Hubing Zhao

Comparison of Factors Affecting Soil Nitrate Nitrogen and Ammonium Nitrogen Extraction

Extraction of soil nitrate nitrogen (NO3 −-N) and ammonium nitrogen (NH4 +-N) by chemical reagents and their determinations by continuous flow analysis were used to ascertain factors affecting analysis of soil mineral N. In this study, six factors affecting extraction of soil NO3 −-N and NH4 +-N were investigated in 10 soils sampled from five arable fields in autumn and spring in northwestern China, with three replications for each soil sample. The six factors were air drying, sieve size (1, 3, and 5 mm), extracting solution [0.01 mol L−1 calcium chloride (CaCl2), 1 mol L−1 potassium chloride (KCl), and 0.5 mol L−1 potassium sulfate (K2SO4)] and concentration (0.5, 1, and 2 mol L−1 KCl), solution-to-soil ratio (5:1, 10:1, and 20:1), shaking time (30, 60, and 120 min), storage time (2, 4, and 6 weeks), and storage temperature (−18 oC, 4 oC, and 25 oC) of extracted solution. The recovery of soil NO3 −-N and NH4 +-N was also measured to compare the differences of three extracting reagents (CaCl2, KCl, and K2SO4) for NO3 −-N and NH4 +-N extraction. Air drying decreased NO3 −-N but increased NH4 +-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO3 −-N and NH4 +-N concentrations compared to other treatments. The concentrations of extracted NO3 −-N and NH4 +-N in soil were significantly (P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO3 −-N and NH4 +-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO3 −-N and 94.9% for NH4 +-N. K2SO4 was not found suitable for NO3 −-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl2 was only 57.3% for NH4 +-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L−1 KCl could fully extract NO3 −-N. A ratio of 10:1 of solution to soil was adequate for NO3 −-N extraction, whereas the NH4 +-N concentration was almost doubled when the solution-to-soil ratio was increased from 5:1 to 20:1. Storage of extracted solution at −18 °C, 4 °C, and 25 °C had no significant effect (P < 0.05) on NO3 −-N concentration, whereas the NH4 +-N concentration varied greatly with storage temperature. Storing the extracted solution at −18 oC obtained significantly (P < 0.05) similar results with that determined immediately for both NO3 −-N and NH4 +-N concentrations. Compared with the immediate extraction, the averaged NO3 −-N concentration significantly (P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH4 +-N varied in the two seasons. In conclusion, using fresh soil passed through a 3-mm sieve and extracted by 0.5 mol L−1 KCl at a solution-to-soil ratio of 10:1 was suitable for extracting NO3 −-N, whereas the concentration of extracted NH4 +-N varied with KCl concentration and increased with increasing solution-to-soil ratio. The findings also suggest that shaking for 60 min and immediate determination or storage of soil extract at −18 oC could improve the reliability of NO3 −-N and NH4 +-N results.

Summer fallow soil management – impact on rainfed winter wheat

Summer fallow soil management is an important approach to improve soil and crop management in dryland areas. In the Loess Plateau regions, the annual precipitation is low and varies annually and seasonally, with more than 60% concentrated in the summer months from July to September, which is the summer fallow period in the winter wheat-summer fallow cropping system. With bare fallow in summer as a control, a 3-year location-fixed field experiment was conducted in the Loess Plateau to investigate the effects of wheat straw retention (SR), green manure (GM) planting, and their combination on soil water retention (WR) during summer fallow, winter wheat yield, and crop water use and nitrogen (N) uptake. The results showed that SR increased soil WR during summer fallow by 20 mm on average compared with the control over 3 experimental years but reduced the grain yield by 8% in the third year and the grain N content by 6–15% in all 3 years. In contrast, GM planting markedly reduced soil WR by 16 mm and 33 mm in the first and third year, respectively, but increased water use efficiency (WUE) by 16% in the third year and nitrate N accumulation in 0–100 cm soil at winter wheat sowing. Their combination did not significantly affect the soil WR or the soil nitrate N content in any of the 3 years, but did increase WUE by 11% in the third year and grain yield by 2.6% in the second year. In conclusion, the combination of SR and GM planting mitigated the negative effects of the individual measures, providing a feasible method for summer fallow management in the semiarid Loess Plateau in China and other similar regions.

Effects of topdressing with nitrogen fertilizer on wheat yield, and nitrogen uptake and utilization efficiency on the Loess Plateau

Studies from various countries show that topdressing with nitrogen fertilizer can effectively increase winter wheat grain yields. However, information on its effects on wheat yields on the Loess Plateau in China is scarce. Thus, we investigated yields, N concentration and uptake, nitrogen use efficiency (NUE), and partial factor productivity of nitrogen (PFPN) of winter wheat at a site on the Plateau in three consecutive years following four treatments: no N application; 150 kg N ha−1 and 46 kg P ha−1 applied as base dressing; 198 kg N ha−1 and 46 kg P ha−1 applied as base dressing; and 150 kg N ha−1 and 46 kg P ha−1 applied as base dressing + 48 kg N ha−1 applied as topdressing in the spring. Topdressing with N fertilizer resulted in significant increases in wheat yield, wheat biomass production, and N concentrations and uptake in wheat grain, straw, and chaff. PFPN was 6.9%, 15.2%, and 5.5% higher, and NUE 28.1%, 31.6%, and 12.5% higher, in the three years with top dressing than with base dressing alone. Topdressing N fertilizer for winter wheat is recommended on the Loess Plateau.

Increased Dryland Winter Wheat Yields by Nitrogen Fertilizer Topdressing and its Relationship to Soil Moisture, Available N, P and K in Northwestern China

ABSTRACT Winter wheat (Triticum aestivum L.) production in northwestern China as a monoculture is hampered by unfertile soil and drought. With the fast-developing Chinese chemical fertilizer industry, many farmers now use more nitrogen (N) fertilizer as topdressing for winter wheat in early spring, in addition to a basal dose of N fertilizer applied in the previous autumn at seeding time. The objective of this study was to evaluate the increase in grain yield of dryland winter wheat by early spring N fertilizer topdressing, and its relationship to soil moisture, available N, phosphorus (P) and potassium (K). Field experiments with no N fertilizer topdressing (Fb) and N fertilizer topdressing (Fb+t) treatments were carried out over two growing seasons at 54 site-years to assess the relationship between increase in winter wheat grain yield by early spring N fertilizer topdressing and soil moisture, available N, P and K in Changwu county, Shaanxi province, China. Compared to Fb treatment, the Fb+t treatment produced grain yields lower at 10 site-years, and increased by <10% at 21 site-years and by >10% at 23 site-years. The results indicated that topdressing N fertilizer could increase wheat grain yield when soil nitrate-N accumulation in the 0–20, 20–40 and 40–60 cm depths was less than 121.7, 36.4 and 24.1 kg N ha−1, and soil moisture content in the 40–60, 60–80 and 80–100 cm depths was more than 15.7%, 16.7% and 16.9%, respectively. The findings also suggested that it is not necessary to analyze soil for ammonium-N, available P and K before topdressing N fertilizer. It is necessary to analyze 0–60 cm soil profile for nitrate-N and 40–100 cm depth for soil moisture before topdressing N fertilizer for winter wheat in dryland areas of northwestern China.