M、MNP处理固碳速率依次为0.246、0.326、0.361 t C?hm-2?a-1。MNP和SNP处理砂粒SOC是CK的3.85和2.94倍、N处理的2.41和1.84倍,MNP处理较CK、NP处理SOC总量只增加了32.50%、18.10%,而砂粒中SOC却提高了285.12%、105.74%,砂粒级有机碳对施肥最敏感。施肥提高了活性有机碳（POC）与矿物结合态有机碳（MOC）的比率（W）,MNP、M、SNP处理的W值达18.62%、16.24%、14.41%,单施氮肥（N）和氮磷配施（NP）仅9.11%、9.99%,施肥提高了有机碳活性,改善了土壤有机碳质量。不施肥大团聚体（＞250 µm）SOC是微团聚体（＜53 µm)的9.14倍,施肥提高了15.83—23.84倍,并提高了大团聚体中土壤C/N比,而对微团聚体C/N影响不大。尽管团聚体含碳量随团聚体粒径增加而增加,但微团聚体有机碳含量增加对土壤固碳速率的作用显著高于大团聚体,对土壤碳的固定与物理保护起着重要作用。【结论】长期增施有机肥、秸秆还田提高了黄土旱塬黑垆土的碳固定与积累,且固碳增量主要分布在砂粒和大团聚体中。因此增施有机肥、秸秆还田是环境友好型土壤培肥措施。     

Growth of Kentucky Bluegrass as Influenced by Nitrogen and Trinexapacethyl

The experiment aimed to evaluate the effects of N and trinexapac-ethyl （TE） to the growth of Kentucky bluegrass. By using the method of randomized blocks design, 4 N levels, 0 （N1）, 20 （N2）, 25 （N3）, and 30 （N4） kg N ha t mon% with TE at 0 （T1）, 312.5 （T2） and 625 （T3） mL ha-1 every 10 d effect on the total height, clippings and chlorophyll concentration of Kentucky bluegrass were evaluated. Results showed that total height and total clippings of Kentucky bluegrass were reduced by treating with TE and increased by treating with N. Kentucky bluegrass treated with 312.5 and 625 mL ha ＇ per 10 d had total clippings and total height reduced 30 and 45% under different N application level. The N × TE interaction was significant for the chlorophyll concentration of Kentucky bluegrass. The chlorophyll concentration of Kentucky bluegrass treated with TE at 625 mL ha-1 every 10 d was significantly higher than that of Kentucky bluegrass treated with 312.5 mL ha-1 every 10 d at the same N level. The chlorophyll concentration of turfgrass treated with TE at 625 mL ha-1 every 10 d receiving 30 kg N ha -1 month-1 was the highest. Based on the index of turf growth and the chlorophyll concentration, turfgrass receiving 20 or 30 kg N ha-1 month-1 with 625 mL TE ha i every 10 d could balance the problem of mowing frequency and growth quickly while keeping a good quality.     

不同利用方式下土壤矿物结合态有机碳特征与容量分析

【目的】土壤矿物结合态有机碳是土壤有机碳固持的重要机制之一。探讨不同利用方式下土壤有机碳及矿物结合态有机碳（＜53 µm）的含量、分配比例及其差异性特征,对于深刻认识土壤碳的固持状态、固碳潜力及其可持续管理均具有重要意义。【方法】通过从中国知网、万方、Science Direct和Springer link等4个文献数据库,设定检索条件“2000-2014年”、“中国土壤有机碳”和“＜53 µm团聚体分组”3个关键词,筛选出已发表的111篇目标文献,收集901组土壤有机碳和矿物结合态有机碳含量与比例的相关数据集。其中,土地利用方式分为4类：农田（n=580）、草地（n=98）、林地（n=193）和其他（果园、茶园等,n=31）。农田包括黑土、水稻土、棕壤、潮土、红壤和灰漠土等六大土壤类型。不同利用方式及土壤类型中有机碳含量与分配比例的差异性均采用Kruskal-Wallis H单向显著性检验。【结果】不同利用方式下土壤总有机碳和矿物结合态有机碳含量的中值均存在显著差异（P＜0.05）。其中,林地土壤总有机碳含量的中值为18.2 g·kg^-1,显著高于草地（12.0 g·kg^-1）和农田（10.3 g·kg^-1）;且林地矿物结合态有机碳含量（12.0 g·kg^-1 soil）也显著高于农田和草地（8.0-7.6 g·kg^-1 soil）。3种利用方式下土壤矿物结合态有机碳与总有机碳之间均呈现极显著的正相关关系（P＜0.001）,农田土壤矿物结合态有机碳所占比例的中值为74.8%,显著高于林地（70.3%）和草地（67.8%）。农田中不同土壤类型的矿物结合态有机碳占总有机碳的比例也存在显著差异。其中,黑土中矿物结合态有机碳的比例最高,中值为87.4%,其次是水稻土（76.7%）和红壤（74.0%）,而灰漠土最低（62.5%）。相关分析表明,土壤有机碳水平相对较高的黑土、水稻土和棕壤,矿物结合态有机碳分配比例随着土壤有机碳含量的增加而显著降低（P＜0.05）。农田、草地和林地中土壤矿物结合态有机碳含量与土壤细颗粒（＜53 µm）含量均呈极显著的正相关关系,与Six等（2002）的估算结果相比,其饱和程度分别为68.4%、58.7%和91.5%。【结论】农田和草地中,土壤矿物结合态有机碳还未达到饱和,仍有一定的提升空间,土壤细颗粒（＜53 µm）仍具有一定的固碳潜力。     

The potential of green manure to increase soil carbon sequestration and reduce the yield-scaled carbon footprint of rice production in southern China

Green manure (GM) has been used to support rice production in southern China for thousands of years. However, the effects of GM on soil carbon sequestration (CS) and the carbon footprint (CF) at a regional scale remain unclear. Therefore, we combined the datasets from long-term multisite experiments with a meta-analysis approach to quantify the potential of GM to increase the CS and reduce the CF of paddy soils in southern China. Compared with the fallow–rice practice, the GM–rice practice increased the soil C stock at a rate of 1.62 Mg CO₂-eq ha^–1 yr^–1 and reduced chemical N application by 40% with no loss in the rice yield. The total CF varied from 7.51 to 13.66 Mg CO₂-eq ha^–1 yr^–1 and was dominated by CH₄ emissions (60.7–81.3%). GM decreased the indirect CF by 31.4% but increased the direct CH₄ emissions by 19.6%. In the low and high CH₄ emission scenarios, the CH₄ emission factors of GM (EF_gc) were 5.58 and 21.31%, respectively. The greater soil CS offset the increase in GM-derived CF in the low CH₄ scenario, but it could not offset the CF increase in the high CH₄ scenario. A trade-off analysis also showed that GM can simultaneously increase the CS and reduce the total CF of the rice production system when the EF_gc was less than 9.20%. The variation in EF_gc was mainly regulated by the GM application rates and water management patterns. Determining the appropriate GM application rate and drainage pattern warrant further investigation to optimize the potential of the GM–rice system to increase the CS and reduce the total CF in China.     

Significant reduction of ammonia emissions while increasing crop yields using the 4R nutrient stewardship in an intensive cropping system

Ammonia (NH₃) emissions should be mitigated to improve environmental quality. Croplands are one of the largest NH₃ sources, they must be managed properly to reduce their emissions while achieving the target yields. Herein, we report the NH₃ emissions, crop yield and changes in soil fertility in a long-term trial with various fertilization regimes, to explore whether NH₃ emissions can be significantly reduced using the 4R nutrient stewardship (4Rs), and its interaction with the organic amendments (i.e., manure and straw) in a wheat–maize rotation. Implementing the 4Rs significantly reduced NH₃ emissions to 6 kg N ha^–1 yr^–1 and the emission factor to 1.72%, without compromising grain yield (12.37 Mg ha^–1 yr^–1) and soil fertility (soil organic carbon of 7.58 g kg^–1) compared to the conventional chemical N management. When using the 4R plus manure, NH₃ emissions (7 kg N ha^–1 yr^–1) and the emission factor (1.74%) were as low as 4Rs, and grain yield and soil organic carbon increased to 14.79 Mg ha^–1 yr^–1 and 10.09 g kg^–1, respectively. Partial manure substitution not only significantly reduced NH₃ emissions but also increased crop yields and improved soil fertility, compared to conventional chemical N management. Straw return exerted a minor effect on NH₃ emissions. These results highlight that 4R plus manure, which couples nitrogen and carbon management can help achieve both high yields and low environmental costs.     

长期施肥对植烟土壤与烤烟产质量的影响

为建立科学施肥制度,实现植烟土壤的可持续利用,采用长期定位试验研究不同施肥模式对植烟土壤和烤烟产量及品质的影响。结果表明:施肥尤其是(MCF)有机肥与化肥配施可显著提高烟叶产量、中上等烟叶比例和烟叶中氮、钾养分含量,并显著降低施木克值和氮碱比。与原始土壤和CK(不施肥)相比,长期施肥显著降低土壤pH值,其中MCF的pH值略高于CF(纯施化肥);另外,CF和MCF的土壤有效磷含量也显著提高。与原始土壤相比,CF的有机质含量显著降低,MCF则有一定程度提高,且MCF较CF显著升高;MCF对土壤全氮含量有一定提高,碱解氮含量较CK和CF均有显著提高;与CK相比,CF的微生物量碳含量有一定提高,但微生物量氮含量则有小幅降低,MCF可大幅提高土壤的微生物量碳、氮含量,其中微生物量碳含量的提升效果达显著水平。可见,有机肥与化肥长期持续配施不仅可以实现烤烟持续增产提质,而且可以减缓土壤酸化、提高土壤有机质含量和优化土壤微生物群落结构、改善土壤养分供应状况。     

Does heat accumulation alter crop phenology,fibre yield and fibre properties of sunnhemp (Crotalaria juncea L.) genotypes with changing seasons?

Field experiments were carried out in split plot design during the dry and wet seasons for two years(two seasons each in 2016–2017 and 2017–2018) with two genotypes(SH4 and SUIN053), two plant geometry(30×15 cm and 45×15 cm main plots) and three levels of NPK(20 kg N ha~(–1), 40 kg P ha~(–1) and 40 kg K ha~(–1); 20 kg N ha~(–1), 60 kg P ha~(–1) and 60 kg K ha~(–1); 20 kg N ha~(–1), 80 kg P ha~(–1) and 80 kg K ha~(–1)) with an objective to study the relationship between fibre yield of sunhmep and thermal indices. The results indicated that the thermal units such as cumulative heat unit(CHU), photo thermal unit(PTU) and helio thermal unit(HTU) were the highest during dry seasons, while relative temperature disparity(RTD) was the highest during wet seasons irrespective of the genotypes, plant geometry and fertilizer levels. The combined analysis of variance showed that the suitability of sunnhemp genotypes for obtaining fibre and seed yields varied with season. The results further indicated that sunnhemp grew during dry seasons with longer photoperiod and higher values of growing degree days(GDD), HTU and PTU resulted in a higher fibre yield, while a higher seed yield and relatively longer, finer and stronger fibres were obtained during wet seasons with higher RTD values. Regression analysis indicated that CHU was positively related to fibre yield, while RTD was positively related to seed yield. CHU beyond 2 000 °C d reduced seed yield and favoured fibre production. In contrary to CHU, RTD values were positively related to seed yield and negatively related to fibre yield. Similarly, HTU had an inverse relationship with fibre yield while PTU had a positive relationship with fibre yield. The genotype SH4 produced a seed yield of 1 361 kg ha~(–1) during wet seasons, which was significantly higher than SUIN053, while a fibre yield of 990 kg ha~(–1)(significantly higher than that of SH4) was obtained for SUIN053 that required less CHU to attain the phenological events during dry seasons. The per unit area yields of seed and fibre with the closer spacing(30 cm×15 cm) by virtue of higher plant density were 17.0 and 14.9% higher than those with the spacing of 45 cm×15 cm, respectively. Higher doses of P and K resulted in higher seed and fibre yields.     

Residue management induced changes in soil organic carbon and total nitrogen under different tillage practices in the North China Plain

Crop residue retention has been considered a practicable strategy to improve soil organic carbon(SOC) and total nitrogen(TN), but the effectiveness of residue retention might be different under varied tillage practices. To evaluate the effects of residue management on the distribution and stocks of SOC and TN under different tillage practices, a bifactorial experiment with three levels for tillage practices(no-tillage, rotary tillage, and conventional tillage) and two levels for residue managements(residue retention and residue removal) was conducted in the North China Plain(NCP). Results showed that after a short experimental duration(3–4 years), concentrations of SOC and TN in the 0–10 cm layer were higher under no-tillage than under conventional tillage, no matter whether crop residues were retained or not. Residue retention increased SOC and TN concentrations in the upper layers of soil to some degree for all tillage practices, as compared with residue removal, with the greatest increment of SOC concentration occurred in the 0–10 cm layer under rotary tillage, but in the 10–30 cm layer under conventional tillage. The stocks of SOC in the 0–50 cm depth increased from 49.89 Mg ha–1 with residue removal to 53.03 Mg ha–1 with residue retention. However, no-tillage did not increase SOC stock to a depth of 50 cm relative to conventional tillage, and increased only by 5.35% as compared with rotary tillage. Thus, residue retention may contribute more towards SOC sequestration than no-tillage. Furthermore, the combination between residue retention and no-tillage has the greatest advantage in enhancing SOC and TN in the NCP region.     

Impacts of Fertilization Alternatives and Crop Straw Incorporation on N2O Emissions from a Spring Maize Field in Northeastern China

Spring maize is one of the most popular crops planted in northeastem China. The cropping systems involving spring maize have been maintaining high production through intensive management practices. However, the high rates of nitrogen （N） fertilizers application could have introduced a great amount of nitrous oxide （N2O） into the atmosphere. It is crucial for sustaining the maize production systems to reduce N2O emissions meanwhile maintaining the optimum yields by adopting alternative farming management practices. The goal of this study was to evaluate effects of alternative fertilization and crop residue management practices on N2O emission as well as crop yield for a typical maize field in northeastern China. Field experiments were conducted during the 2010-2011 maize growing seasons （from early May to late September） in Liaoning Province, northeastern China. N2O fluxes were measured at the field plots with six different treatments including no N fertilizer use （CK）, farmers＇ conventional N fertilizer application rate （FP）, reduced N fertilizer rate （OPT）, reduced N fertilizer rate combined with crop straw amendment （OPTS）, slow-release N fertilizer （CRF）, and reduced N fertilizer rate combined with nitrification inhibitor （OPT＋DCD）. The static chamber method combined with gas chromatography technique was employed to conduct the measurements of N2O fluxes. The field data showed that N2O emissions varied across the treatments. During the maize growing season in 2010, the total N2O emissions under the treatments of CK, FP, OPT, OPTS, and CRF were 0.63, 1.11, 1.03, 1.26, and 0.98 kg N ha-1, respectively. The seasonal cumulative N2O emissions were 0.54, 1.07, 0.96, 1.12, and 0.84 kg N ha1, respectively, under CK, FP, OPT, OPTS, and OPT＋DCD in 2011. In comparison with FP, CRF or OPT＋DCD reduced the N2O emissions by 12 or 21%, respectively, while the crop yields remained unchanged. The results indicate that the reduction of N-fertilizer application rate in combination with the slow-release fertilizer type or nitrification inhibitor could effectively mitigate N2O emissions from the tested field. The incorporation of crop residue didn＇t show positive effect on mitigating N2O emissions from the tested cropping system. The field study can provide useful information for the on-going debate on alternative N fertilization strategies and crop straw management in China. However, further studies would be needed to explore the long-term impacts of the alternative management practices on a wide range of environmental services.     

无害化污泥堆肥施用量对沙质潮土土壤活性有机碳组分的影响

无害化污泥堆肥是指城市生活污水处理过程中产生并经无害化处理最终符合《城镇污水处理厂污泥处理土地改良用泥质》(GB/T 24600—2009)土地利用标准的堆肥产品(以下简称为污泥堆肥)。以河南省小麦-玉米轮作区沙质潮土为研究对象,通过2013—2016年田间连续定位试验,研究了污泥堆肥不同施用梯度对土壤活性有机碳组分含量和活性有机碳组分在土壤有机碳(SOC)中分配比例的影响,试验处理设置为不施污泥堆肥(CK)、15 t·hm~(-2)污泥堆肥(SW1)、30 t·hm~(-2)污泥堆肥(SW2)和45 t·hm~(-2)污泥堆肥(SW3)。结果表明,较CK处理,施用污泥堆肥处理土壤SOC、全氮(TN)含量和土壤综合肥力指数(IFI)均显著升高,尤其是施用量为45 t·hm~(-2)时效果最显著(P0.05),分别增加了265.83%、284.31%和55.51%。施用污泥堆肥处理各活性碳组分含量均显著提高,且与其施用量呈正比,施用污泥堆肥处理中活性碳库各组分含量呈现:颗粒态有机碳(POC)轻组有机碳(LFOC)溶解性有机碳(DOC)微生物量碳(SMBC)。施用污泥堆肥处理促进微生物量碳分配比例(SMBC/SOC),其中SW3处理促进效果最为显著,较CK增加了256.84%(P0.05)。主成分分析结果与以上结果基本一致,表明污泥堆肥主要是通过施入量的不同影响土壤中活性碳组分及其分配比例。冗余分析结果进一步发现,土壤肥力水平、速效养分、pH和土壤水分对土壤活性碳组分含量及其分配产生影响,其中土壤综合肥力IFI指数显著影响土壤活性有机碳组分含量及其分配率(P0.05),解释率达64.3%。综上可知,连续施用4年污泥堆肥能提高沙质潮土土壤肥力,改善土壤质量,施入量为45 t·hm~(-2)时效果最为显著。     

Combining rhizosphere and soil-based P management decreases the P fertilizer demand of China by more than half based on LePA model simulations

Phosphorus (P) is a finite natural resource and is increasingly considered to be a challenge for global sustainability. Agriculture in China plays a key role in global sustainable P management. Rhizosphere and soil-based P management are necessary for improving P-use efficiency and crop productivity in intensive agriculture in China. A previous study has shown that the future demand for phosphate fertilizer by China estimated by the LePA model (legacy phosphorus assessment model) can be greatly reduced by soil-based P management (the building-up and maintenance approach). The present study used the LePA model to predict the phosphate demand by China through combined rhizosphere and soil-based P management at county scale under four P fertilizer scenarios: (1) same P application rate as in 2012; (2) rate maintained same as 2012 in low-P counties or no P fertilizer applied in high-P counties until targeted soil Olsen-P (TP_Olsen) level is reached, and then rate was the same as P-removed at harvest; (3) rate in each county decreased to 1–7 kg ha^–1 yr^–1 after TP_Olsen is reached in low-P counties, then increased by 0.1–9 kg ha^–1 yr^–1 until equal to P-removal; (4) rate maintained same as 2012 in low-P counties until TP_Olsen is reached and then equaled to P-removal, while the rate in high-P counties is decreased to 1–7 kg ha^–1 yr^–1 until TP_Olsen is reached and then increased by 0.1–9 kg ha^–1 yr^–1 until equal to P-removal. Our predictions showed that the total demand for P fertilizer by whole China was 693 Mt P₂O₅ and according to scenario 4, P fertilizer could be reduced by 57.5% compared with farmer current practice, during the period 2013–2080. The model showed that rhizosphere P management led to a further 8.0% decrease in P fertilizer use compared with soil-based P management. The average soil Olsen-P level in China only needs to be maintained at 17 mg kg^–1 to achieve high crop yields. Our results provide a firm basis for government to issue-relevant policies for sustainable P management in China.     

Emission and Fixation of CO2 from Soil System as Influenced by Long-Term Application of Organic Manure in Paddy Soils

The observations of 25-yr long-term experiment in Zhejiang paddy soils showed that the soil organic matter could increase continuously with applying organic manure, and the increase in rate enhanced along with the application rates of organic manure. By mathematical modeling, the soil organic matter increased by 22 kg when 1 t of fresh FYM was applied. The CO2 emission resulting from the mineralization of soil organic matter increased with the increase in the application rate of the organic manure as well as the increase in the root residues. It is expected that the CO2 emission will be at 10.04-21.61 t ha^-1 yr^-1 when 16.5-49.5 t ha ^-1 yr^-1 of fresh FYM is applied. The soil organic carbon from mineralization and release of applied organic carbon （fresh FYM and root residues） will affect the CO2 concentration in the atmosphere. So, the higher the application rate of organic manure, the more is the fixed organic carbon. The CO2 fixation will be at 1.885-3.463 t ha^-1 yr^-1 when 16.5-49.5 t ha^-1 yr^-1 of fresh FYM is applied. Thus, the CO2 fixation will increase by 46.7 kg by applying 1 t fresh FYM. To apply organic manure continuously in rice fields may reduce the contribution to the increase of CO2 concentration in the atmosphere.     

Yield gap and production constraints of mango (Mangifera indica) cropping systems in Tianyang County,China

Mango is an important cash crop in the tropics and subtropics. Determining the yield gap of mango and production constraints can potentially promote the sustainable development of the mango industry. In this study, boundary line analysis based on survey data from 103 smallholder farmers and a yield gap model were used to determine the yield gap and production constraints in mango plantations in the northern mountain, central valley and southern mountains regions of Tianyang County, Guangxi, China. The results indicated that the yield of mango in three representing regions of Tianyang County,Northern Mountains, Central Valley and Southern Mountains, was 18.3, 17.0 and 15.4 t ha~(–1) yr~(–1), with an explainable yield gap of 10.9, 6.1 and 14.8 t ha~(–1) yr~(–1), respectively. Fertilization management, including fertilizer N, P_2O_5 and K_2O application rates, and planting density were the main limiting factors of mango yield in all three regions. In addition, tree age influenced mango yield in the Northern Mountains(11.1%) and Central Valley(11.7%) regions. Irrigation time influenced mango yield in the Northern Mountains(9.9%) and Southern Mountains(12.2%). Based on a scenario analysis, the predicted yield would increase by up to 50%, and fertilizer N use would be reduced by as much as approximately 20%. An improved understanding of production constraints will aid in the development of management strategy measures to increase mango yield.     

Effect of grazing time and intensity on growth and yield of spring wheat(Triticum aestivum L.)

A simulated grazing field experiment was conducted to determine the effect of timing and intensity of grazing on the growth and yield of a mid-late maturing spring wheat(cv. Flanker) under different watering regimes, at Wagga Wagga in southeastern Australia. The experiment was a factorial design of watering regime and pasture "grazing" as factors, with three replications. The two watering regimes were rainfed(R) and supplemental irrigation(I). There were four simulated grazing treatments: no grazing, "crash" grazing by mowing to 5 cm height on 13 June(Cut1-5), "crash" grazing by mowing to 5 cm on 15 July(Cut2-5) and "clip" grazing by mowing to 15 cm height on 15 July(Cut2-15). The lowest dry matter(simulated grazing) was obtained from RCut1-5(0.13 t ha~(–1)) and the highest(0.86 t ha~(–1)) was from ICut2-5. There was no significant difference(P0.05) among the grain yields of the grazing treatments in the respective watering regimes. However, there was significant difference(P0.05) between the grain yields of the rainfed(3.60 t ha~(–1)) and irrigated(6.0 t ha~(–1)) treatments. Under both watering regimes, the highest grain yield was obtained from the late "clip" grazings: 3.79 t ha~(–1)(RCut2-15) for rainfed and 6.47 t ha~(–1)(ICut2-15) for irrigated treatments. The lowest grain yield for the rainfed treatment was 3.26 t ha~(–1)(RCut1-5) and for the irrigated treatments, the lowest grain yield was 5.50 t ha~(–1)(ICut2-5). Harvest index(HI) was not significantly affected(P0.05) by either the watering regime or grazing. Seed weight was significantly(P0.05) affected both by the watering regime and grazing with the lowest value for 1 000-seed weight of 30.05 g(RCut2-5) and the highest value of 38.00 g(ICut2-15). Water use efficiency was significantly(P0.05) affected both by the watering regime and grazing with the lowest value of 9.94 kg ha~(–1) mm~(–1)(ICut2-5) and the highest value 13.43 kg ha~(–1) mm~(–1)(RCut2-5). By "crash" grazing late(just before stem elongation stage) to a height of 5 cm, a significantly higher(P0.05) above ground dry matter can be grazed without significantly affecting the yield both in seasons with low amount of rainfall and high amount of rainfall(irrigated in this study) although in a wet season a slightly lower(15% lower) grain yield is obtained relative to "clip grazing" to 15 cm height. Grazing of mid-late maturing wheat cultivars has the potential to fill the feed gap without significantly affecting grain yield.