Effects of the reduction of controlled-release urea application on nitrogen leaching in double cropping paddy field.

Nitrogen (N) leaching is a major pathway of N losses in paddy fields. Here, an experiment was conducted to assess the effects of the reduction of controlled-release urea application on grain yield and N leaching in a double-cropping paddy field. Fertilization treatments included zero-N (CK, control, 0 kg N·hm-2), conventional urea (CU, 180 kg N·hm-2), and four polymer-coated urea fertilization levels, i.e., 1.0CRU, 0.9CRU, 0.8CRU, 0.7CRU, which represented 0, 10%, 20% and 30% reduction of fertilizer inputs relative to CU, respectively. Leachate was collected at the soil depth of 60 cm using field leakage pool method. Nitrogen leaching peaked shortly after fertilization, implying that measures should be taken to prevent N leaching in the early period. Nitrogen losses from leaching were 42.3 kg N·hm-2 for 0.8CRU, and by 37.7 kg N·hm-2 for 0.7CRU, significantly lower than the leaching in CU (53.9 kg N·hm-2). Nitrogen leaching in 0.7CRU was significantly lower than that in 1.0CRU (51.3 kg N·hm-2). 11.9%-13.5% of the fertilizer N was lost via leaching across the six treatments with comparable N loss rates. Rice yields, N utilization efficiency and N harvest index were significantly higher in 0.8CRU and 0.7CRU relative to CU. Our findings suggested that the use of CRU would permit a reduction in N application by 20%-30%, which could maintain the rice yield and obtain a reduction in N leaching.

Nitrogen Use Efficiency Is Mediated by Vacuolar Nitrate Sequestration Capacity in Roots of Brassica napus.

Enhancing nitrogen use efficiency (NUE) in crop plants is an important breeding target to reduce excessive use of chemical fertilizers, with substantial benefits to farmers and the environment. In Arabidopsis (Arabidopsis thaliana), allocation of more NO3 (-) to shoots was associated with higher NUE; however, the commonality of this process across plant species have not been sufficiently studied. Two Brassica napus genotypes were identified with high and low NUE. We found that activities of V-ATPase and V-PPase, the two tonoplast proton-pumps, were significantly lower in roots of the high-NUE genotype (Xiangyou15) than in the low-NUE genotype (814); and consequently, less vacuolar NO3 (-) was retained in roots of Xiangyou15. Moreover, NO3 (-) concentration in xylem sap, [(15)N] shoot:root (S:R) and [NO3 (-)] S:R ratios were significantly higher in Xiangyou15. BnNRT1.5 expression was higher in roots of Xiangyou15 compared with 814, while BnNRT1.8 expression was lower. In both B. napus treated with proton pump inhibitors or Arabidopsis mutants impaired in proton pump activity, vacuolar sequestration capacity (VSC) of NO3 (-) in roots substantially decreased. Expression of NRT1.5 was up-regulated, but NRT1.8 was down-regulated, driving greater NO3 (-) long-distance transport from roots to shoots. NUE in Arabidopsis mutants impaired in proton pumps was also significantly higher than in the wild type col-0. Taken together, these data suggest that decrease in VSC of NO3 (-) in roots will enhance transport to shoot and essentially contribute to higher NUE by promoting NO3 (-) allocation to aerial parts, likely through coordinated regulation of NRT1.5 and NRT1.8.

[Effect of atmospheric CO2 concentration and nitrogen application level on absorption and transportation of nutrient elements in oilseed rape].

Effect of elevated atmospheric-CO2 (780 µmol . mol-1) on the absorption and transportation of secondary nutrient elements (calcium, magnesium, sulphur) and micronutrient elements (iron, manganese, zinc, molybdenum and boron) in oilseed rape at the stem elongation stage were studied by greenhouse simulated method. Compared with the ambient CO2 condition, the content of Zn in stem was increased and the contents of other nutrient elements were decreased under the elevated atmospheric-CO2 with no nitrogen (N) application; the contents of Ca, S, B and Zn were increased, and the contents of Mg, Mn, Mo and Fe were decreased under the elevated atmospheric CO2 with N application (0.2 g N . kg-1 soil); except the content of Mo in leaf was increased, the contents of other nutrient elements were decreased under the elevated atmospheric-CO2 with two levels of N application. Compared with the ambient CO2 condition, the amounts of Ca and S relative to the total amount of secondary nutrient elements in stem and the amounts of B and Zn relative to the total amount of micronutrient elements in stem were increased under the elevated-CO2 treatment with both levels of N application, and the corresponding values of Mg, Fe, Mn and Mo were decreased; no-N application treatment increased the proportion of Ca distributed into the leaves, and the proportion of Mg distributed into leaves was increased by the normal-N application level; the proportions of Mn, Zn and Mo distributed into the leaves were increased at both N application levels. Without N application, the elevation of atmospheric CO2 increased the transport coefficients of SFe, Mo and SS,B, but decreased the transport coefficients of SMg,Fe, SMg, Mn and SS,Fe, indicating the proportions of Mo, S transported into the upper part of plant tissues was higher than that of Fe, and the corresponding value of B was higher than that observed for S, the corresponding value of Mg was higher than that of Fe and Mn. Under normal-N application, the elevation of atmospheric CO2 increased the transport coefficients of SMg,Fe, SMg,Mn and SS,B, but decreased the transport coefficients of SCa, Mg, SFe,Mo and SS,Fe indicating the proportions of Fe, Mn and Ca transported into the upper part of plant tissues was higher than that of Mg; the corresponding value of B was higher than that observed for S, the corresponding value of Fe was higher than that of Mo, and the corresponding value of S was higher than that of Fe.

[Changes of heavy metals form during aerobic high temperature composting of pig manure and the effects of passivators].

Sequential extraction method was employed to study the heavy metals concentration and form change during aerobic high temperature compositing of pig manure, and the effects of amendment with different proportion of passivators on the concentration and form change. During the composting process, the concentrations of total As, Cu, and Zn in the manure all increased to some extent. As for the form change of the heavy metals, the exchangeable As and Zn decreased while the residual As and Zn increased, indicating that the availability of As and Zn declined through the composting process. On the other hand, the exchangeable and residual Cu decreased while the carbonate-, Fe/Mn-, and organic bound Cu increased, suggesting the potential environmental risk of the future application of the compost. Among the passivators amended, 5.0% of sepiolite and 2.5% of bentonite had the best effect in reducing the availability of As and Zn, with the residual form of As and Zn after composting increased by 79.8% and 158.6%, respectively, and 7.5% of sepiolite induced the least decrement (39.3%) of residual Cu, compared with the control. Therefore, amendment with appropriate proportion of passivator during pig manure composting could decrease the availability of heavy metals in the manure, and reduce the environmental risk of applying the compost to farmland.

[Emergy analysis of agro-ecolomic system in Shanxi Province].

By the methods of emergy, this paper studied the input and output, working efficiency, and environmental loading of the agro-ecolomic system in Shanxi Province in 2005. The results showed that in 2005, the agro-ecolomic system in Shanxi still stayed in the period of traditional agriculture, which mainly depended on manpower and environmental resources. The emergy investment ratio (EIR) was 1.07, emergy yield ratio (EYR) was 0.99, and environmental loading ratio (ELR) was 6.55. In the structural adjustment of agriculture, stockbreeding had made great strides forward, but grain crops other than rice and wheat, vegetables, and fruits still had smaller emergy yield and were far from becoming dominant industry. The efficiency of the agro-ecolomic system was lower, and its environmental loading press was bigger. For the future, the surplus labors in agriculture in Shanxi should be shifted continually to other industries, and the high quality emergy such as agricultural science and technology should be increased to improve the use efficiency of environmental resources and the input and output of the system emergy.