Dry Matter Distribution Research Articles

The Canon of Potato Science: 46. Potato Crop Modelling

What is it? Potato crop performance can be described in terms of development and growth. Developmental stages are tuber initiation, tuber growth, maturity, dormancy, sprouting, emergence (after planting), development of leaves, stems and roots. Development is mainly determined by temperature and day length and is variety dependent. These factors determine the moment of organ initiation and the subsequent relative allocation of dry matter to them. Higher temperatures reduce the time between the various stages and shorter photoperiods lead to earlier tuber initiation, more dry matter allocated to the tubers – hence less to the foliage – and earlier maturing crops. Temperatures above the optimum for growth disfavour tuber growth and thus exert an influence on dry matter distribution. Crop growth – the difference between assimilation and respiration – is determined by yield determining factors: the amount of photosynthetically active radiation and the carbon dioxide level in the air provided temperatures are in an optimal range and all resources such as water and minerals are in ample supply. Temperatures below optimum slow down assimilation processes and too high temperatures speed up respiration; both reducing growth. Carbon dioxide levels are the same everywhere in the world but gradually increase over the years thereby leading to higher intracellular CO2 levels in the leaves which accelerates photosynthesis. The stomata need slightly less aperture because of higher carbon dioxide levels which leads to a reduction of transpiration and increased water-use efficiency. At a higher level of aggregation than photosynthesis and respiration, growth may be described as the dry matter produced by the foliar apparatus following interception of photosynthetically active radiation (about half of global radiation).

Production and Nutritive Value of Grazed Simple and Complex Forage Mixtures

Sustainability of forage production in the Northeast USA is affected by environmental and climatic variability. Complex forage mixtures may be better adapted than simple mixtures to variable environments and produce greater dry matter (DM) yield more evenly throughout the growing season, thereby increasing sustainability of forage production. A grazing trial was set up to evaluate forage production, nutritive value, and botanical composition dynamics of well‐adapted and commonly sown forage species. The forage treatments consisted of simple mixtures (two and three species) and complex mixtures (six and nine species). The experiment was mob‐grazed with cow–calf (Bos taurus L.) pairs five times each year. Dry matter distribution during the growing season was independent of mixture complexity; it was, instead, influenced mainly by the weather. When averaged across all 3 yr, mixtures containing six species produced greater (P < 0.001) forage yield (9900 kg DM ha−1) compared with two‐species (8700 kg DM ha−1) or three‐species mixtures (8400 kg DM ha−1). However, forage production varied within species richness groups. In general, regardless of the initial botanical composition, the predominant species in most mixtures by the end of the experiment were orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), and white clover (Trifolium repens L.). Variation in nutritive value among mixtures was explained mainly by variation in the proportions of grasses and legumes. We conclude that when it comes to large yields and top nutritive value, the most important consideration is the individual species, not the complexity of the mixtures.

Dry Matter Partitioning, Carbohydrate Composition, Protein Reserves, and Fruiting in ‘Autumn Bliss’ Red Raspberry Vary in Response to Pruning Date and Cane Density

In a 2-year experiment (1994 and 1995), plants of primocane-fruiting red raspberry cultivar ‘Autumn Bliss’ grown in a plastic greenhouse were destructively harvested at different growth stages to determine the effect of pruning date and cane density on dry matter distribution, carbohydrate concentration, and soluble protein concentration in different plant parts. Three summer-pruning dates (early, mid, and late July) and four cane densities (8, 16, 24, and 32 canes/m row) were imposed. Relative root biomass decreased from pruning to first flower stage and remained constant thereafter for all pruning dates. Earlier pruning dates corresponded to earlier fruit production, but yield was significantly reduced on later pruning dates and higher cane densities. Sucrose concentration was higher in fine roots than in suberized roots and had a slight decrease during flowering and the beginning of harvest. Soluble protein concentrations did not differ significantly between pruning dates. Reserve carbohydrates in the root system were unaffected by pruning and cane density, and were rapidly used during active vegetative growth, began to recover just after bloom, and were fully recovered at the end of the season. Our experiment suggested that in red raspberry plants grown under poor environmental conditions, current yield is reduced but there is enough carbohydrate accumulation to support next year's growth.

Effect of water supply on leaf area development, stomatal activity, transpiration, and dry matter production and distribution in young olive trees

Two-year-old olive trees cv. Cornicabra, trained in a central leader form for hedgerow planting, were grown outdoors in 45-L weighing lysimeters to evaluate the effect of water supply on growth and development. Four treatments were established and maintained for 155 days during spring–autumn. Treatment T100 was irrigated to maintain the potting medium close to water-holding capacity by progressive replenishment of consumption that was measured at weekly intervals by weighing and recording drainage. Treatments T80, T60, and T40 received 80, 60, and 40%, respectively, of the water applied to T100. For these treatments, transpiration and leaf area were measured every fortnight. Dry matter in roots, stems, and leaves was measured at the beginning and end of the experiment. Leaf conductance was measured at 09 : 00 and 12 : 00 solar time every fortnight and at c. 2-hourly intervals throughout one day each month. Over the experimental period, T100 produced 0.42 ± 0.01 m2 leaf area, 319.6 ± 60.4 g dry biomass, and transpired 77.5 ± 1.1 L water. Water stress significantly reduced leaf area development and dry matter production (P < 0.05) in T60 and T40, but not in T80. There was no effect on dry matter partitioning to the various organs of the trees or the roots/aerial part ratio. Leaf conductance was more sensitive to water stress than vegetative growth, with significant differences (P < 0.05) established among treatments 3 weeks before differences were observed in transpiration. In autumn, transpiration and leaf conductance increased in all treatments independently of soil water status. Over the experiment, transpiration efficiency (TE, g/L) increased with reduced water supply, with a significant difference (P < 0.10) between T100 and both T60 and T40. The study has established that maximum growth of young olive plants can be achieved, without effect on the distribution of biomass between organs, at water supply less than that required to support maximum transpiration.

Timing of GA3 Application to Indian Mustard (Brassica juncea L.): Dry Matter Distribution, Growth Analysis and Nutrient Uptake

Timing of GA3 Application to Indian Mustard (Brassica juncea L.): Dry Matter Distribution, Growth Analysis and Nutrient Uptake

Effect of harvest period on foliage production and dry matter distribution in five cassava cultivars during the second plant cycle

The objective of this work was to study the leaf production pattern and dry matter distribution in cassava during the second plant cycle. The completely randomized experimental design with four replications was used, with five cultivars in the main plots and ten harvest times in the sub-plots. Foliage production was affected by plant age, being higher in hot periods. Leaf blades and petioles dry matter content presented a linear increase due to a progressive decrease in the amount of young leaves and ontogenetic factors. The stems provided, temporarily, carbohydrates to the plant re-growth, delaying the availability and use of storage roots dry matter. The dry matter content in the storage roots was lower during the vegetative and higher during rest period. The storage roots diameter increased considerably when the amount of leaves was higher, indicating the importance of leaf area in the cassava plant production.

Hydraulic conductance characteristics of peach (Prunus persica) trees on different rootstocks are related to biomass production and distribution

We investigated hydraulic conductance characteristics and associated dry matter production and distribution of peach trees grafted on different rootstocks growing in the field. A single scion genotype was grown on a low ('K146-43'), an intermediate ('Hiawatha') and a high ('Nemaguard') vigor rootstock. 'K146-43' and 'Hiawatha' rootstocks had 27 and 52% lower mean leaf-specific hydraulic conductances, respectively, than the more vigorous 'Nemaguard' rootstock. Tree growth rates and patterns of biomass distribution varied significantly among rootstocks. Mean dry mass relative growth rates of trees on 'K146-43' and 'Nemaguard' were 66 and 75%, respectively, of the rates of trees on 'Nemaguard', and the scion to rootstock dry mass ratios of trees on 'K146-43' and 'Hiawatha' were 63 and 82%, respectively, of the ratio of trees on 'Nemaguard'. Thus, differences in dry matter distribution between the scion and rootstock, which may be a compensatory response to the differences in leaf specific hydraulic conductance among rootstocks, appeared to be related to differences in growth rates. Correspondingly, there was a positive linear relationship between the scion to rootstock dry mass ratio and the rootstock to scion hydraulic conductance ratio when conductance was normalized for dry mass. This study confirms that rootstock effects on tree water relations and vegetative growth potential result, at least in part, from differences in tree hydraulic conductance associated with specific peach rootstocks.

Field yield, ensiling properties and digestibility by sheep of silages from two forage sorghum varieties

This study examines the yield, composition, digestibility and ensiling properties of the new sorghum brown-midrib hybrid BMR-101. The commercial forage sorghum FS-5 was used as a reference variety. Forages were grown in a typical Mediterranean climate in five replicate plots, irrigated with 250 mm water, combine harvested at the soft dough stage and ensiled under both laboratory and commercial conditions. Both varieties were tall (>2.0 m). The dry matter (DM) content at harvest of FS-5 was higher than that of BMR-101 (296 g/kg forage versus 255 g/kg forage, P<0.05). BMR-101 plants suffered from higher lodging than FS-5 plants (60% versus 16.7%, P<0.05). Dry matter (DM) yield of the green forage was higher for FS-5 than BMR-101 (12.1 t/ha versus 9.89 t/ha, P<0.05). The distribution of DM among plant organs was similar for the two varieties, which contained also similar levels of neutral detergent fiber (aNDFom, 560–563 g/kg DM). BMR-101 raw plants had higher content of crude protein (CP) and hemicellulose and lower content of water-soluble carbohydrate (WSC), cellulose and lignin than FS-5 plants. Ensiling of the two varieties in glass silos resulted in moderate DM losses (<0.08 of yield) mostly as volatile gases, solubilisation of 0.04–0.12 hemicellulose, and high conversion of WSC mostly into lactate, ethanol and acetate. Ensiling in large scale bunker silos resulted in more extensive fermentation of WSC and lactate into acetate and ethanol, but in similar low pH (<4). In vitro DM digestibility of the two silages was similar, but in vitro NDF digestibility was higher for BMR-101 silage than FS-5 silage (P<0.05). Eight Assaff rams were assigned randomly into two dietary groups of four rams each and fed the two silages in a 2 × 2 crossover design. Intake and digestibility by sheep of silage DM and CP were similar for both varieties. Digestibility of silage NDF, cellulose and hemicellulose was higher for sheep fed BMR-101 as compared with FS-5 (P<0.05). The production of digestible silage DM was calculated to be higher for FS-5 than BMR-101 (7.14 t/ha versus 6.13 t/ha, P<0.05). These data highlight the advantages of commercial FS-5 relative to the new BMR-101 variety: its better resistance to lodging and higher production of silage DM and digestible DM per ha.

The relationship of hydraulic conductance to root system characteristics of peach (Prunus persica) rootstocks

Specific rootstocks can differentially influence the vegetative growth and development of fruit trees. However, the physiological mechanism involved in this phenomenon has been elusive. Recent research comparing different peach (Prunus persica L. Batsch) rootstocks suggests that the rootstock effect on vegetative growth in peach trees is associated to water relations and more specifically to differences in rootstock hydraulic conductance. This study was intended to confirm differences in hydraulic characteristics of similar size peach trees grafted on different rootstocks and to examine root system characteristics that could be associated with rootstock hydraulic limitations. Trees on rootstocks that were known to have a size‐controlling effect when grown under field conditions had lower rootstock conductance than trees on the vigorous (control) rootstock when rootstock hydraulic conductance was measured with both the high‐pressure and evaporative flow methods. Rootstocks with the lowest hydraulic conductance had less fine root surface area and length per unit root dry weight than the more vigorous (control) rootstock. However, contrary to previous field studies, in this study there were no significant differences in dry matter production and distribution among trees on the different rootstocks suggesting that whatever the normal growth control mechanism was, it did not differentially influence growth under the specific conditions of this study. This research confirmed that peach rootstocks exhibiting size‐controlling behavior under field conditions differed in their hydraulic and morphological characteristics under controlled growth conditions even when those growth conditions negated the expression of the size‐controlling behavior.

Improvement of lipid and phospholipid recoveries from sardine ( Sardina pilchardus) viscera using industrial proteases

Enzymatic hydrolysis of sardine viscera by three broad spectrum proteases was investigated using the pHstat method (24 h, pH 8, 50 °C). After hydrolysis, three fractions (sludge, aqueous phase and oily phase) were collected. For each fraction, lipids and phospholipids were quantified and molecular weights of aqueous phase peptides were determined. Under these conditions, the degree of hydrolysis (DH) varied from 1.9% (Flavourzyme), 3.1% (Protamex) and to 3.3% (Alcalase). Dry matter distribution indicated that all hydrolysis performed increased solubilisation of proteins: protein recovery for each hydrolysis ranged from 57.4% to 61.2%. Furthermore, the total lipid content in the liquid parts (oily and aqueous phases) increased (at least 85% of lipids quantified in the raw material are in these phases) which may improve lipid recovery for commercial applications. In addition, these lipids were richer in phospholipids than those extracted by classical chemical extraction, especially after Alcalase hydrolysis.

Seasonal changes in the effects of free-air CO 2 enrichment (FACE) on dry matter production and distribution of rice ( Oryza sativa L.)

It is reported that stimulating effect of elevated atmospheric [CO 2] on photosynthesis of rice ( Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO 2]. A free-air CO 2 enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol −1 above ambient) [CO 2] and supplied with 25 g N m 2, which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO 2] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique).

Response of Corn (Zea mays) and Weeds to Planting Pattern and Herbicide Use

ABSTRACT The use of narrow row arrangement in corn (Zea mays) has been suggested as a technological alternative to obtain grain yield increases through a better use of the resources. The regular pattern could diminish intraspecific competition while favouring interspecific competition with weeds. The objective of this study was to analyse the effect of corn planting pattern and herbicide application on (i) soil water content and photosynthetically active radiation (PAR) dynamics, (ii) below ground and above ground corn biomass and grain yield and (iii) weed suppressive ability of dryland corn sown at square and rectangular plant arrangement. Field experiments were conducted during the growing seasons 2002/03 and 2003/04. Three corn hybrids with two plant arrangement (rectangular: 0.70 × 0.20 m and square: 0.35 × 0.35 m) and herbicide (2.25 kg ai ha−1 of atrazine and 2.32 kg ai ha−1 of metolachlor) use compared with no herbicide use were tested. In the initial stages of the crop there was greater moisture content in the row of corn sowed at square planting pattern while a lower soil water content at maturity was observed. Conversely, between rows, the square plant arrangement registered lower soil water content during the growing cycle of the crop. This soil water profile was a consequence of the uniform corn below ground dry matter distribution. A greater PAR interception with a lower weed above ground dry matter was obtained in square plant arrangement. Corn grain yield was greater in the square-planting pattern than in the rectangular ones. This increase in grain yield was related to better resources use i.e. soil moisture and PAR interception while reduces the competition from weeds. The use of equidistant plant arrangement appeared as an interesting alternative to increase both the grain yield potential and the corn suppressive ability against weeds in dryland Argentinean production systems.

Dry matter production and partitioning in rose ( Rosa hybrida) flower shoots

Dry matter production and allocation to the different organs of rose ( Rosa hybrida, cv. Dallas) flower shoots were investigated during three growth cycles (spring, summer and late autumn). The crop was grown under greenhouse conditions in a Mediterranean climate (Valencia, Spain). Fresh and dry matter, leaf area, and thermal time were determined at eight phenological stages of the flower shoot, from cutting to harvest. The increase in the shoot dry matter followed an expolinear function quite closely, suggesting that the shoot growth rate was near its maximum value at the time of harvest. The appearance of the flower bud drastically changed the dry matter distribution between the organs (stem, leaves and flower bud). Leaves were the first organs to be affected by the bud demand, showing a strong decrease in growth rate just after bud appearance. Stem growth rate was also affected, but later, and to a lesser extent. Flower bud growth was exponential until harvest. When expressed as a function of thermal time, dry matter partitioning was rather similar during the three growth cycles. Empirical functions are proposed that quantify dry matter partitioning in the organs of flower shoots as a function of thermal time. The overall results stressed the key role played by the flower bud in determining the dynamics of dry matter allocation in rose flower shoots.

Contrasting accumulations of calcium and magnesium in seed coats and embryos of common bean and soybean

How plant genotypes affect accumulation and within-seed distribution of Ca and Mg in soybean ( Glycine max L.) and common bean ( Phaseolus vulgaris L.) seed is important because of concerns in regards to human nutrition. Accumulation of seed Ca and Mg in separate experiments, each with 12 genotypes, was studied. Genotype affected seed Mg concentration [Mg] and especially seed Ca concentration [Ca] in the two species. Percentages of total seed Ca in seed coats ranged from 67% to 81% for the common bean genotypes and from 17% to 27% for the soybean genotypes. Percentages of total seed Mg in the seed coats ranged from 16% to 28% for the common bean genotypes and from 6% to 10% for the soybean genotypes. Percentages of seed dry matter in the seed coats were 9.3–11.0% for the common bean genotypes and 7.0–12.4% for the soybean genotypes. Four common bean and two soybean genotypes were next grown under similar environmental conditions in a greenhouse experiment. Results confirmed that seed coats of common bean are enriched in Mg and especially Ca relative to dry-matter distribution. In contrast, seed coats of soybean are enriched in Ca, but to a lesser extent than in common bean, and are not enriched in Mg.

Seed Iron in Diverse Soybean Genotypes

ABSTRACT Iron (Fe) in the embryo fraction of soybean (Glycine max L.) seed is important for seedling growth. Seed Fe accumulation in 27 soybean genotypes differing in seed size was studied at two field locations. Mean seed weight was 148 mg seed−1 with mean individual genotypic values ranging from 68 to 217 mg seed−1. Percentage of total seed dry matter in the seed-coat fraction, which was inversely correlated with individual seed weight, was 8.2%, with mean individual genotypic values ranging from 7.0% to 12.4%. Mean seed-Fe concentration [Fe] was 65 μg Fe g−1, with individual genotypic values ranging from 48 to 81 μg Fe g−1. Seed Fe relative to dry-matter distribution was much more concentrated in seed coats than in embryos of all genotypes. Mean percentage of total seed Fe located in the seed-coat fraction was 29%, with mean genotypic values ranging from 23% to 38%. Neither seed-Fe characteristic was correlated with individual seed weight. Seed [Fe] was not correlated with seed-manganese (Mn) concentration [Mn]. Mean seed [Fe] for the 27 genotypes was different at the two locations, presumably due to differences in available soil Fe. Both genotype and environment affected seed [Fe] of soybean. Soybean seed coats, a major by-product after oil extraction, are a possible rich source of Fe for human nutrition.

Structure and Function of Populus deltoides Agroforestry Systems in Eastern India: 1. Dry matter dynamics

Agroforestry systems based on poplar (Populus deltoides) are becoming popular in eastern and northern parts of India. Therefore studies on the structure and function of the systems are important. The investigations included allometric equations for above- and belowground tree components, crop and plantation floor biomass and litter fall estimation at Pusa, Bihar, India. Biomass, floor litter mass, litter fall and net primary productivity (NPP) of plantations increased with an increase in age of trees whereas, crop biomass for any specific crop interplanted with poplar decreased with the age of the plantation. The total plantation biomass increased from 12.08 to 90.59 Mg ha−1 and NPP varied from 5.69 to 27.9 Mg ha−1 year−1. The biomass accumulation ratio ranged from 2.1 to 3.2. Total annual litter fall was in between 1.95 and 10.00 Mg ha−1 year−1, of which 92–94% was contributed by leaf litter. Compartmental models were developed for dry matter distribution in agroforestry systems involving young (3-year-old) and mature (9-year-old) poplar trees interplanted with various crops, the crops being grown in two rotations maize (Zea mays) – wheat (Triticum aestivum) – turmeric (Curcuma domestica) and pigeonpea (Cajanus cajan) – turmeric. This study substantiates the potential of Populus deltoides G3 under agroforestry combinations.

Creeping Bentgrass Establishment on Amended‐Sand Root Zones in Two Microenvironments

Sand‐based root zones are commonly used for construction of golf course putting greens. Objectives of this field study were to (i) evaluate sand‐based root zone mixtures varying in amendment (fine loam, peat, and inorganic) on the establishment of ‘L‐93’ creeping bentgrass (Agrostis stolonifera L.), (ii) compare findings to related published studies, and (iii) repeat the trial in two locations varying in air circulation to assess microenvironmental effect. Eleven root zone mixtures, using predominantly medium‐sized sand as the majority component, were replicated four times in a randomized complete block design nested within the two microenvironments. Plots were seeded in May 1998 and establishment was assessed to June 1999. Mixtures with a capillary porosity (−3 kPa water potential) at the high end of, or slightly exceeding, the United States Golf Association (USGA) criterion range (0.15–0.25 m3 m−3) provided more rapid establishment and better turf performance, yet root mass was lowest in these mixtures. Thus, variation in water availability among mixtures appeared sufficient to affect distribution of dry matter between roots and shoots. Mixtures amended to provide greater nutrient retention improved turf establishment; however, low water retention in the inorganic mixtures negated this advantage longer term as irrigation and fertilization shifted from establishment toward a maintenance objective. While shoot response to microenvironment was more limited, total root mass 1 yr after seeding was 24% greater in the open microenvironment than the enclosed, indicating that the initial effect of enclosed microenvironments on growth may go unrecognized during grow‐in unless rooting is assessed.

GROWTH, WATER RELATIONS AND LEAF GAS EXCHANGE OF PLANTS OF ILAMA (Annona diversifolia Saff.) UNDER WATER STRESS CONDITIONS.

They were studied some morphological and physiological characteristics or Annona diversifolia Saff. in relation to soil moisture availability conditions. Soil moisture level affected leaf area and dry matter distribution. Leaf water potential decreased as soil water potential did, with values of -1.26, -1.51, 1.73, 1.76 and 2.36 MPa, for the control, drought 1, drought 2, drought 3 and non-irrigated treatment, respectively. The rate of gas exchange also decreased significantly at the three levels of soil moisture. Proline concentration was negatively correlated to osmotic potential; however, regression analysis did not show any defined tendency. Ten days after the recuperation irrigation, the rate of gas exchange recovered almost entirely for moderate stress treatments.

Kernel set in maize genotypes differing in nitrogen use efficiency in response to resource availability around flowering

Environmental conditions affect grain yield in maize (Zea mays L.) mainly by altering the kernel number per plant (KNP). This number is determined during a critical period of about 2 weeks around silking. The objectives of this study were to assess how the rate and timing of nitrogen (N) fertilizer applications affect biomass partitioning and KNP in two genotypes with different N use efficiency, and to compare kernel set of these genotypes under varying regimes of carbohydrate and N availability during the critical period for kernel set. In the first field experiment, plant density and the rate of N supply per plant were varied independently. In the second field experiment, N availability was controlled via the application of N fertilizer, and carbohydrate availability was controlled by shading or thinning at silking. In both experiments, low rates of N supply reduced KNP more strongly in the non-efficient genotype when compared to the efficient genotype. The genotypic differences in kernel set were neither associated with N uptake into the above-ground biomass at maturity, nor above-ground biomass at silking. In the non-efficient genotype, application of N fertilizer at silking increased KNP. This increase was not associated with an increase in plant growth but with increased partitioning of biomass towards the reproductive organs during the critical period for kernel set. The genotype which had been selected for its high N use efficiency also showed higher kernel set at high plant density and shading during flowering when compared to the non-efficient genotype. Under conditions of restricted resource availability per plant, plant and ear growth rates during the critical period of about 14 days after onset of flowering declined compared with non-limiting conditions. However, these growth rates were less reduced in the efficient genotype. Pooling treatments of different plant density and different available N, each hybrid showed linear responses of KNP to plant growth rate and to ear growth rate. Furthermore, in the efficient genotype KNP was reduced to a lesser extent in response to decreasing growth rates. We conclude that higher kernel set of the efficient genotype compared to the non-efficient genotype under stressful conditions was associated with low sensitivity of plant growth and dry matter distribution towards reproductive organs to low assimilate availability during the critical period of kernel set, and particularly with low sensitivity of kernel set to decreasing plant and ear growth rates.

Dry Matter and Nitrogen Distribution at Maturity of Three Rice (Oryza sativa L.) Cultivars Exposed to Ammonia at Two Growth Stages

AbstractA substantial proportion of ammonical fertilizers applied to lowland rice is lost as gaseous N from the soil–plant system. Besides various environmental factors, the low N use efficiency of flooded rice is also attributed to this factor. As atmospheric ammonia found in the leaf environment of the plants could also be responsible for differences in N use efficiency and fertilizer N losses from lowland rice, a greenhouse study was conducted on three rice cultivars varying in physio‐morphological characteristics for their dry matter and nitrogen distribution to grains at maturity in response to ammonia (NH3) exposure at tillering and anthesis growth stages. The results revealed that ammonia exposure of plants at two growth stages did not affect the total dry matter and total N yield of the rice cultivars at maturity; however, the grain yield and grain N yield were negatively effected by NH3 exposure of the plants at anthesis. The variation observed in dry matter and N partitioning at maturity to grains/roots of the plants exposed to NH3 at anthesis indicated that the growth stage of the plants at which they are exposed to NH3 has an influence on N use efficiency of crop plants and subsequent vegetative as well as total N losses from the soil–plant system.