Mineralization of urea,coated urea and nitrification inhibitor treated urea in different rice growing soils

Mineralization of urea, sulphur coated (SCU), neem cake coated urea (NCU) and N-Serve treated urea (NSU) was studied in four important rice growing soils of India, namely, an alluvial soil (Entisol-Fluvent), a black cotton soil (Vertisol-Ustert), two laterite soils (Oxisol-Acrothox) and an acid sulphate soil (Entisol-Sulphaquent) for a period of four weeks at a temperature of 30°C ± 2°C and a water tension of 1/3 bar. Hydrolysis of urea was faster in alkaline alluvial and black cotton soils than in acid laterite and acid sulphate soil. NH₄-N content in soil was the highest with N-Serve during the entire period of study. SCU maintained lower NH₄-N in soil than urea only during the first two weeks of incubation. N-Serve was much more effective in inhibiting nitrification than neem cake in all the soils. Inhibition of nitrification by neem cake was most at the end of first week in alkaline and at the end of second week in all other soils. Coating of urea with neem cake imparted both slow-release and nitrification inhibiting properties.     

致孔剂对植物油包膜尿素养分释放特性的影响

为了探讨致孔剂对植物油包膜尿养分释放特性的影响,该研究通过25、30、35℃恒温静水培养方法对植物油包膜尿素养分释放特征曲线、肥效期、温度依存性以及养分释放活化能等进行了研究。结果表明：添加致孔剂ST（淀粉）和致孔剂SB（黏土矿物）均能加快植物油包膜尿素养分释放,均能缩短肥效期,当致孔剂ST用量从0增加至5%时,肥效期从122.20 d缩短为54.76 d,而添加不同用量致孔剂SB的植物油包膜尿素养分释放特征曲线基本重合;添加致孔剂ST植物油包膜尿素温度依存性Q10随用量增加而减小,而添加致孔剂SB则随着用量增加而增大;添加致孔剂会减小植物油包膜尿素养分释放活化能,当致孔剂ST和致孔剂SB用量分别为3%、4%时,养分释放活化能分别较不添加处理减少了40.20、23.28 kJ/mol。该文可为今后致孔技术在控释肥料研制中的应用提供参考。     

聚苯乙烯包膜尿素的缓释效果研究

采用实验室不同温度水培和淋洗试验,研究了膜材料比例、膜厚度、堵孔材料加入量以及尿素颗粒大小与包膜尿素养分释放的关系,温度对养分释放的影响,以确定不同释放速率系列包膜尿素配方。结果表明,膜材料增加、膜厚度增加,包膜尿素养分释放速率降低;单用网孔状膜材料包裹尿素,养分释放速率过快,肥料氮从土壤淋出量大,不可能用于水田作物;加入堵孔材料2%后,30℃水中养分释放期超过70 d,膜材料抗水性、耐挤压性好;在温度低于30℃条件下,温度对养分释放影响不大,温度高于45℃影响膜稳定性。     

分光光度法测定树脂包衣尿素溶出的研究

研究了对二甲氨基苯甲醛分光光度法应用于树脂包衣尿素养分溶出测定的可行性。对二甲氨基苯甲醛与尿素在酸性条件下生成黄色物质,其吸光值与尿素溶液的浓度成正比。结果表明,该方法与蒸馏后滴定法测定尿素相关性非常好,测定过程中缩二脲和硝态氮、铵态氮的干扰少。树脂包衣尿素养分溶出测定期间,尿素样品分解量少,分光光度法与蒸馏后滴定法的测定结果相关性非常好。试验证明两种方法测定包衣尿素溶出均可给出满意的结果,但分光光度法更快速、简便,适合于大批量样品的测定。     

桐油包膜尿素养分释放机理的研究

以桐油为包膜材料,采用土壤盆栽试验和水中静置试验,对控释肥料养分释放动态进行了研究。结果表明,以桐油为包膜材料的包膜尿素,在土壤中养分初期溶出率为12.6%,在水中养分初期溶出率为20.1%,是比较理想的包膜材料。在水中与土壤中养分释放期为1∶1.2;N素的释放可用LOGISTIC动力学方程描述,释放常数k值可用来判断控释尿素的N素释放速率大小。     

包膜尿素对芹菜产量、品质及氮素平衡的影响

通过盆栽试验研究了包膜尿素(自制)和尿素等肥料在两种质地灰潮土上对芹菜产量、品质、氮素吸收和氮平衡的影响。结果表明,施用包膜尿素较尿素使当季芹菜增产11.5％-15.2％,氮素吸收增加5.9％-9.5％,氨挥发损失N减少14.2％-14.9％,淋失和反硝化氮损失减少25.5％-28.3％,氮素利用率提高19.2％-27.1％,土壤持留氮增加32.0％-37.3％。芹菜植株硝态氮含量降低44.2％-58.9％,维生素C含量显著提高,品质改善;后茬作物生菜增产14.4％-35.2％。     

桐油包膜尿素的制备及其肥料缓释效应研究

以桐油为主要成膜材料对尿素实施了包膜处理，研究了桐油、桐油/改性树脂混合物及其与无机调理剂的混合物的粘度和粘度指数，对包膜尿素的表面形貌、包膜尿素的缓释性及其在黑麦草种植中的肥料效应进行了研究，以确定最佳的包膜工艺条件。实验结果表明：采用桐油和E₁或E₃无机调理剂的混合物，在包膜率9%～15%之间制得的桐油包膜尿素的养分释放期为24～62 d，能为黑麦草生长提供较长时间的养分供给并延长其绿色期。     

硫包衣尿素用量对旱作区胡麻生长及产量性状的影响

针对旱作区胡麻生产中种肥无法满足全生育期养分需求,缺乏灌溉条件,无法进行追肥的问题,于2015～2016年,在宁夏彭阳县旱作雨养农业区以硫包衣尿素为供试肥料,开展田间试验,研究硫包衣尿素用量对旱地条件下胡麻的营养生长、干物质积累、经济性状和籽粒产量的影响,综合评价了硫包衣尿素不同用量的增产效果及氮肥利用效率。结果表明:硫包衣尿素能有效促进旱作区胡麻的营养器官生长,有助于干物质累积,显著提高了经济性状指标、籽粒产量及水肥利用效率,在干旱年份增幅尤为明显。随着硫包衣尿素用量的增加,胡麻植株的生长量、经济性状指标及籽粒产量也随之增加,两年间各项指标变化趋势基本一致。在187.5 kg/hm~2的施肥水平,其两年的植株高度、地上部鲜重、地上部干重、籽粒产量平均值均达到最大,分别达到55.98 cm、8.72 g、2.57 g、1 648.64 kg/hm~2,较对照增加13.55%、137.09%、115.07%、32.16%。     

施用尿素、有机-无机复混肥和包膜有机肥对几种水稻田土表水层pH的影响

采用不同类型的3种水稻田土壤进行模拟培养,研究施用尿素、有机-无机复混肥和包膜有机肥对土表水层pH变化的影响。实验表明:淹水培养5天以后土表水层pH变化趋势明显。水稻田土壤类型不同,培养期间土表水层pH变化差异显著。在培养后5～15天期间,不施肥对照、施用包膜有机肥处理和施用复混肥处理,红壤、灰潮土和盐碱土土表水层pH都明显上升;施用尿素处理在灰潮土和盐碱土上土表水层pH值略微下降,而在红壤上仍呈上升趋势。     

4种不同材料包膜尿素对油菜的生长效应

通过盆栽试验研究了自制的4种不同材料包膜尿素对油菜生长效应及品质效应的影响,重点从土壤脲酶活性、油菜产量、品质及肥料利用率等方面对不同包膜肥料进行了评价。选出了一种控释效果较好的包膜肥FSU-4,其一次施用能满足油菜整个生育时期对养分的需求,使油菜生物产量比施用尿素提高70.8%,Vc含量提高7.8%,叶绿素含量提高46.1%,而硝酸盐含量则下降46.0%。施用包膜肥FSU-4比施用尿素N肥利用率提高36%,可有效减少N的损失。研究表明,在油菜生长前期包膜肥对脲酶有抑制,后期则有促进作用,其机理有待进一步深入研究。     

Influence of nitrogen on cellulose and lignin mineralization in blackwater and redwater forested wetland soils

 Microcosms were used to determine the influence of N additions on active bacterial and active fungal biomass, cellulose degradation and lignin degradation at 5, 10 and 15 weeks in soils from blackwater and redwater wetlands in the northern Florida panhandle. Blackwater streams contain a high dissolved organic C concentration which imparts a dark color to the water and contain low concentrations of nutrients. Redwater streams contain high concentrations of suspended clays and inorganic nutrients, such as N and P, compared to blackwater streams. Active bacterial and fungal biomass was determined by direct microscopy; cellulose and lignin degradation were measured radiometrically. The experimental design was a randomized block. Treatments were: soil type (blackwater or redwater forested wetlands) and N additions (soils amended with the equivalent of 0, 200 or 400 kg N ha^–1 as NH₄NO₃). Redwater soils contained higher concentrations of C, total N, P, K, Ca, Mn, Fe, B and Zn than blackwater soils. After N addition and 15 weeks of incubation, the active bacterial biomass in redwater soils was lower than in blackwater soils; the active bacterial biomass in blackwater soils was lower when 400 kg N ha^–1, but not when 200 kg N ha^–1, was added. The active fungal biomass in blackwater soils was higher when 400 kg N ha^–1, but not when 200 kg N ha^–1, was added. The active fungal biomass in redwater wetland soils was lower when 200 kg N ha^–1, but not when 400 kg N ha^–1, was added. Cellulose and lignin degradation was higher in redwater than in blackwater soils. After 10 and 15 weeks of incubation, the addition of 200 or 400 kg N as NH₄NO₃ ha^–1 decreased cellulose and lignin degradation in both wetland soils to similar levels. This study indicated that the addition of N may slow organic matter degradation and nutrient mineralization, thereby creating deficiencies of other plant-essential nutrients in wetland forest soils. Received: 7 April 1999     

Effect of cropping systems on nitrogen mineralization in soils

 Understanding the effect of cropping systems on N mineralization in soils is crucial for a better assessment of N fertilizer requirements of crops in order to minimize nitrate contamination of surface and groundwater resources. The effects of crop rotations and N fertilization on N mineralization were studied in soils from two long-term field experiments at the Northeast Research Center and the Clarion-Webster Research Center in Iowa that were initiated in 1979 and 1954, respectively. Surface soil samples were taken in 1996 from plots of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha^–1 before corn and an annual application of 20 kg P and 56 kg K ha^–1. N mineralization was studied in leaching columns under aerobic conditions at 30  °C for 24 weeks. The results showed that N mineralization was affected by cover crop at the time of sampling. Continuous soybean decreased, whereas inclusion of meadow increased, the amount of cumulative N mineralized. The mineralizable N pool (N _o) varied considerably among the soil samples studied, ranging from 137 mg N kg^–1 soil under continuous soybean to >500 mg N kg^–1 soil under meadow-based rotations, sampled in meadow. The results suggest that the N _o and/or organic N in soils under meadow-based cropping systems contained a higher proportion of active N fractions. Received: 10 February 1999     

Influence of four levels of pyrophosphatase activity on the rate of pyrophosphate hydrolysis in organic soils

Abstract

In this study, the rate of pyrophosphate hydrolysis was measured in four organic soil materials similar in pyrophosphate retention values and in all other respects except pyrophosphatase activity. These soil materials had a bulk density of 0.20 kg/L and a pH (0.01 M CaCl₂) of 5.1, and contained 16% ash and 103 mg P/kg as Mehlich No. 1 extractable P. The difference in pyrophosphatase activity between the soil materials was attributed to response to Cu of previous crops at low values of 1 N HCl‐extractable Cu (10 vs 76 mg Cu/kg) and to pyrophosphatase inhibition by Cu at high Cu values (201 and 479 mg Cu/kg). Pyrophosphatase activity increased from 35.6 to 38.3 mmol/kg/(2h) with Cu contents increasing from 10 to 76 mg/kg, and decreased to 31.9 and 28.3 mmol/kg/ (2h) with Cu contents increasing respectively to 201 and to 479 mg/kg. However, no significant difference in course of pyrophos‐phate hydrolysis was observed among the soil materials under both laboratory and field conditions. The half‐life of pyrophosphate was nearly 1 day under laboratory conditions. The decrease in substrate concentration over time and the corresponding increase in products competing with substrate on active sites of enzymes tended presumably to mask the difference shown in pyrophosphatase activity among organic soil materials. Thus, a difference in pyrophosphatase activities larger than the one considered in this study would be required to influence the rate of pyrophosphate hydrolysis in organic soils of similar pyrophosphate retention characteristics. Such a difference in activity levels was not obtained despite a large difference in Cu contents among the soil materials. It was thus apparent that Cu contents, exceeding that generally found in Quebec organic soils, would not reduce the rate of orthophosphate production from polyphosphate fertilizers containing large amounts of pyrophosphate. Pyrophosphate hydrolysis would be rapid and not affected by a small reduction in pyrophosphatase activity.     

Effect of pH on nitrogen mineralization in crop-residue-treated soils

Summary This study compares N mineralization in soils treated with crop residues [corn (Zea mays L.), soybean (Glycine max (L.) Merr.), sorghum (Sorghum vulgare Pers.)] or alfalfa (Medicago sativa L.) at three adjusted soil pH values (4, 6, and 8); pH was adjusted with dilute H₂SO₄ or KOH. A sample of soil (20 g) was treated with 0.448 g plant material (equivalent to 50t ha^–1), mixed with 20 g silica sand adjusted to the pH of the soil, and packed in a leaching tube. The soil-sand mixture was leached with 100 ml 5 mM CaCl₂ adjusted to the same pH as that of the treated soil to remove the initial mineral N, and incubated at 30°C. The leaching procedure was repeated every 2 weeks for 20 weeks. Results from three soils showed that N mineralization increased as the soil pH increased. In one soil (Lester soil), significant amounts of NH ₄ ⁺ -N accumulated at pH 4 during the first 12 weeks. Treatment with corn and soybean residues resulted in a marked reduction in N mineralization, especially at pH 4. The percentage of organic N mineralized from sorghum residue and alfalfa added to soils increased as the soil pH increased; the values ranged from 7.7% to 37.0% for sorghum and from 17.2% to 30.1% for alfalfa.     

Influence of incubation temperature on the behavior of triethylamine-extractable glyphosate (N-phosphonomethylglycine) in four soils

The behavior of glyphosate, extracted from four soils using aqueous triethylamine, was investigated at two temperatures. For each soil, and at both temperatures, there was a marked loss in the amount of extractable glyphosate immediately after addition of the herbicide to soil. This rapid loss of glyphosate was ascribed to adsorption of the herbicide into a nonextractable form. For three of the four soils used when incubated at 25 degrees C, the rates of loss of extractable glyphosate were similar to previously measured rates of degradation of this herbicide in these soils. However, loss of extractable glyphosate from the Culgoa clay loam was due not only to substrate degradation but also to slow sorption of glyphosate into the nonextractable form in this soil over the experimental period. For the Rutherglen and Walpeup soils, when incubated at 10 degrees C, the rates of loss of extractable glyphosate were half of the previously measured rate of degradation of this herbicide in these soils. However, there was no measured loss of extractable glyphosate from the Wimmera clay. As previous work has shown glyphosate to decompose readily in these soils at this temperature, these findings suggest that desorption of glyphosate may occur at a rate greater than degradation at this temperature and, hence, that temperature may play a pivotal role in sorption processes. Investigations with these soils when sterilized by gamma-irradiation showed that for the Walpeup, Wimmera, and Rutherglen soils, sorption was complete soon after the addition of the herbicide; however, for the Culgoa soil, further adsorption occurred over the entire experimental period.     

石灰氮对土壤中尿素转化的影响

Laboratory incubation experiment was conducted to study the effect of lime nitrogen(LN) on transfor-mation of urea-N in three paddy soils.The results showed that LN had an inhibitory effect on urease activity in these soils especially in the first 5 days.and that in the first 20 days of incubation,the amount of NH4^ -N derived from urea was lower in the soil with LN than in the soil without LN,While after 30 days the amount of NH4^ -N was higher in the mature haplic paddy soil developed on Quaternary red clay (MHPS)with LN than that in the soil without LN.The amount of NH3-N volatilized was decreased in the earlier stage and increased in the later stage of incubation in the MHPS by the addition of LN.     

Bacteriological studies on the mineralization of organic nitrogen in paddy soils

In this report we studied the effects of mechanical grinding of paddy soils on nitrogen mineralization and bacterial number when soils were incubated under a submerged condition after grinding.

Nitrogen mineralization was increased by grinding soil samples as compared with those without grinding. The value of (Nd-Nu)/Nu, where Nd is the amount of ammonia-nitrogen formed by incubation of disrupted samples and Nu those of the undisrupted soils, was in good correlation with clay/humus ratio.

Although significant difference was not observed between the number of aerobic bacteria with undisrupted and disrupted soil samples, higher anaerobic bacterial numbers were found with disrupted than with undisrupted ones.

A significant correlation was also obtained between the amounts of nitrogen mineralization increased by the grinding of soil and the numbers of anaerobic bacteria.     

Nitrogen mineralization of leguminous crops in soils

Organic‐N production by legumes is a key benefit of growing cover crops and green manures. A soil sample was mixed with legume residue commonly used as green manure in Kenya at a rate of 500 mg N (kg soil)^–1. Silica sand equal to the weight of the soils was added and mixed thoroughly. The mixture was packed in a leaching tube and leached with 100 mL of 5 mM of CaCl₂ ^. 2H₂O and incubated at 30°C. The leaching was repeated every 2 weeks for a total of 16 weeks and analyzed for N as NH , NO , and NO . Five legume residues and five different soils were used in this study. Nitrogen mineralization of the legume residues conformed to an exponential model. Application of a two‐components exponential model showed two phases of N mineralization. The relationship between the organic N remaining after each incubation period and time of incubation was controlled by two first‐order reactions. The initial fast rate (k₁) changed to a slow rate (k₂) at incubation times ranging from 2 to 8 weeks, depending on the legume residue and the soil used. The percentage of N in each phase varied among the legume residue and soils. Linear regression analyses showed that net cumulative amounts of N mineralized from individual legume residues was significantly correlated with the total polyphenols and polyphenol‐to‐N ratios for two soils. Nitrogen mineralization of dolichos and field bean was significantly and negatively correlated with clay and sand, respectively; of field bean and alfalfa was significantly correlated with C_mic; and of dolichos significantly but negatively correlated with the total N and organic N in soils. Linear regression analysis of the pooled data showed that net cumulative amounts of N mineralized and percentage N mineralized were significantly correlated with C : N ratios of the residues (r = 0.44 and 0.48 at p < 0.05, respectively), and that net cumulative N mineralized was significantly correlated with (lignin + polyphenols)‐to‐N ratios (r = 0.41 at p < 0.05) and with lignin contents (r = 0.61 at p < 0.001).