Response of maize yield and nitrogen recovery efficiency to nitrogen fertilizer application in field with various soil fertility.

Appropriate nitrogen (N) management system is essential for effective crop productivity and minimizing agricultural pollution. However, the underlying mechanistic understanding of how N fertilizer regulates crop yield via soil properties in soils with different fertilities remains unresolved. Here, we used a field experiment that spanned 3 cropping seasons to evaluate the grain yield (GY), aboveground biomass and N recovery efficiency (NRE) after treatment with five N fertilizer application rates (N0, N75, N112, N150, and N187) in soils with three levels of fertility. Our results indicated that the highest GY across low, moderate, and high fertility soils were 1.5 t hm-2 (N150), 4.9 t hm-2 (N187), and 5.4 t hm-2 (N112), respectively. The highest aboveground biomass and NRE were observed at N150 for all three levels of soil fertility, while only the N uptake by aboveground biomass of low and high fertility soils decreased at N187, confirming that excessive N fertilization results in a further decline in crop N uptake. The relationship between GY, NRE and N fertilizer application rates fit the unary quadratic polynomial model. To achieve a balance between grain production and environmental benefits in N fertilizer, appropriate N fertilizer rates were determined to be 97.5 kg hm-2, 140 kg hm-2 and 131 kg hm-2 for low, moderate and high fertility soils, respectively. Structural equation modeling suggested that GY was significant correlated with soil microbial biomass carbon (SMBC) and N directly in low fertility field, with SMBC directly in moderate fertility field, and via SOC and NO3 -N in high fertility field. Therefore, a soil-based management strategy for N fertilizers could enhance food security while reducing agricultural N fertilizer inputs to mitigate environmental impacts.

Effect of replacing synthetic nitrogen fertilizer with animal manure on grain yield and nitrogen use efficiency in China: a meta-analysis.

To reduce reliance on synthetic nitrogen (N) fertilizer and sustain food production, replacing synthetic N fertilizer with animal manure as an effective method is widely used. However, the effects of replacing synthetic N fertilizer with animal manure on crop yield and nitrogen use efficiency (NUE) remain uncertain under varying fertilization management practices, climate conditions, and soil properties. Here, we performed a meta-analysis of wheat (Triticum aestivum L.), maize (Zea mays L.), and rice (Oryza sativa L.) based on 118 published studies conducted in China. Overall, the results indicated that substituting synthetic N fertilizer with manure increased yield by 3.3%-3.9% for the three grain crops and increased NUE by 6.3%-10.0%. Crop yields and NUE did not significantly increase at a low N application rate (≤120 kg ha-1) or high substitution rate (>60%). Yields and NUE values had higher increases for upland crops (wheat and maize) in temperate monsoon climate/temperate continental climate regions with less average annual rainfall (AAR) and lower mean annual temperature (MAT), while rice had higher increases in subtropical monsoon climate regions with more AAR and higher MAT. The effect of manure substitution was better in soil with low organic matter and available phosphorus. Our study shows that the optimal substitution rate was 44% and the total N fertilizer input cannot be less than 161 kg ha-1 when substituting synthetic N fertilizer with manure. Moreover, site-specific conditions should also be considered.

Achieving high yield and nitrogen agronomic efficiency by coupling wheat varieties with soil fertility.

Wheat breeding has progressively increased yield potential through decades of selection, markedly increased the capacity for food production. Nitrogen (N) fertilizer is essential for wheat production and N agronomic efficiency (NAE) is commonly index used for evaluate the effects of N fertilizer on crop yield, calculated as the difference of wheat yield between N fertilizer treatment and non-N fertilizer treatment divided by the total N application rate. However, the impact of variety on NAE and its interaction with soil fertility remain unknown. Here, to clarify whether and how wheat variety contributes to NAE, and to determine if soil conditions should be considered in variety selection, we conduct a large-scale analysis of data from 12,925 field trials spanning ten years and including 229 wheat varieties, 5 N fertilizer treatments, and a range of soil fertility across China's major wheat production zones. The national average NAE was 9.57 kg kg-1, but significantly differed across regions. At both the national and regional scales, variety significantly affected NAE, and different varieties showed high variability in their performance among low, moderate, and high fertility soils. Here, superior varieties with both high yield and high NAE were identified at each soil fertility fields. The comprehensive effect of selecting regionally superior varieties, optimizing N management, and improving soil fertility could potentially decrease the yield gap by 67 %. Therefore, variety selection based on soil conditions could facilitate improved food security while reducing fertilizer inputs to alleviate environmental impacts.

Mechanism of Al toxicity alleviation in acidic red soil by rice-straw hydrochar application and comparison with pyrochar.

In the past decade, biochar has been widely regarded as a new type of soil conditioner that can effectively control soil acidification and alleviate Al toxicity. Hydrochar is identified as a more economical carbon material than pyrochar, but its effect on Al toxicity and the associated mechanism have not been studied. Thus, a two-stage indoor incubation experiment was conducted to investigate the effect of rice-straw hydrochar (HC, application rate: 1/2/3 %) on maize seedling root growth, soil solution Al activity, soil exchangeable Al and pH buffering ability in acidic red soils from two sites. We also used pyrochar (PC, application rate: 3 %) produced from the same rice straw for comparison. Except for HC-1 %, both hydrochar and pyrochar addition significantly stimulated relative root elongation (136.36 % ~ 284.09 %), diminished the cell death ratio (27.96 % ~ 85.56 %) and Al content in root tips (18.80 % ~ 80.11 %) by decreasing the total Al content (44.78 % ~ 76.10 %) and the proportion of Al3+ species (27 % ~ 32 %) in soil solution. Hydrochar did not significantly promote the soil pH buffer capacity (pH-BC) or effective cation exchange capacity (ECEC), while PC-3 % did. The DOC (dissolved organic carbon) content of soil solution was dramatically elevated by 203.9 % ~ 783.2 % after hydrochar addition. Hydrochar mitigates Al activity in soil solution mainly through Al-DOC complexation and adsorption, thus suppressing the Al toxicity of maize roots. Hydrochar may be an economical soil amendment for ameliorating Al toxicity despite its overall alleviation effect on Al toxicity being lower than pyrochar.

Mechanism of Potassium Release from Feldspar by Mechanical Activation in Presence of Additives at Ordinary Temperatures.

To improve the potassium availability of feldspar at ordinary temperatures, the mechanical grinding and addition of sodium hydroxide/salts were employed to study the effects of mechanical activation and strong alkali addition on particle characteristics, water-soluble potassium, and the available potassium of feldspar. A laser particle size analyzer was utilized for the direct determination of particle size distribution (PSD) using ground samples. The Brunauer-Emmett-Teller (BET) method was employed for specific surface areas. X-ray diffraction (XRD) was employed for structural characterization, scanning electron microscopy (SEM) for morphology exploration, and energy dispersive spectroscopy (EDS) to determine the chemical composition of potassium feldspar powder. The results revealed that the mechanical activation of potassium feldspar could reduce the particle size and produce agglomerated nanoparticles in the later period. The addition of NaOH and sodium salt did not cause agglomeration, and NaOH dissolved the nanoparticles. The water-soluble potassium content of feldspar in each treatment increased during mechanical grinding, from 21.64 mg kg-1 to 1495.81 mg·kg-1, by adding NaOH 5% weight of potassium feldspar powder and to 3044.08 mg·kg-1 by adding NaOH 10% weight with effects different from those of mechanical shaking. By comparison, only 162.93 mg·kg-1 water-soluble potassium was obtained by adding NaOH 5% weight. The dissolved potassium in the former case was significantly higher than in the latter, and the addition of NaOH and sodium salts significantly enhanced the water-soluble potassium contents due to ion exchange. Furthermore, the addition of sodium hydroxide improved the water-soluble potassium due to its mechanochemical action on potassium feldspar. The mechanical energy changed the crystal structure of potassium feldspar, explaining the increase in available potassium. The addition of sodium salts did not promote change in the feldspar's structure, thereby did not raise the available potassium content. The reason for this was related to the mechanochemical action on sodium hydroxide and feldspar, which could promote the dissolution of fine particles, thereby incrementing the available potassium.

Investigation of the spatial heterogeneity of soil microbial biomass carbon and nitrogen under long-term fertilizations in fluvo-aquic soil.

Soils are heterogeneous and microbial spatial distribution can clearly indicate the spatial characteristics of the soil carbon and nitrogen cycle. However, it is not clear how long-term fertilization affects the spatial distribution of microbial biomass in fluvo-aquic soil. We collected fluvo-aquic soil samples (topsoil 0-7.5 cm and sub-topsoil 7.5-20 cm) using a spatially-explicit design within three 40.5 m2 plots in each of four fertilization treatments. Fertilization treatments were: cropping without fertilizer inputs (CK); chemical nitrogen, phosphorus, and potassium fertilizer (NPK); chemical fertilizer with straw return (NPKS); and chemical fertilizer with animal manure (NPKM). Variables included soil microbial biomass carbon (MBC) and nitrogen (MBN), and MBC/MBN. For both soil layers, we hypothesized that: microbial biomass was lowest in CK but with the largest spatial heterogeneity; and microbial biomass was highest in NPKM and NPKS but with the lowest spatial heterogeneity. Results showed that: (1) Fertilization significantly increased MBC and MBN more in topsoil than sub-topsoil but had no MBC/MBN changes. (2) The coefficient of variation (CV) and Cochran's C showed that variation was largest in CK in topsoil and NPK in sub-topsoil and that variation of topsoil was generally lower than in sub-topsoil. The sample size of the three variables was largest in CK in topsoil but had little variation among the other treatments. (3) The trend-surface model showed that within-plot heterogeneity varied substantially with fertilization (NPKM = NPK > NPKS > CK), but Moran's I and the interpolation map showed that spatial variability with fertilization followed the order NPK > NPKS > CK = NPKM at a fine scale in topsoil. In sub-topsoil, the trend-surface model showed that within-plot heterogeneity followed the order NPKM = CK > NPK > NPKS and that the fine-scale pattern was NPKM>NPK = NPKS>CK. MBC had the highest spatial heterogeneity among the three variables in both soil layers. Our results indicate that the application of organic fertilizer (straw or manure) reduced the variation of MBC and MBN but increased the spatial variability of MBC and MBN. The spatial variation of the three variables was MBC > MBN > MBC/MBN regardless of whether variation was considered at the plot-scale or the fine-scale in both layers.