Growth and yield studies of potato development in a semi-arid region. 3. Effect of water stress and amounts of nitrogen top dressing on physiological indices and on tuber yield and quality of several cultivars

Summary The response of five potato cultivars (Alpha, Cardinal, Désirée, Spunta and Up-to-Date) to a range of amounts of irrigation nitrogen top dressing (N.t.) in a rainless region was studied by means of the line-source sprinkler method. The irrigation-to-evaporation ratio,K _p, ranged from 0.14 to 1.27 and N.t. from 12 kg/ha to 201 kg/ha, respectively. In all cultivars, the yield increased linearly up toK _p=1.0; at higher ratios there was a yield decline in all cultivars except for Cardinal, in which the yield function flattened off. Spunta was the highest yielding cultivar (16t/ha) in the dry range (K _p=0.14; N.t.=12 kg/ha). Désirée was the highest yielding cultivar (64 t/ha) in the wet range (K _p=1.0; N.t.=201 kg/ha), and Alpha was the lowest yielding cultivar in both the dry and wet range (9 and 46 t/ha, respectively). Leaf permeability, leaf water potential and photosynthesis rate decreased, and tuber dry matter percentage increased with decreasingK _p: these indices also varied with plant age, and among cultivars. Yields were adversely affected when soil water potential at the 30-cm depth dropped below −0.4 bar. Contributon from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No E-811, 1983 Series.     

Growth and yield studies of potatoes developed in a semi-arid region 1. Yield response of several varieties grown as a double crop

Summary The yielding capacity of European potato varieties was tested in the spring and the autumn. The environmental characteristics for the spring crop (February–June) are increasing day length and temperature from planting to harvest, with the opposite for the autumn crops (August–December). In the spring crop, using imported seed tubers of about 5–6 months' chronological age, the stem density of different varieties varied between 120 000 and 240 000 per ha, and the weekly yield rates (total yield/growth period) were 2.6 and 4.7 t/ha. In the autumn crop, when local seed tubers of 3 months' chronological age were planted, the stem density was 2–3 times lower and the weekly yield rates were between 1.6 and 3.9 t/ha. Two groups of potato varieties were selected according to their yield performance as being suitable: a) for the spring crop cvs. Up-to-Date, Désirée and ZPC 71E207; and b) suitable for the autumn crop cvs. Désirée, Draga, Gulliver, Spunta, Ropta A3802, ZPC 71E277, and Cardinal. The variability in yield response of theS. tuberosum varieties to the high temperatures and short photoperiods of the semi-arid environment is discussed. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 280-E, 1980 series.     

In vitro evaluation of resistance of potato cultivars toPhytophthora infestans

Summary The resistance of ten potato cultivars (Agria, Ajax, Désirée, Liseta, Kennebec, Majestic. Monalisa, Prima, Spunta and Tonda di Berlino) toPhytophthora infestans was analyzed in vitro using 8 fungal strains. An assay based on electrolyte leakage was used for screening leaves and tuber tissues with fungal culture filtrates. With almost all cultivars the resistance of leaves did not correlate with the resistance of tubers. Cv. Ajax appeared the least susceptible in both leaf and tuber tests, while the cv. Prima was the most susceptible in tuber tests.     

Unsaponifiable lipids from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary Fractions containing Δ⁵- and Δ⁷-sterols, 4-methyl-sterols, triterpenic alcohols, tocopherols and hydrocarbons were isolated by TLC from petroleum ether extracts of the haulm and tuber sprouts of cv Désirée. Sterol and triterpenic alcohol fractions of unsaponifiable lipids of the haulm and tuber sprouts were found to contain twelve sterols and four triterpenic alcohols, respectively. 24R-4-stigmasten-3-on, Δ⁷, Δ⁷, lanosterol, cycloeucalenol and obtisufoliol have not been identified previously in unsaponifiable lipids from haulm and sprouts. In the hydrocarbon fractions of the haulm extract, C₂₃-to C₃₃-n-parafins, C₁₉-and C₃₁-cyclohexyl hydrocarbons, C₂₂-to C₃₈-olefins and squalene were identified, and in the hydrocarbon fractions of the tuber sprouts C₁₂-to C₂₆-olefins and squalene were identified.     

Inductive and noninductive conditions on in vitro tuberisation and microtuber dormancy in potato (Solanum tuberosum subspeciestuberosum and subspeciesandigena)

Summary The effect of growth conditions (medium and photoperiod) on in vitro tuberisation and microtuber dormancy of the cv. Désirée (Solanum tuberosum subspeciestuberosum) and Imilla Negra (Solanum tuberosum subspeciesandigena) was evaluated. The short photoperiod and presence of CCC in the medium reduced the dry matter of plants as well as the size of microtubers. The two cultivars showed a difference, in favour of Désirée, in the percentage of plants having more than one tuber and in the average time of sprouting after storage. The average time of sprouting was more rapidly obtained under long days and in a medium without CCC. The CCC and short days caused the same dormancy conditions and the same K⁺ quantity in the microtubers. The microtubers mineral composition is involved in the dormancy status.     

The influence of rates of nitrogen and potassium application on the yield and specific gravity of four potato varieties

Summary The influence of four nitrogen and four potassium levels on tuber yield, specific gravity and dry matter yield was investigated with the varietiesAristo, Irene, Libertas andIJsselster grown on twelve trial fields on sandy soils. Potassium did not improve dry matter yields, since the improvement in tuber yield was cancelled by a corresponding linear decrease in dry matter content (measured as specific gravity). The same result was found with application of more than 80 kg N/ha, except in the varietyLibertas. Nitrogen caused a linear decrease in specific gravity except in the varietyLibertas which reacted weakly and with an optimum curve. Varieties showed different responses in their specific gravity to the various combinations of nitrogen and potassium. The influence of field on yields and specific gravity was considerable, but could not be explained by the known soil factors, such as moisture retention. pH, % organic matter, etc. This applied also for the variations between fields in their reaction to nitrogen, potassium or variety.

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Zusammenfassung Der Einfluss von 0, 80, 160 und 240 kg N/ha (je zur H?lfte als Salpeter und Ammoniak), je kombiniert mit 1, 100, 200 oder 300 kg K₂O/ha (als Sulfat), auf Knollenertrag, spezifisches Gewicht und Trockensubstanzertrag wurde an den SortenAristo, Irene, Libertas undIJsselster auf zw?lf Versuchsfeldern (sandiger Boden) untersucht. Obwohl die B?den ungenügend mit Kalium versehen waren, verbesserte eine Kaliumgabe die Trockensubstanzertr?ge nicht, da die Erh?hung des Knollenertrages durch eine entsprechende lineare Abnahme des Trockensubstanzgehaltes (Bestimmung des spezifischen Gewichtes) ausgeglichen wurde (Abb. 1). Eine Gabe von 80 kg N/ha bewirkte ein bedeutendes Ansteigen des Trockensubstanzertrages, aber eine weitere Gabe von 80 kg N/ha hatte keinen Einfluss, ausgenommen bei der SorteLibertas, die eine schwache Zunahme zeigte. Eine nochmalige Erh?hung der N-Gabe um 80 kg/ha verursachte bei allen Sorten ein Absinken des Trockensubstanzertrages (Abb. 1). Die Anwendung von Stickstoff verursachte bei den SortenAristo, Irene undIJsselster eine Abnahme des spezifischen Gewichtes, nurLibertas reagierte mit einer Zunahme, gefolgt von ciner Abhahme (Abb. 1). Die Sorten reagierten in ihrem spezifischen Gewicht unterschiedlich auf die verschiedenen Kombinationen der angewendeten Stickstoff-und Kaliummengen (Abb. 4). Nach Umrechnung des spezifischen Gewichtes in Trockensubstanzgehalte wurden die Gesamtmengen an Trockensubstanz und Wasser ermittelt. Bei h?heren Stickstoffgaben stieg die Wassermenge deutlich an, was die Transportkosten erh?hte, w?hrend der Trockensubstanzertrag keine Zunahme zeigte. Die einzige Wirkung der Kaliumdüngung bestand in der Zunahme der Wassermenge in den Knollen. Die sortenbedingten Unterschiede waren betr?chtlich (Abb. 5). Nach Errechnung des Ertrages an Chips auf der Grundlage des spezifischen Gewichtes dürfte die Ertragsabnahme infolge der Stickstoffgabe bei 0% (Libertas) bis 0,7% (Aristo) für die ersten 80 kg/ha, und bei 0% (Libertas) bis 0,8% (Aristo) für die zweiten 80 kg N/ha liegen. Die Kaliumgabe dürfte eine Ertragsabnahme von 0,3 bis 0.5% pro 100 kg K₂O/ha bewirken. Die Zunahme des Oelgehaltes der Chips dürfte sich im gleichen Rahmen bewegen.

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Résumé L'auteur a étudié l'influence de doses de 0, 80, 160 et 240 kg N/ha (moitié en nitrate, moitié en ammoniaque), chaque dose combinéc avec 0, 100, 200 et 300 kg K₂O/ha (en sulfate) sur la production de tubercules, le poids spécifique et la production en matière sèche, avec les variétésAristo, Irene, Libertas etIJsselster, cultivées dans douze champs d'essais sur sol sablonneux. Malgré une déficience des sols en potassium, celui-ci n'a pas amélioré les productions de matière sèche, l'augmentation de la production de tubercules étant neutralisée par une diminution linéaire correspondante de la teneur déterminée par le poids spécifique (Fig. 1). Une application de 80 kg N/ha a augmenté nettement la production de matière séche, mais une dose supplémentaire de 80 kg N/ha n'a eu aucune influence sauf chez la variétéLibertas où s'est marquée une légère augmentation. Une autre dose supplémentaire de 80 kg N/ha a amené une chute brusque des productions de matière sèche chez toutes les variétés (Fig. 1). L'application d'azote a causé une diminution du poids spécifique chezAristo, Irene etIJsselster, tandis queLibertas réagissait par une augmentation suivie d'une diminution (Fig. 1). Les variétés ont réagi différemment dans leur poids spécifique aux diverses combinaisons des quantités d'azote et de potassium appliquées (Fig. 4). On a calculé les quantités totales produites de matière sèche et d'eau après conversion des poids spécifiques en teneurs en matière sèche. Des doses élevées d'azote ont augmenté la quantité d'eau produite, accroissant ainsi les frais de transport, tandis que la production de matière sèche ne montre aucun accroissement. Le seul effet de la fertilisation potassique est d'accroitre la production d'eau. Les différences variétales sont considérables (Fig. 5). Après conversion du poids spécifique en production de pommes ‘chips’, la diminution de production causée par l'application d'azote pourrait être de l'ordre de 0% (Libertas) à 0,7% (Aristo) pour les premiers 80 kg N/ha, et de 0% (Libertas) à 0,8% (Aristo) pour les seconds 80 kg N/ha. L'effet du potassium pourrait être de diminuer la production de 0,3 à 0,5% par 100 kg K₂O/ha. L'augmentation de la teneur en huile des chips poura?t être du même ordre.

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Then stationed at the Provincial Research Centre for Agriculture in Drenthe, Assen, The Netherlands. Present address     

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 1. Turgor maintenance and stomatal behaviour

Summary The response of six potato cultivars, Désirée, Up-to-Date, Alpha, Elvira, Spunta and Troubadour, to water stress under high ambient temperatures was investigated. Osmotic regulation in the leaves of all six cultivars was highest in Alpha and the lowest in Troubadour. Concomitantly, Alpha maintained the highest turgor potential under water stress while Troubadour had the lowest values indicating a relationship between the degree of osmotic regulation and maintenance of turgor. The highest stomatal conductance under water stress was exhibited by Désirée while both stressed and non-stressed plants of Up-to-Date had the lowest values. In addition, Up-to-Date had a larger root system than Désirée. The association of these traits with tolerance to short periods of drought in the potato is discussed. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No 295-E, 1981 series. The investigation was supported in part by a grant from the Ministry for Development Cooperation of the Netherlands.     

Relation between growth conditions and dormancy of seed potatoes. 2. Effects of temperature

Summary In two indoor experiments under short day conditions, the effect of temperature during tuber bulking on dormancy of tubers was investigated for cvs Diamant and Désirée. Temperature treatments started after tuber initiation and lasted for 4 weeks, after which the haulm was removed. In Experiment 1, the day/night temperature regimes 18/12, 22/22, 26/18 and 32/12 °C (T18/12 etc.) were compared. In Experiment 2, three day temperatures (18, 24 and 30 °C) were combined with three night temperatures (12, 18 and 24 °C), resulting in nine treatments. The dormancy of cv. Diamant was shortest after very high day temperatures (30–32 °C), but intermediate day temperatures (22–26 °C) had no shortening effect compared to T18/12. Dormancy of cv. Désirée was not shortened, but rather tended to be prolonged by high temperatures (22–32 °C) during growth. High temperatures during growth resulted in more sprouts per tuber after dormancy had ended.     

Utilisation des engrais chemiques sous conditions tropicales. 1. Effet de l'application d'azote,phosphore et potasse sur les rendements de la pomme de terre en Afrique centrale

Résumé Des essais NPK ont été menés au Rwanda avec une variété précoce et une variété demi-tardive, sur trois types de sols (volcanique, alluvionnaire et latéritique), en saisons séches et pluvieuses. Les augmentations de rendements, calibres, nombre de tiges et tubercules par plante sont représentés en fonction de doses de N (urée), P (triple phosphate) et K (chlorure de potasse). Les engrais ont été plus efficaces sur les sols les plus pauvres et en saison de pluie. L'optimum pour N dépendait de la précocité de la variété et de la saison. Les engrais n'ont pas eu d'action sur le calibre, mais l'augmentation des rendements a surtout été influencée par le nombre de tubercules récoltés par plante.

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Summary Over 120 000 ha of potatoes are grown every year in the region stretching from Zaire to the Nile: Burundi, Uganda, Rwanda and Zaire. The yield is low (7 t/ha), largely because of late blight caused byPhytophthora infestans and poor soils. Fungicides and fertilizers are still rarely used. The National Programme for the Improvement of Potatoes (PNAP) in Rwanda has initiated trials on chemical fertilizers (see Table 1) such as urea, superphosphate and KCl from 1982 to 1985. Trials were carried out on three soil types (Table 2) with two cultivars, Montsama (early maturing) and Sangema (semi-late), under two different seasons: dry and rainy with 250 and 500 mm rainfall respectively during a 110-day growing season. Tables 3 and 4 show the effect of fertilizers as affected by soil type and season on yield for each cultivar. Chemical fertilizers were more effective in poor soils and in rainy seasons. The optimum for N was on average 50 kg/ha with the semi-late cultivar and 100 kg/ha with the early cultivar. Optimum values for P and K were not even reached with levels of 200 kg/ha of P₂O₅ and 200 kg/ha of KCl. Tuber size was not markedly affected by treatment with N, P and K (Figs 1 and 2). Final yields were related mostly to the number of tubers per plant which in turn was directly related to the number of stems per plant and the number of tubers per stem (Fig 2). The three soil types were more deficient in phosphorus than in the other elements and yields obtained with P₂O₅ were significantly greater than those with nitrogen. Given the cost of fertilizers and of potatoes and bearing in mind the results obtained in this study, the use of a mixture of KCl and diammonium phosphate to give an NPK ratio of 63:161:120 is advised in Rwanda.

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Zusammenfassung Mehr als 120 000 ha Kartoffeln werden j?hrlich auf der Krete Za?re-Nil in Burundi, Rwanda, Ouganda und Za?re angebaut. Die Ertr?ge sind tief (7 t/ha) besonders wegen Krautf?ulebefall (Phytophthora infestans) und der armen B?den. Fungizide und Dünger werden eher selten verwendet. Das nationale Programm zur Verbesserung des Kartoffelanbaues (PNAP) in Rwanda hat in den Jahren 1982–83 Versuche mit folgenden Kunstdüngern angelegt: Harnstoff, Triplesuperphosphat und KCl (Tab. 1). Die Versuchen wurden auf 3 verschiedenen Bodentypen (Tab. 2) mit zwei Sorten, Montsama (frühe) und Sangema (mittelsp?te), angelegt und in den folgenden zwei Saisons angebaut: trockene und feuchte mit 250 und respektiv ungef?hr 500 mm Regenfall w?hrend einer Vegetationsdauer von 110 Tagen. In den Tabellen 3 und 4 wird der Einfluss der Düngung je nach Bodenart, Jahreszeit und Sorte dargestellt. Die Kunstdünger waren wirksamer in armen B?den und in feuchter Saison. Das Optimum für N ist im Mittel 50 kg/ha für die mittelsp?te Sorte und 100 kg/ha für die frühe Sorte. Die Optima für P und K wurden mit den gegebenen Gaben von 200 kg/ha P₂O₅ und 200 kg/ha KCl noch nicht erreicht. Das Knollenkaliber wurde nicht bedeutend beeinflusst mit der N, P und K Düngung (Abb. 1 und 2). Die Ertr?ge sind vor allem von der Anzahl Knollen pro Pflanze abh?ngig und diese wiederum ist direkt abh?ngig von der Anzahl Stengel pro Pflanze und der Knollen pro Stengel (Abb. 2). Der Phosphor ist das wichtigste Mangelelement in den 3 geprüften Bodentypen; die P₂O₅ Düngung gab h?her signifikante Resultate als die Stickstoffdüngung. In Betracht der Dünger- und der Kartoffelpreise, sowie der erzielten Ergebnisse, empfiehlt die Beratung in Rwanda die Anwendung eines Gemisches und von Diammonphosphor und KCl im Verh?ltnis von 63 N:161 P:120 K.

     

The response of potato (Solanum spp.) to photoperiod and light intensity under high temperatures

Summary The growth, development and yield of seven cultivars were evaluated under field conditions with photoperiods from 11.5 to 16 hours and light intensities from full light (≧12 MJ/m²/day) to only 42% light in in 3 experiments in the Philippines. The longer photoperiod significantly delayed and reduced tuberization, promoted profuse haulm growth, resulting in: more branching, increased plant height, more flowering, many secondary stems and delayed plant senescence. ‘DTO-33’ was least affected by long photoperiod, followed by ‘Red Pontiac’ and ‘Désirée’. Shading resulted in delayed tuber initiation, taller plants, thinner stems, smaller leaves but longer canopy duration and a slightly larger canopy. ‘DTO-33’ was least affected by shading followed by ‘Désirée’, ‘LT-2’ and ’Red Pontiac’. ‘LT-5’ and ‘P-3’ suffered the greatest tuber yield reduction through shading.     

Shortening dormancy of seed potatoes by a haulm application of gibberellic acid and storage temperature regimes

In three experiments with cvs Diamant (short dormancy) and Désirée (long dormancy), the effect of a haulm application of gibberellic acid (GA) on the dormancy of seed potatoes harvested immature was investigated. Several storage temperature regimes were imposed to examine the interaction between GA and storage temperature. The storage regimes included 18 and 28 C continuously, hot pre-treatments of different duration (different periods at 28 C and subsequently 18 C) and a cold pre-treatment (20 days at 2 C and subsequently 18 C). A foliar spray of 375–750 g GA/ha 3–6 days before haulm killing shortened dormancy, and minimally induced sprouting before harvest. The magnitude of the GA effect depended on the cultivar and storage temperature regime. Compared to untreated tubers stored at 18 C, dormancy was shortened by about 40 days by a GA application and storage at 18 C (Diamant) or by about 90 days by a GA application and storage at 28 C (Désirée).     

Varietal differences in the response of potatoes to repeated short periods of water stress in hot climates. 2. Tuber yield and dry matter accumulation and other tuber properties

Summary The effect of repeated short periods of water stress during the hot season on six potato cultivars was investigated. The number of tubers per plant tended to decrease in response to water stress in cultivars which had more than 9.8 tubers per control plant (Désirée, Alpha, Elvira). In the other cultivars, no consistent effect of water stress on tuber number per plant was observed. Except for Spunta, the percentage of large tubers (>60 g/tuber) was reduced in the water-stressed plants. Consequently, the average weight of these tubers was greater than that of tubers harvested from the unstressed plants, indicating that the sink force of the individual tuber was not impaired by drought. However, tuber yield per plant was reduced due to drought in all cultivars tested. The smallest decrease in dry matter accumulation as well as the greatest lowering of the osmotic potential in the tuber tissue was found in Alpha. No consistent effect of water stress on the percentage of misshapen and sprouting tubers was observed, indicating the marked effect of the high temperature on these traits. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No 310-E, 1981 series. This investigation was sponsored by a grant from the Ministry for Development Cooperation of the Netherlands.     

Morphological changes in tuber buds during dormancy and initial sprout growth of seed potatoes

Summary Potato tuber dormancy is usually defined as lasting from tuber initiation until a sprout of 2 mm long has been formed under storage conditions optimal for sprouting. We tried to find out whether there is a period during which buds of seed tubers do not grow and whether different batches of seed take the same time to grow sprouts 2 mm long. We measured changes in number of leaf primordia and length of tuber buds of cvs Diamant and Désirée over two years. After early haulm pulling, buds did not grow for at least 60 days (‘Diamant’) or 95 days (‘Désirée’). Buds in both cultivars and two tuber weights of ‘Diamant’ took about 20 days from the estimated onset of sprouting to grow 2 mm long. We question whether this period is always similar and thus whether the moment sprouts 2 mm long have formed is a good criterion for the end of dormancy.     

Advancing growth vigor of seed potatoes by a haulm application of gibberellic acid and storage temperature regimes

Seed tubers that are planted soon after their harvest give low yields because of dormancy and low growth vigor. In the research reported in this paper, we investigated the advancing effect of a haulm application of gibberellic acid (750 g GA/ha) 6 days before haulm pulling and its interaction with storage temperature regimes on the growth vigor of immaturely harvested seed tubers of three cultivars. The effects on tuber yield were also examined in one experiment. The storage regimes were: 18 C continuously, hot pre-treatments of different duration (different periods at 28 C and subsequently 18 C) and a cold pre-treatment (20 days at 2 C and subsequently 18 C). Both a foliar spray with GA and storage at 28 C enhanced physiological aging of the tubers and greatly advanced the growth vigor, without negative effects on the morphology of the plants. There was a clear interaction between the GA treatment and the storage temperature regime. At early planting, the effect of the treatments on tuber yield were small for Diamant (short dormancy), but strongly positive for Désirée and Draga (long dormancy).     

Physiological age index: a new,simple and reliable index to assess the physiological age of seed potato tubers based on haulm killing date and length of the incubation period

Chronological and physiological age of seed tubers have major impacts on potato yields. This paper presents a new, simple and reliable physiological age index (PAI) that considers and reconciles the effects of chronological and physiological age. PAI calculation is based on the haulm killing date of the seed crop (T₀) and the end of the incubation period of seed tubers, measured under standardized conditions. The PAI formula is T₁/T₂, where T₁ is the time from haulm killing date (T₀) to possible planting date and T₂ the time from T₀ to the end of the incubation period. The PAI expresses physiological ageing of seed potato tubers within a range from 0 (for physiologically young) to 1 (old) tubers. To test the PAI existing data were re-evaluated and re-elaborated and specific experiments regarding seed origin and storage conditions for different cultivars were performed during 1994–1999. The PAI proved useful in assessing differences due to differences in growing conditions, cultivar, haulm killing, seed origin and storage system, and pre-planting treatments. For example, for cv. Spunta 6 days after haulm killing the PAI was 0.025 and after 100-storage days the PAI was 0.56, 0.52 and 0.49 for seed tubers stored in heaps in the field, at relatively high temperatures, natural diffuse light and a cold (4°C) and ventilated store, respectively. The PAI is related to ground cover duration and yield of the future crop. For a PAI of 0.55 tuber yield was 55 t ha⁻¹, while for a PAI of 0.80 tuber yield was 40 t ha⁻¹. The PAI is easy to measure, non-invasive, objective, reproducible and reliable and could be used for modelling purposes to describe performance of seed tubers.     

The effect of chloride fertilization on blackspot susceptibility and other quality characteristics and on yield of potato

Summary Trials were carried out in two years on a sandy loam and on a heavy clay soil with two cultivars to examine the potential of chloride fertilization as a tool to reduce blackspot susceptibility of potatoes and to investigate other effects on yield and quality. Blackspot susceptibility was significantly reduced in cv. Marijke, but not in cv. Bintje as a result of increasing doses of applied chloride from 0 to 400 kg ha1. Dry matter concentration, assessed as under-water weight, was reduced by chloride in both cultivars at the two locations. Fry colour of French fries was improved by chloride. Applying 400 kg ha⁻¹ Cl⁻ to both soil types decreased net tuber yield >35 mm of cv. Bintje but not of cv. Marijke. Chloride caused slower emergence, retarded crop development and less stems per plant on the sandy loam soil but not on the heavy clay soil.     

Validation of a critical nitrogen dilution curve for hybrid ryegrasses

One of the challenges of modern grassland systems is to minimize nitrogen (N) fertilization without negatively affecting the forage yield. Therefore, critical N dilution curves (Nc = a_c W^?b) have been developed in different species to improve N fertilization management. The aim of this study was to validate a critical N dilution curve for hybrid ryegrasses. Two field experiments were conducted in southern Chile. Treatments were the factorial combination of two hybrid ryegrasses (Shogun and Trojan cultivars) and seven N fertilization rates (0, 50, 100, 200, 350, 525 and 700 kg N/ha). Factors were arranged in a split‐plot design, where forage species were assigned to main plots and N rates to subplots that were randomized into four blocks. A wide range in forage yield and plant N concentration was observed (yield: 0.16 and 3.9 Mg DM/ha and N: 1.6% and 5.1%). The variations in these traits were principally explained by the N levels and harvest times. Relative yield responses of both cultivars were significantly (p < 0.001, R² = 0.81–0.87) related to the nitrogen nutrition index (NNI) calculated with different critical N dilution curves. However, the NNI calculated with N dilution curves from annual ryegrass best described the relative yield response of hybrid ryegrass. Therefore, this validated critical N dilution curve (%N_c = 4.1W^?0.38) will serve as a useful diagnosis tool for improving the N fertilization management of grazing systems for hybrid ryegrasses.     

Effect of cultivar and seed rate of perennial ryegrass and strategic fertilizer nitrogen on the productivity of grass/white clover swards

Four cultivars of perennial ryegrass (intermediate diploid cv. Talbot and tetraploid cv. Barlatra, and late diploid cv. Parcour and tetraploid cv. Petra) were each sown at 10,20 and 30 kg ha^-1, all with 3 kg ha^-1 of white clover cv. Donna. Herbage productivity was measured over 3 harvest years, 1982–84. under two annual rates of fertilizer N (0 and 150 kg ha^-1); the 150 kg ha^-1 rate was split equally between March and August applications. Fertilizer N increased total herbage DM production; the 3-year means for the 0 and 150 kg ha^-1 N rates were 8·04 and 8·91 t ha^-1, respectively. In successive years, total herbage responses to N (kg DM (kg N applied)^-1) were 6·6, 35 and 72 (overall mean, 58). Mean white clover DM production over the 3 years was reduced from 4·48 t ha^-1 at nil N to 2·82 t ha^-1 at the 150 kg ha^-1 rate, a fall of 37%. Grass seed rate did not influence total herbage production or white clover performance. The two intermediate perennial ryegrass cultivars had a marginal advantage in total herbage production over the two late cultivars, but white clover content and production were higher with tetraploids than diploids. It is concluded that the value of increased herbage production from strategic use of fertilizer N has to be weighed against its depressive effect on white clover performance; application of 75 kg ha ha^-1 N in both spring and autumn was excessively high if maintenance of a good white clover content in the sward is an objective. There is considerable flexibility in the grass: clover seed ratio in seeds mixtures. Modern highly-productive perennial ryegrass varieties do not differ substantially in compatibility with white clover but tetraploids permit better clover performance than diploids.     

山西省北部地区玉米化肥施用现状——基于应县大黄巍乡玉米种植户施肥状况调研

通过系统分析山西省朔州市应县玉米种植户化肥投入现状发现,农户的玉米平均产量为10.3 t/hm~2,平均施肥总量为465 kg/hm~2,氮、磷、钾肥的用量分别为262、123、84 kg/hm~2,氮、磷、钾偏生产力分别为42、69、135 kg/kg。基于土壤养分测试,该地区推荐的氮、磷、钾施肥量分别为225、90、45 kg/hm~2。与推荐施肥量相比,氮、磷、钾肥施用过量农户的比例分别为75%、81%和93%。过量的养分投入并没有显著增加玉米产量。     

Effect of physiological age on growth vigour of seed potatoes of two cultivars. I. Influence of storage period and temperature on sprouting characteristics

Summary The influence of storage temperature and storage period on sprouting capacity and incubation period has been studied for 3 years with cvs. Jaerla and Désirée, stored at 4°C and 12°C, as a part of a combined study on the effect of physiological age on growth vigour. During storage the sprouting capacity gradually increased to a maximum and then declined. The maximum sprouting capacity was reached about 80 to 100 days earlier when tubers were stored at 12°C than at 4°C, and it was reached about 50 days earlier by cv. Jaerla than by cv. Désirée at both storage temperatures. The incubation period deereased linearly with time for both cultivars at both storage temperatures, being most rapid at 12°C, and the period was shorter for cv. Jacrla than for cv. Désirée during the whole storage period.

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Zusammenfassung In der allgemeinen Einführung wird das Ziel der gemeinsamen Forschung, den Einfluss des physiologischen Alters auf die Wachstumintensit?t zu untersuchen, beschrieben, und es werden spezielle Ausdrücke definiert, die in dieser und in den folgenden Mitteilungen verwendet werden. In dieser gemeinsamen dreij?hrigen Untersuchung (1979–1981) sind Pflanzknollen der Sorten Jaerla und Désirée aus gleicher Herkunft verwendet worden, die bei 4°C und 12°C gelagert wurden (Tab. 1). Es wird der Einfluss der Lagerzeit und der Temperatur auf das Keimgewicht diskutiert, auf den Gewichtsverlust durch Atmung und Verdunstung und auf die Keimungskapazit?t. die Keiml?nge und auf die Inkubationsperiode. Bei einer Lagertemperatur von 12°C wurden das Keimgewicht pro Knolle und der durch Atmung und Verdunstung bedingte Gewichtsverlust der Knollen und Keime kr?ftig stimuliert (Tab. 2). Bei beiden Sorten wurde w?hrend der Lagerung bei 12°C eine exponentielle Beziehung zwischen dem Keimgewicht und dem Gewichtsverlust durch Atmung und Verdunstung gefunden. wobei die Sorte Jaerla einen h?heren Gewichtverlust pro Keim aufwies (Abb. 1). Die bei 12°C gelagerten Knollen der Sorte Jaerla keimten früher als diejenigen der Sorte Désirée und erreichten eine h?heres durchschnittliches Keimgewicht. Die Keimungskapazit?t und die Inkubationsperiode wurden w?hrend der Lagerung in Abst?nden durch Entkeimen der Knollen und Wiederaustreiben lassen bei 18°C bestimmt. Die Keimungskapazit?t wurde nach 4 Wochen bestimmt an Hand des Keimfrischgewichtes pro Knolle, ausserdem wurde die L?nge des l?ngsten Keimes bestimmt. Die Inkubationsperiode wurde definiert als der Zeitraum zwischen der Keimung und der Bildung kleiner Knollen an den Keimen. Die Keimungskapazit?t erreichte w?hrend der Lagerung ein Maximum, um danach abzufallen (Abb. 2). Dieses Maximum wurde etwa 80 bis 100 Tage früher erreicht, wenn die Knollen bei 12°C gelagert wurden. Bei beiden Lagertemperaturen war die maximale Keimungskapazit?t bei der Sorte Jacrla etwa 50 Tage früher erreicht als bei der Sorte Désiréc. Die maximale L?nge des l?ngsten Keimes korrespondiert in nahezu allen F?llen mit der maximalen Keimunskapazit?t, wobei zwischen beiden Merkmalen cine gute bis sehr gute lineare Beziehung besteht (Tab. 3). Bei beiden Sorten und beiden Lagertemperaturen verringerte sich die Inkubationsperiode linear mit der Zeit, und zwar am schnellsten bei der h?chsten Lagertemperatur. Die Inkubationsperiode der Sorte Jaerla war in allen F?llen kürzer als diejenige der Sorte Désirée (Abb. 3). Wenn das Maximum der Keimkapazit?t überschritten wird, besteht bei beiden Sorten und bei beiden Temperaturen, 4°C und 12°C, eine postive lineare Bezichung zwischen dem Abfallen der Keimungskapazit?t und der Verringerung der Inkubationsperiode (Tab. 4).

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Résumé Dans l'introduction générale l'objectif des recherches concertées concernant l'influence de l'age physiologique sur la vigucur de croissance est décrit et plusieurs termes employés ici et dans plusieurs articles antérieurs sont définis. Les études ont été réalisées durant trois ans (1979–1981) avec des plants des variétés Jaerla et Désirée de même origine conservés à 4°C et 12°C (tableau 1). L'influence de la durée et de la température de conservation sur le poids de germes, les pertes de poids par évapotranspiration, la capacité germinative, la longueur des germes et la période d'incubation est discutée. Le poids de germes par tubercule, les pertes de poids dues à l'évapotranspiration et la germination sont fortement stimulés à 12°C (tableau 2). Il existe une relation exponentielle entre le poids de germes et les pertes de poids des tubercules dues à l'evapo-transpiration pour les deux variétés convervées à 12°C, avec toutefois une perte plus élevée par poids de germes pour la variété Jaerla (figure 1). Les tubercules de cette dernière conservés à 12°C germent plus rapidement que ceux de Désirée et ont un poids moyen de germes plus élevé. La capacité germinative et la période d'incubation sont déterminés à intervalles réguliers durant la conservation par égermage des tubercules suivi d'une germination à 18°C. La capacité germinative est déterminée après quatre semaines par la mesure du poids frais des germes par tubercule et la longueur du plus long germe. La période d'incubation est définie comme étant le temps s'écoulant entre le début de la germination et la formation de petits tubercules sur les germes. La capacité germinative durant la conservation augmente dans le temps puis décline (figure 2). Le maximum est d'environ 80 à 100 jours plus précoce lorsque les tubercules sont conservés à 12°C. Pour les deux températures de conservation, la capacité germinative maximum est pour Jaerla approximativement de 50 jours plus précoce que pour Désiréc. La longueur maximum du plus long germe correspond dans preque tous les cas au maximum de capacité germinative avec une haute ou très hute corrélation (tableau 3). La période d'incubation diminue linéairement avec le temps pour les deux variétés et les deux températures de conservation, bien que plus rapidement pour la température la plus élevée. La période d'incubation de la variété Jaerla est dans tous les cas plus courte que celle de Désirée (figure 3). Lorsque la capacité germinative maximum est passée, il existe une elation linéaire positive entre la diminution de celle-ci et la diminution de la période d'incubation au sein de la même variété pour 4°C et 12°C (tableau 4).