Potato Rotation Research Articles

Combined Application of Chemical Fertilizer and Organic Amendment Improved Soil Quality in a Wheat–Sweet Potato Rotation System

The long-term excessive use of chemical fertilizers may result in soil degradation, but manure and straw application is considered to be an effective approach for alleviating this problem. The aim of this study is to examine the long-term impacts of different fertilization patterns on soil quality variables in a wheat–sweet potato rotation system. Four treatments were conducted in a field trial for a duration of twelve years, including (1) no fertilizer (control, CK); (2) application of mineral fertilizers (NPK) alone; (3) NPK with crop straw return (NPKs); (4) combined use of NPK and farmyard manure (NPKm). Thirteen physical, chemical, and biological soil parameters were measured. The results showed that the NPKm and NPKs significantly improved the proportion of macroaggregates (>0.25 mm) by 24.7% and 21.9% compared to the NPK alone, respectively. The proportion of microaggregates (0.053–0.25 mm) under the NPKm was 47.4% significantly higher than the NPKs. Additionally, the NPKm resulted in a 22.2% and 19.6% increase in the SOC content than the NPK and NPKs, respectively. In terms of soil-available K, the NPKs resulted in levels that were 42.1% and 49.6% higher than the NPKm and NPK alone, respectively. Long-term fertilization significantly decreased soil pH by 0.95–1.85 units compared to the control, whereas manure application could alleviate soil acidification, as shown when the pH increased by 10.6–18.7%. The NPKm and NPKs resulted in significantly increased soil pHs by 10.6% and 18.7% compared to the NPK alone, respectively. In addition, the NPKm and NPKs increased N-acetyl-β-D-glucosaminidase activity by 52.6% and 60.3% compared to the NPK alone. Determined by the minimum data set method, the NPKm treatment exhibited the highest soil quality index, followed by the NPKs and NPK. Our findings suggested that the combined use of chemical fertilizers with organic amendments proved beneficial for enhancing soil quality.

Effects of Long-Term Fertilizer Application on Crop Yield Stability and Water Use Efficiency in Diversified Planting Systems

Exploring crop yield stability and the relationship between the water–fertilizer effect and annual precipitation type in a broomcorn millet–potato–spring corn rotation system under long-term fertilization on chestnut cinnamon soil in loess tableland can provide a scientific basis for rational fertilization in the northwest Shanxi region in years with different precipitation. This study was based on a 33-year long-term fertilizer experiment, using four fertilizer treatments: no fertilizer as control (CT), single fertilizer nitrogen (N), single organic fertilizer (M), and nitrogen fertilizer with organic fertilizer (NM). The results showed that broomcorn millet and maize had the highest yield in wet years, while potatoes had the highest yield in normal years and the yield under NM treatment was the highest. The sustainable yield index (SYI) values for potato and maize were higher than the SYI for the broomcorn millet during years with different precipitation and the SYI for the NM treatment was the highest. The water use efficiency of NM treatment was the highest. The yield of broomcorn millet and maize was affected by nitrogen fertilizer, organic fertilizer, and precipitation during the growth period, while the potato yield was mainly affected by nitrogen fertilizer and organic fertilizer. Therefore, the rotation of potato–maize and the rational allocation of organic and inorganic fertilizer (NM) is the best planting system in this region.

Effects of cultural practices on weed community and seedbank dynamics in a potato rotation

ContextStagnant yields and declining soil health are common characteristics of high-intensity, low-residue cropping systems, such as potato, particularly in northeastern North America. Incorporating cultural practices including cover cropping and manure application is a way to combat declines in agroecosystem health and potato productivity. However, manure application and the use of cover crops may exacerbate weed issues through seedbank additions. ObjectiveThis study was aimed at investigating how the cultural practices of cover cropping and manure application and their associated management activities can alter weed community dynamics and weed seedbank composition in a northeastern North American potato rotation. MethodsThe study evaluated the use of eight cover crop mixtures—annual and perennial grasses and legumes—grown over two years with/without manure added in year one of the rotation. It also examined the effects of the cover crop mixtures and the presence/absence of manure on the weed community and on seedbank dynamics within a three-year potato rotation between 2019 and 2021. ResultsIn year one of the study and directly after application, manure plots had greater weed seedbank density and species richness; however, this did not result in greater in-season weed biomass. Manure application resulted in a gradual decline in weed seedbank density over time regardless of cover crop treatment. Further, manure application increased the in-season competitive ability of cover crops, resulting in greater weed suppression per unit of cover crop biomass. In contrast, in the absence of manure, weed seedbank density remained largely unchanged through time regardless of cover crop treatment. We found that management practices associated with annual and perennial cover crops had distinct ecological filtering effects throughout the rotation on the weed community and prevented the dominance of any particular species. ConclusionTogether, our results demonstrate that combining the cultural practices of annual or perennial cover cropping and manure application contributes to weed suppression and should be considered an important component of sustainable potato production.

Summer Rice–Winter Potato Rotation Suppresses Various Soil-Borne Plant Fungal Pathogens

Growing potatoes (Solanum tuberosum) using the idle rice fields in Southern China and the Indo-Gangetic Plains of India in the winter season through the rice–potato rotation (RC) system could support future food security. However, the modulation capacity of the RC system on soilborne fungal pathogens is still unclear. In the current study, a pot experiment was designed and conducted to monitor the dynamics of soil fungal community composition between the potato monoculture (CC) system and the RC system, where the two systems were set with the same soil conditions: autoclaving with fertilization; autoclaving without fertilization; autoclave-free with fertilization; and autoclave-free without fertilization. Then, the uncultivated soil (CK) and root-zone soil samples of conditions under the two systems were collected, and then soil physiochemical properties and enzymatic activities were determined. Next, the high-variable region (V5–V7) of fungal 18S rRNA genes of the samples were amplified and sequenced through the PCR technique and the Illumina Miseq platform, respectively. Finally, the fungal species diversity and composition, as well as the relative abundance of fungal pathogens annotated against the Fungiuld database in soil samples, were also investigated. The results showed that the RC could significantly (p < 0.05) increase soil fungal species diversity and decrease the relative abundance of soil fungal pathogens, where the RC could suppress 23 soil fungal pathogens through cultivating the rice during the summer season and 93.75% of the remaining pathogens through winter-season cultivation. Seven-eighths of the conditions under RC have lower pathogenic MGIDI indices (6.38 to 7.82) than those of the CC (7.62 to 9.63). Notably, both rice cultivation and winter planting reduced the abundance of the pathogenic strain ASV24 under the Colletotrichum genus. The bipartite fungal network between the pathogens and the non-pathogens showed that the pathogenic members could be restricted through co-occurring with the non-pathogenic species and planting crops in the winter season. Finally, the redundancy analysis (RDA) indicated that soil pH, electronic conductivity, available phosphorus content, and various enzyme activities (cellulase, urease, sucrase, acid phosphatase, catalase, polyphenol oxidase) could be the indicators of soil fungal pathogens. This experiment demonstrated that the rice–potato rotation system outperformed the potato monoculture on suppressing soilborne fungal pathogenic community.

Impact of extended dryland crop rotation on sustained potato cultivation in Northwestern China

Sustainable agricultural development is challenged by the growing population and increasing instances of drought. Over multiple years, the continuous planting of potatoes can lead to a decrease in both potato yield and soil quality. Crop rotation proves to be a viable solution for enhancing soil productivity, especially in arid and semi-arid areas. A 5-year field experiment was conducted in northwestern China's semi-arid region to evaluate the impact of different potato rotation treatments (1-year rotation with maize, 3-year rotation with maize, oil flax and broad bean; 2-year continuous potato planting rotated with maize and 5-year continuous potato planting) and mulching techniques (unmulched and plastic film) on potato yield and soil fertility. The results showed that crop rotation (1-year and 3-year) improved plant height, dry matter accumulation, soil quality, and reduced water footprint. Under plastic film mulching mode, 1-year rotation resulted in an increase in number of potatoes per plant by 38.24%, economic benefits by 9.70%, water use efficiency by 41.86 and soil fertility in comparison to the 5-year continuous planting, the tuber yield significantly increased by 78.86%, and the green/grey/total water footprint reduced by 28.8%–46.4%. We recommend the 1-year rotational cropping system using plastic film mulch as an effective technique for addressing the challenges of continuous potato cultivation in arid and semi-arid regions.

Increasing potato profitability through rotation systems and winter cover, nitrogen fertilizer, and supplemental irrigation in Atlantic Canada

AbstractAverage potato yield in Prince Edward Island, Canada, has been stagnant since 2006. Two field studies were conducted on Charlottetown fine sandy loam soil to address this concern. In the first experiment, two alternative crop rotations, grain corn (Zea mays L.)–sorghum sudan grass (Sorghum × drummondii)–potato (C–SS–P) and soybean (Glycine max (L.) Merr.)–mustard (Brassica juncea (L.) Czern.)–potato (Soy–M–P), were compared to a conventional barley (Hordeum jubatum L.) (under seeded with red clover)–red clover (Trifolium pratense L.)–potato (Solanum tuberosum L.) (B–RedCl–P) rotation. This experiment was conducted for two 3‐year cycles comparing the effects of potato rotation, nitrogen fertilizer, and supplemental irrigation. The second experiment evaluated the inclusion of winter cover crops in a 3‐year potato crop rotation. The profitability of potatoes in each rotation was assessed using a stochastic budget of yields and fertilizer and crop prices. The effects of supplemental irrigation were not significant; however, nitrogen fertilization increased potato yields by 48%. Potato yields and net revenues in C–SS–P increased by 10.5% and 32.6% and in Soy–M–P by 6.7% and 20.5%, respectively, compared to potato in B–RedCl–P rotation. The use of winter rape cover increased potato yields by 18.6% compared to a system without winter covers, although some of these increases could be due to the use of sudan grass instead of red clover in B–RedCl–P rotation. It is recommended that potato producers implement the alternative rotation with additional fertilization and winter cover crops to increase yields and profits.

Crop diversification improves the diversity and network structure of the prokaryotic soil microbiome at conventional nitrogen fertilization

BackgroundSustainable agriculture seeks to optimize the application of nitrogen (N) fertilizers to reduce adverse economic and ecological effects. Crop diversification has been proposed to increase the efficiency of N fertilization. An open question is how the soil microbiome responds to these beneficial practices.MethodsIn a field study we investigated the effects of mineral N fertilizer with a 0-control, a conventional amount of 150 kg N ha−1 and an excessive application of 250 kg N ha−1 on the soil microbiome within a diversified cropping system with oil radish and undersown ryegrass over a period of 2.5 years and a non-diversified control, both in rotation of potato, winter rye and maize.ResultsN-fertilizations and crop rotations altered the pH, but differences were less pronounced with the diversified system. Compared to the crop species and season, N fertilization and crop diversification had less influence on the abundance of soil bacteria, archaea and fungi. The crop diversification showed a much stronger effect on archaeal than on bacterial or fungal abundances, while the microbial carbon use efficiency correlated strongly with bacterial abundance. At the end of the growing seasons, crop diversification increased prokaryotic richness and Shannon diversity in response to N addition, with a greater increase in the conventional N. At conventional N supply, prokaryotic co-occurrence networks revealed a much denser and complex structure in the diversified system.ConclusionsThe diversified cropping system under conventional N application rates showed positive effects on the prokaryotic soil microbiome by increasing their richness, Shannon diversity, and promoting a more elaborated network structure.

Durum Wheat–Potato Crop Rotation, Soil Tillage, and Fertilization Source Affect Soil CO2 Emission and C Storage in the Mediterranean Environment

At present, the role of agricultural practices on the dynamic of GHGs is being investigated worldwide. In this study, the effects of soil tillage practices (conventional vs. conservation techniques) and fertilization sources (inorganic vs. organic) on soil CO2 emissions in durum wheat (Triticum durum Desf.)–potato (Solanum tuberosum L.) rotation in the Mediterranean area were evaluated. This study aimed to understand the changes in the soil carbon content and the soil CO2 emissions under different soil tillage practices (moldboard plow (P), subsoiler (R), and spading machine (S)) and fertilization sources (mineral (M) and organic (O) with municipal organic waste). Soil CO2 flux, soil water content, and soil temperature data were collected for both crops using a portable closed-chamber infrared gas dynamics system. Significant relationships were detected between soil CO2 emissions and soil temperate and soil water content. However, these relationships were found only for durum wheat crops. Our findings indicate that including sustainable agricultural practices in wheat–potato rotation system could act as an appropriate alternative option to increase soil organic carbon, mitigate CO2 emissions, and reduce the dependence on chemical inputs and energy.

Back to the Future: Agricultural Booms, Busts, and Diversification in Maine, USA, 1840–2017

In temperate forested regions, historical agricultural production and value have been characterized by booms and busts. Agricultural diversification can encourage more stable agricultural development in the future. Agricultural Census and Survey data from 1840 to 2017 were used to estimate crop and livestock species’ product production and value for Maine, USA. These data were also used to calculate agricultural diversity indicators over time such as species richness, relative abundance, effective number of species, species diversification index, evenness, Shannon-Weiner index, and composite entropy index. Maine’s historical grass-based livestock systems included crops raised to feed livestock from the state’s establishment until the 1950’s. Since the 1950’s, production and value of livestock commodity products (e.g., meat chicken, eggs) have busted after initial booms. Three categories where diversity indicators have become more favorable since the 1950’s in Maine include livestock, livestock forage/feed, and potatoes and potato rotation crops. Mixed vegetables, fruits, nuts, and specialty crops as a category have had diversity increases during the 1970’s back-to-the-land movement and over the past two decades. Floriculture, propagation, and X-Mas trees as a category have witnessed volatile diversity indicator changes over time. Past diversification strategies can inspire farmers to go “back to the future” to improve sustainability.

Cultivating Salix Viminalis in Agricultural-Riparian Transition Areas to Mitigate Agriculturally Derived N2O Emissions from Potato Cropping Systems on Prince Edward Island

Cultivating shrub willow (Salix viminalis) in agricultural-riparian transition areas has been proposed as a strategy for mitigating elevated riparian nitrous oxide (N2O) emissions in agricultural regions. Nitrogen-based fertilizers are water soluble, enter riparian areas through surface runoff and subsurface lateral flow, and are converted to N2O by incomplete anaerobic denitrification. Salix buffer strips can intercept and recycle fertilizer nitrate (NO3−) into their biomass and/or promote complete denitrification, reducing N2O emissions. We investigated the impact of Salix viminalis buffers on N2O emissions relative to grassed buffers and upslope cultivated fields in potato rotations at 5 research sites across Prince Edward Island (PEI), Canada. Greenhouse gas (N2O, CO2, CH4) flux at the soil-atmosphere interface was measured using non-steady-state static chambers in 2018 and 2019. NO3− exposure, soil temperature, and soil moisture content were quantified. Agricultural-riparian Salix significantly reduced N2O emissions even when high NO3− inputs occurred and following precipitation events. Mean cumulative seasonal reductions of 1.32 kg N2O–N ha−1 (− 0.02 to 6.16 kg N2O–N ha−1) were observed in Salix relative to cultivated fields; however, they were not significantly different than grass. The mean cumulative average global warming potential of Salix was 613 kg CO2e ha−1 lower than cultivated fields, with reductions of up to 2918 kg CO2e ha−1. Differences in N2O flux between vegetation types were the greatest influencing factor. No hot moments of N2O emission were observed in Salix following high rainfall events, which coincided with up to 95% decreases in N2O emissions in Salix relative to cultivated fields.

Nitrate leaching and potato tuber yield response to different crop rotations

Intensive potato production causes nitrate leaching and contributes to groundwater nitrate contamination. This study investigated the impacts of five potato rotations on nitrate leaching and tuber yield using a plot-based field experiment in combination with numerical modeling in Prince Edward Island, Canada, from 2014 to 2021. The rotations included barley underseeded with red clover–red clover–potatoes (B–RC), three buckwheat–buckwheat–potatoes rotations with buckwheat harvested for seed (BWS), terminated mid-season by disking (BWD) and terminated mid-season by mowing (BWM), and barley underseeded with timothy–timothy–potatoes (B–T). The buckwheat rotations represented typical management options for wireworm control, B–RC represented the local industry standard rotation, and B–RC and B–T acted as controls. Rotation-based total nitrate leaching that occurred from 23 October 2014–20 July 2020 (covering two 3-year rotation cycles) was calculated using a combination of lysimeter sampling and soil drainage numerical modeling. The three buckwheat rotations had comparable effects on total nitrate leaching and marketable tuber yield in most cases. When treated as a group, the buckwheat rotations (BW) were shown to significantly reduce total nitrate leaching by 30% within the two rotation cycles, while significantly increasing marketable tuber yield (mean of 2016 and 2019 potato yields) by 16% compared to B–RC. However, BW produced 58% more total nitrate leaching than B–T and had a comparable marketable tuber yield. Total nitrate leaching and tuber yield were highly correlated (R 2 = 0.95) with nitrogen (N) surplus (calculated as total N supply minus N removal at crop harvest within the total nitrate leaching accounting period), with higher N surplus producing higher nitrate leaching and lower tuber yield. Nitrogen removal accounted for 33%, 36% and 53% of total N supply for B–RC, BW and B–T, respectively, indicating very low N use efficiency. These findings suggest that N surplus was the key explanatory variable for the variations in total nitrate leaching and tuber yield, and adequately accounting for N credits from the preceding rotation crop (especially red clover) is important to minimize nitrate leaching while maximizing potato productivity. • Buckwheat–buckwheat–potatoes produced 30% less N leaching and 16% more tuber yield than barley–red clover–potatoes. • Buckwheat–buckwheat–potatoes produced 58% more N leaching and comparable tuber yield, compared with barley–timothy–potatoes. • Adequately accounting for N credits from preceding crops is required to reduce N leaching and enhance tuber productivity.

Effects of different rotation cropping systems on potato yield, rhizosphere microbial community and soil biochemical properties.

Continuous potato cropping systems cause yield reduction, soil-borne disease aggravation, and soil degradation, but crop rotation can alleviate these negative effects. However, there are limited studies on the relationships between microbial community and other soil biochemical properties of continuous potato cropping at both pre-planting and harvest in North China. A 4-year study was conducted to explore the effects of different rotation system on soil biochemical properties, microbial community at pre-planting and harvest, and potato yield, tuber number and black scurf incidence at harvest in 2020 and 2021, which included 4 treatments vis. potato-potato-potato-potato (PC), potato-oat-faba bean-potato (PR), oat-faba bean-potato-oat (O), and faba bean-potato-oat-faba bean (B). The results showed that soil biochemical properties and microbial community among all treatments showed no significant difference at pre-planting after a long cold winter generally. At harvest, PC reduced tuber yield and number and significantly increased black scurf incidence relative to potato rotation systems. PC also reduced soil enzyme activities, the content of soil nutrients, and fungal community diversity, and increased bacterial community diversity compared with the other treatments, insignificantly when compared with PR. Relative abundance of microorganisms related to the degradation of organic residues, soil nitrogen cycling, and disease suppression, such as the genera Devosia, Aeromicrobium, Paraphoma, and Papiliotrema, were significantly higher in O or B than in PC and PR, while microorganisms related to disease infection such as the genera Pseudomonas, Colletotrichum, Plectosphaerella, Fusarium, and Verticillium exhibited increased in PC and PR. Principal Coordinates Analysis (PCoA) showed that there were significant differences in the microbial community structure of PC and PR at harvest compared with that of O and B. Redundancy analysis (RDA) revealed that soil available potassium (AK), acid phosphatase (ACP), available phosphorus (AP), sucrase (SUC) and pH were the dominant factors that significantly affected bacterial and fungal community structure. Partial least squares structural equation model indicated rotation system had significant negative effect on fungal community. It was concluded that growing oat or faba bean after potato can increase soil beneficial microorganisms and maintain the ecosystem healthy, thus reducing the incidence of tuber black scurf and increasing potato yield.

Effect of Biofumigation on Population Densities of Pratylenchus spp. and Verticillium spp. and Potato Yield in Eastern Canada

Biofumigation has been proposed as an alternative to soil fumigation to manage soil-borne diseases including potato early dying disease complex (PED). This study examined the potential of using brown mustard (Mustard juncea) biofumigation to manage PED under rain-fed potato production in New Brunswick, Canada in two trials between 2017 and 2020 in comparison with chloropicrin fumigation and a conventional barley rotation. Biofumigation increased yield in one trial, but not in a second trial where the potato crop experienced severe drought, whereas chloropicrin fumigation increased yield in both trials. Biofumigation was effective in suppressing root-lesion nematode (RLN, Pratylenchus spp.) counts in both trials, but was ineffective in suppressing V. dahliae population density. Chloropicrin fumigation was effective in suppressing RLN counts and V. dahliae population density only in the hill where injected, but the effect was short-lived as the population density of V. dahliae in the hill increased to the level of the control in one potato growing season. Biofumigation may be an alternative to chloropicrin fumigation in managing PED, particularly in fields with high RLN population but relatively low Verticillium population density. However, neither biofumigation nor fumigation used alone may be sustainable in the short-term potato rotations commonly used in New Brunswick, and additional beneficial practices are required to sustain productivity in the long-term.

Characterizing Dominant Field-Scale Cropping Sequences for a Potato and Vegetable Growing Region in Central Wisconsin

Crop rotations are known to improve soil health by replenishing lost nutrients, increasing organic matter, improving microbial activity, and reducing disease risk and weed pressure. We characterized the spatial distribution of crops and dominant field-scale cropping sequences from 2008 to 2019 for the Wisconsin Central Sands (WCS) region, a major producer of potato and vegetables in the U.S. The dominant two- and three-year rotations were determined, with an additional focus on assessing regional potato rotation management. Our results suggest corn and soybean are the two most widely planted crops, occurring on 67% and 36% of all agricultural land at least once during the study period. The most frequent two- and three-year crop rotations include corn, soybean, alfalfa, sweet corn, potato, and beans, with continuous corn being the most dominant two- and three-year rotations (13.2% and 8.5% of agricultural land, respectively). While four- and five-year rotations for potato are recommended to combat pest and disease pressure, 23.2% and 65.9% of potato fields returned to that crop in rotation after two and three years, respectively. Furthermore, 5.6% of potato fields were planted continuously with that crop. Given potato’s high nitrogen (N) fertilizer requirements, the prevalence of sandy soils, and ongoing water quality issues, adopting more widespread use of four- or five-year rotations of potato with crops that require zero or less N fertilizer could reduce groundwater nitrate concentrations and improve water quality.

Response of potato yield, soil chemical and microbial properties to different rotation sequences of green manure-potato cropping in North China

Continuous cropping of potato (Solanum tuberosum L.) can result in soil degradation and yield decline. These negative effects could be alleviated by crop rotation. Green manure-potato rotation is being proposed as an alternative that can sustain high yield and soil quality in potato production system. However, the mechanisms by which biotic and abiotic factors are affected by different cropping sequences remain unclear. A 12-year green manure (G)-potato (P) rotation experiment was conducted to explore the response of potato yield, soil chemistry properties, and microbial community composition to different rotation sequences in North China, the cropping sequence treatment included 2-year of green manure and 1-year of potato (P1G2), 1-year of green manure and 2-year of potato (P2G1), and continuous cropping potato (P3), with a rotation period of 3-year. The content of NH4+-N (AN), organic matter (OM), available potassium (AK), total phospholipid fatty acids (PLFAs), and bacterial PLFAs in soil, and potato yield were higher in P1G2 compared with those in P2G1 and P3, while the ratio of fungal to bacterial biomarkers was decreased significantly than that in P3. Soil dominant bacterial phyla Bacteroidetes, Gemmatimonas, Proteobacteria, and Nitrospirae presented higher abundance in P1G2 relative to those in P2G1 and P3; however, phyla Actinobacteria decreased significantly in P1G2 than other two treatments. The beneficial microflora Sphingomonas, Haliangium, Gemmatimonas, and Pseudogymnoascus increased significantly in P1G2 over P2G1 and P3, and the pathogenic fungal Fusarium, Stagonosporopsis, Alternaria, and Lectera showed higher abundance in P3 than P1G2 and P2G1. The redundant analysis showed that soil AN, OM, AP, and AK were positively correlated with dominant flora of bacteria and fungi in P1G2, and were negatively correlated with dominant flora of bacteria and fungi in P3. Partial least squares path modeling revealed that the conversion of cropping sequences had a direct positive effect on the fungal community rather than the bacterial community. Overall, the rotation cropping combined green manure and potato attained higher potato yield by maintaining higher soil fertility and healthy ecosystem, we also gave a suggestion on rotation sequences combined yield and economic benefits of potato.

Long-term fertilization with high nitrogen rates decreased diversity and stability of diazotroph communities in soils of sweet potato

Sweet potato (Ipomoea batatas Lam) could produce acceptable root yield in low-nitrogen (N) soils, with substantial N uptake potentially attributed to supplies provided via biological N2-fixation by free-living diazotrophs. However, dynamics of diazotrophic communities as influenced by soil properties across the N fertilization gradients are still largely unclear. Long-term fertilization experiment under wheat-sweet potato rotation was established in an acid yellow brown soil since 2011. Soil samples were collected after sweet potato harvest (October 2018). The nitrogenase (nifH) gene real-time polymerase chain reaction (RT-PCR) and Hiseq high-throughput sequencing technologies were applied to soil samples from four N fertilizer treatments (0, 60, 120 and 180 kg ha−1). The results showed that long-term N fertilization significantly decreased abundance of the nifH gene, which was closely related to decreases in the content of available phosphorus (AP). The long-term high-N (120 and 180 kg ha−1) fertilization dramatically altered structure of soil diazotrophic community and lead to in decreased diversity of diazotrophs, whereas low-N (60 kg ha−1) fertilization maintained diazotrophic community diversity and stability. Compared with the low-N fertilizer inputs (0 and 60 kg ha−1), the high rates of N fertilization (180 kg ha−1) significantly decreased the relative abundance of nifH-harboring microorganisms, especially the phylum Cyanobacteria known as potential N2-fixers that could sustain fertility of sweet potato soils. There were negative correlations between N fertilization rates and the relative abundance of Proteobacteria, whereas the Bacteroidetes and Firmicutes showed a positive correlation. Moreover, the structural equation model (SEM) results suggested that the diazotrophic community diversity and structure were influenced mostly by soil pH rather than SOM and N forms (TN, NH4+-N and NO3−-N), and diazotrophs abundance mainly regulated by soil AP content. Our results implied that appropriate N fertilization is beneficial to sustain the stability and diversity of the diazotrophic community.

Effects of Different Potato Rotation Patterns on Fungal Community Structure in Rhizosphere Soil

Effects of Different Potato Rotation Patterns on Fungal Community Structure in Rhizosphere Soil

Impact of Microwave Irradiation Energy Levels on Molecular Rotation, Structural, Physicochemical, Proximate and Functional Properties of Potato (Ipomoea batatas) Starch

Starch isolated from potato was subjected to microwave treatment at different energy levels (200 - 800 W) to modify the functional, structural and physicochemical properties, as well as induce molecular rotation of the hydroxyl group on the starch polysaccharide. Proximate analyses revealed that moisture content reduced, while ash, protein, fat and fibre increased after modification. Fourier-transform infrared spectroscopy spectra indicated a strong shift in absorption band of OH from 3441 to 3454 cm-1. Optical light microscopy revealed that starch granules were oval and spherical in shape with hyla on some of the granules. Least gelation concentration reduced following microwave treatment. Compared with the native starch, the pasting parameters of the microwave treated starches decreased, with the exception of set­back viscosity for starch modified at 800 W. Onset temperature (TO), peak temperature (TP) and conclusion temperature (TC) of gelatinization increased in microwave treated starches compared with native potato starch. Also, gelatinization enthalpy increased from 8.21 J/g in native starch to 15.39, 16.36, 17.76 and 38.06 J/g in microwave treated starches at 200, 400, 600, and 800 W, respectively. It was concluded that the energy of microwave irradiation can induce and accelerate molecular rotation of the hydroxyl group on the starch polysaccharide.

Systematic relationship between soil properties and organic carbon mineralization based on structural equation modeling analysis

Previous studies have focused mostly on the effects of the single application of biochar on soil organic carbon mineralization. However, these studies were not able to infer the effect of extended biochar supplementation at distinct concentrations on the systematic relationship between soil properties and organic carbon mineralization. Thus, we investigated the soil characteristics, such as organic carbon mineralization, hydraulics, aggregation, and microbiota under the biochar supplementation for an experimental period of six years in a rapeseed-sweet potato rotation field experiment in upland red soil in southeast China. The structural equation modeling (SEM) was constructed to reflect the systematic relationship between soil properties and organic carbon mineralization. The results of our study revealed that the biochar significantly reduces the soil bulk density and enhances the soil water holding capacity, but these effects diminished with the time. We also found that low-medium biochar application rates (0.5% and 1%) considerably increased the soil microbiota, aggregation, and potentially mineralizable carbon (C0). Moreover, high application rates (2%) of biochar inhibited the carbon mineralization and increased the soil organic carbon fixation. Besides, the outcome of SEM demonstrated that the hydraulics, aggregation, and microbiome of soil impacted the C0. The effects of soil aggregation and microbiota on C0 were higher during 2014–2016 than they were in 2011–2013, and the negative impact of soil hydraulics on C0 diminished with time. In conclusion, the effects of biochar on physicochemical characteristics and organic carbon mineralization of soil differ with the dosage and duration of biochar supplementation. Also, a high dose of biochar addition can substantially reduce CO2 emission from soil to the atmosphere.

Nitrogen in potato rotations with cover crops: Field trial and simulations using DSSAT

AbstractA 2‐yr field trial was conducted in 2014−2015 in northern California to determine the N availability from different legume and grass cover crops grown during the summer and incorporated in fall. Russet Norkotah potato (Solanum tuberosum L.) were planted the following spring. The objectives of this study were to determine whether potato yield can be successfully predicted with the Decision Support System for Agrotechnology Transfer (DSSAT) model for different cover crop treatments and to assess the risk of nitrate (NO3−) leaching losses with winter precipitation. The total amount of N in the aboveground biomass of the legumes ranged from 73 to 253 kg ha−1. The potato yield of the unfertilized control reached 39 Mg ha−1, while it ranged from 34.8 to 47.9 Mg ha−1 in the cover crop treatments. The DSSAT model considerably underestimated the soil mineral N content before potato was planted in the treatments with legume cover crops. The results suggest that the legumes likely covered a larger proportion of their N requirements through N2 fixation and less through uptake of soil mineral N than predicted by the model. The inaccurate simulation of cover crop soil N uptake contributed to a poor prediction of potato yields for individual treatments. In contrast, the model was successful in simulating N mineralization from cover crop residues. Using weather data from a 30‐yr period revealed that NO3− leaching below the root zone of the subsequent potato crop is minimal in most winters.