Dryland corn response to tillage and nitrogen fertilization. II. P,K, CA,MG

Abstract

Nitrogen fertilization and tillage practices may influence the availability and uptake of essential plant nutrients other than N. This study was conducted to assess the interactive effects of N rate and timing and tillage practices on uptake and concentration of P, K, Ca and Mg in corn grown under dryland conditions. Potassium accumulations in no till (NT) soils were greater than in conventional till (CT) near the surface and lower than CT in the subsoil. Phosphorus and Ca levels decreased with soil depth, while Mg tended to accumulate in the subsoil. Phosphorus uptake and concentration of 5‐leaf stage corn was increased as tillage intensity decreased. Nitrogen rate at planting increased 5‐leaf P uptake but reduced P concentration; however, by silking no effect of tillage or N fertilization practice on ear leaf P concentration was obtained. Increases in 5‐leaf corn K uptake and concentration as tillage intensity decreased may have reduced Mg and Ca concentrations via cation antagonism. Ear leaf Mg and Ca concentrations were increased by N rate, probably as a result of solubilization of Ca and Mg and improved crop growth. Distribution of essential elements in the soil due to tillage in combination with varying N fertilization practices can influence temporal nutrient uptake, thereby altering plant nutrient diagnosis.     

Mineral uptake and growth of sorghum colonized with VA mycorrhiza at varied soil phosphorus levels

Mineral nutrient uptake can be enhanced in plants inoculated with vesicular‐arbuscular mycorrhizal fungi (VAMF). The effects of the VAMF Glomus fasciculatum on uptake of P and other mineral nutrients in sorghum [Sorghum bicolor (L.) Moench] were determined in greenhouse experiments for plants grown on a low P (3.6 mg kg^‐1) soil (Typic Argiudolls) with P added at 0, 12.5, 25.0, and 37.5 mg kg^‐1 soil. Enhancements of growth and mineral nutrient uptake because of the VAMF association decreased as soil applications of P increased above 12.5 nig kg^‐1 soil. Root colonization with VAMF without added soil P resulted in increased dry matter yield equivalent to 12.5 mg P kg^‐1 soil (25 kg P ha^‐1). Total root length colonized with VAMF decreased as soil P level increased. Regardless of P added to the soil, mycorrhizal plants had higher leaf P concentrations and contents than did nonmycorrhizal plants. Enhanced contents, but not necessarily concentrations, of the other mineral nutrients were noted in shoots of mycorrhizal compared to nonmycorrhizal plants. Mycorrhizal plants had enhanced shoot contents of P, K, Zn, and Cu which could not be accounted for by increased growth. The VAMF associations with sorghum roots enhanced mineral nutrient uptake when P was sufficiently low in the soil.     

Yield response of corn to lime and urea application on an acidic tropical soil

Abstract

The effects of liming (7 500 kg CaCO₃/ha) and rate of urea application (0,50,100, and 200 kg N/ha) and its placement at the surface or at 5 cm depth on grain yield and nutrient uptake by corn grown on an acidic tropical soil (Fluventic Eutropept) were studied. Liming significantly increased grain yield, N uptake, and P and K uptake although Ca and Mg uptake, generally, were unaffected. Sub‐surface application of urea increased N uptake only. Yield response to applied N was observed up to 50 kg N/ha when limed but at all rates in the absence of liming. It therefore, reduced the fertilizer N requirement for optimum grain yield. Liming the acidic soil also reduced exchangeable Al but increased nitrification rate and available P in the soil profile (at least up to 0.6 m depth).     

Root growth,nutrient uptake and use efficiency by roots of tropical legume cover crops as influenced by phosphorus fertilization

The root is an important organ which supplies water and nutrients to growing plants. Data related to root growth and nutrient uptake by tropical legume cover crops are limited. The objective of this study was to evaluate root growth of tropical legume cover crops and nutrient uptake and use efficiency under different phosphorus (P) levels. The P levels used were 0 (low), 100 (medium) and 200 (high) mg kg^?1 of soil and 5 cover crops were evaluated. Root dry weight, maximum root length, specific root length were significantly influenced by P and cover crop treatments. Maximum values of these root growth parameters were achieved with the addition of 100 mg P kg^?1 soil. The P X cover crops interaction for all the macro and micronutrients, except manganese (Mn) was significant, indicating variation in uptake pattern of these nutrients by cover crops with the variation in P rates. Overall, uptake pattern of macronutrients was in the order of nitrogen>calcium>potassium>magnesium>phosphorus (N > Ca > K > Mg > P) and micronutrient uptake pattern was in the order of iron>manganese>zinc>copper (Fe > Mn > Zn > Cu). Cover crops which produced maximum root dry weight also accumulated higher amount of nutrients, including N compared to cover crops which produced lower root dry weight. Higher uptake of N compared to other nutrients by cover crops indicated that use of cover crops in the cropping systems can reduce loss of nitrate (NO₃^?) from soil-plant systems. Increase in root length and root dry weight with the addition of P can improve nutrient uptake from the soil and less loss of macro and micronutrients from the soil-plant systems.     

Erosional impacts on soil properties and corn yield on Alfisols in central Ohio

Accelerated soil erosion can impact upon agronomic productivity by reducing topsoil depth (TSD), decreasing plant available water capacity and creating nutrient imbalance in soil and within plant. Research information on soil‐specific cause – effect relationship is needed to develop management strategies for restoring productivity of eroded soils. Therefore, two field experiments were established on Alfisols in central Ohio to quantify erosion‐induced changes in soil properties and assess their effects on corn growth and yield. Experiment 1 involved studying the effects of past erosion on soil properties and corn yield on field runoff plots where soil was severely eroded and comparing it with that on adjacent slightly eroded soil. In addition, soil properties and corn grain yield in runoff plots were compared on side‐slopes with that on toe‐slopes or depositional sites. Experiment 2 involved relating corn growth and yield to topsoil depth on a sloping land. With recommended rates of fertilizer application, corn grain yield did not differ among erosional phases. Fertilizer application masked the adverse effects of erosion on corn yield. Corn grain yield on depositional sites was about 50 per cent more than that on side‐slope position. Corn plants on the side‐slope positions exhibited symptoms of nutrient deficiency, and the ear leaves contained significantly lower concentrations of P and Mg and higher concentrations of Mn and K than those grown on depositional sites. Corn grain yield in experiment 2 was positively correlated with the TSD. Soil in the depositional site contained significantly more sand and silt and less clay than that on the side‐slope position. There were also differences in soil properties among erosional phases. The soil organic carbon (SOC) content was 19\7 g kg⁻¹ in slightly eroded compared with 15\1 g kg⁻¹ in severely eroded sites. Aggregate stability and the mean weight diameter (MWD) were also significantly more in slightly eroded than severely eroded soils. Adverse effects of severe erosion on soil quality were related to reduction in soil water retention, and decrease in soil concentration of N and P, and increase in those of K, Ca and Mg. Severe erosion increased leaf nutrient contents of K, Mn and Fe and decreased those of Ca and Mg. Corn grain yield was positively correlated with aggregation, silt and soil N contents. It was also negatively correlated with leaf content of Fe. Copyright © 2000 John Wiley & Sons, Ltd.     

Root Growth,Nutrient Uptake,and Nutrient-Use Efficiency by Roots of Tropical Legume Cover Crops as Influenced by Phosphorus Fertilization

Roots are important organs that supply water and nutrients to growing plants. Data related to root growth and nutrient uptake by tropical legume cover crops are limited. The objective of this study was to evaluate root growth of tropical legume cover crops and nutrient uptake and use efficiency under different phosphorus (P) levels. The P levels used were 0 (low), 100 (medium), and 200 (high) mg kg^?1 of soil, and five cover crops were evaluated. Root dry weight, maximum root length, and specific root length were significantly influenced by P and cover crop treatments. Maximum values of these root growth parameters were achieved with the addition of 100 mg P kg^?1 soil. The P?×?cover crops interactions for all the macro- and micronutrients, except manganese (Mn), were significant, indicating variation in uptake pattern of these nutrients by cover crops with the variation in P rates. Overall, uptake pattern of macronutrients was in the order of nitrogen (N) > calcium (Ca) > potassium (K) > magnesium (Mg) > P and micronutrient uptake pattern was in the order of iron (Fe) > Mn > zinc (Zn) > copper (Cu). Cover crops which produced maximum root dry weight also accumulated greater amount of nutrients, including N, compared to cover crops, which produced lower root dry weight. Greater uptake of N compared to other nutrients by cover crops indicated that use of cover crops in the cropping systems could reduce loss of nitrate (NO₃ ^?) from soil–plant systems. Increase in root length and root dry weight with the addition of P can improve nutrient uptake from the soil and lessen loss of macro- and micronutrients from the soil–plant systems.     

Soil Aluminum Effects on Growth and Nutrition of Cacao

In acid soils, Al toxicity and nutrient deficiencies are main constraints for low yield of cacao (Theobroma cacao L.). A controlled growth chamber experiment was conducted to evaluate the effect of three Al saturations (0.2, 19, and 26%) adjusted by addition of dolomitic lime on growth and nutrient uptake parameters of cacao. Overall, increasing soil Al saturation decreased shoot and root dry weight, stem height, root length, relative growth rate, and net assimilation rate. However, increasing soil Al saturation increased leaf area, specific leaf area (total leaf area/total leaf dry wt), and leaf area ratio (total leaf area/shoot+root wt). Increasing soil Al saturation decreased uptake of elements. Nutrient influx (IN) and transport (TR) decreased significantly for K, Ca and Mg, and showed an increasing trend for S and P as soil Al saturation increased. However, increasing soil Al saturation significantly increased nutrient use efficiency ratio (ER, mg of shoot weight produced per mg of element in shoot) of Ca, Mg and K and decreased ER for other elements. Reduction of soil acidity constraints with addition of lime and fertilizers appear to be key factors in improving cacao yields in infertile, acidic, tropical soils.     

Soil Aluminum Effects on Growth and Nutrition of Cacao

In acid soils, Al toxicity and nutrient deficiencies are main constraints for low yield of cacao ( Theobroma cacao L.). A controlled growth chamber experiment was conducted to evaluate the effect of three Al saturations (0.2, 19, and 26%) adjusted by addition of dolomitic lime on growth and nutrient uptake parameters of cacao. Overall, increasing soil Al saturation decreased shoot and root dry weight, stem height, root length, relative growth rate, and net assimilation rate. However, increasing soil Al saturation increased leaf area, specific leaf area (total leaf area/total leaf dry wt), and leaf area ratio (total leaf area/shoot+root wt). Increasing soil Al saturation decreased uptake of elements. Nutrient influx (IN) and transport (TR) decreased significantly for K, Ca and Mg, and showed an increasing trend for S and P as soil Al saturation increased. However, increasing soil Al saturation significantly increased nutrient use efficiency ratio (ER, mg of shoot weight produced per mg of element in shoot) of Ca, Mg and K and decreased ER for other elements. Reduction of soil acidity constraints with addition of lime and fertilizers appear to be key factors in improving cacao yields in infertile, acidic, tropical soils.     

Growth and uptake rates of P,K, Ca and Mg in wheat 1

The relation between plant age and nutrient absorption properties of red winter wheat (Triticum aestivum L.) roots were investigated. Understanding the change in ion uptake parameters with increasing plant age is helpful in devising efficient fertilization systems. Such information can be used to determine the nutrient levels needed in the soil to supply nutrients rapidly enough to the root surface to minimize deficiencies. Wheat was grown for periods up to 40 days in solution culture in a controlled climate chamber. Sequential harvest and nutrient influx measurements were made. Shoot growth was exponential with time to 30 days and linear thereafter. Root dry weight increased linearly with time at a slower rate than shoot dry weight. Root length increased linearily with time. With increasing plant age there was a reduction in average P and K uptake rate while average uptake rates for Ca and Mg remained relatively unchanged. With increasing plant age, the maximum influx, I_max. for P and Mg remained constant, but for K and Ca, there was a decrease. For the Michael is constant, Km, no change was observed for P, an increase occurred for K, and a decrease for Ca and Mg, as the wheat plant grew from 5 to 40 days.     

启动磷肥不同施用方式对玉米养分吸收及生长和产量的影响

为了探索启动磷肥不同施用方式对玉米生长和产量的影响,设置启动磷肥大田滴施(T1)、穴施(T2)和不施启动磷肥(CK)3个施肥处理,其中启动肥磷肥用量为P₂O₅ 30 kg·hm^-2,探究启动磷肥不同施用方式对玉米生长、养分分配和产量构成的影响;设置启动磷肥根箱土壤滴施(P1)、穴施(P2)和不施启动肥(CF)3个处理,其中启动肥磷肥用量为P₂O₅ 0.2 g·kg^-1土,探究启动磷肥施用后土壤中磷素的空间分布与迁移效果。结果表明,玉米四叶期和六叶期,T1和T2处理均显著增加了苗期玉米总根长,根表面积,地上、地下部生物量和N、P、K养分积累量。在六叶期,T1和T2处理玉米总根长较CK分别增加了21.10%和30.35%,根系表面积分别增加了23.48%和29.20%,地上和地下部生物量分别增加了31.24%和52.38%、33.61%和57.81%。与CK相比,T1和T2处理促进了玉米N、P、K养分的积累,同时促进了养分由营养器官向生殖器官的转移。在玉米吐丝期至成熟期,T1和T2处理玉米N、P、K养分转移量较CK分别增加了29.75和44.73 kg·hm^-2、10.76和14.65 kg·hm^-2、2.20和24.67 kg·hm^-2。玉米穗长、行粒数、产量和磷肥偏生产力均表现为T2>T1>CK,玉米穗秃尖长度表现为T2相似文献   

Response of corn to NPK fertilization grown in a Latosol in South Sulawesi,Indonesia

Abstract

Corn (Zea mays L.) is next to rice as an important food crop grown in South Sulawesi, Indonesia. However, yields obtained by farmers are rather low, around 0.6 to 1.0 ton/ha. Efforts to increase yield have been tried through the application of NPK fertilizers. A study was conducted to determine the effects of N, P and K application on corn yield and what soil constrains, in terms of nutrient elements in the corn plants, exist in the latsols found at Desa Tokka, Sinjai, and South Sulawesi. It was found that application of K significantly increased the growth and corn grain yields on the latosols at Sinjai. Without K, grain yield and the K content in the ear leaf were low. The correlation between grain yield and rate of K shows that an application of 72 kg K₂O/ha together with 90 kg N and 80 kg P₂O₅ per ha produce the best yield of 3.6 tons/ha. The K content in the ear leaf of 1.8% was related to this maximum yield.     

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.     

Availability in Soil and Acquisition by Plants as the Basis for Phosphorus and Potassium supply to Plants

This report summarizes research aimed at describing the processes and quantifying the factors affecting transfer of P and K from soil into plants. Soil properties related to availability and plant properties reflecting nutrient acquisition were determined. Their interactions in the rhizosphere and their importance for nutrient supply of plants were studied by a combination of measurements and calculations using a simulation model. Phosphorus and potassium uptake by roots decreased P and K concentration at the root surface and caused characteristic depletion profiles in the adjacent soil. The shape of the profiles depended on the effective diffusion coefficient, the concentration of the nutrient in soil, morphological properties of the roots and on influx into roots. The degree of depletion at the root surface indicated the proportion of the nutrient potentially available in the soil. The shape of the depletion profiles reflected the amount of the nutrient taken up by a root section. The parameters found to describe nutrient acquisition are (i) influx per unit root length, (ii) root length per unit shoot weight (root/shoot ratio), and (iii) the period of time a root section absorbs nutrients. Plant species differed considerably in these properties. In order to integrate the processes involved and to evaluate the importance of individual factors, the Claassen-Barber model was used. Depletion profiles and nutrient uptake calculated with this model were in good agreement with measured values in a number of cases. However, at low P supply, plants absorbed substantially more P than the model predicted. This indicates that influx in this case is supported by mechanisms not properly taken into account yet. Influx per unit root length depends on morphological properties of and nutrient mobilization by roots. Root hairs increase root surface area per unit root length. In addition, because of their small diameter and geometric arrangement in soil, root hairs are specially apt to gain from diffusion when concentration gradients are small. This applies even more to VA-mycorrhizae. Their hyphae are longer and thinner than root hairs and can thus deplete larger volumes of soil per unit root length. Root-induced changes of soil pH increased the size of P depletion profiles, indicating that roots can mobilize soil P by this mechanism. Both acid and alkaline phosphatase enzyme activities were found to be markedly increased at the soil-root interface suggesting that soil organic P may contribute to the P supply of plants.     

Irrigation water salinity affects soil nutrient distribution,root density,and leaf nutrient levels of citrus under drip fertigation 1

The purpose of this study was to determine the effects of irrigation water salinity on soil nutrient distribution, citrus leaf nutrition and root density. Irrigation water, salinized to an EC of about 0.3,1.6, or 2.5 dS/m using a 3:1 ratio of NaCl:CaCl₂ plus uniform weekly applications of liquid fertilizer, was applied through a drip system. Soil samples were taken at depths of 0–15 and 15–30 cm, both directly under the drippers and 45 cm outward from the drippers, near 8‐year old ‘Valencia’ orange trees on either Carrizo citrange or Sour orange rootstocks growing in a Candler fine sand in lysimeter tanks.

In both undisturbed and uniformly mixed soil profiles, soil pH and concentrations of Na, Ca, and P were higher under the dripper than 45 cm outward from the dripper at both depths regardless of salinity level. Soil N and Cl tended to be higher outward from the drippers than near the drippers, except in undisturbed soil at the 0–15 cm depth. Increasing salinity levels in the mixed soil profile not only increased soil EC, Na, Cl, and Ca, but also increased the concentration of P and decreased the concentration of Mg.

Root density of both rootstocks were increased by high salinity. Root densities and organic matter percentages were higher in soil sampled under drippers than that sampled outward from drippers. Leaf nutritional values and responses to salinity were dependent on rootstock as trees on sour orange had higher K and Ca, but lower Mg and Cl than trees on Carrizo. Although there were no nutrient deficiencies, K of trees on Carrizo citrange and Mg of trees on sour orange were rereduced by high salinity. An increase in leaf Ca concentrations when irrigated with salinized irrigation water likely minimized the effects of salt stress.     

Root growth,nutrient uptake and yield of soybean cultivars grown in the field

Abstract

Soybean (Glycine max L. Merr.) cultivars differ in their root morphology and their nutrient uptake capabilities. The relation between root growth, P and K uptake, and grain yield was investigated using eight cultivars grown in the field on Raub (Aquic Argiudoll) silt loam which received 49 kg P/ha and 93 kg K/ha. Hobbit (maturity group III, determinate) was among the highest in grain yield, P and K uptakes, and root system length. However, this cultivar was intermediate in its relative efficiency to utilize P and K to produce grain yield; among the most efficient cultivars were Asgrow 3127 (maturity group II) and Williams‐79 (maturity group III). The hay cultivar, Wilson‐6, was the least efficient. It was concluded that even though grain yield was correlated with nutrient uptake, selection for higher yields was not necessarily a selection for higher efficiency in utilization of fertilizer for grain production.     

Subsoil compaction effects on crops in Punjab, Pakistan:II. Root growth and nutrient uptake of wheat and sorghum

Crop yields can be reduced by soil compaction due to increased resistance to root growth, and decrease in water and nutrient use efficiencies. A field experiment was conducted during 1997–1998 and 1998–1999 on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) to study subsoil compaction effects on root growth, nutrient uptake and chemical composition of wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench). Soil compaction was artificially created once at the start of the study. The 0.00–0.15 m soil was manually removed with a spade. The exposed layer was compacted with a mechanical compactor from 1.65 Mg m⁻³ (control plot) to a bulk density of 1.93 Mg m⁻³ (compacted plot). The topsoil was then again replaced above the compacted subsoil and levelled. Both compacted and control plots were hoed manually and levelled. Root length density, measured at flowering stage, decreased markedly with compaction during 1997–1998 but there was little effect during 1998–1999. The reduction in nutrient uptake by wheat due to compaction of the subsoil was 12–35% for N, 17–27% for P and up to 24% for K. The reduction in nutrient uptake in sorghum due to subsoil compaction was 23% for N, 16% for P, and 12% for K. Subsoil compaction increased N content in wheat grains in 1997–1998, but there was no effect on P and K contents of grains and N and P content of wheat straw or sorghum stover. During 1997–1998, K content of wheat straw was statistically higher in control treatment compared with compacted treatment. In 1998, P-content of sorghum leaves was higher in compacted treatment than uncompacted control. Root length density of wheat below 0.15 m depth was significantly reduced and was significantly and negatively correlated with soil bulk density. Therefore, appropriate measures such as periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction.     

Availability of phosphate and potassium as the result of interactions between root and soil in the rhizosphere

A number of findings are summarized in order to show the significance of individual plant properties and soil factors on the availability of phosphate and potassium to plants growing in soil. The flux of a nutrient into a given plant root depends directly on the concentration of the nutrient in the adjacent solution. In nutrient solution, P and K influx follows Michaelis-Menten kinetics. Almost maximum rates of influx have been observed in the range of soil solution concentrations usually found in German arable soils. Roots exhaust P and K from solutions to about 0.2 μmol P and 1 μmol K 1^?1 if not replenished. At the root surface P and K concentrations in soil decrease rapidly within one day; small changes occur after this period. Initially, the extent of the depletion zone is very small but it extends radially with time. After the initial phase therefore, P and K supply to the plant depends on transport from more remote parts of the soil and also on release from undissolved sources. The degree of depletion and the extent of the depletion zone are related to the diffusion coefficient; they decrease with increasing clay content of soil. Root hairs penetrate the soil and extend the volume of soil supplying nutrients to a unit of root. P and K influx therefore increase with the length of root hairs. Proton release of roots mobilize P and K in soil. This is clearly detected by the HCl-soluble P and K fractions within 2 mm of the root surface. The activity of acid and alkaline phosphatases strongly increase in the soil in the vicinity of the root surface of several plant species. It is supposed that organic P compounds can therefore be utilized by plants. P and K influx per unit of root length and root length per unit of shoot weight differed widely between species. The product of these two parameters however was closely related to the P and K concentration of the shoots. Calculations from a mathematical model were in good agreement with measured K depletion profiles and K uptake by plants. It is therefore concluded that the main factors influencing the P and K availability of plants growing in soil have been accounted for in the mathematical model and that the parameters have been accurately measured.     

Modeling approach to nitrogen uptake by field‐grown corn

Although the plant root system is one of the most important plant parameters affecting nutrient uptake by plants, root studies in field experiments are rarely conducted in plant nutrition and fertility studies. Since collection of root samples and measurements are difficult and time consuming, they are not considered as a routine plant parameter. Therefore, the effect and importance of the corn root system on plant nitrogen (N) uptake and grain yield was studied under field conditions in Adana, Turkey. Nitrogen was applied at rates of 200, 250, 300, and 350 kg N ha^‐1 as urea in a randomized complete block design experiment with three replications. During course of the experiment, soil, plant, root, and grain samples were collected and prepared for chemical analysis. Nitrogen uptake by plants was predicted using a COMP8 mathematical computer model and compared to actual plant uptake. Grain yield and leaf N content increased with increasing N rates, but root length did not change statistically. Predicted N uptake increased with added N, but was much smaller than observed N uptake under field conditions. Consequently, additional soil and plant parameters should be considered in nutrient uptake models to make the prediction more sensitive.     

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。     

不同灌溉策略下冬小麦根系的分布与水分养分的空间有效性

通过田间试验研究了少量多次和少次多量的灌溉方式下冬小麦根系的分布与水分养分的空间有效性。结果表明 :少量多次的灌溉方式降低了冬小麦返青后表层根系的生长 ,减少了拔节后该层根系的衰退。在少次多量的灌溉方式下返青期不灌水促进了表层根系的生长 ,然而拔节后该层根系衰退较多 ,但中层 ( 3 0～ 60cm)根系生长高于少量多次的灌溉方式。不同灌溉策略下根系分布的差异并不影响冬小麦对土壤水分和养分的吸收 ,由于播前土体内蓄水不足 ,三种灌溉方式下 0～ 90cm土壤可用水在收获后均消耗殆尽。灌溉促进了表层硝态氮的吸收和向下迁移 ,但两种灌溉方式下硝态氮在土体内的迁移均未超出 60cm土体 ,仍在根层之内。而不同的灌溉方式对冬小麦全生育期内土体速效磷钾的分布没有影响。扬花前两种灌溉方式下冬小麦的生长发育和养分的吸收并无差异 ,扬花后少次多量的灌溉方式由于水分供应不足 ,影响了灌浆 ,降低了千粒重 ,进而影响了产量 ,同时土壤水分缺乏也减少了该时期养分的吸收。而在少量多次的灌溉方式下 ,扬花后灌水不仅可以促进冬小麦灌浆 ,提高千粒重 ,而且增加了对养分的吸收。