Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)

It is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g cm^–3 to 1.66 g cm^–3. Rhizotrons with a soil layer 7 mm thick were used and pre‐germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30 % with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20 % and 50 % for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15 % of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots.     

Changes in nutrient allocation between roots and shoots of young maize plants during sulfate deprivation

Hydroponically grown maize (Zea mays L.) plants were deprived of the external source of sulfate following an initial period of 13 d during which the sulfur (S) supply was sufficient. The amounts of dry mass (DM), water, sulfate, sulfur, nitrate, ammonium, nitrogen, phosphorus, potassium, magnesium, calcium, boron, iron, copper, zinc, and manganese were monitored in the shoots and the roots for 10 d. The deprivation altered the nutritional balance between them, causing a 70% decrease of sulfate in shoots and roots after 2 d. At 10 d, 95% of sulfate had vanished in both shoots and roots. Total S remained rather constant in shoots or was slightly decreased in roots after 4 d. This coincided with a decrease of Fe in shoots after 4 d. The calculated decreases of S and Fe in –S shoots, up to 6 d were linearly correlated. Kinetic analysis of the changes revealed a sequence in their onset, and we distinguished early and late changes. Among the early changes, we highlight the following ones: (1) an increased amount of Cu in both shoots and roots at 2 d; Fe was 40% decreased in both shoots and roots at 2 d; (2) a decrease in transpiration rate by 35% after 2 d; (3) alterations in boron allocation; in –S shoots the % changes in S were linearly correlated with the corresponding % changes in B; (4) calcium content was not affected by the S deprivation in –S shoots, whilst it increased in –S root after d 2; (5) Mn and Mg decreased from the beginning and in a uniform fashion in both –S shoots and roots. Day 6 may be considered as the boundary between the early and late changes. The root fraction of DM increased progressively after 4 d. Changes in DM seemed to be similar to those of P. Changes of Zn also took place rather late. In –S shoots and for the time interval between 6 d and 10 d, linear correlations were found between the corresponding % changes of the pairs DM–S, DM–P, DM–N, DM–water, S–N, S–P, and N–P.     

Image analysis for non‐destructive and non‐invasive quantification of root growth and soil water content in rhizotrons

Studies aiming at quantification of roots growing in soil are often constrained by the lack of suitable methods for continuous, non‐destructive measurements. A system is presented in which maize (Zea mays L.) seedlings were grown in acrylic containers — rhizotrons — in a soil layer 6‐mm thick. These thin‐layer soil rhizotrons facilitate homogeneous soil preparation and non‐destructive observation of root growth. Rhizotrons with plants were placed in a growth chamber on a rack slanted to a 45° angle to promote growth of roots along the transparent acrylic sheet. At 2‐ to 3‐day intervals, rhizotrons were placed on a flatbed scanner to collect digital images from which root length and root diameters were measured using RMS software. Images taken during the course of the experiment were also analyzed with QUACOS software that measures average pixel color values. Color readings obtained were converted to soil water content using images of reference soils of known soil water contents. To verify that roots observed at the surface of the rhizotrons were representative of the total root system in the rhizotrons, they were compared with destructive samples of roots that were carefully washed from soil and analyzed for total root length and root diameter. A significant positive relation was found between visible and washed out roots. However, the influence of soil water content and soil bulk density was reflected on seminal roots rather than first order laterals that are responsible for more than 80 % of the total root length. Changes in soil water content during plant growth could be quantitifed in the range of 0.04 to 0.26 cm³ cm^—3 if image areas of 500 x 500 pixel were analyzed and averaged. With spatial resolution of 12 x 12 pixel, however, soil water contents could only be discriminated below 0.09 cm³ cm^—3 due to the spatial variation of color readings. Results show that this thin‐layer soil rhizotron system allows researchers to observe and quantify simultaneously the time courses of seedling root development and soil water content without disturbance to the soil or roots.     

不同耐密性玉米品种的根系生长及其对种植密度的响应

根系形态和分布对土壤中养分和水分的吸收有重要影响。增加耐密性是现代玉米（Zea may L.）育种的主要方向,而耐密性与根系的关系尚了解不多。本文以70年代主推的2个不耐密型品种（中单2号与丹玉13）和2个当代耐密型现代品种（先玉335和郑单958）为材料,将田间试验和室内水培试验相结合,在3个密度水平下,研究了不同耐密性玉米品种的根系差异及其对种植密度的响应。结果表明,目前推广的耐密型品种的根系要小于不耐密的老品种。不同耐密性品种之间的差异主要表现在040 cm。随着密度的增加,根显著变小、变细。密度主要降低020 cm土层中的根系生长,对深层根系影响较小。先玉335和中单2的根系长度对密度的反应较弱,郑单958和丹玉13较强。这说明先玉335主要依靠其小根系适应高密度,而郑单958既依靠较小的根系,同时依靠较高的根系反应性适应高密度。     

Tillage effects on soil properties and maize productivity in western Turkey

Information regarding the evaluation of long-term tillage effects on soil properties and summer maize growth after winter vetch in western Turkey is not available. Therefore, this study was conducted for 5 years with three types of tillage including conventional (mouldboard plough) and conservation (rototiller and chisel). Results indicated that tillage had no significant effect on penetration resistance, except at the bottom of 20 cm soil depth where it was higher in mouldboard plough than in rototiller and chisel. Bulk density in the topsoil of 10 cm decreased with the degree of soil manipulation during tillage practices. Rototiller caused significantly higher root, leaf and stems biomass and plant height than the other systems. The root dry weight was higher in the topsoil of 10 cm than at the bottom of this soil depth for all systems. The highest root dry weight was found in fourth year of chisel, but the lowest was recorded in the same year of plough, especially at the bottom of 20 cm due to higher penetration. Rototiller improved soil properties and maize growth compared to other systems in 2 of 5 years. We concluded that using rototiller for maize after winter vetch will be more effective compared with other systems.     

Aggregate stability of a silt loam soil as affected by roots of corn,soybeans and wheat

Abstract

A greenhouse experiment was conducted to investigate the effect of root growth and exudation of 3 crop species on soil aggregation. Two plant populations for each of 3 crops (corn, soybeans, and wheat) were grown in a Fincastle silt loam for 5 time periods (7, 14, 21, 28, and 41 days) and compared with fallow controls. Aggregate stability was estimated by the wet‐sieve method on both initially moist and air‐dry samples.

Soil water content of initially moist soil samples varied widely among replicates, crops, and sampling dates. Wet‐sieving using initially moist soil showed that samples with higher initial soil water content had greater aggregate stability. Wet‐sieving performed on initially air‐dry soil samples was used for subsequent interpretation because the water content variable was removed.

The presence of any crop and its roots in the planted soils versus the fallow controls was associated with increases in aggregate stability. No differences in aggregate stability were found among the different crops or over the established range of root length densities. Aggregate stability decreased from the original level during the first 14 to 21 days of the experiment, possibly due to daily watering. After 21 days, as root growth continued to increase, restabilization occurred until the original aggregate stability of the soil was exceeded for all crops. The observed increase in aggregate stability may be due in part to the physical entanglement of aggregates by roots and to the increased production of root exudates resulting from increased root growth.     

Effects of N‐fertilization on shoots and roots of rape (Brassica napus L.) and consequences for the soil matric potential

The underlying question of these investigations asked, how and to which extent rape plants react with transpiration and soil water uptake to different degrees of nitrogen fertilization. Therefore repeated campaigns with concurrent measurements of plant surfaces (leaves, stems, pods), diurnal courses of leaf transpiration and root length density of rape plants growing on heavily (240 kg ha^—1), moderately, (120 kg ha^—1), and nil N‐fertilized plots of an experimental field in northern Germany were performed during two growing seasons. Additionally, matric potentials at different soil depths were measured. In the first year (1994) investigations were concentrated primarily on shoot area development and transpiration, whereas in the subsequent year (1995) root measurements were mainly undertaken. Also, the influence of soil management (ploughing, conservation tillage) was taken into consideration. The plots where the shoot measurements were carried out were ploughed in 1994 and rotovated in 1995. Matric potentials were measured in both years in ploughed soil and, for comparison, also in soils with conservation tillage. Shoot area index, as measure of the transpiratory capacity of the canopy, increased on ploughed soil and reached a maximum before flowering. Thereafter it decreased until harvest when the relative amount of green stems and pods was increasing. Then, the measured transpiration rate per pod surface area was equal to, or higher than, the transpiration rate per leaf surface area. Plant surface area was smaller in plots with conservation tillage and decreased generally with decreasing N‐fertilization. Increasing plant surface area was joined by an increasing density of plant canopy. Light interception was thus highest in the plots receiving 240 kg N ha^—1. Although the shading effect may cause a reduction of transpiration per plant, the total plant mass per area generally resulted in a greater water loss from these plots. Roots reached at least 110 cm depth. Root length density was significantly higher in the upper 10—30 cm of soil than at greater depths. Root mass was smaller in soil with conservation tillage than in ploughed soil. Oscillations of soil matric potentials in the diurnal and long‐term periods were highest in the upper 10 cm of soil. Here, they corresponded well with the cumulative diurnal transpiratory water loss. It is concluded that the soil water dynamics depends largely on the distribution of plant roots. As a result, rape plants did not change their specific transpiration capacity as a response to increased nitrogen fertilization. However, the transpiring plant surface and root length density increased the turnover rate of water by a higher plant density per plot. This effect was more pronounced in ploughed than in rotovated plots.     

Chloride effects on corn

Abstract

Chloride (Cl) toxicity was suspected in corn (Zea mays L.) growing in a poorly‐drained Atlantic Coast Flatwoods soil where Cl toxicity of soybean {Glycine max (L.) Merr.} was a problem. Field and greenhouse research was conducted with rates of applied Cl in an effort to induce Cl toxicity in corn.

‘Trojan 114’ corn was grown in the greenhouse with Cl rates (KCl) of 0, 364, and 728 ug/g and in the field with rates of 0, 85, 170, and 340 kg/ha. Potassium sulfate (K₂SO₄) treatments were included to supply equivalent amounts of K as that in KCl.

Phytotoxicity of corn did not occur in greenhouse or field experiments with any fertilizer treatment. In the greenhouse Cl concentrations in 26‐day old corn plants grown in a poorly‐drained Flatwoods soil (Leefield sand ‐ arenic Plinthaquic Paleudult) for the 0 and 728 ug Cl/g treatments were 5.0 and 32.7 g/kg in shoots, 1.6 and 14.9 g/kg in ear leaves, and 1.3 and 16.5 g/kg in stalks, respectively. In the field, Cl treatments applied to corn grown in a poorly‐drained Flatwoods soil (Alapaha sand ‐ arenic Plinthic Paleaquults) were not as effective in increasing Cl concentrations in shoots and ear leaves as that for corn grown in a well‐drained soil (Tifton loamy sand ‐ thermic Plinthic Paleudult) apparently because of the greater amount of residual soil Cl in the poorly‐drained soil. Concentrations of Cl in shoots of corn receiving O and 340 kg Cl/ha were 3.8 and 18.0 g Cl/kg, respectively, for corn grown in the well‐drained soil and 16.1 and 18.0 g Cl/kg, respectively, for corn grown in the poorly‐drained soil. Grain yields were not affected by fertilizer treatments on either soil and Cl concentration in grain for corn grown in the Tifton soil was not different among treatments. These data indicate that corn is not very susceptible to high levels of soil Cl.     

土壤容重对玉米光合特性的影响及调控研究

以耕地棕壤为试验材料,采用盆栽方法,研究不同土壤容重对玉米光合指标(光合速率、气孔导度、胞间二氧化碳浓度)及叶绿素(a、b)的影响,并进一步研究了施用不同有机肥量及模拟不同耕作深度对玉米光合指标的调控效果。结果表明:不同容重处理之间对玉米叶绿素含量的影响拔节期前差异不显著,拔节期后达极显著差异(p<0.01),叶绿素含量在研究的生育期内始终增长。光合速率与容重、胞间二氧化碳浓度呈负相关,与气孔导度呈正相关。高容重土壤有机质调节至40～50 g kg-1即可以获得比较理想的效果;低容重的土壤有机质在研究含量范围内效果始终显著增长,有机质含量在15 g kg-1左右制约玉米生长,有机质含量应至少调节至3%以上。耕层厚度增加能提高所测定生理指标,但耕层厚度处理对叶绿素、光合指标影响不显著,当耕层厚度调节至30～40 cm时,各项指标增加基本达到限值,再增加耕层厚度作用不再明显。     

Comparison of Copper,Manganese, and Zinc Extraction with Mehlich 1, Mehlich 3, and DTPA Solutions for Soils of the Brazilian Coastal Tablelands

Deficiency of micronutrients is increasing in crop plants in recent years in Oxisols and Ultisols in the tropics. The predominant soils in the coastal tablelands of Brazil are Ultisols and Oxisols, with low cation exchange capacity and kaolinitic clay mineralogy. Soil copper (Cu), manganese (Mn), and zinc (Zn) extracted by the Mehlich 1 solution, currently used in the regional soil-testing laboratories, were compared with those extracted by the Mehlich 3 and diethylenetriaminepentaacetic acid (DTPA) solutions in a greenhouse experiment with 10 soil samples (0–20 cm deep) collected from representative Ultisols and Oxisols from various locations in the region. Corn was grown as a test crop, and its dry matter and micronutrient uptake was measured at 30 days of growth. Soil Cu, Mn, and Zn extracted with the three solutions were significantly correlated (0.65–0.95 range for r values), with the Mehlich 3 solution extracting greater quantities than the Mehlich 1 and DTPA solutions. Zinc and Cu taken up by corn plants were significantly related to their soil-extractable levels measured at harvest with all three of the solutions, except for Zn DTPA. However, similar relations between plant uptake and soil extractable Mn were poor, except for DTPA extracting solution.     

Comparison of root and root hair growth in solution and soil culture

Aerated solution culture is frequently used for studying plant growth. Few comparisons have been made of root growth in solution with that found in soil. The objective of this study was to compare root growth and root hair development in these two mediums. Corn (Zea mays L.) grown in aerated solution at two temperatures (18 and 25°C) and three P concentrations (2, 10, and 500 μmol L^‐1) was compared with that in three soils, Raub (Aquic Argiudoll) and two Chalmers (Typic Haplaquoll) silt loams, in a controlled climate chamber over 21d. Corn plant weight and root growth were similar in solution culture and Raub soil when grown at an air and soil temperature of 18°C. At 25°C both yield and root growth were greater in Raub soil, even though P uptake by corn was 7‐fold greater in solution culture. The same difference was found when corn grown at 25°C in solution culture at 3 different P concentrations was compared with that grown in Chalmers soil at two P levels. Percentage of total root length with root hairs, root length and density and consequently root surface area, were all greater in the Chalmers soil than in solution culture. An increase in soil P, resulted in a decrease in root hair growth. No such relationship was found in solution culture. Although the recovery and measurement of plant roots and root hairs is more convenient in solution culture, results from this study indicate that the usefulness of solution culture for determining those factors which control root growth and root hair development in soil is limited.     

Spatial Distribution Assessment of Maize Roots by 3D Monolith Sampling

Spatial distribution of roots is of paramount importance for nutrient acquisition by crop plants. The objective of this study was to assess the spatial distribution of root length density (RLD), root mass density (RMD), and root morphological parameters in maize. Soil monoliths were completely sampled in form of 84 cubic samples of 10-cm edge length. Total root length and mass were dominated by fine roots (<1 mm diameter). Root parameters revealed variability in all three spatial dimensions, notably also parallel to the plant row. Root morphological parameters depended more on the horizontal location with respect to location of plants than on depth. Multiple regression analysis indicated that RLD, proportion of fine roots, and root diameters can be predicted from RMD, soil depth, and distance to plant. These three-dimensional (3D) data could be utilized for evaluation of 3D root growth and nutrient uptake models.     

Silage maize quality in different uses of Italian ryegrass and soil management methods after liming

The effects of lime application with multiple soil management methods and uses on dry matter (DM) yield and crude protein (CP) content of Silage maize cropping in succession with Italian ryegrass (ryegrass) from 2009 to 2014 in a southern Brazilian Oxisol were studied. The experimental design was completely randomized block in split-plot with four replications. The main plot treatments were the four soil management methods: conventional tillage (CT), minimum tillage (MT), no-tillage (NT) and chiseled no-tillage (CNT). The sub-plots treatments were the three uses of Italian ryegrass (ryegrass): cover crop (CC), silage (S), and grazing dairy heifers as part of integrated crop-livestock system (ICL). In all the years, the maize was sown approximately 30 days after the ryegrass desiccation with herbicide. In the medium-term (5 yrs.) after liming, soil management methods did not change DM yield and CP content in silage maize. The use of ryegrass for S and ICL did not change DM yield, but notably maintained or increased CP content in silage maize after liming. The use of ryegrass only as CC provided less measurable benefits than the combined production system of silage maize with ryegrass.     

Comparative studies on the photosynthesis of higher plants

1) CO₂ compensation points of the plants tested correlate well with the leaf anatomy. Low CO₂ compensation plants had well-developed VBS containing large and specialized chloroplasts but no plant with a high CO₂ compensation point possessed chloroplasts in the VBS.

2) CO₂ Compensation Points Closely Correlated With The Major Carboxylation Pathway In Photosynthesis. Low Compensation Plants Fixed CO₂ Via The C-4 Pathway (C-4 Plants) While High Compensation Plants Carried Out CO₂ Fixation By The Calvin Cycle (C-3 Plants).

3) Close correlations could be established for the CO₂ compensation point, the major carboxylation pathway, and glycolate oxidase activity. Glycolate oxidase activity was much higher in C-3 plants than in C-4 plants. On the other hand, dark respiration in C-4 plants was higher than that in C-3 plants.

4) TCA cycle activity in detached leaves was not inhibited to any large extent by illumination.

In C-3 plants, the release of ¹⁴CO₂ from alanine-1-¹⁴C increased with an increase in the ambient O₂ concentration; whereas, radioactivity in the sugar fraction was quite small at all O₂ concentrations. In C-4 plants the release of ¹⁴CO₂ was little affected by the ambient O₂ concentration while sugar formation was stimulated at high O₂ concentrations. This indicates that in C-3 plants CO₂ fixation is blocked at a high O₂ concentration, therefore, internal ¹⁴CO₂ is released from the leaf without being refixed, but in C-4 plants internal ¹⁴CO₂ can be efficiently refixed and metabolized to sugar by a combination of active PEP carboxylase and the ‘Kranz type’ of leaf anatomy.     

玉米细根形成和土壤中无机磷分级平衡对缺磷的特异性响应

Plants have diverse strategies to cope with phosphorus (P) deficiency. To better understand how maize responds to P deficiency, a field experiment with two P levels, 0 and 100 kg P2O5 ha-1 (P0 and P100, respectively), was carried out as a part of a long-term Pfertilizer field trial. Plant and soil analyses showed that P-deficient maize reduced its growth rate, increased P use efficiency, and formed more thin roots with the diameter less than 0.6 mm at jointing and silking stages, compared to the plants treated with P100. Further, there were no differences in major inorganic P fractions (Ca 2 -P, Ca 8 -P, Al-P, Fe-P, occluded P and Ca 10 -P) between the rhizospheric and bulk soils at each harvest, even when soil Olsen-P was only 1.38 mg kg-1 . These results suggested that maize responded to P deficiency by reducing the internal P demand for growth and increasing P acquisition ability by favorable root morphological alteration at low carbon cost.     

Effect of lime water – manure organic fertilizers on the productivity,energy efficiency and profitability of rainfed maize production

ABSTRACT

Agro-industrial activities such as livestock production and maize processing generate large amounts of waste that can pollute the environment if not treated. To reduce the environmental impact of such wastes, the use of nejayote and ovine manure as fertilizers in maize production was evaluated in terms of yield (GY), energy efficiency (EE) and benefit-to-cost ratio (BCR), during 2015 and 2016. A factorial experiment was designed combining nejayote (0, 75 and 150 m³ ha^?1) with manure (0, 25 and 50 Mg ha^?1), those treatments were compared with a chemical fertilizer treatment (120N–60P–30K); treatments were done in three replicates. Nejayote-manure fertilizers were characterized physical and chemically. Inputs and outputs used/obtained during the production cycle were registered in terms of their energy equivalents and economic value. At the end of each cycle GY, EE and BCR were calculated. Results showed that nejayote-manure mixtures were 19% more energy efficient and produced a yield 12% greater than chemical fertilization (P = 0.001), thus generating a BCR of 6.3 (P = 0.023). Organic fertilizers were useful as waste treatments and produced greater benefits than chemical fertilizers. Additionally, the water recovered from nejayote was enough to provide a 7.5 or 15 mm of gross irrigation during the crop cycle.     

接种自生固氮菌对玉米根际土壤酶活性和细菌群落功能多样性的影响

为了探索玉米根际土壤微生态特征对接种自生固氮菌的响应机理,在盆栽实验条件下,研究了3株自生固氮菌褐球固氮菌（Azotobacter chroococcum YCYS）、芸苔叶杆菌（Phyllobacterium brasssicacearum QL54）和类芽孢杆菌（Paenibacillus sabinae MX31）接种盆栽玉米（Zea mays L.）之后,玉米根际土壤酶活性和细菌群落功能多样性的变化。结果表明,接种自生固氮菌对玉米根际土壤酶活性和细菌群落功能多样性产生了一定的影响,而且不同自生固氮菌之间的接种效果有一定的差异。接种褐球固氮菌（A. chroococcum YCYS）和类芽孢杆菌（P. sabinae MX31）玉米根际土壤脲酶活性分别比对照高20.55%和9.58%。然而接种处理对玉米根际土壤碱性磷酸酶活性的影响差异不显著（P0.05）。BIOLOG结果显示,接种自生固氮菌可以提高细菌总代谢活性,其中接种褐球固氮菌（A. chroococcum YCYS）处理的AWCD是对照的1.8倍,并且细菌群落丰富度指数（R）显著高于对照（P0.01）。不同接种处理土壤根际细菌生理碳代谢优势群落结构不同。主成分分析（PCA）表明接种自生固氮菌可以调控根际土壤细菌群落功能多样性。