Soil Nitrogen Fractions Research Articles

Comparisons of the effects of different drying methods on soil nitrogen fractions: Insights into emissions of reactive nitrogen gases (HONO and NO)

Reactive nitrogen (Nr) emission from soils, e.g., nitrous acid (HONO) and nitric oxide (NO), is a key process of the global nitrogen (N) cycle and has significant implications for atmospheric chemi...

Characteristics of soil nitrogen cycle and mechanisms underlying the increase in rice yield with partial substitution of mineral fertilizers with organic manure in a paddy ecosystem: A review

Partial substitution of mineral fertilizers with organic manure is a key strategy for stable and increase crop yield accompanying with zero growth of mineral fertilizers. Based on recent stu-dies, we reviewed the effects of partial substitution of mineral fertilizers with organic manure on rice yield, nitrogen utilization efficiency, soil nitrogen fractions, and microbial nitrogen fixation, ammonification, nitrification, and denitrification in rice paddy ecosystems. We further compared the cha-racteristics of soil nitrogen cycle of mineral fertilizers alone and partial substitution of mineral fertili-zers with organic manure. The partial substitution altered key processes of nitrogen cycling, including enhancement of ammonification, mediation of nitrification and denitrification, reduction of ammonia volatilization and nitrogen loss, improved the status of nitrogen supplements (enriching the supplement of low-molecular-weight organic nitrogen, adjusting the distribution of inorganic nitrogen components, increasing the amount of microbial biomass nitrogen, and decreasing the loss of total nitrogen), improved soil nitrogen supply (increasing supply of small molecule organic nitrogen, coordinating inorganic nitrogen components and proportions, and increasing soil microbial biomass nitrogen and total nitrogen fixation), which promoted nitrogen uptake and regulated nitrogen allocation in rice plant to realize stability and enhancement of rice yield.

Erosional effects on distribution and bioavailability of soil nitrogen fractions in Belgian Loess Belt

Soil erosion strongly influences the transport and fate of carbon (C) and nitrogen (N) in hillslope soils. However, in dynamic landscapes, erosional effects on soil N cycling and primary controls on N bioavailability are not well understood: particularly with respect to differences between topsoil and subsoil. Here we aim to explore the influence of erosion on (i) spatial distributions of soil N fractions and (ii) controls on N bioavailability in eroding vs. depositional sites within the Belgian Loess Belt. Soil samples were fractionated by aggregate size and density. In addition, intact soil samples were incubated to determine the influence of oxygen status (0, 5, and 20%) and labile organic matter on mineralization and nitrification of N in the context of erosion. The results showed that the deposition of eroded upslope soil materials led to N enrichment throughout entire soil profiles. Across both eroding and depositional sites, more than 93% of the total N was associated with minerals. Increased macro-aggregate- and mineral-associated N at the depositional site indicated that aggregation and N stabilized by minerals contribute to N enrichment in the depositional soils. Inorganic N, mostly NO3−-N, was also larger at the depositional site. Oxygen concentrations were positively related to net N nitrification and mineralization rates regardless of geomorphic position. Glucose addition significantly reduced net N mineralization and nitrification rates. In conclusion, our results indicate that soil erosion might not only lead to spatial variations of N pools but also potentially affect the transformation and bioavailability of N along eroding hillslopes. Future research should consider the fate of different N species in eroding landscapes and consequences for both carbon sequestration and N leaching.

Carbon and nitrogen fractions in soil during maize growth under long-term fertilizer management practices to maize-wheat cropping

A field experiment was conducted to study the effect of long-term fertilizer management (viz. control, 100% N, 100% NP, 100% NPK and 100% NPK+FYM) on the carbon (C) and nitrogen (N) fractions in soils under maize-wheat cropping. Soil samples were collected from on-going experiment (started in 1971) during maize growing season in kharif 2011 to discern long-term effect of field treatments on changes in different pools of C and N viz. soil organic C (SOC), water soluble C (WSC) and KMnO₄ oxidizable C (KMnO₄-C) and ammonical-N (NH₄⁺-N) and nitrate-N (NO₃⁻-N) content. Soil samples were analyzed after 1, 3, 5, 7 and 9 weeks interval during maize growth period. The SOC, NO₃⁻-N and NH₄⁺-N concentration increased significantly with combined application of NPK+FYM as compared to the control. The concentration of SOC increased after 3 weeks, and was reached the highest at harvesting. However, the WSC and KMnO₄-C concentration increased up to 5ᵗʰ week after sowing and it decreased afterwards. The NO₃⁻-N and NH₄⁺-N concentration decreased with increased maize growth stage, and decreased to the lowest value at harvesting. The dry matter yield of maize at maturity correlated well with SOC, WSC, KMnO₄-C, NH₄⁺-N and NO₃⁻-N concentration. Crop yield of maize and N uptake increased with NPK+FYM application at all growth stages.

Effects of winter flooding on the soil nitrogen fractions and organic rice growth in a paddy field with low nitrogen fertility

Effects of winter flooding on the soil nitrogen fractions and organic rice growth in a paddy field with low nitrogen fertility

Soil aggregation and potential carbon and nitrogen mineralization with cover crops under tropical no-till

Sustainability of agriculture with no-tillage (NT) production requires appropriate cover cropping and not a simple and random approach of any cover crop species. However, relatively little is known of the long-term soil surface impacts of different cover crops in rotation with soybean (Glycine max) under NT in the tropics. We evaluated the impacts of different cover crops on soil aggregation, soil organic carbon (C) and nitrogen (N) fractions, and soil microbial activity of a Typic Rhodudalf at the end of 12 years under NT in Sao Paulo state of Brazil. Treatments included main plots during the winter dry season (triticale [× Triticosecale] and sunflower [Helianthus annuus]) and subplots during the spring cover crop season (pearl millet [Pennisetum glaucum], sunn hemp [Crotolaria juncea], forage sorghum [Sorghum bicolor], and fallow with occasional chiseling). All eight of these treatments followed soybean in summer. Winter crop treatments had no effect on soil aggregation, but total organic C and N concentrations were greater (p

Soil carbon and nitrogen fraction dynamics affected by tillage erosion

Understanding the impact of tillage erosion on soil organic carbon (SOC) and nitrogen (N) fractions is essential for targeted soil conservation in mountainous and hilly areas. However, little is known about this issue. In this study, we selected a tillage erosion-dominated hillslope from the Sichuan Basin, China, to determine the effect of tillage erosion on particulate OC (POC), dissolved OC (DOC), light fraction OC (LFOC), ammonium N (NH4+-N), nitrate N (NO3−-N) and alkali-hydrolysable N (AN). Additionally, we investigated the microbial activities in relation to soil C and N dynamics, including soil microbial biomass, β-glucosidase and urease activities. Tillage erosion induced serious soil loss in upper slope positions and soil deposition in lower slope positions. The observations of the various labile OC fraction distributions across the hillslope suggest that tillage erosion exerts less impact on DOC and LFOC dynamics but a notable effect on POC. The distribution pattern in total organic carbon under tillage erosion mainly depends on POC redistribution. The POC redistribution is a major factor affecting microbial activities. The AN is more prone to the tillage erosion impact than NH4+-N and NO3−-N. Effective soil conservation measures should be taken to weaken the adverse impacts of tillage erosion on POC and AN redistribution in sloping farmlands.

Effects of long-term organic material applications on soil carbon and nitrogen fractions in paddy fields

Soil organic carbon (C) and nitrogen (N) pools are the most important soil components, and their characteristics directly or indirectly determine the stability of the soil structure and the soil fertility. Using a rice fields experiment in the coastal areas of Southeast China, how a long-term (10 years) continuous application of organic materials consisting of green manure (Chinese milk vetch), pig manure, and rice straw affected the soil C and N fractions were studied. The results showed that 10-year continuous applications of organic materials to the paddy fields significantly increased the C fraction content in terms of parameters such as the soil organic C (SOC), microbial biomass C (MBC), and active organic C (AOC). It also increased the soil N fraction content, including the soil total N (TN), dissolved total N (DTN), microbial biomass N (MBN), and active N. The rice straw return had the most significant effect in relation to increasing the SOC and dissolved organic C (DOC), with 23.9% and 42.3% increases, respectively, compared to applying chemical fertilizer alone. Organic pig manure had the most significant effect on the soil MBN and DTN, with 49.3% and 50.7% increases, respectively, compared to the application of chemical fertilizer alone. MBC and MBN are the primary components of soil AOC and active N, respectively. The application of organic materials increased the ratio of soil MBC and AOC to SOC, as well as the ratio of MBN, DTN, and active N to the soil TN. Our findings indicated that long-term applications of organic materials could improve and enhance paddy soil fertility and promote increased rice yields.

Increasing Labile Soil Carbon and Nitrogen Fractions Require a Change in System, Rather Than Practice

The influence of tillage, carbon (C) and nitrogen (N) inputs and perennialization on labile fractions of soil organic matter (SOM) has been widely investigated, but research on the temporal and depth variation of labile C and N fractions in long‐term agroecosystems representative of the US Corn Belt is lacking. In this study, labile soil fractions as influenced by different agriculture management approaches common in the north‐central United States were characterized through measurements of potentially mineralizable N (PMN), mineralizable C (C‐min), and permanganate oxidizable C (POXC), which are known indicators of the biologically active pool of SOM. Soils were sampled five times in six different cropping systems at the Wisconsin Integrated Cropping Systems Trial: three annual cropping systems (continuous corn, strip‐till corn–soybean, organic grain) and three forage cropping systems (conventional forage, organic forage, grazed pasture). Across all sampling dates (May–September) and soil depth (0–15 and 15–30 cm), forage‐based cropping systems generally had greater PMN, C‐min, and POXC, with C‐min and PMN expressing the largest differences between forage and grain‐based cropping systems. Labile soil C and N fractions across cropping systems were typically greatest in July or August and were ∼50% greater in the top 0 to 15 cm of soil than the 15 to 30 cm. These results suggest sampling timing and depth for PMN, POXC, and C‐min need to be standardized to optimize their use as soil health indicators and that shifts in the system toward perenniality will be required to increase labile C and N fractions on the highly fertile Mollisols of the US Corn Belt.

Effects of thinning on soil carbon and nitrogen fractions in a Larix olgensis plantation.

Thinning, an important forest management strategy, can alter forest structure and stability, and consequently affect ecosystem biogeochemical cycles. The effects of thinning on soil carbon and nitrogen is far from conclusive especially due to the lack of long-term experiments. Here, we investigated soil carbon and nitrogen in Larix olgensis plantations in Mengjiagang Forest Farm, Heilongjiang Province, with four thinning treatments (i.e., 4 times low-intensity thinning, LT4; 3 times medium-intensity thinning, MT3; 2 times high-intensity thinning, HT2; and un-thinned control). The effects of thinning on soil total organic carbon and total nitrogen were examined from the perspective of the composition of labile and recalcitrant pools (labile carbon or nitrogen pool I; labile carbon or nitrogen pool II; and recalcitrant carbon or nitrogen pool) by an acid hydrolysis approach. The results showed that thinning significantly increased soil total organic carbon and nitrogen by 48.7%-50.3% and 28.9%-42.7%, respectively. The carbon and nitrogen contents in all the labile I, labile II, and recalcitrant pools were increased by thinning, with the magnitudes varying across different pools and thinning types. LT4, MT3, and HT2 improved the recalcitrant carbon by 71%, 69% and 75%, respectively, which was significantly higher than the increment of two labile carbon pools. In addition, the percentage of recalcitrant carbon in total organic carbon was increased by thinning. LT4 significantly increased microbial biomass and microbial quotient, but no significant change was found in MT3 and HT2 treatments. Overall, our results indicated that thinning might increase the input of soil recalcitrant carbon components such as suberin and lignin by producing more coarse woody residues, thus leading to decline of organic matter decomposition and ultimately enhancement of soil organic carbon.

Linking plant community composition with the soil C pool, N availability and enzyme activity in boreal peatlands of Northeast China

Plant species composition influences belowground ecosystem function. However, there are few data on the interactive effects of plant diversity and soil function. We surveyed plant species diversity, and determined soil carbon (C), nitrogen (N) fractions and enzyme activity in five peatlands with different vegetation-types. We also investigated the interactions between plant species diversity and richness, and soil biochemical properties. We found a close relationship between plant species diversity and total carbon (TC) in both surface (0–15 cm) and subsoil (15–30 cm) layers. Plant diversity and richness positively correlated with soil dissolved organic carbon (DOC), NH4+-N in both soil layers and subsoil moisture and total nitrogen (TN), as well as topsoil pH. Plant species diversity and richness were also positively correlated with subsoil moisture, pH, protease, acid phosphatase activity and topsoil urease activity. Soil β-glucosidase, invertase, urease, protease, and acid phosphatase activity positively correlated with soil TC, TN, DOC, available N and soil moisture. Our findings demonstrate that plant community diversity is linked with soil C and N turnover through soil enzyme activity. These results will improve our ability to more fully understand the linkages between aboveground and belowground components in peatland ecosystems.

Conservation of Soil Organic Carbon and Nitrogen Fractions in a Tallgrass Prairie in Oklahoma

Native grasslands in the Great Plains of North America have mostly disappeared in the past century due to agricultural expansion. A grazing study was established on Paleustolls and Argiustolls supporting a remnant, but historically grazed tallgrass prairie in central Oklahoma. Stocking method of beef cattle was differentiated into continuous and rotational treatments (10 sub-paddocks) in 2009 and these treatments continued until present. Soil was sampled in 2009 and 2012 at depths of 0–6, 6–12, 12–20, and 20–30 cm and in 2017 at depths of 0–15 and 15–30 cm. Total, particulate, microbial biomass, and mineralizable C and N fractions were highly stratified with depth, having 2–10 times greater concentration at a depth of 0–6 cm as that at 20–30 cm. Strong associations existed among most of these soil organic C and N fractions, given the large range that resulted from sampling at multiple depths. No discernable differences in soil organic C and N fractions occurred due to stocking method at any sampling time or depth. Evidence for biological nitrification inhibition suggested a mechanism for conservation of available N with less opportunity for loss. In addition, strong association of available N with biologically active C indicated slow, but sustained release of N that was strongly coupled to C cycling. We conclude that stocking method had a neutral effect on conservation of already high antecedent conditions of soil organic C and N fractions during the first 8 years of differentially imposed management.

Soil carbon and nitrogen stocks and fractions for improving soil quality and mitigating climate change

Soil carbon and nitrogen stocks and fractions for improving soil quality and mitigating climate change

Assessing the Response of Tomato Yield, Fruit Composition, Nitrogen Absorption, and Soil Nitrogen Fractions to Different Fertilization Management Strategies in the Greenhouse

A greenhouse field experiment involving tomato (Solanum lycopersicum) was performed using different nitrogen (N) management regimes: sole application of differing rates of chemical N fertilizer (SC) (SC treatments: N0, N1, N2, and N3) and combined application of manure and chemical N fertilizer (MC) (MC treatments: MN0, MN1, MN2, and MN3). These were used to understand the relationship between comprehensive fruit composition, yield, and N fractions (soil mineral N; soil soluble organic N; soil microbial biomass N, and soil fixed ammonium) under greenhouse conditions. The results showed that the MC treatments significantly increased vitamin C and soluble sugar content compared with SC treatments. In addition, the MN2 treatment produced a high yield and had a positive effect on fruit composition. The N3 (563 kg N/ha) and MN3 (796 kg N/ha) treatments resulted in a high loss of N below the root zone (0–30 cm), consequently reducing N use efficiency. Soil mineral N, soil soluble organic N, and soil fixed ammonium tended to be higher during the first fruiting period, whereas soil microbial biomass N tended to be higher during the second fruiting period. MC treatments significantly increased the N fraction in the 0- to 30-cm soil layer; N fractions tended to be higher with the MN2 treatment. According to an optimum regression equation, soil fixed ammonium during the first fruiting period and soil microbial biomass N during the second fruiting period had a more significant influence on tomato yield and fruit composition. Overall, application MC at an appropriate rate (MN2: 608 kg N/ha) is a promising approach to achieving high yields and optimum taste, and it offers a more sustainable fertilizer management strategy compared with chemical N fertilization.

The influence of climate, topography, parent material and vegetation on soil nitrogen fractions

Soil nitrogen (N) is controlled by climate, topography, parent material and vegetation in less-disturbed ecosystems. However, a comprehensive understanding of the interactions among these soil-forming factors on soil N fractions (SNFs) is still unclear. We measured SNFs at 89 sites across a 3300-m gradient elevation in the southeastern Tibetan Plateau, which spans a large range of climates, parent materials and plant communities. The results showed that different SNFs were correlated with different predictors. Inorganic N was related to elevation and plant species diversity; labile organic N was mainly controlled by parent material; and moderate and recalcitrant organic N were governed by mean annual temperature, parent material and plant species diversity. We concluded that the combined effects of the soil-forming factors controlled SNFs; plant species diversity and parent material were the first and second crucial factors for predicting SNFs. Aspect, elevation and mean annual temperature not only directly affected some fractions, but also indirectly influenced them via plant species diversity. Our results stress the importance of incorporating abiotic and biotic factors when predicting soil N–environment feedback across a large scale.

Responses of soil organic carbon, aggregate stability, carbon and nitrogen fractions to 15 and 24 years of no-till diversified crop rotations

Diversification within a cropping system together with no-till (NT) soil management can help to improve soil organic carbon (SOC). The present study was conducted to assess the impacts of crop diversity through crop rotations on SOC and other selected soil properties. The long-term experimental sites were located in Beresford and Brookings, South Dakota, USA. The Beresford site was initiated in 1991 (24 years) on Egan soil series (fine-silty, mixed, superactive, mesic Udic Haplustolls), whereas, the Brookings site was established in 2000 (14 years) on a Barnes clay loam soil (fine-loamy, mixed, superactive, frigid Calcic Hapludolls) under a randomised complete block design with four replications. Treatments at both sites consisted of a 2-year (corn (Zea mays L.)–soybean (Glycine max L.)), and a 4-year (corn–soybean–winter wheat (Triticum aestivum L.)–oat (Avena sativa L.)) rotation, all managed under NT soil management. Soil samples were collected in the fall of 2015 after crop harvest under the corn phase. Data showed that 4-year rotation increased SOC stock (8.3% in Brookings and 22% in Beresford) compared with that under 2-year rotation (not always significant) in the soil profile 0–60cm. Soil particulate organic matter and organic matter were always higher under 4-year rotation than under 2-year rotation at 0–5 and 5–15cm depths at both sites. Surface soil aggregate stability was improved in both locations under 4-year rotation (12% in Brookings, 4% in Beresford). Additionally, at 0–5cm depth, the 4-year rotation increased light fractions of carbon (18% in Brookings, and 32% in Beresford) compared with 2-year. Results from this study showed that the use of diverse crop rotations (4-year) for longer (>24 years) duration enhanced SOC, carbon and nitrogen fractions, and soil aggregation compared with those under corn–soybean (2-year) rotation.

Variations of soil nitrogen-fixing microorganism communities and nitrogen fractions in a Robinia pseudoacacia chronosequence on the Loess Plateau of China

Afforestation greatly alters soil nitrogen (N) dynamics and soil microbial community, but the response of soil N dynamics to microbial activity, particularly to that of N-fixing microbes, remains unclear. In the present study, soil samples were collected from areas with a chronosequence of 17, 27 and 42 years of Robinia pseudoacacia L (RP17a, RP27a, and RP42a) and a sloped farmland (FL) as a control. The nifH gene was sequenced with the Illumina MiSeq platform to analyze soil microbial diversity and composition, and soil N fractions (TN, AN, NN, MBN, DON) were estimated. The soil N stocks, N fractions, and diversity of N-fixing microorganisms increased with the chronosequence of R. pseudoacacia. Beta diversity, analyzed using nonmetric multidimensional scaling, revealed that afforestation effectively improved soil microbial communities. The profiles of the N-fixing microorganism communities at sites 17a, 27a and 42a were clearly separated from the farmland, and soil N-fixing microbial community compositions generally changed in the farmland from Actinobacteria-dominated to Proteobacteria- dominated with stand ages. Redundancy analysis revealed that soil N fractions were positively correlated with the main species, particularly for AN, which had a 34.7% explanatory space in axis one and was significantly correlated with the Proteobacteria at the phylum level. Results implied the evolutionary tendency of the dominant microbial groups, and demonstrated the variation of the N fractions and some other physical-chemistry properties along the chronosequence of R. pseudoacacia, and that AN was the most sensitive N fraction to the N-fixing microorganism composition. Thus, our results provide evidence that the variation of soil compositions of N-fixing microbial communities is linked to the level of N fractions, especially the content of AN.

Introduction of a leguminous shrub to a rubber plantation changed the soil carbon and nitrogen fractions and ameliorated soil environments

The conversion of monoculture rubber (Hevea brasiliensis) plantations into rubber-based agroforestry systems has become a common trend in forestry management in the past few decades. Rubber–Flemingia macrophylla (a leguminous shrub) systems are popular in southwestern China’s Xishuangbanna region. The biogeochemical cycles of soil carbon and nitrogen in forests are mainly affected by their fractions. This study investigated the effect of introducing Flemingia macrophylla to rubber plantations of different ages on soil carbon and nitrogen fractions. The experimental treatments included R1 (young rubber plantation), RF1 (young rubber–Flemingia macrophylla system), R2 (mature rubber plantation) and RF2 (mature rubber–Flemingia macrophylla system). The results showed that the introduction of Flemingia macrophylla to rubber plantations of different ages significantly changed soil carbon and nitrogen fractions, improved soil labile organic carbon and nitrogen contents, and ameliorated soil environments. The average soil microbial biomass organic carbon, nitrogen and nitrate-nitrogen in the 0–10 cm soil layer during the experimental period was 38.9%, 55.5%, and 214.7% higher in RF1 than R1, respectively, and 22.1%, 22.2%, and 652.2% higher in RF2 than R2, respectively. Therefore, Flemingia macrophylla can be used as an alternative interplanted tree species within rubber plantations in similar environments of southeastern Asia.

Green Manuring Effect on Changes of Soil Nitrogen Fractions, Maize Growth, and Nutrient Uptake

Green manure is a promising, at least partial, substitution for chemical fertilizer in agriculture, especially for nitrogen (N), which in soil can be radically changed by exogenous input. However, it is not well understood how, after green manure incorporation, soil N changes coordinate with crop N uptake and consequently contribute to fertilizer reduction in a maize–green manure rotation. A four-year field study was performed consisting of (1) control, no fertilization; (2) F100, recommended inorganic fertilization alone; (3) G, green manure incorporation alone; (4) F70 + G (70% of F100 plus G); (5) F85 + G; and (6) F100 + G. The results show that treatments with 15–30% reduction of inorganic fertilizer (i.e., F70 + G and F85 + G) had similar grain yield, dry matter (DM) accumulation, and N uptake as F100 treatment. F100 + G maize had 17% greater DM and 15% more N uptake at maturity relative to F100. Of the five soil N fractions examined, dissolved organic N (DON) and mineral N (Nmin) explained over 70% of the variation of maize DM and N accumulation. Partial least squares path modeling further revealed that soil N fractions had positive indirect effects on DM production through N uptake, which might be coordinated with improved DON and Nmin status at both early and mid-late stages of maize growth. Overall, the results highlight enhanced maize production with reduced fertilizer inputs based on green manure incorporation in temperate regions.

Soil nitrogen fractions under long-term crop rotations in the Loess Plateau of China

Long-term crop rotation may influence soil N storage, mineralization, and availability. We studied the 30 yr effect of crop rotations on soil N fractions at 0–15 and 15–30 cm depths in the Loess Plateau of China. Crop rotations were continuous winter wheat (Triticum aestivum L.) (W), corn (Zea mays L.)-winter wheat-winter wheat-millet (Eleusine coracana L.) (CWWM), pea (Pisum sativum L.)-winter wheat-winter wheat-millet (PWWM), and sainfoin (Onobrychis viciifolia Scop.)-winter wheat-winter wheat-sainfoin (SWWS); pea-winter wheat-winter wheat-corn (PWWC); alfalfa (Medicago sativa L.) (4 yr)-potato (solanum tuberosum L.) (1 yr)-winter wheat (3 yr) (A4PoW3), and fallow (F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4–N, and NO3–N. The STN and PON at 0–15 cm were greater in CWWM and at 15–30 cm were greater in A4PoW3 than F and W. The PNM at both depths was greater in A4PoW3 than other crop rotations, except SWWS and CWWM. The MBN was greater in CWWM, PWWM, SWWS, and A4PoW3 than other crop rotations. The NH4-N content was greater in F than other crop rotations, except PWWC. The NO3-N content at 0–15 cm was greater in CWWM and at 15–30 cm was greater in PWWM than F. Most soil N fractions were correlated with each other and also with the length of the crop rotation. Diversified crop rotations with increased root biomass N returned to the soil and longer year rotations enhanced soil N storage, mineralization, and availability compared with monocropping and fallow.