Reduced Soil NO3 Research Articles

Effects of 3-year biochar application on carbon sequestration, nitrogen retention and nitrate leaching of fluvo-aquic soil profiles in vegetable rotation fields

The impacts of biochar application on the carbon (C) and nitrogen (N) cycles in soil profiles in vegetable fields have rarely been reported. A three-year field experiment (CK, control; BC, biochar; N, nitrogen fertilizer; BCN, biochar and nitrogen fertilizer) was conducted in fluvo-aquic soil with a wild cabbage-Chinese cabbage rotation to investigate biochar effects on soil organic carbon (SOC) sequestration, N retention, and nitrate (NO3−) leaching in the soil profile (topsoil, 0–20 cm; subsoil, 20–50 cm; third-layer soil, 50–100 cm). The results showed that the biochar-induced increase in topsoil SOC under N fertilization was greater for Chinese cabbage season than for wild cabbage season. Excluding biochar-N, biochar application caused an extra increase in topsoil total nitrogen (TN) under N fertilization. Biochar decreased the NO3−-N concentration of third-layer soil solution, particularly under N fertilization, indicating that biochar reduced the potential source of NO3− leaching. Under N fertilization, biochar reduced the abundances of carbon-degrading bacteria (Streptomyces, Bacillus, Mycobacterium, and Sphingomonas) and genes (sga, xylA, lig, and pgu) in the topsoil, as well as the abundances of ammonia-oxidizing bacteria (Nitrosospira and Nitrosomonas) and gene (amoA) in the third-layer soil. However, biochar increased the abundance of ammonia-assimilating bacteria (Rhodococcus) and gene (glnA) in the topsoil. Biochar inhibited the microbial function associated with C degradation by affecting soil TN, thus enhancing topsoil SOC sequestration. Biochar promoted the soil microbial function related to ammonia assimilation by affecting dissolved organic carbon (DOC), subsequently enhancing ammonia assimilation. Moreover, biochar initially inhibited ammonia oxidation in the third-layer soil by increasing soil DOC, subsequently affecting nitrite oxidation and ultimately reducing soil NO3− leaching. Biochar significantly increased the N use efficiency of vegetables in the last two years. This study provides insights into biochar effects on the changes in soil microbial function, which promoted SOC sequestration, enhanced N retention and mitigated nitrate leaching in a vegetable rotation field.

Effects of microplastic polystyrene, simulated acid rain and arbuscular mycorrhizal fungi on Trifolium repens growth and soil microbial community composition

Microplastic pollution is a global and ubiquitous environmental problem in the oceans as well as in the terrestrial environment. We examined the fate of polystyrene (PS) beads in experimental soil in the presence and absence of symbiotic arbuscular mycorrhizal fungi (AMF) and simulated acid rain to determine whether combinations of these three factors interact to alter growth of the white clover Trifolium repens. We found that PS, simulated acid rain or AMF added singly to soil did not alter T. repens growth or yields. In contrast, PS and AMF together significantly reduced shoot biomass while simulated acid rain and PS together significantly reduced available soil phosphorus independent of AMF presence. PS, AMF and simulated acid rain together significantly reduced soil NO3–-N. AMF added singly also enriched for beneficial soil bacteria of the genus Solirubrobacter while PS combined with AMF significantly enriched the potential plant pathogenic fungus Spiromastix spp. AMF innoculated with PS increased the abundance of soil hydrocarbon degraders independent of the presence of simulated acid rain. In addition, the abundance of soil nitrate reducers was increased by the presence of PS especially in the presence of AMF and simulated acid rain. Moreover, the latter increased the abundance of soil pathogens within the fungal community including antibiotic producers. These findings indicate that the coexistence of microplastics, acid rain and AMF may exacerbate the adverse effects of microplastics on soil and plant health.

Leaching is the main pathway of nitrogen loss from a citrus orchard in Central China

Due to the high application rates and low utilization efficiency of inorganic nitrogen (N) fertilizer, conventional citrus orchards tend to cause N losses and extensive pollution. In order to address these issues, it is essential to identify the leading cause of N loss by citrus orchard N mass balance. In the present study, a two-year field experiment was performed on 4 different treatments (CK: no N fertilizer; CF: conventional N fertilizer; NR: 70% of conventional N fertilizer; OM: NR with organic manure) to quantify the pathways of N loss in citrus orchards in Hubei Province, China. Our findings revealed that leaching (17.0%) was the dominant N loss pathway in the conventional citrus orchard of central China, followed by runoff (2.9%), NH3 volatilization (2.3%), and N2O emission (0.5%). Reduced N fertilizer rates (−30.0%) led to a significant reduction in gaseous N loss (−34.9%), runoff N loss (−20.3%), and N leaching (−13.0%) via the reduced content of soil NH4+ and soil NO3-. Interestingly, the presence of organic manure reduced 15.2% of runoff N loss, 3.8% of N leaching and 6.9% of total N loss via reduced soil NO3-, but increased 39.6% of gaseous N loss via increased soil DOC. On the other hand, the low N fertilizer rates suppressed N uptake of citrus by reducing the content of soil NO3-, while organic manure promoted N uptake of citrus via the increased content of soil DOC. Overall, using organic manure as a substitute provides a better solution to fertilization for the citrus orchards in central China compared to reducing N fertilizer rates.

Soil nitrogen and carbon storages and carbon pool management index under sustainable conservation tillage strategy

Agricultural practices are significant to increase the soil nitrogen and organic carbon sequestration to adapt and mitigate the climate change in a recent climate change scenario. With this background, we carried out research in the Longzhong Loess Plateau region of China. This research was conducted under a randomized complete block design, with three replicates. Adopt the method of combining outdoor positioning field test with indoor index measurement to explore the soil bulk density (BD), nitrogen components (viz., nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), total nitrogen (TN), microbial biomass nitrogen (MBN) and nitrogen storage (NS), and carbon components [viz., soil organic carbon (SOC), easily oxidized organic carbon (EOC), microbial biomass carbon (MBC) and carbon storage (CS), carbon pool index (CPI), carbon pool activity (A) and carbon pool activity index (AI) and carbon pool management index (CPMI)] and C/N, ratio under different tillage practices [namely., conventional tillage (CT), no tillage (NT), straw mulch with conventional tillage (CTS) and straw mulch with no tillage (NTS)]. Our results depicted that different conservation tillage systems significantly increased soil BD over conventional tillage. Compared with CT, the NTS, CTS and NT reduced soil NO3−-N, increased the soil NH4+-N, TN, MBN and NS, among them, NS under NTS, CTS and NT treatment was 25.0, 14.8 and 13.1% higher than that under CT treatment, respectively. Additionally, conservation tillage significantly increased SOC, EOC, MBC, CS, CPI, AI, CPMI and C/N, ratio than CT. Inside, CS under NTS, CTS and NT treatment was 19.4, 12.1 and 13.4% higher than that under CT treatment, respectively. Moreover, during the 3-year study period, the CPMI under NTS treatment was the largest (139.26, 140.97, and 166.17). Consequently, we suggest that NTS treatment was more sustainable strategy over other investigated conservation tillage practices and should be recommended as climate mitigation technique under climate change context.

Effects of Reducing Nitrogen Application Rate under Different Irrigation Methods on Grain Yield, Water and Nitrogen Utilization in Winter Wheat

We conducted a two-year field experiment on winter wheat (Triticum aestivum L.) from 2016–2018 to compare the effects of reducing nitrogen application rate in spring under three irrigation methods on grain yield (GY), water and nitrogen use efficiency in the North China Plain (NCP). Across the two years, GY of conventional irrigation (CI), micro-sprinkling irrigation (SI) and drip irrigation (DI) decreased by 6.35%, 9.84% and 6.83%, respectively, in the reduced nitrogen application rate (N45) than the recommended nitrogen application rate (N90). However, micro-irrigation (SI and DI) significantly increased GY relative to CI under the same nitrogen application rate, and no significant difference was observed in GY between SI and DI under N45, while SI obtained the highest GY under N90. The difference among different treatments in GY was mainly due to the variation in grain weight. The seasonal evapotranspiration (ET) in N45 was decreased more significantly than N90, and there was no significantly difference in ET among different irrigation methods under N45, but micro-irrigation significantly decreased the ET relative to CI under N90. Micro-irrigation significantly improved water use efficiency (WUE) compared to CI at the same nitrogen application rate. Under N45, compared with CI, WUE in SI and DI increased by 9.09% and 4.70%, respectively; however, the WUE increased by 15.9% and 7.23%, respectively, under N90. Reducing nitrogen application rate did not have a significant impact on WUE under CI, but it did have a substantial negative impact on SI and DI. Nitrogen accumulation in wheat plants at maturity (NAM) in N45 deceased significantly compared with N90 under the same irrigation method. Compared with CI under the same nitrogen application rate, micro-irrigation treatments significantly increased NAM, while SI was the largest. In comparison to N90, under three irrigation methods, N45 significantly increased nitrogen fertilizer use efficiency (NfUE). The highest NfUE was attained in SI, followed by DI, while CI was the lowest. Moreover, N45 significantly decreased soil NO3−-N accumulation (SNC) in three irrigation methods, and micro-irrigation significantly decreased the SNC in deep soil layers compared with CI when nitrogen is applied at the same level. Overall, micro-irrigation with a reduced nitrogen application rate in spring can achieve a relatively higher production of winter wheat while increasing the use efficiency of water and nitrogen and reducing soil NO3−-N leaching into deep soil layers in the NCP.

Biochar reduced soil N losses and improved N balance in a rainfed winter-wheat cropping agroecosystem

Adding biochar to agricultural soils is an innovative method to improve soil fertility and sequester recalcitrant carbon. However, effects of biochar application on soil nitrogen balance under dryland conditions have not been assessed. In this study, we applied biochar at four rates [no biochar (B0), 5 t ha−1 (B5), 10 t ha−1 (B10), and 20 t ha−1 (B20)] to a rainfed winter-wheat agroecosystem on the Loess Plateau in China in October 2011 and 2016. Biochar application at the low and medium rates (5 and 10 t ha−1) reduced nitrogen losses through NH3 volatilization and N2O emissions by 9.23–15.41 % and 2.77–10.44 %, respectively, in all the three experimental study seasons from 2016 to 2019. In addition, biochar application reduced soil NO3−-N leaching by 14.71–37.96 % within 100 cm soil depth in a dose-dependent manner. The reduced nitrogen losses increased the retention of soil total nitrogen in the 0–60 cm soil layer (particularly in the 0–20 cm layer). Biochar application increased the crop and grain nitrogen uptake by 5.07–17.77 % and 1.73–21.74 %, respectively, and this effect was more pronounced at higher biochar application rates (10 and 20 t ha−1). Estimation of N inputs and outputs indicated that biochar application significantly (P < 0.05) increased the mean soil nitrogen balance by 52.09–116.84 % through decreased nitrogen losses and increased soil nitrogen retention. The results indicate that biochar application at 10 t ha−1 could be recommended as the optimal dose for sustainable nitrogen management in rainfed wheat cropping ecosystems on the Loess Plateau.

Cover crop mixtures: A powerful strategy to reduce post-harvest surplus of soil nitrate and leaching

Cover cropping is a practice with potential to reduce post-harvest surplus of soil nitrate (NO3-), a mobile form of nitrogen naturally susceptible to losses. Increased soil NO3- leaching occurs when high soil NO3- coincides with high drainage events – a common occurrence during the non-growing season in cold and humid climates. The potential of cover crops to reduce NO3- leaching can be affected by the performance of the cover crop and by edaphic-climatic conditions (e.g., freeze-thaw cycles, soil type) and is subjected to interannual variation. Here, we evaluate soil type and crop rotation effects on soil parameters (i.e., NO3- concentration, temperature, water content) and on NO3- leaching under freeze-thaw conditions, using a high-frequency weighing lysimeter system. The soil type consisted of silt loam (SIL) and loamy sand (LS) soils and the crop rotation consisted of a rotation with a mixture of leguminous/non-leguminous cover crops (+CC) and no cover crop (-CC). This research was conducted during periods of 2017/2018 and 2018/2019 subjected to significant drainage. Our results indicated that cover crops did not affect drainage but affected soil temperature, with warmer soils observed over the winter when cover crops were used (+CC) than without cover-crops (-CC). Moreover, the cereal-crucifer-legume mixture after spring wheat reduced soil NO3- content by 80% compared to -CC during 2017/2018. For 2018/2019, due to poor establishment of the cereal-legume mixture under-seeded to corn, no reduction in soil NO3- content was observed. The reduction in soil NO3- in +CC plots for 2017/2018 translated to a significant reduction (by 67%) in NO3- leaching averaged across soil types. Soil drainage, NO3- content and NO3- leaching were not affected by soil type, an effect in part influenced by the boundary controls of the lysimeter system which mimicked soil conditions of a non-LS adjacent/reference field. To expand our results, we estimated the potential drainage of a hypothetical excessively drained LS (ED-LS) – a soil naturally subjected to high hydraulic conductivity and low water holding capacity. Overall, our results indicated that cover cropping can reduce NO3- leaching independent of soil type but the effect can be pronounced for ED-LS.

Winter cereal rye cover crop decreased nitrous oxide emissions during early spring

AbstractDespite differences between the cover crop growth and decomposition phases, few greenhouse gas (GHG) studies have separated these phases from each other. This study's hypothesis was that a living cover crop reduces soil inorganic N concentrations and soil water, thereby reducing N2O emissions. We quantified the effects of a fall‐planted living cereal rye (Secale cereale L.) cover crop (2017, 2018, 2019) on the following spring's soil temperature, soil water, water‐filled porosity (WFP), inorganic N, and GHG (N2O‐N and CO2–C) emissions and compared these measurements to bare soil. The experimental design was a randomized complete block, where years were treated as blocks. Rye was fall planted in 2017, 2018, and 2019, but mostly emerged the following spring. The GHG emissions were near‐continuously measured from early spring through June. Rye biomass was 1,049, 428, and 2,647 kg ha–1 in 2018, 2019, and 2020, respectively. Compared to the bare soil, rye reduced WFP in the surface 5 cm by 29, 15, and 26% in 2018, 2019, and 2020 and reduced soil NO3–N in surface 30 cm by 53% in 2019 (p = .04) and 65% in 2020 (p = .07), respectively. Rye changed the N2O and CO2 frequency emission signatures. It also reduced N2O emissions by 66% but did not influence CO2–C emissions during the period prior to corn (Zea mays L.) emergence (VE). After VE, rye and bare soils N2O emissions were similar. These results suggest that nitrous oxide (N2O‐N) sampling protocols must account for early season impacts of the living cover.

Organic amendment enhanced microbial nitrate immobilization with negligible denitrification nitrogen loss in an upland soil

Both soil microbial nitrate (NO3−-N) immobilization and denitrification are carbon (C)-limited; however, to what extent organic C addition may increase NO3−-N immobilization while stimulate denitrification nitrogen (N) loss remains unclear. Here, 15N tracing coupled with acetylene inhibition methods were used to assess the effect of adding glucose, wheat straw and peanut straw on NO3−-N immobilization and denitrification under aerobic conditions in an upland soil, in which NO3−-N immobilization has been previously demonstrated to be negligible. The organic C sources (5 g C kg−1 soil) were added in a factorial experiment with 100, 500, and 1000 mg N kg−1 soil (as K15NO3) in a 12-d laboratory incubation. Microbial NO3−-N immobilization in the 12-d incubation in the three N treatments was 5.5, 7.7, and 8.2 mg N kg−1 d−1, respectively, in the glucose-amended soil, 5.9, 4.2, and 2.4 mg N kg−1 d−1, respectively, in the wheat straw-amended soil, and 4.9, 5.1 and 4.4 mg N kg−1 d−1, respectively, in the peanut straw-amended soil. Therefore, under sufficient NO3−-N substrate, the higher microbial NO3−-N immobilization in the glucose than in the crop residue treatments was likely due to the slow decomposition of the latter that provided low available C. The 15N recovery in the N2O + N2 pool over the12-day incubation was <2% for all treatments, indicating negligible denitrification N loss due to low denitrification rates in the aerobic incubation in spite of increasing C availability. We conclude that external C addition can enhance microbial NO3−-N immobilization without causing large N losses through denitrification. This has significant implications for reducing soil NO3−-N accumulation by enhancing microbial NO3−-N immobilization through increasing C inputs using organic materials and subsequently mitigating nitrate pollution of water bodies.

Scavenging and recycling deep soil nitrogen using cover crops on mid-Atlantic, USA farms

In the mid-Atlantic USA region, nitrogen uptake by crops ceases about four weeks prior to harvest maturity, leaving substantial mineral N in the soil profile, which is prone to leach during the winter. Deep-rooted cover crops planted by early-September can potentially take up residual N and recycle some of it for following cash crops. We performed experiments on 19 minimum-tillage, grain farms investigating four unfertilized cover crop systems (forage radish (Raphanus sativus L.), winter cereal or grass, forage radish + winter cereal + crimson clover (Trifolium incarnatum L.), and a no cover crop control). We measured cover crop biomass, N uptake, and inorganic N distribution within the upper 210 cm of soil in late-fall and early-spring, and the following corn (Zea mays L.) crop’s growth and yield. In late-fall, radish reduced soil NO3 in the upper 90 cm by 66 %, while winter cereal or mix cover crops reduced NO3 in the upper 60 cm by 67 % and 56 %, respectively, compared to a no cover crop control. In the spring, the radish and mix cover crops resulted in comparable nitrate levels to the no cover crop control in the topsoil layer (> 30 kg ha−1) and less nitrate than the no cover crop control in subsoil layers. The winter cereal cover crop had low nitrate levels in the topsoil (∼20 kg ha−1) layer and subsoil layers. The biomass and N content of corn seedling (5 leaf) were influenced by the previous cover crop treatment in the order radish (4.0 g biomass plant−1) > mix (3.0 g biomass plant−1) = control (3.5 g biomass plant−1) > winter cereal (2.4 g biomass plant−1). At the farmers’ standard N fertilizer application rate, corn yield following radish was higher than following the winter cereal or mixed species cover crop but corn yield following radish was not different than following no cover crop. Corn yield following the winter cereal cover crop was lower than following no cover crop. Cover crops can be fit within the framework of existing cropping systems to scavenge residual N, therein reducing subsoil inorganic N. Radish and mixed species cover crops can be used prior to corn without reducing the overall short-term N use efficiency of the cropping system.

Growing season nitrate leaching as affected by nitrogen management in irrigated potato production

AbstractNitrate leaching from potato (Solanum tuberosum L.) production is of great concern because of its potential effects on water resources. Suction lysimeters were used in combination with a one‐dimensional flow model to quantify NO3–N leaching under irrigated potato produced on sandy soils near Québec City, QC, Canada. The 3‐yr (2010−2012) study compared a single application of polymer‐coated urea (PCU) and split‐applied soluble N fertilizers (ammonium nitrate, AN; ammonium sulfate, AS) at three N rates (120, 200, and 280 kg N ha−1) in addition to an unfertilized control. Fertilizer N application increased total seasonal NO3–N leaching. A single application of PCU increased total seasonal NO3–N leaching in 2011 compared with AN and AS, which was attributed to a greater soil NO3–N concentration under the PCU treatment in combination with increased rainfall during the tuber bulking phase (60−90 d after planting). Total seasonal NO3–N leaching in 2012 was reduced with PCU and AS compared with AN, which was attributed to reduced soil NO3–N concentrations between planting and hilling when rainfall was high. Regardless of the fertilizer N source, NO3–N leaching was primarily driven by precipitation, as leaching occurred when elevated soil NO3–N concentrations coincided with excess water in the soil. The results suggest that a single application of PCU is an effective strategy for reducing NO3–N leaching in years when there is significant rainfall during the period between planting and hilling.

Animal‐Based Organic Amendments and Their Potential for Excessive Nitrogen Leaching and Phosphorus Loading

Nitrate contamination of groundwater has been attributed to application of poultry litter to amend soil organic matter on raspberry farms in British Columbia, Canada. A field study assessed the risk of organic amendments that cause nitrate leaching and nutrient accumulation. The amendments, poultry litter, municipal compost, horse manure, and three types of dairy manure solids, were applied at 25 or 50 Mg dry matter ha–1 to match farm rates before new plantings. Plots were either unseeded or seeded with a grass mix to simulate berry establishment with grass alley crop. Soil was sampled at 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 60‐cm depths 15 times over 14 mo and analyzed for concentrations of NH4+ and NO3–, and at 0 to 15 cm for total C, N, and P at 6 mo after application. Three grass harvests were analyzed for yield and N offtake. Poultry litter supplied more than twice the total mineral N and total P compared to the dairy solids and horse manure, while the compost was intermediate. At 25 Mg ha–1, poultry litter increased concentrations of soil (0–15 cm) NH4+ and NO3– (&gt;150 and &gt;300 mg kg–1, respectively), compared with small short‐term increases by compost (∼70 and 100 mg kg–1, respectively). There was almost no increase from dairy and horse amendments. Grass N offtake reduced soil NO3– concentrations but did not eliminate the risk of leaching from poultry litter. We conclude that dairy solids and horse manure present less risk of nitrate leaching and P loading than poultry litter or municipal compost.Core Ideas Poultry manure and compost amendments greatly increased soil NH4+, NO3– and P. Grass ‘alley’ crop did no sufficiently mitigate soil mineral N from poultry manure. Little risk of nitrate leaching or P loading with dairy solids or horse amendments.

Effects of conservation tillage measures on soil water and NO3--N leaching in dryland maize cropland

Based on a field experiment on conservation tillage over 15 years in Weibei Highland maize cropland, six conservation tillage patterns, i.e., conventional tillage (CT), no-tillage (NT), no-tillage plus biochar (NB), no-tillage and straw mulching (NS), no-tillage and plastic film mulching (NF), and no-tillage and straw-plastic film mulching (NSF), were investigated for their effects on soil water and nitrate nitrogen(NO3--N) leaching, to seek sustainable agricultural cultivation measures suitable for the region. Results showed that, compared with NT treatment in the first water recharge period, CT had no effect on water recharge in 0-100 cm soil layer, and NS, NB, NSF and NF significantly reduced soil water recharge. In 100-300 cm soil layer, NS, NB, NF and NSF significantly increased soil water recharge, but CT significantly reduced soil water recharge. During the second water recharge period, water recharge depth was mainly concentrated in 0-100 cm soil layer, and there was no significant difference between each treatment and NT. During the water depletion period, compared with NT treatment, other treatments had no significant effect on water depletion in 0-100 cm soil layer, but NF and NSF increased soil water depletion by 33.9% and 59.9% in 100-300 cm soil layer, respectively. In 0-200 cm soil layer, compared to NT, CT significantly increased the accumulation of NO3--N by 2.2 fold, NS, NB, NF and NSF reduced soil NO3--N accumulation by 44.6%, 61.5%, 69.2% and 69.8%, respectively. In 200-300 cm soil layer, NS significantly reduced the accumulation amount of NO3--N, but CT had no significant effect on the accumulation amount of NO3--N, and NS, NB, and NSF all had negative effects on NO3--N accumulation. Soil water movement had significant effect on the distribution of NO3--N in soil profile. Soil NO3--N was mainly distributed in 0-40 cm soil layer for NB, NF and NSF treatments, in 0-100 cm and 200-300 cm soil layers for NS treatment, and over the entire profile for NT and CT, and NS, NT and CT treatments had two NO3--N accumulation peaks in soil profile. Different agricultural cultivation measures could reduce soil NO3--N leaching by regulating soil water content, and subsequently improve nitrogen utilization efficiency. Among those measures, NSF could effectively control soil water movement to reduce the NO3--N leaching and accumulation, and thus is a feasible measure to improve soil water and fertility conditions and increase dryland maize yields.

Amelioration effect of humic acid on saline-alkali soil

A field experiment was conducted to investigate the effects of three types of humic acid, i.e. oxidized humic acid (OHA), aminated humic acid (AHA) and microbial-humic acid (MHA), on physico-chemical properties of saline-alkali soil and maize growth. Results showed that the application of all humic acid materials had no significant effect on soil pH in the current season. However, the soil electrical conductivity (EC), the contents of water-soluble Na+ and K+, and sodium adsorption ratio (SAR) decreased under all three treatments of humic acid application measured in up to 40 cm soil depth. OHA had the strongest effect in reducing soil EC, while no significant differences were detected among the three tested materials in reducing contents of water-solu-ble Na+ and K+ and SAR. In addition, humic acid reduced soil NO3--N content and increased soil NH4+-N content, soluble organic nitrogen (SON) content and total soluble nitrogen (TSN) content, with higher effects of AHA and MHA than OHA. Moreover, the application of humic acid materials increased the content of soil available phosphorus, which was most significant in MHA. Humic acid addition could significantly enhance the yield and function leaf SPAD value of maize, which did not vary among the tested humic acid materials. The rank of effect size on apparent utilization efficiency of N and P fertilizer was in the order of AHA>MHA>OHA. While OHA treatment had the highest agronomic efficiency of N and P, AHA treatment achieved the highest partial factor productivity of applied N and P.

Field-aged biochar reduces the greenhouse gas balance in a degraded vegetable field treated by reductive soil disinfestation.

Reductive soil disinfestation (RSD) is proposed as a pre-plant, non-chemical soil disinfestation technique to control several soilborne phytosanitary issues. However, limited information is available on the evaluation of greenhouse gas (GHG) balance and soil quality during the soil remediation process as affected by RSD method. A 44-day field experiment including four different treatments was conducted to investigate the effects of conventional RSD and field-aged biochar-amended RSD on GHG balance and soil quality in a degraded vegetable field. Results showed that the conventional RSD application can significantly decrease the soil nitrate (NO3-) concentrations and electrical conductivity (EC) and oxidation-reduction potential (Eh) by 51.4-67.3%, 5.3-23.6%, and 10.9-15.1%, respectively, while significantly increase soil pH and cation exchange capacity (CEC) by 0.37-0.42units and 7.8-32.2%, respectively, in relation to the control (CK). Compared with the conventional RSD treatment, aged biochar-amended RSD significantly reduced soil NO3- concentrations, EC and Eh. No significant differences on CH4 emissions were observed among all the treatments during the experimental period. However, the conventional RSD application significantly increased the cumulative nitrous oxide (N2O) and carbon dioxide (CO2) emissions by 66.2-124.7% and 64.3-130.0%, respectively, and thus resulted in a significant GHG balance of 64.1-130.1% in relation to the CK. On the contrary, although resulted in more N2O emissions compared with the conventional RSD treatment, aged biochar-amended RSD significantly reduced the cumulative CO2 emissions and thus had an overall decrease in GHG balance by 20.7-28.7%. Therefore, aged biochar-amended RSD can simultaneously achieve lower GHG balance and better improvement of soil quality in degraded vegetable field, and thus can be utilized as an effective technology for soil remediation in intensive vegetable production.

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N2O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown. In this study, we measured the impacts of DMPP on N2O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha−1 and 0.5% of the urea-N application rate. The application of N significantly increased N2O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N2O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO3−-N content and N2O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes. Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N2O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

Improved crop yield and reduced nitrate nitrogen leaching with straw return in a rice-wheat rotation of Ningxia irrigation district

Field experiments were conducted in rice-wheat rotation under conventional management to determine the effects of straw return ((half straw return, HS) and (total straw return, TS)) on crop yield, N uptake, soil properties and soil NO3−–N leaching. We found that straw return significantly increased crop yield and N uptake. TS significantly increased soil SOM at depths of 20 cm and 30 cm. Straw return had significantly increased soil NO3−–N leaching at a depth of 10 cm, whereas significantly decreased soil NO3−–N leaching at depths of 30 cm and 90 cm in the rice season. In wheat season, HS and TS performed better than conventional fertilization management without straw return in reducing soil NO3−–N leaching at depth of 90 cm. Soil NO3−–N leaching was significantly decreased through enhancing total N uptake, improving soil aggregation and decreasing soil NO3−–N concentration. Our results indicated that total straw return has the potential to increase crop yield, improve soil aggregation and decrease soil NO3−–N concentration, thus increasing total N uptake and reducing soil NO3−–N leaching in the rice-wheat rotation system of Ningxia Yellow river irrigation district. In the future, the long-term observation of crop yield and nitrate nitrogen leaching are necessary to identify the environmentally friendly straw return practices for rice-wheat rotation.

Short-Term Response of Switchgrass to Nitrogen, Phosphorus, and Potassium on Semiarid Sandy Wasteland Managed for Biofuel Feedstock

It is important to understand switchgrass (Panicum virgatum L.) productivity with relation to diverse nutrient deficiency conditions in order to optimize continuous biomass production in marginal lands. This study was conducted on a wasteland sandy soil (Aridosol) to assess biomass yield, nutrient uptake and nitrogen (N) recovery of switchgrass, and soil nitrate-N (NO3−-N) accumulation responses to N (120 kg N ha−1), phosphorus (P, 100 kg P2O5 ha−1), and potassium (K, 45 kg K2O ha−1) applications during 2015 and 2016 in Inner Mongolia, China. The experiment layout was a randomized complete block design with fertilizer mixture treatments of N, P, and K (NPK), P and K (PK), N and K (NK), N and P (NP), and a control with no fertilizer input (CK). Plant height and stem diameter remained unaffected by the different fertilizer treatments. Biomass yield with the NPK treatment in 2015 was 8.9 Mg ha−1 and in 2016 it was 7.3 Mg ha−1. In 2015, compared with the NPK treatment, a significant yield reduction of 33.7% was found with PK, 22.5% with NK, 28.1% with NP, and 40.5% with CK; however, in 2016, yield declined significantly only with CK compared to the rest of the fertilizer treatments, for which yields were statistically similar. Plant N content was reduced for the treatment PK (i.e. N omission); conversely, plant P and K content remained unaffected with P and K omission treatments. Plant nutrient uptake, particularly of N and K, was severely decreased by the nutrient omission treatments when averaged across 2 years. Apparent N recovery (ANR; quantity of N uptake per unit of N applied) was reduced for the NP and NK treatments, which led to an increase in soil NO3−-N accumulation in the top 0–20 cm layer, compared with the NPK treatment. However, ANR was the highest (37.2% in 2015) with the NPK treatment, which also reduced soil NO3−-N accumulation. A balanced N, P, and K fertilizer management approach is suggested to sustain switchgrass yield and stand persistence on semiarid, marginal, sandy wasteland.

The quality and quantity of exogenous organic carbon input control microbial NO3− immobilization: A meta-analysis

The accumulation of NO3− in the soil has resulted in increased nitrogen (N) loss through runoff, leaching, and gaseous emissions. Microbial immobilization of NO3− as an important process in reducing soil NO3− accumulation has been for a long time neglected due to the predominant viewpoint that microbes preferentially immobilize NH4+-N. Microbial NO3− immobilization is generally carbon (C)-limited, and thus exogenous organic C input may enhance microbial NO3− immobilization. However, the effect of the quality and quantity of exogenous organic C input on soil microbial NO3− immobilization is poorly understood, and a synthetic assessment on such an effect is lacking. We thus assessed the impact of exogenous organic C type, the application rate of simple organic C (glucose and acetate), complex organic C type (animal manure, plant residue) and the C/N ratio of complex organic C on soil microbial NO3− immobilization rate using a meta-analysis. We found that the quality and quantity of exogenous C input affect soil microbial NO3− immobilization: microbial NO3− immobilization was enhanced with the addition of simple organic C at rates >500 mg C kg−1, or complex organic C with C/N ratios >18. Furthermore, a positive relationship between the natural log of response ratio of soil microbial NO3− and NH4+ immobilization indicates the simultaneous utilization of NH4+ and NO3− under elevated C availability. We conclude that specific exogenous organic C input at a high rate or with a high C/N ratio can enhance microbial NO3− immobilization and reduce soil NO3− accumulation.

Influence on wine biogenic amine composition of modifications to soil N availability and grapevine N by cover crops.

Vineyard soil management can modify the nitrogen soil availability and, therefore, grape amino acid content. These compounds are precursors of biogenic amines, which have negative effects on wine quality and human health. The objective was to study whether the effect of conventional tillage and two cover crops (barley and clover) on grapevine nitrogen status could be related to wine biogenic amines. Over 4 years, soil NO3- -N, nitrogen content in leaf and wine biogenic amine concentration were determined. Barley reduced soil NO3- -N availability and clover increased it. In 2011, at bloom, nitrogen content decreased with barley treatment in both blade and petiole. In 2012, nitrogen content in both leaf tissues at bloom was greater with clover than with tillage and barley treatments. Also, total biogenic amines decreased in barley with respect to tillage and clover treatments. There were correlations between some individual and total biogenic amine concentrations with respect to nitrogen content in leaf tissues. Wine biogenic amine concentration can be affected by the grapevine nitrogen status, provoked by changes in the soil NO3- -N availability with both cover crop treatments. © 2017 Society of Chemical Industry.