Long-term Cotton Research Articles

Effects of nitrification and urease inhibitors on nitrous oxide emissions and concentrations driven by soil moisture in sandy soils

Soil moisture and nitrogen (N) fertilizer control the balance between nitrous oxide (N₂O) production and consumption in soil. However, the impact of nitrification and urease inhibitors on soil N₂O production and consumption under varying soil moisture levels remains insufficiently understood. In this study, a soil column experiment was conducted to investigate N₂O concentrations and accumulation at different soil depths (0, 5, 15, 30, and 60 cm) in sandy soil over two months. The soil was collected from a drip-irrigated field subjected to long-term cotton cultivation in an arid region. Four fertilizer treatments were applied: urea, urea + nitrification inhibitor (Dicyandiamide, DCD), urea + nitrification and urease inhibitors [N-(n-butyl) thiophosphoric triamide, NBPT], and an unfertilized control. These treatments were tested under three soil moisture levels [23%, 46%, and 70% water-filled pore space (WFPS)]. The results showed that treatments with inhibitors significantly reduced cumulative surface N₂O emissions by 33.2%–58.2% compared to urea alone. Notably, the treatment with both DCD and NBPT achieved the greatest reductions in surface emissions and in N₂O concentrations at 5 cm and 15 cm soil depths at 70% WFPS. Additionally, across all N fertilizer sources, 70% WFPS led to increased N₂O concentrations in the soil profile compared to lower soil moisture levels. Column N₂O accumulation was positively correlated with surface cumulative N₂O emissions under all three moisture conditions. Our study highlights that under high soil moisture conditions, DCD and NBPT can significantly mitigate intense N₂O emissions in sandy soils. This emission reduction is likely attributed to enhanced nitrification within the 0–15 cm soil layer rather than reduced N₂O diffusivity and denitrification along the soil profile. Therefore, we recommend applying nitrification and urease inhibitors under high soil moisture conditions as an effective strategy to reduce N₂O emissions in sandy soils.

Spatial heterogeneity response of soil salinization inversion cotton field expansion based on deep learning.

Soil salinization represents a significant challenge to the ecological environment in arid areas, and digital mapping of soil salinization as well as exploration of its spatial heterogeneity with crop growth have important implications for national food security and salinization management. However, the machine learning models currently used are deficient in mining local information on salinity and do not explore the spatial heterogeneity of salinity impacts on crops. This study developed soil salinization inversion models using CNN (Convolutional Neural Network), LSTM (Long Short-Term Memory Network), and RF (Random Forest) models based on 97 field samples and feature variables extracted from Landsat-8 imagery. By evaluating the accuracy, the best-performing model was selected to map soil salinity at a 30m resolution for the years 2013 and 2022, and to explore the relationship between soil electrical conductivity (EC) values and the expansion of cotton fields as well as their spatial correlation. The results indicate that:(1) The CNN performs best in prediction, with an R2 of 0.84 for the training set and 0.73 for the test set, capable of capturing more local salinity information. (2) The expansion of cotton fields has reduced the level of soil salinization, with the area of severely salinized and saline soils in newly added cotton fields decreasing from 177.91 km2 and 381.46 km2 to 19.49 km2 and 1.12 km2, respectively. (3) Regions with long-term cotton cultivation and newly reclaimed cotton fields exhibit high sensitivity and vulnerability to soil salinity. This study explores the excellent performance of deep learning in salinity mapping and visualizes the spatial distribution of cotton fields that are highly sensitive to soil salinity, providing a scientific theoretical basis for accurate salinity management.

Arbuscular Mycorrhizal Association is Induced by Long-Term Cotton Cropping and Enhances P Uptake and Initial Growth of Cotton Plants by Legacy P Exploration in Soil

Arbuscular Mycorrhizal Association is Induced by Long-Term Cotton Cropping and Enhances P Uptake and Initial Growth of Cotton Plants by Legacy P Exploration in Soil

Long-term cotton stubble return and subsoiling improve soil organic carbon by changing the stability and organic carbon of soil aggregates in coastal saline fields

Cotton stubble return and subsoiling significantly enhanced soil fertility and cotton yield in coastal saline soils. Despite these benefits, the mechanisms influencing soil organic carbon (SOC) sequestration remain poorly understood. To address this gap, a comprehensive ten-year study was undertaken, focusing on the effects of stubble management (either removal or return) and tillage (either non-subsoiling or subsoiling) on the physicochemical properties of both topsoil (0–20 cm) and subsoil (20–40 cm) layers, as well as on cotton yield. The objectives were to (i) quantify interannual variability (2013–2022), stubble return, and subsoiling on the soil physicochemical properties of the topsoil (0–20 cm) and subsoil (20–40 cm) and cotton yield and (ii) elucidate the mechanism by which these agricultural practices affect SOC sequestration. Findings from this decade-long investigation indicated that ten consecutive years of cotton stubble return and subsoiling at three-year intervals significantly ameliorated soil conditions by reducing the salt content, pH, and the proportion of silt plus clay, while increasing macro-aggregates, mean weight diameter (MWD), aggregates organic carbon (AOC) across various particle sizes, SOC, total nitrogen (TN) in both soil layers, and ultimately, the cotton lint yield. Interestingly, the effect of stubble return on micro-aggregates varied between the two soil layers, leading to a reduction in micro-aggregates by 11.16% in the topsoil, in contrast to a 5.7% increase in the subsoil, when compared to conditions where stubble was removed. The partial least squares path modeling (PLS-PM) indicated that the enhancements in MWD attributable to stubble return and subsoiling were primarily due to significant reductions in soil pH and salt content in both layers, which in turn fostered an increase in AOC, ultimately contributing to higher SOC levels. However, the pathways through which AOC influenced SOC varied significantly between the topsoil and subsoil, with stubble return and subsoiling increasing SOC through an increase in the macro-AOC in the topsoil, and micro-AOC in the subsoil. In summary, long-term cotton stubble return and subsoiling significantly optimize the aggregate particle size distribution and enhance the carbon sequestration potential in coastal saline cotton fields.

Effects of aftercrop tomato and maize on the soil microenvironment and microbial diversity in a long-term cotton continuous cropping field.

Long-term continuous cropping affects the soil microecological community and leads to nutrient imbalances, which reduces crop yields, and crop rotation can increase soil productivity. To study the effects of the cultivation of tomato (Solanum lycopersicum) and corn (Zea mays) on the microbial community, physical and chemical factors and the structure of aggregates in cotton (Gossypium hirsutum) long-term continuous cropping soils were examined. Four cropping patterns were established, including one continuous cropping pattern and three crop rotation patterns, and the diversity of the soil microecological community was measured using high-throughput sequencing. The physical and chemical properties of different models of soil were measured, and the soil aggregate structure was determined by dry and wet sieving. Planting of aftercrop tomato and corn altered the bacterial community of the cotton continuous soil to a lesser extent and the fungal community to a greater extent. In addition, continuous cropping reduced the diversity and richness of the soil fungal community. Different aftercrop planting patterns showed that there were very high contents of soil organic carbon and organic matter in the cotton-maize rotation model, while the soil aggregate structure was the most stable in the corn-cotton rotation model. Planting tomato in continuous cropping cotton fields has a greater effect on the soil microbial community than planting maize. Therefore, according to the characteristics of different succeeding crop planting patterns, the damage of continuous cropping of cotton to the soil microenvironment can be alleviated directionally, which will enable the sustainable development of cotton production.

Cotton stubble return and subsoiling alter soil microbial community, carbon and nitrogen in coastal saline cotton fields

Long-term cotton stubble return and subsoiling improve root growth and soil properties and alter microbial colonization in the rhizosphere. However, it is unknown if cotton stubble return and subsoiling would change the soil microbial biomass carbon (MBC) and nitrogen (MBN) sequestration by changing the microbial community in coastal saline soil. We used an experiment to quantify the effects of stubble management (removal or return), tillage (non-subsoiling or subsoiling), and soil compartments (non-rhizosphere or rhizosphere) on the bacterial and fungal communities after 9-year treatments. Soil compartments were the main factor affecting the soil bacterial community. The abundance of Bacillus, Pseudomonas, and Sphingomonas in the rhizosphere soil increased by 63.64%, 20.40%, and 109.24%, respectively, compared to the non-rhizosphere soil. Moreover, Bacillus was increased by both stubble return and subsoiling. The Chao1, Simpson, and Shannon indices in alpha diversity of the bacterial community were increased by rhizosphere soil, stubble return, and subsoiling. The MBC and MBN in the rhizosphere soil was 22.4% and 13.2% higher than in the non-rhizosphere soil. Stubble management was the main factor affecting the fungal community composition. Stubble return significantly increased some fungal abundance, e.g., Cephalotrichum and Fusarium, by 243.11% and 95.24% than stubble removal. The abundance of Cephalotrichum, Fusarium, and Alternaria in the rhizosphere soil was significantly higher than that in the non-rhizosphere soil. The Chao1, Simpson, and Shannon indices of the fungal community were only significantly increased by stubble return. Compared with cotton stubble removal, stubble return increased MBC and MBN by 31.8% and 23.0%, respectively. The effects of the plant growth promoting rhizobacteria (PGPR) (Bacillus and Pseudomonas) on rhizosphere microbial community and MBC and MBN were higher than those of pathogenic fungi (Fusarium and Alternaria) from Structural Equation Models (SEM). Our results suggest that long-term cotton stubble return and subsoiling could play a role in improving soil microbial community and C and N and enhance the sustainability of coastal saline soil.

A comprehensive review on salinity effects, mechanism of tolerance and its management strategies in cotton

Cotton is produced in more than eighty countries and plays a critical role in the economies of all. Soil depletion is occurring at an unprecedented rate as a result of salinity. Salinity is an emerging global issue which significant harm cotton productivity. In this situation, cotton requires long-term development; various salinity mitigation strategies can lead to long-term cotton economic output. Developing resilient cotton varieties is the first step in overcoming this long-term challenge. Numerous researchers are eager to improve various strategies (by applying modern biological tools) so that of cotton can combat the many threats face through its life cycle. Cotton's plant adaptation can be established by utilizing a variety of biotechnological methods. The improvement of suitable field conditions for optimum crop development is also taken into account; fertilizer application, good quality water supply and soil reclamation are all necessary to reduce saline situations and improve cotton output.

Winter wheat cover crop increased subsoil organic carbon in a long-term cotton cropping system in Tennessee

Long-term cover-cropping and no-tillage practices can facilitate soil organic carbon (SOC) accumulation in agroecosystems for soil health and climate mitigation benefits. However, the contribution of these conservation management practices to SOC gain from the subsoil layers is not extensively studied. To understand this knowledge gap, it is essential to determine the distribution of total SOC and SOC fractions in response to management practices across the soil profile. Therefore, this study was conducted by leveraging a 40-year replicated field experiment in a continuous cotton (Gossypium hirsutum) system. The management treatments examined included three cover crop treatments: 1) hairy vetch, HV (Vicia villosa); 2) winter wheat, WW (Triticum aestivum L.), and 3) no cover crop, NC; and two tillage treatments: 1) chisel-tillage, CT (10 cm deep) and 2) no-tillage, NT. Soil samples were collected from four depths (0–5, 5–10, 10–30, and 30–60 cm) and analyzed for total SOC and C fractions such as microbial biomass (MBC), particulate organic matter (POM-C), and mineral-associated organic matter (MAOM-C). Results showed that the profile-scale (0–60 cm) SOC stock was greater for WW (33.7 Mg ha −1) compared to HV (29.1 Mg ha −1) and NC (24.4 Mg ha −1), while the tillage effect was non-significant (28 Mg ha −1 for NT and 29.3 Mg ha −1 for CT). The NT increased SOC in the top 5-cm layer, which was reflected in the concentrations of POM-C and MBC. Below the tillage depth (10–30 cm), SOC accrual was greater under CT (10.4 Mg ha −1) than NT (8.9 Mg ha −1), despite similar profile-scale SOC stocks. Further analysis revealed that total SOC in topsoil and subsoil were driven by POM and MAOM-related parameters, respectively. We also observed a limited accumulation of C in POM fraction (0.2–6.1 g C kg−1 soil in tilled topsoil and 0.01–0.71 g C kg−1 soil in subsoil) with a weak relationship with total SOC concentration (topsoil slope = 0.29, subsoil slope = 0.13). Contrastingly, accumulation of C in MAOM fraction was greater (2.7–12.7 g C kg−1 soil in topsoil and 0.6–5.4 g C kg−1 soil in subsoil), and it was strongly related to total SOC concentration than POM-C, especially in the subsoil (topsoil slope = 0.43, subsoil slope = 0.71). Growing deep-rooted winter wheat cover crop increased SOC in the subsoil, indicating the need for climate, soil, and ecosystem-specific management practices for profile-scale net SOC accumulation and redistribution in agroecosystems.

Effects of saline-water furrow irrigation on the stability of soil water-stable aggregates in cotton field

It is of great importance to explore the effects of saline-water furrow irrigation on soil water-stable aggregates for safe and efficient utilization of saline water resources. We conducted a long-term cotton experiment with six levels of saline-water furrow irrigation (1, 2, 4, 6, 8, 10 g·L-1) since 2006 and analyzed the variations of soil salinity and water-stable aggregates in the 10th and 15th years under saline irrigation. The results showed that soil salinity in the 0-30 cm layer at the ditch increased with increasing salinity level of irrigation water. There were significant differences between the 6, 8, 10 g·L-1 and 1 g·L-1 treatments. Soil salinity in each treatment increased gradually with increasing soil depth. Saline-water furrow irrigation tended to reduce the stability of soil water-stable aggregates. When the salinity level of the irrigation water was ≥6 g·L-1, the mass fraction of macroaggregates (>0.25 mm), the mean weight diameter and geometric mean diameter of water-stable aggregates significantly decreased. In contrast, the fractal dimension and mean weight specific surface area increased significantly. The stability of soil water-stable aggregates decreased with soil depth in all treatments. Under the condition of saline-water furrow irrigation for several years, there was no accumulation of soil salinity and instability of water-stable aggregates in the 0-30 cm soil layer at the ditch with each passing year. With the irrigation scheduling of this study, saline-water furrow irrigation with salinity ≤4 g·L-1 did not affect soil salinity and water-stable aggregate stability of cotton field in this area.

Long-term cotton stubble return and subsoiling increases cotton yield through improving root growth and properties of coastal saline soil

Short-term cotton stubble return increased cotton yield in coastal saline soil. Due to high groundwater level, salt return from deep soil would affect the sustainability of long-term cotton stubble return on the improvement of soil properties and yield in coastal saline soil. However, subsoiling can cut off the capillary and inhibit the seasonal salt return. Here we quantified the effects of long-term cotton stubble management (removal or return) and tillage (non-subsoiling or subsoiling) on soil properties, root growth and cotton yield. Cotton yield increased 36.3.% after stubble return than after stubble removal, and enhanced 22.8% after subsoiling compared to non-subsoiling. Structural equation model showed that stubble return increased cotton yield by reducing salt content, pH and bulk density, increasing total porosity, small macro-aggregates, root weight density (RWD) in the topsoil, total organic carbon (TOC), nitrogen (N), and their fractions in both layers, while subsoiling increased yield by reducing salt content, pH and bulk density, and increasing total porosity, small macro-aggregates, RWD in the subsoil. Compared to stubble removal, TOC, dissolved OC (DOC) and microbial biomass C (MBC) increased 54.3%, 33.2% and 24.8% in the topsoil, 37.4%, 18.8% and 39.1% in the subsoil after stubble return. Stubble return increased TN and its fractions in the topsoil, and DON, MBN, ammonium nitrogen in the subsoil compared to stubble removal. Maximum root shoot ratio can be obtained only when two measures are combined. Combination of stubble return and subsoling increased yield by optimizing soil properties and root growth in two layers, which is much better than only stubble return or subsoiling. Our analyses demonstrate combination of cotton stubble return and subsoiling can increase cotton yield and be widely applied as an effective measure in coastal saline fields.

Dynamics of soil properties under cotton - alfalfa crop rotation

The aim of the study: Monocrop cultivation is known to affect negatively soil physical properties and decrease soil fertility. To eliminate these undesirable consequences, application of mineral and/or organic fertilizers, as well as other agricultural practices, are employed. Other aspects of agronomy (soil cultivation, fertilizer and plant protection systems, the acquisition of new seeds) require significant material costs. Increasing the yield of agricultural crops, and cotton in particular, can be achieved by crop rotation. The aim of the study was to analyze some physico-chemical soil properties and dynamics of soil processes under cotton-alfalfa crop rotation. Location and time of the study. The research was carried out in 2014-2018 in the Northern Mugan in the Republic of Azerbaijan, as the region is one of the largest agricultural regions of the country, supplying cotton and grain. The studies were carried out on irrigated meadow serozem, or Endogleyic Calcisol, according to the WRB, soils of the Kura-Araks lowland of Azerbaijan. Methodology. Field and laboratory work was carried out according to generally accepted methods of soil science. The particle size distribution was determined by the pyrophosphate method; density, humus content, humidity, temperature, and morphological characteristics were determined using conventional methods. Statistical processing of the obtained data was carried out using the Microsoft Office Excel program. Main results. The long-term cotton crop was found to decrease agrophysical and agrochemical properties of soil. After three years of cotton production the humus content decreased by 20%, whereas the content of water-resistant aggregates increased by 40%, and soil permeability decreased three-fold, soil bulk density increased by 7%, all these resulting in the reduced cotton productivity. Crop rotation showed that soil fertility, decreased after three consecutive years of cotton growth, could be almost fully restored by following with two years of alfalfa crop. Conclusion. Compared with a monoculture of crops, crop rotation leads to a rearrangement in soil microflora and a change in soil biological and biochemical activity, helps to reduce the possibility of a unilateral influence of plants on soil, which in turn helps to restore soil fertility and obtain high sustainable crop yields in the cotton system. Therefore, the use of cotton-alfalfa crop rotations is very important for attaining the goal of increasing two-fold the production of all types of feed in Azerbaijan. To maintain potential fertility, obtain high sustainable yields of soil-protective, resource-saving crops, five-field cotton-alfalfa crop rotation is recommended for the farmers of the Mugan steppe.

Effects of cotton-maize rotation on soil microbiome structure.

Verticillium wilt is a disastrous disease in cotton‐growing regions in China. As a common management method, cotton rotation with cereal crops is used to minimize the loss caused by Verticillium dahliae. However, the correlation between soil microbiome and the control of Verticillium wilt under a crop rotation system is unclear. Therefore, three cropping systems (fallow, cotton continuous cropping, and cotton–maize rotation) were designed and applied for three generations under greenhouse conditions to investigate the different responses of the soil microbial community. The soil used in this study was taken from a long‐term cotton continuous cropping field and inoculated with V. dahliae before use. Our results showed that the diversity of the soil bacterial community was increased under cotton–maize rotation, while the diversity of the fungal community was obviously decreased. Meanwhile, the structure and composition of the bacterial communities were similar even under the different cropping systems, but they differed in the soil fungal communities. Through microbial network interaction analysis, we found that Verticillium interacted with 17 bacterial genera, among which Terrabacter had the highest correlation with Verticillium. Furthermore, eight fungal and eight bacterial species were significantly correlated with V. dahliae. Collectively, this work aimed to study the interactions among V. dahliae, the soil microbiome, and plant hosts, and elucidate the relationship between crop rotation and soil microbiome, providing a new theoretical basis to screen the biological agents that may contribute to Verticillium wilt control.

Effects of Long-term Cotton Continuous Cropping on Soil Microbiome

Verticillium wilt is a severe disease of cotton crops in Xinjiang and affecting yields and quality, due to the continuous cotton cropping in the past decades. The relationship between continuous cropping and the changes induced on soil microbiome remains unclear to date. In this study, the culture types of 15 isolates from Bole (5F), Kuitun (7F), and Shihezi (8F) of north Xinjiang were sclerotium type. Only isolates from field 5F belonged to nondefoliating pathotype, the others belonged to defoliating pathotype. The isolates showed pathogenicity differentiation in cotton. Fungal and bacterial communities in soils had some difference in alpha-diversity, relative abundance, structure and taxonomic composition, but microbial groups showed similarity in the same habitat, despite different sampling sites. The fungal phyla Ascomycota, and the bacterial phyla Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria and Gemmatimonadetes were strongly enriched. Verticillium abundance was significantly and positively correlated with AN, but negatively correlated with soil OM, AK and pH. Moreover, Verticillium was correlated in abundances with 5 fungal and 6 bacterial genera. Overall, we demonstrate that soil microbiome communities have similar responses to long-term continuous cotton cropping, providing new insights into the effects of continuous cotton cropping on soil microbial communities.

The effectiveness of crop rotation on management of Verticillium wilt over time

The objective of this research was to determine the effectiveness of using grain crops in rotation with cotton in managing Verticillium wilt of cotton over a 10-year period. The circular shaped field (52 ha) was divided into six equal sized wedges and cotton or grain crops (sorghum, corn, wheat) were rotated from 2001 to 2018, with some wedges having cotton more frequently and others rotated with grain crops more frequently. Verticillium wilt, which is caused by Verticillium dahliae, was first seen in the field in 2007. Verticillium wilt incidence increased as long-term cotton (host) frequency (HF) increased during 2008–2010 and 2012–2014, but wilt incidence was unaffected by HF in 2016–2018. Grain crops planted in rotation with cotton in one of the two previous years reduced wilt incidence in rotated cotton relative to continuous cotton in 2008–2010, but either had no affect or increased wilt incidence in rotated cotton in 2012–2014 and 2016–2018, relative to continuous cotton. Verticillium dahliae microsclerotia density (MS/cm3 soil)1/2 increased with increasing HF for all three time periods. Three consecutive years of cotton increased MS1/2 relative to rotated cotton in 2008–2010 and 2012–2014, but either did not affect MS1/2 or negatively affected MS1/2 density by 2016–2018 (relative to rotated cotton). Yield, adjusted each year to a 0 to 1 scale, decreased with increasing HF in all three time periods. Yield decreased with three consecutive years of cotton relative to rotated cotton in 2008–2010 and was unaffected by rotated cotton in 2012–2014 and 2016–2018. Crop rotation with nonhosts for management of Verticillium wilt, initially (first four years) was very effective at reducing MS, wilt incidence, and increasing yield. However, 9–11 years after the initial Verticillium wilt symptoms occurred, short-term crop rotation no longer reduced Verticillium wilt incidence, reduced microsclerotia density, or increased cotton yield.

Analysis of the succession of structure of the bacteria community in soil from long-term continuous cotton cropping in Xinjiang using high-throughput sequencing.

The present study aimed to identify the structural succession of the bacteria community in soil during long-term continuous cotton cropping and its relationship with continuous cropping obstacles in Xinjiang, China. High-throughput sequencing was used to analyze and compare the composition of the bacterial community in the soil at the cotton root zone after years of continuous cotton cropping and crop rotation over 30years of cultivation. Cotton cultivation increased the structural diversity of the bacterial community, among which the populations of Actinobacteria, Acidobacteria, Firmicutes, Nitrospirae, and Chloroflexi changed considerably. A 0-year sample and samples after continuous short- and long-term cropping, along with some with crop rotation, were gathered into three individual clusters. The findings of the rotation sample were similar to those of the sample of continuous long-term cropping. Cropping is the main cause of changes in the structure of the bacteria community; however, the new structure formed under continued duress of both long-term cotton cultivation and the associated farming methods gradually stabilizes after 10years of repeated fluctuations. Crop rotation can lead to the rapid recovery of some species of soil bacteria.

Long-Term Cotton Yield Impacts from Cropping Rotations and Biocovers under No-Tillage

Sustaining crop yields assumedly entails crop rotations and biocovers. To test this, cropping sequences and biocover effects on cotton (Gossypium hirsutum L.) yields were assessed under long-term no-tillage. Main plots were eight cropping sequences of cotton, corn (Zea mays L.), and soybean (Glycine max L.) on a Loring silt loam at the Research and Education Center at Milan, TN. Sequences were repeated in 4-yr cycles (i.e., Phases I, II, and III) from 2002 to 2013. Split-plots were biocovers, which consisted of hairy vetch (Vicia villosa L.), Austrian winter pea (Pisum sativum L. sativum var. arvense), wheat (Triticum aestivum L.), poultry litter, and fallow control. Continuous cotton had greater yield than cotton grown in rotations [3.1 and 2.8 Mg ha-1, respectively; p = 0.02 (averaged across biocovers and phases)]. Biocover did not increase yield in continuous cotton (p > 0.05). However, various cropping sequences did result in higher yield than continuous cotton within 4-yr cycles. Specifically, corn-corn-soybean-cotton rotations were highest yielding during Phase II (4.0 Mg ha-1), which was equivalent to cotton-corn-cotton-soybean (3.5 and 3.8 Mg ha-1, respectively); and cotton-corn-cotton-corn during Phases II and III (3.6 and 3.8 Mg ha-1, respectively). All aforementioned rotations increased yield above continuous cotton during Phases I and III (p < 0.05). Results indicate increasing cropping diversity with one and two years of soybean or corn, respectively, in a 4-yr cycle maintains cotton seed yield long-term.

Effect of Long-Term Continuous Cotton Mono-Cropping on Depletion of Soil NPK and Changes in Some Selected Soil Chemical Characters on Vertisols and Fluvisols

A long-term cotton exhaustion trial was conducted on lowland Vertisols and Fluvisols at Werer Agricultural Research Center during the 1968–2002 in Ethiopia to investigate nutrient depletion rate and changes in selected soil chemical properties. Treatments used include cultivated fallow, control, 80kgN ha_-1, 80-80 kgNP ha_-1, 80-80kgNKha_-1 and 80-80-80kgNPKha_-1 arranged in RCBD with four and six replications in Vertisols and Fluvisols, respectively. The cotton was grown as a test crop and the status of soil N, P, K, OC, pHe and ECe were periodically monitored every seasons. Seed cotton yield had shown significant response to treatments imposed after 10 and 3 years of continuous cotton mono-cropping, respectively, on Vertisols and Fluvisols, and consistently continued for further 3 consecutive periodical checking years. Then onwards, until the end of the experiment, seed cotton yield didn't showed consistent yield response. Combined analysis revealed highly significant (p < 0.01) yield response to N applications. Despite the long-term continuous mining of soil nutrients through seed cotton harvest and crop residue removal, soil analytical result revealed no indication of depletion in total nitrogen, available K and P. Soil pHe (in both soil types) and ECe only in Fluvisols tend show gradual increase.

Levels and patterns of organochlorine pesticides in agricultural soils in an area of extensive historical cotton cultivation in Henan province, China.

Organochlorine pesticides (OCPs) have attracted widespread concern because of their environmental persistence and toxicity. The historical influence of different agricultural land use types on soil concentrations of OCP residues was investigated by collecting a total of 52 surface soil samples from long-term cotton fields and fields with other crops in Lvdian township, Henan province, eastern central China. The concentration, composition, and possible sources of 16 OCPs were determined and a health risk assessment of these soils was conducted. Hexachlorocyclohexane (HCH), heptachlor, chlordane, and dichloro diphenyl trichloroethane plus its main metabolites (DDTs) were the most frequently detected OCPs with concentrations of 2.9-56.4 ng g(-1), 4.3-14.0 ng g(-1), 18.0-1254.4 ng g(-1), and below detection limit (BDL) -206.1 ng g(-1), respectively. Analysis of variance of p,p-DDE shows significant (P < 0.05) differences while other OCPs show no significant differences between historical cotton fields and fields containing other crops. Compositional analysis suggests that the HCH is derived mainly from the use of lindane and that there are recent inputs. Analysis of variance and compositional analysis indicate that the p,p-DDE in surface soil from long-term cotton fields is derived mainly from the aerobic biodegradation of historical residues. The sum of carcinogenic risk values of OCPs for soil samples were found to be 1.58 × 10(-6), posing a low cancer risk to the inhabitants of the region studied.

Early changes due to sorghum biofuel cropping systems in soil microbial communities and metabolic functioning

Evaluation of biofuel production cropping systems should address not only energy yields but also the impacts on soil attributes. In this study, forage sorghum (Sorghum bicolor L. Moench) cropping systems were initiated on a low organic matter soil (<0.9 %) with a history of intensively tilled low-input cotton production in the semiarid Southern High Plains of the U.S. Sorghum cropping systems were evaluated in a split-plot design with sorghum cultivar as the main plot and the combination of irrigation level (non-irrigated and deficit irrigated) and aboveground biomass removal rate (50 % and 100 %) as the split plot. The sorghum cultivars used varied in yield potential and lignin content, which are important features for feedstock-producing crops. Within 1 year, the transition from long-term cotton cropping systems to sorghum biofuel cropping systems resulted in increased soil microbial biomass C (16 %) and N (17 %) and shifts in the microbial community composition as indicated by differences in fatty acid methyl ester (FAME) profiles. Additionally, enzyme activities targeting C, N, P and S cycles increased 15–75 % (depending on the enzyme) after two growing seasons. Increased enzyme activities (16–19 %) and differences in FAME profiles were seen due to irrigation regardless of aboveground biomass removal rate. Biomass removal rate and the cultivar type had little effect on the soil microbial properties during the time frame of this study. Early results from this study suggest improvements in soil quality and the sustainability of sorghum biofuel cropping for low organic matter agricultural soils.

Effects of long-term cotton plantations on Fusarium and Verticillium wilt diseases infection in China

The population density of Fusarium oxysporum f. sp. vasinfectum, disease index of cotton fusarium wilt along with the relation of the wilt disease and pathogen density in long-term cotton plantations were studied by the methods of dilution plating and field investigation. Microsclerotium densities of Verticillium dahliae and disease index of verticillium wilt were also studied. The results showed that both pathogen densities were first increased and reached their maximum at the 10th continuous cropping year and then, gradually decreased. Very similarly, the disease indexes of fusarium and verticillium wilts exhibited the same variation trend, thereby, indicating that disease-suppressive soil may be formed in long-term cotton plantations that need to be further studied. Key words: Long-term cotton plantations, continuous cropping, fusarium and verticillium wilt diseases, Fusarium oxysporum f. sp. vasinfectum, Verticillium dahliae, microsclerotia, population density, disease-suppressive soil.