|
African Crop Science Journal, Vol. 9, No. 1, March 2001, pp. 147-155.
A. A. Tawfik
Code Number: CS01043 ABSTRACT The response of Spunta potato (Solanum tuberosum L.) plants to different rates of potassium (60 and 120 kg Fed-1 ) in presence or absence of Ca nutrition was studied. The study was performed in sandy-loam soil under a drip-irrigation system during fall seasons of 1996 and 1997 years. Plants fertilised with high rate of K (120 kg K. Fed-1) showed 25-30% increase in fresh weight of tubers and lower fresh weight of foliage at 75 and 90 days after planting (DAP) as compared to those of low K (60 kg K. Fed-1). This resulted in at least 50% higher tuber/foliage ratio of high K treated plants at 75 and 90 DAP. Also, plants that received higher rate of K showed 10-20% increase in multiplication rate as compared to those plants that received low K. High K fertilised plants consistently gave 10-20% more tuber yield than those receiving lower dosage. The marketable yield exhibited the same trend as total yield. Compared with low rate of K application, high rate increased yield of medium (28-60 mm) and over-sized tubers (> 60 mm) by about 15 and 40%, respectively. Calcium showed fluctuating effect on all yield parameters during the two seasons of study. The injection of soluble form of calcium fertiliser increased calcium concentration in peel and medulla tuber tissues as compared to non-calcium treated plants even in soil which contained enough calcium for vegetative growth. It is concluded that K nutrition is a key factor for potato production in sandy soils and studies with emphasis on the relationship between soil exchangeable K and K fertilisation rate as well as variety requirement for different production purposes should be continued. Our results also suggest a potential for improving tuber Ca-content by application of soluble form of calcium fertiliser during bulking even in soil containing sufficient calcium for optimum vegetative growth. Key Words: Egypt, mineral nutrition, sandy soils, spunta potato RÉSUMÉ La réponse de la pomme de terre (Solanum tuberosum L.) aux differentes doses de potassium (60 et 120 kg Fed-1) en présence ou absence da la nutrition en calcium a été étudiée. Cette étude a été conduite dans un sol limon-sableux sous un système d'irrigation à goutte pendant les saisons de 1996 et 1997. Les plantes fertilisées avec une dose élevée de K (120 KG. Fed-1) ont montré un augmentation du poids frais des tubercules et une réduction du poids frais des feuilles à 75 et 90 jours après plantation (DAP) par rapport à ceux ayant reçu une faible dose de K (60 kg K.Fed-1). Ceci a abouti au moins à 50% du rapport élevé tubercule/ feuille des plantes traitées evec une dose élevée de K à 75 et 90 jours DAP. Aussi les plantes ayant reçu la dose la plus élevée de K a montré une augmentation de 10-20 % du taux de multiplication par rapport à celles ayant reçu une faible dose de K. Les plantes fortement fertilisées ave K ont constamment donné 10-20% de rendement plus que celles ayant reçu une faible dose. Le rendement commercialisable a exhibé une même tendance que celle du rendement total. En comparaison avec la faible dose de K, la dose la plus élevée a augmenté le rendement des tubercules moyen (28-60 mm) et des tubercules de grande taille (>60 mm) d' environ de 15 et 45% respectivement. Le Ca a montré une variation chez tous les paramètres pendant les deux saisons d' étude. L'injection de la forme soluble du calcium a augmenté la concentration du Ca des épluchures et des tissus médullaires des tubercules par rapport aux plantes non traitées au calcium et même dans le sol qui contient suffisament de Ca pour une croissance végétative. Il a été conclu que la nutrition au K est un facteur clé pour la production de la pomme de terre dans des sols sableux et des études mettant l'accent sur la relation entre le K exchangeable du sol et les doses de fertilisation du K aussi bien que les exigences des variétés pour les differents objectifs de production devraient être continues. Nos résultats suggèrent aussi un potentiel d'améliorer le contenu en Ca des tubercules par l' application de la forme soluble du Ca pendant le grossissement dans un sol contenant assez de Ca pour une optimale croissance végétative. Mots Clés: Egypte, nutrition minérale, sols sableux, pomme de terre spunta INTRODUCTION In Egypt, potato (Solanum tuberosum L.) is a crop of major significance in human nutrition and export. As a result, large expansion and introduction of potatoes, into the recently reclaimed sandy soils are continuing. A major drawback of this type of soil, however, is the lack of enough mineral nutrients to satisfy plant needs to achieve high quantity and quality of tuber production (Westermann and Davis, 1992). Potassium (K) is an important plant nutrient well known for its effect on tuber storability and quality of potato tubers. Potassium promotes vegetative growth (Abo-Sedera and Shehata, 1994), tuber yield and keeping quality during storage (Ashour, 1979; Abo-Sedera and Shehata, 1994; Rabie, 1996). Contrasting results for the optimal level of potassium fertilisation in Delta region have been reported in Egypt. The highest tuber yield reported by Ashour (1979) was with 72 kg K2O and 120 kg N Fed-1 (Fed=0.4 ha). That obtained by Rabie (1996) was with the application of either 96 kg K2O combined with 180 kg N Fed-1 or 80 kg K2O with 150 kg of N Fed-1. In contrast, high tuber yield was achieved when 90 K2O was applied with 100 kg N. Fed-1 (Abo-Sedera and Shehata, 1994). In addition, inconsistent yield improvement was reported by many potato growers in sandy soils as rates of potassium increased than to 96 kg K2O Fed-1 when applied with 150-180 kg N Fed-1. Plant Ca uptake is known to decrease due to K/Ca competition at uptake sites in the root system (Marschner, 1986; Locascio et al., 1992), especially under conditions of high rates of K application. Calcium deficiency often occurs in plant organs having low transpiration rate (Tibbitts and Palzkill, 1979). Therefore, a potato tuber shows less Ca concentration (Wiersum, 1966) as compared to the vegetative portion of the plant (Dunn and Rost, 1948). Accordingly, if field conditions do not insure enough available Ca, plant productivity might be altered (Simmons and Kelling, 1987; Simmons et al., 1988) and might end up with tuber Ca-deficiency disorders (Tzeng et al., 1986; Sterrett and Henninger, 1991; Tawfik, 1993), especially in low available Ca sandy soils. Since K is one of the cations that competes with Ca for uptake (Rhue et al., 1986), it is important to investigate the behaviour of plant and tuber Ca concentration as influenced by K and Ca applications. The objective of the present study, therefore, was to study the effect of potassium application rate and calcium nutrition on vegetative growth, tuber yield, yield component and leaf and tuber Ca concentration in drip-irrigated sandy-loam soil. MATERIALS AND METHODS The present investigation was conducted during fall seasons of 1996 and 1997
using Spunta certified seed tubers on sandy-loam soil at a private farm located
about 60 km North West of Cairo. Cultural management and disease and pest control
programmes were followed according to the Egyptian Ministry of Agriculture recomme-ndations.
Forty soil cores were randomly collected at soil sampling depth of 30 and 60
cm. Samples of each sampling depth were then combined and submitted to the Soil
and Plant Analysis Laboratory, Ministry of Agriculture. The chemical characteristics
of the experimental soil are given in Table 1. Analysis of irrigation water
revealed a pH of 7.3, EC of 0.5 m.mohs. cm-1 and 1.2% of Ca (Co3)2. The sulphate of potash (48% K2O=40% K) was used as potassium (K) source. In
the present work, the term K is used to express potassium. However, in many
field studies potassium is expressed as K2O, but we used instead, the term K
in the present work. Total amount of applied K was either 60 or 120 kg K. Fed-1.
Regardless of the rate of potassium, 50% of the total potassium was applied
before planting, while the rest was added at 35 days after planting (DAP) before
hilling. At 75 and 90 DAP, twenty plants from each treatment were harvested to determine fresh weight (FW) of foliage and tubers and to calculate tuber/foliage ratio. At harvest, multiplication rate, total and marketable yields of 4 rows (36 m2) per each experimental unit were recorded. The multiplication rate was calculated by dividing weight of total tuber yield at harvest by the total weight of seed tubers used to plant the same harvested area. The marketable yield was calculated after discarding decayed, miss-shaped or mechanically injured tubers. Marketable yield was, then, graded into under-, medium- and over-sized tubers according to tuber diameter. The fourth leaf from the top of the plant was used to determine leaf K and Ca concentrations (Westermann, 1993) during 1997. Samples were randomly collected at 54, 75 and 96 DAP where leaves were washed with distilled water and dried at 65°C for 48 h in air-forced ventilated oven. At harvest, tubers from each experimental unit of medium-sized grade (28-60
mm) were selected per treatment to determine percentage of dry matter (DM) and
Ca concentration. After washing with distilled water, 15 tubers were peeled
to get tuber peel (1.5-2 mm thickness). Peeled tubers were sliced longitudinally
from the apical to the rose end and were termed medulla tissue. Peel and medulla
tissues were oven-dried at 65° for 48 h in air-forced ventilated oven. Leaf
and tuber samples were submitted to the Soil and Plant Analysis Laboratory,
Ministry of Agriculture for nutrient determination. Percentage of DM was determined
by grating 5 tubers from each experimental unit, weighing and oven-drying at
105° to constant weight. RESULTS Fresh weight of tubers and foliage. Plants subjected to high potassium rate (120 kg K Fed-1) showed an overall 25-30% increase in FW of tubers at 75 and 90 DAP in both years, regardless of Ca nutrition, (Table 2). In 1996, non-calcium plants of high K exhibited about 17 and 25% higher tuber FW than those of low one (60 kg K Fed-1) at 75 and 90 DAP, respectively. The respective increases of tuber FW of Ca-fertilised plants were 28 and 21% at 75 and 90 DAP, respectively. Plants grown under high K conditions in 1997 with no Ca had about 40 and 29% increase of tuber FW than their counterparts of low K rate at 75 and 90 DAP, respectively. At 75 and 90 DAP, Ca fertilised plants of high K rate showed, respectively, 35 and 27% higher tuber FW than their corresponding ones of low K rate (Table 2). The effect of potassium rate as well as Ca-nutrition on fresh weight of foliage
was inconsistent during the two years of study (Table 2). In 1996, plants subjected
to low rate of K application (60 kg K Fed-1) exhibited 20-22% higher foliage
FW at 75 DAP than those grown with high K (120 kg K Fed-1), regardless of Ca
nutrition. On the other hand, non of potassium rates as well as Ca application
showed any significant effect at 90 DAP (Table 2). In 1997, low K treatments
had higher foliage FW than those of high rates at 75 and 90 DAP. Non-calcium
fertilised plants of low K rate showed about 43 and 20% increase in foliage
FW as compared with those of high K treatment at 75 and 90 DAP, respectively.
Fertilisation with high rate of K resulted in about 14% higher foliage FW of
calcium fertilised plants than low K application during both years (Table 2). Multiplication rate and total and marketable tuber yields. High K fertilisation rate (120 kg K Fed-1) had significantly (P=0.05) the highest multiplication rate, except in 1996 where application of lower rate (60 kg K Fed-1) with Ca-nutrition revealed comparable values (Table 3). In 1996, plants subjected to high K rate with no calcium had 26% higher multiplication rate than those exposed to low K (60 kg K Fed-1). The use of high K rate in 1997 resulted in 18 and 20% higher multiplication rate as compared to low one, for Ca- and non-calcium treatments, respectively (Table 3). Total yield (t Fed-1) was influenced by rate of potassium application during both years (Table 3). In both years, tuber productivity of non-Ca fertilised plants that received high rate of K (120 kg K Fed-1) was about 20% higher than those obtained with low K (60 kg K. Fed-1). In combination with calcium, fertilisation with high K rate resulted in 10 and 21% higher tuber yield as compared with low rate of K application in 1996 and 1997, respectively. Yield of marketable tubers displayed the same trend of total yield as affected by the treatments (Table 3). Non-Ca plants that received high K rate (120 kg K Fed-1) produced about 18 and 20% higher marketable yield than those fertilised with low K during 1996 and 1997 investigations, respectively. The respective values of high potassium treatment in the presence of Ca-nutrition were 11 and 20%, respectively, as compared to low potassium. Thus, calcium nutrition had inconsistent effect on total and marketable yields, regardless of rate of potassium application (Table 3). Yield components. Yield of under-sized tubers (<28 mm) was not consistently affected by any of the studied fertilisation treatments in both years (Table 4). Plants subjected to high potassium rate (120 kg K. Fed-1) produced the highest yield of medium-sized tubers (28-60 mm). Without Ca-fertilisation, application of high K rate showed higher yield of medium-sized tubers, above 16 and 14% than that of low rate of K during 1996 and 1997, respectively. The respective values with Ca-fertilisation during 1996 and 1997 were 5 and 17%. Marketable yield of low K application rate (60 kg K Fed-1) showed the highest significant (P=0.05) proportion (%) of medium-sized tubers in 1997, irrespective of Ca-nutrition (Table 4). Total yield of over-sized tubers (>60 mm) and percentage of marketable yield were significantly influenced by rate of potassium application in the 1997 study. Without Ca-fertilisation, high K (120 kg K Fed-1) application increased yield of over-sized tubers by 73% (1.179 t Fed-1) as compared to the application of low K rate. The respective value in the presence of calcium fertilisation was approximately 52% higher yield (0.9 tFed-1) than the use of low K rate. Marketable yield of non-calcium fertilised plants grown with high potassium rate (120 kg K Fed-1) showed significantly (P=0.05) higher proportion (15.5%) of over-sized tubers than that of calcium and non-calcium plants subjected to low K rate, in 1997 work. Leaf K and Ca concentration. Plants subjected to high rate of K (120
kg K Fed-1) showed higher leaf K concentration (g. 100 g-1 DW) than those of
low K (60 kg K Fed-1) at 54, 75 and 96 DAP (Fig. 1). In contrast, calcium nutrition
slightly reduced leaf K concentration at all sampling dates, regardless of rate
of potassium. Leaf K content of high potassium (120 kg K Fed-1) fertilised plants
increased with the increase in plant age from 54 to 75 DAP even with Ca-nutrition.
That of lower K rate (60 kg K Fed-1) with Ca-nutrition was negatively reduced
at 75 DAP. Marked reduction of leaf K-content was evident in low rate of K treatments
as plant age increased from 75 to 96 DAP, in contrast to high potassium fertilised
plants (Fig. 1). Leaf Ca-concentration of all treatments was in the sufficient range at all sampling dates (Fig. 1). However, differences among treatments were detected. At 54 DAP, Ca-fertilised plants grown with low rate of potassium (60 kg K Fed-1) had the highest leaf Ca concentration, while those subjected to high K rate without Ca showed the lowest values. Plants fertigated with soluble calcium showed higher concentration of leaf Ca than those of non-calcium treatment, at 75 and 96 DAP. The least differences in leaf Ca concentration between Ca and non-Ca plants was at 75 DAP. On the contrary, among Ca and non-Ca plants those of high rate of K (120 kg K Fed-1) showed the lowest values of leaf Ca at 96 DAP (Fig. 1). Dry matter and calcium content of tubers. The studies showed inconsistent effects on tuber DM percentage during both years (Table 5). In 1996, plants fertilised with high potassium rate (120 kg K Fed-1), in general, had significantly higher tuber DM than those of low one fertigated with calcium. Regardless of rate of potassium application, Ca-fertilised plants showed significantly higher tuber peel Ca-concentration (mg. kg-1 DW) than those of non-calcium grown ones. In both years, tuber peel of Ca-fertilised plants, irrespective of potassium fertilisation level, contained about 20% more Ca as compared to their corresponding non-calcium fertilised ones. The same trend was evident for tuber medulla tissue Ca-concentration in both years. In 1996, Ca-fertigated plants of high and low rates of potassium, respectively, showed 33 and 35% higher medulla Ca-concentration than their corresponding non-calcium fertilised plants, respectively. The respective increases in tuber medulla Ca-concentration of Ca-fertilised plants in 1997 were 39 and 38%. DISCUSSION Positive responses of tuber FW (Table 2), total and marketable yields (Table 3) to increased rate of applied potassium (120 kg K Fed-1) are in agreement with previous reports (Ashour, 1979; Abo-Sedera and Shehata, 1994; Rabie, 1996). This effect of high rate of K application could be due to the high bulking rate (Satyanarayana and Arora, 1985) indicated by increased tuber/foliage ratio (Table 2) and high multiplication rate (Table 3). Also, it could be attributed to the attained high yield of medium- and over-sized tubers (Table 4) (Singh and Singh, 1995). In the present investigation, soil analysis revealed low available K content (0.2 meq.L-1). Thus, soil application with high K rate (120 kg K Fed-1) probably increased soil exchangeable K (Mercik, 1989) and, consequently, high plant K stimulated phloem loading and translocation of assimilates to tubers (Beringer et al., 1990). Another possible explanation is that high soil exchangeable K might have increased leaf K concentration (Sharma and Arora, 1988) insuring sufficient leaf K level for optimum plant growth and physiology. In the present study, soil application of high rate of K resulted in sufficient level of leaf K concentration (Westermann, 1993), at 75 and 90 DAP (Fig. 1). Hence, optimum stomatal regulation and photosynthesis (Marschner, 1986) as well as carbohydrate synthesis and translocation (Nelson, 1970) are expected to be ideally performed during later growth stages resulting in high tuber yield. The fact that Ca application (110 kg Ca Fed-1) had no effect on all yield parameters (Clough, 1994) suggests that the positive effect of high K rate (120 kg K. Fed-1) was independent of Ca application. Soil Ca application (110 kg Ca Fed-1) showed no significant effect (P=0.05) on all yield parameters (Tables 2, 3 and 4). In the work of Simmons and Kelling (1987), Ca application in soil having exchangeable Ca lower than 350 mg kg-1 improved tuber yield. Soil analysis under the present study (Table 1) displayed lower calcium than that reported above. Under our condition, however, we observed no foliar symptoms of Ca deficiency where leaf Ca concentration (Fig. 1) was at the sufficient range reported by Westermann (1993) without Ca fertilisation. Therefore, differences in yield response to Ca application between the present work and that of Simmons and Kelling (1987) might be due to differences in Ca requirement of the potato varieties used in both studies. Leaf (Fig. 1) and peel and medulla (Table, 5) Ca concentrations showed significant
responses to applied calcium as earlier reported (Locascio et al., 1992;
Clough, 1994). Although high K rate reduced leaf Ca concentration (Singh and
Brar, 1985; Sharma and Arora, 1988; Locascio et al., 1992), leaf Ca level
remained at the sufficient range (Westermann, 1993), indicating excess or high
Ca uptake in low potassium treated plants removed by K competition in high K
fertilised ones. On the other hand, peel and medulla Ca concentrations were
not affected by K rate, in contrast to the reports of Locascio et al.
(1992). This is, probably, due to the effective method of calcium application
followed in our study Ca being fertigated at the tuber region, thus, increasing
the efficacy of tuber Ca uptake. Besides, we used soluble grade of Ca-nitrate
that could be advantageous for high soil Ca availability in comparison to the
gypsum used in their work. It, furthermore, proposes that the positive effect
of Ca application on elevating tuber calcium concentration was independent of
potassium application rate. REFERENCES
Table 1. Chemical characteristics of the experimental soil
Table 2. Effect of K and Ca nutrition on fresh weight (g. plant-1) of tubers and foliage and Tuber/Foliage ratio of potato plants at 75 and 90 days after planting during 1996 and 1997 years
Means followed by the same letter within the same column are
not significantly different (P=0.05 LSD test)
Table 3. Effect of K and Ca nutrition on multiplication rate, total and marketable tuber yields of potato plants during 1996 and 1997
Means followed by the same letter within the same column are
not significantly different (P=0.05; LSD test)
Table 4. Effect of K and Ca nutrition on yield component of potato tubers at harvest during 1996 and 1997 years
Means followed by the same letter within the same column are
not significantly different (P=0.05; LSD test)
Table 5. Effect of K and Ca nutrition on dry matter percentage and calcium concentration (mg. kg-1 DW) of potato tubers at harvest during 1996 and 1997 years
Means followed by the same letter within the same column are
not significantly different (P=0.05; LSD test)
Figure 1. Effect of K and Ca nutrition on leaf K+ (A) and Ca2+ (B) concentrations (g. 100 g-1 DW) at 54, 75 and 96 days after planting during 1997. Values are means of three replicates. The following images related to this document are available:Line drawing images[cs01043a.gif] |
|