Release Kinetics of Nonexchangeable Potassium by Different Extractants from Soils of Varying Mineralogy and Depth

Abstract

Nonexchangeable potassium (K) release kinetics of six major benchmark soil series of India as affected by mineralogy of clay and silt fractions, soil depth and extraction media was investigated. The cumulative release of nonexchangeable K was greater in smectitic soils (353 mg K kg^?1 at 0‐ to 15‐cm depth and 296 mg K kg^?1 at 15‐ to 30‐cm depth, averaged for 2 soils and 3 extractants) than in illitic (151 mg K kg^?1 at 0‐ to 15‐cm depth and 112 mg K kg^?1 at 15‐ to 30‐cm depth) and kaolinitic (194 mg K kg^?1 at 0‐ to 15‐cm depth and 167 mg K kg^?1 at 15‐ to 30‐cm depth) soils. Surface soils exhibited larger cumulative K release in smectitic and illitic soils, whereas subsurface soils had larger K release in kaolinitic soils. Among the extractants, 0.01 M citric acid extracted a larger amount of nonexchangeable K followed by 0.01 M CaCl₂ and 0.01 M HCl. The efficiency of citric acid extractant was greater in illitic soils than in smectitic and kaolinitic soils. Release kinetics of nonexchangeable K conformed fairly well to parabolic and first‐order kinetic models. The curve pattern of parabolic diffusion model suggested diffusion controlled kinetics in all the soils, with a characteristic initial fast rate up to 7 h followed by a slower rate. Greater nonexchangeable K release rates in smectitic soils, calculated from the first‐order equation (b=91.13×10^?4 h^?1), suggested that the layer edge and wedge zones and swelling nature of clay facilitated the easier exchange. In contrast to smectitic soils, higher release rate constants obtained from parabolic diffusion equation (b=39.23×10^?3 h^?1) in illitic soils revealed that the low amount of exchangeable K on clay surface and larger amount of interlayer K allowed greater diffusion gradients, thus justifying the better fit of first‐order kinetic equation in smectitic soils and parabolic diffusion equation in illitic soils.     

Kinetics of Iron and Manganese Release from Contaminated Calcareous Soils

Knowledge of the release of heavy metals (HM) and their chemical speciation is necessary for characterizing HM behavior in soils. The kinetics and characteristics of iron (Fe) and manganese (Mn) release were studied in 10 contaminated calcareous soils using 0.01 M calcium chloride (CaCl₂), 0.01 M ethylenediamine tetraacetic acid (EDTA), and 0.01 M malic acid (malic acid) extractions. Iron and Mn in soil samples were fractionated before and after 2084 h kinetic release using a sequential extraction procedure. The proportion of Fe and Mn released by EDTA was greater than that with CaCl₂ and malic acid. A power model satisfactorily described Fe and Mn release from soils. In general, the mean release rate of Fe was greater than that of Mn, indicating a greater rate of Fe release from contaminated soils. It was shown that Fe and Mn distributions were similar in native soils and they were mainly found in Fe-Mn oxides and organic-matter (OM) fractions. There were changes in the proportional distribution of Fe and Mn in all soils during the 2084 h kinetic study with different extraction solutions. In general, the proportions of Fe and Mn associated with carbonate (CARB) and OM fractions tended to decrease, with corresponding increases in the Fe-Mn oxides for Mn and residual (RES) fractions for Fe during the kinetic study with all extraction solutions. The Fe and Mn solubility at the initial and final stages of release was controlled by siderite (FeCO₃), vivianite [(Fe)₃(PO₄)₂·8H₂O], MnCO₃(am), MnHPO₄, and rhodochrosite (MnCO₃) minerals in all extraction solutions. Based on a risk assessment and percentage of release of metals, there is a high potential for Mn release into the food chain from contaminated soils.     

Study on the Threshold Values of Soil Potassium Parameters for Release and Fixation: A Prognostic Approach to Improve the Use Efficiency of Soil and Fertilizer Potassium

The reserve of nonexchangeable potassium (K), threshold levels for release and fixation of intermediate K, and the Gapon exchange selectivity coefficient for K to calcium (Ca) and magnesium (Mg) exchange were studied in soils of widely varying properties, with a view to optimize the efficiency of native as well as added fertilizer K for plant uptake. The illite-dominated soils recorded greater reserve of nonexchangeable K and showed greater cumulative K release. The threshold values of soil K parameters for release and fixation of intermediate K were found to vary with the change in background electrolyte concentration. The soils dominated by illite were found to possess greater K threshold release and fixation values. In general, the fixation threshold level was greater than release threshold level. The Gapon exchange selectivity coefficient for K to Ca exchange revealed that K ions were more tightly held in the specific sites than in planar sites.     

Influence of Aluminum Hydroxide on Potassium Release from Two Colombian Soils

Abstract

The effect of sesquioxides on the mechanisms of chemical reactions that govern the transformation between exchangeable potassium (Kex) and non‐exchangeable K (Knex) was studied on acid tropical soils from Colombia: Caribia with predominantly 2∶1 clay minerals and High Terrace with predominantly 1∶1 clay minerals and sesquioxides. Illite and vermiculite are the main clay minerals in Caribia followed by kaolinite, gibbsite, and plagioclase, and kaolinite is the major clay mineral in High Terrace followed by hydroxyl‐Al interlayered vermiculite, quartz, and pyrophyllite. The soils have 1.8 and 0.5% of K₂O, respectively. They were used either untreated or prepared by adding AlCl₃ and NaOH, which produced aluminum hydroxide. The soils were percolated continuously with 10 mM NH₄OAc at pH 7.0 and 10 mM CaCl₂ at pH 5.8 for 120 h at 6 mL h^?1 to examine the release of Kex and Knex. In the untreated soils, NH₄ ⁺ and Ca²⁺ released the same amounts of Kex from Caribia, whereas NH₄ ⁺ released about twice as much Kex as Ca²⁺ from High Terrace. This study proposes that the small ionic size of NH₄ ⁺ (0.54 nm) enables it to enter more easily into the K sites at the broken edges of the kaolinite where Ca²⁺ (0.96 nm) cannot have access. As expected for a soil dominated by 2∶1 clay minerals, Ca²⁺ caused Knex to be released from Caribia with no release by NH₄ ⁺. No Knex was released by either ion from High Terrace. After treatment with aluminum hydroxide, K release from the exchangeable fraction was reduced in Caribia due to the blocking of the exchange sites but release of Knex was not affected. The treatment increased the amount of Kex released from the High Terrace soil and the release of Knex remained negligible although with Ca²⁺ the distinction between Kex and Knex was unclear. The increase in Kex was attributed to the initially acidic conditions produced by adding AlCl₃ which may have dissolved interlayered aluminum hydroxide from the vermiculite present, thus exposing trapped K as exchangeable K. The subsequent precipitation of aluminum hydroxide when NaOH was added did not interfere with the release of this K, and so was probably formed mostly on the surface of the dominant kaolinite. Measurement of availability of K by standard methods using NH₄ salts could result in overestimates in High Terrace and this may be a more general shortcoming of the methods in kaolinitic soils.     

Potassium Release Kinetics in Potato Growing Alluvial Soils of North Western India

Potassium (K) release and kinetics were studied in soils of north western India varying in soil properties. Mathematical equations were tested for their applicability to describe K release in the alluvial soils. The major portion of total K was released within 1 h of the reaction. The initial rapid K release was followed by a slower rate of K release. The linear equation adequately described the K release kinetics. The next best fit to satisfactorily describe the reaction rates of K release was the first order equation. There existed two separate first order equations indicating different rates of K release. Soils having higher native potassium and clay released higher amounts of K and at a faster rate. However, the first order equation showed that the faster rate of reaction might be inhibited by higher amounts of clay, probably because of the restrictive properties of illites.     

吉林省主要耕作土壤中钾的固定与释放

通过X—射线衍射、室内模拟实验及常规分析研究了吉林省主要耕作土壤中钾的固定与释放。结果表明,土壤对钾的固定与释放与土壤的矿物组成有关,3种土壤的固钾量均随钾加入量的增加而增大,而固钾率则随施钾量的增加而逐渐下降。随钾加入量的增加,固钾量和固钾率均有黑土>白浆土>黑钙土的趋势。土壤释钾量有黑钙土>黑土>白浆土的趋势。相关分析表明,蒙脱石、蛭石为主要的固钾矿物,而伊利石为主要的释钾矿物。     

Oxalic Acid Effect on Potassium Release from Typical Rice Soils of Kashmir

Batch experiments were employed to examine the influence of oxalic acid on release kinetics of potassium (K) from soils along with adsorption and desorption of soil K⁺. The soils used were three rice soils from high-, mid-, and low-altitude zones. The results showed that soil K extracted using 0.2 mol L^–1 oxalic acid was similar to that of 1 mol L^–1 boiling nitric acid (HNO₃). The relation between K release (y) and concentrations of oxalic acid (c) could be best described as y = a + b log c, whereas the best-fit kinetic equation of K release was y = a + b √t. The K release for soils was in the order Bonbagh > Ganasthan > Kreeri. An oxalic acid solution with low pH was able to release more K. Oxalic acid decreased soil K⁺ adsorption and increased desorption, the effect of which tended to be greater at lower pH.     

土壤水分对包膜尿素养分释放特性的影响

试验采用土壤培养的方法,以释放期分别为60 d(肥料A)和90 d(肥料B)的两种肥料作为供试肥料,研究了土壤绝对含水量、干湿交替、相对含水量和水势因素对3种土壤中包膜尿素养分释放特性的影响。结果表明:在3种土壤中,土壤绝对含水量从50 g/kg增到200 g/kg时,包膜尿素养分释放率均随土壤水分含量的增加而显著增加,此时水分因素是控制包膜尿素养分释放的主要因素。在干湿交替条件下,两种供试肥料间释放率的差异变大,其中肥料B在潮土中释放速率较其他两种土壤中下降更多。当相对含水量在0%~50%田间持水量范围内,或水势在60~100k Pa范围内时,供试肥料在红壤中的释放显著低于潮土和水稻土,这与红壤中黏粒含量高有关;当相对含水量大于100%田间持水量时,或水势低于60 k Pa时,土壤水分和土壤类型对包膜尿素养分释放的影响基本不再显著。常用的Sugihara方程可以较好地拟合包膜尿素在试验设定水分条件下的养分释放特性,相关系数r0.95。3种不同土壤水分参数均可以用来预测包膜尿素的释放率和释放期,其中水势(x)与包膜尿素释放期(y)的拟合效果最好,关系式为y=64.79e~(0.0066x),r=0.91。     

华北与西北地区典型土壤固钾能力差异研究

试验在我国华北和西北小麦玉米种植地区进行,研究了几种典型土壤在连续13年的K肥施用及小麦秸秆还田条件下耕层土对外源K素的固定能力差异.结果表明:相比常年只施NP肥处理,连续施用K肥或秸秆还田可显著降低土壤对外源K素的固定量,土壤固K量随环境溶液中K素浓度的增加而增加,但固定率下降.随土层变深,各定位点土壤固K量和固K率均随之增加,华北两定位点相对明显.轮作地区各处理0 ～ 20 cm土层土壤对外源K素的固定量(率)均远高于原始土壤,而单作区土壤的固K量(率)稍高或低于原始土.土壤固K能力表现出地带性规律,整体看取自华北两个定位点的土壤对外源K的固定能力强于取自西北两个定位点的土壤.     

Plant Availability Index by Potassium Exchange Isotherms in Selected Rice Soils of Lesser Himalayas

Potassium (K) exchange isotherms (quantity–intensity technique, Q/I) and K values derived from the Q/I relationship provide information about soil K availability. This investigation was conducted to study Q/I parameters of K, available K extracted by 1 N ammonium acetate (NH₄AOc) (exchangeable K plus solution K), K saturation percentage (K index, %), and the properties of 10 different agricultural soils. In addition, the relationship of mustard plant yield response to the K requirement test based on K exchange isotherms was investigated. The Q/I parameters included readily exchangeable K (ΔK₀), specific K sites (K_X), linear potential buffering capacity (PBC^K), and energy of exchange of K (E_K). The results of x-ray diffraction analysis of the oriented clay fractions indicated that some mixed clay minerals, illite clay minerals, along with chlorite/hydroxy interlayered vermiculite and kaolinite were present in the soils. The soil solution K activity ratio at equilibrium (AR₀) ranged from 8.0 × 10^?4 to 3.1 × 10^?3 (mol L^?1)^0.5. The readily exchangeable K (ΔK₀) was between 0.105 to 0.325 cmol_ckg^?1 soil, which represented an average of 88% of the exchangeable K (K_ex). The soils showed high capacities to maintain the potential of K against depletion, as they represented high linear potential buffering capacities (PBC^K) [13.8 to 50.1 cmol_c kg^?1/(mol L^?1)^0.5. The E_K values for the soils ranged from ?3420 to ?4220 calories M^?1. The percentage of K saturation (K index) ranged from 0.7% to 2.2%. Analysis of variance of the dry matter (DM), K concentrations, and K uptake of mustard plants indicated that there were no significant differences among the adjusted levels of K as determined by the exchange-isotherm curve.     

Soil Reserves of Potassium: Release and Availability to Lolium perenne in Relation to Clay Minerals in Six Cropland Soils from Eastern China

An 8‐month greenhouse experiment with ryegrass (Lolium perenne L.) examined the relationship between the dynamics of potassium (K) reserves in soil and changes in clay minerals, using X‐ray diffraction. The capacity of soil to release K was consistent with its ability to supply it and was the highest in the soil samples collected from Laiyang (H₁T₂a), Harbin (H₁T₁) and Beibei (H₂T₄), followed by the sample from Jiangyan (H₁T₂b), and the lowest in the samples from Gao'an (H₂T₃a) and Wangcheng (H₂T₃b). Removal of soil K decreases the intensity of reflections for illite and increases that for interstratified clay minerals. The centre of gravity values of the clay fractions was significantly negatively correlated to the depletion of soil K reserves, as ascertained through chemical extraction or through plant action. The quantitative regression equations between the centre of gravity values and the dynamics of soil reserves of K can be used for predicting the release and plant availability of K even without growing a crop. Copyright © 2017 John Wiley & Sons, Ltd.     

Simultaneous Dynamics and Kinetics of Soil Phosphorus Under Different Fertilizer Systems During Two-Growth Seasons of Maize

This study investigated phosphorus (P) dynamics and kinetics in calcareous soil under inorganic, organic, and integrated (inorganic+organic) fertilizer systems during two growing seasons of maize in two soil depths (0–0.15 and 0.15–0.30 m). A field experiment was conducted with 150, 300, and 400 kg ha^?1 triple superphosphate (TSP), 7.5 and 15.0 ton ha^?1 (on dry matter basis) farmyard manure (FYM), and integrated systems. In order to analyze Olsen P, soil samples were collected in 30-day-intervals after planting. The results showed that at the end of the two growing seasons of maize, the lowest magnitudes of Olsen P_0–0.15 m were 6.0, 6.8, 7.4, and 7.6 mg kg^?1 for the control, 7.5 FYM, 15 FYM, and 150 TSP, respectively. The highest magnitudes of Olsen P_0–0.15 m were 12.4, 11.5, 11.4, and 11.1 mg kg^?1 for 300 TSP+15 FYM, 400 TSP+7.5 FYM, 400 TSP+15 FYM, and 300 TSP+7.5 FYM, respectively. The same trends were observed for Olsen P_{0.15–0.30 m}. Heterogeneous diffusion model demonstrated that Elovich equation could best describe the experimental data (mean; R² = 0.98, SE = 0.29). The highest P supply rates (PSR) were 4.73, 3.91, and 3.86 mg kg^?1day^?1 (days after application) for 400 TSP, 400 TSP+15 FYM, and 300 TSP, respectively. The models of P supply capacity of soil could estimate P supply of soil under different fertilizer systems (R² = 0.84–0.95). The present study improved the understanding of the capacity and rate of P supply by considering P uptake by grain maize. Fertilizer recommendations depend on the accessibility of fertilizer types suggested to help choose the best fertilizer systems.     

控释尿素对土壤供氮能力及旱作玉米产量的影响

通过田间试验,探明控释尿素输入对土壤无机氮变化及春玉米氮素吸收利用特性的影响,为宁夏南部山区氮肥高效利用及玉米高产提供理论依据和技术支撑。以先玉698为供试材料,在等氮量(225 kg/hm~2)条件下,以不施氮为对照(CK),设置UR(100%普通尿素,2/3基施,1/3小喇叭口期追施)、CRU1(1/3控释尿素+1/3普通尿素基施,1/3普通尿素小喇叭口期追施)、CRU2(2/3控释尿素+1/3普通尿素一次基施)、CRU3(100%控释尿素基施)4种施氮模式,探明控释尿素输入对土壤无机氮分布、玉米氮素吸收运转、氮素利用效率以及产量的影响。结果表明,相对于UR处理,控释尿素输入显著提升了春玉米生育中后期土壤硝态氮和铵态氮的含量,其中以CRU2处理效果最明显。CRU输入能提高春玉米产量及氮肥利用率,与UR相比,2年内平均增产0.67 t/hm~2,氮肥偏生产力提高2.92 kg/kg,氮肥利用率提高6.02%。CRU处理间尤其以CRU2效果最佳,与CRU1、CRU3相比,2年内分别平均增产0.10,0.53 t/hm~2,氮肥偏生产力分别提高0.30,2.23 kg/kg,氮肥利用率分别提高2.49%,9.44%。由此可见,控释/普通尿素配施有利于提高土壤养分供应与春玉米氮素吸收的吻合度,初步建议采用控释尿素基施150 kg/hm~2+普通尿素基施75 kg/hm~2的施肥模式,以提高宁夏旱区春玉米产量和氮肥利用率。     

Potassium Fixation and Release Characteristics of Several Normal and K-Exhausted Soils in the Middle and Lower Reaches of the Yangtse River,China

Potassium (K) fixation and release in soil are important factors affecting K availability to plants and the utilization efficiency of K fertilizer. Three typical soils (red soil, yellow cinnamon soil, and alluvial soil) were collected from the middle and lower reaches of Yangtse River, China, to study the K-fixation and K-release characteristics of the normal and K-exhausted soil. Results showed that K fixation of added K in K-exhausted soils were significantly (P < 0.05) greater than that of the normal soils. There were significantly (P < 0.05) negative correlations among K-fixation capacity, concentration of soil-available K, and K⁺ saturation. Irrespective of soil K exhaustion, K fixation of added K was in the order of red soil > yellow cinnamon soil > alluvial soil, but the cumulative amount of K released from the three soils during successive extractions with 1.0 mol L^?1 nitric acid (HNO₃) was in the opposite order. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions. The K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was lower in K-exhausted soil than in normal soil. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

长期施肥对旱地红壤团聚体磷素固持与释放能力的影响

在中国科学院红壤生态试验站26年的旱地红壤长期肥料定位试验中,选取无机肥试验区的NPK、NK处理,有机无机肥配施试验区的对照(CK)、CK+稻秆(RS)、CK+花生秸秆还田(PS)、CK+绿肥(FR)及CK+猪厩肥(PM)等7个肥料处理土壤,采用湿筛法逐级提取并得到粒级依次为2 mm、2~1 mm、1~0.25 mm与0.25~0.053 mm的团聚体土壤样品;通过室内分析获得了土壤及各粒级团聚体的全磷(TP)、有效磷(Available P)、水溶性磷(CaCl_2-P)、土壤磷素吸持指数(PSI)及土壤磷素饱和度(DPS)等指标值,并探讨了上述测定指标间的相关关系。结果表明:长期施用磷肥可有效保持旱地红壤的供磷水平,配施猪厩肥可显著增加旱地红壤及大小团聚体的TP、有效磷及CaCl_2-P含量、降低土壤PSI并显著增大旱地红壤DPS,加大了旱地红壤磷素的流失风险;随着土壤中1 mm粒级团聚体数量的增多,旱地红壤磷素储量显著增加,磷素固持能力显著下降,土壤磷释放潜能随之增大。由DPS、有效磷及CaCl_2-P的分段线性拟合方程可以推断得出,当旱地红壤中有效磷为168~260 mg kg~(-1)时或DPS28%,土壤磷素具有潜在流失风险;当有效磷≥260 mg kg~(-1)或DPS≥28%,土壤磷素具有极高的流失风险,应立即停止施用磷肥尤其是有机磷肥,并重新调整施肥方案,以避免土壤磷素流失及其对水体环境的污染。     

Responses of Soil Enzyme Activities and Microbial Community Composition to Moisture Regimes in Paddy Soils Under Long-Term Fertilization Practices

The effects of fertilization on activity and composition of soil microbial community depend on nutrient and water availability;however,the combination of these factors on the response of microorganisms was seldom studied.This study investigated the responses of soil microbial community and enzyme activities to changes in moisture along a gradient of soil fertility formed within a long-term(24 years)field experiment.Soils(0–20 cm)were sampled from the plots under four fertilizer treatments:i)unfertilized control(CK),ii)organic manure(M),iii)nitrogen,phosphorus,and potassium fertilizers(NPK),and iv)NPK plus M(NPK+M).The soils were incubated at three moisture levels:constant submergence,five submerging-draining cycles(S-D cycles),and constant moisture content at 40%water-holding capacity(low moisture).Compared with CK,fertilization increased soil organic carbon(SOC) by 30.1%–36.3%,total N by 27.3%–38.4%,available N by 35.9%–56.4%,available P by 61.4%–440.9%,and total P by 28.6%–102.9%.Soil fertility buffered the negative effects of moisture on enzyme activities and microbial community composition.Enzyme activities decreased in response to submergence and S-D cycles versus low moisture.Compared with low moisture,S-D cycles increased total phospholipid fatty acids(PLFAs)and actinomycete,fungal,and bacterial PLFAs.The increased level of PLFAs in the unfertilized soil after five S-D cycles was greater than that in the fertilized soil.Variations in soil microbial properties responding to moisture separated CK from the long-term fertilization treatments.The coefficients of variation of microbial properties were negatively correlated with SOC,total P,and available N.Soils with higher fertility maintained the original microbial properties more stable in response to changes in moisture compared to low-fertility soil.     

长期施用钾肥和稻草对红壤双季稻田土壤供钾能力的影响

以红壤双季稻区长期定位施肥试验(1981―2012年)为基础,研究了长期施用化肥和稻草对双季稻集约化种植下水稻产量、作物吸钾量和土壤供钾能力的影响。结果表明,施钾能增加水稻稻谷和稻草的产量;水稻从土壤中的吸钾量随钾肥施用量的增加而显著增加,年平均吸钾量顺序为NPK+RS(施氮磷钾化肥+稻草)NPK(施氮磷钾化肥)NP+RS(施氮磷化肥+稻草)CK(不施任何肥料)NP(施氮磷化肥);长期不施用或施用不足量钾肥(CK、NP、NP+RS)会导致耕层土壤速效钾、缓效钾和全钾数量的亏缺。长期施用钾肥和稻草不仅有利于土壤伊利石含量的增加,而且有利于晶格不良伊利石向晶格良好伊利石的方向发展;施钾能增加土壤黏粒中的游离伊利石和伊利石的含量,长期施用钾肥和稻草会使土壤黏粒中的蛭石向伊利石转化。土壤钾素的容量-强度(Q/I)曲线参数可以解释长期施用钾肥和稻草处理土壤供钾能力强是由于这些处理的活性钾(-ΔK°)量高、专性吸附钾位(Kx)多、有效钾强度(AReK)强、紧吸持K+量多,而潜在缓冲容量(PBCK)、吉布斯自由能(-ΔG)和阳离子交换系数(KG)较长期不施钾肥处理低。综上,在施氮磷肥的基础上,配施钾肥和稻草还田不仅能提高水稻高产、稳产的能力,而且对促进水稻对钾的吸收量、增强土壤的钾吸持能力、保持农田钾素平衡以及提高土壤供钾能力有重要作用。     

中国小麦土壤速效钾丰缺指标与适宜施钾量研究

系统总结我国开展的小麦土壤速效钾丰缺指标与适宜施钾量研究,结果表明:30a来我国小麦土壤速效钾丰缺指标明显提高;不同区域之间小麦土壤速效钾丰缺指标差异颇大,以缺钾处理相对产量90%指标为例,土壤NH4OAc-K含量变动于80～246 mg/kg;除黄淮海平原、四川盆地、关中灌区和河套灌区外,我国小麦土壤速效钾丰缺指标研究存在很多空白区域;小麦土壤缺钾较为普遍,第2～4级为土壤速效钾集中分布的丰缺级别,缺钾处理相对产量大多处在70%～100%;土壤养分丰缺指标研究的试验点数不宜过少,丰缺指标高端和低端采用外推数据需谨慎,并应予以注明;适宜施钾量与土壤速效钾丰缺级别线性负相关,与小麦目标产量线性正相关,与钾肥当季利用率线性负相关;当钾肥当季利用率50%、目标产量3.0～12 t/hm2时,土壤速效钾丰缺级别第1～7级的小麦适宜施钾量范围依次为0、17～67、34～134、50～202、67～269、84～336和101～403 kg/hm2。     

Identification of Minimum Data Set Under Balanced Fertilization for Sustainable Rice Production and Maintaining Soil Quality in Alluvial Soils of Eastern India

The scarcity of non-renewable fertilizers resources and the consequences of climate change can dramatically influence the food security of future generation. Introduction of high yielding varieties, intensive cropping sequence and increasing demand of food grains day-by-day, application of recommended dose of fertilizers could not fulfill our targets due to outdated fertilizers recommendations are yet in practice. It not only alters soil quality, nutrient balance, microbial and enzymatic ecology but also affected productivity and sustainability of rice in Gangetic alluvial soils of India. The effect of fertilizers application based on “fertilizing the soil versus fertilizing the crop” which insure real balance between the applied and available soil nutrient is urgently needed. Hence, the present study was conducted during three consecutive crop seasons (2010, 2011, and 2012) to assess the effect of imbalance and balance fertilization based on initial soil test values and targeted yields, and to determine the effect of farmyard manure (FYM) when superimposed with balanced fertilizers on identification of minimum data set for the development soil quality, nutrient acquisition, and grain yield of rice. The six fertilizer treatments were laid out in a randomized block design with three replications. The treatments were: T₁-control (no fertilization), T₂-farmyard manure @ 5 t ha^?1, T₃-farmers practice (60:30:30 kg N:P₂O₅:K₂O ha^?1), T₄-precise application of mineral fertilizers based on initial soil test values (77:24:46 kg N:P₂O₅:K₂O ha^?1) for targeted grain yield of 4.0 t ha^?1, T₅-precise application of mineral fertilizers based on initial soil test values (74:23:43 kg N:P₂O₅:K₂O ha^?1) plus FYM (5 t ha^?1) for targeted grain yield of 4.0 t ha^?1 and T₆-precise application of mineral fertilizers based on initial soil test values (135:34:65 kg N:P₂O₅:K₂O ha^?1) for targeted rice grain yield of 5.0 t ha^?1. Result revealed that the targeted rice grain yield of 4.0 and 5.0 t ha^?1 was achieved in T₄ and T₆ treatments with 1.59% (4.06 t ha^?1) and –3.40% (4.83 t ha^?1) deviations, respectively. T₄, T_5, and T₆ significantly increased crop growth, nutrient uptake, available P (P_a) and K (K_a) and augmented rice grain yield by 10.6, 20.2 and 31.6%, respectively, over T₃. Microbial biomass carbon, soil respiration and enzymatic activity were enhanced significantly in T₅ as compared to T₆. Highest soil quality index was found in T₅ (0.95) followed by T₆ (0.90) and, lowest was in T₁ (0.63). The contribution of minimum data set (MDS) toward the SQI was in the descending order of ALP (30.6%) > SOC (21.5%) > K_a (11.3%) > PSM (9.68%) > N_a (8.51%). Overall, rice yield and soil quality was improved by using balance fertilization based on fertilizing the crop Vs fertilizing the soil in alluvial soils of India.