Effect Of Zinc Fertilization To Soil On Zinc Nutritional Quality Of Winter Wheat And Zinc Fractions And Transformation In Potentially Zn-deficient Soil

In China, wheat is mainly grown on calcareous soils, of which DTPA-Zn is potentiallydeficient, being0.5-1.0mg·kg-1. Wheat grain Zn concentration is relativey low, averagely26.8mg·kg-1, which leading to Zn deficiency in human beings. Zinc fertilization is the mostdirect and efficient method to solve Zn deficiency. However, results from the previous fieldexperiments on calcareous soil showed that, Zn fertilization to soil with a low level had a littleeffect on increasing grain Zn concentration and then should grain Zn concentration beingincreased with the increasing level of Zn fertilizer? Meanwhile, Zn fixation in calcareous soilis the main inhibitory factor for low Zn effectiveness. How to increase grain Zn concentrationby Zn fertilization on potentially Zn-deficient soil, it is very important to research thedynamic changes of Zn fractions and Zn fixation on potentially Zn-deficient soil after Znfertilization to soil. Meanwhile, in practical producation, nitrogen and phosphorus also affecton Zn fertilizer effectiveness and the antagonist effect between P and Zn becomes a hot topic.However, the interaction between P and Zn in soil and the information of combined P with Znfertilization on Zn fraction was little. Therefore, three field location experiments onpotentially Zn-deficient soil were conducted to study the effects of Zn fertilization withdifferent levels, combined N and Zn fertilization and combined P and Zn fertilization on grainZn nutritional quality of winter wheat and Zn fractions in soil. The main results were asfollows.1. The effectiveness of Zn application to a potentially Zn-deficient calcareous soil wasmeasured using two winter wheat cultivars and five Zn fertilizer rates (0,7.5,15,30,45kg Znha-1). The results showed that Zn fertilizer increased grain Zn concentration in2008-2009by11.4to33.2%. The apparent Zn utilization efficiency was between0.14and0.98%with thelowest Zn effectiveness in45kg Zn ha-1treatment. The after effect of Zn had no significanteffect on grain Zn concentration in2009-2010. The Zn uptake in shoots were0.13-1.29%inthe levels of Zn fertilizer in the two cropping. There was no significant effect of Znfertilization on grain phytic acid (PA) content and the PA: Zn molar ratio. Therefore, grain Znconcentration was not increased with the increasing Zn fertilizer levels and the effectiveness of Zn was also relatively reduced.2. A two-year experiment was conducted to investigate the effects of combined N-Znfertilizers on growth and Zn accumulation of10varieties of winter wheat. Results showedthat the effect of single Zn fertilizer application on yield and grain Zn concentration weresignificantly different among various varieties of winter wheat. Single Zn fertilizerapplication increased grain Zn concentrations of Xiza1, Wunong148, and Zhengmai9023.Combined N-Zn fertilizer increased grain Zn concentration of9varieties of wheat exceptXiaoyan22and the increment was7.3%-54.7%. There was no significant effect of single Znfertilizer application on Zn uptake. While single N fertilizer supply significantly enhancedshoot Zn uptake which primarily accumulated in wheat stem and leaf. Combined N-Znfertilizer significantly increased Zn uptake in wheat shoots, by6.5%and29.8%in the twoyears experiment. Combined N-Zn fertilizers significantly increased Zn fertilizereffectiveness compared to single Zn fertilizer application. The Zn uptakes in shoots were0.25%and1.5%of the levels of Zn fertilizer in the single Zn fertilizer application and theapplication of N and Zn fertilization. Therefore, the application of N and Zn fertilization is asensible method to increase grain Zn concentration on potentially Zn-deficient soil.3. A two-year field experiment was conducted to investigate the effects of combinedapplication of Zn and phosphorus fertilizers on Zn nutritional quality of winter wheat. Resultsshowed the application of50kg P₂O₅ha-1combined with Zn fertilizer (P50Zn7) increasedgrain Zn concentrations by37.7%in2006-2007and8.8%in2007-2008compared to theP0Zn0treatment. However, the P₂₀₀Zn₇treatment reduced grain Zn concentrations by37.6%in2006-2007and17.0%in2007-2008compared to the control (P₀Zn₀). The PA concentrationand the PA: Zn molar ratio in wheat grain increased as P fertilizer application rate increased,regardless of the Zn fertilizer application rate. Meanwhile, the PA: Zn molar ratio wasrelatively lower in combined P with Zn fertilization compared to single P fertilization. Inconclusion, on potentially Zn-deficient calcareous soil, combined P with Zn fertilizationreduced grain Zn nutritional quality and P fertilizer application rates used in this study shouldbe <100kg P2O5ha-1to ensure the effectiveness of the Zn fertilizer.4. Zinc fertilization with the extent of7.5-45kg·ha-1and combined P-Zn fertilizerincreased the accumulation of grain micronutrients, such as Zn, Fe, Cu and Mn. However, theeffect of Zn fertilization on the distribution of Zn, Fe, Cu and Mn was little. The uptake of Znwas gradually reduced and Fe was increased with P levels increased in the combined P and Znfertilization treatment. Therefore, the balance of micronutrient uptake in grain of wheat wasbroken. Under different experimental conditions, the interaction between phytic acid and Zn,Fe, Cu, Mn was also different. Therefore, it is a big work to increase Zn, Fe, Cu, Mn concentration and at the same time to reduce phytic acid content.5. A two-year field experiment was conducted to study the effect of Zn fertilizerapplication on soil DTPA-Zn. Results showed that soil DTPA-Zn content was significantlyincreased with Zn levels increasing. After7d of Zn fertilizer application to soil, soilDTPA-Zn increased by267-529%, after639d, the extent was68-137%. Therefore, with timeelapsing, soil DTPA-Zn content was relatively reduced and in the two cropping, the soilDTPA-Zn was also higher than1.0mg·kg-1. The results in combined N with Zn fertilizationand combined P with Zn fertilization, these two application methods relatively had a littleeffect on reduced soil DTPA-Zn concent compared to single Zn fertilizer application.Especially in the combined P with Zn fertilization, the content of soil DTPA-Zn was graduallyreduced with P levels increasing in soil.6. In the soil Zn appeared mainly in the following fractions, mineral bonded Zn (Min-Zn)accounted for91.5%-97.6%of total Zn, Zinc weakly bound to organic matter (Wbo-Zn)accounted for1.34%-5.53%of total Zn and carbonate bonded Zn (Carb-Zn) accounted for0.47%-1.55%of total Zn. The analysis of path analysis and principal component showed thatthe exchangeable Zn (Ex-Zn), the Wbo-Zn, the Carb-Zn could indicate the availability Zn insoils in various degrees, respectively. Zinc congcentration of wheat grain showed a strongpositive correlation with Ex-Zn and Wbo-Zn. Carbonate bounded Zn and Wbo-Zn accountedfor most parts of total Zn in calcareous soil. To stimulate and control the Zn nutrient conditionin calcareous soil, it is an important measure to increase the content of the Carb-Zn and theWbo-Zn in soil.7. A two-year field experiment was conducted to study the effect of Zn fertilizerapplication on soil Zn fractions. Results showed that, within one week of Zn fertilizerapplication, soil Wbo-Zn and Carb-Zn content was significantly increased by amountsequivalent to63.4-84.0%and6.5-10.3%of the fertilizer Zn application, respectively. TheWbo-Zn fraction decreased gradually over time. Calculations indicated that42.4-69.0%and62.0-78.1%of the Zn fertilizer was mineral bound after231d and639d, respectively. In thecombined N-Zn fertilization and combined P-Zn fertilization treatments, the interactionbetween N-Zn had no significant effect on Zn fractions; however, P0Zn7and P50Zn7treatments significantly increased soil Wbo-Zn content by4.0and4.4folds, respectively. Onthe other hand, P₁₅₀Zn₇and P₂₀₀Zn₇treatments significantly reduced soil Wbo-Zn andCarb-Zn content.Based on these results of the three field experiments, conclusions can be made:(1) Onpotentially Zn-deficient soil, Zn fertilization to soil significantly can increase soil DTPA-Zncontent within two cropping; however, the effect of Zn fertilizer on grain Zn concentration is relatively little. Respect to Zn effectiveness, combined N-Zn fertilization has a higher Zneffectiveness compared to single Zn fertilization.(2) High P levels combined with Znfertilization reduces soil Wbo-Zn, Carb-Zn content and grain Zn bioavailability. Therefore, onpotentially Zn-deficient soil, P fertilizer application rates used should be <100kg P2O5ha-1.(3) The Ex-Zn, the Wbo-Zn, the Carb-Zn could indicate the availability Zn in soils in variousdegrees, respectively. Meanwhile, these two Zn fractions significantly are positively relatedwith grain Zn concentration.(4) Zinc fertilizer application to soil is firstly transformed intomore effective Zn fractions and then gradually transforms into Min-Zn. After wheat harvest, alarge part of Zn fertilizer can be transformed into Min-Zn. Therefore, on potentiallyZn-deficient soil, sensible N and P application rate could increase Zn fertilizer effectivenessand to solve Zn deficiency in human, it is possible to increase grain Zn concentration byincreasing soil Wbo-Zn content.