Chlorophyll meter readings,N leaf concentration and their relationship with N use efficiency in oregano

Plant-based diagnostic techniques such as chlorophyll meter (CM) readings and nitrogen (N) leaf concentration are used to determine the level of crop N nutrition, but research is limited on perennial crops and especially on aromatic and medicinal plants such as Greek oregano (Origanum vulgare spp. hirtum). The objectives of this study were to determine in a perennial crop species whether there is a relationship between the CM readings, N leaf concentration, and N use efficiency (NUE) and to use CM readings as a diagnostic tool for predicting dry matter yield in response to N fertilization. The CM readings varied across environments, growth stages, and fertilization treatments and were correlated with NUE. NUE was also affected by the environment, N fertilization, and interactions among these variables. This study provides new information about the effect of N application on CM readings, N leaf concentration, and NUE in a perennial crop such as oregano.     

Ammonium concentration in solution affects chlorophyll meter readings in tomato leaves

Abstract

Combinations of NH₄‐N:NO₃‐N usually result in higher tomato (Lycopersicon esculentum Mill.) yields than when either form of nitrogen (N) was used alone. Leaf chlorophyll content is closely related to leaf N content, but the effect of the NH₄‐N:NO₃‐N ratio on leaf greenness was not clear. The objective of this study was to determine the influence of NH₄‐N:NO₃‐N ratios on chlorophyll meter (SPAD) readings, and evaluate the meter as a N status estimator and tomato yield predictor in greenhouse production systems. Fruit yield and SPAD readings increased as the amount of NH₄‐N in solution increased up to 25%, while higher ratios of NH₄‐N resulted in a decline in both. The N concentration in tomato leaves increased as concentration of NH₄‐N in solution increased. Fruit yield increased as chlorophyll readings increased. SPAD readings, total N in leaves, fresh weight of shoots, and fruit yield all showed a quadratic response to NH₄‐N, reaching a peak at 25 or 50% of N as NH₄‐N. SPAD readings taken at the vegetative and flowering stages of growth had the highest correlation (r²=0.54) with N concentration in leaves, but this could not be used as a reliable estimate of N status and fruit yield. Lack of correspondence between high N concentration values and fruit yield indicated a detrimental effect of NH₄‐N on chlorophyll molecules or chloroplast structure. The SPAD readings, however, may be used to determine the optimum NH₄‐N concentration in solution to maximize fruit yield.     

A simple,low‐cost technique for in situ measurement of leaf P concentration in field‐grown rice

Simple tools for diagnosing crop nutritional status are in great demand by agricultural extension staff, particularly in low‐fertility environments. We developed the first practical method for in situ diagnosis of phosphorus (P) nutrition in field‐grown cereal crops by using a handheld colorimeter. The concentration of P in extracts from fresh leaves of lowland rice grown under various P availabilities was closely correlated with that of oven‐dried leaves measured with the standard molybdenum‐blue method in the laboratory, over a range of values from 0.319 to 1.420 mg P g ^?1 DW (r = 0.885^**, n = 14). It takes only 3–5 min to estimate the P concentration of plant samples using the new technique. Although not as accurate as the laboratory method, the new method can easily detect P deficiency of rice in the field (and possibly other cereal crops) without requiring costly, off‐site equipment. Thus, extension staff and agronomists can easily adopt this technique.     

滴灌番茄临界氮浓度、氮素吸收和氮营养指数模拟

作物的氮浓度随生物量的增加而下降,临界氮浓度是指在一定的生长时期内获得最大生物量时的最小氮浓度值。该文在滴灌条件下,基于3a不同的氮素水平试验,构建了加工番茄地上部生物量的临界氮浓度稀释曲线模型。结果表明,临界氮浓度与地上部最大生物量之间符合幂指数关系,相关系数为R~2=0.947,加工番茄最高(%Nmax)、最低(%Nmin)临界氮浓度稀释模型亦符合幂指数关系,相关系数分别为R~2=0.959、R~2=0.925。基于临界氮浓度建立了加工番茄氮素吸收模型(Nupt)、氮素营养指数模型(NNI),可作为加工番茄氮素营养状况的判别指标,氮素吸收和氮营养指数模型对新疆北疆加工番茄种植区的适宜施氮量诊断结果一致,均以300kg/hm2为最佳施氮量。该研究所建立的临界氮浓度稀释曲线模型较前人建立的模型更具机理性,因此,该模型所得出的分析结果是合适和可靠的,并且可用于指导加工番茄动态精准施肥及为氮素优化管理的建立提供参考。     

A SIMPLE AVAILABLE SOIL NITROGEN INDEX

Available soil-N values in commonly cultivated East African soils were determined in the laboratory by several methods, and correlated with one another. Mineralizable-N was correlated more with total-N than with organic-C. The values of mineralizable-N (Δ mineral-N) obtained on aerobic incubation were correlated with crop yield and nitrogen uptake in greenhouse experiments. The yield of dry matter and N uptake by the tomato crop in the absence of applied nitrogen were significantly correlated with Δ mineral-N in the soils; the degree of correlation decreased with increasing rates of fertilizer-N applied and Δ mineral-N and dry-matter yield were not correlated at the largest rate used. N uptake by the crop was significantly correlated with Δ mineral-N at all rates of applied nitrogen. The Δ mineral-N value determined on soil samples conditioned by 6 weeks incubation followed by 3 weeks air drying was considered to provide a good index to available nitrogen.     

Interaction matters: Synergy between vermicompost and PGPR agents improves soil quality,crop quality and crop yield in the field

Organic amendments not only promote soil quality and plant performance directly but also facilitate the establishment of introduced microbial agents. A field experiment with a fully factorial design was conducted using three levels of vermicompost (without vermicompost, low dose of 15 Mg ha⁻¹ and high dose of 30 Mg ha⁻¹), with and without plant growth-promoting rhizobacteria (PGPR) to investigate their effects in a tomato – by spinach rotation system. Our results demonstrated that applying PGPR alone had no effect on soil properties and crop performance. Vermicompost enhanced the beneficial effects of PGPR on both soil and crop, with the extent of promotion depending on the dose of vermicompost and crop types. In the presence of vermicompost, PGPR significantly (P < 0.05) reduced soil carbon and nitrogen but increased soil microbial biomass carbon and nitrogen. PGPR also significantly increased the yield of tomato and spinach under the low dose of vermicompost, but only significantly increased tomato yield under the high dose of vermicompost. There were strongly synergistic effects between vermicompost and PGPR on crop quality, with crop nitrate concentration being significantly decreased, while the vitamin C in tomato and soluble protein in spinach was significantly increased. Our results revealed the high potential of integrating vermicompost and microbial agents to substitute for regular chemical fertilization practices.     

Arsenic uptake,distribution, and accumulation in tomato plants: Effect of arsenite on plant growth and yield

The response of tomato (Lycopersicum esculentum Mill, cultivar Marmande) plants to different levels of arsenic (As) in nutrient solution was investigated—the processes of uptake, distribution and accumulation of As, and the effect of arsenite on yield and plant growth (plant height, diameter of stem, stem and root length, fresh and dry weight of root, stems, leaves, and fruit). The experiment was performed at three levels of As: 2, 5 and 10 mg/L [added as sodium arsenite (NaAsO₂)] in a nutrient solution, together with the corresponding control plants. Arsenic uptake depended on the As concentration in solution and As content in the roots increased as the time of treatment increased. The most important finding was the high toxicity of arsenite to roots. The concentration in stems, leaves, and fruit was correlated with the As level in the nutrient solution. Although the As level of 10 mg/L damaged the root membranes, resulting in a significant decrease in the upward transport of As. Arsenic exposure resulted in a drastic decrease in plant growth parameters (e.g., maximum decrease of 76.8% in leaf fresh weight) and in tomato fruit yield (maximum reduction of 79.6%). However, it is important to note that the As concentration in the fruits was not toxic or harmful for human consumption.     

Boron Foliar Application in Nutrition and Yield of Beet and Tomato

The objective of this work was to evaluate the effect of the application of boron (B) by foliar spraying for the yield of beet (Beta vulgaris L.) and tomato (Solanum lycopersicum L.) crops. An experiment for each crop was done in a greenhouse at the São Paulo State University (UNESP), Jaboticabal campus, in Brazil. The experiments evaluated the B concentrations of 0, 0.085, 0.170, 0.255, and 0.340 g L^?1; applied in the 20, 35, and 50 days after the transplant (DAT) of beet cv. ‘Tall Top Early Wonder’, and in the 20, 40, and 60 DAT for the tomato cv. ‘Raisa N’. The plants were cultivated in pots with washed sand with 5 dm³ for the beet crop and 10 dm³ for the tomato crop. The beet and tomato crops were harvested 58 and 154 DAT, respectively. The leaves and fruits numbers; the foliar area; the dry matter of leaves, bark and roots; the fresh and dry matter of the fruits and the tuberous root; the dry matter of the total plant and the B foliar content were evaluated. The total dry matter of beet and tomato the plant were influenced by the concentration of the foliar B spray. The highest yield of the tuberous root and the total plant dry matter of beet occurred with B foliar concentration of 0.065 g L^?1 and it was associated with the B foliar content of 26 mg kg^?1. The highest yield of fruit and total plant dry matter of tomato occurred with the B foliar spraying of 0.340 g L^?1 and it was associated with the B foliar content of 72 mg kg^?1.     

Compost Maturity Effects on Nitrogen and Carbon Mineralization and Plant Growth

Improved predictive relationships between compost maturity and nitrogen (N) availability are needed. A total of 13 compost samples were collected from a single windrow over a 91 d period. Compost stability and maturity were assessed using both standard chemical analyses (total C and N, mineral N, total volatile solids) and other methods (CO₂ evolution, commercial maturity kits, and neutral detergent fiber, and lignin). Compost N and carbon (C) were evaluated during a 130 d aerobic incubation in a sandy loam soil after each compost was applied at 200 mg total kg^?1 soil. The effect of compost maturity on plant growth was evaluated by growing two ryegrass (Lolium perenne L.) crops and one barley (Hordeum vulgare L.) crop in succession in compost-amended soil under greenhouse conditions. Potential phytotoxicity from compost was assessed by growing tomato (Lypersicum esculentum L.) seedlings in compost-amended soil. Regression and correlation analyses were used to evaluate the relationship between compost maturity parameters, the rate and extent of net N and C mineralization, plant yield and N uptake, and phytotoxicity. Commonly used maturity parameters like total C, total N, and C:N ratio were poorly correlated with the rate and extent of mineralization, and with plant growth parameters. The N mineralization rate during the first 48 d of aerobic incubation was strongly correlated (r= ?0.82 to ?0.86) to compost fiber and lignin concentration, and to the Maturity Index (r=0.85). Trends in C mineralization were similar. There were few differences in C mineralization between composts after 48 d of aerobic incubation in soil. Ryegrass harvested 35 and 70 d after compost application was not strongly affected by compost maturity, and relatively immature composts were phytotoxic to tomato seedlings. Methods of characterizing compost maturity and stability that more realistically reflect the composting process are better predictors of N release and potential plant inhibition after incorporation into soil.     

Maize grain production,plant nutrient concentration and soil chemical properties in response to different residue levels from two previous crops

ABSTRACT

The incorporation of previous crop residues in agricultural management benefits soil fertility, crop production, and environment. However, there is no enough information about maximum residue application level without negative effect over next crop yield. To evaluate maize (Zea mays L.) yield under short-time conservation management with incorporation and/or importation of different residue levels, a biannual rotation experiment was conducted in ash volcanic soil in south-central Chile. The experiment consisted of two previous crops, canola (Brassica napus L.) and bean (Phaseolus vulgaris L.), and four levels of residue incorporation (0%, 50%, 100%, and 200% of generated residue; from 0 to 21.4?Mg?ha^?1 for canola and from 0 to 19.0?Mg?ha^?1 for bean). Previous crop species and residue level affected some nutrients concentrations in grain and plant and some soil chemical properties, without effect in maize yield, which averaged 16.6?Mg?ha^?1. Bean residue increased Ca and reduced S in maize plant, increasing soil P, Ca, Mg and K (P?<?0.05). Maize grain Ca content was positively and proportionally affected by canola residue level and negatively and proportionally affected by bean residue level. All canola residue levels increased soil pH and Mg, but the highest level reduced soil S; soil P concentration increased proportionally with bean residue level. The highest bean residue level increased soil S. Different crop and levels of residue did not affect maize yield but did some plant nutrient concentration, and also affected some soil chemical properties.     

填闲与减少施肥措施提高华北温室种植体系中的番茄产量及土壤养分

Overuse of fertilizers and the resultant pollution and eutrophication of surface and groundwater is a growing issue in China. Consequently, improved management strategies are needed to optimize crop production with reduced nutrient inputs. Conventional fertilization (CF), reduced fertilization (RF), and reduced fertilization with maize (Zea mays L.) as a summer catch crop (RF+C) treatments were evaluated in 2008 and 2009 by quantifying tomato (Lycopersicon esculentum) fruit yield and soil nutrient balance in a greenhouse tomato double-cropping system. Fertilizer nitrogen (N) application was reduced by 37% in the RF and RF+C treatments compared to the CF treatment with no significant reduction in fruit yield. Mean soil mineral N (N_min) content to a depth of 180 cm following tomato and maize harvest was lower in the RF and RF+C treatments than in the CF treatment. Residual soil Nmin content was reduced by 21% and 55% in the RF and RF+C treatments, respectively, compared to the CF treatment. Surplus phosphorus (P) and potassium (K) contents in the RF+C treatment were significantly lower than those in the RF treatment, mainly due to additional P and K uptake by the catch crop. We concluded that for intensive greenhouse production systems, the RF and RF+C treatments could maintain tomato fruit yield, reduce the potential for nitrate (NO₃^--N) leaching, and with a catch crop, provide additional benefits through increased biomass production.     

稻草与生石灰对设施土壤微量元素含量和番茄产量的影响

为了探究设施内添加稻草与生石灰对土壤微量元素含量和番茄产量的影响,以长期施肥定位试验为依托,比较了施用鸡粪(M)的基础上,添加稻草(MR)、生石灰(MCa)、稻草与生石灰同时添加(MRCa)各处理全土及各粒级团聚体中有效态Fe、Mn、Cu、Zn含量和番茄产量的变化。结果表明:(1)添加稻草可增加土壤中有效态Fe、Mn、Zn含量,MR处理较M处理分别增加3.2%,80.9%,15.1%,对有效态Cu含量无显著影响;添加生石灰也可增加土壤中微量元素含量,其中Mn含量增加显著。土壤中有效态Fe、Mn、Cn、Zn含量与pH呈极显著负相关(P<0.01),与有机质含量呈极显著正相关(P<0.01)。(2)随着土壤团聚体粒级的减小,有效态微量元素含量呈下降趋势。添加稻草和生石灰可增加1~0.25mm粒级中有效态Mn含量,MRCa处理较其他处理增加6.6%~46.6%;添加稻草可增加<0.25mm粒级中有效态Zn含量。土壤中有效态Fe含量与<1mm粒级中含量呈显著正相关(P<0.01);土壤中有效态Mn、Zn含量分别与各粒级中含量呈显著正相关(P<0.01);土壤中有效态Cu含量与1~0.25mm粒级中含量呈显著正相关(P<0.01)。(3)施入稻草或生石灰可增加番茄产量,且稻草和生石灰同时施入产量最高,MRCa处理较MCa、MR处理分别增加12.6%,33.8%。土壤有效态Fe、Cu含量与产量正相关,其中有效态Fe含量对产量具有直接作用,决策系数最高,土壤有效态Cu含量对产量具有间接作用。因此,可以通过长期添加稻草和适量生石灰缓解设施土壤微量元素短缺的现状,且可获得最高作物产量,为设施内土壤可持续利用和设施农业可持续发展提供保障。     

Effects of Salinity Stress at Different Growth Stages on Tomato Growth,Yield, and Water-Use Efficiency

This study investigated the effects of salinity stress at different growth stages on the growth, yield, fruit quality, and water-use efficiency (WUE) of tomato (Solanum lycopersicum) plants cultivated under soilless conditions. Six different growth stages were exposed to the same salinity stress treatments using a completely randomized design, with three pots (six plants) per treatment. It was found that short-term (<21 days) salinity stress during any of the growth stages did not affect tomato growth or WUE, and during the vegetative stage did not affect yield. Salinity stress during the flowering and fruiting stages caused a reduction in tomato yield, which was due to a reduction in the number of fruit produced rather than the fruit size. However, salt exposure at the fruiting stage also improved fruit quality. The effect of salinity stress on the yield and fruit quality of the frontal and later truss depended on the developmental stage of the truss at the time when the stress occurred.     

Effects of nitrogen form,nighttime nutrient solution strength,and cultivar on greenhouse tomato production

Higher greenhouse tomato (Lycopersicon esculentum Mill.) yield is obtained by using 25% of NH₄‐N in solution compared to using NO₃‐N as the sole nitrogen (N) source. However, blossom‐end rot (BER) may occur in tomato fruit when NH₄‐N was present in nutrient solutions. High nutrient solution strengths improve tomato fruit quality, but can also increase BER. Two NH₄‐N concentrations in solution (0 and 25%), and two nighttime solution strengths (NSS) (1X and 4X Steiner solution strength applied at 7 p.m.) were used to grow five indeterminate type greenhouse tomato cultivars: Caruso, Jumbo, Match, Max, and Trust. A significant interaction occurred between NH₄‐N concentration and NSS factors: 0% NH₄‐N and high NSS increased marketable yield and fruit:whole plant ratio, and reduced BER. In contrast, a concentration of 25% NH₄‐N and high NSS reduced marketable yield and the fruit:whole plant ratio, and increased BER incidence. Max, Match, and Trust tomato cultivars produced high marketable yield and high dry weight of stem and leaves, but were susceptible to BER. Use of NH₄‐N in solution reduced vegetative growth, and high NSS increased stem and leaf dry weight of the tomato plants. Fruit firmness was greater for the Max cultivar, and was unaffected by NH₄‐N and NSS at the mature green, breaker, and red ripe fruit development stages. However, at the fully ripe stage, fruit firmness was higher with high NSS and with 25% NH₄‐N.     

Competition for Nitrogen Between Thorn Apple and Tomato and Pepper

The effect of emergence time of the weed Datura stramonium (thorn apple) on tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum L.) was evaluated in a greenhouse experiment. The closer emergence of the weed was to that of the crops, the greater was the weed's growth, seed production, and nitrogen (N) uptake. As a result, growth, fruit yield, and N uptake of the crops was reduced. Shoot N content was reduced in tomato, as was fruit N content in pepper. There was competition by the weed with the crops for N, even when weed emergence was as late as the beginning of flowering. This competition, and the damage it caused, was always more severe with respect to pepper than tomato, irrespective of weed emergence time. The earlier the emergence of Datura stramonium, the fewer were the number of fruits produced by either crop. Average fresh fruit weight in tomato was also reduced. In pepper, the average fruit weight was reduced only when the weed emerged up to the four-leaf stage of the crop. The drop in pepper fruit yield caused by weed emergence up to the four-leaf stage of the crop could be due to competition for light by the weed, in addition to competition for N. Tomato competed better against the weed than did pepper.     

Sulfur and nitrogen supply influence growth,product appearance,and glucosinolate concentration of broccoli

The effects of insufficient and optimal sulfur (S) and nitrogen (N) supply on plant growth and glucosinolate formation were studied under controlled experimental conditions in broccoli “Monaco”. Here, we report on the interaction between S and N supply, plant growth, and quality parameters and discuss the relevance of this interaction in relation to crop‐management strategies. Broccoli plants supplied with insufficient amounts of S or N showed typical deficiency symptoms and yield decreases. In contrast, total glucosinolate concentrations were high at insufficient N supply, independent of the S level, and low at insufficient S supply in combination with an optimal N supply. This was mainly due to the presence of the alkyl glucosinolates glucoraphanin and glucoiberin. Furthermore, with S concentrations above 6 g (kg DM)^–1 and an N : S ratio lower than 10:1, the glucosinolate concentrations were on average around 0.33 g (kg fresh matter)^–1 and differed significantly from those plants characterized by an S concentration below 6 g (kg DM)^–1 and an N : S ratio above 10:1. In addition, N : S ratios between 7:1 and 10:1 promoted plant yield and enhanced overall appearance. Therefore, to produce broccoli (and potentially other Brassicaceae) with higher crop yields and enhanced product quality in the field, it is vital to establish the optimal S and N nutritional status of the plant and to integrate this information into crop‐management strategy programs.     

Effects of crop growth and soil treatments on microbial C,N, and P in dry tropical arable land

We studied the dynamics of microbial C, N, and P in soil cropped with rice (Oryza sativa) and lentils (Lens culinaris) in a dryland farming system. The crop biomass and grain yield were also studied. The microbial biomass and its N and P contents were larger under the lentil than under the rice crop. Microbial nutrients decreased as the crops grew and then increased again. Farmyard manure and NPK fertilizer applications increased the level of microbial nutrients, crop biomass, and grain yield by 35–80%, 55–85%, and 74–86%, respectively. However, these applications had no significant effect on most of the soil physicochemical properties in the short term. The microbial biomass was correlated with the crop biomass and grain yield. The calculated flux of N and P through the microbial biomass ranged from 30–45 and 10–19 kg ha^-1 year^-1, respectively. Cultivation of a cereal crop followed by a leguminous crop sustains higher levels of microbial nutrients and hence greater fertility in impoverished tropical arable soils. The soil microbial biomass appears to contribute significantly to crop productivity by releasing nutrients, and applications of manure, either alone or with fertilizers, promote this effect more strongly than the application of NPK fertilizers alone.     

连作对加工番茄植株生理活性和物质生产的影响

加工番茄是新疆"红色产业"的基础,但随着区域化布局和产业化的发展,连作障碍突出,严重制约着当地加工番茄种植业的可持续发展。因此,本研究于2013年在石河子大学农学院试验站进行田间试验,以当地主栽的加工番茄品种‘里格尔87-5’为试验材料,以3年休闲土壤为正茬对照,选取相邻的连作3年、5年和7年加工番茄种植地块,研究连作对加工番茄植株保护酶活性和物质生产的影响,试图从植株的生理生态特性入手探明加工番茄连作障碍的原因。结果表明:加工番茄连作3年后,在其整个生育进程中均表现出连作障碍效应且随连作年限的延长呈显著增强现象。同一生育时期,随着连作年限的增加,POD活性先增大后减小,CAT和SOD活性及根系活力不断降低,同时MDA含量显著增加,且连作对根系中保护酶活性的影响大于叶片。在试验的年限范围内,连作条件下加工番茄的物质生产力降低,其中连作7年土壤栽培与对照相比差异最显著,其开花前贮藏物质的转运量、转移率和贡献率分别比对照降低57.3%、21%和35.6%;连作条件下加工番茄物质生产力的降低最终导致其产量下降,连作3年、5年和7年的产量分别比对照降低9.4%、15.6%和33.9%;连作条件下加工番茄根冠比对其产量有直接影响,二者呈一元二次显著相关(R2=0.973 5)。说明加工番茄长期连作种植条件下,植株体内保护酶系统受到破坏,组织器官老化,最终导致植株生产库源关系的失调是造成产量下降的主要原因之一。可见,大田生产应合理轮作,避免多年连作,同时调控花果期适宜群体叶面积,建立合理的根冠比,从而减轻连作障碍效应,保证加工番茄获得高产高质。     

Effects of Rhizobial inoculant and nitrogen fertilizer on yield and nodulation of common bean

A two‐year field experiment was conducted to determine if using mixed strains of Rhizobium inoculant and starter nitrogen (N) fertilizer could improve yield and nodulation of four common bean varieties on a Vertisol at Alemaya, Ethiopia. A granular mixed inoculant of CIAT isolates 384, 274, and 632 and a starter N fertilizer at a rate of 23 kg N ha^‐1 (50 kg urea ha^‐1) were applied separately at planting. Inoculation with mixed strains and starter N fertilizer gave a significantly higher grain yield, nodule number, and dry matter yield for most varieties used. Both grain yield and dry matter yield showed a significant correlation (r=0.93 and r=0.87; P<0.05 for grain yield and dry matter yield, respectively, for 1991 crop season and r=0.90 and r=0.86; P<0.05 for grain yield and dry matter yield, respectively, for 1992 crop season) with nodule number. It is recommended that resource‐poor farmers adopt the practice of using a Rhizobium inoculant or starter N to improve common bean yields in the Hararghe highlands, Ethiopia.     

SEASONAL CHANGES IN LEAF NITROGEN OF OLIVE TREES GROWN UNDER DIFFERENT IRRIGATION REGIMES AND CROP LEVEL

An experiment was conducted over 12 months using field-grown olive trees (Olea europaea) to assess the combined effect of soil water availability and fruit number on seasonal changes in leaf nitrogen (N) concentration. Three irrigation regimes were established and three trees per irrigation treatment were thinned to reduce their yield to about half that of unthinned trees. The N concentration of fully-expanded leaves from either the current-year growth or one-year old part of fruiting shoots was determined every two months. Nitrogen concentration was higher in current-year leaves than in one-year old ones at most sampling dates. Maximum values of leaf N were measured in spring, minimum values in August. Leaf N concentrations were positively correlated with leaf water potential during fruit development. This relationship was weak at the onset of rapid oil accumulation in August and became more evident at harvest. There was no correlation between leaf N and crop level.