Xiaopeng Gao

Improving zinc bioavailability in transition from flooded to aerobic rice. A review

Zinc (Zn) deficiency is a widely occurring constraint for rice production and for human nutrition. Scarcity of water is leading to a shift from flooded to aerobic rice production, which can have an impact on Zn deficiency in rice. Zinc bioavailability is a function of both soil and plant factors that can be altered by water management, particularly in relation to conditions in the rhizosphere. Biogeochemical modeling based on bulk soil conditions failed to predict the effect of water management on Zn bioavailability, but revealed that dissolved organic anions, pH, and redox conditions were major determinants. Rhizosphere sampling is needed to understand the difference in Zn mobilization and uptake between flooded and aerobic cultivation systems. Zinc bioavailability is not only affected by changes in the chemical properties of the soils, but also by biological processes such as mycorrhizal inoculation and root release of organic compounds into rhizosphere. Phytosiderophores and organic acids are two classes of Zn chelators secreted from roots that have been linked to the release of Zn from soil-bound forms and its subsequent uptake by plants. A shift to aerobic condition provides a favorable environment for activity of mycorrhizal fungi and enhanced mycorrhizal inoculation under aerobic conditions has been shown to increase plant Zn uptake. Aerobic rice genotypes with varying tolerance to Zn deficiency display a trade-off between mycorrhizal Zn responsiveness and root exudation of Zn chelator in the rhizosphere, which is probably due to a competition for carbon. Potential agronomic management practices in aerobic rice production systems are discussed, with an emphasis on their roles in improving bioavailability of Zn. Addition of Zn fertilizers by soil or foliar application have been shown to increase Zn concentration in cereal grains but the extent of the increase differs among crop species. The shift from flooded to aerobic condition can cause significant N transformations, which may consequently affect Zn mobilization and uptake. An appropriate N management strategy, including an effective combination of source, rate, application method, and timing, should consider the effects on soil pH. Application of P fertilizer should be done with careful consideration to the effect on Zn uptake. A reasonable cropping system (intercropping and crop rotation) could prevent Zn deficiency and offer an effective and sustainable pathway to Zn biofortification. Keeping these points in mind, this review describes our current knowledge of Zn bioavailability as affected by changes in soil–plant interactions caused by the transition from flooded to aerobic rice cultivation.

Concentration of cadmium in durum wheat as affected by time, source and placement of nitrogen fertilization under reduced and conventional-tillage management

Cadmium concentration in durum (Triticum durum L.) grain may be influenced by fertilizer management. A three year field study was conducted at two locations in southwestern Manitoba, Canada, to determine the effect of source, timing and placement of N fertilizer on grain Cd concentration of durum wheat under reduced-tillage (RT) and conventional-tillage (CT) management. There was a significant year-to-year variation in grain yield and grain Cd concentration, indicating a strong effect of environment on phytoavailability of Cd. Soil type also had a dominating effect on Cd in durum grain. Grain Cd concentration and accumulation were always lower at the Newdale clay loam (CL) location than the Stockton fine sandy loam (FSL) location. Compared to CT, RT management decreased grain Cd concentration and accumulation. Application of N fertilizer significantly increased grain Cd concentration and decreased grain Zn concentration. The increase in grain Cd could be due to the increasing Cd concentration in soil solution, the improved crop growth, or a competitive interaction between Cd and Zn for binding sites in the soil system and for uptake sites in the roots, following the application of N fertilizer. Time, source and placement of N fertilization showed inconsistent effect on grain yield and grain Cd concentration. The effects when observed were minor compared to effects of year and soil type on grain Cd concentration. Application of anhydrous ammonia (NH3) generally resulted in higher Cd concentration in durum grain than application of same level of other N sources including urea ammonium nitrate (UAN), urea and ammonium nitrate (AN), probably due to greater N efficiency from the NH3 as compared to the other sources. Where differences due to placement occurred, banded application of fertilizers generally resulted in higher Cd concentration in durum grain than did dual-banded placement, indicating a higher fertilizer availability. Soil type, year and N fertilization greatly affected concentration of Cd in durum grain. Selection of a suitable source, timing and placement combination of N fertilization is important in optimizing crop yield and minimizing grain Cd concentration.

Effect of nitrogen fertilizer rate on nitrous oxide emission from irrigated potato on a clay loam soil in Manitoba, Canada

Gao, X., Tenuta, M., Nelson, A., Sparling, B., Tomasiewicz, D., Mohr, R. M. and Bizimungu, B. 2013. Effect of nitrogen fertilizer rate on nitrous oxide emission from irrigated potato on a clay loam soil in Manitoba, Canada. Can. J. Soil Sci. 93: 1-11. This study examined the effect of N fertilizer application rate on N2O emissions for irrigated potato production on a clay loam soil near Carberry, Manitoba, over two growing seasons. Treatments were an unfertilized control, and urea-N fertilizer application rates of 80, 160 and 240 kg N ha-1, which were applied as split applications. The marketable yield increased at 80 kg N ha-1 relative to the unfertilized control, but did not respond to higher rates of fertilizer. Peak emission of N2O followed fertilizer application and rain or irrigation events. Emission rates following fertilizer application and water addition events were greater from hill than from furrow position in 2009, but not in 2010. In the latter, ponding of water in furrows likely resulted in the greater emissions than from the hill positions. Cumulative N2O emissions and yield based N2O intensity increased linearly with N application rate. The growing season emission factor (EFgs) for percent of added N emitted as N2O was 0.73% and did not increase with N application rate. The adjusted whole-year emission factor (EFwy) assuming 30% of annual emissions are emitted during winter and thaw was 1.04%, being lower than the Canadian IPCC Tier II protocol value of 1.72% for irrigated cropland in Canada. The lower measured EFwy may be because the protocol assumes that under irrigation water input (rain plus irrigation) equals potential evapotranspiration (PET) from May to October, implying no restriction of N2O emissions by water limitation. For the current study, however, the ratio of water input to PET averaged 70%, suggesting water may have restricted N2O emission, therefore resulting in a lower EFwy than predicted by the Tier II protocol. The results of the current study also suggest that a reduction in N2O emissions can be achieved by avoiding fertilizer N applications beyond optimal for marketable yield, limiting irrigation soon after application of N fertilizer, and managing irrigation to prevent ponding of water in furrows.

Mycorrhizal colonization and grain Cd concentration of field-grown durum wheat in response to tillage, preceding crop and phosphorus fertilization.

BACKGROUND A 3-year field trial was conducted to investigate the effect of agricultural management practices including tillage, preceding crop and phosphate fertilization on root colonization by arbuscular mycorrhizal (AM) fungi and grain cadmium (Cd) concentration of durum wheat (Triticum turgidum L.). The relationship between grain Cd and soil and plant variables was explored to determine the primary factors affecting grain Cd concentration. RESULTS Mycorrhizal colonization of the roots was reduced by conventional tillage or when the preceding crop was canola (Brassica napus L.), compared to minimum tillage or when the preceding crop was flax (Linum usitatissimum L.). In contrast, grain Cd was not consistently affected by any treatment. Grain Cd was generally below the maximum permissible concentration (MPC) of 100 microg Cd kg(-1) proposed by WHO. Grain Cd varied substantially from year to year, and could be predicted with 70% of variance accounted for by using the model: grain Cd concentration = - 321.9 + 44.5x ln(grain yield) + 0.26x soil DTPA-Cd + 182.5x soil electrical conductivity (EC)- 0.98x grain Zn concentration. CONCLUSIONS These common agricultural management practices had no effect on grain Cd concentration in durum wheat though they impacted mycorrhizal colonization of roots. Grain yield and to a lesser extent soil conditions of EC and DTPA-Cd and grain Zn influenced grain Cd, whereas mycorrhizal colonization levels did not.

Cadmium Concentration in Flax Colonized by Mycorrhizal Fungi Depends on Soil Phosphorus and Cadmium Concentrations

Effect of arbuscular mycorrhizal (AM) fungus on cadmium (Cd) concentration in flax was investigated in a pot experiment. Flax inoculated with Glomus intraradices and uninoculated controls were grown in a pasteurized soil that received Cd (0, 2.5, and 10 mg kg−1) and phosphorus (P; 10 and 50 mg kg−1) additions. Root colonization was not affected by Cd addition but was reduced by high P addition. Effect of G. intraradices on Cd was evident only at low P supply. Inoculation with G. intraradices decreased shoot Cd at no or low Cd addition, which was attributed to reduced root-to-shoot Cd translocation. In contrast, G. intraradices inoculation increased shoot Cd at high Cd addition, which might be associated with the greater absorption of Cd by extraradical hyphae and lower rhizosphere pH. Our results indicate that a benefit of AM fungus in reducing Cd in crops is achievable at Cd and P concentrations commonly in agricultural soils.

Lower Nitrous Oxide Emissions from Anhydrous Ammonia Application Prior to Soil Freezing in Late Fall Than Spring Pre-Plant Application

Fall application of anhydrous ammonia in Manitoba is common but its impact on nitrous oxide (NO) emissions is not well known. A 2-yr study compared application before freeze-up in late fall to spring pre-plant application of anhydrous ammonia on nitrous oxide (NO) emissions from a clay soil in the Red River Valley, Manitoba. Spring wheat ( L.) and corn ( L.) were grown on two 4-ha fields in 2011 and 2012, respectively. Field-scale flux of NO was measured using a flux-gradient micrometeorological approach. Late fall treatment did not induce NO emissions soon after application or in winter likely because soil was frozen. Application time did alter the temporal pattern of emissions with late fall and spring pre-plant applications significantly increasing median daily NO flux at spring thaw and early crop growing season, respectively. The majority of emissions occurred in early growing season resulting in cumulative emissions for the crop year being numerically 33% less for late fall than spring pre-plant application. Poor yield in the first year with late fall treatment occurred because of weed and volunteer growth with delayed planting. Results show late fall application of anhydrous ammonia before freeze-up increased NO emissions at thaw and decreased emissions for the early growing season compared to spring pre-plant application. However, improved nitrogen availability of late fall application to crops the following year is required when planting is delayed because of excessive moisture in spring.

Cadmium and Zinc Concentration in Grain of Durum Wheat in Relationto Phosphorus Fertilization, Crop Sequence and Tillage Management

Field experiments were conducted at two locations in Manitoba, Canada, to determine the effect of crop rotation, phosphorus (P) fertilization and tillage on grain yield and grain concentrations of Cd and Zn in durum wheat (Triticum durum L.). Compared to conventional tillage (CT), reduced tillage (RT) management decreased grain Cd and increased grain yield and grain Zn in half of the site-years. The type of preceding crops of spring wheat-flax or canola-flax had little influence. Rate and timing of P application had little effect on grain Cd, but increasing P rate tended to decrease grain Zn. No interactive effect was detected among tested factors. Grain Zn was not related to grain Cd, but positively to other nutrients such as Fe, Mn, P, Ca, K, and Mg. Both grain Zn and Fe correlated positively with grain protein content, suggesting protein may represent a sink for micronutrients. The study suggested that the tillage management may have beneficial effects on both grain yield and quality. Phosphorus fertilizer can remain available for subsequent crops and high annual inputs in the crop sequence may decrease crop grain Zn. Understanding the environment is important in determining the impact of agricultural management on agronomic and nutrient traits.

Greenhouse gas emissions from pig slurry applied to forage legumes on a loamy sand soil in south central Manitoba

Gao, X., Tenuta, M., Buckley, K. E., Zvomuya, F. and Ominski, K. 2014. Greenhouse gas emissions from pig slurry applied to forage legumes on a loamy sand soil in south central Manitoba. Can. J. Soil Sci. 94: 149-155. Information regarding the greenhouse gas (GHG) emissions resulting from the application of pig slurry to forage in western Canada is limited. This study examined the effects of addition of pig slurry and soil water content with landscape position on nitrous oxide (N2O) and methane (CH4) emissions from forage legumes [sainfoin (Onobrychis viciifolia) and alfalfa (Medicago sativa)] on a sandy loam soil in Brandon, Manitoba, over two growing seasons. Pig slurry was surface applied with a rolling aerator-type tine at a rate of 35000 L ha-1 and 38000 L ha-1, providing 62-15-50 and 205-45-86, actual N-P-K kg ha-1, in 2006 and 2007, respectively. Emissions were measured on and between surface bands of the slurry applied to soil. Soil concentrations of -N and -N, moisture, and temperature were also monitored. In both years, slurry application increased growing season cumulative N2O emissions. Net increase in cumulative N2O-N emissions with slurry treatment ranged from 0.04 to 0.05% of total N ha-1 applied in 2006 but from 0.7 to 0.9% in 2007. The coherence of rapidly increasing N2O emissions following slurry application with decreasing soil and increasing concentration, in combination with the fact that emissions continued even when soil concentrations were undetectable, suggest nitrification and denitrification were sources of N2O. Emissions of CH4 were generally slightly negative and unaffected by addition of slurry. Higher soil water content at lower landscape position did not affect emissions of CH4 but did increase those of N2O in 2007. The current study was conducted at one field location. Examination of slurry additions to additional sites is required for reliable estimation of N2O emissions from slurry applied to perennial legume forages in prairie Canada.

Interactive effect of N fertilization and tillage management on Zn biofortification in durum wheat (Triticum durum)

Gao, X. and Grant, C. A. 2011. Interactive effect of N fertilization and tillage management on Zn biofortification in durum wheat (Triticum durum ). Can. J. Plant Sci. 91: 951-960. A 3-yr field study was conducted at two locations in southwestern Manitoba, Canada, to determine the interactive effect of application of four sources of N fertilizer and two tillage management systems on grain Zn concentration of durum wheat. There was a significant year-to-year variation in grain yield and grain Zn concentration, indicating a strong environmental influence. Soil type also had a dominating effect, with grain Zn concentration generally being higher at the clay loam location than the fine sandy loam location, reflecting the native soil Zn status. Tillage management showed little influence on grain Zn, suggesting that reduced tillage practices can be adopted by local farmers without decreasing mineral concentrations in grain. Compared with the control treatment, which did not receive extra N fertilizer, N fertilization at 60 kg ha-1 decreased grain Zn concentration in 4 of 6 site-years. Grain Zn accumulation was, however, generally not affected by extra N fertilization, in spite of a positive fertilization effect on grain yield. The four N sources did not differ in their effect on grain yield and grain Zn, indicating that at the rate of N applied there were no differential fertilizer source effects on Zn availability. The results of the present study suggest that for wheat production on Canadian prairies, a regular N fertilization rate using the currently registered cultivars is not likely to produce wheat grain that meets the recommended dietary allowance for Zn. Application of Zn fertilizer, in combination with optimum N fertilization or other agronomic practices that can increase grain Zn, is required to produce improved grain quality for human health.

Soil property and cotton productivity changes with nutrient input intensity in the Taklimakan desert of China

Abstract Conversion of native desert into irrigated cropland is common in southern Taklimakan desert of China though the effect on soil fertility are not well understood. This study examined the effect of cultivation intensity on soil properties and crop productivity using 9-year data from cotton grown at three intensities of no fertilizer, low, and high fertilizer inputs. A native desert with sparse vegetation of Alhagi sparsifolia Shap. was used as a check. Treatment effects on soil properties fluctuated during 2005–2009 due to mineralization of applied manure or weather variation, and kept stable during 2010–2013. Soil organic carbon (SOC) during 2010–2013 increased with intensity, being 1.0–2.4 times greater in the fertilized than unfertilized cotton and desert. Soil total N, plant available N, and P content increased with fertilizer inputs. Available N content in the desert was 28.8 mg kg−1, being comparable to the low fertilizer treatment but approximately double that of unfertilized cotton, suggesting N fixing capacity of the leguminosae A. sparsifolia. Available K content was highest in desert and decreased with cultivation intensity. There were positive relationships between SOC and available N and P contents, suggesting SOC as a nutrient reservoir. Soil C:N ratio during 2010–2013 increased with intensity, being 8.7, 9.7, 10.8, and 12.0, for desert, no fertilizer, low, and high fertilizer input, respectively. Fertilizer application increased the 2010–2013 average cotton seed yield by 4.3–6.4 times compared to the unfertilized cotton field. In conclusion, our results suggest the intensive inputs of fertilizers are crucial to accelerate soil fertility and maintain the productivity of the recently converted lands from the desert.