Chang-Wen Du

Effect of Long-Term Rice Straw Return on Soil Glomalin, Carbon and Nitrogen

A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted in a significant increase in both soil easily extractable glomalin (EEG) and total glomalin (TG) concentrations, as compared with application of only chemical fertilizer or no fertilizer application. The EEG and TG concentrations of the NPKS (nitrogen, phosphorus, and potassium fertilizer application + rice straw return) plot were 4.68% and 5.67% higher than those of the CK (unfertilized control) plot, and 9.87% and 6.23% higher than those of the NPK (nitrogen, phosphorus, and potassium fertilizer applied annually) plot, respectively. Application of only chemical fertilizer did not cause a statistically significant change of soil glomalin compared with no fertilizer application. The changes of soil organic C (SOC) and total N (TN) contents demonstrated a similar trend to soil glomalin in these plots. The SOC and TN contents of NPKS plot were 15.01% and 9.18% higher than those of the CK plot, and 8.85% and 14.76% higher than those of the NPK plot, respectively. Rice straw return also enhanced the contents of microbial biomass C (MBC) and microbial biomass N (MBN) in the NPKS plot by 7.76% for MBC and 31.42% for MBN compared with the CK plot, and 12.66% for MBC and 15.07% for MBN compared with the NPK plots, respectively. Application of only chemical fertilizer, however, increased MBN concentration, but decreased MBC concentration in soil.

Enhancement of Phosphorus Solubility by Humic Substances in Ferrosols

Abstract An investigation was conducted to study the effect of humic substance (HS) on the phosphorus (P) solubility in acidic soil. The soil (2.5 g), HS (0, 0.5, and 2.5 g), and P as monocalcium phosphate (0.31 and 1.25 g P kg−1 soil) were mixed with 50 mL distilled water and two different sequences of adding HS and P were used. The results indicated that the P concentration in water and 0.01 mol L−1 CaCl2 solution increased with increasing amounts of humic substance. The concentrations of Fe and Al were also increased. However, Olsen P decreased with increasing amount of humic substance. Water-soluble P concentrations from P rates at 0.31 and 1.25 g P kg−1 soil in the treatment with 0.5 g (2.5 g) humic substance addition were 360% and 70% (500% and 90%) higher, respectively, than those in the treatment with no humic substance addition. P extracted by 0.01 mol L−1 CaCl2 in the treatments with 0.5 and 2.5 g humic substance addition was increased by 400% and 540%, respectively, compared with that in the treatment without humic substance at the rate of 0.31 g P kg−1 soil, while the corresponding P concentrations were increased by 80% and 90% at the rate of 1.25 g P kg−1 soil. The order of mixing humic substance and phosphate did not significantly affect desorbed P and labile P extracted with CaCl2.

Effect of CO2 enrichment on the growth and nutrient uptake of tomato seedlings

Exposing tomato seedlings to elevated CO2 concentrations may have potentially profound impacts on the tomato yield and quality. A growth chamber experiment was designed to estimate how different nutrient concentrations influenced the effect of elevated CO2 on the growth and nutrient uptake of tomato seedlings. Tomato (Hezuo 906) was grown in pots placed in controlled growth chambers and was subjected to ambient or elevated CO2 (360 or 720 µL L^(-1)) and four nutrient solutions of different strengths (1/2-, 1/4-, 1/8-, and 1/16-strength Japan Yamazaki nutrient solutions) in a completely randomized design. The results indicated that some agricultural characteristics of the tomato seedlings such as the plant height, stem thickness, total dry and fresh weights of the leaves, stems and roots, the G value (G value = total plant dry weight/seedling age), and the seedling vigor index (seedling vigor index = stem thickness/(plant height × total plant dry weight) increased with the elevated CO2, and the increases were strongly dependent on the nutrient solution concentrations, being greater with higher nutrient solution concentrations. The elevated CO2 did not alter the ratio of root to shoot. The total N, P, K, and C absorbed from all the solutions except P in the 1/8- and 1/16-strength nutrient solutions increased in the elevated CO2 treatment. These results demonstrate that the nutrient demands of the tomato seedlings increased at elevated CO2 concentrations.

Potassium Fractions in Soils as Affected by Monocalcium Phosphate, Ammonium Sulfate, and Potassium Chloride Application

Abstract Soil potassium (K) deficiency has been increasing over recent decades as a result of higher inputs of N and P fertilizers concomitant with lower inputs of K fertilizers in China; however, the effects of interactions between N, P, and K of fertilizers on K status in soils have not been thoroughly investigated for optimizing N, P, and K fertilizer use efficiency. The influence of ammonium sulfate (AS), monocalcium phosphate (MCP), and potassium chloride application on K fractions in three typical soils of China was evaluated during 90-d laboratory soil incubation. The presence of AS significantly altered the distribution of native and added K in soils, while addition of MCP did not significantly affected K equilibrium in most cases. Addition of AS significantly increased water-soluble K (WSK), decreased exchangeable K (EK) in almost all the soils except the paddy soil that contained considerable amounts of 2:1 type clay minerals with K added, retarded the formation of fixed K in the soils with K added, and suppressed the release of fixed K in the three soils without K added. These interactions might be expected to influence the K availability to plants when the soil was fertilized with AS. To improve K fertilizer use efficiency, whether combined application of AS and K was to be recommended or avoided should depend on K status of the soil, soil properties, and cropping systems.

Influence of Humic Acid on Interaction of Ammonium and Potassium Ions on Clay Minerals

Abstract Interaction of ammonium (NH+4) and potassium (K+) is typical in field soils. However, the effects of organic matter on interaction of NH+ and K+ have not been thoroughly investigated. In this study, we examined the changes in major physicochemical properties of three clay minerals (kaolinite, illite, and montmorillonite) after humic acid (HA) coating and evaluated the influences of these changes on the interaction of NH+4 and K+ on clay minerals using batch experiments. After HA coating, the cation exchange capacity (CEC) and specific surface area (SSA) of montmorillonite decreased significantly, while little decrease in CEC and SSA occurred in illite and only a slight increase in CEC was found in kaolinite. Humic acid coating significantly increased cation adsorption and preference for NH+4, and this effect was more obvious on clay minerals with a lower CEC. Results of Fourier transform infrared spectrometry analysis showed that HA coating promoted the formation of H-bonds between the adsorbed NH+ and the organo-mineral complexes. HA coating increased cation fixation capacity on montmorillonite and kaolinite, but the opposite occurred on illite. In addition, HA coating increased the competitiveness of NH+ on fixation sites. These results showed that HA coating affected both the nature of clay mineral surfaces and the reactions of NH+4 and K+ with clay minerals, which might influence the availability of nutrient cations to plants in field soils amended with organic matter.

Rapid Determination of N Isotope Labeled Nitrate Using Fourier Transform Infrared Attenuated Total Reflection Spectroscopy

Abstract Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy was utilized to quantify nitrate contents, 14NO3-N and 15NO3-N in KNO3 solution and soil. The results showed that the characteristic band of nitrate in solution and soil was 1200–1500 cm−1, and about 35 cm−1 of red shift was observed in the characteristic band of 15NO3− compared with 14NO3−. The intensity of the characteristic band of nitrate increased with the nitrate concentration and with less interference involved. The linear regression was made between the first principal component of characteristic band and nitrate-N content with a correlation coefficients of 0.9840, which indicated that FTIR-ATR spectroscopy was feasible for rapid monitoring of nitrate in solution and soil. Furthermore, based on the red shift of 15NO3− absorption, partial least squares (PLS) method was employed to predict the nitrate -N labeled with different N-isotope in solution and soil. As a result, all the prediction models were excellent. For 14NO3-N and 15NO3-N in solution, the determination coefficients (R2) were 0.9980 and 0.9982, respectively, and corresponding RPD were 6.44 and 4.76, respectively. For 14NO3-N and 15NO3-N in soil, the determination coefficients (R2) were 0.9794 and 0.9679, respectively, and the corresponding RPD were 5.75 and 4.78, respectively. Therefore, FTIR-ATR spectroscopy can be applied for rapid monitoring different N-isotope labeled nitrate in solution and soil, which provides a new method for in situ and fast analysis of nitrification process in soil.

Rapid Determination of Nitrate in Chinese Cabbage Using Fourier Transforms Mid-infrared Spectroscopy

Abstract The nitrate content in Chinese cabbage was rapidly predicted using the techniques of mid-infrared spectroscopy (diffusion reflectance spectroscopy, photoacoustic spectroscopy and attenuated total reflectance spectroscopy). There existed interferences in the characteristic bands of nitrate (1200–1500 cm−1) for all the infrared spectra. The interferences for diffusion reflectance spectra were strongest, followed by photoacoustic spectra, and the weakest for the attenuated total reflectance spectra, which were also verified by the principal component regressions between infrared spectra and nitrate content in Chinese cabbage, and the coefficient (R2) were 0.4003, 0.4874 and 0.8741, respectively. Based on attenuated total reflectance spectra, the chemometrics method of partial least squares was involved to improve the prediction model of nitrate, the prediction accuracy was significantly decreased, the coefficient was 0.8851, and the RPD value was 3.19. Therefore, the technique of mid-infrared attenuated total reflectance spectroscopy was feasible for rapid monitoring of nitrate in Chinese cabbage.

In Situ Measurement of Ammonia Concentration in Soil Headspace Using Fourier Transform Mid-Infrared Photoacoustic Spectroscopy

Ammonia (NH3) volatilization is one of the important pathways of nitrogen loss in alkaline soil, and the NH3 concentration in soil headspace is directly linked with the NH3 volatilization. Ammonia was characterized by Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) and two typical absorption bands in the region of 850–1200 cm−1 were observed, which could be used for the prediction of NH3 concentration in the soil headspace. An alkaline soil from North China was involved in the soil incubation, pot and field experiments under three fertilization treatments (control without N input (CK), urea and coated urea). Ammonia concentrations in the soil headspace were determined in each experiment. In the soil incubation experiment, the NH3 emissions were initiated by the N input, reached the highest concentration on day 2, and decreased to the level as measured in CK after 8 d, with significantly higher NH3 emissions in the urea treatment compared to coated urea treatment, especially during the first 4 d. The NH3 concentration in soil headspace of the pot experiment showed the similar dynamics as that in the incubation experiment; however, the NH3 concentration in the soil headspace in the field experiment demonstrated a significantly different emission pattern with those of the incubation and pot experiments, and there was a 4-d delay for the NH3 concentration. Therefore, the NH3 concentration in the incubation and pot experiments could not be directly used to model the real NH3 emission in the field due to the differences in fertilization method and application rate as well as soil temperature and soil disturbance. It was recommended that light irrigation in the second week after fertilization and involvement of controlled release coated urea could be used to significantly decrease N loss from the perspective of NH3 volatilization.