Variation within a bread wheat cultivar for grain yield,protein content,carbon isotope discrimination and ash content

The study was undertaken to assess the variation within a bread wheat (Triticum aestivum L.) cultivar, primarily for grain yield, and the implications for wheat breeding. During the 1998–1999 growing season, cv. Nestos was established in a non-replicated (NR-0) honeycomb experiment, in the absence of competition (11 547 plants ha⁻¹). Ten high yielding (H) and 10 low yielding (L) plants were selected, the seeds of which were used to form the respective H and L lines. The 20 lines, along with their original cultivar, were evaluated in two locations either in the absence of competition (11 547 plants ha⁻¹) during the 1999–2000 season or under competition (5 000 000 plants ha⁻¹) during the 2000–2001 season. Results showed significant differentiation between lines for grain yield, determined both in the absence of competition at the single-plant level, i.e. yield per plant (YP), and under competition at the crop yield level, i.e. yield per plot (CY). Significant differences between lines were also found for grain protein content (PC), grain carbon isotope discrimination (Δ), and grain ash content (ASH), either in the absence of competition or under competition. A positive relationship was found between YP and CY (r=0.53,P<0.02). Results showed that selection within a bread wheat cultivar, under very low density and on the basis of individual plant grain yield, could be an effective way to either upgrade or maintain the cultivar, whereas the use of Δ or ASH as indirect selection criteria instead of grain yield was not supported by the study.     

Effect of N rate,timing and splitting and N type on bread-making quality in hard red spring wheat under rainfed Mediterranean conditions

Three different experiments were designed to study the effects of N fertilizer rate, timing and splitting, and the response to combined application of N and S fertilizer on the bread-making quality of hard red spring wheat (Triticum aestivum L.) over a 3-year period in Vertisols under rainfed Mediterranean conditions. The following parameters were analyzed: grain yield, test weight, grain protein content, gluten index and alveograph parameters (W: alveogram index; P: dough tenacity; L: dough extensibility; P/L: tenacity–extensibility ratio). The N rate experiment included rates of 0, 100, 150 and 200 kg N ha⁻¹ applied on four different sites. The experiment was designed as a randomized complete block with four blocks. For the experiment on N timing and splitting, a single rate of 150 kg N ha⁻¹ was used, different fractions being applied at sowing, tillering and stem elongation, at a single site; again, experimental design was a randomized complete block with four blocks. Finally, for the experiment on the response to combined application of N and S fertilizer, a single fertilizer dose of 150 kg N ha⁻¹ was applied in two forms (urea+ammonium nitrate and urea+ammonium nitrosulfate) with one leaf application at ear emergence (zero, 25 kg S ha⁻¹, 25 kg N ha⁻¹, $\text{25}\text{kg}\text{S}\text{ha}{}^{\mathrm{-1}}\text{+25}$ kg N ha⁻¹ and 50 kg N ha⁻¹), also at a single site, using a split-plot design with four replications. Year-on-year variation in rainfall led to marked variations in wheat yield, grain protein content and bread-making quality indices. A close correlation was observed between rainfall over the September–May period and both grain yield and grain protein content (optimum values for both being recorded in the rainfall range 500–550 mm) as well as the alveogram index. A negative correlation was observed between mean maximum temperatures in May and both test weight and alveogram index (W). N fertilizer rate had a more consistent effect on bread-making quality than on grain yield. The highest values for grain yield were recorded at an N rate of 100 kg ha⁻¹, while maximum grain protein content values were recorded at 150 kg ha⁻¹. Application of half or one-third of total fertilizer N at stem elongation improved grain yield and grain protein content with respect to applications at sowing alone or at both sowing and tillering. Increased N rates led to a considerable increase in W values and to a reduction in the P/L ratio, thus improving dough balance, with a negative effect on the gluten index. Leaf application of N at ear emergence only affected grain protein content and the W index. Soil or leaf application of S had no effect on protein quality indices. The response of grain yield and grain protein content to fertilizer N differed from that reported for temperate climates.     

Intraspecific responses in crop growth and yield of 20 soybean cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in crop growth and grain yield of 20 soybean cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The supplemental UV-B radiation was 5.00 kJ m⁻², simulating a depletion of 20% stratospheric ozone at Kunming (25°N, 1950 m). Out of the 20 soybean cultivars tested, 17 and 15 showed significant change in plant height at 80 DAP (days after planting) and ripening stages, respectively. Sensitivity in plant height was greater at 80 DAP than at ripening. The plant height of 3 cultivars increased, and that of 17 cultivars decreased. Under UV-B radiation, LAI (leaf area index), biomass and grain yield decreased, respectively. The greatest percent decrease was 95.7, 93.9 and 92.8, respectively. RI (response index) was the sum of percent change in plant height at ripening, LAI, biomass and grain yield. The results showed that all 20 soybean cultivars had a negative RI, indicating inhibition by UV-B radiation on soybean growth. The RI of 6 tolerant cultivars was higher than −163.1 and 5 out of 6 originated from south China (low latitude). The RI of the most tolerant cultivars, Yunnan 97801, was −72.4. Meanwhile, the RI of 5 sensitive cultivars was lower than −256.9 and 4 out of the 5 originated from north China (high latitude). The RI of the most sensitive cultivar, Huanxianhuangdou, was −295.7. These UV-B tolerant cultivars identified in this study might be useful in breeding programs.     

Interannual variation in soybean yield: interaction among rainfall,soil depth and crop management

Using data from large, grower-managed fields we investigated the variation in yield of dryland soybean in an area with low and variable summer rainfall, and soils that are variable in depth and poor in phosphorus (P). First, using data from unfertilised, wide-row (0.7 m) crops grown under standard management between 1989 and 1992 (Series 1), we quantified the relationship between yield and W, a rainfall-based estimate of water availability during the period of pod and grain set. Separate functions were established for deep (depth ≥ 1 m) and shallow soils (0.75 m ≥ depth ≥ 0.5 m). Second, we partially tested these functions using two independent data sets (Series 2 and 3). Third, we evaluated the effects on yield of large (18 kg P ha⁻¹, Series 4) or moderate doses of P fertiliser (8–12 kg P ha⁻¹) in narrow-row crops (0.35 m, Series 5). To investigate water × management interaction we (i) calculated ΔY, the difference between actual yield in Series 4 and 5 and yield calculated with the functions derived from Series 1, and (ii) tested the association between ΔY and actual W. In a set of 24 crops (Series 1), yield varied between 2.1 and 3.1 t ha⁻¹ in deep soils and between 1.3 and 2.6 t ha⁻¹ in shallow soils; non-linear functions described fairly well, the response of yield to W. Fertilisation with 18 kg P ha⁻¹ increased yield by 0.6 t ha⁻¹ irrespective of water availability. The combination of narrow rows and a moderate dose of fertiliser increased yield in 73% of crops in deep soil but only in 53% of crops in shallow soil. There was a positive association between ΔY and W in deep soil but no relationship between these variables in shallow soil. Yield responses to management were thus differentially affected by rainfall in deep and shallow soils.     

Genetic gains in grain yield and related physiological attributes in Argentine maize hybrids

Genetic gains in grain yield and related phenotypic attributes have been extensively documented in maize (Zea mays L.), but the effect of breeding on the physiological determinants of grain yield is yet poorly understood. We determined genetic gains in grain yield and related physiological traits for seven maize hybrids developed for the central region of Argentina between 1965 and 1997. Gains were expressed as a function of the year of release (YOR). Hybrids were cropped in the field at five stand densities (from almost isolated plants to supra-optimal levels) during two contrasting growing seasons (E₁ and E₂). Water and nutrient stress were prevented and pests controlled. Genetic gains in grain yield (≥13.2 g m⁻² YOR⁻¹) were mainly associated with improved kernel number, enhanced postsilking biomass production, and enhanced biomass allocation to reproductive sinks, but computed gains were affected by the environment. Differences among hybrids arose at the start of the critical period, and were evident as improved mean radiation use efficiency (≥0.026 g MJ⁻¹ YOR⁻¹), enhanced plant growth rate at near optimum stand density (≥0.04 g pl⁻¹ YOR⁻¹), and improved biomass partitioning to the ear around silking (0.0034 YOR⁻¹, only for E₁). Improved biomass production after silking was related to an increased light interception (≥4.7 MJ m⁻² YOR⁻¹), and allowed for an almost constant source–sink ratio during grain filling. This trend determined no trade-off between kernel number and kernel weight. In contrast to previous studies, genetic gains were detected for potential productivity (e.g., maximum grain yield) on a per plant basis (i.e., under no resource competition), a promising aspect for the improvement of crop grain yield potential.     

Identification of quantitative trait loci controlling nodulation and shoot mass in progenies from two Brazilian soybean cultivars

Nitrogen (N) demand of soybean [Glycine max (L.) Merrill] can be supplied via biological nitrogen fixation (BNF), however, higher yielding cultivars increase plant demand for N. Phenotypes differing for traits associated with biological nitrogen fixation result from the expression of the multiple genes of both the host plant and the microsymbiont, but limited studies have been done on the genetics of the soybean BNF. Integrated maps of soybean with simple sequence repeat (SSR) markers [Cregan, P.B., Jarvik, T., Bush, A.L., Shoemaker, R.C., Lark, K.G., Kahler, A.L., Kaya, N., Van Toai, T.T., Lohnes, D.G., Chung, J., Specht, J.E., 1999. An integrated genetic linkage map of the soybean genome. Crop Sci. 39, 1464–1491.] offer an excellent opportunity for the identification of traits related to BNF. This study aimed at the identification of quantitative trait loci (QTLs) controlling BNF and nodulation in an F₂ population of 160 plants derived from an intraspecific cross between two Brazilian cultivars, Embrapa 20 × BRS 133, previously identified as having good potential for mapping of QTLs [Nicolás, M.F., Arias, C.A.A., Hungria, M., 2002. Genetics of nodulation and nitrogen fixation in Brazilian soybean cultivars. Biol. Fertil. Soils 36, 109–117.]. From 252 SSR markers tested in the parental genotypes 45 were polymorphic with high heterozygotes resolution. Mapping was performed with those 45 SSR markers for nodulation [nodule number (NN) and nodule dry weight (NDW)] and plant growth [shoot dry weight (SDW)] phenotypes in F_2:3 lines. A total of 21 SSR loci were mapped with a likehood of odds (LOD) value of 3.0 and a maximum Haldane distance of 50 cM, and were distributed in nine linkage groups with coverage of 251.2 cM. The interval mapping analysis with Mapmaker/QTL revealed two genomic regions associated with NN and NDW, with a contribution of putative QTLs of 7.1 and 10%, respectively. The regression analysis identified 13 significant associations between the marker loci and QTLs due to additive effects, with some of them being significantly associated with more than one phenotypic trait. Effects were observed in all variables studied, ranging from 2 to 9%. A one-way analysis of variance (ANOVA) also detected 13 significant associations, related to dominance effects. A two-way-ANOVA showed six epistatic interactions among non-linked QTLs for SDW, NN and NDW, explaining up to 15% of the trait variation and increasing the phenotypic expression from 8 to 28%. The data obtained in this work establish the initial stage for additional studies of the QTLs controlling BNF and indicate that effective marker-assisted selection using SSR markers may be feasible for enhancing BFN traits in soybean breeding programs.     

Genotypic increases in coleoptile length improves stand establishment,vigour and grain yield of deep-sown wheat

Timely sowing is critical for achieving high grain yields in winter cereals. However, inadequate seed-zone moisture for germination commonly delays sowing to reduce biomass and subsequent yield in semi-arid environments. Sowing deep to reach soil moisture is often avoided by growers of Rht-B1b and Rht-D1b semi-dwarf wheat as these wheat show poor emergence when sown deep. Their reduced cell elongation associated with insensitivity to endogenous gibberellins, results in shorter coleoptiles and smaller early leaf area. Alternative dwarfing genes responsive to endogenous gibberellins (e.g. Rht8) are available for use in wheat breeding. These reduce plant height without affecting coleoptile length and offer potential to select longer coleoptile wheat for deep sowing. Nine semidwarf (Rht8, Rht-B1b, and Rht-D1b) and seven tall (rht) wheat genotypes were sown at depths of 50, 80 and 110 mm at three locations in 2 or 3 years. Coleoptile lengths measured in a growth cabinet at four temperatures (11, 15, 19 and 23 °C) were strongly correlated with coleoptile length (r_p = 0.77–0.79^**) and plant number (r_p = 0.49^*–0.79^**) in deep-sown plots in the field. Furthermore, differences in coleoptile length were genetically correlated with greater numbers of emerged seedlings (r_g = 0.97^**), shallower crown depth (−0.58^**), greater seedling leaf area (0.59^**) and seedling biomass (0.44^*). Wheat containing the Rht-B1b or Rht-D1b dwarfing genes produced significantly (P < 0.01) shorter coleoptiles (97 mm) than both Rht8 (118 mm) and tall (117 mm) wheat. In turn, compared with emergence from 50 mm depth, the Rht-B1b and Rht-D1b wheat produced significantly fewer seedlings at 110 mm sowing depth (−62%) than either Rht8 (−41%) or tall (−37%) wheat. Effects of deep sowing early in the season were maintained with reductions in spike number and biomass at both anthesis and maturity. Kernel number was also reduced with deep sowing leading to reductions in grain yield. Over all entries, genotypic increases in plant number were associated with increases in fertile spike (r_g = 0.61^**) and kernel number (0.21^*), total biomass (0.26^*) and grain yield (0.28^*). Reduction in spike number and grain yield with deep sowing was smallest for the Rht8 (−18 and −10%) and rht (−15 and −7%) wheat, and largest for the Rht-B1b/D1b (−39 and −16%) wheat. Plant height and coleoptile length were independent among Rht8 and tall wheat genotypes. This study demonstrates the importance of good seedling emergence in achieving high wheat yields, and the potential use of alternative dwarfing genes such as Rht8 in development of long coleoptile, reduced height wheat suitable for deep sowing.     

Radiation interception and the accumulation of biomass and nitrogen by soybean and three tropical annual forage legumes

Field experiments were conducted at Gatton and Dalby in southeastern Queensland to determine parameters associated with radiation interception and biomass and nitrogen (N) accumulation for the ley legume species, phasey bean (Macroptilum lathyroides (L.) Urban) and vigna, (Vigna trilobata (L.) Verdc.). Sesbania (Sesbania cannabina Retz.), a native legume species, and soybean (Glycine max (L.) Merrill)) were included in the study for comparison. The most important differences between species related to differences in radiation interception, radiation-use efficiency (RUE), N-accumulation efficiency and the partitioning of N to plant parts. During early growth, soybean intercepted more radiation than the other species, primarily because of its greater leaf area index (LAI). Sesbania had the highest RUE (1.08 g MJ⁻¹) followed by phasey bean (0.94 g MJ⁻¹), soybean (0.89 g MJ⁻¹) and vigna (0.77 g MJ⁻¹). The efficiency of N-accumulation was greater in soybean (0.028 g N g⁻¹) and phasey bean (0.030 g N g⁻¹) than in vigna (0.022 g N g⁻¹) and sesbania (0.021 g N g⁻¹). In all species, the proportion of N allocated to leaves declined throughout the experimental period, being more rapid in soybean than in sesbania and phasey bean. Despite this decline in total N partitioned to the leaves, both soybean and phasey bean maintained a relatively stable specific leaf nitrogen (SPLN) throughout the experimental periods although sesbania and vigna displayed rapid decreases in SPLN. The large variation between species in RUE and N-accumulation efficiency indicates that the development of ley legume cultivars with a combination of traits for more efficient legume production, water use and soil N-accumulation in the water-limited environments of the grain belt of eastern Australia may be possible. The sensitivity of forage production, water use and soil N-accumulation to variation in RUE and N-accumulation efficiency needs to be quantified using modeling techniques prior to embarking on screening programs to select appropriate germplasm for evaluation studies.     

Breeding Novel Short Grain Rice for Tropical Region to Combine Important Agronomical Traits,Biotic Stress Resistance and Cooking Quality in Koshihikari Background

Breeding program strategies to develop novel short grain white rice varieties such as japonica (short grain) that introgress biotic stress resistance and high grain quality have been developed using indica rice (Pin Kaset + 4 and Riceberry) for applications in japonica rice (Koshihikari) improvement. Four breeding lines showing promising agronomic performance with short grain and low amylose content (< 20%) were obtained. In addition, sensory testing of these breeding lines showed high scores that similar to Koshihikari. Two promising lines, KP48-1-5 and KP48-1-9, which possessed a combination of four genes resistance to different biotic stresses (Bph3 + TPS + Xa21 + Pi-ta) and four genes for grain quality (GS3 + SSIIa + wx^b + badh2), were developed using marker-assisted selection (MAS) with the pedigree method. The current study clearly illustrated the successful use of MAS in combining resistance to multiple biotic stresses while maintaining a high yield potential and preferred grain quality. Moreover, the results indicated that this breeding program, which includes crossing temperate japonica with indica, can create novel short grain rice varieties adapted to a tropical environment, like the japonica type.     

Effect of N fertilizer top-dressing at various reproductive stages on growth,N2 fixation and yield of three soybean (Glycine max (L.) Merr.) genotypes

Soybean (Glycine max (L.) Merr.) is one of the most important food and cash crops in China and a key protein source for the farmers in northern China. Previous experiments in both the field and greenhouse have shown that N₂ fixation alone cannot meet the N requirement for maximizing soybean yield, and that N top-dressing at the flowering stage was more efficient than N top-dressing at the vegetative stages. However, the effect of N fertilizer application at other reproductive stages of soybean is unknown. Thus, a field experiment was conducted to study the effects of N applications at various reproductive stages on growth, N₂ fixation and yield of three soybean genotypes. The results showed that starter N at 25 kg ha⁻¹ resulted in minimum yield, total N accumulation and total amount of N₂ fixed in all three genotypes. N top-dressing at 50 kg ha⁻¹ at either the V2 or R1 stages, significantly increased N accumulation, yield and total amount of N₂ fixed in all three genotypes. However, N top-dressing at the same rate at either the R3 or R5 stage did not show this positive effect in any of the three genotypes. Thus, the best timing for N top-dressing during reproduction is at the flowering stage, which increased seed yield by 21% for Wuyin 9, 27% for You 91-19, and 26% for Jufeng, respectively, compared to the treatment without N top-dressing.     

Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Deceleration in rice (Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T₁), one-third of recommended fertilizer doses (T₂), two-thirds of recommended fertilizer doses (T₃), full doses of recommended fertilizers (T₄), T₂+5 t CD and 2.5 t ash ha⁻¹ (T₅) and T₃+5 t CD and 2.5 t ash ha⁻¹ (T₆) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T₁ was 5.33 t ha⁻¹ per year, while the yield with T₂ was 6.86 t ha⁻¹ per year. Increased fertilizer doses with T₃ increased the grain yield to 8.07 t ha⁻¹ per year, while the application of recommended chemical fertilizer doses (T₄) gave 8.87 t ha⁻¹ per year. The application of CD and ash (T₅ and T₆) increased rice yield by about 1 t ha⁻¹ per year over that obtained with chemical fertilizer alone (T₂ and T₃, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T₃ through T₆, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.     

Note on effects of soil surface crust on the grain yield of sorghum (Sorghum bicolor) in the Sahel

The prominent effects of a soil surface crust on crop production, impedance to seedling emergence and reduced infiltration rate, were examined using a quantitative land evaluation model under the Sahelian environmental and soil conditions of north-central Burkina Faso. The model integrated data from climate, soil and crop for quantifying potential grain yield of sorghum (Sorghum bicolor), grown on a sandy loam soil for 14 production years (1977–1990). Crust development was induced using `simulated rainfall' with an intensity of 75 mm h⁻¹ from a 2 m height. Results revealed that seeding sorghum in small holes without sufficiently breaking the surface crust depressed grain yield. Observed and potential yield correlated closely over a 7-year period (r = 0.79, p < = 0.05). Substantial yield gap was found between estimated potential yield (crust broken scenario set to 75% of the predicted yield) and observed, indicating however, the possibility of significantly improving yield by using appropriate tillage to break the crust before seeding.     

Consistent differences among wheat cultivars in osmotic adjustment and their relationship to plant production

Osmotic adjustment (OA) is generally considered an important component of drought resistance. Several reports by J.M. Morgan [Morgan, J.M., 1983. Osmoregulation as a selection criterion for drought tolerance in wheat. Aust. J. Agric. Res. 34, 607–614; 1992. Osmotic components and properties associated with genotypic differences in osmoregulation in wheat. Aust. J. Plant Physiol. 19, 67–76; 1995. Growth and yield of wheat lines with differing osmoregulative capacity at high soil water deficit in seasons of varying evaporative demand. Field Crops Res. 40, 143–152; Morgan, J.M., Condon, A.G., 1986. Water-use, grain yield and osmoregulation in wheat. Aust. J. Plant Physiol. 13, 523–532] from Australia concluded that consistent genetic differences in OA existed among wheat cultivars and that high OA cultivars tended to yield better than low OA cultivars under drought stress. Our study was performed to assess his results with his and other genetic materials.Two of Morgan’s spring wheat lines with high OA (‘H.Osm-134’) and low OA (‘L.Osm-136’) capacity in addition to eight other diverse spring wheat cultivars were tested for OA and plant production when grown in small plots under a rain exclusion shelter at Bet Dagan, Israel in 1996. OA of five of these cultivars (including Morgan’s lines) was also measured in two independent greenhouse tests in 1997 (Israel) and 1998 (Texas).The five cultivars differed significantly and ranked consistently for OA in all tests. No significant cultivar by test interaction for OA was revealed. OA was well correlated across cultivars between tests. The significantly higher OA capacity of H.Osm-134 as compared with L.Osm-136 was repeated in all tests. OA of all ten cultivars was positively correlated with biomass (r = 0.73; p = 0.02) and yield (r = 0.55; p = 0.09) under pre-flowering drought stress in the rain exclusion shelter. H.Osm-134 line performed significantly (p ≤ 0.05) better than L.Osm-136 line for both biomass and yield under drought stress. We therefore support Morgan’s results and conclude that consistent differences in OA exist among wheat cultivars and that these differences can be associated with plant production under pre-flowering drought stress.     

Growth and distribution of maize roots under nitrogen fertilization in plinthite soil

To improve efficiency of soil N and water use in the savanna, maize (Zea mays L.) cultivars with improved root systems are required. Two rainfed field experiments were conducted in Samaru, Nigeria in the 1993 and 1994 growing seasons with five maize cultivars under various rates of nitrogen fertilizer. The capacity of maize for rapid early root growth and to later develop a deep, dense root system was assessed. In addition, the effect of N fertilization on root growth of maize was studied in 1994. The widely cultivated cultivar TZB-SR had a poor root system in the surface soil layer and was more susceptible to early-season drought, as indicated by low plant vigor and aboveground dry matter yield during that time. It had a lower grain yield and a relatively small harvest index, but ranked among the highest in total aboveground dry matter production compared to other cultivars. The size of root system alone did not always relate well with grain yield among cultivars. Partitioning of dry matter within the plant was important in determining differences in grain yield and N stress tolerance between cultivars. A semiprolific cultivar (SPL) had high seedling vigour and a dense root system in the surface soil layer that conferred a greater tolerance to early-season drought stress and improved uptake of the early-season N flush, as indicated by a greater dry matter yield at 35 days after sowing (DAS). It also had a fine, deep, dense root system at flowering that could have improved water- and N-use efficiency in the subsoil (> 45 cm), thereby avoiding midseason drought stress in 1994. SPL had a large harvest index and the greatest yield among cultivars in 1994. Averaged across cultivars, greater root growth and distribution was observed at a moderate N rate of 0.56 g plant⁻¹ than at zero-N or high N (2.26 g plant⁻¹). Differences in root morphology could be valuable as selection criteria for N-efficient and drought-tolerant maize.     

Growth,competition, yields advantage and economics in soybean/pigeonpea intercropping system in semi-arid tropics of India: II. Effect of nutrient management

Low native nitrogen (N) and phosphorus (P) coupled with imbalanced nutrient application is a major constraint limiting productivity of intercropping systems on Vertisols of the semi-arid tropical India. In a 3-year field experiment competition behaviour of component crops for nutrients use in soybean/pigeonpea intercropping system was assessed based on relative yield (RY), relative nitrogen yield (RNY) and relative phosphorus yield (RPY) under three nutrient levels (0 NPK, 100% NPK (N:P:K = 30:26:25 kg ha⁻¹) and 100% NPK + 4 t FYM ha⁻¹). The result showed that before soybean harvest, the RY and RNY of soybean were greater (1.0) than the corresponding values of RY and RNY of pigeon pea (0.6). This implied that competition exists for soil N between the component crops during the first half of the cropping system. It was observed that soybean harvest did not coincide with peak flowering of pigeonpea, the stage when biological nitrogen fixation (BNF) was maximum. Thus, BNF dependency of pigeonpea was low before soybean harvest and the plants suffered from N deficiency more when no fertilizer-N was applied and diminished at a high-N level. Pigeon pea attained its peak flowering after the harvest of soybean and increased its dependency on BNF when soil N was exhausted by soybean. Thus, after the harvest of soybean, RY and RNY of pigeon pea gradually increased and approached 1.0 at maturity at all nutrient levels. The RPY values showed that phosphorus was not the limiting factor to any of the crop in the system even if it was not applied. The study thus suggests that in the soybean/pigeonpea intercropping system, N is a limiting factor for growth of pigeonpea intercrop during the first half of its growth and application of 100% NPK (30 kg N) + 4 t FYM could meet N demand of pigeonpea in N deficient soils as this nutrient management option gave higher yield, root length density and profit under soybean/pigeonpea intercropping system than 100% NPK and control.     

Responses of sunflower yield and grain quality to alternating day/night high temperature regimes during grain filling: Effects of timing,duration and intensity of exposure to stress

In order to quantify the effects, at different stages during grain filling, of alternating day/night high temperature regimes on sunflower grain yield and quality, heads were exposed to high temperatures during 7 or 6 days starting either 10–12 days after anthesis (daa, HT1), 18 daa (HT2) or 24 daa (HT3). Also, heads were exposed to high temperatures for periods of 2, 4 or 6 days in each of HT1 and HT2. Temperatures covered a range of mean daily grain temperature of 20–40 °C and peak grain temperatures (i.e., those prevailing during the central 5 h of the daylight period) of 26–45 °C. High temperature stress for periods of 4 days or longer produced significant (p < 0.05) reductions in grain yield and grain quality. Early (HT1) exposure to stress reduced yield by 6%/°C above a mean grain temperature threshold of 29 °C; later (HT2 + HT3) exposures reduced yield by 4%/°C above a threshold of 33 °C. These reductions in yield were attributable to reductions in unit grain weight at all positions (periphery, intermediate, central) on the head, and an increase in the proportion of very small (10–30 mg) grains, termed half-full (HF) grains in this paper. In both full and HF grains, stress in either HT1 or HT2 reduced final pericarp weight, associated with fewer number of cell layers and thinner cell walls in the schlerenchyma. High temperatures reduced both the rate and duration of oil deposition in the grain, with the greatest effects being found with early (HT1) exposures. The unsaturation (oleic acid/linoleic acid) ratio of oil from mature grain was altered only when exposure to heat stress overlapped with the cessation of deposition of storage lipids. The effects of duration and intensity of heat stress on relative (to control) grain yield and oil content could be reasonably summarized using a linear response to cumulative hourly heat load calculated with a base temperature of 30 °C. We conclude that: (i) 4 days of alternating day/night temperatures resulting in mean daily grain temperatures of >30 °C can reduce sunflower grain yield and quality; (ii) the magnitude of these effects is strongly dependent on the timing of exposure and their nature on the grain growth processes active at the time of stress; and (iii) an hourly heat load (base = 30 °C) provides a useful integrative estimator of the effects of exposure to heat stress on grain yield and oil content for a given phase of grain filling.     

The efficiency of nitrogen fertiliser for rice in Bangladeshi farmers’ fields

Bangladesh is currently self sufficient in rice (Oryza sativa L.), which accounts for approximately 80% of the total cropped area, and 70% of the cost of crop production. However, farmers are increasingly concerned about the perceived decline in productivity, expressed as the return on fertiliser inputs. Agronomic efficiency is a measure of the increase in grain yield achieved per unit of fertiliser input that can provide a way to quantify the observation of farmers. This study indicates that the yields achieved where only P and K fertiliser were applied ranged from 3–5 t ha⁻¹, indicating good soil fertility, particular in terms of soil N supply (37–112 kg N ha⁻¹). However, at recommended rates and at rates used by farmers, the yield response to application of fertiliser N was low. Data shows that grain yields were significantly correlated in both years (R² = 0.77 and R² = 0.67) with plant uptake in nitrogen. The internal nitrogen use efficiency seems to confirm that sink formation was limited by factors other than nitrogen. Low agronomic efficiency (5–19 kg grain kg⁻¹ N) was caused by poor internal efficiency (45–73 kg grain kg⁻¹ N), rather than low supply of soil N or loss of fertiliser N. Thus, often the applications of large amounts of N fertiliser (39–175 kg N ha⁻¹) by farmers to increase yields of high yielding variety Boro rice were not justified agronomically and ecologically. A rate of 39 kg N ha⁻¹ is very low, hardly an environmental threat. No one single factor could be identified to explain the low internal efficiency. Therefore, it is concluded that the data presented tend to confirm the indication that yields are limited by a factor other than nitrogen, which could be crop establishment, plant density, water or pest management, micro-nutrients deficiency, poor seed and transplanted seedling quality, varieties and low radiation.     

Grain weight response to increases in number of grains in wheat in a Mediterranean area

This study explored whether the average grain weight of wheat tends to be reduced when grain number is increased due to either competition or, to a consistent increase in the relative proportion of grains of smaller weight potential. Three field experiments considering environmental, genetic and environmental × genetic effects on yield and its main components were analysed during the 2003/2004 growing season in two different locations within the Mediterranean area of Catalonia, Spain. The relationship between grain weight and number of grains per unit land area was analysed for both the average of all grains (AGW) and for grains in specific positions of the main-shoot spikes: proximal (CPg) and distal (CDg) grains of central spikelets, and proximal grains of the near apical (APg) and near basal (BPg) spikelets. The proportional contribution of grains per spike for the different grain positions and the relative contribution of spikes per m² made by the main shoot or tillers were also examined.In the three experiments, AGW was reduced when grain number was increased due to genetic and/or environmental factors. However, the slopes of the straight-lines that represented the negative relationship between grain number and grain weight were lower (less negative) and less significant for CPg (b = −0.20, P > 0.20), CDg (b = 0.06, P > 0.20) and BPg (b = −0.21, P > 0.20) than for AGW (b = −0.40, P < 0.05). The proportional contribution of distal grains and tiller spikes (both with relatively light grains) were directly related to grain number increases. Therefore, as grain number increased there was a higher proportion of grains of low potential weight. Thus, the average grain weight was concomitantly reduced when grain number increased by increasing the proportion of “small grains” in the canopy independently of any competitive relationship between growing grains.