The effects of stem density of tropical swards and age of grazing cattle on their foraging behaviour

The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile‐resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m^?2) and two ages of cattle (1‐ and 3‐year‐old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf‐only swards, mature cattle achieved a much greater BA (106·5 vs. 57·9 cm²), BM (0·88 vs. 0·47 g DM) and IIR (46·9 vs. 17·2 g DM min^?1) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile‐resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.     

The nitrogen response of potato (Solanum tuberosum L.) in the field: nitrogen uptake and yield, harvest index and nitrogen concentration

Summary The response of potato to different rates of nitrogen supply ranging from 0–40 g m⁻² N was studied in five field experiments near Wageningen. NL (52⁰ North). In total two late potato cultivars and two sites were used during successive seasons. The results are summarized in a set of regression equations separately for total crop and tubers. The relation between nitrogen taken up (g m⁻²) in the total crop and total dry matter production (g m⁻²) could be described with the exponential equation: 1942–1900 * 0.93^X (r²=0.953, n=62). Nitrogen concentrations in the dry matter increased linearly with nitrogen uptake. Harvest indices for dry matter and nitrogen tended to decline with increase in N uptake. Cultivars differed only in the effect on N on tuber dry matter concentration. The relation between nitrogen uptake and nitrogen supply could be fitted with quadratic regression models. but coefficients were influenced by site and season.     

Effect of nitrogen supply on leaf growth,leaf nitrogen economy and photosynthetic capacity in potato

Literature reports show little effect of nitrogen supply on radiation use efficiency in potato and in other dicotyledonous C₃ species. This paper tests the hypothesis that potato reduces leaf size rather than leaf nitrogen concentration and photosynthetic capacity when nitrogen is in short supply. Four pot experiments with different rates of nitrogen supply were conducted in glasshouses. For two leaf numbers measurements were made of leaf area, P_max (rate of photosynthesis for saturating irradiance), specific leaf weight, and concentrations of total nitrogen and nitrate, all as a function of leaf age.Area per leaf was sensitive to nitrogen supply (about a factor 3 between extreme N treatments). P_max declined with leaf age. There were no systematic effects of nitrogen supply on P_max and on its change with leaf age, except that in some cases P_max of leaves of high N treatments was lower than P_max of low N treatments during part of the life span (leaf age of ca. 20–50 days). The dominant effect of nitrogen supply was on leaf size and not on P_max or leaf N content. P_max versus areal organic nitrogen concentration (g N m⁻² leaf area) showed considerable scatter and, for a given nitrogen concentration, a slightly lower P_max for high N treatments than for low N treatments. Comparison with other species showed a comparatively low value of P_max in potato.     

密度和施氮量对强筋小麦藁优2018产量和抗倒性的影响

为明确减量播种和减施氮肥对强筋小麦品种藁优2018茎秆质量和抗倒性的影响,采用双因素裂区试验,研究了种植密度(D210,210万株·hm-2;D330,330万株·hm-2;D450,450万株·hm-2)和施氮量(N0,0kg·hm-2;N120,120kg·hm-2;N240,240kg·hm-2)对小麦倒伏高发期茎秆形态的影响,以及抗倒伏指数与茎秆形态指标的相关性。结果表明,在籽粒形成期和蜡熟期,密度由D210增加至D330,小麦茎秆重心高度显著增加,基部节间充实度、秆壁厚度、茎秆机械强度和抗倒伏指数降低;茎秆重心高度以N0最小,N240最高;基部节间秆壁厚度在3个施氮量处理间差异不显著;茎秆充实度、茎秆机械强度和抗倒伏指数随施氮量增加呈降低趋势,但在乳熟期和蜡熟期N120和N240差异不显著。相关分析表明,基部第1节间抗倒伏指数与节间粗度、充实度和第1节间秆壁厚度呈极显著正相关,与第2节间秆壁厚度相关性不显著。逐步回归分析表明,种植密度对小麦抗倒性的影响大于施氮水平。籽粒产量在不同密度处理间差异性不显著,但在不同施氮量间表现为N120和N240处理显著高于N0处理。因此,210万株·hm-2至330万株·hm-2的种植密度和120kg·hm-2的氮素水平在获得较高产量的同时具有较强的抗倒伏能力,是本试验条件下小麦抗倒高产的最优组合。     

氮肥和密度互作对冬小麦石4366群体、茎秆特性和产量的影响

为探索施氮量和种植密度互作对冬小麦品种石4366生长特性的影响,2020-2021年度在长期氮肥定位试验田通过裂区试验,设置4个施氮水平(施氮量分别为75 kg·hm^-2、150 kg·hm^-2、225kg·hm^-2和300 kg·hm^-2,分别用N75、N150、N225和N300表示)和5个种植密度水平(分别为225×10⁴株·hm^-2、300×10⁴株·hm^-2、375×10⁴株·hm^-2、450×10⁴株·hm^-2和525×10⁴株·hm^-2,分别用D225、D300、D375、D450和D525表示),比较分析了不同处理间该品种旗叶面积、穗部发育、群体动态、秸秆特性和产量的差异。结果表明,施氮量和种植密度对石4366群体、茎秆特性和产量均有显著影响。N75条件下穗长、总小穗...     

Surface and subsurface losses of N and P from salt-affected rice paddy fields of Saemangeum reclaimed land in South Korea

The present study was carried out to evaluate nutrient losses that occur during the course of agricultural activity from rice paddy fields of reclaimed tidal flat. For this study, we chose a salt-affected rice paddy field located in the Saemangeum reclaimed tidal area, which is located on the western South Korean coasts. The plot size was 1,000 m² (40 m × 25 m) with three replicates. The soil belonged to the Gwanghwal series, i.e., it was of the coarse silty, mixed, mesic type of Typic Haplaquents (saline alluvial soil). The input quantities of nitrogen and phosphorus (as chemical fertilizer) into the experimental rice paddy field were 200 kg N ha⁻¹ and 51 kg P₂O₅ ha⁻¹ per annum, and the respective input quantities of each due to precipitation were 9.3–12.9 kg N ha⁻¹ and 0.4–0.7 kg P ha⁻¹ per annum. In terms of irrigation water, these input quantities were 4.5–8.2 kg N ha⁻¹ and 0.3–0.9 kg P ha⁻¹ per annum, respectively. Losses of these nutrients due to surface runoff were 22.5–38.1 kg N ha⁻¹ and 0.7–2.2 kg P ha⁻¹ for the year 2003, and 26.8–29.6 kg N ha⁻¹ and 1.6–1.9 kg P ha⁻¹ for the year 2004, respectively. Losses of these nutrients due to subsurface infiltration during the irrigation period were 0.44–0.67 kg N ha⁻¹ and 0.03–0.04 kg P ha⁻¹ for the year 2003, and 0.15–0.16 kg N ha⁻¹ and 0.05–0.06 kg P ha⁻¹ for 2004. When losses of nitrogen and phosphorus were compared to the amount of nutrients supplied by chemical fertilizers, it was found that 11.3–19.1% of nitrogen and 0.5–1.7% of phosphorus were lost via surface runoff, whereas subsurface losses accounted to 0.2–0.8% for nitrogen and only 0.02–0.04% for phosphorus during the 2-year study period.     

Potato Stem Density Effects on Canopy Development and Production

Controlled environment studies with potato frequently assume responses from single-stem potato plants can be extrapolated to the field where multiple-stemmed plants are common. Controlled environment studies were conducted to characterize differences in canopy growth, development, and dry matter production between single- and multiple-stemmed potted potatoes. Leaf area distribution was influenced by stem density, with main stem and apical lateral branch leaf area being 150% to 200% larger in triple-stemmed (3S) versus single-stemmed (1S) pots (P < 0.01), while basal lateral branch leaf area was 50% less (P < 0.01). Basal lateral branches were more developed in 1S pots with longer branch lengths, more leaf area, and higher orders of branching. In a second experiment, more leaves were initiated in higher-density pots; however, individual leaf areas were approximately 50% smaller than those in 1S pots. Total leaf area and total, vegetative, and tuber dry matter production were unaffected by stem density in either experiment on a per pot basis. Development and growth of lower basal lateral branches in the 1S potato canopy offset any initial advantage in leaf numbers in the multiple-stemmed plants. These results appeared to validate the assumption that, given a late maturing cultivar and adequate nutrition, responses from single-stemmed plants can be extended to multiple-stemmed plants when expressed on a production area basis. These findings have practical considerations for potato researchers who conduct growth chamber experiments and potato modelers.     

Water,Nitrogen and Plant Density Affect the Response of Leaf Appearance of Direct Seeded Rice to Thermal Time

Field experiments were conducted in the Ebro Delta area (Spain), from 2007 to 2009 with two rice varieties:Gleva and Tebre. The experimental treatments included a series of seed rates, two different water management systems and two different nitrogen fertilization times. The number of leaves on the main stems and their emergence time were periodically tagged. The results indicated that the final leaf number on the main stems in the two rice varieties was quite stable over a three-year period despite of the differences in their respective growth cycles. Interaction between nitrogen fertilization and water management influenced the final leaf number on the main stems. Plant density also had a significant influence on the rate of leaf appearance by extending the phyllochron and postponing the onset of intraspecific competition after the emergence of the 7th leaf on the main stems. Final leaf number on the main stems was negatively related to plant density. A relationship between leaf appearance and thermal time was established with a strong nonlinear function. In direct-seeded rice, the length of the phyllochron increases exponentially in line with the advance of plant development. A general model, derived from 2-year experimental data, was developed and satisfactorily validated; it had a root mean square error of 0.3 leaf. An exponential model can be used to predict leaf emergence in direct-seeded rice.     

Beziehungen zwischen Stengel- und Knollenzahl bei der Kartoffel in Abhängigkeit von wichtigen Einflußfaktoren. II. Der Einfluß des Jahres

Zusammenfassung In sieben Versuchsjahren beeinflusste die jahrestypische Stengelzahl die Zahl der Knollenanlagen pro Pflanze positiv (r=+0,77^*) und der Knollenanlagen pro Stengel in der Tendenz negativ (r= −0,39). Die signifikanten Jahresunterschiede in der Zahl erntef?higer Knollen (>3 cm) pro Pflanze und pro Stengel wurden in gewissem Grade durch die Zahl der angelegten Knollen (r= −0,53 bzw. +0,63), in st?rkerem Ausma? jedoch durch die jahrestypische Reduktionsrate der Knollen bestimmt (r= −0,72 bzw. −0,91^*). Diese war hoch, wenn ein Wechsel von guter Wasserversorgung w?hrend der Knollenbildung zu Wassermangelsituationen w?hrend der Knollenwachstumsphase erfolgte.

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Summary In seven years of field experiments, there were significant differences in the numbers of stems per plant and the number of harvestable tubers (>3 cm) at maturity, per plant and per stem, averaged for two cultivars and three seed treatments (Table 1). There was only a weakly positive correlation between the typical stem number for each year and the number of harvestable tubers per plant (r= +0.2, Table 2), whilst the correlation with the number of tubers initiated was much closer (r= +0.77^*, Table 2). The negative influence of number of stems on number of tubers per stem is shown byr= −0.39 and −0.47 (Table 2). Identical stem populations in the wet, cold spring of 1987, and the warm, dry season of 1983 initiated fewer tubers per stem than in 1989 with its average temperatures and modest precipitation (Table 1). Tuber set per plant and per stem correlated positively with the number of harvested tubers per plant and per stem (r= +0.53 and +0.63) and accounted for some of the yearly variation. A much stronger effect on the number of harvestable tubers came from the annual reduction of tubers (r= −0.72 and −0.91^*, Table 2). This was high if the availability of water deteriorated in the period of growth succeeding tuber formation (Table 1, Fig. 1). The same applied to the seed treatments planted at different stages of development. Tuber development occurred earlier with chitted seed, often at times when there was an adequate water supply. A large number of tubers were initiated and these were in large part reduced in the short dry spells which followed (Figs 2 and 4). Irrigation programmes must take account of this relationship.

     

减氮对豫北限水灌溉冬小麦冠层结构和光合特性的影响

为了解节水栽培条件下冬小麦光合对减氮的反应,以豫北地区冬小麦为研究对象,在限水灌溉(春浇一水)条件下,以当地冬小麦生产中常规施氮量(底施氮量+追施氮量:120+210 kg·hm~(-2))为对照,设置不同减氮处理(底施氮量+追施氮量分别为120+150、120+90、120+0、0+0 kg·hm~(-2)),研究减氮对冬小麦冠层叶片和非叶器官形态特征、冠层光分布和光合速率的影响。结果表明,随施氮量的减少,小麦开花期单茎叶面积、上三叶面积及旗叶节以上非叶绿色器官面积均呈下降趋势,降幅分别为9.7%～28.0%、10.6%～30.3%和5.2%～16.8%,叶器官面积和上三叶面积下降幅度均高于旗叶节以上非叶绿色器官面积的下降幅度。减氮处理下,开花期上三叶长和宽分别减少4.4%～8.8%和11.8%～15.6%,叶片变窄变短,而倒四叶叶型无明显变化。另外,上三叶平均比叶重随氮肥减少总体呈增加趋势,表明适量减氮有助于改善上三叶叶片质量。随施氮量的减少,花后各叶层透光率呈增加趋势,其中灌浆中前期(开花至花后20 d)减氮处理的倒四叶层、倒三叶层、倒二叶层和旗叶层透光率分别比对照高39.0%、38.0%、23.8%和9.4%。随施氮量的减少,花后上三叶光合速率总体均呈先略升后降的趋势,其中旗叶和倒二叶光合速率在花后均以120+210 kg·hm~(-2)、120+150 kg·hm~(-2)和120+90 kg·hm~(-2)处理较高,且处理间差异较小,而倒三叶光合速率在开花至花后18 d均以120+150 kg·hm~(-2)和120+90 kg·hm~(-2)处理较高,分别比对照高38.7%和24.7%。这说明,减氮减少了冬小麦单茎叶面积,增加了非叶器官面积占单茎总光合面积的比例,且上三叶叶片变小,叶片质量提高,增加了花后冠层下部叶片受光比率,改善了冠层下部叶片的受光状况,有利于提高冠层下部叶片的光合速率。     

Effect of nitrogen source on growth and morphogenesis of three micropropagated potato cultivars

Summary Different nitrogen sources (NO₃ ⁻, NH₄ ⁺, glutamic acid and their combinations) influenced the growth and morphogenic responses (node number, shoot length, and stem, leaf and root dry weight) of three micropropagated potato cultivars (Spunta, Kennebec, Huinkul). Addition of reduced nitrogen (NH₄ ⁺ or glutamic acid) in a nitrate medium increased shoot length and leaf number. The large increase in growth in plants fed with NO₃ ⁻, NH₄ ⁺ could be explained by higher organic nitrogen content and enhanced dry matter partition to the shoot. This suggests that reduced nitrogen source is required, at least as a supplement to NO₃ ⁻, to enhance N assimilation and growth.     

Physiological determinants of maize and sunflower grain yield as affected by nitrogen supply

Utilisation of nitrogen (N) has been closely related to increases in crop productivity. However, not all crops respond similarly and the objective of this study is to identify physiological processes that determine responses to N supply for maize and sunflower. Grain yield in maize (range: 210–1255 g m⁻²) was greater and more responsive to N supply than in sunflower (106–555 g m⁻² in carbohydrate equivalents) over a wide range of total N uptake (3–>20 g N m⁻²). In maize, differences in grain yield among levels of N supply were associated more with variation in biomass than in harvest index. In sunflower, differences in grain yield (in carbohydrate equivalents) among levels of N supply were related similarly to variation in both biomass and harvest index. The decrease in biomass production with decreasing N supply was associated with decreases in both radiation interception and radiation use efficiency (RUE). Decreased interception was due to effects of N supply on reducing canopy leaf area, whereas the reduced RUE was associated with decreased SLN. Total biomass production in maize was more responsive to N supply than in sunflower. The major determinants of the differences in response of biomass accumulation to N supply found between maize and sunflower are: (i) sunflower tends to maintain SLN with increase in partitioning of N to leaves under N limitation whereas maize tends to maintain leaf area with increase in partitioning of biomass to leaves and (ii) the ability of maize to maintain N uptake following cessation of leaf production.     

Irrigation water reduction using System of Rice Intensification compared with conventional cultivation methods in Iraq

A field study was conducted at Al-Mishkhab Rice Research Station (MRRS) during the summer season 2009 to evaluate irrigation water use efficiency (IWUE) using Anbar 33 variety with the System of Rice Intensification compared to traditional methods. During the growth phase, the number of leaves, stems, and roots, and the average plant height were measured every 15 days for the two sets of methods. At maturity, the depth and length of plant roots was assessed, along with leaf area index (LAI) of the flag leaf and plant height. The amount of irrigation water applied was measured by water meter for both methods. SRI principles for plant age, spacing, etc., were implemented in the SRI plots. The results indicated more vigorous growth of roots under SRI methods, reaching 13,004 cm plant⁻¹ compared with non-SRI results of 4,722 cm plant⁻¹. There was 42% increase in grain yield when SRI methods were used. These had water use efficiency (WUE) of 0.291 kg m⁻² compared with WUE of 0.108 kg m⁻² for non-SRI cultivation, almost a threefold difference. SRI practices reduced the need for irrigation water by 38.5%.     

Effect of nitrogen supply on leaf appearance,leaf growth,leaf nitrogen economy and photosynthetic capacity in maize (Zea mays L.)

Leaf area growth and nitrogen concentration per unit leaf area, N_a (g m⁻² N) are two options plants can use to adapt to nitrogen limitation. Previous work indicated that potato (Solanum tuberosum L.) adapts the size of leaves to maintain N_a and photosynthetic capacity per unit leaf area. This paper reports on the effect of N limitation on leaf area production and photosynthetic capacity in maize, a C4 cereal. Maize was grown in two experiments in pots in glasshouses with three (0.84–6.0 g N pot⁻¹) and five rates (0.5–6.0 g pot⁻¹) of N. Leaf tip and ligule appearance were monitored and final individual leaf area was determined. Changes with leaf age in leaf area, leaf N content and light-saturated photosynthetic capacity, P_max, were measured on two leaves per plant in each experiment. The final area of the largest leaf and total plant leaf area differed by 16 and 29% from the lowest to highest N supply, but leaf appearance rate and the duration of leaf expansion were unaffected. The N concentration of expanding leaves (N_a or %N in dry matter) differed by at least a factor 2 from the lowest to highest N supply. A hyperbolic function described the relation between P_max and N_a. The results confirm the ‘maize strategy’: leaf N content, photosynthetic capacity, and ultimately radiation use efficiency is more sensitive to nitrogen limitation than are leaf area expansion and light interception. The generality of the findings is discussed and it is suggested that at canopy level species showing the ‘potato strategy’ can be recognized from little effect of nitrogen supply on radiation use efficiency, while the reverse is true for species showing the ‘maize strategy’ for adaptation to N limitation.     

Comparative performance of three small seed tuber sizes and standard size seed tubers planted at similar stem densities

Summary Small seed tubers of 1–5 g, 5–10 g and 10–20 g were planted at the same sprout densities as standard size seed tubers of 40–60 g in order to give similar stem densities. Early ground cover by foliage, total yield, and yield of tubers >45 mm were consistently greater in plots planted with larger seed tubers. The effect of seed tuber size on yield and tuber number per stem varied between years but 1–5 g seed tubers always gave lower yields per stem than larger seed tubers. Reducing the spacing between rows from 90 cm to 60 cm and maintaining the same sprout density was more effective in increasing yields from small seed tubers than increasing sprout density from 20 to 40 sprouts per m² by reducing plant spacing within the row.     

Impact of earthen waste storage on nitrate concentration of surface water

In 1992 and 2002, investigations on the water quality and hydrology were carried out in a small agricultural catchment where swine waste was stored in earthen waste storage. The in-stream nitrogen loads and the nitrogen inputs on a sub-catchment scale were estimated and compared between 1992 and 2002. For the entire catchment, the estimated nitrogen inputs increased from 22.5 to 32.9 ton year⁻¹ (from 406 to 594 kg ha⁻¹ year⁻¹), whereas the nitrate nitrogen concentration at the outlet was constant—27 mg l⁻¹. In a sub-catchment (area C) with earthen waste storages, the nitrate nitrogen concentrations at the outlet were high, 42–51 mg l⁻¹. In a sub-catchment (area A) with an earthen waste storage, which was not in service since 1990, although the nitrogen inputs were maintained at 390 kg year⁻¹ (53 kg ha⁻¹ year⁻¹), the nitrate nitrogen concentrations at the outlet decreased from 26 to 4.9 mg l⁻¹. With assuming that the nitrogen transport rates for sources except swine waste are equal to the rates estimated for a sub-catchment without earthen waste storage, the in-stream nitrogen loads for area A were estimated to decrease from 1,334 to 94 kg year⁻¹ and the transport rates for area A were estimated to decrease from 3.95 to 0.73. These results suggest that the effluent from earthen waste storage has affected surface water quality two years after the storage was out of service and its effect largely decreased after a decade.     

Stomatal resistance of three potato cultivars as influenced by soil water status, humidity and irradiance

Summary Leaf stomatal resistance varies considerably in response to changes in environmental conditions. Understanding cultivar differences in the response of stomata to these conditions is important for effectively simulating water-use and growth. In this study the stomatal resistance of three field grown potato (Solanum tuberosum L.) cultivars Atlantic. Monona and Norchip was observed in response to photosynthetic photon flux density, leaf to air vapour pressure difference and root zone available soil water. Substantial variation in stomatal resistance was accounted for by functions of the environmental variables for both Monona and Norchip. The explained variation for Atlantic was considerably less. Light saturation occurred near 500 μmol m⁻² s⁻¹. Increasing stomatal resistance above 1000 μmol m⁻²s⁻¹ was also observed but is likely an artifact of stomatal closure on days in which mid-day leaf water potentials dropped below critical levels. Although the leaf presumably insufficient to obtain substantial effects. The soil water status was partially linked to the average 1000 h to 1500 h stomatal resistance on clear, sunny days. Significant differences were observed among the cultivars in the response of stomata to changes in the available soil water.     

The effect of the density and physical properties of grass stems on the foraging behaviour and instantaneous intake rate by cattle grazing an artificial reproductive tropical sward

In reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems’ barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20‐cm leaves and 15‐cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m^?2) and two levels of stem tensile resistance [low (LTRS) and high tensile‐resisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13·4, 13·6 and 5·1 cm for 0, 100 and 400 stems m^?2, respectively), bite area (89·3, 50·8 and 47·6 cm² for 0, 100 and 400 stems m^?2, respectively), bite mass (0·51, 0·29 and 0·11 g for 0, 100 and 400 stems m^?2, respectively) and IIR (23·8, 10·5 and 3·6 g sec^?2 for 0, 100 and 400 stems m^?2, respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems’ barrier effect on bite dimensions and IIR.     

Radiation-use efficiency of sunflower crops: effects of specific leaf nitrogen and ontogeny

Loss of nitrogen from the leaves and a reduction in specific leaf nitrogen (SLN, g N m⁻²) is associated with grain filling in sunflower (Helianthus annuus L.). To explore the relationship between crop radiation-use efficiency (RUE, g MJ⁻¹) and SLN, crop biomass accumulation and radiation interception were measured between the bud-visible and physiological-maturity stages in crops growing under combinations of two levels of applied nitrogen (0 and 5 g N m⁻²) and two population densities (2.4 and 4.8 plants m⁻²). Both nitrogen fertilization and density had significant (P = 0.05) effects on crop biomass yield, nitrogen uptake, leaf area index and SLN, but the nitrogen effects were more pronounced for these and other crop variables. Linear regressions of accumulated biomass (OCdwt, corrected for the energy costs of oil synthesis in the grain) on accumulated intercepted short-wave radiation between bud visible and early grain filling provided appropriate and significantly (P = 0.05) different estimates of RUE for the pooled 0 g N m⁻² (1.01 g OCdwt MJ⁻¹) and 5 g N m⁻² (1.18 g OCdwt MJ⁻¹) treatments. When calculated for each inter-harvest interval, crop RUE varied in a curvilinear fashion during the season, with a broad optimum from 40 to 70 days after emergence of the crops, and with lower values earlier and later in the season. The reduction in RUE toward physiological maturity was particularly marked. A plot of RUE against SLN revealed a reduction in RUE at small SLN values, but the relationship may be confounded by ontogenetic changes in other factors. A published model (Sinclair and Horie (1989), Crop Sci., 29: 90–98) was used to explore the RUE/SLN relationship. The model was unable to reproduce the decline in RUE during the second half of the grain-filling period. It is suggested that an important cause of this failure may be the partition, in the model, of a fixed, rather than a variable, fraction of crop gross photosynthesis to respiration.     

Morphological traits and allocation patterns related to stress-tolerance and seed-yield in wild and domesticated evening primrose (Oenothera L. Onagraceae)

Wild evening primrose species (Oenothera spp.) native to Argentina, have been suggested as a new crop for irrigated valleys of semi-arid Patagonia. This paper describes patterns of biomass allocation, morphological traits related to stress-tolerance and seed-yield in four species of Oenothera grown in a common garden at three plant densities. Wild and domesticated species are compared. The effect of resource availability on those traits during three phenological stages (vegetative, reproductive and maturity) is described. Native species were characterized by traits related to stress-tolerance (high root allocation and low specific leaf area) during the vegetative stage. This suite of traits resulted in low biomass accumulation and low seed-yield. The domesticated O. biennis was characterized by a combination of traits related to stress-tolerance (low specific leaf area) and high productivity (high leaf allocation and leaf area ratio and low root allocation). Domesticated species accumulated more biomass than natives. Total biomass and total non-structural carbohydrates present in roots were positively correlated to seed-yield.Oenothera biennis showed the highest seed-yield, although this species showed yield instability in response to changes in the environmental quality. No changes in seed-yield in response to plant density were recorded for either O. lamarckiana or native species. Oenothera biennis showed an optimum density of 20 plants m⁻² and yielded 260 g m⁻², a seed-yield similar to that reported in other countries. Low seed-yield of native species is major drawback that must be overcome. Improving seed-yield in these species could be possible by selection oriented to increase total biomass. Since no detrimental effect of density was found in O. lamarckiana and natives, a higher plant density might increase yield production per unit area.