Green manure addition to soil increases grain zinc concentration in bread wheat

Zinc (Zn) deficiency is a major problem for many people living on wheat-based diets. Here, we explored whether addition of green manure of red clover and sunflower to a calcareous soil or inoculating a non-indigenous arbuscular mycorrhizal fungal (AMF) strain may increase grain Zn concentration in bread wheat. For this purpose we performed a multifactorial pot experiment, in which the effects of two green manures (red clover, sunflower), ZnSO4 application, soil γ-irradiation (elimination of naturally occurring AMF), and AMF inoculation were tested. Both green manures were labeled with 65Zn radiotracer to record the Zn recoveries in the aboveground plant biomass. Application of ZnSO4 fertilizer increased grain Zn concentration from 20 to 39 mg Zn kg−1 and sole addition of green manure of sunflower to soil raised grain Zn concentration to 31 mg Zn kg−1. Adding the two together to soil increased grain Zn concentration even further to 54 mg Zn kg−1. Mixing green manure of sunflower to soil mobilized additional 48 µg Zn (kg soil)−1 for transfer to the aboveground plant biomass, compared to the total of 132 µg Zn (kg soil)−1 taken up from plain soil when neither green manure nor ZnSO4 were applied. Green manure amendments to soil also raised the DTPA-extractable Zn in soil. Inoculating a non-indigenous AMF did not increase plant Zn uptake. The study thus showed that organic matter amendments to soil can contribute to a better utilization of naturally stocked soil micronutrients, and thereby reduce any need for major external inputs.ISSN:1932-620

Grain (A) and aboveground (B) zinc (Zn) concentrations of wheat grown in a calcareous soil.

<p>Bar filling denoting the different green manure addition treatments is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-g001" target="_blank">Figure 1</a>. Bars show mean values and associated standard errors of five experimental replicates. The significances (**, p<0.01; ***, p<0.001) of the effect of mineral Zn fertilization, soil γ-irradiation of fixed factor four-way analyses of variance are shown. Different letters indicate statistical differences of separate least significant difference tests at p<0.05 for the different green manure addition treatments within the combinations of soil γ-irradiation and mineral Zn fertilization. For full statistical details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-t002" target="_blank">Table 2</a>.</p

Percentage of zinc (Zn) recovered from green manure (Zn_rec-gm) in the aboveground wheat biomass.

<p>Black bar filling denotes treatments with arbuscular mycorrhizal fungus (AMF) inoculation and light grey filling treatments without AMF inoculation. Bar hatching highlights treatments in which the naturally occurring AMF were missing after γ-irradiating the soil. Bars show mean values and associated standard errors of five experimental replicates. The significances (***, p<0.001) of the effect of green manure addition and mineral Zn fertilization from a fixed factor four-way analysis of variance are indicated above the bars. For full statistical details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-t002" target="_blank">Table 2</a>.</p

Grain yield (A) and aboveground biomass (B) of bread wheat grown in a calcareous soil.

<p>Black bar filling denotes the treatments without any added green manure, light grey bar filling the treatments in which the soil was amended with green manure of red clover, and dark grey bar filling those treatments in which green manure of sunflower was added to the soil. Bar hatching highlights the treatment missing the naturally occurring arbuscular mycorrhizal fungi after γ-irradiating the soil. Bars show mean values and associated standard errors of five experimental replicates. The significances (**, p<0.01) of soil γ-irradiation from a four-factorial analysis of variance are indicated. For full statistical details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-t002" target="_blank">Table 2</a>.</p

Effects of green manure addition and ZnSO₄ application to soil, soil γ-irradiation and inoculation of a non-indigenous arbuscular mycorrhizal fungus (AMF) on plant and soil parameters.

<p>DTPA: diethylene-triamine-penta-acetic acid</p><p>Mean values and associated standard errors of five experimental replicates of Zn uptake to the aboveground biomass, Zn in the aboveground biomass derived from green manure (Zn_dgm), Zn derived from soil and fertilizer (Zn_dsoil) and DTPA-extractable Zn from soil at grain maturity are listed.</p

Zinc (Zn) uptake from soil to the aboveground biomass of bread wheat grown in a calcareous soil after addition of two types of green manure.

<p>The Zn taken up from soil either originated from the native soil Zn pool or from soil as well as applied ZnSO₄ fertilizer. Bar filling denoting the different green manure addition treatments is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-g001" target="_blank">Figure 1</a>. Bars show mean values and associated standard errors of five experimental replicates. The significance (***, p<0.001) of the effect of mineral Zn fertilization from a fixed factorial four-way analysis of variance is indicated above the bars. Different letters indicate statistical differences of separate least significant difference tests at p<0.05 for the different green manure addition treatments within the different Zn fertilization levels. For full statistical details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-t002" target="_blank">Table 2</a>.</p

Total soil nitrogen (N) concentration and pH in water at wheat harvest.

<p>DTPA: diethylene-triamine-penta-acetic acid</p><p>The values represent the means and associated standard errors (SE) of 20 experimental units. Different superscript letters of the same type following the SE indicate statistical difference among the means of the three green manure treatments within each soil γ-irradiation treatment at p<0.05, according to least significance difference tests.</p

Grain nitrogen (N) concentration of wheat grown in a calcareous soil.

<p>Bar filling denoting the different green manure addition treatments is the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-g001" target="_blank">Figure 1</a>. Bars show mean values and associated standard errors of five experimental replicates. The significances (*, p<0.05) of the effect of soil γ-irradiation from a four-factorial analysis of variance are shown. Different letters indicate statistical differences of separate least significant difference tests at p<0.05 for the different green manure addition treatments within the combinations of soil γ-irradiation and mineral Zn fertilization. For full statistical details see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0101487#pone-0101487-t002" target="_blank">Table 2</a>.</p