Quantification of airborne N‐input in long‐term field experiments and its validation through measurements using 15N isotope dilution

The N‐deposition in Germany is commonly calculated as values of about 20—30 kg/ha·yr. This range is based on the measurements of the nitrate and ammonium nitrogen bulk deposition, which does not include the gaseous N‐deposition and the direct N‐uptake by plants. The calculation of airbone N‐deposition from N‐balances of the Static Fertilization Experiment Bad Lauchstädt came to 50—58 kg/ha·yr. This is consistent with results from other European long‐term experiments. Using the newly developed ¹⁵N‐based ITNI‐system, the total airborne N‐deposition can be determined. For Bad Lauchstädt analogous to results of former measuring periods an annual N‐deposition of 65 kg/ha·yr was measured in 1998, a figure greater than the balanced values. The balanced and measured values show, that airborne N‐deposition is often underestimated and amounts to at least 50 kg/ha·yr, which is a significant burden on natural ecosystems. By taking this extra N‐input into account in calculations for fertilizer recommendations in agriculture a decrease of N‐losses can be achieved which, in turn can also induce a decrease in airborne N‐deposition.     

小麦蚕豆间作对根际土壤氮转化微生物的影响

通过田间小区试验,采用磷脂脂肪酸(PLFA)、实时荧光定量PCR研究了小麦蚕豆间作不同生育期对根际土壤微生物群落的变化、氨氧化细菌(AOB)、氨氧化古菌(AOA)以及反硝化细菌中亚硝酸还原酶(nirK)、一氧化氮还原酶(norB)和氧化亚氮还原酶(nosZ)基因拷贝数以及土壤酶活性和土壤硝态氮、铵态氮含量的影响。结果表明:与单作相比,小麦蚕豆间作显著提高了根际土壤中总的PLFAs生物量、细菌、真菌、放线菌和好氧菌的生物量。土壤样品中的amoA基因拷贝数在10~5~10~6范围内AOB的amoA基因数量高于AOA。在不同的生育期,根际土壤中nirK的基因拷贝数都是间作高于单作;在拔节期,间作蚕豆的norB基因显著高于其他种植模式(P0.05);在拔节期、抽穗期,nosZ基因均是间作显著高于单作(P0.05),并随着生育期呈现降低的趋势。间作降低了根际土壤NO_3~--N的含量,提高了NH_4~+-N的含量(P0.05)。说明小麦蚕豆间作后改变了根际土壤的微环境,使得土壤微生物群落结构发生改变,这种改变在一定程度上能够对土壤氮素的有效保蓄和供应、同时防止氮素损失和污染起到积极作用,为间作增产提供了氮素营养保障。     

Long‐term effects of fertilization on some soil properties under rainfed soybean‐wheat cropping in the Indian Himalayas

This study aims to examine the effects of long‐term fertilization and cropping on some chemical and microbiological properties of the soil in a 32 y old long‐term fertility experiment at Almora (Himalayan region, India) under rainfed soybean‐wheat rotation. Continuous annual application of recommended doses of chemical fertilizer and 10 Mg ha^–1 FYM on fresh‐weight basis (NPK + FYM) to soybean (Glycine max L.) sustained not only higher productivity of soybean and residual wheat (Triticum aestivum L.) crop, but also resulted in build‐up of total soil organic C (SOC), total soil N, P, and K. Concentration of SOC increased by 40% and 70% in the NPK + FYM–treated plots as compared to NPK (43.1 Mg C ha^–1) and unfertilized control plots (35.5 Mg C ha^–1), respectively. Average annual contribution of C input from soybean was 29% and that from wheat was 24% of the harvestable aboveground biomass yield. Annual gross C input and annual rate of total SOC enrichment from initial soil in the 0–15 cm layer were 4362 and 333 kg C ha^–1, respectively, for the plots under NPK + FYM. It was observed that the soils under the unfertilized control, NK and N + FYM treatments, suffered a net annual loss of 5.1, 5.2, and 15.8 kg P ha^–1, respectively, whereas the soils under NP, NPK, and NPK + FYM had net annual gains of 25.3, 18.8, and 16.4 kg P ha^–1, respectively. There was net negative K balance in all the treatments ranging from 6.9 kg ha^–1 y^–1 in NK to 82.4 kg ha^–1 y^–1 in N + FYM–treated plots. The application of NPK + FYM also recorded the highest levels of soil microbial‐biomass C, soil microbial‐biomass N, populations of viable and culturable soil microbes.     

硝化抑制剂和秸秆对潮棕壤碳氮转化和微生物群落特征的短期影响

氮是植物和微生物生长繁殖的必需营养元素,而氮矿化表征了土壤供氮能力。通过盆栽实验,采用同位素稀释法和磷脂脂肪酸(PLFA)法,研究了添加硝化抑制剂和秸秆条件下,潮棕壤碳氮矿化和微生物群落组成变化特征。结果表明,与施氮量N 0.1 g·kg~(-1)的单施氮肥处理(NF)相比,氮肥配施1%硝化抑制剂(NFI)的土壤铵态氮提高32%,而硝态氮降低53%。氮肥与施用量为5 g·kg~(-1)的秸秆配施(NS),土壤氮素总矿化速率增加36%,微生物生物量碳提高51%,β-葡萄糖苷酶活性提高36%,同时显著增加了土壤总PLFA以及细菌、真菌、真菌/细菌和革兰式阴性菌(P0.05),土壤呼吸熵降低50%。与氮肥配施秸秆处理(NS)相比,氮肥、秸秆和硝化抑制剂配施处理(NSI),土壤铵态氮提高33%,硝态氮下降47%。综上所述,氮肥和秸秆配施可以提高土壤微生物生物量,改变土壤微生物群落组成,配施1%(N)硝化抑制剂后降低土壤硝化速率,增加土壤供氮能力。     

Carbon sequestration dynamic,trend and efficiency as affected by 22‐year fertilization under a rice–wheat cropping system

The maintenance and accumulation of soil organic carbon (SOC) in agricultural systems is critical to food security and climate change, but information about the dynamic trend and efficiency of SOC sequestration is still limited, particularly under long‐term fertilizations. In a typical Purpli‐Udic Cambosols soil under subtropical monsoon climate in southwestern China this study thus estimated the dynamic, trend and efficiency of SOC sequestration after 22‐year (1991–2013) long‐term inorganic and/or organic fertilizations. Nine fertilizations under a rice–wheat system were examined: control (no fertilization), N, NP, NK, PK, NPK, NPKM (NPK plus manure), NPKS (NPK plus straw), and 1.5NPKS (150% NPK plus straw). Averagely, after 22‐years SOC contents were significantly increased by 4.2–25.3% and 10.2–32.5% under these fertilizations than under control conditions with the greatest increase under NPKS. The simulation of SOC dynamic change with an exponential growth equation to maximum over the whole fertilization period predicted the SOC level in a steady state as 18.1 g kg^?1 for NPKS, 17.4 g kg^?1 for 1.5NPKS, and 14.5–14.9 g kg^?1 for NK, NP, NPK, and NPKM, respectively. Either inorganic, organic or their combined fertilization significantly increased crop productivity and C inputs that were incorporated into soil ranging from 0.91 to 4.63 t (ha · y)^?1. The C sequestration efficiency was lower under NPKM, NPKS, and 1.5NPKS (13.2%, 9.0%, and 10.1%) than under NP and NPK (17.0% and 14.4%). The increase of SOC was asymptotical to a maximum with increasing C inputs that were variedly enhanced by different fertilizations, indicating an existence of SOC saturation and a declined marginal efficiency of SOC sequestration. Taken all these results together, the combined NPK plus straw return is a suitable fertilizer management strategy to simultaneously achieve high crop productivity and soil C sequestration potential particularly in crop rotation systems.     

Effects of humus content,farmyard manuring,and mineral‐N fertilization on yields and soil properties in a long‐term trial

Investigations carried out at Field F3 of the Halle long‐term fertilization trials using data from 1974 to 1983 showed that with adequate supply of mineral N‐fertilizer soil organic matter (SOM) had no significant effects of yield. Similarly enhanced SOM did not justify a reduction of mineral N (Stumpe et al., 2000). The studies presented here examine the effects of the SOM differences existing after the termination of those trials in 1986 up until 1997 (then mainly differences of hardly decomposable SOM) in comparison to farmyard manuring with enhanced mineral N application (3‐factor‐experiment). As with total SOM, hardly decomposable SOM did not directly affect yields. The effects of FYM treatment observed at lower mineral‐N levels were compensated for by enhanced mineral‐N supply. The direct effect of FYM (40 t ha^—1) corresponded to a mineral‐N supply of about 60 kg ha^—1 and the residual effect to about 20 kg ha^—1. The differences of the C‐content in the soil at the beginning of the present studies continued throughout the experimental period of 12 years. In addition, significant differentiation has been caused by FYM and N fertilization in comparison to unfertilized treatments. The major finding is that differences in SOM content do not lead to yield differences on physically good soils (chernozem‐like soils) if appropriate compensation by mineral‐N fertilization takes place.     

Long‐term effects of manure and fertilization on soil organic matter and quality parameters of a calcareous soil in NW China

Long‐term applications of inorganic fertilizers and farmyard manure influence organic matter as well as other soil‐quality parameters, but the magnitude of change depends on soil‐climatic conditions. Effects of 22 annual applications (1982–2003) of N, P, and K inorganic fertilizers and farmyard manure (M) on total organic carbon (TOC) and nitrogen (TON), light‐fraction organic C (LFOC) and N (LFON), microbial‐biomass C (MB‐C) and N (MB‐N), total and extractable P, total and exchangeable K, and pH in 0–20 cm soil, nitrate‐N (NO ‐N) in 0–210 cm soil, and N, P, and K balance sheets were determined using a field experiment established in 1982 on a calcareous desert soil (Orthic Anthrosol) at Zhangye, Gansu, China. A rotation of irrigated wheat (Triticum aestivum L.)‐wheat‐corn (Zea mays L.) was used to compare the control, N, NP, NPK, M, MN, MNP, and MNPK treatments. Annual additions of inorganic fertilizers for 22 y increased mass of LFON, MB‐N, total P, extractable P, and exchangeable K in topsoil. This effect was generally enhanced with manure application. Application of manure also increased mass of TOC and MB‐C in soil, and tended to increase LFOC, TON, and MB‐N. There was no noticeable effect of fertilizer and manure application on soil pH. There was a close relationship between some soil‐quality parameters and the amount of C or N in straw that was returned to the soil. The N fertilizer alone resulted in accumulation of large amounts of NO ‐N at the 0–210 cm soil depth, accounting for 6% of the total applied N, but had the lowest recovery of applied N in the crop (34%). Manure alone resulted in higher NO ‐N in the soil profile compared with the control, and the MN treatment had the highest amount of NO ‐N in the soil profile. Application of N in combination with P and/or K fertilizers in both manured and unmanured treatments usually reduced NO ‐N accumulation in the soil profile compared with N alone and increased the N recovery in the crop as much as 66%. The N that was unaccounted for, as a percentage of applied N, was highest in the N‐alone treatment (60%) and lowest in the NPK treatment (30%). In the manure + chemical fertilizer treatments, the unaccounted N ranged from 35% to 43%. Long‐term P fertilization resulted in accumulation of extractable P in the surface soil. Compared to the control, the amount of P in soil‐plant system was surplus in plots that received P as fertilizer and/or manure, and the unaccounted P as percentage of applied P ranged from 64% to 80%. In the no‐manure plots, the unaccounted P decreased from 72% in NP to 64% in NPK treatment from increased P uptake due to balanced fertilization. Compared to the control, the amount of K in soil‐plant system was deficit in NPK treatment, i.e., the recovery of K in soil + plant was more than the amount of applied K. In manure treatments, the recovery of applied K in crop increased from 26% in M to 61% in MNPK treatment, but the unaccounted K decreased from 72% in M to 37% in MNPK treatment. The findings indicated that integrated application of N, P, and K fertilizers and manure is an important strategy to maintain or increase soil organic C and N, improve soil fertility, maintain nutrients balance, and minimize damage to the environment, while also improving crop yield.     

Long‐term fertilization impacts on corn yields and soil organic matter on a clay‐loam soil in Northeast China

A long‐term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay‐loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain‐corn production on this soil type with eight different nitrogen (N)‐, phosphorus (P)‐, and potassium (K)–mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha^–1 y^–1) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha^–1) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha^–1). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain‐yield increases compared to the FYM0 control treatment (3.56 Mg ha^–1). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard‐manure additions for 25 y increased soil organic‐matter (SOM) content by 3.8 g kg^–1 (13.6%) in the FYM1 treatments and by 7.8 g kg^–1 (27.8%) in the FYM2 treatments, compared to a 3.2 g kg^–1 decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic‐matter levels in this soil type.     

Influences of past application rates of nitrogen and a catch crop on soil microbial communities between an intensive rotation

The aim of this study was to investigate influences of six-year past application rates of nitrogen and a catch crop, sweet corn (Zea mays L. ssp. Saccharata Sturt), on soil microbial community and diversity in a greenhouse-based intensive vegetable soil in eastern China. Soil electrical conductivity, pH, mineral nitrogen, phospholipid fatty acids (PLFA) profiles and carbon source utilization patterns under five annually past nitrogen rates (0, 348, 522, 696 and 870?kg?nitrogen?ha^?1) were evaluated after the establishment of sweet corn during 1–1.5-month fallow period over three-year tomato/cucumber/celery rotations. The past nitrogen application rates exerted significant effects on soil electrical conductivity, pH, nitrate-nitrogen, ammonium-nitrogen and carbon source utilization patterns, but not on PLFAs profiles. The sweet corn had a significant effect on soil chemical properties, total and actinobacterial PLFAs, but not on carbon source utilization patterns. Soil electrical conductivity, nitrate-nitrogen and the total PLFAs decreased whilst soil organic carbon, pH and the actinobacterial PLFAs increased after the establishment of sweet corn. Soil microbial functional diversity from carbon source utilization patterns and actinobacterial PLFAs were greatest after the establishment of sweet corn at a 60% of the conventional nitrogen rate (i.e. 522?kg?nitrogen?ha^?1). Soil electrical conductivity and ammonium-nitrogen were two key factors to determine carbon source utilization patterns, whilst soil pH was the key factor to determine PLFAs profiles. A combination of the catch crop sweet corn during summer fallow and a 60% of the conventional nitrogen rate is a sustainable pathway of utilizing greenhouse-based intensive vegetable soils in eastern China.     

Phosphorus dynamics in a long‐term P fertilization trial on Luvic Phaeozem at Halle

The soil of the long‐term experiment laid out 1949 in Halle has the potential to supply much P. The P taken up by plants where no P (P0) or 15 kg ha⁻¹ yr⁻¹ (P1) was applied was much greater than the P applied as fertilizer (P1). A decrease in yield was measured only after the first 25 years on P0 soils but the P1 treatment has, so far, shown no decrease. Lactate extractions of the soil did not reflect P‐uptake suitably. The release of P from insoluble into water soluble forms was at a minimum after 30 years in P0 soils. P1 soils have now also declined to this minimum value and it remains to be seen whether yields decrease in this treatment in the future. Parallel to this trend, the P sorption increased in P0 soils. The subsoil also seems to be an important source for P supply, possibly influenced by root exudates. Further work is needed to gain a better understanding of soil P dynamics in connection with root exudates and microbes and to identify parameters which will provide more reliable means of calculating fertilizer P requirements.     

Long‐term effects of cropped vs. fallow and fertilizer amendments on soil organic matter II. Nitrogen

The present study evaluated the effect of fertilizer amendments (organic manure and mineral fertilizers), management practices (fallow and untilled vs. cropped and tilled) on changes of N in bulk soil and N associated with different particle‐size fractions. The long‐term field experiment was conducted since 1962 in Gumpenstein, Austria, on a Dystric Cambisol. The N content of the topsoils changed distinctively during 28 and 38 yr of treatments under both fallow and cropped management practices. Highest increase in total N content was found in animal‐manure (liquid)‐treated plots. The remaining ranking was: animal manure (solid) > cattle slurry > half cattle slurry + straw = PK = NPK. Quite short N‐half‐life values of around 2 yr were found for the cattle‐slurry application, while animal manure exhibited longer N‐half‐lives of around 8 yr. Crop removal of N and mineralization losses in cropped plots obviously were higher than N losses from the bare soil plots lacking a plant cover to keep N in the system. This was confirmed by a consistent shift in the natural ¹⁵N abundances. Comparing the mean N contribution of particle‐size fractions to the total N amounts revealed the following ranking after 28 and 38 yr of different treatments: silt > clay > fine sand > coarse sand, with small exceptions. Particle‐size separates showed more significant responses to changes in the N dynamics of the system due to the various treatments than the bulk soil and can be regarded as the better indicators in this respect.     

Cumulative effects of a 17‐year chemical fertilization on the soil quality of cropping system in the Loess Hilly Region,China

Soil‐quality assessment provides a tool for evaluating the sustainability of alternative soil‐management practices. Understanding the effects of the long‐term use of chemical fertilizers on soil quality is essential for sustaining soil productivity. The cumulative effect of a 17‐y‐old chemical‐fertilizer application on integrated soil quality was investigated in the surface (0–15 cm) and subsurface (15–30 cm) soils of a soy–broomcorn–millet cropping system with an experiment design of two factors with three levels for each factor. The treatments were N0P0, N0P1, N0P2, N1P0, N1P1 (local farmer' fertilization strategy), N1P2, N2P0, N2P1, N2P2, and a control NF. The objectives were to describe and quantify the effect of continuous applications of chemical fertilizer through soil‐quality index (SQI) and attempt to offer an efficient and appropriate nutrient‐supply strategy for the local region. Following 17 y of chemical fertilization, the SQI increased markedly in the studied soil layers, and soil chemical indicators changed more significantly than physical properties. The soil‐quality indicators in the surface soil layer were more variable and sensitive to fertilizer application than the subsurface layer. The indicators that sensitively responded to long‐term fertilization could be classified into three types: soil‐fertility indicators (soil organic matter [SOM], total P, and available N), soil‐texture indicators (clay, silt), and soil‐structure indicators (bulk density, mean weight diameter [MWD]). The simplified indicators (SOM, sand, available N, bulk density, and total P in the surface soil and SOM, MWD, and silt content in the subsurface soil) preferably reflected the status of the integrated soil quality as influenced by continuous fertilization. Among the fertilized treatments, the combined‐fertilizer treatments maintained a higher SQI than the single‐fertilizer treatments in the surface and subsurface soils. The N1P2 treatment maintained the highest SQI in both soil layers, followed by N1P1 treatment. However, for the slope cropland, given the relative costs, soil resource, and environmental protection, the traditional treatment of N1P1 may be the optimal fertilizer treatment in the local region.     

Long‐term development of nitrogen fluxes in a coniferous ecosystem: Does soil freezing trigger nitrate leaching?

In many forest ecosystems chronically large atmospheric deposition of N has caused considerable losses of inorganic N by seepage. Freezing and thawing of soil may alter the N turnover in soils and thereby the interannual variation of N seepage fluxes, which in turn makes it difficult to evaluate the N status of forest ecosystems. Here, we analyzed long‐term monitoring data of concentrations and fluxes of dissolved inorganic N (DIN) in throughfall and seepage from a Norway spruce stand at the Fichtelgebirge (SE Germany) between 1993 and 2004. Despite constant or even slightly increasing N inputs in throughfall, N losses with seepage at 90 cm declined from 15–32 kg N ha^–1 y^–1 in the first years of the study period (1993–1999) to 3–10 kg N ha^–1 y^–1 in 2000 to 2004. The large N losses in the first years coincided with extreme soil frost in the winter of 1995/96, ranging from –3.3°C to –1.0°C at 35 cm soil depth. Over the entire observation period, maximum fluxes of nitrate and ammonium were observed in the mineral soil following thawing of the soil. The elevated ammonium and nitrate fluxes resulted apparently from increased net ammonification and nitrification rates in the mineral soil, whereas mineral‐N fluxes in the O horizon were less affected by frost. Our data suggest that (1) extreme soil frost may cause substantial annual variations of nitrate losses with seepage and that (2) the assessment of the N status of forest ecosystems requires long periods of monitoring. Time series of biogeochemical data collected over the last 20–30 y include years with extreme cold winters and warm summers as well as unusual precipitation patterns. Analysis of such long‐term monitoring data should address climate extremes as a cause of variation in N outputs via leaching. The mean loss of 14.7 kg N with seepage water during 12 y of observation suggests that the forest ecosystem was saturated with N.     

Trends in grain yields and soil organic C in a long‐term fertilization experiment in the China Loess Plateau

Changes in grain yields and soil organic carbon (SOC) from a 26 y dryland fertilization trial in Pingliang, Gansu, China, were recorded. Cumulative C inputs from straw and root and manure for fertilizer treatments were estimated. Mean wheat (Triticum aestivum L.) yields for the 18 y ranged from 1.72 t ha^–1 for the unfertilized plots (CK) to 4.65 t ha^–1 for the plots that received manure (M) annually with inorganic N and P fertilizers (MNP). Corn (Zea mays L.) yields for the 6 y averaged 2.43 and 5.35 t ha^–1 in the same treatments. Yields declined with year except in the CK for wheat. Wheat yields for N only declined with time by 117.8 kg ha^–1 y^–1 that was the highest decrease among all treatments, and that for NP declined by 84.7 kg ha^–1 y^–1, similar to the declines of 77.4 kg ha^–1 y^–1 for the treatment receiving straw and N annually and P every second year (SNP). Likewise, the corn yields declined highly for all treatments, and the declined amounts ranged from 108 to 258 kg ha^–1 y^–1 which was much higher than in wheat. These declined yields were mostly linked to both gradual dry weather and nutrients depletion of the soil. The N only resulted in both P and K deficiency in the soil, and soil N and K negative balances in the NP and MNP were obvious. Soil organic carbon (SOC) in the 0–20 cm soil layer increased with time except in the CK and N treatments, in which SOC remained almost stable. In the MNP and M treatments, 24.7% and 24.0% of the amount of cumulative C input from organic sources remained in the soil as SOC, but 13.7% of the C input from straw and root in the SNP, suggesting manure is more effective in building soil C than straw. Across the 26 y cropping and fertilization, annual soil‐C sequestration rates ranged from 0.014 t C ha^–1 y^–1 for the CK to 0.372 t C ha^–1 y^–1 for the MNP. We found a strong linear relationship (R² = 0.74, p = 0.025) between SOC sequestration and cumulative C input, with C conversion–to–SOC rate of 16.9%, suggesting these dryland soils have not reached an upper limit of C sequestration.     

The influence of fertilization and rotation on soil organic matter and plant yields in the long‐term Eternal Rye trial in Halle (Saale), Germany

Six forms of fertilizers and three rotations have been examined for 120 years in the ”︁Eternal Rye trial” in Halle (central German arid region, Haplic Phaeozem on sandy loess). Rank analysis, trend analysis and a new component model have been found to be suitable statistical methods to evaluate long‐term results without true replications. In this trial it was shown that mineral fertilization maintains like farmyard manuring the yield potential although at lower content of soil organic matter (SOM). Without fertilization, yield decline was greater with potato and silage maize than winter rye (Secale cereale L.). Deficiencies in N fertilization lead immediately, and in PK supply after more than 20 years, to a significant yield decrease which could be quickly compensated by full fertilization. Rye and maize monocultures also resulted in yield decreases. The establishing of new steady states in the turnover of SOM took about 50 years after changes in fertilization. Contrary to rye monoculture, both silage maize monoculture and potato alternating with winter rye caused considerable decomposition of SOM. According to analytical pyrolysis (Py‐FIMS and Py‐GC/MS), fertilization affects the SOM composition more than rotation. Without fertilization, a higher percentage of thermically stable SOM remained in comparison to the FYM soils. The introduction of potato into the rotation enhanced the content of easily decomposable SOM.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.     

Soil microbial biomass and community composition as affected by cover crop diversity in a short‐term field experiment on a podzolized Stagnosol‐Cambisol

Background: Cover cropping appears as a useful land management practice with numerous benefits for ecosystem functions. Aim: The objectives of this study were to determine the effects of different winter cover crops on soil microbial biomass, activity, and community composition in intensively managed agriculture systems as function of cover crop diversity. Methods: For this purpose, an on‐farm experiment was conducted at a podzolized Stagnosol‐Cambisol during seven months growing oil radish as single cover crop and five different cover crop mixtures comprising 5 to 13 plant species. A fallow treatment was used as control. Phospholipid fatty acids were used to determine the soil microbial biomass and soil microbial community composition. Basal respiration of the soil microorganisms was measured as a proxy for microbial activity. Results: The results show that none of the cover crop mixture could increase soil organic carbon or total nitrogen content. Three cover crop mixtures and oil radish as single cover crop significantly increased soil microbial biomass by about 50% and all of the investigated cover crops significantly increased microbial respiration and metabolic quotient by 50–150%. Only highly diverse cover crop mixtures significantly increased individual microbial groups such as Gram‐positive and Gram‐negative bacteria, actinobacteria, and saprotropic and mycorrhizal fungi by about 20% compared to the control. However, the ratio of fungi to bacteria was not influenced by any of the cover crop mixtures under study. Conclusion: These findings corroborate that aboveground plant diversity is linked to belowground microbial diversity.     

Application of the DNDC model to predict N2O emissions from sandy arable soils with differing fertilization in a long‐term experiment

Modeling crop growth and soil N dynamics is difficult due to the complex nature of soil–plant systems. In several studies, the DNDC model has been claimed to be well‐suited for this purpose whereas in other studies applications of the model were less successful. Objectives of this study were to test a calibration and validation scheme for DNDC‐model applications to describe a field experiment with spring wheat on a sandy soil near Darmstadt (SW Germany) using different fertilizer types (either application of mineral fertilizer and straw—MSI; or application of farmyard manure—FYM) and rates (low—MSI_L, FYM_L; and medium—MSI_M, FYM_M). The model test is based on a model parameterization to best describe the case MSI_L and applies this parameterization for a retrospective simulation of the other cases (MSI_M, FYM_L, FYM_M) including crop growth and N₂O emissions. Soil water contents were not accurately simulated using either the DNDC default values for a loamy sand or for the next finer texture class or using results from the pedotransfer function provided by ROSETTA. After successful calibration of the soil water flow model using a soil texture class that led to the best fit of the measured water content data, grain yield of spring wheat and cumulative N₂O emission were slightly underestimated by DNDC and were between 91% and 86% of the measured data. A subsequent calibration of the yields and cumulative N₂O emissions from soils of the MSI_L treatment gave a good prediction of crop growth and N₂O emissions in the MSI_M treatment, but a marked underestimation of yields of the FYM treatments. Cumulative N₂O emissions were predicted well for all MSI and FYM treatments, but seasonal dynamics were not. Overall, our results indicated that for the sandy soil in Germany, site‐specific calibration was essentially required for the soil hydrology and that a calibration was useful for a subsequent prediction where greater amounts of the same fertilizer were used, but not useful for a prediction with a different fertilizer type.