Comparison of tomato root distributions by minirhizotron and destructive sampling

Calibration of minirhizotron data against root length density (RLD) was carried out in a field trial where three drip irrigation depths: surface (R0) and subsurface, 0.20 m (RI) and 0.40 m depth (RII) and two processing tomato cultivars: `Brigade' (CI) and `H3044' (CII) were imposed. For each treatment three minirhizotron tubes were located at 10, 37.5 and 75 cm of the way from one plant row to the next. Roots intersecting the minirizotrons walls were expressed as root length intensity (L _a) and number of roots per unit of minirhizotron wall area (N _ra). Root length density (RLD) was calculated from core samples taken for each minirhizotron tube at two locations: near the top of the minirhizotron (BI) and 15 cm apart from it, facing the minirhizotron wall opposite the plant row (BII). Minirhizotron data were regressed against RLD obtained at BI and BII and with their respective means. The results show that for all the situations studied, better correlations were obtained when RLD was regressed with L _a than with N _ra. Also was evident that the relationship between L _a and RLD was strongly influenced by the location of soil coring. RLD was correlated with L _a trough linear and cubic equations, having the last ones higher determination coefficients. For instance at 10 cm from the plant row when values from the top layer (0–40 cm) were analysed separately, L _a was significantly regressed with RLD measured at BII and described by the equations: RLD = 0.5448 + 0.0071 L _a (R ² = 0.51) and RLD = 0.4823 + 0.0074L _a + 8×10^–5 L _a ² – 5×10^–7 L _a ³ (R ² = 0.61). Under the 40 cm depth the highest coefficients of determination for the linear and cubic equations were respectively 0.47 and 0.88, found when L _a was regressed with RLD measured at BI. For minirhizotrons located at 75 cm from the plant row and for location BI it was possible to analyse jointly data from all depths with coefficients of determination of 0.45 and 0.59 for the linear and cubic equations respectively.     

Development of fine and coarse roots of Thuja occidentalis `Brabant' in non-irrigated and drip irrigated field plots

Aboveground dry mass, total root dry mass and root length density of the fine roots of Thuja occidentalis `Brabant' were determined under non- and drip-irrigated field conditions. Two-dimensional diffusion parameters for dynamic root growth were estimated based on dry mass production of the fine roots and the concept of the convective-diffusion model of cylindrical root growth and proliferation. Drip irrigation increased above-ground dry mass and the shoot:root ratio compared with no irrigation. Dry mass of the coarse roots increased as well due to drip irrigation. No effect on total or fine root dry mass was found. Drip irrigation increased root length densities in the top 0.1 m but not significantly. However, drip irrigation decreased root proliferation in depth by 27%, whereas proliferation in the horizontal direction was not altered. Measured root length densities were overestimated by 6–21% by the model (0.68 < R ² < 0.92).     

The growth characteristics and yield potential of rice (Oryza sativa) under non‐flooded irrigation in arid region

The objectives of this field experiment were to study the growth characteristics and yield potential of rice plants under non‐flooded irrigation in arid area. Non‐flooded treatments included drip irrigation with plastic mulching treatments (DIs), furrow irrigation with plastic mulching treatment (FIM) and furrow irrigation with non‐mulching treatment (FIN). Conventional flooded cultivation (F) was check treatment (CK). The four drip irrigation treatments differed in the amount of water applied before and after panicle initiation. Root length density, leaf dry weight, shoot dry weight and root activity were generally higher in the non‐flood‐irrigated treatments (especially the drip‐irrigated treatments) than in the flood‐irrigated treatment at mid‐tillering. However, the growth and development of rice plants were limited after jointing in the non‐flooded irrigation treatments. Increasing the root/shoot ratio and root length density in the 20–40 cm depth and decreasing specific root length at 0–20 cm soil layer were important mechanisms for helping the rice plants to adapt to the non‐flooded environmental stresses. Finally, the grain yield in the non‐flooded irrigation treatments was lower than that in the F treatment. These low yields were mainly attributed to the low root length density at 0–20 cm depth and root activity. Generally speaking, the restricted degrees in the DIs were smaller than that in the FIM and FIN treatments. Among the DIs, both the highest grain yield (8223–8900 kg ha^?1) and the highest water use efficiency (WUE) (0.63) were observed when the soil water content was kept at ?30 kPa before panicle initiation and at ?15 kPa after panicle initiation (referred to as the DI2 treatment). The yield in the DI2 treatment was not significantly different than that in the flood‐irrigated treatment. However, WUE was 2.5 times higher in the DI2 treatment than in the F treatment. These results suggest that drip irrigation technology can be considered as a better water‐saving cultivation of rice plants in arid region.     

Effect of Irrigation Type on Inoculum Density of Macrophomina phaseolina in Melon Fields in Arizona

Charcoal rot, caused by Macrophomina phaseolina, has become increasingly problematic for melon growers using subsurface drip irrigation in Arizona; but has rarely been observed in fields with furrow irrigation. Since the relationship between increasing incidence of charcoal rot on melon and irrigation type is unknown, studies were initiated to determine the effects of edaphic factors on inoculum density. Soil samples were collected once from fields irrigated by subsurface drip, with and without plastic mulch, and by furrow at 10, 20 and 30 cm depths. Samples were analysed for percentage soil moisture, pH, salinity and inoculum density. Percentage soil moisture was significantly higher at 20 and 30 cm depths in the furrow‐irrigated field compared with the drip‐irrigated field with plastic mulch, but not in the field without plastic mulch. Average minimum and maximum temperatures and inoculum density were significantly lower at all three depths in the furrow‐irrigated field compared with both types of drip irrigation. pH was significantly higher in the furrow‐irrigated field compared with both types of drip irrigation at 20 and 30 cm depths but not at 10 cm depth. Differences in inoculum densities of M. phaseolina suggest that drip irrigation may contribute to higher disease incidences.     

Fibrous carrot root responses to irrigation and compaction of sandy and organic soils

Field experiments were performed in Southern Finland on fine sand and organic soil in 1990 and 1991 to study carrot roots. Fall ploughed land was loosened by rotary harrowing to a depth of 20 cm or compacted under moist conditions to a depth of 25–30 cm by three passes of adjacent wheel tracks with a tractor weighing 3 Mg, in April were contiguously applied across the plot before seed bed preparation. Sprinkler irrigation (30 mm) was applied to fine sand when moisture in the 0–15 cm range of soil depth was 50% of plant-available water capacity. For root sampling, polyvinyl chloride (PVC) cylinders (30 × 60 cm) were installed in the rows of experimental plots after sowing, and removed at harvest. Six carrot plants were grown in each of in these soil colums in situ in the field.Fine root length and width were quantified by image analysis. Root length density (RLD) per plant was 0.2–1.0 cm cm^-3 in the 0–30 cm range. The fibrous root system of one carrot had total root lengths of 130–150 m in loose fine sand and 180–200 m in compacted fine sand. More roots were observed in irrigated than non-irrigated soils. In the 0–50 cm range of organic soil, 230–250 m of root length were removed from loosened organic soils and 240–300 m from compacted soils. Specific root surface area (surface area divided by dry root weight) of a carrot fibrous root system averaged 1500–2000 cm² g^-1. Root length to weight ratios of 250–350 m g^-1 effectively compare with the ratios of other species.Fibrous root growth was stimulated by soil compaction or irrigation to a depth of 30 cm, in both the fine sand and organic soils, suggesting better soil water supply in compacted than in loosened soils. Soil compaction increased root diameters more in fine sand than it did in organic soil. Most of the root length in loosened soils (fine sand 90%, organic soil 80%) and compacted soils (fine sand 80%, organic soil 75%) was composed of roots with diameters of approximately 0.15 mm. With respect to dry weight, length, surface area and volume of the fibrous root system, all the measurements gave significant resposes to irrigation and soil compaction. Total root volumes in the 0–50 cm of soil were 4.3 cm³ and 9.8 cm³ in loosened fine sand and organic soils, respectively, and 6.7 cm³ and 13.4 cm³ in compacted sand and organic soils, respectively. In fine sand, irrigation increased the volume from 4.8 to 6.3 cm³.     

塑料大棚渗灌灌水下限对番茄生长和产量的影响

利用土壤水分张力计监测土壤水分吸力的变化,以灌水时30cm土层的土壤水分吸力表示渗灌灌水下限,研究灌水下限为10、16、25、40和63kPa时对塑料大棚番茄生长和产量的影响．结果表明,番茄株高、生物量分别随灌水下限的增大而减小．番茄的产量和水分利用率与灌水下限间的关系曲线为抛物线,而茎粗／株高比与灌水下限间的关系曲线为三次多项式曲线．灌水下限不同,番茄的根／冠比(R／S)动态不同,番茄根系与株冠的生长状况不同．灌水下限在25～33kPa时,番茄植株生长健壮,根冠比例协调,产量大,水分利用率高．此指标作为渗灌灌水下限,灌水时土壤水分的含量比常规灌水低,灌水次数少,有利于提高保护地番茄栽培的水分利用率和劳动生产率．     

Cultivar and planting date effects on soybean root growth

To avoid late summer drought, soybean [Gylcine max (L) Merrill] producers in many southern and border states of the USA modify their cropping systems. Options include use of unadapted cultivars and changing planting dates. Because root function is important to plant health and yield, this study was conducted to determine if planting date and soybean cultivar affect root growth and distribution. Seeds of one cultivar from each of four maturity groups (MG III, IV, V, and VI) were sown in mid-April, mid-May, and mid-June in 1992 and 1993 on a Tiptonville silt loam near Portageville, MO. Root observations were performed 30 and 60 days after emergence (DAE) using a minirhizotron system. Cultivars differed for root length density (RLD) only in the 15 to 28 cm depth in 1992 and in the 15 to 28 cm and 29 to 42 cm depths in 1993, but differences were not related to maturity classification of cultivar. Average RLD was 1.02 cm^–3 for MG III and IV cultivars and 1.21 cm cm^–3 for MG V and VI cultivars. Average RLD for the mid-June planting date was 1.65 cm cm^–3 but only 0.73 cm cm^–3 for the mid-April planting date. An increase in RLD between 30 and 60 DAE occurred at all soil depths. For both years, MG V and VI cultivars produced higher yields than the MG III cultivars. Earlier than normal planting dates inhibited early root growth, but did not reduce yield. Cultivars differed only slightly for the rooting characteristics measured in this study. These rooting characteristics may not be important criteria for cultivar selection.Abbreviations MG maturity group - VCR videocassette recorder - DAE days after emergence - RLD root length density - CRLD change in root length density Contribution from the Missouri Agric. Exp. Station Journal Series Number 12, 153Contribution from the Missouri Agric. Exp. Station Journal Series Number 12, 153     

微灌与播前深松对根际土壤酶活性和夏玉米产量的影响

为探明微灌与播前深松耕作对夏玉米根际土壤酶活性和产量的影响,以大田夏玉米为研究对象,设计微灌灌溉方式(地表滴灌、地下滴灌和微润灌)、灌水量(分别控制土壤含水量下限为田间持水率的50%、65%和80%)和深松深度(20、40、60 cm)3因素、3水平正交田间试验.结果表明: 夏玉米全生育期内,土壤过氧化氢酶和脲酶活性均呈先增加后减小趋势,磷酸酶活性则呈先减小后增加趋势.地下滴灌0~80 cm生育期平均土壤含水率比地表滴灌和微润灌高6.3%和1.8%,且显著提高土壤脲酶活性、夏玉米根系体积和产量;随着灌水量的增加,土壤磷酸酶活性呈先减小后增加趋势,脲酶活性和产量均呈先增加后减小趋势,生育期平均土壤含水率与根系体积均呈增加趋势;深松40 cm比20 cm的产量和根系体积增加量大于深松60 cm比40 cm的增加量,深松40 cm土壤酶活性较高.从提高水资源、氮肥利用率及作物产量角度考虑,该地区夏玉米种植的最优组合应为地下滴灌、灌水下限为田间持水率的65%与播前深松40 cm.     

Field observations on nitrogen catch crops

Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate.The natural logarithm of the total root length, measured in the top 40 cm, L_0–40 (km m^-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m^-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L_0–40 than N0 treatments. The decline in root length density, D (cm cm^-3), with depth, X (cm), was described with the function ln D = ln D₀ – qX, where D₀ is the value of D at zero depth and q the linear coefficient. D₀ was linearly related to L_0–40, without effect of species, time of observation or N supply. The ratio D₀/q, an estimate of the absolute root length, was 1.24 × L_0–40.Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.     

Root distribution of a Mediterranean shrubland in Portugal

The distribution of roots of an Erica (Erica scoparia and Erica lusitanica) dominated Mediterranean maquis was studied using three different approaches: root counts on trench walls (down to 120 cm), estimation of the maximum rooting depth using an allometric relationship and estimation of fine root biomass and fine root length using soil cores (down to 100 cm). Roots were classified according to diameter (fine, 1.0 mm; small, 1.1–5.0 mm; medium, 5.1–10.0 mm; coarse, >10.0 mm) and species (Erica sp., Pteridium aquilinum, Rubus ulmifolius and Ulex jussiaei). The depth corresponding to 50% of all roots (D ₅₀) was determined by fitting a new model to the cumulative root distribution. Fine roots represented 96% of root counts. Root counts of Erica represented 59%, Ulex 34%, Rubus 6% and Pteridium 1%. Overall root counts showed a D ₅₀ of 26 cm. D ₅₀ was higher for Ulex (40 cm) and Erica (22 cm), than for Pteridium (9 cm) and Rubus (3 cm). D ₅₀ for fine roots was 27 cm, for small roots 11 cm, for medium roots 6 cm and for coarse roots 4 cm. The estimated average maximum rooting depth of the 28 deepest Erica roots was 222 cm. The deepest Erica root was estimated to reach 329 cm. A total of 82% of roots growing deeper than 125 cm were not reaching more than 175 cm. The overall fine root length density ranged from 4.6 cm/cm³ at 10 cm to 0.8 cm/cm³ at 80 cm. The overall fine root biomass ranged from 7.7 mg/cm³ at 10 cm to 0.6 mg/cm³ at 40 cm. D ₅₀ for root biomass was 12 cm and D ₅₀ for root length was 14 cm. Fine root biomass was estimated as 1.6 kg/m² and the respective root length as 18.7 km/m².     

滴灌方式对‘赤霞珠’葡萄幼苗根冠功能的调控效应

研究地下穴贮滴灌(自主设计)、膜下滴灌、地表滴灌3种滴灌方式对酿酒葡萄品种‘赤霞珠’幼苗根冠功能的影响.结果表明： 膜下滴灌和地下穴贮滴灌较地表滴灌更促进植株生长,其中地下穴贮滴灌主要促进根系的生长,膜下滴灌主要促进地上部的生长;在20～60 cm土层,地下穴贮滴灌处理根表面积、根体积、根系活力和超氧化物歧化酶活性均高于地表滴灌和膜下滴灌处理,表明地下穴贮滴灌可有效促进根系下扎,提高土壤深层根系的生理活性;同一灌水周期后期地表滴灌处理较早受到干旱胁迫的影响,地下穴贮滴灌和膜下滴灌处理叶片净光合速率(P_n)和气孔导度(g_s)均高于地表滴灌处理,灌水7 d后膜下滴灌处理12:00—14:00实际光化学效率(Φ_PSⅡ)、光化学猝灭系数(q_P)低于地下穴贮滴灌处理,表明叶片荧光日进程中膜下滴灌受到的光抑制程度大于地下穴贮滴灌;对植株根冠功能的相关分析表明,有效增加20~40 cm土层根系的根量指标,保持根系生理活性在较高水平,可促进整体植株地上部生物量的增加和总生物量的积累.综合分析表明,地下穴贮滴灌较膜下滴灌、地表滴灌对植株根冠生长及功能调控有一定优势,可作为果树节水灌溉技术的潜在替代技术.     

Spatial and temporal patterns of root distribution in developing stands of four woody crop species grown with drip irrigation and fertilization

In forest trees, roots mediate such significant carbon fluxes as primary production and soil CO₂ efflux. Despite the central role of roots in these critical processes, information on root distribution during stand establishment is limited, yet must be described to accurately predict how various forest types, which are growing with a range of resource limitations, might respond to environmental change. This study reports root length density and biomass development in young stands of eastern cottonwood (Populus deltoidies Bartr.) and American sycamore (Platanus occidentalis L.) that have narrow, high resource site requirements, and compares them with sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.), which have more robust site requirements. Fine roots (<1 mm), medium roots (1 to 5 mm) and coarse roots (>5 mm) were sampled to determine spatial distribution in response to fertilizer and irrigation treatments delivered through drip irrigation tubes. Root length density and biomass were predominately controlled by stand development, depth and proximity to drip tubes. After accounting for this spatial and temporal variation, there was a significant increase in RLD with fertilization and irrigation for all genotypes. The response to fertilization was greater than that of irrigation. Both fine and coarse roots responded positively to resources delivered through the drip tube, indicating a whole-root-system response to resource enrichment and not just a feeder root response. The plastic response to drip tube water and nutrient enrichment demonstrate the capability of root systems to respond to supply heterogeneity by increasing acquisition surface. Fine-root biomass, root density and specific root length were greater for broadleaved species than pine. Roots of all genotypes explored the rooting volume within 2 years, but this occurred faster and to higher root length densities in broadleaved species, indicating they had greater initial opportunity for resource acquisition than pine. Sweetgum’s root characteristics and its response to resource availability were similar to the other broadleaved species, despite its functional resemblance to pine regarding robust site requirements. It was concluded that genotypes, irrigation and fertilization significantly influenced tree root system development, which varied spatially in response to resource-supply heterogeneity created by drip tubes. Knowledge of spatial and temporal patterns of root distribution in these stands will be used to interpret nutrient acquisition and soil respiration measurements. The US Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper. Mention of a commercial or proprietary product does not constitute endorsement or recommendation by the USDA Forest Service.     

Root distribution,standing crop biomass and belowground productivity in a semidesert in México

In a semidesert community in México (Zapotitlán de las Salinas, Puebla) the vertical distribution of roots and root biomass was estimated at 0–100 cm depth on two sampling dates, November 1995 (wet season) and January 1998 (dry season). Root productivity at 7 to 14.5 cm depth was estimated with the in-growth core technique every two months from March 1996 to February 1998. The relationship between environmental factors and seasonal root productivity was analyzed. Finally, we tested the effect of an irrigation equivalent to 20 mm of rain on root production. Seventy four percent of the total number of roots were found at 0-40 cm depth. Very fine roots (<1 mm diameter) were found throughout the soil profile (0-100 cm). In contrast, fine roots (1-3 mm diameter) were found only from 0–90 cm depth, and coarse roots (>3 mm diameter) from 0–60 cm depth. The root biomass was 971.5 g m^–2 (S.D. = 557.39), the very fine and fine roots representing 62.9% of the total. Total root productivity, as estimated with the ingrowth core technique, was 0.031 Mg ha^–1 over the dry season and 0.315 Mg ha^–1 over the wet season. Only very fine roots were obtained at all sampling dates. Rainfall was significantly correlated with very fine root production. The difference between fine root production in non-watered (0.054 g m^–2) and watered (0.429 g m^–2) treatments was significant. The last value was the same as that predicted for a rain of 20 mm, according to the exponential model describing the relation between the production of very fine roots and rainfall at the site.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Effect of crop residues on root growth and phosphorus acquisition of pearl millet in an acid sandy soil in Niger

The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha^-1 yr^–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha^-1 yr^-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha^-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg^-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg^-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha^-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm^-3) than for +CR–F (4.5 cm cm^-3) and –CR+F (4.2 cm cm^-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm^-3 (30–60 cm soil depth) to 0.2 cm cm^-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw.     

Effects of N application frequency on nitrogen uptake efficiency in Citrus trees

Two irrigation systems were used to compare nitrogen uptake efficiency in citrus trees and to evaluate the NO₃⁻ runoff in «Navelina» orange trees [Citrus sinensis (L.) Osbeck] on Carrizo citrange rootstock (Citrus sinensis × Poncirus trifoliata Raf.). These were fertilized with 125 g N as labelled K¹⁵NO₃ and grown outdoors in containers filled with a sand-loamy soil. Two groups of 3 trees received this N dose either in five equally split applications by a flooding irrigation system or in 66 applications by drip. Trees were harvested at the end of the vegetative cycle (December) and the isotopic ratios of ¹⁵N/¹⁴N were measured in the soil-plant system. The N uptake efficiency of the whole tree was higher with drip irrigation (75 percnt;) than with flooding system (64 percnt;). In the 0-90 cm soil profile, the N immobilized in the organic fraction was similar for both irrigation methods (around 13 percnt;), whereas the N retained as NO₃⁻ was 1 percnt; of the N applied under drip and 10 percnt; under flooding. In the last case, most of NO₃⁻ remained under root system and it could be lost to leaching either by heavy rainfalls or excessive water applications. These results showed that a drip irrigation system was more efficient for improving water use and N uptake from fertilizer, in addition to potentially reduced leaching losses.     

地下滴灌条件下三倍体毛白杨根区土壤水分动态模拟

在根系分布试验观测的基础上,提出了三倍体毛白杨一维根系吸水模型,在考虑根系吸水情况下利用HYDRUS模型模拟了地下滴灌条件下三倍体毛白杨根区的土壤水分动态,通过田间试验对模型进行验证,并利用HYDRUS研究了不同灌水技术参数对土壤湿润模式的影响.结果表明：在灌溉结束和水分再分布24 h后,土壤含水量模拟结果的相对平均绝对误差(RMAE)分别为7.8%和6.0%,均方根误差(RMSE)分别为0.036和0.026 cm³·cm^-3,说明HYDRUS模型能很好地模拟地下滴灌条件下三倍体毛白杨根区的短期土壤水分动态,且所建根系吸水模型合理;与2、4 L·h^-1的滴头流速和连续性灌溉相比,流速1 L·h^-1和脉冲式灌溉(每隔30 min灌水30 min)能增大土壤湿润体体积,且可以减少水分深层渗漏量,因此,对试验地三倍体毛白杨根区进行地下滴灌应首选流速1 L·h^-1的脉冲式灌溉.     

Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass

Complementarity in the distribution of tree and crop root systems is important to minimise competition for resources whilst maximising resource use in agroforestry systems. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare the distribution and dynamics of root length and biomass of a 3-year-old Grevillea robusta A. Cunn. ex R. Br. (grevillea) tree row and a 3-year-old Senna spectabilis DC. (senna) hedgerow grown with Zea mays L. (maize). Tree roots were sampled to a 300 cm depth and 525 cm distance from the tree rows, both before and after maize cropping. Maize roots were sampled at two distances from the tree rows (75–150 cm and 450–525 cm) to a maximum depth of 180 cm, at three developmental stages. The mean root length density (L_rv) of the trees in the upper 15 cm was 0.55 cm cm⁻³ for grevillea and 1.44 cm cm⁻³ for senna, at the start of the cropping season. The L_rv of senna decreased at every depth during the cropping season, whereas the L_rv of grevillea only decreased in the crop rooting zone. The fine root length of the trees decreased by about 35% for grevillea and 65% for senna, because of maize competition, manual weeding, seasonal senescence or pruning regime (senna). At anthesis, the L_rv of maize in the upper 15 cm was between 0.8 and 1.5 cm cm⁻³. Maize root length decreased with greater proximity to the tree rows, potentially reducing its ability to compete for soil resources. However, the specific root length (m g⁻¹) of maize was about twice that of the trees, so may have had a competitive uptake advantage even when tree root length was greater. Differences in maize fine root length and biomass suggest that competition for soil resources and hence fine root length may have been more important for maize grown with senna than grevillea. This revised version was published online in June 2006 with corrections to the Cover Date.     

Root distribution in relation to soil nitrogen availability in field-grown tomatoes

Tomato root growth and distribution were related to inorganic nitrogen (N) availability and turnover to determine 1) if roots were located in soil zones where N supply was highest, and 2) whether roots effectively depleted soil N so that losses of inorganic N were minimized. Tomatoes were direct-seeded in an unfertilized field in Central California. A trench profile/monolith sampling method was used. Concentrations of nitrate (NO₃ ^-) exceeded those of ammonium (NH₄ ⁺) several fold, and differences were greater at the soil surface (0–15 cm) than at lower depths (45–60 cm or 90–120 cm). Ammonium and NO₃ ^- levels peaked in April before planting, as did mineralizable N and nitrification potential. Soon afterwards, NO₃ ^- concentrations decreased, especially in the lower part of the profile, most likely as a result of leaching after application of irrigation water. Nitrogen pool sizes and rates of microbial processes declined gradually through the summer.Tomato plants utilized only a small percentage of the inorganic N available in the large volume of soil explored by their deep root systems; maximum daily uptake was approximately 3% of the soil pool. Root distribution, except for the zone around the taproot, was uniformly sparse (ca. 0.15 mg dry wt g^-1 soil or 0.5 cm g^-1 soil) throughout the soil profile regardless of depth, distance from the plant stem, or distance from the irrigation furrow. It bore no relation to N availability. Poor root development, especially in the N-rich top layer of soil, could explain low fertilizer N use by tomatoes.     

A comparison of minirhizotron,core and monolith methods for quantifying barley (Hordeum vulgare L.) and fababean (Vicia faba L.) root distribution

Root research has been hampered by a lack of good methods and by the amount of time involved in making measurements. The use of the minirhizotron as a quantitative tool requires comparison with conventional destructive methods. This study was conducted in the greenhouse to compare the minirhizotron technique with core and monolith methods in quantifying barley (Hordeum vulgare L.) and fababean (Vicia faba L.) root distribution. Plants were grown in boxes (80 cm long × 80 cm wide × 75 cm deep) in a hexagonal arrangement to minimize the effects of rooting anistrophy. Minirhizotron observations and destructive sampling to a depth of 70 cm using core and monolith methods were performed at the ripening growth stage. Total root length for the entire depth interval was generally higher in barley (159–309 m) than fababean (110–226 m). Significant correlation coefficients between monolith and core methods for root length density (RLD, cm cm^–3) was observed in both crops (p 0.01). A method and depth interaction showed no significant differences in fababean RLD distribution measured by core and monolith methods. However, the RLD was different for the uppermost 40 cm depth in barley. The relationship for RLD between minirhizotron and core methods was significant only in barley (r=0.77^*). For both crops, estimates of RLD in the top 10-cm layer by the minirhizotron technique were lower than those by core and monolith techniques. In contrast, estimates of RLD were higher in fababean at a depth >30 cm. Destructive sampling still remains the method to quantify root growth in the 0–10 cm soil layer. ei]B E Clothier