Identification of an index tissue to predict zinc status of wheat

The critical concentration of Zn in wheat tissues for the prediction of Zn response and diagnosis of Zn deficiency was examined in a glasshouse experiment with wheat (Triticum aestivum, line QT 4118) grown to anthesis in two Vertisols at Zn application rates of 0, 1.25, 2.5, 5, 10, 15 and 30 kg ha^-1 equivalent as ZnSO₄ 7H₂O. The wheat tissues examined were the youngest mature leaf blade (YMB), the leaf immediately below the youngest mature leaf blade (YMB-1), the older leaves, the ear, the stem and the whole tops. The minimum Zn concentration required in a tissue at 0.90 relative yield, referred to as the critical Zn concentration, was determined using the Cate-Nelson graphical and statistical models, the Mitscherlich equation and a two-intersecting straight lines model. The Zn status of wheat was best defined by the Zn concentration in the YMB. Although the critical Zn concentration of the YMB did not vary much with the method of estimation, the Cate-Nelson statistical procedure explained a higher percentage of the variation in Zn concentration in the YMB and relative yield than the Mitscherlich and the two intersecting straight lines models. The critical concentration of Zn in the YMB was 16.0 mg kg^-1 dry matter. It is concluded that determination of Zn concentration in the YMB is the best procedure for evaluating the Zn status of wheat plants.     

A yield control approach to assess phytoavailability of Zn and Cu in irradiated,composted sewage sludges and composted manure in field experiments: I. Zinc

The threat of spreading diseases is a serious concern when organic wastes are applied to farmland. Irradiation and composting are effective methods to reduce pathogens. Field experiments were conducted to assess the influence of these pathogen-eliminating methods on plant availability of Zn in the wastes. Four organic wastes: digested and dewatered (DSS), irradiated (DISS), composted (DICSS) sewage sludge and composted livestock manure (CLM) were applied during two growing seasons at 10, 20, 30, and 40 t solids ha^–1 year^–1. Available N and K in the wastes were estimated and N and K fertilizers were added to the soil to equalize available N and K supply among treatments to avoid dilution of crop Zn concentration. A control treatment (CT) received fertilizers but no waste. Lettuce, snap beans and petunias were grown in 1990, and two cuts of lettuce were harvested in 1991. The influence of waste Zn application on crop Zn concentration was studied within approximately equal crop yields. Crop Zn concentration increased in all crops treated with DSS or DISS, and often reached a maximum at the 30 t ha^–1 rate of application, then slightly decreased at 40 t ha^–1. The response of crop Zn concentration to the amount of Zn applied in the wastes was best described by quadratic equations. Waste application also significantly increased soil Zn availability index, which was a function of DTPA (diethylenetriamine pentaacetic acid)-extractable soil Zn and soil pH. The index was highly correlated with crop Zn concentration. Although Zn concentration in DICSS was similar to those in DSS and DISS, Zn applied in DICSS did not increase crop Zn concentration or soil availability index. Composting reduced the availability of Zn. The similar concentrations of Zn in DSS and DISS in both years allowed the use of a paired t-test to determine the differences in crop Zn concentration caused by application of DSS and DISS. Zinc applied in DISS produced a higher Zn concentration in bean pods than Zn applied in DSS (t > T _0.05 at P < 0.02, df = 15), indicating that irradiation increased phytoavailability of Zn in the sludge. However, no similar effect was found in Zn concentrations in the two cuts of lettuce in 1991 or in soil Zn availability index.     

松嫩平原苏打盐渍化旱田土壤表观电导率空间变异

在松嫩平原西部吉林省大安市乐胜乡,于2013年4月20日选择盐碱程度不均一的典型盐渍化旱田地块,面积为4.8 hm~2作为研究样地。利用EM38大地电导率仪测定结合田间定点采样,并通过经典统计和地统计相结合的方法研究了盐渍化旱田土壤表观电导率空间变异特征,分析了土壤表观电导率与土壤盐碱指标之间的关系。结果表明,盐渍化旱田土壤水平方向表观电导率(EC_h)经对数转换后具有强空间自相关,其变异特征主要是与地形地貌和水文状况等结构性因素有关。垂直方向表观电导率(EC_v)经对数转换后具有中等空间自相关性,其变异特征受结构性因素和随机因素共同作用。EC_h和EC_v半方差模拟的最优模型分别为球状模型和指数模型。Pearson分析表明土壤表观电导率(EC_h和EC_v)与土壤盐碱指标EC_(1∶5)、pH_(1∶5)、SAR、SC、Na~+、CO_3~(2-)、HCO_3~-呈正相关关系(P0.05),EC_h与土壤盐碱指标相关系数均大于EC_v。在实际应用中可以用EC_h来指示土壤的盐碱程度。回归分析表明土壤表观电导率(EC_h和EC_v)与土壤盐碱指标呈线性相关,且EC_h回归模型的决定系数均大于EC_v回归模型的决定系数,可用水平方向土壤表观电导率(EC_h)来计算土壤盐碱指标,进行土壤盐渍化的快速评估。     

Nutrient changes in direct-seeded submerged rice soils with varying nutrio-environments

Summary Nutrient changes in submerged rice soil were studied in soil-water-plant ecosystem in direct-seeded rice crop. Continuous removal of nutrients by the crop resulted in ultimate decrease in the availability of NH₄–N, P, K, Ca, Mg, Mn, Zn and Cu. However, there was a slight increase in Fe availability in soil with increase in period of submergence and crop growth. The data was subjected to statistical function fittings to study the nature of changes. Depending on the R²% values, quadratic type was the best fit for pH, available NH₄–N, K, Mg, Fe, Mn and Cu, whereas logarithmic type was the best fit for available P, Ca and Zn. No response was noticed to the application of P and K. Highest correlation coefficient between grain yield and NH₄–N in soil was obtained at the panicle initiation stage indicating that limiting nitrogen during this period might affect grain yield to the maximum extent compared to tiller initiation and maximum tillering stages.     

基于分数阶微分优化光谱指数的土壤电导率高光谱估算

土壤电导率与含盐量具有高度相关性,精准的土壤电导率监测有助于了解区域土壤的盐渍化程度,对区域盐渍化防治与调控,农业可持续发展以及生态文明建设具有重要意义。为寻求预测土壤电导率的最佳高光谱参数,实现土壤盐分信息的高效监测,本研究对土壤样品进行室内高光谱和电导率测定,利用两波段优化算法对简化光谱指数(nitrogen planar domain index, NPDI)进行波段优化,筛选不同高光谱数据(原始高光谱反射率及其对应的5种数学变换)运算下的最敏感高光谱参数,从而建立土壤电导率高光谱估算模型。结果表明:1)NPDIs与土壤电导率之间的相关性显著,在原数据及其平方根、倒数、对数倒数、1.6阶微分变换形式下,优化光谱指数对土壤电导率的敏感程度更强,相关系数绝对值均超过0.80,且基于1.6阶微分变换的(R_(2020nm)+R_(1893 nm))/R_(1893 nm)波段组合相关系数绝对值最高,达到0.888。2)基于1.6阶微分波段优化的预测模型效果最佳,预测精度为R■=0.84,RMSE_(Pre)=2.07mS/cm,RPD=2.94,AIC=158.11。因此,对高光谱数据的适当数学变换有利于优化光谱指数更好地估算土壤电导率,进一步实现土壤盐渍化高精度动态监测。     

Field assessment of soil biological and chemical quality in response to crop management practices

Soil microbiological and chemical aspects were evaluated to determine the effects of conservation tillage and crop rotation on soil fertility over a 16-year period. A field trial was established to compare two cropping systems (continuous soybean and maize/soybean, soybean/maize rotation). In addition, maize (Zea mays L.) and soybean (Glycine max L., Merr) were grown in two different tillage systems: no tillage and reduced tillage. Soil populations of Trichoderma spp., Gliocladium spp. and total fungi were more abundant when maize or soybean were under conservation tillage and in the maize/soybean and soybean/maize rotation, than in continuous soybean. Furthermore, higher levels of microbial respiration and fluorescein diacetate hydrolysis (FDA), were recorded under no tillage systems. However, soil counts of Actinomycetes and Pythium spp., and Pythium diversity together with soil microbial biomass were not affected by the field treatments. To establish a correlation with soil biological factors, soil chemical parameters, such as pH, organic matter content, total N, electrical conductivity, N–NO₃ ⁻ and P were also quantified, most of the correlations being significantly positive. Under no tillage there was a clear increase of the amount of crop residues and the C and N soil content due to the presence of residues. Also the distribution of crop residues in surface soil due to zero tillage and the quality of these residues, depending on the crop rotation employed, improved on soil biological and chemical characteristics. Crop yield was also enhanced by zero tillage through the management of residues. Although yield values were not directly associated with the development of microorganisms, both yield and microorganisms were influenced by crop management. These results suggest that measuring soil properties over a long period helps to define effective management strategies in order to preserve soil conditions.     

干湿季节下基于遥感和电磁感应技术的塔里木盆地北缘绿洲土壤盐分的空间变异性

土壤盐渍化问题是制约干旱半干旱区植被生长最主要的生态环境地质问题,也是影响绿洲农业生产的障碍性问题.而将遥感与近感技术相结合,是当前评价、监测及预报土壤盐渍化程度的先进方法.以新疆塔里木盆地北缘的渭干河-库车河三角洲绿洲为例,以遥感数据和解译后的电磁感应数据为基础数据源,利用解译后的数据结合GIS和地统计学知识以及野外实测所得到的土壤电导率和盐分资料,分别采用泛克里格(Universal Kriging)、光谱指数回归(Spectral Index Regression)和回归残差泛克里格(Regression-Universal Kriging)3种方法研究了该地区两个关键季节(干季和湿季)土壤盐分的空间变异特征.研究结果表明:研究区的土壤浸提液电导率EC1∶5和土壤盐分呈现显著相关,可以用EC1∶5来代替土壤的全盐量进行分析;电磁感应仪(EM38)所测各季节土壤表观电导率与EC1∶5的相关系数均达到1％显著水平,以表观电导率垂直读数(EMv)和水平读数(EMH)为自变量的多元回归模型拟合效果较好;研究区各季节的表层土壤电导率的空间分布均表现为强相关性,说明土壤采样点间的内部结构性良好,采用能够充分考虑到干旱区表层土壤电导率空间变异的尺度依赖性的球状套合模型,能够更好的拟合土壤表观电导率的空间结构;经过精度比较,回归残差泛克里格法为最优预测方法,这表明将遥感和电磁感应技术相结合,能够有效的提高预测与评估土壤盐分空间分布的精度,为精确地进行土壤盐分预测以及土壤次生盐渍化的防控提供了一定的依据.     

西南喀斯特区坡耕地秸秆覆盖对土壤生态化学计量特征及产量的影响

土壤养分亏缺是限制作物生长的关键因素,同时也是制约作物产量的重要影响因子。为提高西南喀斯特区坡耕地土壤肥力和作物产量,于2018—2019年连续两年在贵州省黔西县开展了野外原位径流小区观测试验。通过该试验探讨不同秸秆覆盖率下土壤碳(C)、氮(N)、磷(P)、钾(K)含量及其生态化学计量特征,揭示不同秸秆覆盖率下土壤养分状况及土壤改良效果。共设6个秸秆覆盖梯度,玉米单作+秸秆覆盖(SM₀—SM₅,0,1111、2222、3889、5556,6944 kg/hm~2),其中SM₀为对照组(CK)。结果表明：(1)秸秆覆盖不同程度增加了土壤有机碳(SOC)、全氮(TN)及全磷(TP)含量,总体上随覆盖量的增加而增加,尤其是覆盖量较多的情况下(SM₄,SM₅),均显著高于对照(P<0.05),但两者之间差异不显著(P> 0.05),而全钾(TK)则随着覆盖量的增加而减少。(2)在高秸秆覆盖条件下(SM₄,SM₅),除了N∶P外,两...     

Availability of iron,manganese, zinc and phosphorus in submerged sodic soil as affected by amendments during the growth period of rice crop

Summary Effect of amendments, gypsum (12.5 tonnes/ha), farmyard manure (30 tonnes/ha), rice husk (30 tonnes/ha) and also no amendment (control) on the availability of native Fe, Mn and P and applied Zn in a highly sodic soil during the growth period of rice crop under submerged conditions was studied in a field experiment. Soil samples were collected at 0, 30, 60 and 90 days of crop growth. Results showed that extractable Fe (1N NH₄OAC pH 3) and Mn (1N NH₄OAC pH 7) increased with submergence upto 60 days of crop growth but thereafter remained either constant or declined slightly. Application of farmyard manure and rice husk resulted in marked improvement of these elements over gypsum and control. Increases in extractable Mn (water soluble plus exchangeable) as a result of submergence and crop growth under different amendments were accompanied by corresponding decreases in easily reducible Mn content of the soil. Application of 40 kg zinc sulphate per hectare to rice crop could substantially raise the available Zn status (DTPA extractable) of the soil in gypsum and farmyard manure treated plots while the increase was only marginal in rice husk and control plots indicating greater fixation of applied Zn. Available P (0.5M NaHCO₃ pH 8.5) behaved quite differently and decreased in the following order with crop growth: gypsum>rice husk>farmyard manure>control.     

Quantitative relationship between zinc transport and plant uptake

Summary The importance of the Zn buffer power and its influence on the Zn concentration in soil solution was investigated in a simulatory experiment where the soil in question, previously treated with Zn and compacted to known bulk density, was eluted with 0.01M CaCl₂ under constant hydraulic head. The data so obtained were correlated with Zn, uptake by maize. The correlation coefficient for effluent Znvs total Zn uptake improved, remarkably when the corresponding Zn buffer power was also incorporated into the computations. It is concluded from this and the earlier investigation² that the Zn buffer power is the most important parameter governing Zn uptake by maize.     

The chemical fractionation of soil zinc and its specific and total adsorption by Egyptian alluvial soils

Summary The Zn contents of twenty-nine alluvial soils from Egypt were chemically fractionated into: water soluble+exchangeable, weakly bound to inorganic sites, organically bound, occluded as free oxide material, and residual mainly in the mineral structure. On the average these fractions constituted about 0.01, 1.20, 28.6, 21.5 and 45.5% of the total soil Zn respectively which averaged 76.25 ppm. Significant correlations were obtained between each individual Zn-fraction and some soil variable.Zinc adsorption isotherms were developed for seven soils suspended in dilute ZnCl₂ solution in the presence of either 0.05M CaCl₂ solution (Specific adsorption) or deionized water (Total adsorption). The Langmuir constants (adsorption maximum and bonding energy) were calculated. The average value of specific adsorption maximum was 1.94 mg Zn/g soil and of total adsorption maxima was 11.54 mg Zn/g soil. Correlation analysis showed that CEC, free Fe₂O₃ and clay content were the dominant soil variables contributing towards specific Zn adsorption. The (Zn) (OH)₂ ion concentration products in the solutions when Zn adsorption corresponded to the Langmuir adsorption maxima were 0.92×10^–17 in the specific adsorption treatment, and 1.35×10^–15 in the total adsorption treatment. These values are within the solubility range of Zn (OH)₂ and ZnCO₃. The values of Langmuir bonding energy constants showed that Zn was more strongly adsorbed by low carbonate or carbonate-free soils than by carbonate-rich soils.     

Effect of zinc sources and levels on the growth and Zn nutrition of soybean (Glycine max. L.) in the presence of chloride and sulphate salinity

A study was conducted in a screen house in pots on a sandy loam soil deficient in Zn. Salinity was induced by adding 44, 88 and 132 me/l of chloride and sulphate salts in the saturation extract. To these treatments, 0, 5 and 10 ppm Zn were added as ZnSO₄·7H₂O or Zn-EDTA. The results indicated that the yield of soybean shoot was lowest at the highest salinity level and highest at the lowest level. Shoot yield improved markedly with Zn application. Both sources of Zn were equally effective in augmenting crop yields. Yields were low in Cl-salinity when compared with equivalent levels of SO₄-salinity. Application of ZnSO₄·7H₂O produced higher yields in SO₄-dominant salinity. Zinc content increased and Zn uptake decreased with increase in Cl-salinity regardless of Zn sources. In SO₄-salinity, ZnSO₄·7H₂O did not influence the Zn content, but uptake was suppressed with increase in SO₄-salinity. Increasing rates of SO₄-salinity enhanced Zn content in the presence of Zn-EDTA.     

Effects of agricultural cropping systems on micronutrients transformation

Summary The effect of cropping systems of wheat-maize (WM), wheat-rice (WR), wheat-groundnut (WG), gram-bajra (GrB), potato-guara (PGu), and raya-mash (RaMa) in combination with treatments of dummy (uncultivated area) and applied Zn 0.0 (Zn₀), 2.8 (Zn₁), 5.6 (Zn₂) 11.2 (Zn₃) kg/ha was studied on the transformation of labile Zn fractions: exchangeable (Exch.), adsorbed (TAd) [weakly (WAd), moderately (MAd), strongly (SAd)], and organic matter (OM) in different layers of sandy loam soil. The added Zn stayed largely in the 0–30 cm layer and was associated with the WAd- and OM-Zn fractions. About 70% of the total labile Zn (PAv) remained in the WAd- and OM-Zn, that is, 33 and 39% in 0–15 cm layer, and 33–39% and 31–36% in 16–150 cm layer. All the Zn fractions in 0–15 cm layer, and only of WAd in 16–30 cm layer, significantly increased with rates of Zn addition. These were also significantly higher in Zn_1–3 than Zn₀ and dummy treatments because of the residual Zn. Diverse effects of cropping systems on soil properties, residual Zn, and labile Zn fractions were found. The influence was strong in 0–15 cm layer decreasing gradually with soil depth due largely to differences in Zn requirement, crop intake of various Zn fractions and the cultural practices of the systems. All the crops and rotations appreciabilly responded to Zn application. Uptake of Zn by crops markedly and successively increased with increasing rates of Zn application. The WR caused a significant increase in soil organic matter whereas WR and WM in CaCO₃. The WR, WM and GrB resulted in a decrease in pH while WG and GrB in CaCO₃. The RaMa and PGu maintained much higher residual Zn than other systems. The systems which caused the maximum decrease in Zn fractions were: cereal-cereal (WM) in Exch. legume-millet (GrB) in all the adsorbed, PAv and the Zn associated with CaCO₃, vegetable-legume (PGu) also in MAd and SAd; and cereal-legume (WG) in OM and PAv. Hence GrB, WG and WM in that order will cause the deficiency of Zn much earlier than the other systems due to greater use and or transformation of WAd- andOM-Zn. Such effects were least under RaMa because it increased the WAd-, MAd- and OM-Zn.     

Interaction between zinc nutritional status of cereals and Rhizoctonia root rot severity

An inverse correlation between plant Zn concentration and the severity of Rhizoctonia root rot, described in an earlier paper, was examined in two experiments in a growth chamber. In the first experiment, wheat (Triticum aestivum cv Songlen) was planted in a Zn deficient soil with and without added Zn, and combined factorially with different inoculum densities of Rhizoctonia solani anastomosis group 8. When Zn was added, the percentage of seminal roots infected with R. solani was significantly lower compared to the treatments without added Zn, showing that low Zn potentiated the disease. A subsequent factorial experiment of four inoculum densities and six Zn levels, (0, 0.01, 0.04, 0.1, 0.4 and 6.0 mg Zn kg^–1 soil) was conducted to investigate the Zn effect in more detail. Disease severity was markedly decreased by the higher Zn applications; the disease score dropped sharply between treatments of Zn_0.04 and Zn_0.1, a difference which was reflected in the plant yield response to Zn. For both experiments the Zn concentrations in shoots were significantly different only among Zn treatments, not among the inoculum treatments. This indicated that inoculum density or disease severity did not reduce Zn concentration in the plant. Thus, disease did not exaggerate Zn deficiency, but rather, Zn sufficiency suppressed disease severity. A potentiating link between Zn nutrition and disease severity is thereby established, although this type of experiment did not indicate the mechanism of the Zn effect.     

微量元素硼和锌在作物营养平衡中的作用

许多土壤中B、Zn由于含量或有效性低而供给不足,成为作物营养平衡与大面积产量提高的重要限制因素。采取各种方法直接施用B、Zn,或者配制在尿素中施用,可以调节作物营养平衡,改善作物-环境生态关系,提高产量和品质。在水稻旱育苗地区还可把Zn配在育苗土壤调制剂中施用。在缺Zn褐土上,施入的Zn迅速转化为各种形态,其中碳酸盐结合态是有效Zn的主要仓库。配合施用P肥对Zn的有效性无不良影响,Zn与N、P配合施用有益于作物营养平衡。     

Soil organic carbon dynamics jointly controlled by climate,carbon inputs,soil properties and soil carbon fractions

Soil organic carbon (SOC) dynamics are regulated by the complex interplay of climatic, edaphic and biotic conditions. However, the interrelation of SOC and these drivers and their potential connection networks are rarely assessed quantitatively. Using observations of SOC dynamics with detailed soil properties from 90 field trials at 28 sites under different agroecosystems across the Australian cropping regions, we investigated the direct and indirect effects of climate, soil properties, carbon (C) inputs and soil C pools (a total of 17 variables) on SOC change rate (r_C, Mg C ha^?1 yr^?1). Among these variables, we found that the most influential variables on r_C were the average C input amount and annual precipitation, and the total SOC stock at the beginning of the trials. Overall, C inputs (including C input amount and pasture frequency in the crop rotation system) accounted for 27% of the relative influence on r_C, followed by climate 25% (including precipitation and temperature), soil C pools 24% (including pool size and composition) and soil properties (such as cation exchange capacity, clay content, bulk density) 24%. Path analysis identified a network of intercorrelations of climate, soil properties, C inputs and soil C pools in determining r_C. The direct correlation of r_C with climate was significantly weakened if removing the effects of soil properties and C pools, and vice versa. These results reveal the relative importance of climate, soil properties, C inputs and C pools and their complex interconnections in regulating SOC dynamics. Ignorance of the impact of changes in soil properties, C pool composition and C input (quantity and quality) on SOC dynamics is likely one of the main sources of uncertainty in SOC predictions from the process‐based SOC models.     

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO₄) revealed a variation range of 23.2–155.9 μg g⁻¹ dry weight (d. wt.) for Zn, 60.3–350.1 μg g⁻¹ d. wt. for Fe and 20.9–53.3 μg g⁻¹ d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO₄) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO₄). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO₄ compared to 2 μM ZnSO₄. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.     

Zinc deficiency tolerance in maize is associated with the up‐regulation of Zn transporter genes and antioxidant activities

• Zinc (Zn) is an essential micronutrient for the growth and development of plants. However, Zn deficiency is a common abiotic stress causing yield loss in crop plants. This study elucidates the mechanisms of Zn deficiency tolerance in maize through physiological and molecular techniques.
• Maize lines tolerant (PAC) and sensitive (DAC) to Zn deficiency were examined physiologically and by atomic absorption spectrometry (AAS). Proteins, H₂O₂, SOD, POD, membrane permeability and gene expression (using real‐time PCR) of roots and shoots of both maize lines were assessed.
• Zn deficiency had no significant effect on root parameters compared with control plants in PAC and DAC but showed a substantial reduction in shoot parameters in DAC. AAS showed a significant decrease in Zn concentrations in both roots and shoots of DAC but not PAC under Zn deficiency, implying that Zn deficiency tolerance mechanisms exist in PAC. Consistently, total protein and membrane permeability were significantly reduced in DAC but not PAC in both roots and shoots under Zn deficiency in comparison with Zn‐sufficient plants. Real‐time PCR showed that expression of ZmZIP1, ZmZIP4 and ZmIRT1 transporter genes significantly increased in roots of PAC, but not in DAC due to Zn deficiency compared with controls. The H₂O₂ concentration dramatically increased in roots of DAC but not PAC. Moreover, tolerant PAC showed a significant increase in POD and SOD activity due to Zn deficiency, suggesting that POD‐ and SOD‐mediated antioxidant defence might provide tolerance, at least in part, under Zn deficiency in PAC.
• This study provides an essential background for improving Zn biofortification of maize.

     

Two classification methods for developing and interpreting productivity zones using site properties

Crop performance is often shown as areas of differing grain yield. Many producers utilize simple GIS color ramping techniques to produce visual yield maps with delineated clusters. However, a more quantitative approach such as an unsupervised clustering procedure is generally used by scientists since it is much less arbitrary. Intuitively the yield clusters are due to soil and terrain properties, but there is no clear criterion for the delineation. We compared the effectiveness of two delineation or classification procedures: quadratic discriminant analysis (QDA) and k-nearest neighbor discriminant analysis (k-NN) for the study of how yield temporal patterns relate to site properties. This study used three production fields, one in Monticello, IL, and two in Centralia, MO. Clusters were defined using maize (Zea mays L.) and soybean (Glycine max (L.) Merr.) yield from three seasons. The k-NN had greater and more consistent successful classification rates than did QDA. Classification success rate varied from 0.465 to 0.790 for QDA while the k-NN classification rate varied from 0.794 to 0.874. This shows that areas of certain temporal yield patterns correspond to areas of specific site properties. Although profiles of site properties differ by crop and production field, areas of consistent low maize yield had greater shallow electrical conductivity (EC_shallow), than those of consistent high maize yield. Furthermore, areas of consistent high soybean yield had lower soil reflectance than those areas of consistent low yields.     

‘On-farm’ seed priming with zinc in chickpea and wheat in Pakistan

A series of on-station trials was implemented between 2002 and 2006 to assess the response of wheat (Triticum aestivum L.) and chickpea (Cicer arietinum) to zinc (Zn) added by soaking seeds (priming) in solutions of ZnSO₄ before sowing. Wheat seed was primed for 10 h in 0.3% Zn and chickpea for 6 h in 0.05% Zn. Seed treatments increased the seed concentration in wheat from 27 to 470 mg/kg and in chickpea from 49 to 780 mg/kg. Priming wheat seeds with 0.3% Zn significantly increased the mean shoot dry mass, Zn concentration and Zn uptake of 15-day-old seedlings relative to non-primed controls and seeds primed with water alone. Using 0.4% Zn further increased shoot Zn concentration but depressed shoot dry mass to the level of the non-primed control. In seven trials, mean grain yield of wheat was significantly increased from 2.28 to 2.42 t/ha (6%) by priming with water alone and to 2.61 t/ha (14%) by priming with 0.3% Zn. Mean grain yield of chickpea in seven trials was increased significantly from 1.39 to 1.65 t/ha (19%) by priming seeds with 0.05% Zn. The effect of priming chickpea seeds with water was intermediate (1.49 t/ha) and not statistically separable from the non-primed and zinc-primed treatments. Increased grain yield due to priming in both crops was associated with increases in total biomass but there was no significant effect of priming on harvest index. In addition to increasing yield, priming seeds with Zn also significantly increased grain zinc concentration, by 12% in wheat (mean of three trials) and by 29% in chickpea (one trial) and the total amount of Zn taken up by the grain (by 27% in wheat and by 130% in chickpea). Using ZnSO₄ to prime seeds was very cost-effective, with net benefit-to-cost ratios of 75 for wheat and 780 for chickpea. An erratum to this article can be found at