Microbial activity and community composition in saline and non-saline soils exposed to multiple drying and rewetting events

Background and aims

The effects of drying and rewetting (DRW) have been studied extensively in non-saline soils, but little is known about the impact of DRW in saline soils. An incubation experiment was conducted to determine the impact of 1?C3 drying and re-wetting events on soil microbial activity and community composition at different levels of electrical conductivity in the saturated soil extract (ECe) (ECe 0.7, 9.3, 17.6 dS m^?1).

Methods

A non-saline sandy loam was amended with NaCl to achieve the three EC levels 21 days prior to the first DRW; wheat straw was added 7 days prior to the first DRW. Each DRW event consisted of 1 week drying and 1 week moist (50% of water holding capacity, WHC). After the last DRW, the soils were maintained moist until the end of the incubation period (63 days after addition of the wheat straw). A control was kept moist (50% of WHC) throughout the incubation period.

Results

Respiration rates on the day after rewetting were similar after the first and the second DRW, but significantly lower after the third DRW. After the first and second DRW, respiration rates were lower at EC17.6 compared to the lower EC levels, whereas salinity had little effect on respiration rates after the third DRW or at the end of the experiment when respiration rates were low. Compared to the continuously moist treatment, respiration rates were about 50% higher on day 15 (d15) and d29. On d44, respiration rates were about 50% higher at EC9.7 than at the other two EC levels. Cumulative respiration was increased by DRW only in the treatment with one DRW and only at the two lower EC levels. Salinity affected microbial biomass and community composition in the moist soils but not in the DRW treatments. At all EC levels and all sampling dates, the community composition in the continuously moist treatment differed from that in the DRW treatments, but there were no differences among the DRW treatments.

Conclusions

Microbes in moderately saline soils may be able to utilise substrates released after multiple DRW events better than microbes in non-saline soil. However, at high EC (EC17.6), the low osmotic potential reduced microbial activity to such an extent that the microbes were not able to utilise substrate released after rewetting of dry soil.     

Response of microbial activity and community structure to decreasing soil osmotic and matric potential

Low soil water content (low matric potential) and salinity (low osmotic potential) occur frequently in soils, particularly in arid and semi-arid regions. Although the effect of low matric or low osmotic potential on soil microorganisms have been studied before, this is the first report which compares the effect of the two stresses on microbial activity and community structure. A sand and a sandy loam, differing in pore size distribution, nutrient content and microbial biomass and community structure, were used. For the osmotic stress experiment, salt (NaCl) was added to achieve osmotic potentials from ?0.99 to ?13.13 MPa (sand) and from ?0.21 to 3.41 MPa (sandy loam) after which the soils were pre-incubated at optimal water content for 10d. For the matric stress experiment, soils were also pre-incubated at optimal water content for 10d, after which the water content was adjusted to give matric potentials from ?0.03 and ?1.68 MPa (sand) and from ?0.10 to 1.46 MPa (sandy loam). After amendment with 2% (w/w) pea straw (C/N 26), soil respiration was measured over 14d. Osmotic potential decreased with decreasing soil water content, particularly in the sand. Soil respiration decreased with decreasing water potential (osmotic?+?matric). At a given water potential, respiration decreased to a greater extent in the matric stress experiment than in the osmotic stress experiment. Decreasing osmotic and matric potential reduced microbial biomass (sum of phospholipid fatty acids measured after 14 days) and changed microbial community structure: fungi were less tolerant to decreasing osmotic potential than bacteria, but more tolerant to decreasing water content. It is concluded that low matric potential may be more detrimental than a corresponding low osmotic potential at optimal soil water content. This is likely to be a consequence of the restricted diffusion of substrates and thus a reduced ability of the microbes to synthesise osmolytes to help maintain cell water content. The study also highlighted that it needs to be considered that decreasing soil water content concentrates the salts, hence microorganisms in dry soils are exposed to two stressors.     

Drying and wetting in saline and saline-sodic soils—effects on microbial activity, biomass and dissolved organic carbon

Aims

There are few studies on the interactive effect of salinity and sodicity in soils exposed to drying and wetting cycles. We conducted a study to assess the impact of multiple drying and wetting on microbial respiration, dissolved organic carbon and microbial biomass in saline and saline-sodic soils.

Methods

Different levels of salinity (EC_1:5 1.0 or 2.5) and sodicity (SAR?<?3 or 20) were induced by adding NaCl and CaCl₂ to a non-saline/non-sodic soil. Finely ground wheat straw residue was added at 20?g?kg^?1 as substrate to stimulate microbial activity. The constant moist (CM) treatment was kept at optimum moisture content for the length of the experiment. The drying and rewetting (DW) treatments consisted of 1 to 3 DW cycles; each DW cycle consisted of 1?week drying after which they were rewet to optimum moisture and then maintained moist for 1?week.

Results

Drying reduced respiration more strongly at EC2.5 than with EC1.0. Rewetting of dry soils produced a flush in respiration which was greatest in the soils without salt addition and smallest at high salinity (EC2.5) suggesting better substrate utilisation by microbes in soils without added salts. After three DW events, cumulative respiration was significantly increased by DW compared to CM, being 24% higher at EC1.0 and 16% higher at EC2.5 indicating that high respiration rates after rewetting may compensate for the low respiration rates during the dry phase. The respiration rate per unit MBC was lower at EC2.5 than at EC1.0. Further, the size of the flush in respiration upon rewetting decreased with each ensuing DW cycle being 50–70% lower in the third DW cycle than the first.

Conclusions

Both salinity and sodicity alter the effect of drying and rewetting on soil carbon dynamics compared to non-saline soils.     

Effects of salinity on microbial tolerance to drying and rewetting

Soil salinity and fluctuations in soil matric potential are stressors for soil microorganisms which, in turn, may affect soil organic matter turnover. In response to salinity and low soil water content, many microorganisms accumulate osmolytes. Therefore, it is conceivable that microorganisms in saline soils are more tolerant to drying and rewetting (DRW) stress than those in non-saline soils. An experiment was carried out with three different salinity levels: electrical conductivity (EC_1:5) 0, 2 and 4 dS m^?1 (EC0, EC2, EC4), and two water treatments: a constantly moist control or two DRW cycles. Respiration as an indicator of microbial activity was measured throughout the 59 days of incubation. At the end of the second dry period (day 35) and at the end of the following moist incubation (day 59), microbial biomass and microbial community structure were determined by phospholipid fatty acid (PLFA) analysis. Increasing salinity decreased microbial activity but did not affect its resistance to DRW. On day 59, cumulative respiration decreased in the order EC0 > EC2 > EC4 with no differences between water treatments. Fungal biomass was negatively affected by salinity at the end of the experiment, while bacterial biomass was unaffected. Microbial community structure in moist treatments differed between salinity levels, with EC4 influencing microbial community structure earlier than EC2. The resistance of microbial communities to DRW stress was salt level dependent; only beyond a critical salinity level adaptation to salt stress was able to reduce the impact of water stress on microbial community structure.     

Quantifying microbial growth and carbon use efficiency in dry soil environments via 18O water vapor equilibration

Soil microbial physiology controls large fluxes of C to the atmosphere, thus, improving our ability to accurately quantify microbial physiology in soil is essential. However, current methods to determine microbial C metabolism require liquid water addition, which makes it practically impossible to measure microbial physiology in dry soil samples without stimulating microbial growth and respiration (namely, the “Birch effect”). We developed a new method based on in vivo ¹⁸O‐water vapor equilibration to minimize soil rewetting effects. This method allows the isotopic labeling of soil water without direct liquid water addition. This was compared to the main current method (direct ¹⁸O‐liquid water addition) in moist and air‐dry soils. We determined the time kinetics and calculated the average ¹⁸O enrichment of soil water over incubation time, which is necessary to calculate microbial growth from ¹⁸O incorporation in genomic DNA. We tested isotopic equilibration patterns in three natural and six artificially constructed soils covering a wide range of soil texture and soil organic matter content. We then measured microbial growth, respiration and carbon use efficiency (CUE) in three natural soils (either air‐dry or moist). The proposed ¹⁸O‐vapor equilibration method provided similar results as the current method of liquid ¹⁸O‐water addition when used for moist soils. However, when applied to air‐dry soils the liquid ¹⁸O‐water addition method overestimated growth by up to 250%, respiration by up to 500%, and underestimated CUE by up to 40%. We finally describe the new insights into biogeochemical cycling of C that the new method can help uncover, and we consider a range of questions regarding microbial physiology and its response to global change that can now be addressed.     

Soil moisture increment as a controlling variable of the “Birch effect”. Interactions with the pre-wetting soil moisture and litter addition

Aims

The Birch effect is a pulse in soil C and N mineralization caused by the wetting of dry soils, but the role of the soil moisture increment (ΔSWC) is still poorly understood. We quantified the relationship between ΔSWC and the Birch effect, and its interactions with pre-wetting soil moisture (preSWC) and substrate supply.

Methods

Two soils (clay loam and sandy loam) under a Pinus halepensis forest were subjected to rewetting in laboratory treatments combining different ΔSWC and preSWC values, with or without additional substrate (5 mg g^-1 P. halepensis needles). Respiration flush (ΔR), changes in microbial biomass C (MBC) and net N mineralization (NMIN) were measured.

Results

Overall, we found a relationship with the form: ΔR?=?a ΔSWC?+?b, where the slope (a) was significant only when pre-wetting water potential was below a threshold value in the range of ?100 to ?1,200 kPa. However, the threshold alone does not fully describe the role of preSWC in slope variability. Substrate addition modified the ΔSWC sensitivity of Birch effect, enhancing it in the clay loam and suppressing it in the sandy loam.

Conclusions

The intensity of the wetting is a dominant factor regulating Birch effect, and ΔSWC is useful for its quantification.     

Incubation studies on mineralization of organic sulphur and organic nitrogen

Summary Incubation studies were carried out to investigate the release of sulphur and nitrogen in West Indian soils. Sulphur and nitrogen released or fixed were estimated at 10 days intervals up to 60 days incubation period.All the soils released sulphate when incubated at 30°C. A rapid initial flush of mineralization of both sulphur and nitrogen took place in Cocal fine sand and Montreal sandy loam. In Piarco sandy clay loam and Mayaro sandy loam sulphur mineralization was not accompanied by a concomitant mineralization of nitrogen. An inconsistent pattern of release of sulphur and nitrogen was noticed in Montserrat clay, Akers sandy clay loam, Bellevue sandy clay loam and Soufriere cindery gravelly loamy sand.The release of sulphur does not appear to be related to the total amount of carbon, nitrogen or sulphur. Nitrogen mineralized was significantly correlated with total nitrogen and total sulphur. The correlation between organic matter and nitrogen mineralized was highly significant (r=0.87^**) whereas with sulphur mineralized it did not reach significance. This suggests that nitrogen and sulphur are not mineralized at the same rate in these soils.     

Interactions between leaf litter quality, particle size, and microbial community during the earliest stage of decay

With global change expected to alter aspects of the carbon (C) cycle, empirical data describing how microorganisms function in different environmental conditions are needed to increase predictive capabilities of microbially-driven decomposition models. Given the importance of accelerated C fluxes during early decay in C cycling, we characterized how varying litter qualities (maple vs. oak) and sizes (ground vs. 0.25 cm² vs. 1 cm²), and contrasting soils (sandy vs. loamy), altered microbial biomass-carbon and community structure, respiration, enzyme activities, and inorganic nutrients over the initial 2 weeks of decomposition. Our hypotheses were (1) mixing ground maple with loam should result in a quicker, more prolonged respiration response than other treatments; and (2) “priming”, or substrate-stimulated soil organic matter turnover, should be minimal over the first few days due to soluble C substrate uptake. Respiration peaks, biomass increases, nutrient immobilization, low enzyme activities, and minimal priming occurred in all treatments over the first 72 h. These general features suggest soluble C compounds are degraded before polymeric substrates regardless of litter size or type, or soil. Ground litter addition to the high C and microbial biomass loam resulted in a more prolonged respiration peak than the poorly aggregated sand. Priming was greater in loam than the C limited sandy soil after the first 72 h, likely due to co-metabolism of labile and recalcitrant substrates. We conclude that the general features of early decay are widespread and predictable, yet differences in litter and soil characteristics influence the temporal pattern and magnitude of C flux.     

Changes in water content of two agricultural soils does not alter labile P and C pools

Aims

An incubation study was conducted to investigate how changes in soil water content affect labile phosphorus and carbon pools, mineralisation patterns and microbial community composition.

Methods

Two soils from different climatic histories were subjected to four long-term (15 weeks) soil water regimes (constant field capacity (m); 3 dry-rewet (DRW) cycles evenly spaced (intermittent, int); 3 DRW cycles with a shorter interval after a long dry period (false break, fb); constantly air-dry (d)) (incubation period 1). In the subsequent incubation period 2, a set of cores from each treatment were subjected to one DRW cycle (air-dry for 7 day; field capacity for 14 day) or maintained at field capacity.

Results

Long-term soil water regime altered soil respiration with the largest CO₂ pulse occurring in soil with the longest dry period. However, changing the distribution of the 3 DRW events within incubation period 1 (int/fb) did not alter cumulative CO₂. In addition, DRW during incubation period 2 did not affect cumulative CO₂ in either treatment (m, int, fb, d) (except for Hamilton int). Our results show that carbon and phosphorus availability and the size and community composition of the microbial biomass were largely unaffected by fluctuating soil water content.

Conclusions

Changes in soil water content altered respiration, phosphatase activity and microbial C:P ratio and indicate physiological and/or functional changes in the microbial community. However, it appeared that these would have little impact on plant P availability.     

Physiology and microbial community structure in soil at extreme water content

A sandy loam soil was brought to 6 water contents (13-100% WHC) to study the effects of extreme soil moistures on the physiological status of microbiota (represented by biomass characteristics, specific respiration, bacterial growth, and phospholipid fatty acid, PLFA, stress indicators) and microbial community structure (assessed using PLFA fingerprints). In dry soils, microbial biomass and activity declined as a consequence of water and/or nutrient deficiency (indicated by PLFA stress indicators). These microbial communities were dominated by G+ bacteria and actinomycetes. Oxygen deficits in water-saturated soils did not eliminate microbial activity but the enormous accumulation of poly-3-hydroxybutyrate by bacteria showed the unbalanced growth in excess carbon conditions. High soil water content favored G bacteria.     

Effect of drying and rewetting on bacterial growth rates in soil

The effect of soil moisture on bacterial growth was investigated, and the effects of rewetting were compared with glucose addition because both treatments increase substrate availability. Bacterial growth was estimated as thymidine and leucine incorporation, and was compared with respiration. Low growth rates were found in air-dried soil, increasing rapidly to high stable values in moist soils. Respiration and bacterial growth at different soil moisture contents were correlated. Rewetting air-dried soil resulted in a linear increase in bacterial growth with time, reaching the levels in moist soil (10 times higher) after about 7 h. Respiration rates increased within 1 h to a level >10 times higher than that in moist soil. After the initial flush, there was a gradual decrease in respiration rate, while bacterial growth increased to levels twice that of moist soil 24 h after rewetting, and decreased to levels similar to those in moist soil after 2 days. Adding glucose resulted in no positive effect on bacterial growth during the first 9 h, despite resulting in more than five times higher respiration. This indicated that the initial increase in bacterial growth after rewetting was not due to increased substrate availability.     

CaCl2 extractable N fractions and K2SO4 extractable N released on fumigation as affected by green manure mineralization and soil texture

Repeated mild wet-dry cycles were imposed on a sandy loam to accelerate the mineralization of organic C involved in stabilising macro-aggregates. Soil maintained continually moist (control soil) was compared to that subjected to a series of 6 wet-dry cycles. Two patterns of rewetting and drying were investigated: (1) incubated dry at 25°C for six days between each wet-dry cycle (dry-incubated), or (ii) incubated moist for six days at 25°C between each cycle (moist-incubated). Changes in the proportion of >2 mm, 1–2 mm, 0.5–1 mm and 0.25–0.5 mm aggregates, and carbohydrate C extracted by hot-water or hot-1.5 M H₂SO₄, were measured after each wet-dry cycle, or weekly in the continuously moist control soil. Respiration rates (CO₂ efflux) were measured during the incubation of the moist soil between the wet-dry cycles and compared with the continually-moist control soil.The wet-dry treatments did not increase soil respiration in soil after re-wetting compared to soil kept continually moist and incubated for the same period of time. Despite this, the treatments caused changes in the amounts of acid- and water-extractable carbohydrate C fractions and substantial changes in aggregation. Macro-aggregation and the proportion of soil in each fraction did not change in the soil maintained continuously-moist for 6 weeks (control). However, effects of the two wet-dry treatments on total macro-aggregation were similar to those in the >2 mm, 1–2 mm and 0.25–0.5 mm aggregate fractions: there was a rapid decline in aggregation by 48–65% over the first two cycles, a sharp recovery to 78–100% of the initial aggregation after three cycles, and a further decline after 4–6 cycles.The resistance of organic C mineralization to mild wet-dry cycles confirmed that the organic C in this soil is very stable and resistant to decomposition. Despite aggregates being disrupted, the organic C stabilising these aggregates was resistant to decomposition as determined by CO₂ efflux. When soil was re-moistened and incubated to allow microbial re-colonization, aggregation was similar to that in the soil where microbial re-colonization was limited by rapid drying treatments. Short term changes in the aggregation of this soil appear to be dominated by chemical and/or physical processes.     

Soil types with different texture affects development of Rhizoctonia root rot of wheat seedlings

The effect of different soil textures, sandy (97.5% sand, 1.6% silt, 0.9% clay), loamy sand (77% sand, 11% silt, 12% clay) and a sandy clay loam (69% sand, 7% silt, 24% clay), on root rot of wheat caused by Rhizoctonia solani Kühn Anastomosis Group (AG) 8 was studied under glasshouse conditions. The reduction in root and shoot biomass following inoculation with AG-8 was greater in sand than in loamy sand or sandy clay loam. Dry root weight of wheat in the sand, loamy sand and sandy clay loam soils infested with AG-8 was 91%, 55% and 28% less than in control uninfested soils. There was greater moisture retention in the loamy sand and sandy clay loam soils as compared to the sand in the upper 10–20 cm. Root penetration resistance was greater in loamy sand and sandy clay loam than in sand. Root growth in the uninfested soil column was faster in the sand than in the loamy sand and sandy clay loam soils, the roots in the sandy soil being thinner than in the other two soils. Radial spread of the pathogen in these soils in seedling trays was twice as fast in the sand in comparison to the loamy sand which in turn was more than twice that in the sandy clay loam soil. There was no evidence that differences among soils in pathogenicity or soil spread of the pathogen was related to their nutrient status. This behaviour may be related to the severity of the disease in fields with sandy soils as compared to those with loam or clay soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

A comparison of fine root distribution and water consumption of mature Caragana korshinkii Kom grown in two soils in a semiarid region, China

Water is a key limiting factor for vegetation restoration in the semi-arid areas of China. Caragana korshinkii Kom is a shrub that is widely planted in this region to control soil erosion and land desertification. The objective of this study was to investigate the fine root distribution of mature C. korshinkii and its water consumption, when grown in either silt loam or sandy soils, in order to understand differences between the water cycles of two such soils found in the transition zone between fertile loess hills and desert of the Northern Loess Plateau. Fine root distributions were measured using the trench-profile method. Soil water dynamics were monitored with a neutron probe during two growing seasons. The results showed that fine root area density (FRAD) declined with increasing soil depth in both soils, with 70.7% and 96.6% of the total fine roots being concentrated in the upper 1-m layer of the silt loam and sandy soils, respectively. Water consumption by C. korshinkii in the silt loam was close to that in the sandy soil. Most water consumption in both soil types was from the upper 1-m layer. Little variation in plant available water (PAW) occurred in the 3–6 m soil layer during the whole study period. However, in this layer, the PAW was significantly lower in the silt loam soil than in the sandy soil. Total actual evapotranspiration (ET_a) was slightly higher from the sandy soil plots than from those of the silt loam soil during both growing seasons. Our study indicated that mature C. korshinkii effectively uses about the same amount of water from either the silt loam or sandy soils, but that more soil water at depth was extracted from silt loam soil than from sandy soil.     

Ammonia volatilization after injection of anhydrous ammonia into arable soils of different moisture levels

Laboratory experiments have shown appreciable losses of ammonia after injection of anhydrous ammonia into dry and wet soils. In this study losses of ammonia injected into a moist (tension 10 kPa), dry (tension 160 kPa) and a wet (tension 1.6 kPa) sandy loam were measured under field conditions using wind tunnels. Losses were insignificant from a moist soil. However losses from a dry and a wet soil were 20% and 50% of injected ammonia, respectively. From the dry soil, losses of gaseous ammonia took place within the first hours after injection, which indicates a rapid transport through cracks and voids. From the wet soil, 20% of the injected ammonia was lost more gradually between 6 h and 6 d. This indicates that upward movement of water due to evaporation may be the cause of these ammonia losses which proceeded for longer periods.     

Transformation of urea and ammonium sulphate in different soils

Summary The transformation of urea and ammonium sulphate in Ladwa sandy loam and Balsamand sand was studied in laboratory. Urea took at least one week in sandy loam and 2 weeks in sandy soils to hydrolyse completely. The process of hydrolysis was faster in finer soil with high organic matter than in coarse soil having low organic matter. There was no nitrification upto 3 days in sandy loam and upto 7 days in sandy soils, respectively, but there was immobilization of NO₃-N during these initial periods. The NO₃-N content at the end of incubation period (35 days) was more in case of urea than in case of ammonium sulphate treated samples in sandy loam soil and reverse was true in sandy soil. The hydrolysis of urea did not follow zero or first order kinetics as proposed in previous studies.     

Effect of alginite amendment on microbial activity and soil water content in forest soils

The effect of the amendment with alginite, an organic rock originating from the biomass of fossilized unicellular algae, on microbial activity of forest soils was tested using a pot experiment. Five variants of soil-alginite mixtures were tested in three replicates with two forest soils: a loose sandy soil and a sandy loam. Gravimetric moisture closely correlated with the dose of alginite in both soils. Basal respiration and catalase activity increased with the dose of alginite in the sandy soil, but not in the sandy loam, where the highest response was observed at intermediate doses of alginite. The correlations of microbial activity parameters with moisture in the sandy soil were also much closer than in the sandy loam. The amendment with alginite was thus effective in improving some of the selected microbial activity indicators, but the optimum dose of alginite strongly depends on soil texture.     

温度对不同粘粒含量稻田土壤有机碳矿化的影响

模拟了亚热带地区3种不同粘粒含量的水稻土(砂壤土、壤粘土、粉粘土)在5种温度(10、15、20、25和30℃)下的有机碳(SOC)矿化特征,分析SOC矿化对温度变化的响应.结果表明:在160d的培养期内,温度对3种水稻土SOC矿化量的影响有一定差异,30℃时砂壤土、壤粘土和粉粘土SOC矿化量分别是10℃时的3.5、5.2和4.7倍.在较低温度(≤20℃)下,SOC矿化速度较低且相对稳定;在较高温度(≥25℃)下,前期SOC矿化速度较高,随着培养时间的延长逐渐降低,并趋于稳定.3种水稻土SOC矿化的温度系数(Q10)随培养时间出现波动,砂壤土的Q10平均值最低,为1.92,壤粘土和粉粘土的Q10平均值较接近,分别为2.37和2.32;3种土壤矿化速率常数(k)与温度呈极显著的指数相关(P<0.01).3种水稻土有机碳矿化对温度变化的响应敏感度依次为壤粘土>粉粘土>砂壤土.     

Soil steaming effects on weed seedling emergence under the influence of soil type,soil moisture,soil structure and heat duration

Soil steaming applied in bands is a new technology with the potential to radically lower the burden of hand‐weeding intra‐row weeds in non‐herbicidal vegetable cropping. Preliminary studies with band‐steaming have shown effective control of viable weed seeds when the maximum soil temperatures reach 60–80°C. This temperature range has a particular agronomic interest, and the present study aimed at investigating the influence of soil factors and heat duration on weed seed mortality of soil steaming targeting 60–80°C. Two soil types (sand versus sandy loam) and two moisture levels (moist versus dry) were studied in one experiment (expt) while two levels of structure of a sandy loam (coarse versus fine) were included in a second experiment. A third experiment was focussing on the significance of heat duration expressed as the speed of cooling‐down after steaming had been stopped. Weed control efficacy was generally greater in sand than in sandy loam and soil irrigation further improved weed control. Steam application to the finely structured soil improved weed control efficacy relative to that obtained with the coarse soil of larger aggregate size. The rapidity of cooling from the maximum temperature did not affect the efficacy of the treatment on weed seed mortality. Based on these experiments, a maximum soil temperature of 80°C should ensure satisfactory weed control under moist soil conditions, especially if the soil is cultivated prior to steaming.     

Impact of Rotylenchulus reniformis on Cotton Yield as Affected by Soil Texture and Irrigation

The effects of soil type, irrigation, and population density of Rotylenchulus reniformis on cotton were evaluated in a two-year microplot experiment. Six soil types, Fuquay sand, Norfolk sandy loam, Portsmouth loamy sand, Muck, Cecil sandy loam, and Cecil sandy clay, were arranged in randomized complete blocks with five replications. Each block had numerous plots previously inoculated with R. reniformis and two or more noninoculated microplots per soil type, one half of which were irrigated in each replicate for a total of 240 plots. Greatest cotton lint yields were achieved in the Muck, Norfolk sandy loam, and Portsmouth loamy sand soils. Cotton yield in the Portsmouth loamy sand did not differ from the Muck soil which averaged the greatest lint yield per plot of all soil types. Cotton yield was negatively related to R. reniformis PI (initial population density) in all soil types except for the Cecil sandy clay which had the highest clay content. Supplemental irrigation increased yields in the higher yielding Muck, Norfolk sandy loam, and Portsmouth loamy sand soils compared to the lower yielding Cecil sandy clay, Cecil sandy loam, and Fuquay sand soils. The Portsmouth sandy loam was among the highest yielding soils, and also supported the greatest R. reniformis population density. Cotton lint yield was affected more by R. reniformis Pi with irrigation in the Portsmouth loamy sand soil with a greater influence of Pi on lint yield in irrigated plots than other soils. A significant first degree PI × irrigation interaction for this soil type confirms this observation.