EFFECT OF N FERTILIZATION AND THE HARVEST DATE ON THE ACCUMULATION OF DRY WEIGHT, ORGANIC AND MINERAL NUTRIENTS IN PLANTS OF SELECTED PEA CULTIVARS

Waldemar Helios¹, Andrzej Kotecki^2
1 Institute of Agroecology and Plant Production Wrocław University of Environmental and Life Sciences, Poland
² Department of Plant Cultivation, Wrocław University of Environmental and Life Sciences, Poland

ABSTRACT

In 2000-2002 a field experiment carried out at the Pawłowice Agricultural Experiment Station, in the vicinity of Wrocław, investigated the effect of N fertilization and the date of harvest on the accumulation of nutrients in two pea morphotypes: Agra – leafless and traditional Rola cultivars. The dry weight accumulation in pea seeds, pod-shells and stems was determined by seed ripening, weather course and pea cultivar-specific factor, however it did not depend on the N fertilization. In the period from green to full maturity the plants demonstrated some changes: the share of seeds in seed yield increased, whereas the share of pod-shells and stems decreased; the content of total protein, fat, fiber and crude ash as well as P, K, Mg in seeds decreased and the share of NFE increased. In pod-shells and in stems the content of total protein, fat, NFE, P and the energy value decreased, while the content of fiber – increased. The share of seeds, pod-shells and stems in organic and mineral nutrients accumulation differed and dependent on the development phase and was cultivar-specific.

Key words: pea, dry weight, cultivar, organic and mineral nutrients, date of harvest, N fertilization.

INTRODUCTION

The rate of dry weight gains and nutrient accumulation increase in above-ground legume plant parts depends, among others, on weather conditions, development phase and genetic properties of cultivars [11]. A loss of water in seeds is essential for changing cell activity from “development program” to “germination-oriented program” [21]. The changes in water content in ripening seeds are observed as a metabolic loss of water at the beginning and seed desiccation at the end of ripening. Decreasing water content in seeds is accompanied by an almost constant weight increase. The share of seeds in the whole plant weight was higher in plants threshed after plant desiccation than in plants combine-harvested [5]. Over plant ripening considerable chemical changes occurred in seeds, mostly a decrease in the amount of simple and readily-soluble compounds, and the formation and accumulation of hardly-soluble and macromolecular compounds.

The dynamics of accumulating basic forms of N at different seed development stages in legume species is similar. In pea N-substances are transported from the vegetative plant parts to seeds, mostly at the beginning of seed development [15]. The supply of N to developing seeds is stopped at the dough maturity, however their transformation into protein takes place up to full maturity. Pisulewska et al. [18] observed significant changes neither in the content of protein nor in the seed yield over ripening.

The content of protein in seeds depends on cultivar [17] and weather conditions over vegetation [9]. In the years of a higher air temperature the level of total protein in seeds increased. Sprinkling irrigation resulted in a decrease in the percentage content of protein in seeds, whereas protein seed yield per 1 ha increased [25]. There was found, e.g. a negative correlation between the content of protein in pea seed and rainfall from the end of April to yellow maturity [14].

Greenwood [4] claims that determining the rate of N-compounds accumulation over ontogeny can be applicable to defining the optimal N doses. In practice it is recommended to apply the so-called starter dose of 20-30 kg N·ha^-1 to strengthen plants at the initial development period, before N being fixed by nodule bacteria [6]. During vegetation pea plants fix an average of 50-80 kg N·ha^-1 [9]. The pea seed and straw yield of 3.5 t per ha can uptake up to 200 kg of N [3]. While growing high-yielding pea cultivars, with a low richness of soil in N and low pre-sowing mineral fertilization, free N fixation by nodule bacteria can appear to be insufficient for the yielding potential to be completely used [7,26]. However, the application of excessive N fertilization does not seem justifiable as it is how legumes are deprived of one of their greatest advantages, self-supply with nitrogen [22]. The results of numerous reports indicate that N fertilization does not always enhance the seed yield of legumes [2,19,20]. Over the last few years there has been a considerable progress in pea breeding; cultivars of a greater yielding potential and a lower lodging tendency have been introduced. Leaf-less cultivars make up for a smaller assimilation area with considerably improved light conditions deep in the canopy and more intensive aeration ensures a higher concentration of CO₂ and enhanced plant health status as a result of a lower transpiration [16]. Varied light conditions in the pea canopy, determined by the foliage type, can shape the dry weight accumulation rate during ontogenesis therefore the working hypothesis has assumed that this process is affected by the cultivar, N fertilization and harvest dates.

MATERIAL AND METHODS

In 2000-2002 field and lab experiments were carried out to investigate the accumulation of dry weight, organic and mineral nutrients over pea maturation. The 3-factor field experiment was set up in split-plot design, in 4 reps at the Pawłowice Agricultural Experiment Station and covered the following factors: I – pea cultivar – leaf-less Agra, and traditional Rola, II – N fertilization 0, 30 and 60 kg N·ha^-1, III – seed harvest dates at green, yellow and full seed maturity stages.

The experiments were located on lessive soil, representing autogenic soils, of good wheat soil suitability complex, III a soil evaluation class, after winter rape. Due to a high content of P and K, no phosphorus and potassium were applied. N fertilizers, in a form of ammonium nitrate, were used right before sowing at one dose, following the experiment scheme. Before sowing the B seeds were dressed with Dithane M-45 80 WP. No nitragina seed treatment was applied. 100 germinating seeds per 1 sq m were sown 4-6 cm deep, at 15 cm row spacing on 06.04.2000, 06.04.2001 and 22.03.2002. The area of the single plot was 19.5 m². Throughout the research years there was observed no greater diseases and pest occurrence intensity which would affect the plant development and seed ripening processes. While hand-harvesting, the fresh weight of stems, pods and seeds was determined for 1 sq m of each plot. The lab of the Wrocław Plant Cultivation Department made the following analyses, separately for seeds, pods and stems with leaves:

• dry weight with oven-drying method at 105 ± 2°C for 5 hours,

• total N – with the modified Kjeldahl method and converted into total protein with the use of 6.25 coefficient value,

• crude fat with the Soxhlett-Hendel method in Soxhlett apparatus,

• crude fibre with the Henneberg-Stohmann method,

• crude ash by plant material mineralization in electric oven at 600°C,

• K and Ca with the flame photometry,

• P and Mg with the colorimetric method.

NFE was determined deducting the total content of the other compounds from 100. The chemical analyses provided the energy value of 1 kg of dry weight in MJ. All the parameters studied were verified statistically at α = 0.05 with the AWA software.

RESULTS

Considering three-year mean, the vegetation period of Agra was 11 days longer than that of Rola cultivar (112 days). The seed development, end of April to the beginning of green maturity, was longest in the moist and cool year 2001 (15 days in Agra and 17 days in Rola) and shortest in 2000 (11 days for both cultivars) and depended slightly on the genetic factor. Similar tendencies were observed in the period from green to yellow stage of pea seed maturity. The highest differences over research years, in both cultivars, were found in the length of the period from yellow to full seed maturity. Due to very high rainfall in 2000, the period from yellow to full seed maturity for Agra was 24 days (111.5 mm) while for Rola it took 9 days accompanied by 4.5 mm of rainfall. In 2001 that period for both cultivars lasted 8 days. In the last research year, Agra, as a result of higher temperatures and lower rainfall, demonstrated a shorter yellow to full seed maturity period than Rola. Also in that year both cultivars reached full seed maturity earliest.

The accumulation of dry weight by pea seeds, pod-shells and stems depended foremost on the ripening process, course of weather and the genetic factor and was not significantly affected by N fertilization (Table 1). On average in the 3-year cycle a higher seed and stem weight per 1 m² was obtained from Rola cultivar. The highest dry weight of the entire plants was observed at full maturity stage for Agra and at green and yellow maturity for Rola (Figs. 1 and 2). Along with ripening there was noted an increase in dry weight of seeds and a decrease, due to assimilate translocation, in pod-shells and in stems. The cultivars tested varied in the dry weight of pod-shells and stems. Rola showed a greater rate of decrease in dry weight of stems and pod-shells over ripening.

The analysis of the effect of the harvest date on the structure of above-ground pea plant parts, irrespective of the cultivar, revealed a regular increase in the share of seeds and decrease in the share of stems, starting from green to full maturity. A high rate of increase in dry weight of seeds and of decrease in dry weight of pod-shells and stems remained up to yellow maturity stage, and then fell (Fig. 3).

Chemical composition of pea seeds, pod-shells and stems was changing over ripening and depended on weather conditions and the cultivar response (Tables 2-7). Agra seeds, as compared with Rola seeds, contained significantly less total protein, crude fibre and ash and higher amounts of NFE and showed a higher energy value. The N fertilization used did not affect the chemical composition of seeds. Along with seed ripening there were observed, especially over green to yellow maturity stage, a decrease in the content of total protein, fat, fibre, ash, P, K and Mg and an increase in NFE content and energy value. A low rainfall in 2000 in the period of green to yellow stage of pea seed maturity enhanced the accumulation of total protein and the energy value; however it decreased the contents of crude fibre and NFE (Tables 2 and 3). Agra pod-shells, as compared with Rola, contained more total protein, crude fat, NFE, Ca and Mg. With seed ripening, especially from green to yellow stage of maturation there were observed a decrease in contents of total protein, crude fat, NFE and P and an increase in the content of fibre, crude ash, K, Ca and Mg. In 2000 with low rainfall in the period of green to yellow stage of pea seed maturity, pea pod-shells accumulated more total protein and crude ash than in moist years (Tables 4-5). Agra pea stems, as compared with Rola stems, contained more total protein, fat and crude ash, P, K, Ca and Mg. Pea seed maturing was accompanied by a decrease in the content of total protein, crude fat, NFE and an increase in crude fibre in stems. The weather conditions in 2000 enhanced total protein and crude ash accumulation in pea stems (Tables 6-7).

The amount of organic and mineral compounds accumulated in pea seeds is a function of their content and seed yield and it increased mostly from green to yellow maturity, which resulted from their translocation from pod-shells and stems to seeds. There was found no effect of varied N doses on the accumulation of organic and mineral nutrients (Tables 8-9).

Agra pod-shells took up less total protein, crude fibre, ash, P and K per 1 m² than Rola pod-shells. N fertilization did not have a significant effect on the amount of all the nutrients researched, while in the period from green to full maturity there was observed a decrease in P, crude fat, total protein and NFE especially. Total protein, crude ash, NFE and P accumulation in pod-shells of pea cultivars was affected by the seed ripening stage (Tables 10-11).

Agra stems removed less crude fibre and NFE and higher P and Ca amounts than Rola stems per 1 m². 60 kg N·ha^-1 applied, as compared with the control, increased the amount of crude fat and Ca per 1m². Over seed maturing there was observed a decrease in all the nutrients analyzed, total protein and NFE, especially (Tables 12-13).

Most of the nutrients researched were affected by the interaction of cultivars and maturity phase; although the direction of changes was mostly similar, the changes themselves over time were mostly cultivar-specific. Irrespective of the cultivar, from green to yellow seed maturity, there was observed a high rate of increase in the total protein, crude fat and crude ash, as well as NFE, P, K and Mg, which decreased considerably in the period from yellow to full maturity (Tables 8-9). A similar tendency was observed in pod-shells as far as total protein, NFE and P are concerned (Tables 10-11). As for stems in both pea cultivars, ripening was accompanied by a decrease in the content of the total protein, crude fat, crude ash, NFE and P, however the rate of this process was cultivar-specific (Tables 12-13).The cultivar-specific share of seeds, pod-shells and stems in the accumulation of organic and mineral nutrition varied and depended on the maturity phase. The share of seeds increased while that of pod-shells and stems increased over plant ripening. The highest rate of changes in the content of the total protein, NFE and P was observed between green and yellow stage of pea maturity. During ontogeny there was observed a decreasing share of total protein, crude fat, NFE, P and Mg in pea pod-shells; changes in the accumulation of crude fibre, crude ash and Ca were not clear (Figs. 4-12).

DISCUSSION

The rate of dry matter gain in above-ground parts of legumes depends, among others, on weather conditions, development phase, genetic properties of cultivars, N fertilization and the sowing rate [11]. In the present research the accumulation of organic and mineral nutrients in seeds per 1m² depended mostly on the maturity stage and weather course and, to less extent, on genetic properties of the pea cultivars tested. According to Jasińska and Kotecki [5], a total weight of pea seeds, pod-shells and stems was highest at yellow maturity, of seeds – at full maturity, of pod-shells – at green maturity. The share of seeds in the total dry weight of plants increased from 22.4% at green maturity up to more than 37% at full maturity. Similar tendencies were also observed in the present study.

The 5-year results of Rubes and Neuberg [23] revealed that the highest seed yield of short-stem pea cultivars were obtained following the application of 15 kg N·ha^-1, while 30-60 kg N·ha^-1 doses increased the weight of stems, only [5]. N fertilization at the dose of 40 and 80 kg N·ha^-1 did not affect the pea seed yield [2]. This research did not show any effect of N fertilization on the dry weight of the above-ground pea plants.

Kozak [13] demonstrated that the total weight of stems and pod-shells at full maturity in Kama pea cultivar was over 40% higher than in Rubin. In the present research Rola produced a greater weight of pod-shells and stems than Agra.

The content of total protein in pea seeds is cultivar-specific and dependent on weather conditions over vegetation period and also on agronomic practices. Variation in protein content in pea seeds affected by weather conditions does not exceed 4.5% [18]. A higher content of total protein in pea seeds is characteristic for years with a higher mean air temperature in July, as compared with the multi-year means [12]. The content of protein in seeds is negatively correlated with rainfall [8]. Andrzejewska et al. [1] found that over dry years the content of total protein in pea seeds was 1.2% higher than in moist years. In 2000, in which low rainfall was noted over seed development, the total protein content was highest over research years.

Songin and Czyż [24] noted that 30 kg N·ha^-1 increased the content of total protein in pea seeds, which was not confirmed by the reports of Ziółek and Kulig [27]. Ziółek et al. [28] reported on the content of crude fibre in seeds decreasing significantly along with a delay in sowing date, while that of fat and ash showed decrease tendencies only. In the research reported by Kotecki and Kozak [10] the content of crude fat decreased, while that of NFE increased over maturation, whereas the content of crude fiber was highest at the green maturity, accompanied by lowest energy value.

In the present research, irrespective of the cultivar, ripening coincided with a greater share of seeds and a lower share of stems in the accumulation of all the nutrients studied. These tendencies are convergent to the earlier report by Kotecki and Kozak [10]. The share of pod-shells in total protein, NFE and P accumulation decreased and of Ca – increased. As far as the other nutrients are concerned, no clear trends were observed.

CONCLUSIONS

1. The cultivar-specific accumulation of dry matter in pea seeds, pod-shells and stems was affected mainly by maturing process and weather conditions, however it did not depend on N fertilization.

2. The contents of total protein, crude fiber and crude ash in Agra seeds were lower and of NFE higher than in Rola; however the energy value of seeds in Agra was higher than in Rola. The cultivars tested did not differ in the accumulation of organic and mineral nutrients per 1 m².

3. In the period from green to full seed maturity the following were observed:

4. The share of seeds, pod-shells and stems in the accumulation of organic and mineral compounds by pea differed and depended on the maturity phase and genetic properties of cultivars.

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Accepted for print: 24.10.2006

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