Corn Root Growth Research Articles

Effects of humic and fulvic acids on the rhizotoxicity of lanthanum and aluminium to corn

Effects of varying lanthanum (La) or aluminium (Al) concentrations (0-30 µM) on corn (Zea mays L.) root elongation were examined in the presence and absence of (i) humic acid (HA) at 35 mg carbon (C)/L, or (ii) fulvic acid (FA) at 15 mg C/L, using dilute nutrient solutions. The organic acids were extracted from a mixture of decomposed grass (Sorghum halepense) and lucerne (Medicago sativa) hay. In the absence of added HA or FA, the addition of La at ≥5 µM and Al at 30 µM was toxic to the root growth of corn. The rhizotoxic effects of La at 5 and 10 µM were negated by HA. The ability of FA to overcome La rhizotoxicity was much less, significantly ameliorating the toxic effects of 5 µM La but not those of 10 or 30 µM La. HA and FA did not precipitate La from solution. Both organic acids ameliorated Al toxicity by complexing Al and reducing monomeric Al in solution. It is concluded that concentrations of HA and FA, commonly present in soil solutions, are capable of forming non-rhizotoxic complexes with La, hence plant tolerance to La in the soil solution may be appreciably higher than would be indicated by results of solution culture experiments in which these ligands are not present.

Growth of corn roots under low-input and conventional farming systems

AbstractChanges in soil physical and chemical properties following conversion from conventional to low-input farming systems could alter root growth in com and hence aboveground growth and yield. The main hypothesis we tested is that low-input and conventional farming systems produce different amounts of corn roots. We compared low-input and conventional farming systems, row position (row and interrow), and soil depth for effects on root length density in a Comly silt loam (Typic Fragiudalf) at the Rodale Institute Research Center in Kutztown, Pennsylvania. On all sampling dates studied (two each in 1989 and 1990) root length density under low-input farming systems was significantly greater than under conventional farming systems. We used analysis of covariance to correct for soil factors that could not be directly controlled. Soil water and bulk density had no clear effect on root length density. In contrast, there was significant covariance of soil organic matter with root length density on two of the four sample dates. Root networks were more dense in soil pockets rich in organic matter for every farming system, row position, and depth. These findings indicate that low-input farmers may be manipulating root production of corn to allow com to absorb more nutrients and water when water in the topsail is limited.

Effect of deep tillage on soil physical characteristics and corn ( Zea mays L.) root growth and production

In years of low rainfall, corn ( Zea mays L.) grain production in parts of Southern Illinois, USA is drastically reduced. The naturally occurring claypans and fragipans in the soils of the region and compaction from farming practices have deleterious effects on crop production. An experiment was conducted from 1989–1993 in Carbondale, IL (USA) on a Stoy silt loam soil (fine-silty, mixed, mesic Aquic Hapludalfs) to investigate the effects of deep tillage (0, 40, 60 and 90 cm) and annual tillage management practices (reduced till and no-till) on soil physical characteristics, corn root development and grain yield. Penetrometer resistance and soil bulk density were reduced to the greatest extent by 90-cm depth of tillage and lesser differences were observed with the other tillage depths. About 35% of the corn root length in the 21–100 cm portion of the soil profile was found below 60 cm depth in the deepest tillage, whereas, less than 5% was below 60 cm in the control. Deep tillage increased root proliferation and the depth to which roots penetrated. In growing seasons with evenly distributed rainfall and lower temperatures, root development was rather uniform in the subsurface soil layers. Deep tillage of the soil resulted in increased corn grain yields with the greatest yield always being obtained with 90 cm tillage. The advantage was dependent on tillage depth and the amount and distribution of rainfall during the growing season. No-till annual management resulted in higher yields than reduced till management (for the 0 and 40 cm tillage depth) mainly because of the moisture conserving properties of the surface residues present. Annual management (no-till vs. reduced till) had less impact on yield as the tillage depth increased.

Modelling corn rooting patterns and their effects on water uptake and nitrate leaching

Water and nitrogen absorption by corn (Zea mays L.) are partly determined by the region in the soil containing roots and, as a result, rooting patterns could change water availability and leaching of nitrates. A two-dimensional model of corn root growth was developed and linked to a two-dimensional model for water, heat and solute transport in soil. The model was calibrated with root distribution and soil environment data obtained in a Mollisol at Lamberton, MN. Changing the root growth parameters allowed the model to be used to compare water uptake and NO3 leaching between a shallow, dense root system and a deep, sparse root system. For the rainfall conditions used in model validation, the model predicted a small amount of water absorption from lower in the soil profile with the deep, sparse root system compared with the shallow root system, but that most of the water for transpiration would come from shallow depths directly below the plant. Nitrate leaching was almost identical for both root systems. However, the model predicted reduced downward movement of N when plant uptake of water occurred than with no plant water uptake. The bulk volume of soil explored by the root system may be more important for determining water availability and possible plant water stress during dry periods than for decreasing fertilizer or pesticide leaching. The model should be useful for other examinations of water and chemical movement in the soil by including the effects of the plant in the system. The model also allows at least a preliminary examination of soil management effects on water and nutrient availability.

Traffic Pattern and Tillage System Effects on Corn Root and Shoot Growth

AbstractControlled wheel traffic is one way to manage compaction in no‐till and ridge‐till systems. This study was conducted from 1990 to 1992 at Kanawha, IA, on a Webster silty clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) to examine the effect of a wheel traffic pattern on corn (Zea mays L.) root distribution, shoot growth, and yield in no‐till, ridge‐till, and chisel‐plow tillage systems. The wheel traffic pattern was configured so that some rows would have wheel tracks on both sides, on one side, or on neither side. Bulk density, hydraulic conductivity, root length density, shoot dry weight, and yield were measured at several positions across the traffic pattern. In general, the effect of tillage systems was not significant averaged across positions. Position relative to the traffic pattern had some effect, however, on all measured parameters. Bulk density was greatest in trafficked interrows (1.36 Mg m~3) and least in untrafficked interrows (1.09 Mg m−3). Hydraulic conductivity near saturation was less in trafficked (39.4 μm s−1) than in untrafficked (104.7 μm s−1) interrows. Root length density in trafficked interrows was on average one‐third of that in untrafficked interrows. Root length density in a particular interrow also was influenced by the traffic pattern in the adjacent interrows. In 2 of the 3 yr, yields of rows with a trafficked interrow on only one side were 7% less than those of rows without trafficked interrows on either side. The wheel traffic pattern, and not just the presence or absence of wheel traffic, affected corn root growth and yield.

Growth and Yield Sensitivity of Four Vegetable Crops to Soil Compaction

A 3-year field study conducted on an Eel silt loam soil (Aquic Udifluvent) compared cabbage (Brussica oleracea L. capitata group), cucumber (Cucumis sativus L.), snap bean (Phaseolus vulgaris L.), and sweet corn (Zea mays L.) for their growth and yield response to an artificially compacted soil layer beginning at about the 10-cm depth. Slower growing cabbage seedlings in compacted plots were more subject to flea beetle damage than the uncompacted controls. Prolonged flooding after heavy rainfall events in compacted areas had a more adverse effect on cabbage and snap bean than on cucumber or sweet corn. Sweet corn showed almost no growth reduction in one of the three years (1993) when relatively high fertilizer rates were applied and leaf nitrogen deficiencies in compacted plots were prevented. Maturity of cabbage, snap bean, and cucumber was delayed, and the average reduction in total marketable yield in (direct-seeded) compacted plots was 73%, 49%, 41%, and 34% for cabbage, snap bean, cucumber and sweet corn, respectively. Yield reduction in transplanted cabbage (evaluated in 1993 only) was 29%. In a controlled environment greenhouse experiment using the same soil type and similar compaction treatment as the field study, compaction caused a reduction in total biomass production of 30% and 14% in snap bean and cabbage, respectively, while cucumber and sweet corn showed no significant response. The growth reductions of snap bean and cabbage in the greenhouse could not be attributed to compaction effects on soil water status, leaf turgor, nutrient deficiency, or net CO, assimilation rate of individual leaves. Root growth of sweet corn was least restricted by the compacted soil layer. The contrast between our field and greenhouse results indicates that the magnitude of yield response to compaction in the field was often associated with species sensitivity to secondary effects of compaction, such as prolonged flooding after rainfall events, reduced nutrient availability or uptake, and prolonged or more severe pest pressure.

Rare earth elements and plant growth: II. Responses of corn and mungbean to low concentrations of lanthanum in dilute, continuously flowing nutrient solutions.

Abstract Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing constant cerium (Ce) concentrations from 0 to 1.31 μM. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 μM. However, the total dry matter production of corn was not significantly increased by Ce addition. With mungbean, the addition of as little as 0.19 μM Ce to the nutrient solution caused significant reductions in the dry weight of root (26%), shoot (48%) and total plant (44%). The youngest leaves of mungbean plants in the treatments containing 0.63 μM Ce displayed symptoms of manganese (Mn) deficiency. These leaves contained deficient Mn concentrations (5 mg/kg). Tissue concentrations of other nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in corn. Roots of both species accumulated m...

Rare earth elements and plant growth: III. Responses of corn and mungbean to low concentrations of cerium in dilute, continuously flowing nutrient solutions.

Abstract Corn (Zea mays cv. Hycorn 82) and mungbean (Vigna radiata cv. Berken) plants were grown for 16 d in dilute nutrient solutions containing constant cerium (Ce) concentrations from 0 to 1.31 μM. Corn root growth was increased approx. 2 fold at Ce concentrations 0.63 μM. However, the total dry matter production of corn was not significantly increased by Ce addition. With mungbean, the addition of as little as 0.19 μM Ce to the nutrient solution caused significant reductions in the dry weight of root (26%), shoot (48%) and total plant (44%). The youngest leaves of mungbean plants in the treatments containing 0.63 μM Ce displayed symptoms of manganese (Mn) deficiency. These leaves contained deficient Mn concentrations (5 mg/kg). Tissue concentrations of other nutrients in mungbean and all essential elements in corn were within ranges where healthy growth would be expected. The concentrations of Ce measured in the roots and shoots of mungbean were higher than in corn. Roots of both species accumulated much higher concentrations of Ce than the shoots. Cerium accumulated in the oldest leaves of both plant species. These patterns of distribution were similar to those reported previously for lanthanum.

Root Growth and Distribution are Affected by Corn‐Soybean Cropping Sequence

AbstractCorn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yield better when grown in rotation than when grown in monoculture, even under high inputs. The explanation for this yield increase due to rotation is not yet known. The objective of this study was to evaluate the effect of cropping sequence on seasonal root development of corn and soybean. We hypothesized that there would be more roots on rotated crops than on crops held in a continuous monoculture. The research was conducted in 1991 and 1992 at the Univ. of Minnesota Southwest Experiment Station on a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll). Destructive root sampling via soil cores was performed at the seedling and flowering stages of both crops. Nondestructive root monitoring was performed weekly and recorded on video cassette tapes via an agricultural research video camera inserted into minirhizotron tubes that had been placed into the soil beneath crop rows. Our hypothesis that there would be more roots on first‐year corn than continuous corn was generally supported. Minirhizotron monitoring suggested that corn grown in rotation had greater root length density than continuous corn, with the exception of the top 12.5 cm, where continuous corn had greater root length density early in the season. Soil cores confirmed 22% more seedling roots in the top 12.5 cm on continuous corn. Our hypothesis that there would be more roots on first‐year soybean than continuous soybean was generally not supported. Minirhizotron monitoring indicated that when there were differences, continuous soybean had more roots than rotated soybean, with the single exception of depths of 37.5 to 50 cm, where rotated soybean had more than twice as many roots at flowering in 1992. Root length density data obtained from soil cores also indicated that rotated soybean had approximately twice as many roots at depths of 36 and 48 cm at flowering. Growth and distribution of both corn and soybean roots were thus affected by cropping sequence. Fewer roots in continuous corn may have been the result of autotoxins from decomposing roots of the previous corn crop. We do not have an explanation for increased soybean roots under monoculture.

Residual effects of slit tillage and subsoiling in a hardpan soil

Subsoiling and slit tillage can increase root growth through subsurface hardpans. In-row subsoiling fractures a section of the pan below the row. Slit tillage cuts a 3-mm-wide slit through the pan with a thin blade mounted on a shallow subsoil shank. Subsoiling is usually repeated annually. Slit tillage has been reported as an alternative to subsoiling that does not need to be repeated annually. This study was conducted to determine the longevity of the effects of tillage on a fine loamy Acrisol at Florence, South Carolina, USA. Corn ( Zea mays) root growth, yield, and soil cone index were measured for 3 years in plots that had been slit tilled, in-row subsoiled, or no-tilled for 4 years immediately prior to the study. During the study, no plots were tilled. Three-year average corn yields were 5.08 Mg ha −1 for residual slit-tilled treatments, 5.34 Mg ha −1 for residual subsoiled treatments, and 5.07 Mg ha −1 for the no-tilled treatments. Three-year mean profile cone indices were 2.53 MPa for residual slittilled treatments, 2.51 MPa for residual subsoiled treatments and 2.61 MPa for no-tilled treatments. Only 10% of the slits could be found 3 years after tillage. The lack of persistence of the slits was a result of either slit infilling with sand from the Ap horizon or collapse of the slit walls. Roots grew to a depth of at least 0.95 m in all treatments. Root growth was not correlated with yield. In this soil, residual subsoiled treatments gave higher yields than no-tillage treatments, but residual slit tillage did not. If deep tillage is not performed annually, subsoiling would be better than not tilling, but slit tillage would not.

Residual Effects of Deep Tillage vs. No-Till on Corn Root Growth and Grain Yield

Tillage pans occur in many coarse-textured soils and must be ripped by a form of deep tillage to maximize yields. This study compared the longevity of slits produced by subsoiling and slit-till (both to 16 in.) to a no-till treatment, and related slit longevity to corn (Zeu mays L.) grain yield and root development. The soil was a Typic Kandiudult with a tillage pan. Both deep tillage treatments were last performed in 1989; this study was conducted from 1990 through 1992. Roots were examined at tasselling each year, and in 1992 thin sections were examined to determine the effects of the tillage slits on root penetration. Corn grain yields were not significantly different among the three tillage treatments in any of the 3 yr. Concentrations of roots in soil profiles did not differ significantly among treatments and roots extended to depths > 40 in. Root observations indicated that the tillage slits affected root development 2 yr after tillage was performed. Residual effects of both subsoiling and slit-tillage on root growth could be seen for up to 2 yr after tillage was imposed, but the effects were gone by the third year. The residual effects of tillage did not affect yield in any year. Research Question Deep tillage methods are the best management practices to use to break tillage pans and deepen root development. While annual subsoiling is recommended, some growers are concerned that such frequent deep tillage is harmful because it brings acidic soil material to the surface, and in the long run may simply cause compact layers to form deeper in the soil. Slit-till is another deep tillage method that cuts a very thin slit in the pan layer. We investigated how long the slits made by the subsoiler and slit-till implements persist in the soil and affect corn root growth and yield over a 3 yr period. Literature Summary Numerous studies have shown that annual subsoiling will increase the yields of corn, tobacco, soybeans, and other crops in soils with tillage pans. The yield increases vary with rainfall, and on sandy soils are greatest during the dry years. Little work has been done to show whether deep tillage must be done annually in order to increase yield, and virtually no work has been done to examine whether slit-tillage works best when done every year. In addition, no work has shown that subsoiling is actually harmful. Study Description We studied a single field that had been deep-tilled for 3 yr prior to our experiment. The tillage treatments that were imposed prior to our study included: subsoiling to 16 in. below the row each year, slit-tilling to 16 in. below the row each year, and no-till. Corn was planted using a notill system for the 3 yr of this study, such that no deep tillage was performed in any of our plots. Root distribution was measured in each treatment at tasselling each year, and soil core samples were collected to assess compaction. Corn grain yields were determined each year as. well. Applied Questions Do the slits formed by subsoilers or slit-till implements persist for more than one growing season? The slits formed by these tillage implements could be seen for up to 2 yr after the tillage treatments were imposed. They also had roots growing in them during this period. By the third year, the slits were difficult to find, and they appeared to have only a small affect on root growth. The tillage pan appeared to have reformed by the third year. How do the residual slits formed by tillage one, two, and three years earlier affect corn grain yield? Corn grain yields were not significantly different among the tillage treatments in any of the 3 yr studied. We interpreted this to mean that the deep tillage slits collapse or fill-in within a year of formation, and don't influence root development to the same degree as freshly made slits do. Using deep tillage every year appears to be the best way to ensure that it will increase yields on soils containing tillage pans.

Root Distribution of Corn: The Effect of Nitrogen Fertilization

AbstractRoot growth and development can affect N uptake. In turn, N additions may affect corn (Zea mays L.) root growth. Prolific (multiple ear) hybrids may need a more active root system to satisfy ear demand. To determine the extent of the effect of N fertilization on root growth in the field, three corn hybrids (Pioneer 3320, and prolific hybrids I202×Mol7 and I117×B73) were grown under fertilizer application rates of 56, 140, and 224 kg N ha−1 to determine (i) whether application of N fertilizer stimulated root growth of corn in the zone of application in the field 20 d before silking, at silking, and at physiological maturity and (ii) whether prolific hybrids have enhanced root development before silking compared with nonprolific hybrids. All three hybrids were grown at a uniformly low plant‐population density. Root length density to a depth of 60 cm, averaged over hybrids, was 1302, 2238, and 1184 m plant−1 in 1987, and 2195, 2833, and 3317 m plant−1 in 1988 for the three sampling dates. There were few genotypic differences in root length density. Root weight averaged over hybrids was 20.4, 40.5, and 21.5 g plant−1 in 1987, and 44.6, 61.7, and 58.9 g plant−1 in 1988 for the three sampling times, respectively. Root weight at harvest declined as N application increased, but increased in response to N at two earlier sampling times. The second year of the study, when rainfall was more plentiful than in the first year, root growth continued after silking for all hybrids. This coincided with higher yields. The data suggest that N stimulated root length in the area of application, without affecting total root length.

Comparison of Bioassay Techniques for Detecting Imazaquin in Soil

Three corn root bioassays were evaluated for detecting imazaquin in soil. Two techniques, one which utilized a cone-shaped tube as the growth container and another, a petri dish, were compared to a method that utilized a thin layer of soil between two 20 by 20 cm glass plates. Corn root growth responded logarithmically to imazaquin regardless of bioassay method. Corn was most sensitive to low imazaquin concentrations when grown using the glass plate apparatus. At a low concentration (0.5 ng/g) of imazaquin, corn root length was reduced 6% using the cone-tube, 2% using the petri dish, and 24% using the glass plate method. In contrast, the cone-tube method provided a better measure of high imazaquin concentration (200 ng/g) than the other methods.

Persistence of Preemergence Applications of Chlorsulfuron, Metsulfuron, Triasulfuron, and Tribenuron in Three Soils in Greece

A pot bioassay, based on root growth of pregerminated corn, was used to evaluate factors influencing field persistence of chlorsulfuron, metsulfuron, triasulfuron, and tribenuron, which were applied preemergence at 0, 10, 20, and 40 g ai ha−1to wheat grown in three soils that differed in texture (sandy loam, sandy clay loam, and silty clay loam) and pH (7.9, 4.7, and 7.6). Residual activity and leaching of all herbicides in all soils increased with increasing rate of application, with the exception of tribenuron which showed practically no residual activity and leaching in sandy clay loam soil. Sunflower sown 4 mo after tribenuron application in all soils was not injured by any rate used but was significantly affected by the other herbicides. Lentil and sugarbeet also were affected by all herbicides in all soils. These three crops sown 8 mo after herbicide application were not affected by any herbicide used in the sandy clay loam soil but were injured by chlorsulfuron, triasulfuron, and metsulfuron in the sandy loam soil. Only lentil and sugarbeet were injured by chlorsulfuron in the silty clay loam soil.

Effects and Absorption of Sethoxydim on Excised Root Tips of Corn ( Zea mays) and Pea (Pisum sativum)

The mechanism of selective herbicidal action of sethoxydim was investigated by using cultured root tips of corn and pea. Sethoxydim inhibited the growth of susceptible corn root at concentrations of 3 nᴍ and above, but did not affect that of pea at 0.1 mᴍ. Meristematic cells in cultured roots were arrested at the G1 and G2 stages of the cell division cycle by sucrose starvation, and resumed growth and cell division (proliferation) upon sucrose addition. Corn root growth was not inhibited by sethoxydim even at 0.01 mᴍ when the roots were arrested by sucrose starvation. Corn roots that resumed growth upon sucrose provision were more sensitive to sethoxydim than those kept in constant growth condition. Better absorption of [14C]sethoxydim into the meristematic region of corn roots was observed when cells were in the proliferative condition, which was not observed when cells were arrested by sucrose starvation. No stronger uptake of the herbicide was observed into pea meristems in either growth condition. In the cell cycle study, stronger absorption of [14C]sethoxydim into the corn root meristem took place at a certain limited period prior to the S (DNA synthesis) stage. The physiological effects and the better absorption of sethoxydim clearly depended on cell cycle progression of the corn root meristem, while fatty acid synthesis, as well as its inhibition by sethoxydim, was neither associated with cell cycle progression nor with stronger absorption of the herbicide. The selective herbicidal action of sethoxydim may be caused by interference with selected stages (G1 and/or the transition step between G1 and S stages) of the cell division cycle, where affinity sites for the herbicide might be expressed.

Effects and Absorption of Sethoxydim in Cell Cycle Progression of Corn (Zea mays) and Pea (Pisum sativum)

The mechanisms of selective herbicidal action of sethoxydim were investigated by using cultured root tips of corn (Zea mays L. cv Goldencrossbantam) and pea (Pisum sativum L. cv Alaska). Meristematic cells in the cultured roots were arrested in G(1) and G(2) of the cell division cycle by sucrose starvation and resumed growth and cell division (proliferation) when sucrose was provided. Corn root growth after sucrose addition was inhibited by sethoxydim at concentrations of 0.01 micromolar and greater when roots were treated in the presence of sucrose but was not inhibited at 10 micromolar sethoxydim when they were treated during sucrose starvation. Greater absorption of [(14)C]sethoxydim into the meristematic region of corn roots was observed when cells were in proliferative condition but not when they were arrested by sucrose starvation, whereas no greater absorption of the herbicide into pea meristems was observed in either growth condition. In the cell cycle study, greater absorption of [(14)C]sethoxydim into the corn root meristem was observed at a certain limited time before S (DNA synthesis) stage. The physiological effects and the greater absorption of sethoxydim clearly depended on cell cycle progression of corn root meristem, whereas fatty acid synthesis, as well as its inhibition by sethoxydim, was not associated with either cell cycle progression or greater absorption of the herbicide.

Growth and gravitropism of corn roots in solution

ABSTRACTGrowth and early gravitropic responses of corn roots in solution have been studied using time‐lapse photography. Aeration was required for both root growth and gravitropism. The optimum pH for gravitropism was in the range 5 to 6. The bending response seemed to be greater for roots in non‐buffered solution than in buffered solution. Fastest growth and maximum curvature occurred with about 0.2 mol m−3 Ca2+. Under some conditions, the gravitropic response started with apparently negligible time delay after the start of the gravitropic stimulus. This may denote graviperception in or near the elongation zone itself. This mechanism for early but relatively weak gravitropism may help to explain a variety of gravitropic responses such as the ‘early wrong way’ curvature, and the behaviour of roots whose columella cells lack amyloplasts. More rapid bending appears to start at about 20 min, which is consistent with observations on roots in humid air and with the accepted statolith model of perception in the root cap.

Effect of Low Root Medium pH on Net Proton Release, Root Respiration, and Root Growth of Corn (Zea mays L.) and Broad Bean (Vicia faba L.)

The effect of low pH on net H(+) release and root growth of corn (Zea mays L.) and broad bean (Vicia faba L.) seedlings was investigated in short-term experiments at constant pH. Broad bean was more sensitive to low pH than corn: the critical values (pH values below which net H(+) release and root growth ceased) were pH 4.00 (broad bean) and pH 3.50 (corn) at 1 millimolar Ca(2+). Both proton release and root growth were progressively inhibited as the medium pH declined. Additional Ca(2+) in the root medium helped to overcome the limitations of low pH for net H(+) release and root growth. Potassium (for corn) and abscisic acid (for broad bean) increased both net H(+) release and root growth rate at the critical pH value. It is concluded that poor root growth at low pH is caused by a lack of net H(+) release that may decrease cytoplasmic pH values. Inhibited net H(+) release at high external H(+) activity is not due to a shortage of energy supply to the H(+) ATPase. Instead, a displacement of Ca(2+) by H(+) at the external side of the plasmalemma may enhance reentry of H(+) into root cells.

Mode of action of the dichloroacetamide antidote BAS 145-138 in corn: I. Growth responses and fate of metazachlor

The effect of BAS 145-138 (BAS) on metazachlor injury to corn and on the fate of [ 14C]metazachlor in corn seedlings was investigated. Corn shoot and root growth were inhibited by metazachlor. The antidote, BAS, increased corn shoot and root tolerance to metazachlor 10.7- and 7.6-fold, respectively. The antidotal activities of BAS and dichlormid were similar. Corn seedlings grown in soil treated with [ 14C]metazachlor ± BAS were dissected at two growth stages prior to emergence and one growth stage immediately after emergence. Parent [ 14C]metazachlor was present as <6% of the total radioactivity with an estimated tissue concentration of <1 μ M in all tissues except the pericarp. This suggests that metazachlor was metabolized rapidly in both antidoted and control plants and that a very low concentration of metazachlor is required for phytotoxicity. BAS treatment reduced the concentration of parent metazachlor in the developing leaves by 82–84%. BAS treatment had three effects that contributed to the reduced amount of parent [ 14C]metazachlor in the developing leaves: ( i) shoot absorption of [ 14C]metazachlor was slightly reduced by antidote treatment; ( ii) the mobility of 14C was reduced in antidoted seedlings, as indicated by the 63–86% decrease of total 14C reaching the developing leaves; ( iii) metabolism of metazachlor in growing tissues may have been stimulated by BAS, as suggested by the lower percentage of 14C present as parent metazachlor. The coleoptile plays a critical role in corn shoot tolerance to metazachlor, since more metazachlor is absorbed through the coleoptile than through the mesocotyl and corn is more sensitive to metazachlor absorbed through the coleoptile than the mesocotyl. Reduced absorption and movement of metazachlor through the coleoptile apparently contribute to antidote activity. Results are consistent with the hypothesis that BAS protects corn from metazachlor injury by reducing levels of parent metazachlor present in sensitive and rapidly growing tissues such as the developing leaves.

Effect of Injected Liquid Beef Manure on Soil Chemical Properties and Corn Root Distribution

Concentrated bands of liquid manure resulting from knife injection may be responsible for documented corn (Zea mays L.) production problems including uneven corn growth, plant yellowing, and lack of corn roots in the manure zone. Soil injected with liquid beef manure was incubated to determine effects on soil chemical properties, soil atmosphere composition, and corn root growth and distribution in or near the manure zone. An equivalent field injection rate of 3000 gal manure/acre was introduced into a 2.5 in. diameter circular band in boxes filled with Derinda silt loam (fine, mixed, mesic Typic Hapludalf) soil. Corn roots did not grow in the manure zone for 26 d after manure application. Chemical transformations found within and at 1.5 in. (from the manure center) below and beside the manure zone indicated possible toxic conditions to root growth. These included: reducing conditions, as indicated by low Eh, high moisture content, and low O2 concentration in the soil atmosphere (plus the presence of CH4) for 28 d after application; NH3 toxicity, as indicated by high concentrations of NH4−N and high pH for 21 d; and accumulation of high concentrations of NO2−N from 14 to 35 d after application. Only limited effects on soil chemical properties and root growth were found beyond 1.5 in. from the center of the manure zone. These results provide plausible explanations for corn growth problems associated with knife injected liquid manure.