不同浸提剂以及保存方法对土壤矿质氮测定的影响

为探明影响土壤矿质氮测定的因素,从棕壤、潮土和黄棕壤3种类型土壤中各采集10个经不同施肥处理的土样,用连续流动注射分析仪测定经不同浸提剂以及不同保存方法处理后土样的NO3-N和NH4-N含量。结果表明:不论是棕壤、潮土还是黄棕壤,2 mol.L?1 KCl提取硝态氮的数量与0.01 mol.L?1 CaCl2提取的数量相关性均达到P<0.01水平;3种土壤各个土样硝态氮含量的测定值多表现为新鲜土<冷冻土<风干土;将鲜样浸提后作短时间的冷冻处理,其效果与鲜样24 h内的测定结果较接近;土样不同保存方式以及浸提液的保存时间对3种土壤NH4-N测定结果的影响规律不及NO3-N明显。     

休闲与施肥对夏玉米生长季节土壤矿质氮的影响

采用田间试验方法研究了休闲、施肥与夏玉米生长季土壤矿质氮动态的关系.结果表明:种植玉米可明显降低0～200cm土层硝态氮残留量,且主要减少100cm土层以下的硝态氮残留量,但对铵态氮残留量及其剖面分布无明显影响.夏玉米吐丝期,种植玉米0～200cm土层的硝态氮残留量是198.1kg·hm-2,休闲小区的残留量是562.2kg·hm2,前者比后者降低364.1kg·hm-2.施肥可明显增加土壤中硝态氮残留,并影响其剖面分布,但对铵态氮的影响较小.夏玉米出苗期施用氮肥处理的0～200cm土层的硝态氮残留量是857.3kg·hm-2,而不施氮肥处理仅为165.7kg·hm-2,前者比后者增加4.2倍;与不施肥相比,出苗期施肥不仅增加表层土壤硝态氮含量,且表层硝态氮随降水和灌水淋失到200cm土层;施肥处理收获期60cm以下土层硝态氮含量明显增加,特别是在180～200cm存在硝态氮的累积峰.     

不同沟灌方式下玉米根区矿物氮迁移动态研究

为探索交替隔沟灌溉下玉米根区矿物氮分布规律, 通过遮雨棚内微区试验, 研究了常规沟灌、交替隔沟灌和固定隔沟灌3 种沟灌方式对玉米根区硝态氮、铵态氮迁移的影响。结果表明: 交替隔沟灌溉根区硝态氮等值线和常规沟灌相似, 沟内硝态氮含量基本沿垄的中心对称分布。固定隔沟灌溉的湿润沟内硝态氮含量小于干燥沟, 施氮后非灌水沟硝态氮保持较高水平。收获时交替隔沟灌溉的根区硝态氮残留量比常规灌溉略高。与硝态氮分布相比, 铵态氮在根区土壤中的含量很小, 3 种沟灌方式在沟和垄中的铵态氮含量没有明显差异。     

Temporal variation in pools of amino acids, inorganic and microbial N in a temperate grassland soil

Plants can take up intact amino acids, even in competition with soil microbes, yet we lack detailed information on which amino acids dominate the soil and whether amino acid composition varies seasonally. This study tested the hypotheses that 1) the pool of amino acid N is generally larger than inorganic N; 2) temporal changes in the concentration of amino acid N is related to changes in the size of the microbial N pool; and 3) amino acid N is dominated by simple, neutral amino acids during warm months, whereas during cold months the amino acid N is dominated by more complex aromatic and basic amino acids. Approximately every month for two years we collected soil from a temperate, sub-alpine grassland in the Snowy Mountains of Australia. We quantified exchangeable pools of amino acids, nitrate and ammonium in 1 M KCl extracts. Microbial N was quantified by chloroform fumigation. Averaged across the 21 monthly samples, nitrate was 13% of the quantified pool of soluble non-protein N, ammonium was 34% and amino acid N was 53%. These data are consistent with our hypothesis that the pool of amino acid N is larger than inorganic N. There was substantial variation between months in concentrations of amino acids and inorganic N, but no clear temporal pattern. Microbial N did not vary between months, and thus changes in amino acid N were unrelated to microbial N. Principal components analysis indicated multivariate groupings of the different pools of N that were broadly indicative of function and/or biosynthetic relationships. Thus PCA identified a grouping of aromatic amino acids (Phe and Try) with amino acids derived from oxaloacetate (Asp, Ala, Val, Leu, Ile), and a second group comprising microbial N, nitrate and glycine. The pool of exchangeable amino acid N was dominated by Arg (26% of amino N) Val (20%) Gln (18%), Try (8%) and Asn (8%). Contrary to our hypothesis, the composition of the amino acid pool did not vary in a consistent way between months, and there was no evidence simple amino acids were relatively more abundant in warm months and complex amino acids in cool months.     

黄土高原旱地土壤质量评价指标研究

基于设置在陇中黄土高原半干旱区的长期定位试验,运用综合评价模型,定量评价了小麦→豌豆双序列轮作系统6种不同耕作方式对土壤质量的影响。结果表明,采用加权综合法和加乘法则对土壤质量进行综合评价,能够较好地反映土壤质量的实际情况,敏感地反映耕作方式对土壤质量的影响。运用逐步判别分析法对6种不同耕作方式[传统耕作(T)、免耕作(NT)、传统耕作秸秆还田(TS)、免耕秸秆覆盖(NTS)、传统耕作地膜覆盖(TP)、免耕地膜覆盖(NTP)]下29项土壤属性指标进行筛选,建立了包括团粒结构、全氮、速效氮、有机质、蔗糖酶活性、作物产量、种植纯收益和产投比8项因子的简化评价指标体系。原始评价指标体系下2种轮作序列土壤质量指数排序均为NTSTSNTPNTTPT;简化评价指标体系下豌豆→小麦轮作序列土壤质量指数排序为NTSTSNTPNTTTP,而小麦→豌豆轮作序列土壤质量指数排序为NTSTSNTNTPTTP。进一步相关分析和方差分析表明,应用逐步判别分析法建立的简化指标体系具有较高的代表性,可适用于黄土高原半干旱区土壤质量评价。     

施氮和秸秆还田对小麦-玉米轮作农田硝态氮淋溶的影响

连续4 a采用渗漏计测定法研究了陕西关中小麦-玉米轮作区施氮和秸秆还田对土壤剖面90 em处NO3--N淋溶的影响.结果表明,NO3--N淋洗主要发生在7、8、9月份或灌溉后,年际间变异较大.监测期内各处理渗漏液NO3--N浓度和淋失量的变幅为0～103.5 mg L-1和0～21.8 kg hm-2,二者均随施氮量的增加呈增加趋势.小麦施氮150 kg hm-2、玉米施氮180 kg hm-2时,连续4a作物均能获得高产.施氮量继续增加,产量不再增加,0 ～100 cm土层NO3--N累积量和90 cm处NO3--N淋失量却相应增加.秸秆还田2 a后作物显著增产,2010年和2011年分别增产15.1％和14.2％,但对NO3--N累积和淋溶的影响不显著.回归分析显示,NO3--N年淋失量和0～ 100 cm土层累积量均随年施氮量的增加呈指数形式增加,说明施氮量越高,NO3--N年淋失量和累积量越高,二者占施氮量的比例也越高.     

Regulation of urease production in soil by microbial assimilation of nitrogen

Summary Studies of the effects of different forms of N on urease production in soils amended with organic C showed that although microbial activity, as measured by CO₂ production, was stimulated by the addition of NH₄ ⁺ or NO₃ ^- to C-amended soils (200 mol glucose-C g^–1 soil), urease production was repressed by these forms of N. The addition of L-methionine sulfoximine, an inhibitor of inorganic N assimilation by microorganisms, relieved the NH₄ ⁺ and NO₃ ^- repression of urease production in C-amended soil. The addition of sodium chlorate, an inhibitor of NO₃ ^- reduction to NH₄ ⁺ by microorganisms, relieved the NO₃ ^- repression of urease production, but did not eliminate the repression associated with NH₄ ⁺. These observations indicate that microbial production of urease in C-amended soils is not directly repressed by NH₄ ⁺ or NO₃ ^-, but by products formed by microbial assimilation of these forms of N. This conclusion is supported by our finding that the biologically active L-isomers of alanine, arginine, asparagine, aspartate, and glutamine, repressed urease production in C-amended soil, whereas the D-isomers of these amino acids had little or no influence on urease production. This work suggests that urease synthesis by soil microorganisms is controlled by the global N regulon.     

Effects of legume green-manuring on nitrogen mineralization and some microbiological properties in an acid rice soil

We studied N mineralization of legume green manures under laboratory and field conditions, and the effects of field green-manuring on the microbiological properties of an acid Alfisol soil. No significant differences were found in the mineralization rates of Sesbania (Sesbania cannabina), sunnhemp (Crotalaria juncea), and cowpea (Vigna unguiculata) green manure. Mineralization was higher in field-capacity moist soil than water-saturated soil. The decomposition of sunnhemp under field wetland conditions, in the absence of a rice crop, was a rapid as it was under in vitro conditions. The decomposition released considerable amounts of mineral N and the level of NH ₄ ⁺ -N was significantly higher than NO ₃ ^– -N. Significant improvements were observed in the microbial biomass, dehydrogenase activity, and bacterial populations in the field soil green-manured for rice for 3 years, compared with fertilized soil.     

Significance of organic nitrogen uptake from plant residues by soil microorganisms as affected by carbon and nitrogen availability

Soil microorganisms can use a wide range of nitrogen (N) compounds. When organic N sources are degraded, microorganisms can either take up simple organic molecules directly (direct route), or organic N may be mineralized first and taken up in the form of mineral N (mineralization-immobilization-turnover [MIT] route). To determine the importance of the direct route, a microcosm experiment was carried out. Two types of wheat residue were added to soil samples, including younger residue with a carbon (C) to N ratio of 12 and older residue with a C to N ratio of 29. Between days 1 and 4, the gross N mineralization rate reached 8.4 and 4.0 mg N kg⁻¹ dry soil day⁻¹ in the treatment with younger and older residue, respectively. During the same period, there was no difference in protease activity between the two residue amended treatments. The fact that protease activity was not related to gross N mineralization, even though the products of protease activity are the substrates for N mineralization, suggests that not all organic molecules released from residue or soil N passed through the soil mineral N pool. In fact, when leucine and glycine were added, only 10 and 53% of the amino acid-N, respectively, was mineralized. The fraction of N taken up via the direct route was estimated to be 55 and 62% for the young and older residue, respectively. After 28 days of incubation, the proportion of amino acid-N mineralized had increased especially in the soil amended with older residue, suggesting that the MIT route became increasingly important. This result is supported by an increase in the activities of enzymes responsible for the intracellular assimilation of ammonium (NH₄⁺). Our results suggest that in contrast to what is proposed by many models of soil N cycling, both the direct and MIT routes were operative, with the direct route being the preferred route of residue N uptake. The direct route became less important over time and was more important in soil amended with older residue, suggesting that the direct route is favored by lower mineral N availabilities. An important implication of these findings is that when the direct route is dominant, gross N mineralization underestimates the amount of N made available from the residue.     

Leaching of mineral nitrogen in the soil influenced by addition of compost and N-mineral fertilizer

This paper deals with the problem of mineral N leaching from arable lands due to the fertilization method. The influence of different doses of compost (50 and 100?Mg ha^?1) and N-mineral fertilizer (35-70-140 kg N ha^?1) on leaching of N_min in a lysimetric experiment with winter wheat. The area of our interest represents the main source of drinking water for the city of Brno and its neighborhoods. To demonstrate the effect of compost and mineral nitrogen addition, the lysimetric experiment was established there. Seven variants of the experiment with different fertilization schemes were studied during two vegetation seasons (2013 and 2014), each with three repetitions. The experiment was carried out in plastic experimental containers of 0.3 m diameter and 0.5 m height. Therefore, each lysimeter was the same size and was filled with 25 kg of subsoil and 25 kg of topsoil. The highest leaching of N_min was detected in the variant C2 where 140 kg N ha^?1 was applied, in both vegetation periods (5.97 kg N_min ha^?1 after the first vegetation period and 17.02 kg N_min ha^?1 after the second vegetation period). The positive effect of compost application (individually or in combination with the mineral N) on decrease in mineral N leaching was found during both vegetation period in comparison with variant C2. The highest doses of compost (100?Mg per ha) significantly decreased the concentration of mineral nitrogen in the soil eluate in both periods (3.03 kg N_min ha^?1 and 5.79 kg N_min ha^?1, respectively), by 197% and 293% in comparison with variant C2. There is evidence that the application of compost has a positive effect on the reduction of N_min leaching.     

Effect of cellulose and straw incorporation in soil on total denitrification and nitrogen immobilization at initially aerobic and permanent anaerobic conditions

Summary Laboratory experiments were used to examine the influence of cellulose and straw on denitrification and N immobilization in a sandy loam soil. The soil was mixed with 300 g nitrate-N/g and incubated in a special vessel under conditions that changed from aerobic to anaerobic or in the permanent absence of O₂. Gases (O₂, CO₂, N₂, N₂O, NO and CH₄) were analysed by gas chromatography at regular intervals and the soil was examined for nitrate, nitrite, ammonium and cellulose. Compared with controls, the application of straw and cellulose (0.5% and 1.0%, respectively) enhanced nitrate immobilization and decreased denitrification, under both anaerobic and originally aerobic (PO₂ = 20 vol%) conditions. However, a comparison of results from the aerobic and the anaerobic incubations shows that an increase in denitrification and N immobilization was apparent at an original O₂ concentration of 20 vol%. N₂ was the major product of denitrification in all experiments. Free methane was apparent as soon as nitrate was respired. The stimulating effect of O₂ on total denitrification in the presence of relatively high amounts of easily decomposable cellulose is ascribed to a higher turnover and an intensified mineralization rate (CO₂ production), which increased the total demand for electron acceptors.     

Mineralisation of crop residues on the soil surface or incorporated in the soil under controlled conditions

In the present work, we compare the effect of mature crop residues mixed into a ferralitic soil or placed as a single layer on soil surface on the mineralisation of C and N over 55 days. As residues, we used dry stems of rice, soybean, sorghum, brachiaria and wheat. There were no significant effects of residue placement on C mineralisation kinetics. Decomposition of the residues on the soil surface slightly increased net N mineralisation for residues having the smallest C/N ratio.     

Temporal variation of total and DTPA-extractable heavy metal contents as influenced by sewage sludge and perlite in a calcareous soil

Continuous application of sewage sludge (SS) as a source of organic matter, may increase available heavy metals (HMs) up to their critical levels. As a consequence their uptake by plants, risks of accumulation in food chain and groundwater pollution increases. To evaluate the effects of perlite and SS on total content and available fraction of iron (Fe), manganese (Mn), lead (Pb), copper (Cu), nickel (Ni), cadmium (Cd) and zinc (Zn) over 45 and 90 days a completely randomized pot experiment was conducted. Treatments consisted of SS (0, 2 and 4%) and combined SS and perlite levels (1:1, 1.5:0.5 and 0.5:1.5% SS:perlite). Mean available Fe, Ni, Cd, Mn and Zn fractions decreased over time by 7–27%, whereas, total contents did not change. Available HMs in SS-treated soils increased by 0.5–25%; whereas, only total Zn, Cu and Pb concentrations increased with SS application (although concentrations fall in the range of critical levels). The lowest (1.6 fold) and highest (22.1 fold) increases obtained for available Cu and Zn, respectively. Perlite could mitigate the adverse effect of high rate application of SS on amplification of HMs extractability. Therefore, their concomitant applications can be suggested considering the perlite durability and its positive effects on soil physical properties.     

Nitrogen conservation in soil and crop residues as affected by crop rotation and soil disturbance under Mediterranean conditions

We investigated conservation and cycling of N under oat–oat and lupine–oat rotations in disturbed and undisturbed soil, when roots or roots plus aboveground residues were retained. Crop residues were labelled with ¹⁵N in Year 1, and differential soil disturbance was imposed after harvest. In Year 2, plant growth, N transfer from residue into the various sinks of the second crop (plant, soil, and residual residues), and changes in microbial activity and numbers were determined. Oat biomass was greater after lupine than after oat due to differences in supply of N from these residues. Buried residues of both crops appeared to decompose faster than when left on the soil surface. Lupine residues decomposed faster than oat residues. Oat biomass was not affected by soil disturbance if grown after lupine but decreased when oat straw was buried in the soil. More residue N was recovered from soil than from the crop. Most ¹⁵N was recovered from disturbed soil, which also had greater dehydrogenase activity and more culturable fungi. At the end of the oat–oat rotation, 20 and 5 kg N ha⁻¹ were derived from the roots of the first crop in undisturbed or disturbed soil, respectively. Equivalent values for the lupine–oat rotation were 18 and 44 kg N ha⁻¹. Returning aboveground residues provided an extra 52–80 kg N ha⁻¹ for oat and 61–63 kg N ha⁻¹ for lupine relative to treatments where they were removed. Over a year, lupine contributed 9 to 20 kg N ha⁻¹ more to the agroecosystem than did oat.     

Regulation of amino acid biodegradation in soil as affected by depth

Dissolved organic nitrogen (DON) and in particular free amino acids represent a key pool in the terrestrial soil C and N cycle. The factors controlling the rate of turnover of this pool in soil, however, remain poorly understood. We investigated the factors regulating the rate of amino acid turnover at different depths (up to 1.2 m) in five low-input, acid soil profiles. Within the root zone (0–60 cm), amino acids constituted 8% of the DON and represented only a small fraction of plant available N. In all the soil profiles, the rate of amino acid mineralisation decreased progressively with depth. The average half-life of the exogenously added amino acids in the soil was 5.8 h in topsoils (0–10 cm), falling to 20 h at a depth of 50 cm and to 33 h at 100 cm. Generally, the rate of amino acid mineralisation correlated positively with total soil C and N, soil microbial activity (basal soil respiration rate) and soil content. The relatively rapid rates of microbial amino acid assimilation in subsoils below the root zone (>60 cm) indicate that long-term transport of amino acids (e.g. from soil to freshwaters) will be low. Based upon the C-to-N ratio of the amino acid substrate and the microbial C assimilation efficiency, we estimate that approximately 40–60% of the amino acid-N will be excreted as . In conclusion, the rapid rate of free amino acid turnover and their low concentration in soil solution indicate that the formation of inorganic N ( and ) in soil is limited primarily by the rate of free amino acid appearance in soil and not by the rate of amino acid mineralisation.     

Carbon dioxide evolution from wheat and lentil residues as affected by grinding,added nitrogen,and the absence of soil

Summary A study was conducted to determine the effects of grinding, added N, and the absence of soil on C mineralization from agricultural plant residues with a high C:N ratio. The evolution of CO₂ from ground and unground wheat straw, lentil straw, and lentil green manure, with C:N ratios of 80, 36, and 9, respectively, was determined over a period of 98 days. Treatments with added N were included with the wheat and lentil straw. Although the CO₂ evolution was initially much faster from the lentil green manure than from the lentil or wheat straw, by 98 days similar amounts of CO₂ had evolved from all residues incubated in soil with no added N. Incubation of plant residues in the absence of soil had little effect on CO₂ evolution from the lentil green manure or lentil straw but strongly reduced CO₂ evolution from the wheat straw. Grinding did not affect CO₂ evolution from the lentil green manure but increased CO₂ evolution from the lentil straw with no added N and from the wheat straw. The addition of N increased the rate of CO₂ evolution from ground wheat straw between days 4 and 14 but not from unground wheat straw, and only slightly increased the rate of CO₂ evolution from lentil straw during the initial decomposition. Over 98 days, the added N reduced the amounts of CO₂ evolved from both lentil and wheat straw, due to reduced rates of CO₂ evolution after ca. 17 days. The lack of an N response during the early stages of decomposition may be attributed to the low C:N ratio of the soluble straw component and to microbial adaptations to an N deficiency, while the inhibitory effect of N on CO₂ evolution during the later stages of decomposition may be attributed to effects of high mineral N concentrations on lignocellulolytic microorganisms and enzymes.     

Yield and yield components of two irrigated red bean cultivars and some soil properties as influenced by wheat residues and nitrogen management

Crop residues are beneficial substances affecting crop production and soil properties. A field experiment was carried out to evaluate the effects of wheat (Triticum aestivum L.) residue rates (0, 25, 50 and 75%) combined with N levels (0, 34.5, 69, 103.5 kg ha^?1) on yield and yield components of two red common bean (Phaseolus vulgaris L.) cultivars and to monitor chemical soil parameters. The experiment was conducted at Research Center, College of Agriculture, Shiraz University, Shiraz, Iran for two years (2008–2009). The experiment was conducted as a split–split plot arranged in a randomized complete blocks design with three replications. The highest seed yield was obtained when 25–50% of residues were incorporated. The highest seed yield, seed weight per plant, 100-seed weight and seed number per pod were obtained with 103.5 kg N ha^?1 with no significant difference to 69 kg N ha^?1. Residue incorporation significantly increased soil organic carbon (SOC) as well as available K and P content. It is possible to sow red common bean as a double cropping by soil incorporation of 25–50% wheat residues with application of 69 kg N ha^?1.     

Importance of organic nitrogen fractions in sandy soils,obtained by electro-ultrafiltration or CaCl2 extraction,for nitrogen mineralization and nitrogen uptake of rape

Summary Sandy soils have low reserves of mineral N in spring. Therefore organic-bound N is the most important pool available for crops. The objective of the present investigation was to study the importance of the organic-bound N extracted by electro-ultrafiltration and by a CaCl₂ solution for the supply of N to rape and for N mineralization. Mitscherlich-pot experiments carried out with 12 different sandy soils (Germany) showed a highly significant correlation between the organic N extracted (two fractions) and the N uptake by the rape (electroultrafiltration extract: r=0.76^***; CaCl₂ extract: r=0.76^***). Organic N extracted by both methods before the application of N fertilizer was also significantly correlated with N mineralization (electro-ultrafiltration extract: r=0.75^***; CaCl₂ extract: r=0.79^***). N uptake by the rape and the mineralization of organic N increased with soil pH and decreased with an increasing C:N ratio and an increasing proportion of sand in the soils. Ninety-eight percent of the variation in N uptake by the rape was determined by the differences in net mineralization of organic N. This show that in sandy soils with low mineral N reserves (NO _inf3 ^sup- -N, NH ₄ ⁺ -N) the organic soil N extracted by electro-ultrafiltration or CaCl₂ solutions indicates the variance in plant-available N. Total soil N was not related to the N uptake by plants nor to N mineralization.     

Distribution and fate of 13C-labeled root and straw residues from ryegrass and crimson clover in soil under western Oregon field conditions

Annual ryegrass (Lolium multiflorum Lam.) and crimson clover (Trifolium incarnatum L.) were pulse-labeled with ¹³C-CO₂ in the field between the initiation of late winter growth (mid-February) and through flowering and seed formation (late May). Straw was harvested after seed maturation (July), and soil containing ¹³C-labeled roots and root-derived C was left in the field until September. ¹³C-enriched and ¹³C-unenriched straw residues of each species were mixed in factorial combinations with soil containing either ¹³C-enriched or ¹³C-unenriched root-derived C and incubated in the field for 10 months. The contributions of C derived from straw, roots, and soil were measured in soil microbial biomass C, respired C, and soil C on five occasions after residue incorporation (September, October, November, April, and June). At straw incorporation (September), 25–30% of soil microbial biomass C was derived from root C in both ryegrass and clover treatments, and this value was sustained in the ryegrass treatment from September to April but declined in the clover treatment. By October, between 20 and 30% of soil microbial biomass C was derived from straw, with the percentage contribution from clover straw generally exceeding that from ryegrass straw throughout the incubation. By June, ryegrass root-derived C contributed 5.5% of the soil C pool, which was significantly greater than the contributions from any of the three other residue types (about 1.5%). This work has provided a framework for more studies of finer scale that should focus on the interactions between residue quality, soil organic matter C, and specific members of the soil microbial community.     

Nitrous oxide emission from a transplanted rice field in alluvial soil as influenced by management of nitrogen fertiliser

We investigated nitrous oxide (N₂O) emission from an irrigated rice field over two years to evaluate the management of nitrogenous fertiliser and its effect on reducing emissions. Four forms of nitrogenous fertilisers: NPK at the recommended application rate, starch–urea matrix (SUM) + PK, neem‐coated urea + PK and urea alone (urea without coating) were used. Gas samples were collected from the field at weekly intervals with the static chamber technique. N₂O emissions from different treatments ranged from 11.58 to 215.81 N₂O‐N μg/m²/h, and seasonal N₂O emissions from 2.83 to 3.89 kg N₂O‐N/ha. Compared with other fertilisers, N₂O emissions were greatest after the application of the conventional NPK fertiliser. Moreover, SUM + PK reduced total N₂O emissions by 22.33% (P < 0.05) compared with NPK during the rice‐growing period (P < 0.05). The results indicate a strong correlation between N₂O emissions and soil organic carbon, nitrate, ammonium, above‐ and below‐ground plant biomass and photosynthesis (P < 0.05). The application of SUM + PK in rice fields is suitable as a means of reducing N₂O emissions without affecting grain production.