Xiaohong Tian

In situ comparisons of ammonia volatilization from N fertilizers in Chinese loess soils

Ammonia volatilization loss from mineral N fertilizers was determined on a calcareous Chinese loess soil with a pH (CaCl2) of 7.7. An original in situ method that required no electricity or laboratory analyses was used. By means of a bellows pump, ambient air was drawn through four conical cups placed onto the soil (total area 400 cm2) and subsequently through an NH3-specific detector tube with direct colorimetric indication of the ammonia concentration (measuring range, 0.05–700 vol.-ppm NH3). Duration of measurement was about 3 min. Following N fertilization to winter wheat in 1990 and to summer maize in 1991, the application methods surface broadcast, uniform incorporation into the 0–15-cm layer, and for maize, a point placement at 10 cm depth were investigated. Ammonium bicarbonate and urea were applied at rates of 100 and 200 kg N ha−1. In the autumn of 1990, ammonia losses following NH4HCO3 application were more than twice as large as with urea, fertilizer incorporation reduced NH3 losses 15-fold, and doubling the nitrogen application rate resulted in a 1.7-fold increase in the percentage of nitrogen loss. Cumulative ammonia fluxes were about 2 times higher in the summer of 1991. Comparing application methods in summer, losses were significantly (3 times) lower only with point placement. The above differences were all significant at the P<0.05 level. Due to the very low air exchange rate (0.9 volumes min−1), actual volatilization rates were underestimated by this method. Though not yielding absolute amounts, the Dräger-Tube method proved very suitable for comparing relative differences in ammonia fluxes. The measurements clearly reflected the characteristic flux patterns for the different treatments and the effects of environmental factors on their time course.

Impacts of phosphorus and zinc levels on phosphorus and zinc nutrition and phytic acid concentration in wheat (Triticum aestivum L.)

BACKGROUND Zinc (Zn) and phytic acid content in grain crops are directly related to their nutritional quality and therefore human health. To investigate the nutritional influences of phosphorus (P) and Zn levels on wheat (Triticum aestivum L.), plants were grown hydroponically to maturity in chelator-buffered solutions. RESULTS Appropriate amounts of P, coupled with sufficient Zn, increased P and Zn concentrations in wheat grain. The Zn supply decreased both phytic acid and the molar ratios of phytic acid to Zn in wheat grain with respect to the Zn(0) treatment. Furthermore, proportions of Zn and P content in the grain relative to that of the whole plant were improved. With increasing P, the proportion of Zn and P content in the grain relative to the whole plant decreased. P and Zn acted antagonistically in roots. Excess P inhibited Zn uptake in roots, while Zn decreased the transfer of P from roots to shoots. For P that had been transported to the shoots, supplemental Zn facilitated its transfer to the grain. CONCLUSION Excess P decreased the distribution of Zn in grain, while Zn enhanced the uptake of Zn and P in grain, The combined application of Zn fertilizer with the extensive use of P fertilizer can effectively increase the P and Zn concentration and Zn bioavailability of wheat grain, and hence Zn nutritional quality.

Comparison of soil and foliar zinc application for enhancing grain zinc content of wheat when grown on potentially zinc‐deficient calcareous soils

BACKGROUND The concentration of Zn and phytic acid in wheat grain has important implications for human health. We conducted field and greenhouse experiments to compare the efficacy of soil and foliar Zn fertilisation in improving grain Zn concentration and bioavailability in wheat (Triticum aestivum L.) grain grown on potentially Zn-deficient calcareous soil. RESULTS Results from the 2-year field experiment indicated that soil Zn application increased soil DTPA-Zn by an average of 174%, but had no significant effect on grain Zn concentration. In contrast, foliar Zn application increased grain Zn concentration by an average of 61%, and Zn bioavailability by an average of 36%. Soil DTPA-Zn concentrations varied depending on wheat cultivars. There were also significant differences in grain phytic acid concentration among the cultivars. A laboratory experiment indicated that Zn (from ZnSO4 ) had a low diffusion coefficient in this calcareous soil. CONCLUSION Compared to soil Zn application, foliar Zn application is more effective in improving grain Zn content of wheat grown in potentially Zn-deficient calcareous soils.

Effect of soil and foliar zinc application on zinc concentration and bioavailability in wheat grain grown on potentially zinc-deficient soil

Three field experiments were conducted to determine the effect of soil Zn, foliar Zn, and soil N application on Zn and phytic acid concentrations in wheat grain grown on potentially Zn-deficient soil. Results showed significant genotypic variation in grain Zn concentrations among fifteen wheat cultivars commonly grown in northwest China. Soil Zn application had mixed effects, increasing grain Zn concentrations of some cultivars by as much as 21%, but reducing grain Zn concentrations of other cultivars by as much as 14%. In comparison, foliar Zn application increased grain Zn concentrations by 26 to 115%. Grain Zn concentrations were 14% larger in the combined (foliar Zn + soil Zn) treatment compared to the foliar Zn treatment, but the added cost of soil Zn application may not be economically justifiable. Wheat grain phytic acid concentrations and phytic acid: Zn molar ratios were less in the foliar Zn and (foliar Zn + soil Zn) treatments compared to the soil Zn and the unfertilized treatments. This indica...

Decomposition characteristics of maize (Zea mays. L.) straw with different carbon to nitrogen (C/N) ratios under various moisture regimes

Decomposition of maize straw incorporated into soil with various nitrogen amended carbon to nitrogen (C/N) ratios under a range of moisture was studied through a laboratory incubation trial. The experiment was set up to simulate the most suitable C/N ratio for straw carbon (C) decomposition and sequestering in the soil. The purpose of this study was to determine organic C decomposition by measuring CO2 evolution using alkali traps. Maize straw mixed with clay loam topsoil was supplied with four initial nitrogen rates (40, 80, 160, 320 mg N/0.5 g C) using (NH4)2SO4, to adjust its C/N ratio to 80, 40, 18 and 9. The soil moisture content was maintained at four moisture levels to achieve 60, 70, 80 and 90% of field capacity. Each of the four nitrogen rates were tested against four moisture levels, arranged in complete randomized design and incubated at 20°C for 52 days. Results reveal that decomposition rates and cumulative CO2-C was increased by about 40% in straw amended treatments as compared to the controls. On average, about 34.56% of the added straw C was mineralized to CO2-C. Also, there was highly significant relationship between CO2-C emission and incubation period (R 2 = 0.98). Further, straw addition with interactive effect of nitrogen and moisture had significant relationships (p < 0.05) with cumulative amounts of CO2-C, soil organic C and microbial biomass nitrogen. In conclusion, straw returning with appropriate N doses and optimum moisture can sequester and restore organic C in soil, thereby improving soil quality.

Tolerance to Zn deficiency and P-Zn interaction in wheat seedlings cultured in chelator-buffered solutions

Zinc deficiency is a common constraint for wheat production in the regions with limited precipitation, particularly in the regions with high levels of available phosphate (P) in soil. Two experiments were conducted using chelator-buffered nutrient solutions to characterize differences in tolerance to Zn deficiency among three winter wheat (Triticum aestivum L.) genotypes and to investigate the relationship between P and Zn nutrition in wheat species. Four indices, Zn efficiency, relative shoot-to-root ratio, total Zn uptake in shoot, and shoot dry weight were used to compare the tolerance to Zn deficiency among three wheat genotypes. The results indicated that the four indices could be used in breeding selection for Zn uptake-efficient genotypes. The genotype H6712 was the most tolerant to Zn deficient, followed by M19, and then X13. Specifically, H6712 had the highest Zn uptake efficiency among the three genotypes. The addition of P to the growth medium increased Zn uptake and translocation from roots to shoots. Total Zn content of the wheat plant was 43% higher with 0.6 mmol/L P treatment than that of control with 0 mmol /L P treatment. The Zn translocation ratios from roots to shoots were increased by 16% and 26% with 0.6 mmol/L P treatment and 3 mmol/L P treatment, respectively, compared with 0 mmol/L P treatment. In contrast, high Zn concentrations in the growth medium inhibited P translocation from roots to shoots, but the inhibitive effects were not strong. Sixty-six percent of P taken up by wheat plants was translocated to the wheat shoots at 0 μmol/L Zn treatment, while the percent was 60% at 3 μmol/L Zn treatment. The result may be due to the fact that the wheat plants need more P than Zn.

Effects of Combined Phosphorus-Zinc Fertilization on Grain Zinc Nutritional Quality of Wheat Grown on Potentially Zinc-Deficient Calcareous Soil

Abstract A 2-year field experiment was conducted (i) to study the effect of combined P and Zn fertilization on the Zn nutritional quality of wheat grown on potentially Zn-deficient calcareous soil and (ii) to identify which soil Zn fraction had the greatest effect on grain Zn concentration. Results showed that Zn fertilization increased grain Zn concentrations by 13% in 2006–2007 and 15% in 2007–2008. However, the application of 200 kg P2O5 ha−1 combined with Zn fertilizer reduced grain Zn concentrations by 38% in 2006–2007 and 17% in 2007–2008 compared with the control (no fertilizer treatment). The phytic acid (PA) concentration and the PA:Zn molar ratio in wheat grain increased as P fertilizer application rate increased, regardless of the Zn fertilizer application rate. Zinc fertilization alone increased diethyltriaminepentaacetic acid–Zn by 220% in 2006–2007 and 470% in 2007–2008 compared with the no Zn fertilizer treatment. The combined application of P and Zn also increased diethyltriaminepentaacetic acid–Zn and loose organic matter–bound Zn, but the increase became smaller as the P fertilizer application rate increased. In conclusion, P fertilizer application rates to the potentially Zn-deficient calcareous soil used in this study should be less than 100 kg P2O5 ha−1 to ensure the efficacy of the Zn fertilizer. Among the soil Zn fractions in this study, loose organic matter–bound Zn had the greatest correlation with grain Zn concentration.

EFFECT OF ZINC ON CADMIUM TOXICITY IN WINTER WHEAT

This nutrient solution experiment investigated the effects of zinc (Zn) and cadmium (Cd) on winter wheat growth and enzymatic activity. Twelve nutrient solution treatments were prepared of four zinc levels (0, 0.5, 5 and 50 mg L−1) and three cadmium levels (0, 5 and 50 mg L−1). Cadmium concentrations ≥5 mg L−1 decreased plant growth, superoxide dismutase activity, and leaf and stem zinc concentrations, but increased plant cadmium concentrations, proline content, and peroxidase and catalase activities. Root activity and zinc concentration were highest in the 5 mg L−1 treatment and lowest in the 50 mg L−1 treatment. Zinc concentrations ≥5 mg L−1 inhibited plant growth, but increased proline content and cadmium concentration in stems and leaves. Low levels of zinc (0.5 mg L−1) increased cadmium-induced toxicity in wheat plants but high levels of zinc (50 mg L−1) reduced. In conclusion, these results indicated that the addition of zinc alleviated cadmium toxicity if the zinc/cadmium ratio was >10/1. Additional study needs to be done to quantify zinc content before zinc is supplied to alleviate cadmium toxicity.

COMPARISON OF ZINC EFFICIENCY AMONG WINTER WHEAT GENOTYPES CULTURED HYDROPONICALLY IN CHELATOR-BUFFERED SOLUTIONS

Zinc (Zn) efficient genotypes grow and yield well in Zn deficient environments. The objective of this study was to compare Zn efficiency and seed Zn content among nine winter wheat (Triticum aestivum L.) genotypes grown in chelator-buffered nutrient solutions containing 0 μmol Zn L−1 (−Zn treatment) or 3 μmol Zn L−1 (+Zn treatment). The Zn efficiency of the genotypes ranged from 24% to 46%. Zinc efficiency was positively correlated with shoot dry weight, shoot Zn content, but there was no significant correlation between Zn efficiency and shoot Zn concentration, seed Zn concentration, or seed Zn content. The results suggested that variation in Zn efficiency among these nine wheat genotypes is genetically inherent. Differences in Zn efficiency among these wheat genotypes, which are widely grown in northern China, indicate the potential to breed for wheat genotypes with increased tolerance to soil Zn deficiency.

Application of ZnSO4 or Zn-EDTA fertilizer to a calcareous soil: Zn diffusion in soil and its uptake by wheat plants

BACKGROUND The objective of this study was to compare the efficiency of two Zn sources and two application methods on (i) Zn diffusion from fertilized soil to unfertilized soil, (ii) grain Zn concentration and (iii) grain Zn bio-accessibility to humans. In the laboratory experiment, 20 mg ZnSO4 or 4 mg Zn-EDTA were applied to a 5 mm and 1 mm-wide space in the soil in the half-cell technique. In the greenhouse experiment, Zn-ZnSO4 or Zn-ethylenediaminetetraacetic acid (Zn-EDTA) was mixed or banded with the soil at a rate of 20 or 4 mg Zn kg(-1) , respectively. RESULTS The results from the diffusion experiment showed that both the extractability and the diffusion coefficient of Zn were higher when Zn fertilizer was applied to a 1 mm-wide space than when it was applied to a 5 mm-wide space. Zn-EDTA had a greater diffusion distance than ZnSO4 . The greenhouse experiment showed that the mixed ZnSO4 application and the Zn-EDTA application (both mixed and banded) treatments significantly increased grain Zn concentration and bio-accessibility. The positive effect of Zn-EDTA on grain Zn concentrations and bio-accessibility was greater than that of ZnSO4 . The banded application reduced the effectiveness of ZnSO4 but not of Zn-EDTA. CONCLUSION It was concluded that Zn-EDTA was a better Zn source than ZnSO4 for increasing grain Zn content in a potentially Zn-deficient calcareous soil.