Shoot Dry Matter Yield Research Articles

Efetividade de rizóbios e caracterização fenotípica dos isolados que nodulam feijão-caupi em solos da Amazônia Central

O feijão-caupi (Vigna unguiculata) é uma cultura importante na Amazônia Central, mas os rizóbios associados a essa leguminosa são poucos estudados. O objetivo deste estudo foi avaliar a efetividade e caracterizar fenotipicamente os isolados de rizóbio que nodulam feijão-caupi na região. As populações de rizóbio de Novo Ayrão proporcionaram as maiores produções de matéria seca da parte aérea e total, raiz, número de nódulos e peso dos nódulos secos nas plantas de feijão-caupi; porém, não diferiram do tratamento testemunha com N. Com base nos critérios fenotípicos avaliados, foi possível identificar uma ampla diversidade de populações de rizóbios contidos nos solos da Amazônia.

Phosphate rock utilization by soybean genotypes on a low-P savanna soil and the status of soil P fractions after a subsequent maize crop

Information on the inter- and intra-specific variability in the acquisition and utilization of phosphorus (P) by promiscuous soybean genotypes under low-P conditions can be helpful in the short-term management of soil P availability. Thirteen promiscuous soybean genotypes were evaluated in a low-P soil at Fashola in the derived savanna of Nigeria to compare their ability to acquire and utilize P from phosphate rock (PR) and single superphosphate (SSP). Changes in soil P fractions after a subsequent maize crop were also assessed. The treatments were 90 kg P/ha added as PR (90-PR), 30 kg P/ha as SSP (30-SSP), and 0 kg P/ha as a control (0-P). Large differences occurred in growth, nodulation, and mycorrhizal infection rates among the soybean genotypes and were related to the P sources. Three genotypes (Tgm 1511, Tgm 1419, and Tgm 1360) increased their shoot dry matter yield significantly with PR application. The efficiency of the genotypes to acquire and utilize fertilizer or soil P differed significantly, and their ranking depended on how efficiency is defined. Shortly after application, 90-PR and 30-SSP resulted in similar increases in available P but the effects of 90-PR on the Ca-bound pool were significantly higher than those of 30-SSP. The difference in Ca-bound P between 90-PR and 0-P decreased from 44 to 26 mg/kg after the second cropping, leading to significantly higher levels of resin- P (p = 0.006) and HCO 3 -Pi (p = 0.038) in the PR treatment than in the control. The results of this study indicate that exploiting genotypic differences in P use efficiency may lead to the selection of soybean genotypes that can potentially enhance productivity in the low-P savanna soils.

Development of mint (Mentha piperita L.) grown on biosolids: evaluation of productivity and essential oil content

Development of Mentha piperita L . on biosolids amended soil with levels equivalent to 0, 28, 56 and 112 t ha-1 was evaluated. In order to measure the productivity and its relation with mint essential oil yield, different indices were determined: leaf area, total and several organ dry matter, leaf area ratio, specific leaf area, net assimilation rate and relative growth rate at 30, 44, 58, 72 and 86 days after planting (DAP), and essential oil yield at 90, 110 and 120 DAP. Physiological indices revealed that biosolids prolonged the vegetative phase of the plants, which adapted themselves to the presence of biosolids with time. Plants showed inverse behaviors in relation to productivity, resulting from the primary metabolism, represented by the shoot dry matter yield, and oil yield, resulting from the secondary metabolism. Adaptation of the mint plants to the growth on biosolids could be due to a phytoremediation function of this species. The intrinsic mechanisms of these processes could be better understood in a further evaluation of residual effects in mint plant shoots.

Growth Responses to Varying Zinc Activities in Rice Genotypes Differing in Zn Efficiency and Zn Density

ABSTRACT The relationship between tolerance to Zn-deficiency and Zn-dense in grain was examined. The results showed that the plant height and leaf growth rate (number) decreased more in the Zn-dense genotype (Biyuzaonuo) than in the Zn-efficient genotype (IR8192) when grown at pZn2+ ≥ 11.0. Shoot dry matter yield decreased about 6 times for the dense CV whereas only around 3 times for the efficient CV at Zn activities pZn2+ 9.7–11.4. Zinc uptake by the whole plant was greater in the Zn-dense genotype than in the Zn-efficient genotype, and the lowest in the Zn-inefficient genotype grown at pZn2+ ≥ 11.0. However, both the efficient and the dense cultivars showed higher Zn translocation efficiency at low Zn activity. These results indicate that Zn uptake by rice seedling and translocation might be more suitable than growth parameters for identifying Zn-efficient and Zn-dense genotype at seedling stage.

Effects of Cadmium, Copper, Lead, and Zinc Contamination on Metal Accumulation by Safflower and Wheat

Accumulation of heavy metals (HMs) in cultivated soils is a continuing environmental problem in many parts of the world. An increase in HM concentration can enhance uptake of toxic metals by crops and enter the human food chain. In this study, the uptake behavior of wheat and safflower was evaluated in a calcareous soil by using 12 undisturbed columns in which half were artificially contaminated. Heavy metals in the form of CdCl2 (15 mg Cd kg− 1), CuSO4 (585 mg Cu kg− 1), Pb(NO3)2 (117 mg Pb kg− 1), and ZnCl2 (1094 mg Zn kg− 1) were sprayed on the soil surface and completely mixed in the top 10 cm. The background total concentrations of Cd, Cu, Pb and Zn were 1.6, 29.5, 17.5 and 61.2 mg kg− 1, respectively. After metal application, half of the columns (3 contaminated and 3 uncontaminated) were sown with wheat (Triticum aestivum) and the other half with safflower (Carthamus tinctorious) and grown for 74 days until maturity. After harvesting, soil columns were cut into 10-cm sections and analyzed for HNO3- and DTPA-extractable metal concentrations. Metal concentrations were also measured in different plant tissues. The results showed that artificial contamination of topsoil decreased the transpiration rate of wheat by 12% and that of safflower by 6%. In contaminated columns, Cd, Cu, Pb, and Zn accumulation in wheat shoot was greater by 8.0-, 1.9-, 3.0-, and 2.1-fold than the control, respectively. Accordingly, these numbers were 46.0-, 1.3-, 1.7-, and 1.6-fold in safflower shoot. Soil contamination with HMs resulted in a 55% decrease in shoot dry matter yield of wheat while it had no significant effect on shoot dry matter of safflower. The normalized water consumption for safflower was therefore not affected by metal contamination (≈ 13 mm H2O g− 1 of dry weight for all safflower and uncontaminated wheat treatments), while contaminated wheat was much less water efficient at about 27 mm H2O g− 1 dry weight. It was concluded that although artificial contamination had a negative effect on wheat growth, it did not affect safflower's normal growth and water efficiency.

Effect of harvesting time on phytomass production and essential oil yield in "alecrim-pimenta" (Lippia sidoides Cham.)

The aim of this study was to evaluate fresh and dry mass, as well as essential oil yield, in Lippia sidoides cultivated in the north of Minas Gerais State, Brazil. The experimental design was in randomized blocks, with five treatments and four replicates. Treatments consisted of the following harvesting intervals: 120, 180, 240, 300 and 360 days after transplanting. Measurements on each harvesting included plant height, stem base diameter, leaf, stem and shoot fresh matter yield, and shoot dry matter yield, besides essential oil content and yield per plant. The highest essential oil content was detected at 180 days, whereas the highest dry matter production was observed at 390 days. Essential oil yield per plant was 2.34±1.15 g and productivity was 124.8 kg ha-1. Thus, harvesting at 180 days is recommended.

Effect of mulching dates modified for nature conservation on the yield and nitrogen fixation of green manure lucerne crops

Organically managed fields are highly attractive for wild animals of open agricultural landscapes because of a high percentage of green covered fields; for example, by green manures, catch crops and underseeds. Forage legumes are the main source of nitrogen in organic farming. Forage legumes are also important habitats for wild animals. The main ecological disadvantage is frequent mowing of forage crops. Increasing the time without disturbance in favour of wild animals may also decrease crop productivity and increase weed pressure. Here, we studied the effect of modified mulching dates on yield, nitrogen fixation and weed colonisation of lucerne green manure under pannonian site conditions during two vegetation periods in Eastern Austria. We compared a natural treatment, where the first mulching took place two weeks earlier and the second mulching two weeks later than in a conventional treatment with the latter. While in the first year the shoot dry-matter yield (−1.5 t ha−1), nitrogen yield and the amount of fixed nitrogen (−44 kg N ha−1) in lucerne were significantly lower in the natural than in the conventional treatment at the first cut, no differences could be detected in the second year. The seasonal amount of nitrogen fixation as well as the percentage of N derived from the atmosphere (Ndfa) at both cuts did not differ between the treatments. The natural treatment also had no disadvantageous effects on weed coverage. Our results show that prolonging the period without disturbance in lucerne crops had no adverse agronomic effects with only one exception: the 14-day shorter development period in the natural treatment at the first cut decreased shoot yield and nitrogen fixation compared with the conventional treatment in the first year, when weather conditions were humid before the first cut and dry afterwards. We therefore recommend shifting mulching dates and prolonging cutting intervals in lucerne on organic farms under pannonian site conditions in favour of wild animals.

Relationship of Soil Qualities to Maize Growth Under Increasing Phosphorus Supply in Acid Soils of Southern Cameroon

A large array of soil properties influences plant growth response to phosphorus (P) fertilizer input in acid soils. We carried out a pot experiment using three contrasted acid soils from southern Cameroon with the following main objectives: i) to assess the main soil causal factors of different maize ( Zea mays L.) growth response to applied P and ii) to statistically model soil quality variation across soil types as well as their relationships to dry matter production. The soils used are classified as Typic Kandiudox (TKO), Rhodic Kandiudult (RKU), and Typic Kandiudult (TKU). Analysis of variance, regression, and principal component analyses were used for data analysis and interpretation. Shoot dry matter yield (DMY) was significantly affected by soil type and P rate with no significant interaction. Predicted maximum attainable DMY was lowest in the TKO (26.2 g pot −1) as compared to 35.6 and 36.7 g pot −1 for the RKU and TKU, respectively. Properties that positively influenced DMY were the levels of inorganic NaHCO 3-extractable P, individual basic cations (Ca, Mg, and K), and pH. Their effects contrasted with those of exchangeable Al and C/N ratio, which significantly depressed DMY. Principal component analysis yielded similar results, identifying 4 orthogonal components, which accounted for 84.7% of the total system variance (TSV). Principal component 1 was identified as soil nutrient deficiency explaining 35.9% of TSV. This soil quality varied significantly among the studied soils, emerging as the only soil quality which significantly ( P < 0.05) correlated with maize growth. The 2nd, 3rd, and 4th components were identified as soil organic matter contents, texture, and HCl-extractable P, respectively.

Salinity Effect on Concentration, Uptake, and Relative Translocation of Mineral Nutrients in Four Olive Cultivars

ABSTRACT The aim of this greenhouse study was to investigate the distribution of some ions in four olive cultivars, (Olea europaea L., cvs. ‘Zard’, ‘Conservolea’, ‘Manzanila’, and ‘Mission’) under saline conditions. One-year old olive seedlings were planted in the plastic pots contained 1:1 sand: perlite medium and irrigated with one-half strength Hoagland's No. 1 nutrient solution. A completely randomized design with factorially arranged treatments and four replications was used. Four salinity treatments [0, 40, 80, and 120 mM sodium chloride (NaCl)] were used during 100 days. At harvest, shoot and root dry matter yield as well as concentration of mineral nutrients was separately determined in root, apical and basal leaves. There was significant (P < 0.05) difference among cultivars in concentration, uptake, and relative translocation of sodium (Na), chloride (Cl), and potassium (K) in different plant tissues. ‘Conservolea’ cultivar had the highest Na and Cl and the lowest K concentration in apical and basal leaves. In all cultivars, with increasing salinity, the tissue concentration of Na and Cl increased while the K concentration decreased. The results showed that under saline conditions, the distribution of mineral nutrients in olive depends on both plant cultivar and the ion of interest.

Yield Physiology of Dry Bean

ABSTRACT Dry bean (Phaseolus vulgaris L.) is an important food legume for the world population. However, its average yield is low worldwide. The main reasons for low yield are biotic and abiotic stresses. Maximum economic yield of a crop can be achieved with appropriate balance between plant and environmental factors during crop growth cycle. Adopting appropriate management practices in favor of high yields can modify some of these factors. Hence, knowledge of yield physiology of dry bean is important for understanding yield formation components during crop growth and development and consequently improving yield. Dry bean growth cycle is divided into vegetative and reproductive growth stages. During vegetative stage, development of roots, trifoliate, node, and branches take place. Main features of reproductive growth stage are flowering, pod and grain formation. Important plant traits associated with yield are root and shoot dry matter yield, pod number, 100 grain weight, leaf area index, grain harvest index, and nitrogen harvest index. These plant traits are genetically controlled and also influenced by soil and plant management practices. Higher yield is possible only when there is an adequate balance among various physiological processes or yield components. The objective of this review is to discuss growth and development of bean plant including yield formation process or traits during crop growth cycle and importance of these yield components in determining yield.

Desempenho de populações de alfafa sob desfolhação

Neste trabalho, objetivou-se verificar a resposta de populações de alfafa à desfolhação. Avaliaram-se duas populações de alfafa Crioula (tipo-feno), selecionada em estádio de plântula de acordo com o comprimento do segundo entrenó (EC = 1,5 cm; EL = 2,5 cm) e uma do cultivar Alfagraze (tipo-pastejo). As plantas foram cultivadas em vasos nos meses de março a agosto de 2005 e submetidas a uma combinação de altura (2 e 8 cm) e freqüência de corte (semanal, quinzenal e mensal) durante 141 dias. Não houve diferença quanto à produção da matéria seca (MS) aérea sob cortes semanais e quinzenais. Com cortes mensais, a população Crioula-EL, com maior altura e quantidade de hastes, superou as demais. Os cultivares Alfagraze e Crioula-EC foram similares quanto à quantidade de MS subterrânea. As populações de alfafa diferiram na resposta ao manejo de corte e apresentaram declínio gradual na MS quando submetidas a cortes mais freqüentes, com maior sobrevivência do cultivar Alfagraze em comparação aos cultivares Crioula-EC e Crioula-EL. O cultivar Alfagraze diferiu das populações do cultivar Crioula e apresentou menor altura, maior diâmetro, maior proporção de hastes da coroa e maior alocação de MS na parte subterrânea, portanto, estas características estão relacionadas ao tipo-pastejo. O comprimento do entrenó da plântula poderia ser utilizado complementarmente para selecionar populações de alfafa com maior aptidão ao pastejo, o que torna possível obter populações com variabilidade de produção de matéria seca e sobrevivência.

Physiological and Mineralogical Properties of Arsenic-Induced Chlorosis in Barley Seedlings Grown Hydroponically

ABSTRACT The experiment was carried out to investigate the effects of arsenic (As) on the physiological and mineralogical properties of barley (Hordeum vulgare L. cv. ‘Minorimugi’). The plants were grown in nutrient solution treated with 0, 6.7, 33.5, and 67 μ M As (0, 0.5, 2.5, and 5 ppm As, respectively) in the phytotron. Dry matter yield of shoots and roots decreased significantly with the As treatments, indicating that barley plants are As-sensitive and As-toxicity depends on the As concentration in the rooting medium. Necrosis in older leaves and chlorosis symptoms (whitish color) in the fully developed young leaves were observed at the 33.5 and 67 μ M As treatments. Arsenic concentration, accumulation, and translocation increased with the increase of As concentration in the rooting medium. Arsenic was mostly concentrated in roots and a little amount was moved to shoots, indicating that As was not easily translocated to shoots of barley seedlings. Concentrations and accumulations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), zinc (Zn), and copper (Cu) decreased significantly in shoots for 33.5 and 67 μ M As treatments as compared to the 0 μ M As treatment. Concentrations of P, K, Ca, Mg, Mn, and Cu decreased in roots, but Zn concentration increased in roots at 67 μ M As treatment. Accumulations of P, K, Ca, Mg, Mn, Zn, and Cu in roots also decreased significantly at 67 μ M As treatment. Accumulation of P and the cations showed negative relationship with As. Concentration of Fe decreased in shoots at 33.5 and 67 μ M As treatments where chlorosis was induced in the young leaf but increased in roots at 33.5 and 67 μ M As treatments. It was suggested that As might induce iron (Fe)-chlorosis in the plants. Among the micronutrients, Fe translocation was more affected than others by As. Phytosiderophore (PS) accumulation in roots, which is a symptom of Fe-deficiency in grasses, did not change significantly between 0 and 33.5 μ M As treatments; indicating that As-induced chlorosis did not enhance PS accumulation in roots and decreased due to As-toxicity at 67 μ M As treatment.

Critical Toxicity Level of Arsenic and Elemental Composition of Arsenic-Induced Chlorosis in Hydroponic Sorghum

Physiological and mineralogical responses of sorghum (Sorghum bicolor L. cv. Fast sorghum) in hydroponic culture at elevated concentrations of arsenic (As) were evaluated. Seedlings were grown in the presence of 0, 6.7, 33.5 and 67 µM As levels (0, 0.5, 2.5 and 5 mg As l−1) up to 14 days after treatments (DAT). Shoot and root dry matter yield were repressed by higher As levels. At low As level (6.7 µM) shoot dry matter yield was enhanced by 2.3% but at 33.5 and 67 µM As levels, the yield decreased by 52 and 79%, respectively. The root growth was similarly enhanced (8%) at the lower As level while the growth decrement at the higher As levels were 33 and 68%, respectively for the two treatments. Considering 10% dry weight (DW) reduction, the critical toxicity level of As was calculated to be 11.7 µg g−1 DW for shoot and 367 µg g−1 DW for root, indicating that shoot was more sensitive to As-toxicity than root. A whitish chlorotic symptom was observed in the fully developed young leaves at the 67 µM As level. The lowest chlorophyll content was also observed at this As level. Arsenic concentration increased both in shoot and in root with increase in solution As concentration. The concentrations of As and Fe were about 16, 28 and 17 times; and 2, 25 and 144 times higher in root than shoot at 6.7, 33.5 and 67 µM As levels, respectively. The concentrations of K, Fe and Cu were significantly lower while Ca, Mg and Mn concentrations were higher in the shoot at the 67 µM As level compared to the control plants. On the other hand, Fe, Mn, Zn and Cu concentrations were higher in root at the 67 µM As level. In the shoot, accumulation and translocation of metal micronutrients, particularly that of Fe, decreased significantly because of the presence of As. The present observations suggested that As might induce a toxic effect on sorghum by hampering the translocation of the metal micronutrients. It is suggested that “As-induced Fe-deficiency” caused chlorotic symptoms in the hydroponically grown sorghum.

Long-term kinetics of phosphate desorption from soil and its relationship with plant growth

Knowledge on the availability of residual P in soils is of great importance for fertilization management. The use of dialysis membrane tubes filled with hydrous ferric oxide solution has recently been reported as an effective way to characterize P desorption over long-term laboratory studies. However, there is relatively little information relating the desorption indices of this method to plant parameters. The objective of this research was to relate the kinetic data generated using the DMT-HFO method to shoot dry matter yield of maize grown under greenhouse conditions. Accordingly, the labile pool rate coefficient (kA) showed a highly significant correlation with both shoot dry matter yield (r = −0.994**) and plant P uptake (r = −0.982**). The less labile rate coefficient (kB) also showed a significant correlation with both shoot dry matter yield (r = −0.856*) and P uptake (r = −0.893**). The correlation between the cumulative P extracted and shoot dry matter yield was highly significant. A strongly significant correlation was also observed between Bray 1P and shoot dry matter yield. Judging from the r-val-ues, both the kinetic parameters and the cumulative amount of P desorbed could serve as reliable indices of plant available P revealing the effectiveness of this method in estimating the availability of residual P in soils. However, assessment of the reliability of this method at field level is important. Data from a wider range of soils is necessary to evaluate the universality of this method.

Organic acids in the rhizosphere and root characteristics of soybean (Glycine max) and cowpea (Vigna unguiculata) in relation to phosphorus uptake in poor savanna soils

Root characteristics associated with phosphorus (P) uptake under limiting soil-P conditions were examined in two sets of greenhouse experiments. Average diameter and length of soybean, cowpea, maize and sorghum roots were assessed after 7 weeks in three low-P soils amended with P fertilizer at 0, 3, 6, 11 and 23 mg P/kg. Organic acids in the rhizosphere of soybean, cowpea and pigeon pea were separately evaluated in one soil amended with or without rock phosphate, iron phosphate, aluminium phosphate, calcium phosphate, or triple super phosphate. Unplanted soil served as the control. The growth of soybean, cowpea, maize, and sorghum was significantly improved with P application in all the soils and the amount of P applied played an important role. The shoot dry matter yield and P accumulation correlated significantly with the root length of cowpea and the average diameter of sorghum roots. Citric acid was the only organic acid detected in measurable quantities in the rhizosphere of all plants tested; on average, it varied from 4 (pigeon pea) to 17 (soybean) imol/g soil. For soybean, the secretion of citric acid appeared important for P acquisition in P-limiting environments whereas for cowpea, the size of the roots may be more important.

How does defoliation management impact on yield, canopy forming processes and light interception of lucerne ( Medicago sativa L.) crops?

The frequency of defoliation is the major management tool that modulates shoot yield and the accumulation of C and N root reserves in lucerne crops. A fully irrigated, 2-year-old lucerne ( Medicago sativa L.) crop was grown at Lincoln University (43°38′S and 172°28′E) and subjected to four defoliation treatments. These involved the combination of two grazing frequencies (28 or 42 days) applied before and/or after mid-summer. Annual shoot dry matter (DM) yield ranged from 12 to 23 t/ha. These differences were largely explained by the amount of intercepted photosynthetically active radiation (PAR i) using a conservative conversion efficiency of 1.6 g DM/MJ PAR i. Part of the reduced PAR i in the frequently defoliated treatments was caused by the shorter regrowth period that impeded crop canopy closure to the critical leaf area index (LAI crit) of 3.6. Canopy architecture was unaffected by treatments and a single extinction coefficient for diffuse PAR i ( k d) of 0.81 was found for ‘Grasslands Kaituna’ lucerne. The pool of endogenous nitrogen (N) in taproots was reduced by frequent defoliations. This explained differences in leaf area expansion rate (LAER), which decreased from 0.016 m 2/(m 2 °C day) at 60 kg N/ha to 0.011 m 2/(m 2 °C day) at 20 kg N/ha. The pool of soluble sugars was also positively associated with LAER but the concentrations of carbohydrates and N reserves and the pool of taproot starch were poorly related to LAER. The slower LAER in the frequently defoliated treatments was mostly caused by the smaller area of primary and axillary leaves, particularly above the 6th node position on the main-stem. Developmental processes were less affected by defoliation frequency. For example, the phyllochron was similar in all treatments at 34 °C day (base temperature of 5 °C) per primary leaf during spring/summer but increased in autumn and ranged between 44 and 60 °C day. Branching and senescence started after the appearance of the 4th main-stem node, and both were unaffected by defoliation frequency. These results suggest that the expansion of individual leaves, both primary and axillary, was the most plastic component of canopy formation, particularly after the appearance of the 6th primary leaf. Future mechanistic modelling of lucerne crops may incorporate the management or environmental responses of LAER that control PAR i and impact on shoot DM yields.

Utilization of phosphorus from different sources by genotypes of promiscuous soybean and cowpea in a low-phosphorus savanna soil

The differential ability of genotypes of soybean (Glycine max) and cowpea (Vigna unguiculata) to thrive under low-phosphorus (P) conditions by utilising P from sources with low solubility was assessed in a greenhouse study with a low-P savanna soil collected from a research field in Fashola, south-western Nigeria. The P sources added (21 mg P kg-1 soil) were calcium phosphate (Ca-P), iron phosphate (Fe-P), aluminium phosphate (Al-P), and triple superphosphate (TSP). Soil without P addition served as a control. The soybean genotypes were TGm 1039, TGm 1196, TGm 1293, TGm 1360, TGm 1420, TGm 1511, and TGm 1540. The cowpea genotypes were Dan‑ila, IT89KD-349, IT89KD-391, IT90K-59, and IT82D-716. Nearly all the soybean genotypes significantly increased their shoot dry matter yield (DMY) and accumulation of P from the various sources when compared with the control; the ranking for P acquisition was control<Al-P<Fe-P<Ca-P=TSP. The shoot DMY and shoot P accumulation of most of the cowpea genotypes were also significantly increased by the addition of Ca‑P, Fe-P, and TSP; the addition of Al-P had no significant effect. The cowpea genotypes varied widely in acquiring P from the P sources. However, the general ranking was control=Al‑P<Fe‑P<Ca‑P=TSP. For both crop species, the shoot DM yields under Ca-P and TSP treatments were not significantly different. From the analysis of shoot P accumulation with the Additive Main Effects and Multiplicative Interaction (AMMI) model, the cowpea genotype IT89KD-391 was better than other genotypes with Ca-P as P source; genotype IT90K-59 was better when Fe-P was the P source. In contrast, most of the soybean genotypes appeared to have access to the P sources in a similar manner Keywords: Soybean, cowpea, genotypes, savanna soil, sparingly soluble phosphorus.

The dynamics of lucerne ( Medicago sativa L.) yield components in response to defoliation frequency

The productive life of lucerne ( Medicago sativa L.) stands depends on the rate of mortality of individual plants. However, self-thinning of plant populations may be compensated for by increases in other yield components, namely shoots/plant and individual shoot mass. Frequent defoliation reduces lucerne yield but it is unclear whether this is caused by an acceleration of plant mortality or changes in these other yield components. To investigate this, crops with contrasting shoot yields were created using constant 28 or 42-day regrowth cycles applied to a ‘Kaituna’ lucerne crop in Canterbury, New Zealand during the 2002/2003 and 2003/2004 growth seasons. Two further treatments switched from 28 to 42 or 42 to 28 days grazing frequency in mid-summer (4th February) of each year. The annual yield of shoot dry matter (DM) ranged from 12 to 23 t/ha for the treatments defoliated consistently each 28 or 42 days, respectively. Plant population was unaffected by treatments and declined exponentially from ∼130 plants/m 2 in June 2002 to 60 plants/m 2 in September 2004. The dynamics of plant and shoot population were associated with the light environment at the base of the canopy. The slope of the size/density compensation (SDC) of plants was −1.67 for the treatment defoliated each 42 days, near the expected self-thinning slope of −1.5 for stands at constant leaf area index (LAI). Self-thinning of shoots resumed after each defoliation when the LAI reached 2.1 and the transmission of photosynthetically active radiation (PAR t) was ∼0.20. At this point the proportion of aerial DM in the tallest (dominant) shoots increased non-linearly from ∼30 to >80%, due to the mortality of intermediary and suppressed shoots. The average maximum shoot population in each rotation was ∼780 shoots/m 2 and unaffected by the decline in plant population due to a compensatory increase from ∼6 to 13 shoots/plant as the stand thinned. A lower asymptote of 43 plants/m 2 was estimated as the minimum plant population at which yield component compensation would maintain the productive potential of these ‘Kaituna’ stands. Differences in shoot yield were explained ( R 2 = 0.97) by changes in the individual shoot mass (ISM) that were consistently lowered by frequent defoliation treatments. Frequent defoliations reduced crop productivity by limiting the assimilation of biomass into each individual shoot with negligible impact on shoot appearance rate, the number of shoots per plant at an LAI of 2.1 or the rate of plant population decay. Inter-specific competition for light was proposed as the main factor controlling self-thinning of plants and shoots regardless of their individual C:N status.

Physiological and mineralogical properties of arsenic-induced chlorosis in rice seedlings grown hydroponically

A hydroponic experiment was conducted to observe the effect of arsenic (As) on a number of physiological and mineralogical properties of rice (Oryza sativa L. cv. Akihikari) seedlings. Seedlings were treated with 0, 6.7, 13.4 and 26.8 µmol L−1 As (0, 0.5, 1.0 and 2.0 mg As L−1) for 14 days in a greenhouse. Shoot dry matter yield decreased by 23, 56 and 64%; however, the values for roots were 15, 35 and 42% for the 6.7, 13.4 and 26.8 µmol L−1 As treatments, respectively. Shoot height decreased by 11, 35 and 43%, while that of the roots decreased by 6, 11 and 33%, respectively. These results indicated that the shoot was more sensitive to As than the root in rice. Leaf number and width of leaf blade also decreased with As toxicity. Arsenic toxicity induced chlorosis symptoms in the youngest leaves of rice seedlings by decreasing chlorophyll content. Concentrations and accumulations of K, Mg, Fe, Mn, Zn and Cu decreased significantly in shoots in the 26.8 µmol L−1 As treatment. However, the concentration of P increased in shoots at 6.7 and 13.4 µmol L−1 As levels, indicating a cooperative rather than antagonistic relationship. Arsenic and Fe concentration increased in roots at higher As treatments. Arsenic translocation (%) decreased in the 13.4 and 26.8 µmol L−1 As treatments compared with the 6.7 µmol L−1 As treatment. Arsenic and Fe were mostly concentrated in the roots of rice seedlings, assuming co-existence of these two elements. Roots contained an almost 8–16-fold higher As concentration than shoots in plants in the As treatments. Considering the concentration of Mn, Zn and Cu, it was suggested that chlorosis resulted from Fe deficiency induced by As and not heavy-metal-induced Fe deficiency.

Zinc Application Effects on Yield and Seed Oil Content of Sunflower Grown on a Saline Calcareous Soil

ABSTRACT Two field experiments (2000–2001 and 2001–2002) were conducted at two nearby fields in the Qanavat region of Qom province, central Iran, to investigate the effects of zinc (Zn) fertilization on production of sunflower. The experiment was conducted in a randomized complete block design with six treatments in three replicates. Treatments were: Zn0 (non-Zn fertilized), Zn10, Zn20, Zn30, and Zn60 (soil application of 10, 20, 30, and 60 kg Zn ha−1, respectively), and ZnSpray (foliar spraying of 0.5 kg Zn ha−1 using ZnSO4). Seeds of sunflower (Helianthus annuus cv. ‘Record’) were planted on June 20, 2000 and June 15, 2001. At harvest, shoot and seed yields as well as concentration of Zn, iron (Fe), manganese (Mn), sodium (Na), and chloride (Cl) in leaves of sunflower were determined. Addition of 20 kg Zn ha−1 significantly increased seed production and shoot dry-matter yield of sunflower, while other Zn treatments had no significant effect on shoot dry-matter yield, or decreased it. The thousand-seed weight was the yield component most affected by Zn fertilization, while plant height and head diameter did not change. The maximum content of seed oil was achieved under the Zn10 treatment, then decreased at higher rates of soil-applied Zn such that oil content of seed under the Zn30 and Zn60, treatments was significantly lower than that of the control. Seed oil content was unaffected by foliar spraying of Zn. The concentration of Zn in sunflower leaves was increased with an increase in soil-added Zn of from 0 to 60 kg Zn ha−1. The highest leaf concentrations of Zn (162 and 175 mg kg−1 day matter (DM) in the first and second year, respectively) were achieved by foliar application of ZnSO4. Leaf concentration of Fe was significantly increased in the Zn20 treatment compared with the control but decreased at the higher rates of soil-added ZnSO4. Soil addition of different levels of ZnSO4 decreased concentration of Na and Cl in leaves. The lowest concentration of Na and Cl in leaves was observed under Zn20. The results of this study suggest that soil application of a suitable amount of Zn has a positive effect on both quantitative and qualitative yield of sunflower in saline, calcareous soils.