Distribution Of Soil Nitrogen Research Articles

Impact of Pre-Plant Fertilizer Rates in Combination with Polysulphate® on Soil Nitrogen Distribution and Yield of Short-Day Strawberries (Fragaria × ananassa cv. Camarosa)

Strawberries are by far the most produced soft fruit (blueberries, raspberries, blackberries, and strawberries) worldwide, with China and the US being the two countries with the most production. In the US, strawberries reached a farm gate value of more than USD 3 billion in 2023 and are predominantly grown in the open field on an annual cycle in hilled-up soil beds using plastic mulch (plasticulture). This process relies on adequate pre-plant fertilizer application for plant establishment and fruit development. In North Carolina (US), it is current practice to apply pre-plant fertilizer containing 67 nitrogen (N) kg/ha; however, with increasing fertilizer costs and environmental concerns, questions remain as to whether or not pre-plant full-spectrum fertilizer rates can be reduced and substituted with organic low-N fertilizer sources, such as Polysulphate, without impacting yield or fruit quality. For this reason, field trials were established to evaluate the impact of pre-plant fertilizer rates on strawberry production (‘Camarosa’). Trials were conducted in the 2019–2020 and 2020–2021 seasons at two locations in North Carolina. The following N-rate pre-plant fertilizer treatments were applied: 80.1, 67.3, 54.1, 41.1, 33.6, 28.0, and 0 kg/ha. NO3 and NH4 content were frequently assessed in each replicate in the raised bed profile between planting and spring fertilizer application. Marketable and total strawberry yields were assessed over 6 weeks in the spring of 2020 and 2021. Our trial results showed that, especially in sandy soil, N rapidly declined under plastic within the first 8 weeks after pre-plant fertilizer application. However, no impact between pre-plant fertilizer rates and plant yield was observed. Treatments that contained Polysulphate and lower amounts of full-spectrum fertilizer showed significantly lower N concentrations in the soil while maintaining similar yields and fruit quality compared to grower-standard pre-plant fertilizer treatments. In summary, our results show that it is possible to reduce N content in pre-plant fertilizer by up to 50% compared to current recommendations without causing yield loss in short-day strawberry cultivars.

Soil Nitrogen Distribution Affects Nitrogen Utilization and Yield of Drip-Irrigated Rice

The cultivation of drip-irrigated rice has resulted in lower yields. However, the decrease in rice yield under drip irrigation and its relationship with the existing water and N regime have not been fully explained. Research and development of optimized water and N-management techniques are crucial for increasing rice yield under drip irrigation. In this study, two irrigation treatments were set: conventional drip irrigation (DIO) and drip irrigation with water stress (DIS). Each irrigation treatment contained four N rates: urea N 240 kg ha−1 (LN), urea N 300 kg ha−1 (MN), urea N 360 kg ha−1 (HN), and ammonium sulfate N 300 kg ha−1 (AN). The soil’s ammonium and nitrate contents were measured on the 2nd and 28th days after N application at panicle initiation stage. At anthesis, the aboveground and root biomass of rice were measured. In heading and maturity stage the N content of aboveground was measured and the yield, yield components, and NPFP were assessed at maturity stage. The results showed the following: (1) On the second day after N application, the contents of soil NO3−-N and NH4+-N in the 0–10 cm soil layer were highest for both the DIO and DIS. On the 28th day after N application, the soil NO3−-N content was highest at the 20–40 cm depth, while the soil NH4+-N content was still highest at the 0–10 cm depth. (2) The aboveground and root biomass in DIO treatment were significantly higher than in DIS. Furthermore, the root biomass at the 0–10 cm depth was significantly greater than at the 10–50 cm depth for both the DIO and DIS treatments. In the DIO treatment, the root biomass at the 10–50 cm depth was significantly higher with the HN and AN treatments compared to MN. However, in the DIS treatment, the root biomass at the 10–50 cm depth did not show significant differences between the MN, HN, and AN. (3) N accumulation in rice was significantly higher for the DIO treatment compared to the DIS treatment. Under the same irrigation treatment, the N accumulation in rice was highest in the AN and lowest in the LN. The PrNTA and PrNTC in DIS were significantly higher than in DIO, while the PoNAA and PoNAC were significantly lower in DIS. (4) The number of panicles, spikelets per panicle, seed-setting rate, 1000-grain weight, and grain yield were significantly lower in DIS. Under the DIS, these parameters were not significantly different among the MN, HN, and AN. In the DIO, the seed-setting rate, 1000-grain weight, and yield were not significantly different between the HN and AN, but were significantly higher than in the MN and LN. (5) NPFP was significantly higher in the DIO compared to the DIS. Among the different N rates, NPFP was highest with the AN treatment and lowest with the LN. In summary, under drip irrigation, there was a mismatch between soil mineral N and the distribution of rice roots, leading to reduced N accumulation and utilization in rice, ultimately impacting yield formation. Increasing N application and soil ammonium nutrition can improve rice yield under drip irrigation. However, optimizing N fertilizer management may not increase rice yield further when irrigation is further limited.

Effects of Aerated Drip Irrigation on the Soil Nitrogen Distribution, Crop Growth, and Yield of Chili Peppers.

In order to study the soil nitrogen (N) distribution pattern in the root zone of chili peppers under aerated drip irrigation (ADI) conditions and analyze the relationship between soil N distribution and crop growth, two irrigation methods (conventional drip irrigation and ADI) and three N levels (0, 140, and 210 kg hm-2) were set up in this experiment. Soil samples were collected by the soil auger method at the end of different reproductive periods, and the uniformity coefficient of soil N in the spatial distribution was calculated by the method of Christiansen's coefficient. The growth status and soil-related indices of pepper were determined at each sampling period, and the relationships between soil N distribution and chili pepper growth were obtained based on principal component analysis (PCA). The results showed that the spatial content of soil nitrate-N (NO3--N) fluctuated little during the whole reproductive period of chili peppers under ADI conditions, and the coefficient of uniformity of soil NO3--N content distribution increased by 5.29~37.63% compared with that of conventional drip irrigation. The aerated treatment increased the root length and surface area of chili peppers. In addition, the ADI treatments increased the plant height, stem diameter, root vigor, and leaf chlorophyll content to some extent compared with the nonaerated treatment. The results of PCA showed that the yield of chili peppers was positively correlated with the uniformity coefficient of soil NO3--N, root vigor, and root length. ADI can significantly improve the distribution uniformity of soil NO3--N and enhance the absorption and utilization of N by the root system, which in turn is conducive to the growth of the crop, the formation of yields, and the improvement of fruit quality.

Optimizing water and nitrogen management can enhance nitrogen heterogeneity and stimulate root foraging

ContextThe root development and soil nitrogen distribution in cotton fields under varying water and nitrogen supplies have rarely been reported in Xinjiang, Northwest China. MethodsTo address this gap, a two-year field experiment was conducted during the 2019 and 2020 growing seasons to determine the impact of two irrigation amounts (I400, conventional irrigation, 400 mm; and I267, limited irrigation, 267 mm) and three N fertilizer rates (N320, 320; N272, 272; and N224, 224 kg N ha−1) on the soil NO3-N distribution, root distribution, aboveground nitrogen accumulation, and water and nitrogen use efficiency. ResultsUnder the I400 condition, soil NO3-N exhibited a 30.4% higher horizontal heterogeneity in the N272 plots compared to the N320 plots. The root length and number in the N272 plots increased by 29.0% and 85.0%, respectively, compared with those in N320. Additionally, the N272 plots exhibited higher root length density and root dry weight in the 40–80 cm soil layers. These advantages of the N272I400 combination resulted in the highest seed cotton yield, nitrogen accumulation, and nitrogen use efficiency. Under the I267 condition, the N320 plots showed significantly increased yield and aboveground N content, enhanced horizontal soil NO3-N heterogeneity, and substantially accelerated root growth in deep soil compared with the N reduction plots. A quadratic correlation was observed between root length and soil NO3-N content. Root length was positively correlated with nitrogen accumulation in aboveground leaves and negatively correlated with soil NO3-N residue. These findings suggest that enhancing the development and distribution of roots promotes plant nitrogen accumulation and photosynthesis and facilitates the soil NO3-N absorption. ConclusionsIn conclusion, nutrient heterogeneity can enhance nutrient uptake and improve plant performance, which have important implications for plant productivity and ecosystem functioning.

Potential mechanisms of soil nitrogen content heterogeneity associated with biocrust development in drylands

AbstractBiological soil crusts (biocrusts) are complex communities of micro‐ and macro‐organisms dwelling at the soil surface in dryland regions worldwide, which contribute to important ecological functions in these areas. Biocrusts may reach different developmental stages, associated to autogenic succession of specific phototrophic organisms. However, notwithstanding the large amount of existing literature, little is known regarding the relationship between biocrust stages of development and soil nutrient dynamics. In this opinion paper, we specifically focused on soil nitrogen, and compared the total nitrogen content and potential nitrogenase activity of different developmental types of biocrust (‐covered) soils. Based on published reports, we looked at a possible relationship between nitrogen content at the soil surface and biocrust development, discussing the potential mechanisms leading to the observed soil nitrogen content heterogeneity. The results showed that a higher nitrogen content remained associated to the presence of moss‐dominated biocrusts, and this biocrust morphotype was characterized by a lower potential nitrogenase activity compared to the cyanobacteria‐ and/or lichen‐dominated biocrusts. We hypothesized that these seemingly contradictory findings might be attributed to three potential mechanisms: nitrogen inheritance, nutrient retention and nutrient transfer, which we hereby examined one by one. Altogether, our opinion supports the theory of biocrust succession from incipient cyanobacteria‐dominated stages to more ‘mature’ stages dominated by mosses. We stress how the heterogeneous distribution of soil nitrogen, which is closely related with biocrust development and community types, eventually affects regional and even global nitrogen dynamic and storage.

Response of soil nitrogen components and its vertical distribution to rainfall redistribution during Robinia pseudoacacia forest restoration on the Loess Plateau

The effects of vegetation restoration on soil moisture dynamics and nutrient content have been widely studied; however, the knowledge on variation in rainfall redistribution and soil nitrogen component characteristics remain limited, particularly with respect to their relationship in restored ecosystems. Therefore, the characteristics of plant community structure, rainfall redistribution, and soil nitrogen components from farmland and Robinia pseudoacacia (RP) plantations of four restoration ages (12, 20, 30, and 45 a) were investigated and measured in the Wuliwan watershed in the Loess Plateau, China. The results showed that changes in plant community structure affected the rainfall redistribution processes. The throughfall and moisture entering the soil (MES) had the largest proportions (79.50 % and 60.25 %) in the initial and second distributions of atmospheric rainfall, respectively. With the increase in restoration age, the content of soil total nitrogen (STN), soil nitrate nitrogen (SNN), soil soluble total nitrogen (SSTN), soil soluble organic nitrogen (SSON), and soil soluble inorganic nitrogen (SSIN) all increased with restoration age in the upper soil (0–40 cm), fluctuated in the middle soil (40–100 cm), and increased and then decreased in the deeper soil (100–200 cm). In addition, the vegetation restoration process can indirectly affect soil nitrogen content and distribution patterns by affecting the rainfall redistribution process. In the upper soil, litter interception (LI) had a significant effect on STN by affecting SSIN and SSON. In the middle soil, both LI and MES had significant effects on STN through SSIN and SSON, respectively. In the deeper soil, LI had no significant effect on any nitrogen component, whereas MES had a significant effect on STN by affecting SSIN. Overall, this study indicates that RP plantation restoration has the potential to transform rainfall redistribution and soil nitrogen distribution, providing an important reference for the reciprocal feedback relationship between water and nitrogen.

Anthropogenic effects on global soil nitrogen pools

The amount of nitrogen stored in terrestrial soils, its “nitrogen pool”, moderates biogeochemical cycling affecting primary productivity, nitrogen pollution and even carbon budgets. The soil nitrogen pools and the transformation of nitrogen forms within them are heavily influenced by environmental factors including anthropogenic activities. However, our understanding of the global distribution of soil nitrogen with respect to anthropogenic activity and human land use remains unclear. We constructed a meta-analysis from a global sampling, in which we compare soil total nitrogen pools and the driving mechanisms affecting each pool across three major classifications of human land use: natural, agricultural, and urban. Although the size of the nitrogen pool can be similar across natural, agricultural and urban soils, the ecological and human associated drivers vary. Specifically, the drivers within agricultural and urban soils as opposed to natural soils are more complex and often decoupled from climatic and soil factors. This suggests that the nitrogen pools of those soils may be co-moderated by other factors not included in our analyses, like human activities. Our analysis supports the notion that agricultural soils act as a nitrogen source while urban soils as a nitrogen sink and informs a modern understanding of the fates and distributions of anthropogenic nitrogen in natural, agricultural, and urban soils.

Predicting Rice Lodging Risk from the Distribution of Available Nitrogen in Soil Using UAS Images in a Paddy Field.

Rice lodging causes a loss of yield and leads to lower-quality rice. In Japan, Koshihikari is the most popular rice variety, and it has been widely cultivated for many years despite its susceptibility to lodging. Reducing basal fertilizer is recommended when the available nitrogen in soil (SAN) exceeds the optimum level (80-200 mg N kg-1). However, many commercial farmers prefer to simultaneously apply one-shot basal fertilizer at transplant time. This study investigated the relationship between the rice lodging and SAN content by assessing their spatial distributions from unmanned aircraft system (UAS) images in a Koshihikari paddy field where one-shot basal fertilizer was applied. We analyzed the severity of lodging using the canopy height model and spatially clarified a heavily lodged area and a non-lodged area. For the SAN assessment, we selected green and red band pixel digital numbers from multispectral images and developed a SAN estimating equation by regression analysis. The estimated SAN values were rasterized and compiled into a 1 m mesh to create a soil fertility map. The heavily lodged area roughly coincided with the higher SAN area. A negative correlation was observed between the rice inclination angle and the estimated SAN, and rice lodging occurred even within the optimum SAN level. These results show that the amount of one-shot basal fertilizer applied to Koshihikari should be reduced when absorbable nitrogen (SAN + fertilizer nitrogen) exceeds 200 mg N kg-1.

High-Resolution Digital Soil Maps of Forest Soil Nitrogen across South Korea Using Three Machine Learning Algorithms

Reliable estimation of the forest soil nitrogen spatial distribution is necessary for effective forest ecosystem management. This study aimed to develop high-resolution digital soil maps of forest soil nitrogen across South Korea using three powerful machine learning methods to better understand the spatial variations of forest soil nitrogen and its environmental drivers. To achieve this, the study used national-level forest soil nitrogen data and environmental data to construct various geographic and environmental variables including geological, topographic, and vegetation factors for digital soil mapping. The results show that of the machine learning methods, the random forest model had the best performance at predicting total soil nitrogen in the A and B horizons, closely followed by the extreme gradient-boosting model. The most critical predictors were found to be geographic variables, quantitatively confirming the significant role of spatial autocorrelation in predicting soil nitrogen. The digital soil maps revealed that areas with high elevation, concave slopes, and deciduous forests had high nitrogen contents. This finding highlights the potential usefulness of digital soil maps in supporting forest management decision-making and identifying the environmental drivers of forest soil nitrogen distribution.

Distribution of Total Nitrogen in Soils of the Tropical Highlands of Cameroon

Distribution of Total Nitrogen in Soils of the Tropical Highlands of Cameroon

Mixed Plantations Induce More Soil Macroaggregate Formation and Facilitate Soil Nitrogen Accumulation

Nitrogen plays a crucial role in limiting plant growth and determining net primary productivity in forest ecosystems. However, variations and influencing factors of soil nitrogen distribution on the aggregate scale in pure and mixed Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations remain unclear. This study aimed to explore how soil aggregate composition, geometric mean diameter (GMD), mean weight diameter (MWD), total nitrogen (TN), total acidolyzable nitrogen (TAN), available nitrogen (AN), nonacidolyzable nitrogen (AIN), amino acid nitrogen (AAN), nitrate nitrogen (NO3−-N), cidolyzable ammonia nitrogen (AMN), unknown-acidolyzable nitrogen (HUN), amino sugar nitrogen (ASN), and ammonium nitrogen (NH4+-N) contents and stocks varied with aggregate size (>2, 1–2, 0.25–1, and <0.25 mm) and stand type [Chinese fir mixed with Michelia macclurei Dandy (CF + MM), Chinese fir mixed with Mytilaria laosensis Lecomte (CF + ML) and pure stands of Chinese fir (CF)] in 0–20 and 20–40 cm soil depth. Soil N content in different stand types of Chinese fir plantations decreased as the aggregate size increased, whereas the soil N stock exhibited the opposite trend. In contrast to CF soil, CF + MM and CF + ML soil displayed a significant increase in MWD, GMD, and aggregate-associated TN, AN, NO3−-N, NH4+-N, AIN, AAN, ASN, and AMN contents and stocks, especially CF + MM soil. Organic N was more sensitive to the response of aggregate size and stand type than mineral N. Redundancy analysis and Pearson’s correlation analysis indicated that the 0.25–1 mm aggregate proportion was the main controlling factor for the variations in soil N content and storage. Overall, this study contributed significantly to the promotion of the sustainable use of soil resources and reference information for the scientific management and sustainable development of Chinese fir forests.

Effect of fertigation frequency on soil nitrogen distribution and tomato yield under alternate partial root-zone drip irrigation

Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation, with the potential to save water and increase nitrogen (N) fertilizer efficiency. A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF. The treatments included three ADF frequencies with intervals of 3 (F3), 6 (F6) and 12 days (F12), and conventional drip fertigation as a control (CK), which was fertilized once every 6 days. For the ADF treatments, two drip tapes were placed 10 cm away on each side of the tomato row, and alternate drip irrigation was realized using a manual valve on the distribution tapes. For the CK treatment a drip tape was located close to the roots of the tomato plants. The total N application rate of all treatments was 180 kg ha-1. The total irrigation amounts applied to the CK treatment were 450.6 and 446.1 mm in 2019 and 2020, respectively; and the irrigation amounts applied to the ADF treatments were 60% of those of the CK treatment. The F3 treatment resulted in water and N being distributed mainly in the 0-40-cm soil layer with less water and N being distributed in the 40-60-cm soil layer. The F6 treatment led to 21.0 and 29.0% higher 2-year average mineral N concentration in the 0-20 and 20-40-cm soil layer, respectively and a 23.0% lower N concentration in the 40-60-cm soil layer than in the CK treatment. The 2-year average tomato yields of the F3, F6, F12, and CK treatments were 107.5, 102.6, 87.2, and 98.7 t ha-1, respectively. The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment, whereas there was no significant difference between the F3 and F6 treatment. The F6 treatment resulted in yield similar to the CK treatment, indicating that ADF could maintain tomato yield with a 40% saving in water use. Based on the distribution of water and N, and tomato yield, a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.

Effect of Deep Placement of Large Granular Fertilizer on Ammonia Volatilization, Soil Nitrogen Distribution and Rice Growth

Excessive fertilization is often applied to produce rice. To reduce nitrogen loss and improve nitrogen use efficiency (NUE), we studied the effects of application depth (surface application, 5 and 10 cm) and shape of nitrogen fertilizers (row application and deep application of large granular fertilizer) on rice growth, soil N distribution and ammonia volatilization. The results showed that grain yield, shoot biomass and total dry biomass of the treatment with N in large granular fertilizer applied at 10 cm depth were significantly higher than those of all other treatments. Moreover, compared with the surface application, the N recovery efficiency and the N agronomic efficiency of deep application treatments were enhanced by 18.1–52.3% and 35.6–95.6%, respectively. Deep application significantly increased NH4+-N concentration at their fertilization points. During the growth season, N in large granular fertilizer treatments (mixed with clay to form an unusually large pellet of 1.0–1.5 cm in diameter) distributed closer to the roots, while N in other treatments, including row application treatments, was more widely distributed. Compared with the surface application, deep application significantly reduced NH3 volatilization and NH4+-N concentration in surface water by 58.7–64.8% and 26.0–72.5%, respectively. Furthermore, the NH3 volatilization from large granular treatment was 7.6–11.0% lower than that in the row application. In conclusion, applying N in large granular fertilizer at 10 cm depth reduces ammonia volatilization, and improves rice growth and grain yield, indicating improved NUE and lowered environmental risks.

Quantifying inter-species nitrogen competition in the tomato-corn intercropping system with different spatial arrangements

CONTEXTIntercropping systems have been widely used worldwide due to their high economic benefits and land-use efficiency. While it is well known that inter-species nutrition competition in intercropping systems leads to high production efficiency, the effects of different spatial arrangements of intercropping species on these mechanisms remain unclear. OBJECTIVEThe objectives of this study were to reveal differences in the soil nitrogen dynamics in the tomato-corn intercropping system with different spatial arrangements of crops and to determine suitable spatial arrangements. METHODSA two-year experiment was carried out during the 2018 and 2019 seasons to determine inter-species nitrogen competition in the tomato and corn systems with different spatial arrangements. The treatments included sole corn (SC), sole tomatoes (ST), two rows of tomatoes intercropping two rows of corn (IC2–2), and four rows of tomatoes intercropping two rows of corn (IC4–2) systems. Additionally, the modified HYDRUS (2D/3D) model was used to quantify soil nitrogen concentrations, solute fluxes, soil nitrogen distribution, and soil nitrogen balance in the crop root zone under the SC, ST, IC2–2, and IC4–2 systems. RESULTS AND CONCLUSIONSThe modified HYDRUS (2D/3D) model could precisely capture the soil nitrogen dynamics with nRMSE ranging from 2.8% to 12.4%. In general, soil NH4-N concentrations in the root zone of tomatoes of different systems decreased as follows: IC2–2 > IC4–2 > ST, while a reverse trend was observed in the root zone of corn. Compared with soil NH4-N, differences in soil NO3-N among different systems were more evident due to its higher mobility. IC2–2 had the highest nitrogen flux, cumulative N flux, N uptake (CNU), and the land equivalent ratio for nitrogen (LERN) among different systems. Among different intercropping systems, the corn's and tomato's highest crop yields occurred in IC2–2 and IC4–2, respectively, with an average of 13,406.0 and 98,732.3 kg ha−1 in both years. Additionally, corn and tomato's highest nitrogen use efficiency (NUE) occurred in IC2–2 and ST, respectively. However, the land-equivalent ratio for nitrogen use efficiency (LERNUE) in IC4–2 was 5.4% higher than in IC2–2. Therefore, IC4–2 is the optimal intercropping system recommended for sustainable agriculture development. SIGNIFICANCEThe findings of this study improve the understanding of the mechanisms of inter-species nitrogen competition between commercial and grain crops. The study also suggests to the farmers and government suitable spatial arrangements of an intercropping system that can be adopted to promote the development of sustainable agriculture.

Effects of Years of Rice Straw Return on Soil Nitrogen Components from Rice–Wheat Cropped Fields

Straw return is an important farmland management practice that influences the activity of soil nitrogen. Few studies have examined the distribution of soil nitrogen and its components in wheat–rice cropping fields in subtropical China. This study assesses the influence of different years of straw return on the distribution and variation of total soil nitrogen (TN), light fraction nitrogen (LFN), heavy fraction nitrogen (HFN), particulate nitrogen (PN), and mineral-bound nitrogen (MN). We conducted a field experiment with eight years of straw retention treatments in 2017 (no straw retention, NR; 1 year of straw retention, SR1; 2 years of straw retention, SR2; 3 years of straw retention, SR3; 4 years of straw retention, SR4; 5 years of straw retention, SR5; 6 years of straw retention, SR6; 7 years of straw retention, SR7) and one more treatment in 2018 (8 years of straw retention, SR8) in a rice–wheat cropping system at Yangzhou University Experimental Station in China. The results demonstrated that as the number of years of treatment increases, the content of TN, LFN, HFN, PN, and MN at each soil layer gradually increases. Compared with NR, the highest increase in TN, LFN, HFN, PN, and MN under SR1-SR8 in the 0–20 cm soils was 38.10%, 150.73%, 35.61%, 79.97%, and 27.71%, respectively, but increases in TN, HFN, and MN content gradually slowed after six years of straw return. The contents or variation of TN were extremely significantly correlated (p < 0.01) with that of LFN, HFN, PN, and MN, while LFN had the highest variation. In general, straw return could improve the quality of the 0–20 cm nitrogen pool. LFN was the best indicator of changes to the soil nitrogen pool affected by years of straw return.

Heterogeneity of Spatial-Temporal Distribution of Nitrogen in the Karst Rocky Desertification Soils and Its Implications for Ecosystem Service Support of the Desertification Control—A Literature Review

In recent years, the study of soil nitrogen distribution (SND) in rocky desertification control ecosystems has increased exponentially. Rocky desertification experiences severe environmental degradation due to its fragile nature, and understanding rocky desertification soil nitrogen (SN) is critical for ecosystem services (ES) to support sustainable development. From the perspective of bibliometrics, this paper systematically, comprehensively, qualitatively and quantitatively describes the progress, trends and hotspots of SND in the field of rocky desertification environment. The results show that: 97.40% of the document type is “Article”; the study of rocky desertification SND shows the characteristics of rapid growth, the volume of published articles in the past three years accounted for 34.30% of the total; active countries are mainly China, Germany, United States, Sweden, Finland, etc. The research hotspots in this field include karst and nitrogen, and the future research hotspots tend to focus on karst rocky desertification ecosystem, soil nutrients and vegetation diversity in south China. It is suggested to construct SN management strategy suitable for rocky desertification fragile ecosystems in the future, strengthen theoretical research and comprehensively understand the characteristics of rocky desertification control ecosystem to put forward sustainable management strategy according to local conditions.

Quantifying the Spatial Distribution of Soil Nitrogen under Long-Term Drip Fertigation

Quantifying the spatial distribution of nitrogen (N) in the soil under long-term drip fertigation events is essential for the optimal regulation of drip fertigation systems. In this study, a greenhouse soil that had been under drip irrigation for 20 years was selected as the research object, and soil samples were collected from the 0–50 cm soil depth. The concentrations of N in the soil samples were measured and their spatial distribution characteristics were quantified by classical statistical analysis and multifractal analysis. The results showed that long-term drip fertigation and the influence of natural factors resulted in the nitrate N mainly accumulating in the shallow layer of the soil and within a distance from the drip irrigation belt, and the spatial heterogeneity gradually decreased with increasing depth. The content of ammonium N was low, and its distribution was observed in the whole section. Multifractal analysis indicated that the Δα value of nitrate N and inorganic N gradually increased with the increase in the research scale, i.e., the spatial heterogeneity gradually increased, and it did not appreciably change for ammonium N. Meanwhile, the local high value region was the main factor leading to the spatial heterogeneity of N, and this dominant effect gradually increased with increasing depth. Multifractal analysis can effectively reflect the local information of the N spatial distribution in the soil and provide a more detailed description of the spatial heterogeneity of soil properties.

Rotary and subsoiling tillage rotations influence soil carbon and nitrogen sequestration and crop yield

Long-term single tillage causes serious deterioration of land quality and reduction of crop yield. Tillage rotation can alleviate the problems caused by long-term single tillage. However, the effects of different tillage rotations are still very limited. A tillage rotation experiment was conducted in the North China Plain to evaluate the impacts of tillage rotation on soil organic carbon (SOC), soil total nitrogen (STN) and crop yield. There were eight treatments with two main factors: tillage practice (four types: rotary tillage (R, 2002–2017), subsoiling tillage (S, 2002–2017), rotary to subsoiling tillage (RS, 2015–2017) and subsoiling to rotary tillage (SR, 2015–2017)) and straw management (two types: straw return (F) and straw removal (0)). RSF treatment yielded the highest SOC, at 12.53 g/kg. RSF significantly increased SOC by 41.4% compared to RF, while SRF significantly reduced SOC by 11.1% compared to SF. In addition, RSF significantly increased STN content by 21.7% compared with that under RF. Compared with SF, SRF promoted the uniform distribution of soil nitrogen in the 0–20 cm soil layer. Among the treatments, the RSF treatment yielded the highest SOC stock (SOC<sub>S</sub>) and STN stock (STN<sub>S</sub>), which were 67.68 t/ha and 6.63 t/ha, respectively. Compared with RF treatment, RSF treatment greatly increased SOC<sub>S</sub>, by 31.7%. Both tillage rotation treatments increased STN<sub>S</sub> by 13.3% under RSF compared to RF, and by 2.3% under SRF compared to SF. In 2016, the annual yield was highest under RSF treatment at 19.80 t/ha. In 2017, the annual yield was highest under SF treatment at 21.37 t/ha, and next highest under RSF at 20.94 t/ha. In summary, long-term rotary tillage followed by subsoiling tillage combined with straw return (RSF) can significantly increase SOC, STN and crop yield. The rotation of rotary tillage to subsoiling tillage combined with the straw return is an effective measure for improving soil quality and increasing crop yields in the North China Plain.

Large-scale digital mapping of topsoil total nitrogen using machine learning models and associated uncertainty map

Understanding the spatial distribution of soil nutrients and factors affecting their concentration and availability is crucial for soil fertility management and sustainable land utilization while quantifying factors affecting soil nitrogen distribution in Qorveh-Dehgolan plain is mostly lacking. This study, thus, aimed at digital modeling and mapping the spatial distribution of topsoil total nitrogen (TN) in Qorveh-Dehgolan plain with an area of 150,000 ha using random forest (RF), decision tree (DT), and cubist (CB) algorithms. A total of 130 observation points were collected from a depth of 0 to 30cm from topsoil surfaces based on a random sampling pattern. Then, soil physicochemical properties, calcium carbonate equivalent, organic carbon, and topsoil total nitrogen were measured. A number of 51 environmental variables including 31 geomorphometric attributes derived from a digital elevation model with 12.5-m spatial resolution, 13 spectral indices and reflectance from SENTINEL-2 satellite (MSIsensor), and five soil properties and two spatial variables of latitude and longitude were used as covariates for digital mapping of topsoil total nitrogen. The most appropriate covariates were then selected by the Boruta algorithm in the R software environment. A standard deviation map was produced to show model uncertainty. The covariate selection resulted in the separation of 14 effective covariates in the spatial prediction of topsoil total nitrogen by using the data mining algorithms. The validation of digital mapping of topsoil total nitrogen by RF, DT, and CB models using 20% of independent data showed root mean square error (RMSE) of 0.032, 0.035, and 0.043%; mean absolute error (MAE) of 0.0008, 0.001, and 0.002%; and based on the coefficients of determination of 0.42, 0.38, 0.35, respectively. Relative importance (RI) of environmental covariates using the %IncMSE index indicated the importance of two geomorphometric variables of midslope position and normalized height along with SAVI and NDVI remote sensing variables in the spatial modeling and distribution of total nitrogen in the studied lands. The RF prediction and associated uncertainty maps, with show high accuracy and low standard deviation in the most part of study area, reveled low overfitting and overtraining in soil-landscape modeling; so, this model can lead to the development of a digital map of soil surface properties with acceptable accuracy for sustainable land utilization.

Effects of Straw Mulching and Nitrogen Reduction on the Distribution of Soil Nitrogen and Groundwater Nitrogen Pollution

To explore the effects of straw mulching and reduced nitrogen fertilization on the temporal and spatial patterns of soil nitrogen, groundwater nitrogen pollution, and summer maize yield, field experiments were carried out in the Hetao irrigation district in 2017 and 2018. The experiment involved the following seven treatments:a control (CK) treatment involving conventional fertilization and traditional tillage, and conventional nitrogen applications reduced by 30% (N1), 20% (N2), and 10% (N3) coupled with either straw surface covering (B) or deep straw burial (S). The results showed that the distribution of soil nitrogen in the CK treatment varied depending on soil depth, with an overall decreasing trend. In the 0-20 cm soil layer under straw surface covering (B) treatments, soil nitrogen was superficially accumulated. NO3--N and NH4+-N content increased by an average of 22.2% and 42.7% compared to the CK treatment, respectively, which decreased significantly at first and then increased slightly with depth. In the 20-40 cm deep soil layer under the deep straw burial (S) treatments, soil nitrogen accumulated and the content of NO3--N and NH4+-N increased by an average of 29.8% and 48.1%, respectively, compared to the CK treatment. Nitrogen accumulation first and then decreased significantly with depth. Nitrogen accumulation under the different straw mulching regimes increased with an increase in the application of reduced nitrogen. After the harvest of summer maize, the accumulation of NO3--N and NH4+-N in the >80 cm soil layer under the B treatments was 19.9%-58.2% and 31.1%-61.7% lower than that of the CK treatment, respectively. This compared to reductions of 36.7%-70.9% and 82.6%-89.2% for the S treatments, respectively. Only the BN3 treatment increased accumulation compared with CK by 0.4% on average, while the SN2 treatment resulted in a 9.3% increase. Summer maize yield and relative indexes were also improved relative to the other treatments. Nonlinear fitting of yield and application reduction showed that deep straw burial was better than surface covering at increasing summer maize production. The effect of deep straw burial and 14%-20% application reduction was better. Straw mulching with reduced nitrogen fertilization can limit nitrogen leaching and thereby reduce the risk of groundwater pollution. After the harvest, groundwater quality was classified in the Ⅱ class, with the risk of nitrogen contamination being lowest under deep straw burial with>20% reduced nitrogen fertilization. These observations show that deep straw deep alongside 14%-20% application reduction could effectively alleviate nitrogen leaching and reduce the risk of nitrogen pollution in groundwater. This approach can help improve the ecological environment and summer maize yields in the Hetao irrigation district.