Mechanisms of conservation tillage on nitrogen-fertilizer reduction and maize grain improvement in Mollisols of Northeast China: Insights from a 15N tracing study.

Conservation tillage is an important management practice to guarantee soil fertility in degraded Mollisols. It is still unclear, however, whether the improvement and stability of crop yield under conservation tillage can be sustainable with increasing soil fertility and reducing fertilizer-N application. Based on a long-term tillage experiment initiated in Lishu Conservation Tillage Research and Development Station by Chinese Academy of Sciences, we conducted a 15N tracing field micro-plot experiment to investigate the effects of reducing nitrogen application on maize yield and fertilizer-N transformation under long-term conservation tillage agroecosystem. There were four treatments, including conventional ridge tillage (RT), no-tillage with 0% (NT0), 100% (NTS) maize straw mul-ching, and 20% reduced fertilizer-N plus 100% maize stover mulching (RNTS). The results showed that after a complete cultivation round, the average percentages of fertilizer N recovery in soil residues, crop usage, and gaseous loss were 34%, 50%, and 16%, respectively. Compared with conventional ridge tillage, no-tillage with maize straw mulching (NTS and RNTS) significantly increased the use efficiency of fertilizer N in current season by 10% to 14%. From the perspective of N sourcing analysis, the average percentage of fertilizer N absorbed by crop parts (including seeds, straws, roots, and cobs) to the total N uptake reached nearly 40%, indicating that soil N pool was the main source of N for crop uptakes. In comparison with conventional ridge tillage, conservation tillage significantly increased total N storage in 0-40 cm by reducing soil disturbance and increasing organic inputs, and thus ensured the expansion and efficiency increment of soil N pool in degraded Mollisols. Compared with conventional ridge tillage, NTS and RNTS treatments significantly increased the maize yield from 2016 to 2018. In all, by improving fertilizer nitrogen utilization efficiency and maintaining the continuous supply of soil nitrogen, long-term management of no-tillage with maize straw mulching could achieve a stable and increasing maize yield in three consecutive growing seasons and simultaneously reduce environmental risks derived by fertilizer-N losses, even under the condition of 20% reduction of fertilizer-N application, and thus actualize the sustainable development of agriculture in Mollisols of Northeast China.

[Effects of fertilization on the P accumulation and leaching in vegetable greenhouse soil].

A packed soil column experiment was conducted to investigate the effect of different fertilization practices on phosphorus (P) accumulation and leaching potential in a vegetable greenhouse soil with different fertility levels. The results showed that the leaching loss of total P in the leachates elevated with the increment of leaching time while the accumulative leaching loss of total P was relatively low, indicating P was mainly accumulated in the soil instead of in the leachate. At the end of the leaching experiment, soil fertility and fertilization treatment affected the content of total phosphorus and Olsen-P significantly. Compared with the low-level-fertility soil, the contents of total P and Olsen-P increased by 14.3% and 12.2% in the medium-level-fertility soil, 33.3% and 37.7% in the high-level-fertility soil. Total P in the combined application of poultry manure and chemical fertilizer (M+NPK) was elevated by 5.7% and 4.3%, compared with the NPK and M treatment. Compared with NPK treatment, Olsen-P in M and M + NPK treatments augmented by 13.0% and 3.1%, respectively. Soil total P and Olsen-P mainly accumulated in the 0-10 cm and 10-20 cm soil layers, and much less in the 20-40 cm soil layer.

[Simulation of relationship between dissoluble phosphorus loss and runoff time].

The environmental sensitive phosphorus point of a cinnamon fluvo-aquic soil was 69.4 mg/kg (Olsen-P) evaluated by fitting soil Olsen-P and CaCl2-P content using Heckrath split-line model. The relationship between dissoluble phosphorus (DP) lost from runoff in soils applied different P rate and runoff time was studied using circular water method. The first-order kinetics model was used to simulate the dynamics of DP transported from soil to water with time. The results indicated that this model could simulate the transport suitably. When the applied P less than 400 kg/hm2, the velocity constant K which is average 1.095 h(-1) unchanged; while when the applied P rates were 800 and 1600 kg/hm2, K decreased by 17.2% and 38.9%, respectively. The exponent function was used to simulate the velocity of DP from soil to water with time and the results showed that it was a suitable model. When the applied P less than 400 kg/hm2, the velocity constant K' which is average 1.037 h(-1) unchanged; while when the applied P rate was higher than 800 kg/hm2, a declining tendency was found for K'. There was significant relationship between soil Olsen-P or CaCl2-P content and soil DPLP or VP0 when surface runoff occurred. This result showed that soil Olsen-P or CaCl2-P content could be used to direct the runoff risk as a gist of estimate soil environment.

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium.

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.