Substitution of Chemical Fertilizer with Organic Fertilizer Affects Soil Total Nitrogen and Its Fractions in Northern China

The impact of chemical to organic fertilizer substitution on soil labile organic and stabilized N pools under intensive farming systems is unclear. Therefore, we analyzed the distribution of soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), dissolved organic N (DON), and mineral N (NO3− and NH4+) levels down to 100 cm profile under wheat–maize rotation system in northern China. The experiment was established with four 270 kg ha−1 N equivalent fertilizer treatments: Organic manure (OM); Organic manure with nitrogen fertilizer (OM + NF); Nitrogen fertilizer (NF); and Control (CK). Results found that the OM and OM + NF treatments had significantly higher STN, PON, MBN, DON, and NO3− contents in 0–20 cm topsoil depths. Conversely, the NF treatment resulted in the highest (p < 0.01) DON and NO3− depositions in 40–100 cm subsoil depths. The NH4+ contents in selected profile depths were significantly highest (p < 0.01) under OM treatment. The correlations between STN and its fractions were positively significant at 0–10 and 10–20 cm topsoil depths. Our results suggest that partial substitution of chemical fertilizer with organic manure could be a sustainable option for soil N management of intensive farming systems.

Long-Term Integrated Nutrient Management in the Maize–Wheat Cropping System in Alluvial Soils of North-Western India: Influence on Soil Organic Carbon, Microbial Activity and Nutrient Status

Integrated nutrient management (INM) is a widely recognized tool to ensure sustainable crop productivity while preserving soil fertility. The addition of organic manures in soil has been evidenced to improve soil characteristics, in addition to improving nutrient availability. The soil samples, with five treatment combinations of chemical fertilizers with farmyard manure (FYM), were collected from a 17-year-old field experiment conducted at PAU, Ludhiana to investigate the effect of INM on the buildup of organic carbon (OC), microbial community, soil nutrient status and improvement in soil physical properties under the maize–wheat cropping system. The INM technique enhanced the OC content (0.44 to 0.66%), available N (152.8 to 164.9 kg ha−1), P (22.8 to 31.4 kg ha−1) and K (140.6 to 168.0 kg ha−1) after 17 years. The DTPA-extractable and total micronutrients (Zn, Cu, Fe, and Mn) status also improved significantly with FYM supplementation. The organic source, coupled with inorganic fertilizers, improved the water holding capacity, total porosity, soil respiration, microbial biomass C, microbial biomass N, and potentially mineralizable N. However, pH, EC, and bulk density of soil decreased with the addition of FYM, coupled with chemical fertilizers.

Changes in Soil Labile Organic Matter as Affected by 50 Years of Fertilization with Increasing Amounts of Nitrogen

Microbially mediated soil organic matter is an extremely sensitive pool that indicates subtle changes in the quality parameters responsible for the soil’s ecological and productive functions. Fifty years of mineral fertilization of a wheat-corn cropping system has a strong impact on soil quality parameters. The goal of the research was to study the dynamics and quality of soil biological parameters affected by increasing amounts of mineral nitrogen. Soil respiration, potentially mineralizable C and N, microbial biomass C and N and light-fraction OM on Cambisol were analyzed in the following treatments: (1) Control (without fertilization); (2) NPK (60/51/67); (3) NPK (90/51/67); (4) NPK (120/51/67); (5) NPK (150/51/67 kg ha−1). The parameters studied were significantly affected by the long-term application of mineral fertilizer compared with both the control and the adjacent native soil. The highest amounts of nitrogen (N150) did not significantly differ from N120 and N90 for most of the parameters studied. Potentially mineralizable C represented the largest labile carbon pool, while microbial biomass N was the largest labile nitrogen pool. The mineralization rates for C and N were oppositely distributed over the seasons. The sensitivity index correlated with the amount of light-fraction OM. The results give a deeper insight into the behavior and distribution of different pools of labile SOM in the agro-landscapes and can serve as a reliable basis for further research focused on zero soil degradation.

The Transformation Dynamics and Homogeneity of Different N Fractions in Compost Following Glucose Addition

The application of compost to soil is a common fertilization practice for improving soil quality and crop growth. The isotopic labeling technique is mostly used to investigate the contribution of compost N to crop uptake. However, compost N includes various N fractions and labeling dissimilarity, which may cause bias when calculating the compost N contribution to plants. Therefore, the labeling dynamics of different N fractions in compost and the homogenous labeling time point should be clarified. Given the 15N-labeling in chemical fertilizer and the carbon source, i.e., glucose, the compost N pools were divided into active N (mineral N, soluble organic N [SON], microbial biomass N [MBN]), stable N (hot-water extractable organic N [HWDON]), and recalcitrant N. The atom percentage excess (APE) of different N in compost notably varied at the beginning of incubation, ranging from 0–3.7%. After the addition of glucose, biological N immobilization was promoted (13.7% and 28.8% for MBN and HWDON, respectively) and promoted the transformation among available N pools. Adding distinct doses of glucose at three stages to 15N-labeled compost resulted in diverse microbial responses, thereby redistributing exogenous N in each fraction (15NH4+-N went into SO15N from day 15 to day 30 and increased by 5.1%; SO15N entered MB15N and HWDO15N during day 30 to day 45 and increased by 5.7% and 5.2%, respectively). On day 45, homogeneous 15N-labeled compost was achieved, which was 2.4% for 15N APE for all N fractions. Overall, the quantitative data for the transformation of N fractions in compost at distinct stages provides a scientific basis for compost labeling trials, in order to identify the time point at which compost N-labeling is homogeneous, which is necessary and meaningful to reduce the bias of the contribution rate of compost-N to plants.

Effects of mowing dominant grasses on root exudation and soil nitrogen cycling in a natural sod culture apple orchard

We evaluated the effects of mowing dominant grasses on root exudation and soil nitrogen (N) cycling by assessing metabolomics analysis of root exudates, microbial metabolism, the abundance of N-cycling-related prokaryotes, and different forms of N concentrations in soil. The treatments included Polygonum aviculare L. mowing (T1), Digitaria sanguinalis (L.) Scop. mowing (T2), and no mowing as the controls (CK1 and CK2). The results showed that compared with the no mowing control (CK1 and CK2), T1 and T2 root exudates contained 223 (178 up-regulated, 45 down-regulated) and 183 (40 up-regulated, 143 down-regulated) differential metabolites, respectively. The average well colour development (AWCD) could reflect the microbial metabolic activity. The AWCD values of T1 were increased while that of T2 decreased on the 2^nd day after mowing. The variation in root exudates was the main reason for the change in soil AWCD values and carbon utilisation of T1 and T2 on the 2^nd day after mowing. Mowing increased soil microbial biomass N content significantly in the T1 and T2 topsoil. The NO₃^–-N and NH₄⁺-N contents in the 0–10 cm soil increased on the 2^nd day after T1 mowing with an increase in the nitrogenase iron protein gene (nifH), glutamate dehydrogenase gene (gdh), ammonia monooxygenase gene (amoA) of ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB) abundance. However, NO₃^–-N content decreased on the 2^nd day after T2 mowing following a decrease in AOA-amoA and AOB-amoA gene abundance. The results of this study will facilitate the optimisation of sod culture orchard N management, reduction of N fertiliser input, and improvement of N utilisation efficiency.

Zinc Plus Biopolymer Coating Slows Nitrogen Release, Decreases Ammonia Volatilization from Urea and Improves Sunflower Productivity

Currently, the global agriculture productivity is heavily relied on the use of chemical fertilizers. However, the low nutrient utilization efficiency (NUE) is the main obstacle for attaining higher crop productivity and reducing nutrients losses from these fertilizers to the environment. Coating fertilizer with micronutrients and biopolymer can offer an opportunity to overcome these fertilizers associated problems. Here, we coated urea with zinc sulphate (ZnS) and ZnS plus molasses (ZnSM) to control its N release, decrease the ammonia (NH3) volatilization and improve N utilization efficiency by sunflower. Morphological analysis confirmed a uniform coating layer formation of both formulations on urea granules. A slow release of N from ZnS and ZnSM was observed in water. After soil application, ZnSM decreased the NH3 emission by 38% compared to uncoated urea. Most of the soil parameters did not differ between ZnS and uncoated urea treatment. Microbial biomass N and Zn in ZnSM were 125 and 107% higher than uncoated urea, respectively. Soil mineral N in ZnSM was 21% higher than uncoated urea. Such controlled nutrient availability in the soil resulted in higher sunflower grain yield (53%), N (80%) and Zn (126%) uptakes from ZnSM than uncoated fertilizer. Hence, coating biopolymer with Zn on urea did not only increase the sunflower yield and N utilization efficiency but also meet the micronutrient Zn demand of sunflower. Therefore, coating urea with Zn plus biopolymer is recommended to fertilizer production companies for improving NUE, crop yield and reducing urea N losses to the environment in addition to fulfil crop micronutrient demand.

Dynamics of Microbial Biomass, Nitrogen Mineralization and Crop Uptake in Response to Placement of Maize Residue Returned to Chinese Mollisols over the Maize Growing Season

Returning residue to soils is not only an effective nutrient management method, but also can reduce the air pollution caused by residue burning, which has become an important factor in global warming. However, it is not clear whether returning residue to the soil can affect the nitrogen mineralization and the nitrogen cycle process, and the environmental impact caused by the nitrogen loss in gaseous forms. Therefore, a pot experiment was conducted to study the effects of residue placement on the nitrogen turnover process, including microbial biomass N (MBN) and C (MBC), inorganic N, crop N uptake, and the contribution of residue-derived N to maize at different maize growth stages. Three treatments were assessed: no residue addition (T0), residue addition to the soil surface (T1), and residue incorporation into the 0–10 cm soil layer (T2). Soil samples were taken at the 0–5 and 5–10 cm layers for all residue treatments. Residue retention (T1 and T2) significantly affected the MBC and MBN contents and decreased MBC/MBN ratio at different maize growth stages. MBC/MBN markedly increased at the R1 stage compared to other growth stages. The differences in total inorganic nitrogen (TIN) were attributed to the balance in net N immobilization and net mineralization in the different maize growth stages. In addition, T2 significantly increased the residue-derived N source for maize by 11.3% compared to T0 in the R3 growth stage. Overall, relative to T1, T2 is a better agriculture management measure to promote N transformation and supply, and enhance residue-derived N release and uptake in maize.

Wheat Straw Incorporation Affecting Soil Carbon and Nitrogen Fractions in Chinese Paddy Soil

Soil organic carbon (SOC) and nitrogen (N) fractions greatly affect soil health and quality. This study explored the effects of wheat straw incorporation on Chinese rice paddy fields with four treatments: (1) a control (CK), (2) a mineral NPK fertilizer (NPK), (3) the moderate wheat straw (3 t ha−1) plus NPK (MSNPK), and (4) the high wheat straw (6 t ha−1) plus NPK (HSNPK). In total, 0–5, 5–10, 10–20, and 20–30 cm soil depths were sampled from paddy soil in China. Compared with the CK, the HSNPK treatment (p < 0.05) increased the C fraction content (from 13.91 to 53.78%), mainly including SOC, microbial biomass C (MBC), water-soluble organic C (WSOC), and labile organic C (LOC) in the soil profile (0–30 cm), and it also (p < 0.05) increased the soil N fraction content (from 10.70 to 55.31%) such as the soil total N (TN) at 0–10 cm depth, microbial biomass N (MBN) at 0–20 cm depth, total water-soluble N (WSTN) at 0–5 and 20–30 cm depths, and total labile N (LTN) at 0–30 cm depth. The primary components of soil LOC and LTN are MBC and MBN. Various soil C and N fractions positively correlated with each other (p < 0.05). The HSNPK treatment promoted the soil MBC, WSOC, and LOC to SOC ratios, and also promoted MBN, WSTN, and LTN to soil TN ratios at a depth of 0–20 cm. To summarize, the application of HSNPK could maintain and improve rice paddy soil quality, which leads to increased rice grain yields.

Nitrogen Immobilisation and Microbial Biomass Build-Up Induced by Miscanthus x giganteus L. Based Fertilisers

Cultivation of Miscanthus x giganteus L. (Mis) with annual harvest of biomass could provide an additional C source for farmers. To test the potential of Mis-C for immobilizing inorganic N from slurry or manure and as a C source for soil organic matter build-up in comparison to wheat (Triticum aestivum L.) straw (WS), a greenhouse experiment was performed. Pot experiments with ryegrass (Lolium perenne L.) were set up to investigate the N dynamics of two organic fertilisers based on Mis at Campus Klein-Altendorf, Germany. The two fertilisers, a mixture of cattle slurry and Mis as well as cattle manure from Mis-bedding material resulted in a slightly higher N immobilisation. Especially at the 1st and 2nd harvest, they were partly significantly different compared with the WS treatments. The fertilisers based on Mis resulted in a slightly higher microbial biomass C and microbial biomass N and thus can be identified as an additional C source to prevent nitrogen losses and for the build-up of soil organic matter (SOM) in the long-term.