Conservation tillage has been applied in vast semi-arid regions of the Guanzhong Plain, Northwest China. The tillage effects on soil aggregation, organic carbon (OC) stabilization and grain yield on this plain have not been fully elucidated. A 9-year field experiment was established from 2002 on a silty clay loam soil (Eum-Orthic Anthrosol) growing winter wheat-maize in a double-cropping system. Six conservation tillage treatments were applied by different combinations of rotary tillage (RT), subsoiling (SS) and no-till (NT), with or without finely chopped straw retention. Conventional tillage (CT) acted as the control. Results showed that in the surface (0-10 cm) soil, the proportion of waterstable aggregates (WSA) <0.05 mm was 18% less while that for WSA >2 mm was 98% more under NT treatments compared with CT. Additionally, the oxidizable OC content in WSA 0.25-2 mm was 27% greater under NT treatments compared with CT. The OC stocks increased under SS by 17%, RT by 16% and NT by 15% relative to CT. Grain yield (wheat + maize) showed similar increasing trends in all the tillage treatments compared with CT. Both OC stocks and grain yield were larger in treatments with than without straw retentions. These results indicate that NT is beneficial for OC accumulation in WSA but is limited in its ability to improve soil structure in this region. SS plus straw retention (fine-chopped or as a mulch) is an effective practice to improve soil structural stability, OC accumulation and soil productivity of Eum-Orthic Anthrosols in Northwest China.
Exogenous C application can improve the physicochemical properties and fertility of soil. This study was conducted to determine whether the application of biochar (BC) was better than straw for improving soil structure and crop growth. The short‐term effects of exogenous C application on the size distribution of water‐stable aggregates, organic C sequestration, and grain yield of winter wheat (Triticum aestivum L.) were investigated on a silty clay loam soil in the Guanzhong Plain, Northwest China. Biochar and straw were applied at equal C rates: 1, 3, and 10% in straw treatments (Str1.0, Str3.0, and Str10.0, respectively) and 0.8, 2.4, and 8% in BC treatments (BC0.8, BC2.4, and BC8.0, respectively). No‐C treatment (CK) was used as the control. The mass proportion of macroaggregates (>0.25 mm) was increased by 16.9% in BC2.4 and 45.8% in BC8.0, and soil organic carbon (SOC) was increased by 13.2 to 155.1% on average in the BC treatments when compared with CK. A small quantity of BC (0.8 and 2.4%) increased microbial biomass C content but decreased dissolved organic C content, while a large quantity of BC (8%) had the reverse effects. Wheat yields were increased by 14.9 and 19.1% in BC0.8 and BC2.4, respectively, while they were decreased by 37.3 and 90.1% in Str3.0 and Str10.0, respectively, when compared with CK. Moderately heavy soil BC amendment (e.g., applied rate, 2.4%) is beneficial to soil structure improvement and wheat growth and effective for harmless disposal of excess plant residues in the Guanzhong Plain, Northwest China.Core Ideas Biochar addition enhanced macroaggregate formation and microaggregate agglomeration. Biochar particles mostly existed in the macroaggregate (>0.25 mm) fractions. Low and moderate biochar application at 0.8% and 2.4% increased microbial biomass C and wheat yield. Heavy straw application at 3% and 10% inhibited wheat growth and yield increase.
We investigated the effects of compost (CM), made from poultry and cattle manure with spent mushroom substrate, plus chemical fertilizers (CFs) on soil organic carbon (C) and nitrogen (N) fractions in silty loam soil of the Loess Plateau. Eight fertilizer practices were applied in a 7‐year‐old ‘Red Fuji’ apple (Malus domestica Borkh.) orchard for 360 days. Compared to CM alone, CM–CFs decreased slightly soil total organic C but increased total N by 4.3–11.6%. Notably, CM–CFs increased soil microbial biomass C (MBC) by 2.7–26.5% and microbial biomass N (MBN) by 7–13.7%. Soil water‐soluble carbon (WSC) was increased by 20.7% and 19.2% when 2% CM plus N and phosphorus (P) (2%M–NP) and 4% CM plus N and P (4%M–NP) were applied, respectively. Whereas 0.5% CM plus N and P (0.5%M–NP) increased WSC by 9.3% on day 30 but decreased it by 7.2% from 30–360 days. Hot water‐soluble C increased by 13.1–14.6% from 0–180 day, but thereafter, the effect disappeared. Compared to CFs, CM–CFs increased MBN by 35.1–115.6%, and increased alkali‐hydrolyzable‐N by 3.5–55.8% over 180–360 days of incubation. Additionally, CM–CFs promoted N mineralization, increasing NH4‐N and NO3‐N contents. Based on the changes in C and N fractions and available nutrients, 2%M–NP (45 t/ha of CM plus 450 kg/ha of N and 157.5 kg/ha of P) may be the optimal fertilizer strategy for stimulating soil microbial growth and activity, and enhancing nutrient cycling for apple growth.
Many agricultural and hydrological processes require the detailed knowledge of soil water content (SWC) in the vertical profile. Quantifying real-time and in situ SWC is difficult due to time, cost, toil, and technical issues. This paper describes the development of a multi-depth SWC monitoring sensor which can estimate the SWC from 4 vertical depths simultaneously. The probe is a type of electromagnetic (EM) sensor that indirectly measures the SWC on the basis of dielectric theory. The sensor was calibrated with soil samples of three distinct topographical locations. The calibration models were established by fitting linear order equations. The performance of the sensor was evaluated in situ field conditions. A multi-depth SWC curve was investigated to examine the impact of continuous estimations of SWC at specified depths on the sensor performance. The sensor was integrated with vertical interpolation technique to improve the measurement accuracy. The results indicated the optimal range of the SWC measurements, and the estimation error was less than 5%, except irrigation cycles. The linear fit coefficient of determination (R2) ranged from 0.957 to 0.993 and root mean square error (RMSE) was ranging from 1.565 to 4.456. The results showed that the sensor performed consistently better for at least 4 months within acceptable soil conditions. The sensor will be advantageous for continuous estimations of SWC, and managing the irrigation practices.
Wavelengths combination optimization in near infrared spectroscopy (NIRS) analysis was very important for improving model prediction effect, simplifying high dimension problems, reducing model complexity and designing special NIRS instruments with high signal noise ratio. Based on the prediction effect of single wavelength linear regression model, a special wavelength set with 25 information data points was filtered out. All wavelengths combinations of these 25 wavelengths were used to establish multiple linear regression (MLR) models respectively. With a prediction effect close to the PLS model based on whole spectral region, the simplest MLR model is the 7-wavelengths combination of 1105.5, 1108, 1895, 2150.5, 2278.5, 2284, 2286.5 (nm), RMSEP, R P , RRMSEP was 0.2505 (%), 0.8753, 15.73% respectively. This indicated that the wavelengths combination selection method based on the prediction effect of single wavelength linear regression model could be applied to the NIRS analysis and could provide valuable reference for designing minitype special NIRS instruments.
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