Low risks of toxicity from boron fertiliser in oilseed rape–rice rotations in southeast China

Yields in intensive rice (Oryza sativa L.) -based rotations in Asia are stagnating or declining because of decreasing nutrient availability and depletion of soil nutrient reserves. In the rape (Brassica napus L.)–rice–rice cropping rotation of southeast China, where boron (B) deficiency is widespread and B fertiliser is needed to correct it, our objective was to evaluate the risks of fertiliser-induced B toxicity in oilseed rape and in rice. Response of oilseed rape to B fertiliser application at rates up to 6.6 kg B ha-1 was studied in seven field experiments on three contrasting soils of Zhejiang province, alluvial, red and blue-purple soils. The effects of up to 3.3 kg B ha-1 in 1 year, 6.6 kg B ha-1 in 2 years or 9.9 kg B ha-1 in 3 years were studied on oilseed rape and the one or two rice crops grown immediately after rape in each annual crop rotation. Soils varied in initial hot CaCl2-extractable B in the 0–15-cm layer from 0.24 to 0.99 mg kg-1. At the stem elongation stage of oilseed rape, 3.3 kg B ha-1 depressed shoot dry matter on soils with low clay and organic matter content. However, the subsequent effects of high fertiliser B on seed yield were minimal even at 6.6 kg B ha-1. Moreover, the application of a total of 6.6 or 9.9 kg B ha-1 as successive annual applications of 3.3 kg B ha-1 to oilseed rape generally had no negative effect on seed yield of oilseed rape. The single exception was on a sandy alluvial soil where a total of 6.6 kg B ha-1 in 2 years slightly depressed seed yield of oilseed rape. Grain yields of rice crops grown in rotation after oilseed rape were unaffected by B applications up to 6.6 kg ha-1. The minimal effects of a total of 6.6 kg B ha-1 applied over 2 years on seed yield were consistent with the modest increase in hot CaCl2-extractable B levels. It is concluded that there is limited risk of B toxicity from the use of borax fertiliser at up to 4–8 times recommended rates in rape–rice cropping rotations in southeast China. The low risk of B toxicity can be attributed to the relatively high B removal in harvested seed, grain and stubble, the redistribution of fertiliser B by leaching in the 0–60 cm layer and to B sorption.     

复合锌镍铁氧体纳米粉体材料的制备实验

以硫酸盐为原料，添加NaOH溶液和NaHCO3粉末，先制备碱式碳酸盐前驱体，350℃空气中焙烧1 h后，制备出复合锌镍铁氧体纳米晶体. 经XRD和TEM分析，粒径约为30 nm，粒度较均匀. 通过改变原料中锌盐与镍盐的配比，制备出Zn0.9Ni0.1Fe2O4, Zn0.8Ni0.2Fe2O4, Zn0.7Ni0.3Fe2O4, Zn0.6Ni0.4Fe2O4和Zn0.5Ni0.5Fe2O4 五种纳米粉.     

298 K时三元体系MeSO4-(NH4)2SO4-H2O的相平衡

用等温溶解平衡法研究了298 K时MeSO4-(NH4)2SO4-H2O三元体系的溶解度,并绘制了平衡相图. 结果表明,在MnSO4-(NH4)2SO4-H2O体系中,有MnSO4×H2O, (NH4)2Mn(SO4)2×6H2O和(NH4)2SO4 3条饱和曲线,组成为MnSO4×H2O和(NH4)2Mn(SO4)2×6H2O及(NH4)2Mn(SO4)2×6H2O和(NH4)2SO4的2个共饱和点,以及平衡固相为(NH4)2SO4, (NH4)2Mn(SO4)2×6H2O和MnSO4×H2O的3个纯盐结晶区. 在ZnSO4-(NH4)2SO4-H2O体系中,有(NH4)2Zn(SO4)2×6H2O, ZnSO4×7H2O与(NH4)2SO4 3条饱和曲线,组成为(NH4)2Zn(SO4)2×6H2O和ZnSO4×7H2O及(NH4)2SO4和(NH4)2Zn(SO4)2×6H2O的2个共饱和点,以及平衡固相为(NH4)2Zn(SO4)2×6H2O, ZnSO4×7H2O和(NH4)2SO4的3个纯盐结晶区. 在(NH4)2SO4-FeSO4-H2O体系中,有(NH4)2Fe(SO4)2×6H2O, FeSO4×7H2O和(NH4)2SO4的3条饱和曲线,组成为(NH4)2Fe(SO4)2×6H2O和FeSO4×7H2O及(NH4)2Fe(SO4)2×6H2O和(NH4)2SO4的2个共饱和点,以及平衡固相为(NH4)2Fe(SO4)2×6H2O, FeSO4×7H2O和(NH4)2SO4的3个纯盐结晶区. 研究结果既为含Fe2+, Mn2+和Zn2+溶液的复盐沉淀深度净化提供了理论指导,同时也为四元体系的研究奠定了基础.     

助剂对苯加氢Ru系催化剂催化性能的影响

以三氯化钌(RuCl3)、硫酸锌(ZnSO4)和硫酸亚铁(FeSO4)为原料,采用共沉淀法制备Ru-Zn及Ru-Fe-Zn催化剂,研究了苯选择加氢制环己烯过程中助剂Zn和Zn/Fe对Ru系催化剂催化加氢性能的影响,并利用透射电镜等对催化剂进行表征。结果表明:Ru-Zn催化剂粒子清晰较为分散,Ru-Fe-Zn催化剂粒径变大,比表面积变小;Ru系催化剂中加入助剂Zn,Ru/Zn摩尔比为7时,环己烯选择性较高,加入第三组分Fe,Zn/Fe摩尔比为10,环己烯选择性进一步提高;Ru-Fe-Zn催化剂具有很好的催化活性和稳定性,苯转化率达54.9%,环己烯选择性达81.8%。     

Needs for controlled-availability micronutrient fertilizers

Use of micronutrients for agronomic and horticultural crops has increased markedly in recent years. Increased use is related to higher nutrient demands from more intensive cropping practices and also from farming marginal lands. Most of the fertilizers used to correct micronutrient deficiencies are water- soluble inorganic sources or soluble organic products such as synthetic chelates or natural organic complexes. These fertilizers may react with soil to decrease their availability to plants. The rates of such chemical reactions may differ considerably with each micronutrient fertilizer and soil environment.Recommended micronutrient rates have been based on results of numerous experiments, and these rates vary with crop, soil, and other factors. The usual application rates (on an elemental basis) range from 1 to 10 kg ha^–1 for Cu, Fe, Mn and Zn; < 1 kg ha^–1 for B; and < 100 g ha^–1 for Mo.Because the metallic micronutrients (Cu, Fe, Mn, and Zn) generally are sorbed strongly by soil clays, they do not move significantly in soil. Hence, they are not leached readily from the zone of application to lower soil depths or into groundwaters. Mobility of these micronutrient cations is higher in sandy soils, especially with high leaching conditions. Therefore, their movement out of the root zone is possible under some situations. Significant residual effects of soluble Cu and Zn sources greatly reduce the need for controlled-availability Cu and Zn products. Controlled-availability Fe and Mn fertilizers have not been effective because the rapid oxidation of Fe and Mn and reactions with soil reduce their availability upon release.Because soluble B fertilizers form boric acid molecules in soil, they are mobile and subject to leaching conditions. While mobility of B is less than that of NO ₃ ^- -N in soil, field results have demonstrated loss of applied B from the root zone in sandy soils. Slightly soluble B fertilizers, such as colemanite and ulexite, and fritted B products (powdered glass-like materials whose solubility is controlled by particle size) have been used in sandy soils for some crops.Molybdenum requirements are much lower than those of the other micronutrients. Deficiencies generally are corrected by liming the soil or by seed or foliar applications, so there is little need for controlled-availability Mo fertilizers.Little research has been conducted on controlled availability micronutrient fertilizers. While fritted products are considered in this category, they are difficult to handle and only may be of value in supplying B under specific conditions. Coating soluble granular micronutrient fertilizers also has been attempted, but there are few reported results of their relative effectiveness in comparison with conventional fertilizers and application methods. New micronutrient products may be needed for specific conditions such as greenhouse-culture or container-grown crops, but plant needs also may be met by multiple applications of soluble sources.     

Increasing nutrient use efficiency in rice with changing needs

The use of N fertilizer in Asia has increased from 24 to 39% of the world's total consumption between 1973 and 1987/88. Approximately 60% of the N fertilizer consumed in Asia is used on rice (Oryza sativa L.). However, the N applied to rice, primarily as urea, is not effectively utilized by the crop. Ammonia volatilization is recognized as a major mechanism of N loss, causing ineffective N utilization. Basal incorporation of urea without standing water; deep placement of urea; and modification of urea with algicides, urea inhibitors or coatings are strategies to reduce ammonia loss. Loss of N by nitrification-denitrification may be a serious problem particularly when soil is dried between rice crops, then flooded for the subsequent rice crop. The use of organic N sources, such as green manure and organic manures, as partial substitutes of inorganic N fertilizer is receiving renewed research interest.The use of P fertilizers for rice is most necessary on Oxisols and Ultisols with high P-fixing capacity. Phosphate rock and partially acidulated phosphate rock are alternatives to soluble P sources used on these soils. Response to K is normally highest on light-textured soils. The limited available information suggests that in lowland rice-upland crop rotations, K fertilizers should be applied to the non-rice crop. Zinc deficiency can be overcome through (a) use of varieties more tolerant to zinc deficiency, (b) application of zinc sulfate, and (c) dipping seedling roots in a zinc oxide suspension.Increasing use of S-free fertilizers, intensive cropping, and use of high yielding rice varieties have led to S deficiency in many rice growing countries. Sulfur deficiency can be corrected by applying S-containing materials even with elemental S. Residual effects have also been reported even at a low rate of 20 kg S/ha. Thus, S does not need to be applied every season.To address the unresolved integrated nutrient management issues, both strategic and applied research are required on interacting soil-plant-water-nutrient-climate processes. Long-term sustainability is one of the parameters that must be considered in evaluating the desirability of alternative rice technologies.Paper presented at the Fertilizer Asia Conference and Exhibition, 15–18 October 1989, Manila.     

Evaluation of mixed cation–anion exchange resins as extractants for potentially available micronutrients in tropical soils

We examined the possibility of using mixed cation–anion exchange resinspre-treated with two organic acid ligands, acetate (R-ACET) and tartrate(R-TART) for extraction of phytoavailable Fe, Mn, Cu and Zn using theconventional diethylenetriaminepentaacetic acid (DTPA) as a referenceextractant. In each soil, variable amounts of Fe, Mn, Cu and Zn were extractedby the different extractants. The amounts of Fe, Mn, Cu and Zn did not followprediction based on stability constants of metal-organic complexes. The R-ACETwas a slightly better predictor of soybean uptake of Cu and Mn, and dry matter(DM) yield responses to Cu than either DTPA or R-TART, though differencesbetweenR-ACET and DTPA were not significant. However, soybean DM yield response to Znwas best predicted by DTPA, while Zn uptake correlated more strongly with DTPAthan R-ACET and R-TART extractable Zn. These results suggest that R-ACET may beused as an alternative extractant for Fe, Mn, Cu and Zn in strongly weatheredtropical soils, but it was not superior to DTPA.     

The value of poultry manure for wetland rice grown in rotation with wheat

Poultry manure applied alone or in combination with urea at different N levels was evaluated as a N source for wetland rice grown in a Fatehpur loamy sand soil. Residual effects were studied on wheat which followed rice every year during the three cropping cycles. In the first year, poultry manure did not perform better than urea but by the third year, when applied in quantities sufficient to supply 120 and 180 kg N ha^–1, it produced significantly more rice grain yield than the same rates of N as urea. Poultry manure sustained the grain yield of rice during the three years while the yield decreased with urea. Apparent N recovery by rice decreased from 45 to 28% during 1987 to 1989 in the case of urea, but it remained almost the same (35, 33 and 37%) for poultry manure. Thus, urea N values of poultry manure calculated from yield or N uptake data following two different approaches averaged 80, 112 and 127% in 1987, 1988 and 1989, respectively. Poultry manure and urea applied in 1:1 ratio on N basis produced yields in between the yields from the two sources applied alone. After three cycles of rice-wheat rotation, the organic matter in the soil increased with the amount of manure applied to a plot. Olsen available P increased in soils amended with poultry manure. A residual effect of poultry manure applied to rice to supply 120 or 180 kg N ha^–1 was observed in the wheat which followed rice and it was equivalent to 40 kg N ha^–1 plus some P applied directly to wheat.     

Evaluation of levels and methods of zinc application to rice in sodic soils

Field experiments were conducted in zinc-deficient sodic soil to study the effect of levels and methods of zinc fertilization on yield, concentration and uptake of zinc by rice. Zinc was incorporated in the soil at the rate of 0, 5.6, 11.2 and 22.4 kg Zn per ha as zinc sulfate; sprayed on the plants at 1% and 2% zinc sulfate solution; and roots of rice seedlings were dipped in 2% and 4% ZnO suspensions in water. Grain yield, zinc content and its uptake increased in all the experiments up to 22.4 kg Zn per ha. Soil applied zinc was significantly correlated with yield of rice (r = 0.80^**) and zinc uptake (r = 0.89^**). Zinc content in 45-day old plants gave a significantly higher correlation with grain yield (r = 0.84^**) than the zinc content of rice straw and grain at maturity. Roots of rice seedlings dipped in 2% or 4% zinc oxide suspension in water were not only comparable with soil application of Zn at 5.6 and 11.2 kg Zn per ha, but also proved to be more economical for sodic soils showing moderate zinc deficiency.     

Efficient and flexible management of nitrogen for rainfed lowland rice

Nitrogen (N) is the most limiting nutrient in the rainfed lowland rice soils of Laos. Indigenous N supply of these soils was low, ranging from 12 to 64 kg N/ha and was correlated with soil organic matter content. Resource-poor farmers and erratic rainfall are characteristic features of Lao rainfed lowland rice systems. Such climatic and economic factors influence farmers' ability to apply N at the recommended time and therefore efficient and flexible recommendations are required. Research on N management focused on the timing of N applications. Splitting the N recommendation into three equal splits at transplanting, active tillering and panicle initiation increased yields by 12% compared to a single application at transplanting. Agronomic efficiency (AE = kg increase in grain yield/kg N applied) was further increased by 9 kg/kg N if a higher proportion of the N was applied during active tillering and panicle initiation when crop N demand is high. Under conditions of suboptimal N supply, the first N application can be applied from transplanting to 30 d after transplanting without lowering grain yield or AE (for medium duration varieties transplanted 1 month after sowing). The last N application can be made between two weeks before to one week after panicle initiation without lowering yield. These findings provide the basis for an efficient (AE of 20 to 25 kg/kg N) and flexible N management strategy for Lao rainfed lowland rice under conditions of suboptimal N supply.     

Comparative study of a Zn-enriched post-methanation bio-sludge and Zn sulfate as Zn sources for a rice–wheat crop rotation

A field experiment was carried out during 2005–2007 to compare the efficacy of Zn-enriched post-methanation bio-sludge (ZEMB, 4.4% Zn) and ZnSO₄ (ZSH, 22% Zn) as Zn source to rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation. A new Zn source (ZEMB) contained most of the Zn (98.4% of total Zn) in citrate-soluble form as compared to ZSH which had all Zn in water-soluble form. Chemical speciation of Zn in the aqueous solution of both fertilizers revealed that 85.8% of water-soluble Zn present in ZEMB existed as complexes of dissolved organic matter. In the field experiment, application of ZEMB at 5 kg Zn ha⁻¹ to I-year rice increased the grain yields of rice and wheat in both years significantly over the control while application of ZSH at 5 kg Zn ha⁻¹ to I-year rice increased only grain yields of I- and II-year rice (first year and second year, respectively). The magnitude of increase in grain yields was also higher with ZEMB than with ZSH. Application of ZEMB at 5 kg Zn ha⁻¹ to I-year rice maintained significantly higher concentrations of Zn in the flag leaves of rice and wheat in both years, in the grains of I- and II-year rice, and also in the straw of I-year rice than ZSH applied at an equivalent dose. Total Zn uptake values for I-year rice and wheat and II-year rice, apparent recovery of applied Zn and also DTPA-extractable Zn in soil were significantly higher with ZEMB at 5 kg Zn ha⁻¹ than with ZSH at an equivalent dose.     

Multiple benefits of manure: The key to maintenance of soil fertility and restoration of depleted sandy soils on African smallholder farms

Manure is a key nutrient resource on smallholder farms in the tropics, especially on poorly buffered sandy soils, due to its multiple benefits for soil fertility. Farmers preferentially apply manure to fields closest to homesteads (homefields), which are more fertile than fields further away (outfields). A three-year experiment was established on homefields and outfields on sandy and clayey soils to assess the effects of mineral nitrogen (N) fertilizer application in combination with manure or mineral phosphorus (P) on maize yields and soil chemical properties. Significant maize responses to application of N and manure were observed on all fields except the depleted sandy outfield. Large amounts of manure (17 t ha⁻¹ year⁻¹) were required to significantly increase soil organic carbon (SOC), pH, available P, and base saturation, and restore productivity of the depleted sandy outfield. Sole N as ammonium nitrate (100 kg N ha⁻¹) or in combination with single superphosphate led to acidification of the sandy soils, with a decrease of up to 0.8 pH units after three seasons. In a greenhouse experiment, N and calcium (Ca) were identified as deficient in the sandy homefield, while N, P, Ca, and zinc (Zn) were deficient or low on the sandy outfield. The deficiencies of Ca and Zn were alleviated by the addition of manure. This study highlights the essential role of manure in sustaining and replenishing soil fertility on smallholder farms through its multiple effects, although it should be used in combination with N mineral fertilizers due to its low capacity to supply N.     

Surfactant-assisted removal of 2,4-dichlorophenol from soil by zero-valent Fe/Cu activated persulfate

The organic compounds contaminated soil substantially threatens the growth of plants and food safety. In this study, we synthesis zero-valent bimetallic Fe/Cu catalysts for the degradation of 2,4-dichlorophenol (DCP) in soils with persulfate (PS) in combination of organic surfactants and exploring the main environmental impact factors. The kinetic experiments show that the 5% (mass) dosage of Fe/Cu exhibits a higher degradation efficiency (86%) of DCP in soils, and the degradation efficiency of DCP increases with the increase of the initial PS concentration. Acidic conditions are favorable for the DCP degradation in soils. More importantly, the addition of Tween-80, and Triton-100 can obviously desorb DCP from the soil surface, which enhances the degradation efficiency of DCP in soils by Fe/Cu and PS reaction system. Furthermore, the Quenching experiments demonstrate that SO₄^-· and ·OH are the predominant radicals for the degradation of DCP during the Fe/Cu and PS reaction system as well as non-radical also exist. The findings of this work provide an effective method for remediating DCP from soils.     

Relationship between soil physical and chemical characteristics and ear-leaf concentration of P,K, Mg,Zn, Fe,Cu, Mn and relative yield of maize in soils derived from sedimentary rocks of South-Western Nigeria

In a four-season field experiment conducted in 18 locations covering two different ecological zones of the sedimentary forest soils of South-Western Nigeria, relationships were established by simple correlation between the ear-leaf content of P, K, Mg, Zn, Fe, Cu, Mn, relative yield of maize (RY), soil physical characteristics and soil nutrient status. Soil pH was strongly related to the relative yield, soil clay, available P, exchangeable Ca, K, Zn, and Mn in soils, P and Cu concentration in the ear-leaf.Organic matter did not appear to play a very significant role in nutrient supply or relate to nutrient element concentration in the ear-leaf and relative yield in soils that are relatively low in soil organic matter.Nitrogen was not determined. Phosphorus among all the elements determined seemed to have a high significant effect on Ca, K, Zn, Mn and RY. However, the effect on RY was negative. Manganese in both soil and ear-leaf had the highest negative significant relationship with yield in the zone.The multiple regression analysis indicated a relationship meaning that the soil physical and chemical properties and ear-leaf content of the elements P, K, Mg, Zn, Fe, Cu, Mn are important to maize cultivation in this zone. Hence consideration of a combination of soils and plant factors are essential before meaningful fertilizer recommendation can be made for maize in the zone under study.     

Acidulated pegmatitic mica: A promising new multi-nutrient mineral fertilizer

Scrap grade pegmatitic phlogopite mica contains 5–7% K (8% K₂O), 10–14% Mg (23% MgO), 1–2% Ca (2.9% CaO), 0.03% Mn and 109 ppm Zn. On acidulation upto 65% of K and Mg and 15–100% Mn and Zn were recovered. Less than 13% of Ca was recovered in solution. Water soluble and Nh₄OAc extractable K and Mg of acidulated mica of pegmatitic origin increased a 10² to 10³ times compared to untreated mica. Acidulated mica remained non-hygroscopic even when mixed with acids at a 2:1 mica to acid ratio. X-ray diffraction analyses demonstrated that interlayer cations were easily leached from the mica structure leaving behind a kaolinitic residue, compared to the more stable tetrasilicate feldspars.The most significant achievement through these experiments was the yield increase obtained in the greenhouse experiment with rice by using the lowest application rate (200 kg ha^–1) so far reported for mica, - an exponential decrease from tonnes/ha previously reported. Acidulated phlogopite mica chips (200 kg ha^–1- 4 kg K, 8 kg Mg, trace elements Mn, Zn etc.) gave a yield increase of over 41% compared to a control with recommended muriate of potash and dolomite (17 kg K, 6 kg Mg). The response to acidulated feldspar (500 kg ha^–1- 1.5 kg K) and an acidulated feldspar-dolomite combined fertilizer (250 kg ha^–1- 0.6 kg K and 6 kg Mg) was not significant.The response to mica clearly shows a multinutrient deficiency in highly weathered tropical soils. The relatively high solubility of the acidulated mica, its range of nutrient element supply, its nonhygroscopic nature and its extremely simple manufacturing process makes mica, a cheap but effective fertilizer for the tropical regions where these nutrients are deficient, especially in highly metamorphosed crystalline terrains.     

杂质Zn,Fe和Cu对BMIC-AlCl3离子液体电解精炼铝的影响

研究了摩尔比为1:2的BMIC-AlCl3离子液体中杂质元素Zn, Fe和Cu对电解精炼铝的影响. 结果表明,离子液体中Zn(II)/Zn, Fe(II)/Fe和Cu(I)/Cu相对于Al(III)/Al的平衡电极电势分别为0.21, 0.63和0.64 V,比其标准电极电势相对值小得多;在温度80℃和电流密度100 A/m2条件下进行电解精炼,铝合金阳极中的绝大部分Zn, Fe和Cu杂质被去除,阴极铝沉积层中杂质含量随阳极杂质含量增加而升高,但杂质的贫化率降低,电流效率均超过94%,能耗为1.59~1.74 kW×h/kg;电解精炼铝含量为75.3%(w)工业铝合金得到了纯度超过99.8%的金属铝,且沉积层致密平整.     

Urea management for lowland transplanted rice as affected by application of farmyard manure

Farmyard manure (FYM) applied to rice-growing soils can substitute for industrial fertilizers, but little is known about the influence of FYM on the effectiveness and optimal management for industrial N fertilizers. A field experiment was conducted in northern Vietnam on a degraded soil in the spring season (February to June) and summer season (July to November) to determine the effect of FYM on optimal timing for the first application of urea. The experimental design was a randomized complete block with two rates of basal incorporated FYM (0 or 6 Mg ha^–1) in factorial combination with two timings of the first application of 30 kg urea-N ha^–1 (basal incorporated before transplanting or delayed until 14 to 16 d after transplanting). The FYM was formed by composting pig manure with rice straw for 3 months. Basal incorporation of FYM, containing 23 kg N ha^–1, increased rice grain yield in both seasons. The yield increase cannot be attributed to reduced ammonia loss of applied urea-N, because FYM did not reduce partial pressure of ammonia (pNH₃) following urea application in either season. Basal and delayed applications of urea were equally effective in the absence of FYM, but when FYM was applied rice yields in both seasons were higher for delayed (mean = 3.2 Mg ha^–1) than basal (mean = 2.9 Mg ha^–1) application of urea. Results suggest that recommendations for urea timing in irrigated lowland rice should consider whether farmers apply FYM.     

玫瑰红色素对羊毛和蚕丝的媒染性能

以FeSO4和ZnSO4·7H2O为媒染剂,采用玫瑰红提取液对羊毛和蚕丝进行染色,探讨了媒染温度、时间、媒染剂用量、玫瑰红提取液用量对媒染性能的影响,以及染色织物的牢度。结果表明,媒染剂FeSO4和ZnSO4·7H2O用量为2g／L、提取液用量为10mL、羊毛和蚕丝织物均为2g时,染色织物具有较深的色泽和良好的色牢度。     

Chlorosis in sugarcane: Associated soil properties,leaf mineral composition,and crop response to iron and manganese

Attempts were made to find out the nature and cause of a widespread sugarcane chlorosis in a cane growing area. Soils from chlorotic and nonchlorotic fields did not differ markedly in pH, CaCO₃, electrical conductivity, organic C, and soil test P, Zn, Cu, and Mn levels, but the chlorotic field soils had relatively more NH₄OAc-extractable K and less clay and DTPA-extractable Fe. Chlorotic and green leaf blades contained about the same concentration of P, S, Mg, Fe, Zn, Cu, and Mo, but the former leaf blades had more K and less Ca and HCl soluble Fe than the green ones. Green leaves of plants that seemed to have naturally recovered in chlorotic fields were higher in Mn. A foliage spray with 2.5% FeSO₄.7H₂O solution resulted in greening of leaves and a field experiment showed marked crop response to Fe and some response to Mn. The results thus suggest that the chlorosis is due to a lime-induced Fe-deficiency with the possibility of some role of Mn in Fe nutrition in calcareous soil conditions.Deceased 22 September 1988     

Dynamics of copper fractions and solubility in a savanna soil under continuous cultivation

An understanding of the influence of soil management practices on the distribution, form and solubility of trace metals in soils is required to formulate appropriate guidelines for the applications of organic manures and inorganic fertilizers for sustainable soil fertility and environmental protection. The distribution, forms and solubility of Cu were investigated in a savanna soil under long-term cultivation and varying management practices which included fertilization with NPK, farmyard manure (FYM), NPK+FYM and a control which received neither NPK nor FYM for 50 years. Total Cu varied between 5 and 13 mg kg^–1. Long-term application of FYM and FYM+NPK significantly increased DTPA extractable Cu in the surface horizon, and in the subsurface horizon in FYM fertilized fields. Averaged across the sampling depths, cultivation and management history did not affect the concentration of DTPA extractable Cu, water-soluble Cu, organically complexed Cu and residual Cu. But fertilization with FYM and FYM+NPK significantly increased organically complexed Cu in the surface layer as compared to NPK fertilization. Solubility equilibria studies indicated that Cu²⁺ activities in soil solution approached an apparent equilibrium with cupric ferrite (CuFe₂O₄), suggesting that the control on Cu²⁺ solubility was either a CuFe₂O₄ or a Cu solid with solubility similar to cupric ferrite. The soil management practices involving combined application of inorganic fertilizers and farmyard manure did not seem to pose any risk of inducing Cu deficiency, but sole application of inorganic NPK poses such a risk.