Effects of controlled‐release potassium fertilizer on available potassium,photosynthetic performance,and yield of cotton

Potassium (K) is one of the major mineral elements required for normal growth of cotton. However, understanding the effect of controlled‐release K fertilizer on leaf photosynthesis and K use efficiency (KUE) of cotton is currently limited. A two‐year pot experiment was consecutively conducted in 2014 and 2015 with three kinds of K fertilizer including K₂SO₄, KCl, and polymer‐coated KCl (CRK), each at four application rates (0.00, 0.86, 1.73, and 2.59 g K plant⁻¹, respectively). For each type of K fertilizer, the yield and K uptake of cotton increased but the KUE decreased with higher K fertilizer application. The release characteristics of K from CRK corresponded well to the K requirements during cotton growth. Plant‐available soil K, as well as leaf SPAD values, net photosynthetic rate (P_n), maximal photochemical efficiency (Fv/Fm), and effective quantum yield of photosystem II (ΦPSII) in CRK treatments were increased after full bloom stage compared to conventional K fertilizers under the same potassium application rate. Consequently, the CRK treatments significantly increased lint cotton yields by 8.1–32.7% and 3.7–20.8%, while the KUE increased by 15.5–54.8% and 14.5–45.4% compared to KCl and K₂SO₄ treatments, respectively. The results indicate that the application of CRK is intensively recommended to replace conventional potassium fertilizers for gaining greater yields and higher KUE of cotton.     

长期秸秆还田下基于东北水稻高产和钾素平衡的钾肥用量研究

  【目的】  通过5年定位试验,系统研究东北稻区秸秆还田条件下不同钾肥用量对水稻产量、钾素利用率和土壤供钾能力的影响,为秸秆还田下水稻钾肥合理施用提供科学依据。  【方法】  于2015—2019年在东北水稻主产区吉林省前郭县开展田间定位试验。共设6个钾肥用量 (K₂O) 处理,分别为0 (K0)、30 (K30)、60 (K60)、90 (K90)、120 (K120) 和150 kg/hm2 (K150),水稻收获后,测定籽粒产量与生物产量、植株钾含量及0—20和20—40 cm土层土壤速效钾、缓效钾和全钾含量,并计算作物钾积累量、钾素利用效率和土壤-作物系统的钾素表观平衡状况。  【结果】  施钾可提高水稻籽粒产量和生物产量,与不施钾相比,平均增幅依次为7.6%～14.5%、6.3%～10.9%,以K60和K90处理籽粒产量和生物产量最高。不同施钾处理间收获指数没有显著差异。钾素表观回收率、农学利用率和偏生产力均随钾肥用量的增加而下降。K60、K90、K120和K150处理0—40 cm土壤速效钾和缓效钾含量高于K0和K30处理,全钾含量6个处理间没有显著差异。K90、K120和K150处理0—40 cm土壤速效钾和缓效钾含量间也没有显著差异。在5年试验中,K0和K30处理土壤钾素表观平衡均表现为亏缺,K60处理农田钾素投入量和输出量基本平衡,当钾肥用量增加至90 kg/hm2以上,农田钾素表观平衡呈现盈余状态,并随钾肥用量的增加显著增加。盈余率与钾肥用量、籽粒产量、土壤速效钾含量、钾素利用效率分别进行拟合得出,当盈余率为0时,钾肥用量为53.1 kg/hm2,籽粒产量为10035 kg/hm2,0—20和20—40 cm土壤速效钾含量分别为103.04和91.56 mg/kg,钾素表观回收率为40.4%,钾素农学利用率为21.2 kg/kg,钾素偏生产力为202.2 kg/kg。  【结论】  在秸秆还田条件下,施用钾肥对水稻依然有明显增产效果。年施K₂O 30 kg/hm2,土壤钾素处于亏缺状态;年施K₂O 60 kg/hm2增产效果最好,且土壤钾素处于基本平衡状态,土壤速效钾和缓效钾含量处于稳定状态;年施K₂O超过90 kg/hm2后,虽然钾盈余量增加,但对土壤速效钾和缓效钾含量没有进一步增加的效果,水稻产量甚至还有下降的趋势。以理论盈余率为0时钾肥用量的95%为置信区间,钾肥用量在50～56 kg/hm2范围内既可保证较高的水稻产量和钾素利用效率,又可维持土壤供钾能力,可作为东北稻区秸秆还田下水稻钾肥推荐用量。     

干旱胁迫与正常供水钾肥影响甘薯光合特性及块根产量的差异

【目的】干旱胁迫影响甘薯叶片光合特性及块根产量,研究通过施肥缓解干旱胁迫机理可为甘薯抗旱高产栽培提供理论依据。【方法】选用食用型甘薯品种“泰中6号”为材料,以硫酸钾(K2SO4)为供试肥料,水分处理设为土壤最大持水量的60%~70%(正常供水W1)和30%~40%(干旱处理W0); 钾肥设K0、 K1、 K2、 K3四个水平,K2O用量分别为0、 12.0、 24.0和36.0 g/m2。分析不同钾肥用量对不同生长时期甘薯叶片相对含水量、 叶绿素荧光参数、 光合特性及收获期块根产量的影响。【结果】在干旱胁迫和正常灌水条件下,施钾处理均显著增加了甘薯叶面积和叶片叶绿素含量,提高净光合速率(Pn),增加光合产物的生产和积累,提高块根产量和收获指数。两种水分条件下,块根产量均以K2处理最高, 干旱胁迫下K2与K3处理差异显著,正常灌水处理不显著。两种水分条件下,甘薯叶片光合参数对钾肥的响应存在显著差异,干旱胁迫下施钾使叶片水分利用效率(WUE)增大,气孔导度(Gs)降低,气孔阻力增大,蒸腾速率(Tr)和胞间CO2浓度(Ci)降低,水分蒸腾量减少; 而正常灌水条件下上述指标对钾肥的响应趋势相反。两种水分条件下施钾均可以增大叶片相对含水量(RWC),提高实际光化学效率(ΦPSII)和最大光化学效率(Fv/Fm),但是干旱胁迫下施钾增幅较大。【结论】干旱胁迫下适量施钾可以提高甘薯的抗旱性,增加甘薯产量,过量施钾使甘薯产量显著降低,而正常水分供应时,稍多钾肥对产量影响不显著。干旱胁迫与正常灌水条件下施钾对叶片光合参数的调控效应存在显著差异。施用钾肥可增大叶面积,提高叶绿素含量和光合性能,调节叶片气孔关闭,增大叶片气孔阻力,减少水分蒸腾损失,增加叶片相对含水量,提高水分利用效率和净光合速率; 施钾还能提高叶片PSⅡ原初光能转换效率和实际光化学效率,减少过剩激发能对光合机构的破坏,提高甘薯叶片的光合能力。干旱条件下钾肥的调节功能优于正常水肥供应。     

Soil available potassium affected by rice straw incorporation and potassium fertilizer application under a rice–oilseed rape rotation system

Data from 147 field trials were collected to study the influence of straw incorporation on soil potassium (K) under an intensive rice–oilseed rape rotation system, while pot experiments were conducted to evaluate the effects of rice straw incorporation on soil K availability. A significant correlation was observed between the soil available K and the relative yield (RRY) and the relative K uptake (RKU) of oilseed rape, with R² values ranging from 0.07 to 0.08 and from 0.10 to 0.11, respectively, when data were fitted to a logarithmic equation model. In approximately 30% of trials, RRY reached 90%, while soil test available K values were below the critical limit, indicating that soil K values at the time of sampling (within 1 week of rice harvest) underestimated the actual soil K supply capacity. The pot experiment results showed that soil available K was affected by straw incorporation and soil type in the fallow period. The NH₄OAc‐K and NaBPh₄‐K concentrations of soils increased at first, and then, plateaued after 28 days. Straw incorporation significantly influenced the critical soil K concentration, which is important for making accurate K fertilizer recommendation. These results suggested that straw K should be seriously considered in making K fertilizer recommendations. Extending the sampling time from 1 to 3 weeks after the harvesting of rice to stabilize the effects of straw incorporation may help achieve a more accurate evaluation of soil available K.     

水钾耦合对花生生理性状及产量的影响

为明确不同水钾耦合对花生生理性状及生殖生长的影响,以‘花育25’为试验材料,采用水分[土壤含水量为35%(水分胁迫,W1)、50%(轻度水分胁迫,W2)、65%(水分适中,W3)、80%(水分过量,W4)田间持水量]和钾肥[0 g(K2O)·kg~(-1)(土)(缺钾,K0)、0.15 g(K2O)·kg~(-1)(土)(低钾,K1)、0.30 g(K2O)·kg~(-1)(土)(中钾,K2)、0.45 g(K2O)·kg~(-1)(土)(高钾,K3)]2因素4水平随机区组设计,通过遮雨棚盆栽试验探讨不同水钾耦合下花生叶片保护酶活性在结荚期后期的差异,以及生殖生长的差异,为干旱半干旱地区花生的高效水肥管理技术提供一定的理论依据。结果表明,水分对花生叶片相对含水量和叶绿素含量的影响极显著,叶片含水量对叶绿素有明显的稀释作用,随灌水量的增加叶片相对含水量(RWC)和叶绿素含量呈现出相反的变化趋势,两者为极显著负相关。水分和钾肥对超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性均存在显著或极显著的正交互效应。3种酶对不同的逆境响应不同,SOD活性在缺钾(K0)或高钾(K3)条件下升高明显,POD酶在水分胁迫(W1)或K3时升高极显著,CAT酶在W1或K0时升高显著。随土壤含水量的升高,叶片CAT活性迅速下降,且与叶绿素含量呈极显著正相关,说明CAT在花生结荚期后期可减缓叶绿素降解,延长叶片功能期。钾肥和灌水对单株开花总量的影响分别达显著和极显著水平,施钾肥能显著推迟始花时间,而减少灌水量能提前终花时间。在中钾(K2)时各水分处理有效花量和有效花率均处于较高水平。在水分适中(W3)时,钾肥对单粒仁重有促进作用,水分轻度胁迫(W2)也有利于单粒仁重的增加。单株荚果数显著增加和双仁果率提高是水分效应增产的重要原因。以中水中钾W3K2处理花期最短(25 d)、有效花率最大,达51.0%,籽仁产量最高。     

Potassium‐fertilizer management in winter oilseed‐rape production in China

Optimal potassium (K) fertilization is beneficial for oilseed‐rape (Brassica napus L.) yield and quality. However, the discrepancy between the high K demand of winter oilseed rape and low soil fertility and insufficient potassium input has limited the sustainable development of oilseed‐rape production. A series of on‐farm experiments in the key winter oilseed‐rape domains of China was conducted from 2004 to 2010 to evaluate K‐fertilizer management for winter oilseed rape. Currently, the average NH₄OAc‐extractable K content in the 0–20 cm soil layer is 89.1 mg kg^–1 indicative of “slight deficiency”. In addition, farmers in China usually fail to use sufficient K fertilizer in oilseed‐rape production, the average mineral‐potassium‐fertilizer input in 2010 being only 35 kg K ha^–1, far lower than the recommended rate of potassium for winter oilseed rape. Adequate potassium fertilization significantly raises seed yield. The average yield‐increase rate for the major production regions due to K‐fertilizer application was 18.5%, and the average K fertilizer–use efficiency 36.1%. Based on the negative correlation between yield response to potassium fertilization and available soil K content, a soil‐K‐test index was established for winter oilseed rape with a threshold value for NH₄OAc‐extractable soil K of 135 mg kg^–1. When available soil K‐content is below this threshold value, more K fertilizer should be applied to achieve high seed yield and to increase soil fertility. The major challenge for K‐fertilizer management in winter oilseed‐rape production in China will be to guide farmers in the different regions in making reasonable use of K fertilizer through soil K‐testing technology in order to maintain both seed yield and soil fertility.     

Organic‐carbon fractions in an agricultural topsoil assessed by the determination of the soil mineral surface area

According to recent conceptual models, the organic carbon (OC) of soils can be divided into OC fractions of increasing stability from labile free OC to resistant OC associated with the soil mineral phase. In this study, we present a method for quantifying two OC fractions based on soil aggregate–size fractionation and the N₂ gas–adsorption method. For this purpose, we analyzed soil material of the plow layer of a Haplic Chernozem subjected to different fertilizer treatments (no fertilizer, mineral fertilizer, mineral and organic fertilizer). The total organic‐C concentration (TOC) and the clay content of the different size fractions were determined as well as the specific surface area (SSA_mineral) and the sample pore volume after thermal oxidation (OC‐free). The TOC of the different soil‐aggregate fractions was linearly related to SSA_mineral. Clay‐associated OC and nonassociated OC fractions of the different soil samples were quantified using two methods based on the OC surface loading at the clay fraction. The application of organic fertilizer increased the amount of nonassociated OC but hardly affected the concentration of clay‐associated OC. This finding agrees with previous studies on C dynamics in soils and indicates a finite capacity of soil materials to sequester OC. Even without any addition of organic fertilizer, the mineral phase of the analyzed soil material appears to be C‐saturated.     

Effect of potassium fertilization on soil potassium pools and rice response in an intensive cropping system in China

In order to assess the changes in soil K pools as affected by K‐fertilizer application and the impact of the changes on K balance, grain yield, and K uptake, an experiment was conducted in Central Zhejiang Province, E China, in a continuous double‐cropping rice system. Two sites were selected: (1) the Agricultural Research Institute of Jinhua (ARI) where soil is calcareous and (2) the Shimen Research Farm (SM) where soil is acidic. Eight consecutive crops were grown (1997–2000) in ARI and five consecutive crops (1998–2000) at SM. Treatments included unfertilized control (CK) and three different fertilizer treatments (NP, NK, and NPK). Potassium extracted by ion‐exchange resin decreased from 26 mg kg^–1 to 5–10 mg kg^–1 after eight consecutive seasons of growth at the ARI site. Addition of 100 kg K ha^–1 for each rice crop was not enough to maintain initial K availability, especially in the calcareous soil at ARI site. In treatments with K, a small increase in readily available K was observed only in SM soil. The K extracted by HNO₃ also decreased significantly in the treatments without K addition and was increased slightly in the treatments with K application. In the NP treatment, the decrease in HNO₃‐K was several times greater than resin‐K, indicating that nonexchangeable K may be the major source of K supply to rice. Soil K depletion was greater for hybrid rice than for inbred rice, and this difference in K demand should be taken into account in developing fertilizer recommendations for irrigated rice.     

Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations

The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m^–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)^–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)^–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)^–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)^–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)^–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m^–1 may have a deleterious effect on maize growth.     

Reaktion der Zuckerrübe (Beta vulgaris var. altissima) auf die Kaliumdüngung – ein 20‐jähriger Feldversuch

Response of sugar beet ( Beta vulgaris var. altissima ) to potassium fertilization—a 20‐year field experiment A long‐term fertilizer experiment was performed to develop a K fertilization strategy to achieve highest extractable sugar yields (BZE). Sugar beet was grown in a crop rotation with wheat and barley on an alluvial soil (clayic silt) in Lower Saxony with annual recycling of straw and beet tops, respectively. Since 1983, the treatments were as follows: 1) K fertilization with 0, 29, 58, 87,174, and 524 kg K ha^–1 a^–1 corresponding to 0, 0.5, 1, 1.5, 3, and 9 times the average annual K removal by the marketable products of the crop rotation—since 1995, the two highest treatments (3 and 9 times the removal) received only 174 kg ha^–1 every third year; 2) K fertilization according to the average K removal, given each year (58 kg K ha^–1) or every third year (174 kg ha^–1) to sugar beet; 3) annual K fertilization of 87 kg K ha^–1 (1.5 times the removal) applied in autumn or spring, respectively; 4) annual K fertilization, applied as mineral fertilizer or as organic material (recycling of grain and straw or root and leaves); 5) application of 29 kg NaCl ha^–1 to sugar beet supplemental to a yearly application of 58 kg K ha^–1. Both root yield and soil concentration of lactate‐soluble K increased with K fertilization up to the highest K treatment. The extractable sugar content reached a maximum at a yearly application of 174 kg K ha^–1. Averaged over years, the extractable sugar yield (BZE) increased up to the highest K application. The time of K application (autumn or spring) and the source of K (mineral fertilizer or organic material) had no effect on BZE. An additional fertilization with NaCl increased BZE only slightly in single years. Low‐grade muriate of potash containing 33% K and 3% Na can thus be used. The economically optimal K‐fertilization rate was 174 kg K ha^–1 given once in the crop rotation to sugar beet. A soil K concentration of about 110 mg (kg soil)^–1 (lactate‐extractable K) is sufficient in this soil to achieve a high BZE.     

三种有机无机复混钾肥钾素的释放与供应特征

在实验室条件下,通过间歇淋洗培养和土壤培养试验研究了不同有机无机复混钾肥钾素的释放与供应特征。在等化肥钾量投入条件下,与化学钾肥相比,供试的3种有机无机复混钾肥没有显著影响到钾素在石灰性土壤中的释放规律;土壤速效钾含量有所增加,糖渣系、糠醛渣系和污泥系有机无机复混钾肥处理的土壤速效钾含量分别比化学钾肥处理增加了13.5%、12.7%和1.6%。与化学钾肥处理相比,糖渣系、糠醛渣系有机无机复混钾肥处理的钾素(K)固定量分别减少了42和39 mg/kg。     

Current potassium‐management status and grain‐yield response of Chinese maize to potassium application

The great achievement of the development of intensive in agriculture in China can be partly attributed to substantial increases in mineral‐nutrient application. However, whereas farmers tend to apply high levels of nitrogen (N) and phosphorus (P) application of potassium (K) has been neglected. A greater understanding of the relationship between maize (Zea mays L.) grain yield and K‐application rate is thus required to provide an improved rationale for K fertilization for farmers in the various agro‐ecological regions of China. In this study, a total of 2765 farmers' survey data and 3124 on‐farm experiments across major maize agro‐ecological regions in China were collected and evaluated for farmers' K‐management status and to determine grain‐yield response to K application. Nationally, the average K‐application rate on farms was 26 kg K ha^–1 and varied from 0 to 158 kg K ha^–1, with a coefficient of variation of 107%, but the applied K‐fertilizer rates were not related to grain yield. Maize grain yields at recommended K rates increased by 14.0%, 14.7%, 19.4%, and 4.3% in Northeast China, North China Plain, Southwest China, and Northwest China, respectively, compared to zero K fertilization (K₀). Increased yield due to K fertilization (IY_max, difference between maximum yield across all treatments and K₀‐treatment yield for each experiment) averaged 1.4 t ha^–1 but varied widely in different agro‐ecological regions. Soil extractable K (NH₄OAc‐K) and intercounty variation resulted in large variation in IY_max in agro‐ecological regions, as did other factors, such as use of particular maize hybrids, soil types, or years in different regions.     

吉林省玉米施钾增产效应及区域差异

【目的】本研究利用测土配方施肥项目田间试验的大样本数据,分析吉林省玉米施钾增产效应在生态区及县域尺度上的差异,为促进玉米高产稳产和钾肥资源高效利用提供参考。【方法】基于2005-2013年吉林省玉米"3414"田间试验中推荐施钾(N2P2K2)和不施钾(N2P2K0)处理,分析生态区及县域尺度上玉米施钾的产量反应、农学利用率和肥料贡献率,建立玉米施钾产量、钾肥贡献率与基础产量之间的关系,从而评估吉林省玉米施钾的增产效应及区域差异。【结果】不施钾条件下,吉林东部湿润山区、中部半湿润平原区和西部半干旱平原区玉米的基础产量平均分别为8.44 t/hm^2 (3.29~14.5 t/hm^2)、9.45 t/hm^2 (3.77~15.3 t/hm^2)和8.11 t/hm^2(3.89~12.84 t/hm^2)。施用钾肥显著提高三大区域玉米产量,东、中、西部平均分别增产1.31 t/hm^2 (18.1%)、1.06t/hm^2 (12.2%)和1.30 t/hm^2 (17.4%)。推荐施钾条件下,东、中、西部玉米施钾的平均农学利用率分别为19.7、14.6和20.2 kg/kg,平均肥料贡献率分别为13.9%、10.2%和13.6%。统计分析显示,三大区域之间玉米施钾的增产量无显著差异,东部增幅显著高于中部,农学利用率和肥料贡献率东部也显著高于中、西部。回归分析发现,各区域玉米的施钾产量均与基础产量呈极显著正相关关系,符合线性模型,东部为y=0.769 x+3261 (R^2=0.616^**),中部为y=0.883 x+2158 (R^2=0.757^**),西部为y=0.873 x+2328 (R^2=0.637^**);而钾肥贡献率均与基础产量呈极显著负相关关系,符合对数模型,东部为y=–28.4 ln(x)+270.1 (R^2=0.348^**),中部为y=–15.9 ln(x)+156.1 (R2=0.172^**),西部为y=–16.3 ln(x)+160.6 (R2=0.123^**)。随土壤基础供钾能力的提高,东部玉米施钾产量的增幅和钾肥贡献率的降幅明显高于中、西部。【结论】吉林省玉米的钾肥管理应根据区域土壤钾素状况、自然气候条件和钾肥效应进行合理配置,现阶段应适当增加东部湿润山区玉米生产的钾肥资源配置,提高土壤供钾能力,促进玉米高产稳产。     

长期秸秆还田提升稻麦轮作系统土壤供钾容量和强度

[目的]农作物秸秆中含有丰富的钾素,秸秆还田不仅为植物生长提供钾素,还可以补充农田土壤钾库容.本研究利用动力学模型,评估长期秸秆还田对土壤供钾能力的影响.[方法]基于稻麦轮作制长期秸秆还田定位试验,设置4个处理:秸秆不还田、不施肥(CK);不施肥、每季秸秆还田量为6000 kg/hm2(RS);施化肥、秸秆不还田(NP...     

Mineral‐nutrient synergism and dilution responses to nitrogen fertilizer in field‐grown maize

Nitrogen (N)‐fertilizer applications to field‐grown maize may result in a dilution response whereby essential mineral‐element concentrations in shoots would decrease as shoot‐dry‐matter accumulation increased. To investigate this, the effect of N‐fertilizer treatments (no N or fertilizer rate based upon 5.3 or 8.5 t ha^–1 yield goal) on maize (Zea mays L.) shoot dry weight and shoot mineral concentrations (N, P, K, S, Mg, Ca, and Mn) at the sixth leaf (V6), twelfth leaf (V12), and tassel (VT) development stages were investigated in a 2‐year study conducted at Brookings, South Dakota (USA). With increasing N‐fertilizer application rates, shoot dry weight was greater and shoot P and K concentrations decreased. A possible explanation of this dilution response is that planting‐time P and K fertilizers, which were applied in a band near the seed furrow, may have enhanced the uptake of P and K in a manner that was independent of N‐fertilizer treatments. Increased shoot‐dry‐weight production due to the application of N fertilizers, if P and K uptake were similar across N‐fertilizer treatments, would lead to decreased shoot P and K concentrations in N‐sufficient compared with N‐deficient plants. Conversely, N‐fertilizer‐induced increases in shoot dry weight were accompanied by increased shoot concentrations of N, Ca, and Mn. This synergistic response between dry‐weight accumulation and shoot N concentration was present at all leaf developmental stages studied, while that for Ca was present only at VT. Thus, N fertilizer applications that increase shoot dry weight can affect the dilution and synergistic responses of specific mineral nutrients in maize shoots. Crop developmental stage as well as the location of these specific mineral nutrients in the soil profile might play important roles in mediating these responses.     

Calibration of the mehlich 3 soil test for potassium using leaf analyses and potassium deficiency symptoms in cotton plants

Abstract

A new calibration of the Mehlich 3 soil test for potassium (K) is proposed for the Mississippi Delta area, based on leaf analyses and K deficiency symptoms in cotton plants. The calibration reflects the need to supply adequate K concentrations to plants during the fruiting period of greatest K demand. The lowest levels and highest percent of sites exhibiting K‐deficiency symptoms were associated with the fifth week of flowering; or at the peak bloom stage of plant growth. The fifth week of flowering was selected to base soil and plant evaluations for K needs. A 1.5% leaf K level was selected as the critical leaf K level (the level that plants experience a nutrient deficiency and yield reductions), based on visual leaf K‐deficiency symptoms observed in plants 95% of the time. Leaf K concentrations below 1.51% identifies K‐deficiency symptoms in the upper leaves through eight weeks of flowering. A simplified equation [Topsoil K (lb/A) = 480 + 5 x CEC (Milliequivalents/100g soil)] defines critical soil test K concentrations with respect to the cation exchange capacity (CEC) in soils. This equation can be used to determine present topsoil K needs for cotton in the Mississippi Delta area based on a 1.5% critical leaf K level during the fifth week of flowering.     

枸溶性钾肥的水稻肥效

通过盆栽试验研究了5种钾肥[粉碎性钾矿粉(K1)、全部枸溶性钾肥(K2)、含25%水溶性钾的枸溶性钾肥(K3)、含50%水溶性钾的枸溶性钾肥(K4)和硫酸钾(K5),施钾量均为K2O 150 mg/kg]及其施用量(0.5K2、K2、1.5K2和2K2,施钾量分别为K2O 75、150、225和300 mg/kg)和配施(0.5K2+0.5K5)对水稻产量、钾素吸收量以及土壤速效钾含量的影响。研究结果表明,与不施钾相比,施钾肥处理(除K1外)均显著提高水稻产量、钾素吸收量以及土壤速效钾含量。在相同施钾量下,随着肥料水溶性钾比例的增加,水稻产量、钾素吸收量以及土壤速效钾含量表现为先上升后下降的趋势,其中水稻产量、钾素吸收量以及土壤速效钾含量以K4(分别为240.90 g/盆、2.60 g/盆、75.4 mg/kg)和K3(分别为234.86 g/盆、2.24 g/盆、73.9 mg/kg)处理最高。与水溶性钾肥(K5)处理相比,K4和K3处理均显著提高了水稻产量、钾素吸收量和土壤速效钾含量,分别提高了9.35%和6.61%、40.43%和21.26%、22.01%和19.58%(P0.05)。水稻产量、钾素吸收量及土壤速效钾含量随同一种枸溶性钾肥(K2)施用量的增加而增加,以2K2最高。综合结果表明,在相同施钾量下,含25%~50%水溶性钾的枸溶性钾肥(K4和K3)对水稻的增产效果最佳,而全部枸溶性钾肥在2倍施钾量下可获得相同增产效果。     

Response of soil exchangeable and crop potassium concentrations to variable fertilizer and cropping regimes in long-term field experiments on different soil types

Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha^?1 year^?1 in rotation I, compared with 10–26 kg ha^?1 year^?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (K_ex). Significant depletion of K_ex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.     

The relationship of soil and leaf nutrients to rice leaf oranging

A symptom called leaf‐oranging, indicating a deficiency of many nutrients, occurs in paddy rice (Oryzasativa L.) when production expands into some upland soils. Rice (Gui Chou cv.) was grown in culture pots in a flooded, weathered, upland soil (Nacogdoches) and compared to rice growth in a flooded soil currently used for paddy rice production (Dacosta) in Texas to understand the soil and plant factors involved in leaf‐oranging. Fertilizer rates of 0, 10, and 100 mg N/kg as (NH₄)₂SO₄ were applied to each soil along with phosphorus (P) and potassium (K) fertilizer. The orange Leaf Index (OLI), a measure of leaf‐oranging, was determined weekly and increased to 60–70% for plants grown in the upland soil but its progression was delayed by higher N treatments. No leaf‐oranging was observed in the paddy soil. The soil evoking leaf‐oranging was low in silicon (Si) and high in iron (Fe). In addition, analysis of leaves from these plants showed 19–25% higher leaf ammonium‐nitrogen (NH₄‐N), 9–137% higher manganese (Mn) levels and lower total N:NH₄ concentration compared to normal rice leaves four weeks after transplanting. This inferred that leaf‐oranging probably was associated with some degree of NH₄‐N toxicity and antagonism with K. Leaf‐oranging was also associated with low calcium (Ca) assimilation or Ca uptake inhibition because of the heavy Fe‐oxide coating of the roots of the affected rice plants. In this experiment, leaf‐oranging was not associated with toxic levels of Fe or Mn.     

Effect of long‐term fertilization and manuring on potassium release properties in a Typic Ustochrept

A long‐term fertilizer experiment, over 27 years, studied the effect of mineral fertilizers and organic manures on potassium (K) balances and K release properties in maize‐wheat‐cowpea (fodder) cropping system on a Typic Ustochrept. The treatments consisted of control, 100% nitrogen (100% N), 100% nitrogen and phosphorus (100% NP), 50% nitrogen, phosphorus, and potassium (50% NPK), 100% nitrogen, phosphorus, and potassium (100% NPK), 150% nitrogen, phosphorus, and potassium (150% NPK), and 100% NPK+farmyard manure (100% NPK+FYM). Nutrients N, P, and K in 100% NPK treatment were applied at N: 120 kg ha^—1, P: 26 kg ha^—1, and K: 33 kg ha^—1 each to maize and wheat crops and N: 20 kg ha^—1, P: 17 kg ha^—1, and K: 17 kg ha^—1 to cowpea (fodder). In all the fertilizer and manure treatments removal of K in the crop exceeded K additions and the total soil K balance was negative. The neutral 1 N ammonium acetate‐extractable K in the surface soil (0—15 cm) ranged from 0.19 to 0.39 cmol kg^—1 in various treatments after 27 crop cycles. The highest and lowest values were obtained in 100% NPK+FYM and 100% NP treatments, respectively. Non‐exchangeable K was also depleted more in the treatments without K fertilization (control, 100% N, and 100% NP). Parabolic diffusion equation could describe the reaction rates in CaCl₂ solutions. Release rate constants (b) of non‐exchangeable K for different depth of soil profile showed the variations among the treatments indicating that long‐term cropping with different rates of fertilizers and manures influenced the rate of K release from non‐exchangeable fraction of soil. The b values were lowest in 100% NP and highest in 100% NPK+FYM treatment in the surface soil. In the sub‐surface soil layers (15—30 and 30—45 cm) also the higher release rates were obtained in the treatments supplied with K than without K fertilization indicating that the sub‐soils were also stressed for K in these treatments.