Effect Of Straw Recycling On Zinc Fractions And Its Availability In Calceous Soil

Large area of calcareous soil in our country is potentially Zn deficient, confronting withseries of problems, such as low Zn availability and low soil Zn capacity. All of these affect ofthe increase of grain Zn concentration of crops and thus threaten the population health in thisarea. Owing to its benefits on increasing grain Zn concentration of wheat in calcareous soiland improving the population Zn nutritional conditions, Zn fertilization has drew increasinglypublic attention. However, Zn fertilization has limited effect on wheat grain Zn enrichment forthe soil condition of high soil pH, high soil CaCO₃content and low organic matter content inthis calcareous soil according to our former studies. Therefore, in this paper we havediscussed the effect of straw recycling on soil Zn capacity in calcareous area. Two fieldincubation experiments and one long-term located experiment have been conducted in No1.Experiment Farm, Northwest A&F University from Nov. of2009to Jul. of2011. The effect ofstraw recycling with different kind, and different Zn concentration, as well as fertilization (Znand N fertilizer) on soil Zn fractions and availability in calcareous soil. The results are asfollows:The effect of maize straw recycling on soil Zn forms and availability in calcareous soilwas illustrated by the maize straw recycling experiment, by using the method of nylon mashbags buried in soil. And the results showed that compared to Zn fertilization, straw returningto field showed smaller contribution to improve soil total Zn content; both Zn fertilization andstraw returning to field increased the soil DTPA-Zn content significantly, and the increase ratecaused by Zn fertilization was much bigger; Zn in high Zn concentration maize straw returnedto soil were more likely to be released and then converted into soil DTPA-Zn with theconversion rate of49.0%, compared to low zinc concentration straw. After the straw returnedto the soil, the DTPA-Zn conversion in straw addition treatments followed the tendency ofdecreasing after increasing, however, Zn fertilization treatments did not changed too much.The soil weakly organic bound Zn (Wbo-Zn) in Zn fertilization treatments were significantlyhigher than control and straw addition solely treatments. At the same time, the high soil Wbo-Zn content under Zn fertilization added maize straw recycling treatment could last muchlonger time when compared with Zn fertilizer solely treatment.(2) Though the wheat straw field incubation experiment, the effect of wheat strawrecycling on Zn capacity and on exogenous Zn behavior in calcareous soil was studied. Theresults illustrated that both Zn fertilization and straw returning to field increased soilDTPA-Zn and Wbo-Zn content significantly, and the increase rate caused by Zn fertilizationwas much bigger (The DTPA-Zn content in Zn fertilizer solely treatment increased257⁴60%,and the Wbo-Zn content increased90.3³75%compared to control.); Zn fertilization alsoincreased the soil carbonate bound Zn and total Zn contents. Wheat straw returning to thefield also increased strongly organic bound Zn (Sbo-Zn) and Manganese oxides bound Zn(OxMn-Zn) slightly; but it has nearly no contribution on total Zn content. Zn in high Znconcentration wheat straw returned to soil was more likely to be released and then convertedinto soil DTPA-Zn. Besides, when wheat straw was returned to the filed, it could do activatesoil Zn at the same time, even the amount of activated Zn by straw seemed more than its ownreleasing. So, it may be more meaningful.(3) Though the long-term located experiment, the effect of long-term wheat strawrecycling on soil Zn fractions and its availability was illustrated. And the results showed thatsoil DTPA-Zn contents in various treatments were decreased significantly after six seasons ofwinter wheat growing. But wheat straw recycling could do alleviate this decrease. After wheatharvest in2010, the soil DTPA-Zn in straw mulching and furrow treatments (two strawreturning to the field treatments) were both significantly higher than the control (theconventional growing patterns), and the increase rate was19.7%and15.2%, respectively. Butthere were no significant difference between the straw mulching and furrow treatments.Wheat straw returning to the field could increase wheat grain Zn concentration slightly. Andwhen combined with N fertilization, it would be more effective, especially when the N rate240kg·hm-2(N240). The grain Zn contents under straw mulching and furrow treatments inN240were23.7%and24.5%higher than its correspondingly N0. Among the six soil Znfractions, Wbo-Zn and OxMn-Zn were positively correlated with wheat grain Znconcentration significantly. Long-term wheat straw returning to the field has increased soilOxMn-Zn and Carb-Zn,(especially when combined with high level of N fertilization), but haslittle effect on other fractions. N fertilization was in favor of the increase of soil Wbo-Zn andOxMn-Zn contents.In conclusion, Zn fertilization with straw returning to the field could boost soil Znavailability and Zn capacity in calcareous soil. And wheat straw recycling with N fertilizationdoes not only increase soil Zn availability, but also benefit on the Zn enrichment of wheat grain. Therefore, if we could combined straw recycling with N and Zn fertilization together, itmay increase soil Zn capacity in calcareous, and at the same time enhance the Zn enrichmentof the wheat grain and thus improve Zn nutrition of human beings in calcareous area. So, thismaybe becomes one of the most effective measures to maintain the sustainable agriculturaldevelopment in this area.