EFFECT OF TILLAGE SYSTEMS, MICROELEMENT FOLIAR FERTILIZATION AND HARVEST METHODS ON THE GERMINABILITY AND VIGOR OF NARROW-LEAF LUPIN SEEDS

Danuta Kurasiak-Popowska¹, Jerzy Szukała^2
1 Department of Genetics and Plant Breeding, Agricultural University of Poznan, Poland
² Department of Soil and Plant Cultivation, Agricultural University of Poznań, Poland

ABSTRACT

The paper examines the influence of tillage systems: conventional, reduced tillage and direct drill, plant foliar fertilization with microelement fertilizers (Mikrosol, Ekolist and Wuxal) and harvest methods (two-stage – entire plants or pods only, one-stage – manual and using a combine harvester) on the quality of narrow-leaf lupin (Lupinus angustifolius L.) seeds of the Zeus cultivar. The vigor of the seeds was determined using the conductometric method, seedling growth test and seedling evaluation test. Additionally, vigor index, the weight of 1000 seeds, and the sum of seedling length were measured. The analyzed tillage systems not so much modified the seeds germination ability, as influenced their vigor. Compared to the control, the analyzed foliar fertilizers did not modify the germination ability and seed vigor of narrow-leaf lupin when combine-harvested and when the entire plants were harvested in two stages. The seeds from combine harvest and two-stage harvest of entire plants showed the greatest vigor and germination considering their vigor index and seedling growth test.

Key words: narrow-leaf lupin, tillage methods, microelement foliar fertilization, harvest methods, seed germination and vigor.

INTRODUCTION

The most important criterion of seed quality is their vigor, determined by germinating ability [4,6,9,15,30]. The lab germination in laboratory conditions is not always the same as in the field, especially with planting in cold and humid soil [20,24,30]. The differences are caused by varied vigor of seeds with the same germination ability.

The difficulty in determining vigor lies in the fact that it depends on many factors such as: seed ripeness, seed formation, topophysical differentiation, harvest method, incidence of defects, infections or pest activity, as well as aging. As observed by many authors, there is no single method (test) determining such a complex seed characteristic [3,8,9,12,14]. Hence it seems appropriate to determine the vigor of seeds using parallel methods [14].

The analysis of vigor in leguminous plants is usually performed using a conductometric test or seedling growth analysis [2,7,9,11,12,14,22,23]. Grzys et al. [14] claim that the methods based on germination e.g. the method of sprout or seedling growth analysis should be more useful than intermediary methods. The authors also stress that the drawback of direct methods is that they are labor-intensive and time-consuming.

The hypothesis assumes that such agricultural practices factors as different tillage systems, microelement foliar fertilization, as well as harvest methods will modify the vigor and viability of narrow-leaf lupin seeds. The aim of this study was to determine the effect of tillage systems, microelement foliar fertilization and harvest methods on the quality of narrow-leaf lupin seeds of the Zeus cultivar.

MATERIAL AND METHODS

The study was conducted on narrow leaf lupin seeds of the Zeus cultivar planted between the years 2002-2003, from a three-factor field experiment, in four reps, at the Złotniki Research and Education Station of the Department of Soil and Plant Cultivation of August Cieszkowski Agricultural University in Poznań.

The tillage systems were the first class of factors: conventional (plough) tillage, reduced (ploughless) tillage and direct sowing (zero tillage). The second class of factors – foliar micro-fertilization included: control – without foliar fertilization, plant fertilization with Mikrosol U, Ekolist Standard, Wuxal Top N Uniwersal used once (1×) during the final stage of budding, and Mikrosol U, Ekolist Standard and Wuxal Top N Uniwersal used twice (2×) during the final stage of budding (first dose) and when in full flowering (second dose). The single dose of all the fertilizers mentioned, both administered the first and second time equaled 3 dm³·ha^-1. The harvest methods were a third-class factor: two-stage – entire plants or pods only, one-stage – manual (manual shelling of seeds) and with a combine harvester.

Two- and one-stage harvesting was performed manually in the phase of yellow ripeness of the seeds. With two-stage harvesting, the entire plants and pods were dried naturally to 14-15% seed moisture content, and then the seeds were threshed on an experimental thresher. One-stage harvesting consisted in manual shelling and natural drying of seeds to obtain 14-15% moisture. One-stage harvesting using a Wintersteiger combine was done during the phase of full ripeness of the seeds with 14-15% seed moisture. All analyses pertaining to the viability and vigor of the seeds were based on seed samples collected from each experimental plot and carried out at the Laboratory at the Department of Soil and Plant Cultivation of the Poznań Agricultural University from December to February. The germination was determined in accordance with ISTA rules on randomly chosen 100 seeds from each replication.

Three methods were used to determine vigor in samples of seeds from each experimental plot [7,15]: electrical conductivity test (conductometric method), seedling growth test and seedling growth speed test. Electrical conductivity measurement of the leachate was performed using the Elmetron CC-551 microcomputer conductometer. The weighted seed samples (50 from each experimental plot) were placed in 250 cm³ beakers which were then placed in a thermostat at the temperature of 20°C. The leachate conductivity measurements were taken 24 hours after stirring the liquid (without removing the seeds from the beakers). The results were recorded in μS·cm^-1·g^-1.

During the seedling growth test, the roll of moistened filter paper with 25 seeds was placed in a thermostat at 20°C. When the test was complete, the length (cm) of normal sprouts was measured and an average sprout length was calculated as indicated by ISTA. To indicate the speed growth, the normal seedlings from each roll were dried at 80°C for 24 hours, weighted and their dry mass was divided by the number of normal seedlings from the roll.

The vigor index was calculated as the product of average seedling length in cm and average germinating in % [7]. Additionally, while testing the seedling growth, a sum of the length of all sprouted seedlings was determined, and it was treated as the length sum of all normal seedlings in a roll.

The weight of 1000 seeds was determined based on seed samples from each experimental plot (2 × 500 seeds) [15].

The results obtained were statistically analyzed, using the variation analysis in STATPAK software. The significance of the differences was determined with the Tukey test at α = 0.05. The variation analysis concerning seed germination was performed after conversion to Bliss values. The relationship between the seed characteristics was determined with the Pearson correlation coefficient.

RESULTS

The greatest average germination was found in seeds harvested using the two-stage method for entire plants; in two-stage harvesting of pods it was significantly lower by 4.5%, and the lowest (by 10.4%) in one-stage manual harvesting. The seed germination ability differed depending on foliar fertilizers combined with specific harvesting methods (Table 1). With the two-stage harvest of pods, when Wuxal was applied twice, it caused the lowering of seed germination ability, compared to the control group. In manual one-stage harvesting of lupin, Mikrosol in both doses improved the crucial parameters of the seed germination when compared to the control group.

The greatest average vigor measured with the electroconductivity test was found in seeds form conventional tillage, the lowest vigor was found in seeds from reduced tillage and direct sowing. There were no significant differences between the last two methods (Fig. 1). The seeds harvested in two stages and dried in entire plants were characterized by a significantly lower leakage of exudates, and hence greater vigor when compared to other harvesting methods in all three tillage systems. Considering the combined effect of the type of tillage system and seed harvesting system, with combine harvesting as the most common, the lowest vigor was found in seeds harvested in the direct sowing. This characteristic made these seeds largely distinct from the ones collected from other experimental plots.

Manual one-stage harvesting and two-stage harvesting of pods, when compared with two-stage entire-plant harvesting, caused a lowering of seedling length of medium significance – by 12% and over 26%, respectively (Fig. 2). In the tillage system, the greatest length of seedlings was recorded for the two-stage of whole plants and one-stage harvesting (both forms). The length of the seedlings was significantly lower in two-stage harvesting of pods alone. In the conventional system, the seedlings were longest when harvested as entire plants in two-stages or when combine-harvested in one stage, significantly shorter when harvested with the two remaining methods. In direct sowing, the two-stage harvest of pods yielded significantly worse results than in the three remaining harvesting methods.

On average, the highest parameters in the seedling evaluation test were obtained when harvesting entire plants in two stages, and manually harvesting seeds in one stage, while significantly lower parameters were obtained in one-stage combine harvesting, and especially with two-stage harvesting of pods alone (Table 2). The test of seedling growth speed presented varied results, depending on the harvesting method combined with the application of foliar fertilizers. Narrow-leaf lupine seedlings presented the greatest dry weight in control groups and when harvested as entire plants in two stages. Upon comparing the vigor of the seeds collected from the control groups, it was shown that the dry weight of seedlings was significantly lower if the seeds were taken from one-stage combine harvesting and two-stage pod harvesting.

The greatest average vigor index was found in seeds harvested as entire plants in two stages and combine-harvested in one stage. Manual one-stage harvest yielded significantly lower vigor index, and two-stage pod harvest yielded the lowest vigor index (Fig. 3). In the conventional system and direct sowing, the greatest vigor index was found for seeds coming from two-stage harvesting of entire plants or one-stage combine harvesting. Manual harvesting done subsequent to the two-stage pod harvesting gives significantly lower results. If the narrow-leaf lupin was farmed using the conventional system, the best vigor index was found in the seeds harvested from entire plants in two-stages and with harvester. The remaining two harvesting methods yielded significantly lower results.

The value of the vigor index in the two-stage harvest of entire plants and one-stage manual harvest did not change significantly as compared to the control when using foliar fertilizers (Table 3). When narrow-leaf lupin was combine-harvested in one stage, then using Ekolist significantly improved the seed vigor index as compare to the control group.

The two-stage harvesting of entire plants and one-stage combine harvesting proved, on average, the best harvesting methods as far as the seedling lengths are concerned. Poorer results were obtained with one-stage manual harvesting and two-stage pod harvesting, respectively (Fig. 4). In the conventional system and direct sowing, the most beneficial parameters of the seedling length sum were obtained in two-stage harvest of entire plants and one-stage combine harvesting. Significantly lower parameters were seen in seeds harvested manually in one-stage, and the lowest – in two-stage pod harvesting. The sum of seedling lengths from the conventional system was highest also with the two-stage harvesting of entire plants and one-stage combine harvesting; however, the two remaining tillage methods resulted in a significant drop in this value.

For the weight of 1000 seeds, two-stage pod harvesting and one-stage manual harvesting proved to yield the best average results, whereas combine harvesting – the worst method (Fig. 5). In conventional and reduced tillage systems, the harvesting methods did not affect the weight of 1000 seeds, whereas in direct sowing, only the one-stage combine harvesting significantly influenced the weight of 1000 seeds as compared to the previous three harvesting methods. Reduced tillage system proved the most beneficial for the weight of 1000 combine-harvested seeds. The remaining two tillage systems gave significantly lower results for this characteristic.

Linear Pearson correlation between respective vigor tests, germination ability, and the weight of 1000 seeds and the sum of seedling length showed that these parameters were correlated to a varied extent (Table 4). Two strongest links were presented in Figs. 6-7.

DISCUSSION

So far legume seed plantations have usually been established on ploughed plots. Both domestic and foreign studies treat the vigor and viability of seeds on the basis of experiments on plot experiments with yellow lupin [1,10,25,26,27,31,34], narrow-leaf lupin [1] and white lupin Lupinus albus L. [29,35] with the traditional ploughing method. The results of the present research showed that the vigor of narrow leaf-lupin seeds changed depending on combination of the type of tillage system with the harvesting method. The highest yields with respect to the seedling growth test, vigor index and additionally the sum of seedling length in narrow-leaf lupin seeds were obtained using reduced tillage system, combine-harvesting, and two-stage harvesting of entire plants.

The harvesting method may be listed as one of the agricultural practices influencing the biological value of the seeds. According to Siwiło and Wrona [32] in machine harvest, threshing damages the seeds the most. Prusiński [30] maintains that the critical factor responsible both for the tearing of pods to release seeds as well as mechanical damage to seeds is the threshing cylinder speed which should be reduced to the minimum. The study carried out by Orzechowski et al. [21] shows that the work of a combine harvester may result in macro-damage of 4.9-8.9% in narrow-leaf lupin seeds, and the loss of moisture during harvest results in even greater damage to seeds.

The effect of the harvesting method on the quality of seeds in legume plants has widely been covered in the literature. Certain authors maintain that the two-stage harvesting method positively affect the vigor and viability of legume seeds. Some authors found that two-stage harvesting proved to be better for the viability and vigor of unripe seeds; however, the harvesting method did not matter if the seeds were harvested at full maturity [33,34,35]. Over the last few years many studies conducted on yellow lupin [25,27], pea [17,36], faba bean [20] or soybean [37] show that the seeds collected in two stages develop greater vigor and germination than those harvested in one stage, which was also observed in the present study on narrow-leaf lupin. The best results of seed viability and vigor determined with electroconductivity test, seedling evaluation test, seedling growth test, vigor index, and the sum of seedling length were noted for narrow-lupin harvested in two-stage method of entire plants. The most highly beneficial effect of two-stage harvesting of narrow-leaf lupin in the present study was due to the transfer of nutrients from the plant into the seeds, and their slow desiccation under natural conditions. This is supported by the studies of Davies and Williams [5] where lupin seeds ripening in fleshy pods reached a significantly higher weight of 1000 seeds and germination 10-12 days earlier than ones harvested in one stage. According to the researchers, this resulted from the thickness of the pod walls and its participation in the accumulation of dry mass by the seeds. Similarly, Kotecki and Kozak [18,19] noted that threshing immediately after harvest, as compared with drying in sheaves, resulted in smaller accumulation of selected chemical ingredients in seeds of broad bean and pea, while the reverse was true for stems and pod walls. The researchers suggest a possibility of migration of chemicals from stems and pod walls into the seeds, when the plants are drying in sheaves.

The lowest viability of narrow-leaf lupin was observed with one-stage manual harvest, whereas the lowest vigor expressed in seedling growth test, vigor index and the sum of the seedling lengths with the two-stage harvest of pods. The reason might be that the pods were dried without any contact with the entire plant and were threshed without straw, unlike in the two-stage harvest of entire plants. The seeds when threshed by the same threshing machine might have been damaged to a greater extent. Similarly, the lowest viability of seeds harvested manually in one stage might be attributed to higher desiccation damage. This is because one-stage manual harvesting was carried out at the same time as two-stage harvesting, i.e. in the stage of yellow ripeness, in order to demonstrate the role of pods and other vegetative parts of plants in two-stage harvesting.

Prusiński [28] maintains that if seeds are dried too fast it may cause disruption of cell membranes and their internal structure, and as he found, in the fast-dried seeds leakage of phosphates, carbohydrates and dissolvable proteins was observed. The present research shows that seeds which have undergone manual one-stage harvest suffered the fastest moisture loss which explains their low vigor and viability. Slow drying, characteristic for two-stage harvest of entire plants allows the development of mechanisms protecting cellular membranes of seeds from damage during germination [16].

CONCLUSIONS

1. The analyzed tillage systems did not significantly modify the germination ability of the narrow-leaf lupin seeds; however, they influenced the vigor of the seeds.

2. When compared to control groups, none of the foliar fertilizers used did not change the germination ability or the vigor of the seeds measured with an electroconductivity test and vigor growth tests when using the most commonly practiced harvesting methods – with a combine, and one-stage and two-stage harvesting of entire plants.

3. The highest narrow-leaf lupin viability of seeds, including also vigor index and the sum of the length of seedlings, was recorded for the two-stage harvest of entire plants and one-stage combine harvest. Seeds coming from two-stage harvesting of entire plants showed a greater vigor in electroconductivity test than those obtained following combine harvest.

4. Analyzing the relationship between the tillage systems and harvesting methods, the greatest seed vigor was found in conventional system, harvest of entire plants in two stages or combine harvest. Only the electroconductivity test showed significantly greater vigor of seeds obtained from the two-stage harvest of entire plants, than in those from the one-stage combine harvest.

5. The study found a strong correlation between the vigor index and seedling growth test, as well as between the seedling growth test and the sum of seedling lengths.

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Accepted for print: 20.11.2007

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