Use of in-growth soil cores in mesh bags for studies of relations between soil compaction and root growth

Using in-growth soil cores in cylindrical mesh bags, the effects of 3 soil compaction treatments on growth of crop roots were studied in a sandy soil. The bags were inserted after crop emergence in holes (70 mm diameter; 60 cm depth) augered in the soil in crop row interspaces. In 1984 (with rapessed), at all sampling dates, root biomass in the inserted cores decreased with increased compaction of the plough layer (0–25 cm) as well as the subsoil (25–60 cm). Root biomass in the subsoil was low. In 1985 (with wheat), the effects of compaction in the subsoil were similar, although root biomass was greater than in 1984. However, in the plough layer there were significant differences in root biomass on only one sampling date. The mesh bag technique should be a useful complement to other field methods in studies of relations between physical soil characteristics or tillage treatments and root growth.     

Microbial biomass and microbial C:N ratio in bulk soil and buried bags for evaluating in situ net N mineralization in agricultural soils

The in situ net nitrogen mineralization (N_net) was estimated in five agricultural soils under different durations of organic farming by incubating soil samples in buried bags. Simultaneously, soil microbial C and N was determined in buried bags and in bulk soil under winter wheat and after harvest. The aim was to check for variations in soil microbial biomass contents and microbial C:N ratios during the incubation period, and their importance for N_net rates. Microbial C and N contents were highest in soils that had been organically farmed for 41 years, whereas N_net rates were highest in a short‐term organically managed soil that had been under grassland use until 36 years ago. The mean coefficient of variation in the bulk soil for microbial C estimates ranged from 5 to 12 %. Microbial N contents were similar inside buried bags and in the bulk soil at the end of the incubation periods. Under winter wheat during the incubation period until harvest, microbial C contents and microbial C:N ratios (in 10—27 cm depth only) decreased more strongly inside buried bags than in the bulk soil. Following harvest of winter wheat and ploughing, microbial biomass increased while in situ N_net decreased, presumably due to N immobilization. The N_net rates were not correlated with microbial N contents or changes in microbial N contents inside buried bags. At the end of the vegetation period of winter wheat, N_net rates were negatively correlated with microbial C:N ratios. Because these ratios concurrently decreased more inside buried bags than in the bulk soil, the N_net estimates of the buried bag method may differ from the N_net rates in the bulk soil at that time.     

Nitrogen availability in some Wisconsin forests: comparisons of resin bags and on-site incubations

Summary Estimates of ammonium and nitrate availability in conifer and hardwood forests using an ion exchange resin (IER) bag method and with on-site incubations of soil cores in buried bags were compared. Correlations between the two methods were generally high. Correlation coefficients (r) between IER nitrate and buried-bag mineralized nitrate ranged from 0.87 to 0.92. Both methods also correlated well with aboveground net primary production, litter fall N content, and fine root biomass. The major differences between the methods related to the relative importances of ammonium and nitrate forms of available N. The IER method indicated that both ammonium and nitrate were important on all sites, with nitrate predominating in most soils. The buried-bag results indicated that available N was primarily in the form of nitrate (all ammonium was oxidized), but that nitrate was insignificant on infertile sites.     

Comparison of buried bag and PVC core methods for in situ measurement of nitrogen mineralization rates in an agricultural soil

Abstract

We compared estimates of soil nitrogen (N) mineralization rates using the buried bag and PVC core methods in an ongoing investigation of the effects of earthworms and N fertilizer sources on agroecosystem N dynamics. Over a seven‐month period, we paired monthly buried bag and PVC core soil incubations within research plots receiving one of three N treatments (inorganic, legume, or manure fertilizers) and with manipulated earthworm populations (reduced, ambient, or increased numbers). Soil moisture within both the buried bags and the PVC cores fluctuated in response to changes in the surrounding soil, violating assumptions of the buried bag method that soil moisture remains constant during incubation. For both methods, overall CV's for net ammonification, nitrification, and N mineralization rates were very high (104 ‐ 628%). Overall, results for the two methods were significantly correlated for net ammonification (r = 0.89), net nitrification (r = 0.58), and net N mineralization (r = 0.24). In general, the two methods yielded similar seasonal estimates of net N mineralization and nitrification. However, on one occasion in the plots with the inorganic N treatment, buried bag estimates of net N mineralization were significantly higher than the PVC core estimates (1.5 versus ‐0.4 mg N‐kg^‐1 soil‐d¹, respectively). Under some conditions, the two methods may lead to quite different interpretations of soil N mineralization processes.     

Critical soil bulk density and strength for pea seedling root growth as related to other soil factors

Bulk density and soil strength are two major soil physical factors affecting root growth of pea seedlings. This study was conducted to determine the influence of soil texture, organic carbon content and water content on critical bulk density and strength. Soil from the plough layer (PL) and beneath the sub-soil (SUB) was used. By soil packing and adjusting the water content between 30% and 100% of field water capacity (FWC) a wide range of bulk density (1.3–1.7 Mg m⁻³) and strength (0.24–6.66 MPa) were obtained. Pea (Pisum sativum L.) was grown in the packed cores of 100 cm³ for 72 h at 20°C. Regression models were developed to explain root growth in terms of bulk density, soil strength, silt and clay (<60 μm) content, organic carbon, and water content. The regression curve of root growth as a function of soil strength showed that 40% of maximum root length can be regarded as an indicator of very poor root growth. By substituting this value into the root growth equations we calculated a critical bulk density and strength in terms of fraction<60 μm, organic carbon percentage and water content. The values of critical bulk density in both layers and of critical soil strength in the sub-soil increased with a decreasing content of fraction<60 μm. Irrespective of fraction<60 μm content, the critical bulk density and strength decreased as soil water content decreased. Critical soil strength was more sensitive than critical bulk density to changes in fraction<60 μm content and water content. This study provides data and a method for predicting critical bulk density and soil strength in relation to other soil properties for pea seedling root growth.     

Enclosing decomposer food web: implications for community structure and function

We designed a field experiment to evaluate how restriction of soil faunal movements affects decomposer community structure, food web architecture, and decomposition of organic matter. Intact soil cores (3cm thick, diameter 16cm) were placed either in “open” (mesh size 1mm, allowing all meso- and microfauna to move through) or “closed” (27μm, animal movement prevented except for the smallest microfauna) mesh bags in early May. Before being buried in the forest floor of a mixed spruce stand, hay litter was placed in the mesh bags in separate litter bags. The samplings took place 2 and 6 months after establishing the experiment. Additional “field samples” were taken from the adjacent soil to determine possible side effects of the mesh-bags. Physicochemical conditions, decomposition rate of hay litter, and total respiration of soil cores were identical in the two bag treatments. Enchytraeids increased significantly in the closed treatment, while macrofauna, such Coleoptera larvae and dipteran larvae, went close to extinction in the closed bags. The elevated enchytraeid number is in accordance with the findings of closed microcosm studies, and is best explained by reduced predation by macrofauna. Although a set of 14 mite taxa was found to distinctively reflect the degree of isolation, neither the total number of individuals nor the number of microarthropod taxa differed between the bag treatments, or between the bags and the field samples. It is concluded that in the time-span of one growing season, reduction in the spatial scale does not necessarily reduce the diversity of fauna but can significantly change the decomposer food-web architecture. Received: 5 February 1997     

Facilitation of seedling growth and nutrient uptake by indigenous arbuscular mycorrhizal fungi in intensive agroecosytems

A modified in-growth core technique was employed to determine the contribution of indigenous arbuscular mycorrhizal fungi (AMF) to plant growth and nutrient uptake in intensive agroecosystems at two Experimental field sites at Shangzhuang (Experiment I) and Quzhou (Experiment II) in North China. The growth cores (26.5 cm depth, 5 cm diameter for maize plants, and 4 cm for alfalfa and tomato plants) were covered with 40-μm nylon mesh (restriction of hyphal growth) and buried in the soil. They either remained static (static mesh) or were regularly rotated (rotated mesh) to disrupt hyphal penetration into the cores. A non-rotated 0.45-μm mesh (block mesh, inhibition of hyphal growth) treatment which remained static was also included to compare with the rotated mesh treatment (Experiment I). Growth cores from the two experimental sites had different soil types and two contrasting low P levels. The soil in the growth cores was sieved and sterilized before being placed into the growth core. Three plant species, namely maize, tomato and alfalfa were selected. The growth periods for maize plants were 35 days (Experiment I) and 39 days (Experiment II), respectively, and the corresponding growth periods for tomato and alfalfa were 67 days (Experiment I) and 53 days (Experiment II). At harvest the AMF species inside and outside the in-growth cores were identified by polymerase chain reaction (PCR), cloning and sequencing. Irrespective of plant species or genotype (maize), root colonization rates and hyphal length density (Experiment I) were generally suppressed in the rotated mesh treatment. The inhibition of hyphal growth by block mesh was comparable to that by the rotated mesh treatment. The growth of all three plant species in static mesh at the two Experimental sites, at both low (Experiment I) and sub-optimal soil P supply levels (Experiment II), was significantly higher than in the rotated (or block mesh) treatment. Root colonization rates of three maize genotypes were positively correlated with plant P concentration (Experiment II). Uptake efficiencies of P and N were significantly higher in static mesh than in the rotated (or block) treatment. AMF species detected (Experiment I) were all Glomerales, including the genera Glomus and Rhizophagus. One identified species of Rhizophagus intraradices and one Glomus viscosum-like phylotype were the dominant species. We conclude that the indigenous AM are crucial for early seedling growth, particularly for plants with small seeds and low P reserves and when seedlings exhibit P deficiency. The facilitation effect is highly relevant to enhanced root P (and possibly N) uptake and P delivery by the fungal mycelium. Our results have implications for the importance of maintenance of intact hyphal networks in intensive agroecosystems.     

Comparison of Disturbed and Undisturbed Soil Core Methods to Estimate Nitrogen-Mineralization Rates in Manured Agricultural Soils

Ion exchange resin?/?soil cores are a common in situ approach to estimating soil nitrogen (N) mineralization rates. However, no studies compare the two common methods of core preparation (disturbed and undisturbed). The objective of our study was to compare N mineralized and soil temperature in disturbed versus undisturbed cores of manured agricultural soils. Undisturbed cores were prepared by driving aluminum tubes (25 cm long with 10 cm inner diameter) into soil, removing the tubes, and then inserting an ion-exchange resin bag beneath the soil at the bottom of the tube. Disturbed cores were prepared with the same materials, but soil was excavated, mixed, and then filled into tubes fitted with ion-exchange resin bags at the bottom. Soil from six agricultural fields (five of which had more than 10 years of regular dairy manure application) was incubated over four time periods during summer and winter. A total of 13 soil?/?incubation-period combinations were tested. Disturbed cores tended to have more N mineralized than undisturbed cores (P < 0.10), especially in cores prepared with the lowest clay content soil. However, variability of N mineralized was lower in disturbed cores than undisturbed cores for 11 of the 13 soil?/?incubation periods. This lower variability was significant in two of the four incubation periods (P < 0.10). There was little difference in mean soil temperatures in disturbed versus undisturbed cores or within cores versus outside but adjacent to cores. However, in summer, the daily temperature range inside cores was significantly greater than the temperature range in soil outside cores (P < 0.01).     

玉米生长后期的根系分布研究

为了研究玉米生长后期根系的生长发育规律,利用中国气象局固城农业气象试验站大型根剖面系统,采用微根管观测系统及方形整段标本法和地下根系室玻璃窗,对‘屯玉46号’玉米根系的生长状况进行了试验研究。结果表明:垂直方向上,方形整段标本法和微根管法测得的根长密度占整层总根长密度比例的变化趋势一致,相关系数分别为0.987和0.717,且两种方法在0~20 cm土层的根长密度比例均为最大。0~60 cm土层为玉米根系生长活跃区,方形整段标本法测得根长密度生长量为其余层的4倍。两种方法测得的根长密度无显著差异,相关系数为0.830,均匀性水平较好。玉米成熟期根系的水平幅度较乳熟期窄,下层根系仍处于生长中,垂直深度增加。玻璃窗与方形整段标本法观测的根深测定结果存在差异,这可能与观测环境条件不一致有关。     

Soil acidity and its relationship to root growth in declining forest stands in Germany

Ingrowth core studies were used to investigate the influence of 3 different soils on root growth of Norway spruce in two stands in Northwest Germany. Root growth was significantly inhibited by the acid soil treatment. The amount of roots which had grown into the limed ingrowth cores were much higher and the percentage of dead roots was less when compared to the unlimed treatment. This is attributed to improved Ca/A1-ratios after liming. The fertilized peat-sand soil delivered optimal conditions for root growth indicated by maximum root biomass and 0% root mortality. The importance of soil acidification induced by acid deposition as the cause of the root disturbance in declining stands is addressed.     

Improved root penetration of soil hard layers by a selected genotype

Abstract

Crops can be effectively grown on hardpan soils and water effectively used from deep in the profile if hard layers in soils can be penetrated or if they are broken up by tillage. Addition of gypsum to the soil or exploitation of genetic differences in root penetrability may help improve root penetration through hard layers with less need to depend on the energy requirements of deep tillage. To test this theory, a single‐grained Ap horizon of Norfolk loamy sand soil was compacted into soil columns to compare root penetrability of soybean [Glycine max (L.) Merr.] genotypes Essex and PI 416937 in the presence and absence of gypsum and at two soil compaction levels (columns with uniform compaction at 1.4 g cm^‐1 and columns with increasing compaction with depth from 1.4 to 1.75 g cm^‐1). Compaction treatments were imposed by constructing soil columns composed of 2.5‐cm‐deep, 7.5‐cm‐diameter cylindrical cores compacted to predetermined bulk densities (1.40,1.55,1.65,and 1.75 g cm^.3). Soil penetration resistances were measured on duplicate cores using a 3‐mm‐diameter cone‐tipped penetrometer. Columns were not watered during the study; soybean genotypes were grown in the columns until they died. Both genotypes lived one day longer in columns with lower bulk density and penetration resistance. Although root growth was more abundant for Essex than for PI 416937, root growth of PI 416937 was not decreased by compaction as much as it was for Essex. These results suggest that PI 416937 may possess the genetic capability to produce more root growth in soils with high penetration resistance. This study suggests that genetic improvement for root growth in soils with hard or acidic layers may potentially reduce our dependence on tillage. Gypsum did not affect root growth in this study.     

不同秸秆还田方式对春玉米产量、水分利用和根系生长的影响

为探究耕作方式和秸秆还田对春玉米产量、土壤水肥及根系分布的影响,通过连续两年设置耕作方式(旋耕、翻耕)与秸秆还田方式(秸秆还田、秸秆不还田)两因素田间定位试验,研究了春玉米产量和水分利用效率、根系及土壤水肥分布的特性。结果表明:旋耕和翻耕处理春玉米产量和水分利用效率差异不显著,但前者显著增加了干旱年份(2015年)0—30cm土层的根长密度、根表面积密度和根干重密度,而后者显著降低了10—30cm土层的土壤容重和紧实度,降低了0—40cm土层的土壤含水量、有效磷和速效钾含量,提高了干旱年份30—60cm和湿润年份(2016年)0—60cm土层的根长密度、根表面积密度和根干重密度;秸秆还田较秸秆不还田处理显著增加了春玉米产量和水分利用效率,增加幅度分别为9.5%和7.3%,促进了干旱年份0—60cm土层的根长密度和湿润年份30—60cm土层的根长密度、根表面积密度和根干重密度的增加,还提高了0—60cm土层的土壤含水量、硝态氮、有效磷和速效钾含量。因此,实施旋耕秸秆还田和翻耕秸秆还田可以改善土壤水肥分布,促进深层根系发育,提高春玉米的产量和水分利用效率。     

The establishment of winter wheat root system architecture in field soils: The effect of soil type on root development in a temperate climate

Winter wheat (Triticum aestivum L.) is an important cereal crop in the temperate climates of western Europe. Root system architecture is a significant contributor to resource capture and plant resilience. However, the impact of soil type on root system architecture (RSA) in field structured soils is yet to be fully assessed. This work studied the development of root growth using deep cultivation (250 mm) during the tillering phase stage (Zadock stage 25) of winter wheat across three soil types. The three sites of contrasting soil types covered a geographical area in the UK and Ireland in October 2018. Root samples were analysed using two methods: X-ray computed tomography (CT) which provides 3D images of the undisturbed roots in the soil, and a WinRHIZO^™ scanner used to generate 2D images of washed roots and to measure further root parameters. Important negative relationships existed between soil bulk density and root properties (root length density, root volume, surface area and length) across the three sites. The results revealed that despite reduced root growth, the clay (Southoe) site had a significantly higher crop yield irrespective of root depth. The loamy sand (Harper Adams) site had significantly higher root volume, surface area and root length density compared with the other sites. However, a reduction in grain yield of 2.42 Mt ha⁻¹ was incurred compared with the clay site and 1.6 Mt ha⁻¹ compared with the clay loam site. The significantly higher rooting characteristics found in the loamy sand site were a result of the significantly lower soil bulk density compared with the other two sites. The loamy sand site had a lower soil bulk density, but no significant difference in macroporosity between sites (p > 0.05). This suggests that soil type and structure directly influence crop yield to greater extent than root parameters, but the interactions between both need simultaneous assessment in field sites.     

Container and Installation Time Effects on Soil Moisture,Temperature, and Inorganic Nitrogen Retention for an in situ Nitrogen Mineralization Method

Mineralization contributes significantly to agronomic nitrogen (N) budgets and is difficult to accurately predict. Models for predicting N‐mineralization contributions are needed, and development of these models will require field‐based data. In situ mineralization methods are intended to quantify N mineralization under ambient environmental conditions. This study was conducted to compare soil moisture and temperature in intact soil cores contained in cylinders to those in adjacent bulk soil, compare the effect of two resin‐bag techniques on water content of soil within cylinders, and assess the effect of installation duration on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn (Zea mays L.) site and an irrigated no‐tillage corn site in eastern Nebraska. Soil in cylinders was slightly wetter (<0.05 g g^?1) and warmer (<1 °C) than adjacent soil. Soil water content was <80% water‐filled pore space (WFPS) at all sampling times and differed little between the two resin‐bag techniques. Greater soil water content and temperature conditions (though small) observed during most of the study period likely enhanced N mineralization within the cylinder compared to N mineralization in adjacent bulk soil, but the magnitude is likely much less than core‐to‐core variation normally observed in a field. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. Care is needed during installation to ensure that compaction of soil below the cylinder does not impede water movement through the intact soil core. The in situ method utilizing intact soil cores and resin bags replaced at 28‐ to 40‐day intervals is a viable method for measuring N mineralization.     

Bacterial-feeding nematodes enhance root growth of tomato seedlings

We prepared soil with greater populations of bacterial-feeding nematodes, compared to a normal field soil, to determine the effects of bacterial-feeding nematodes on the root development of tomato seedlings. Soil mixed with either pig manure or rice straw was placed in a mesh bag, and then surrounded by an outer layer of unamended soil. Nematodes were able to migrate through a 1 mm diameter mesh bag into the outer soil, thus giving greater populations than in soil surrounding a control treatment of a 5 μm diameter mesh bag, through which nematodes cannot migrate. After 28 and 35 days incubation, respectively, the outer soil contained a nine-fold increase in nematode numbers in the pig manure treatment and a six-fold in the rice straw treatment, compared to control soil. The increased nematodes were mainly bacterial-feeders, accounting for 98.2% of total nematodes in the pig manure treatment and 90.5% in the rice straw treatment. Tomato seedlings were grown in the outer soil and root parameters (total length, average diameter, total surface area, numbers of forks and numbers of tips) determined after 5 and 10 days growth at 20 °C. We found that the tomato seedlings grown in the soil containing more bacterial-feeding nematodes developed a highly branched root system with longer and thinner roots.     

Penetration resistance and root growth of oats in tilled and untilled loess soil

Penetration resistance, bulk density, soil water content and root growth of oats were intensively studied in a tilled and an untilled grey brown podzolic loess soil. Bulk density and penetration resistance were higher in the top layer of the untilled soil compared with the tilled soil. In the latter, however, a traffic pan existed in the 25–30 cm soil layer which had higher bulk density and penetration resistance than any layer of the untilled soil. Above the traffic pan, rooting density (cm root length per cm³ of soil) was higher but below the pan it was lower than at the same depth in the untilled soil. Root growth was linearly related to penetration resistance. The limiting penetration resistance for root growth was 3.6 MPa in the tilled Ap-horizon but 4.6-5.1 MPa in the untilled Ap-horizon and in the subsoil of both tillage treatments. This difference in the soil strength-root growth relationship is explained by the build up of a continuous pore system in untilled soil, created by earthworms and the roots from preceding crops. These biopores, which occupy < 1% of the soil volume, can be utilized by roots of subsequent crops as passages of comparatively low soil strength. The channeling of bulk soil may counteract the possible root restricting effect of an increased soil strength which is frequently observed in the zero tillage system.     

Compaction and penetration resistance of an Alfisol and Entisol and their influence on root growth of maize seedlings

Traffic and tillage induced compaction affect soil physical, chemical and biological properties and processes directly and influences plant root growth indirectly. In a pot experiment with an Entisol and an Alfisol, the effect of 0, 50, 100 and 200 kPa of compactive stress on bulk density, penetration resistance, and on root growth of maize seedlings, at the early stages of development, was studied.

Compaction resulted in a progressive increase in bulk density and penetration resistance for both soils. The Entisol reached a greater bulk density and penetration resistance than the Alfisol. Bulk density or penetration resistance were closely correlated with compactive stress. The correlation between bulk density and penetration resistance was not so close.

Increased bulk density and penetration resistance resulted in a reduction of all the root growth parameters such as number of roots, mean and total root length, rateof root elongation and fresh and dry root mass. Significant linear or curvilinear relationships were found between bulk density or penetration resistance and most of the root growth parameters studied. However, the relationships were improved when relative values (expressed as fractions of the controls) of bulk density or penetration resistance and of any one of the root growth parameters were considered. Roots grown in more compact soil had a smaller ratio of fresh to dry mass.     

Yearly variation of root distribution with depth in relation to nutrient uptake and corn yield

Abstract

Root length and root distribution in the soil profile is important in determining the amount of nutrients and water taken up by the plant. Data about year to year variation of corn (Zea mays L.) root growth and its relation to nutrient uptake are limited. An evaluation of the importance of root system size and distribution on P and K uptake and corn yield was made from samples taken annually from a long‐term fertility experiment on Raub silt loam, fine silty, mixed, mesic Aquic Argiudolls. Root density varied with soil depth among years, whereas P and K fertilizer treatment had no measureable influence on total root length. Ear leaf P concentration was highly correlated with the amount of roots in the 0 to 15 cm layer which contained most of the available P. Since P was not appreciably limiting corn yield, no significant relation was found between yield and P content of the ear leaf. Yields on K deficient plots were positively correlated with root density in the topsoil. Correlations of root densities in the deeper soil layers with both yield and ear leaf nutrient concentration became increasingly smaller with depth in the soil profile. The results indicate that root length plus root distribution in the soil may influence year to year variation in yield particularily on soils having low available nutrient levels. This variation in root growth may be responsible for differences among years in the response of crops to applied P and/or K.     

土壤紧实胁迫对黄瓜生长、产量及养分吸收的影响

用容重分别为1.2、1.4和1.6.g/cm3的土壤进行盆栽试验,研究了土壤紧实度对黄瓜生长、产量及养分吸收的影响。结果表明,当土壤紧实度增大时,黄瓜秧苗的株高在定植后的15.d后受到显著抑制;第4叶的叶宽和叶长在定植后9～17.d内增加;茎粗则是在稍紧的土壤中(R.1.4)最大,过紧的土壤中(R.1.6)最小;根系伸长生长受阻,干物质质量及活力显著下降,根冠比降低;生物学产量、经济产量、经济系数的变化情况及植株对氮、磷、钾吸收量的变化与茎粗的变化趋势相同。在本试验条件下,容重为1.2.g/cm3的土壤利于株高及根系的生长,容重1.4g/cm3的土壤则利于茎粗、根系养分的吸收及产量的增加。