Effects of soil water content and nitrogen supply on the productivity of Miscanthus × giganteus Greef et Deu. in a Mediterranean environment

Miscanthus × giganteus is one of the most promising biomass crops for non-food utilisation. Taking into account its area of origin (Far East), its temperature and rainfall requirements are not well satisfied in Mediterranean climate. For this purpose, a research was carried out with the aim of studying the adaptation of the species to the Mediterranean environment, and at analysing its ecophysiological and productive response to different soil water and nitrogen conditions. A split plot experimental design with three levels of irrigation (I₁, I₂ and I₃ at 25%, 50% and 100% of maximum evapotranspiration (ETm), respectively) and three levels of nitrogen fertilisation (0 kg ha⁻¹: N₀, 60 kg ha⁻¹: N₁ and 120 kg ha⁻¹: N₂ of nitrogen) were studied. The crop showed a high yield potential under well-watered conditions (up to 27 t ha⁻¹ of dry matter). M. × giganteus, in Mediterranean environment showed a high yield potential even in very limited water availability conditions (more than 14 t ha⁻¹ with a 25% ETm restoration). A responsiveness to nitrogen supply, with great yield increases when water was not limiting, was exhibited. Water use efficiency (WUE) achieved the highest values in limited soil water availability (between 4.51 and 4.83 g l⁻¹), whilst in non-limiting water conditions it decreased down to 2.56 and 3.49 g l⁻¹ (in the second and third year of experiment, respectively). Nitrogen use efficiency (NUE) decreased with the increase of water distributed (from 190.5 g g⁻¹ of I₀ to 173.2 g g⁻¹ of I₂); in relation to N fertilisation it did not change between the N fertilised treatments (N₁ and N₂), being much higher in the unfertilised control (177.1 g g⁻¹). Radiation use efficiency (NUE) progressively declined with the reduction of the N fertiliser level (1.05, 0.96 and 0.86 g d.m. MJ⁻¹, in 1994, and 0.92, 0.91 and 0.69 g d.m. MJ⁻¹, in 1995, for N₂, N₁ and N₀, respectively).     

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.     

Effect of irrigation and nitrogen fertilization on biomass yield and efficiency of energy use in crop production of Miscanthus

The perennial C₄ grass Miscanthus has been proposed as a biomass energy crop in Europe. Effects of crop age, irrigation and nitrogen fertilization on biomass and energy yields and N content of Miscanthus were investigated and the energy costs of production determined. After an establishment period of 1 year, cultivation of Miscanthus resulted in a dry matter production of over 37 t ha⁻¹ year⁻¹ over a period of 4 years. Irrigation and nitrogen level greatly affected Miscanthus biomass yield. In absence of N fertilization, irrigation did not modify biomass yield and the effect of irrigation increased with the increase in N level. The average N response ranged from 37 to 50 kg biomass kg⁻¹ N applied. Because the calorific value of Miscanthus biomass (16.5 MJ kg⁻¹) was not affected by irrigation and N fertilization, energy production depended exclusively on biomass yield. Maximum energy yield was 564 GJ ha⁻¹ year⁻¹. Without N supply and irrigation, energy yield was 291 GJ h⁻¹. Net energy yield, calculated as the difference between energy output and input, but without inclusion of drying costs, was 543 GJ ha⁻¹ with N fertilization and irrigation and 284 GJ ha⁻¹ without; the ratios of energy output to input in crop production were 22 and 47, respectively.     

Effect of nitrogen supply on crop conductance,water- and radiation-use efficiency of wheat

Water-use efficiency (WUE_DM) is directly related to radiation-use efficiency (RUE) and inversely related to crop conductance (g_c). We propose that reduced WUE_DM caused by shortage of nitrogen results from a reduction in RUE proportionally greater than the fall in conductance. This hypothesis was tested in irrigated wheat crops grown with contrasting nitrogen supply; treatments were 0, 80 and 120 kg N ha⁻¹ in 1998 and 0, 80, 120 and 160 kg N ha⁻¹ in 1999. We measured shoot dry matter, yield, intercepted solar radiation and soil water balance components. From these measurements, we derived actual evapotranspiration (ET), soil evaporation and transpiration, WUE_DM (slope of the regression between dry matter and ET), WUE_Y (ratio between grain yield and ET), RUE (slope of the regression between dry matter and intercepted radiation), and g_c (slope of the regression between transpiration and intercepted radiation). Yield increased from 2.3 in unfertilised to an average 4.7 t ha⁻¹ in fertilised crops, seasonal ET from 311 to 387 mm, WUE_DM from 23 to 37 kg ha⁻¹ mm⁻¹, WUE_Y from 7.6 to 12.4 kg ha⁻¹ mm⁻¹, RUE from 0.85 to 1.07 g MJ⁻¹, while the fraction of ET accounted for soil evaporation decreased from 0.20 to 0.11. In agreement with our hypothesis, RUE accounted for 60% of the variation in WUE_DM, whereas crop conductance was largely unaffected by nitrogen supply. A greater fraction of evapotranspiration lost as soil evaporation also contributed to the lower WUE_DM of unfertilised crops.     

Salinity reduces radiation absorption and use efficiency in soybean

The potential rate of plant development and biomass accumulation under conditions free of environmental stress depends on the amount of radiation absorption and the efficiency of utilizing the absorbed solar energy to drive photosynthetic processes that produce biomass materials. Salinity, as a form of soil and water stress, generally has a detrimental effect on plant growth, and crops such as soybean are usually sensitive to salinity. Field and greenhouse experiments were conducted to determine soybean growth characteristics and the relative impact of salinity on radiation absorption and radiation-use efficiency (RUE) at a whole plant level. Cumulative absorption of photosynthetically active radiation (∑APAR) was estimated using hourly inputs of predicted canopy extinction coefficients and measured leaf area indices (LAI) and global solar radiation. On 110 days after planting, soybean plants grown under non-saline conditions in the field accumulated 583 MJ ∑APAR m⁻². A 20% reduction in ∑APAR resulted from growing the plants in soil with a solution electrical conductivity (EC) of about 10 dS m⁻¹. Soybeans grown under non-saline conditions in the field achieved a RUE of 1.89 g MJ⁻¹ ∑APAR for above-ground biomass dry materials. The RUE reached only 1.08 g MJ⁻¹ ∑APAR in the saline soil, about a 40% reduction from the non-saline control. Salinity also significantly reduced ∑APAR and RUE for soybeans in the greenhouse. The observed smaller plant and leaf sizes and darker green leaves under salinity stress were attributed to reductions in LAI and increases in unit leaf chlorophyll, respectively. Reductions in LAI exceeded small gains in leaf chlorophyll, which resulted in less total canopy chlorophyll per unit ground area. Analyzing salinity effect on plant growth and biomass production using the relative importance of ∑APAR and RUE is potentially useful because APAR and total canopy chlorophyll can be estimated with remote sensing techniques.     

Intra-specific competition in maize: early establishment of hierarchies among plants affects final kernel set

Reduced plant biomass and increased plant-to-plant variability are expected responses to crowding in monocultures, but the underlying processes that control the onset of interplant interference and the establishment of hierarchies among plants within a stand are poorly understood. We tested the hypothesis that early determined plant types (i.e. dominant and dominated individuals) are the cause of the large variability in final kernel number per plant (KNP) usually observed at low values of plant growth rate (PGR) around silking in maize (Zea mays L.). Two hybrids (DK696 and Exp980) of contrasting response to crowding were cropped at different stand densities (6, 9 and 12 plants m⁻²), row spacings (0.35 and 0.70 m), and water regimes (rainfed and irrigated) during 1999/2000 and 2001/2002 in Argentina. The onset of interplant competition started very early during the cycle, and significant differences (P<0.05) in estimated plant biomass between stand densities were detected as soon as V_4–6 (DK696) and V_6–7 (Exp980). Plant population and row spacing treatments did not modify the onset of the hierarchical growth among plants, but did affect (P<0.02–0.08) the dynamic of the process. For both hybrids, the rate of change in relative growth between plant types was larger at 9 and 12 plants m⁻² (ca. 0.12 g/g per 100 °C day) than at 6 plants m⁻² (ca. 0.07 g/g per 100 °C day). For all treatments, the largest difference in estimated shoot biomass between plant types took place between 350 (V₇) and 750 °C day (V₁₃) from sowing, and remained constant from V₁₃ onwards. Dominant plants always had more kernels per plant (P<0.05) than the dominated ones, but differences between plant types in PGR around silking were significant (P<0.05) only at 12 plants m⁻². Our research confirmed the significant (P<0.01) curvilinear response of KNP to PGR around silking, but also determined a differential response between plant types: the mean of residual values were significantly (P<0.01) larger for dominant than for dominated individuals. Estimated ear biomass at the onset of active kernel growth (R₃) reflected the variation in KNP (r²≥0.62), and was significantly (P<0.01) related to estimated plant biomass at the start of active ear growth (ca. V₁₃). This response suggested that the physiological state of each plant at the beginning of the critical period had conditioned its reproductive fate. This early effect of plant type on final KNP seemed to be exerted through current assimilate partitioning during the critical period.     

Modeling chickpea growth and development: Nitrogen accumulation and use

Quantitative information regarding nitrogen (N) accumulation and its distribution to leaves, stems and grains under varying environmental and growth conditions are limited for chickpea (Cicer arietinum L.). The information is required for the development of crop growth models and also for assessment of the contribution of chickpea to N balances in cropping systems. Accordingly, these processes were quantified in chickpea under different environmental and growth conditions (still without water or N deficit) using four field experiments and 1325 N measurements. N concentration ([N]) in green leaves was 50 mg g⁻¹ up to beginning of seed growth, and then it declined linearly to 30 mg g⁻¹ at the end of seed growth phase. [N] in senesced leaves was 12 mg g⁻¹. Stem [N] decreased from 30 mg g⁻¹ early in the season to 8 mg g⁻¹ in senesced stems at maturity. Pod [N] was constant (35 mg g⁻¹), but grain [N] decreased from 60 mg g⁻¹ early in seed growth to 43 mg g⁻¹ at maturity. Total N accumulation ranged between 9 and 30 g m⁻². N accumulation was closely linked to biomass accumulation until maturity. N accumulation efficiency (N accumulation relative to biomass accumulation) was 0.033 g g⁻¹ where total biomass was <218 g m⁻² and during early growth period, but it decreased to 0.0176 g g⁻¹ during the later growth period when total biomass was >218 g m⁻². During vegetative growth (up to first-pod), 58% of N was partitioned to leaves and 42% to stems. Depending on growth conditions, 37–72% of leaf N and 12–56% of stem N was remobilized to the grains. The parameter estimates and functions obtained in this study can be used in chickpea simulation models to simulate N accumulation and distribution.     

Performance of aerobic rice varieties under irrigated conditions in North China

In Northern China, high-yielding aerobic rice varieties are released to farmers to grow rice as a supplementary-irrigated upland crop to cope with water scarcity. If the key factors contributing to the high yield of these varieties are understood, rapid advancements can be made in developing aerobic rice varieties for water-scarce environments in other parts of Asia. In 2001–2002, we conducted experiments with aerobic varieties HD502 and HD297 and lowland variety JD305 under aerobic and flooded conditions. Five irrigation treatments were implemented in aerobic soil to create different soil moisture regimes. Under flooded conditions, all three varieties had comparable radiation use (RUE) efficiencies of 2.09–2.26 g dry matter (DM) MJ⁻¹ in 2001 and 2.40–2.53 g DM MJ⁻¹ in 2002, and harvest indices (HI) of 0.38–0.40 in both years. Differences in yield among the varieties are explained by differences in growth duration. Under aerobic conditions, mean RUE over water treatments dropped to 1.70–1.72 g DM MJ⁻¹ for all three varieties in 2001, and to 1.62 for HD502, 1.71 for HD297 and 1.86 for JD305 in 2002. With increasing dryness of the soil, the amount of intercepted light decreased at about the same rate for all varieties, but RUE decreased faster in the lowland than in the two aerobic varieties. The HI of JD305 decreased dramatically with increasing soil dryness and reached values of 0.19–0.21 in 2002. In contrast, the HI of both aerobic varieties remained relatively high under aerobic conditions, with lowest values of 0.27–0.28 for HD297 and 0.34–0.35 for HD502 in 2002. The relatively high HI of the aerobic varieties compensated for their relatively short growth duration so that their yields were higher than that of JD305 in all treatments. A high percentage filled grains is a key factor contributing to the high HI of the aerobic varieties under aerobic conditions.     

Nutrient and assimilate partitioning in two tropical maize cultivars in relation to their tolerance to soil acidity

The use of Al-tolerant and P-efficient maize cultivars is an important component of a successful production system on tropical acid soils with limited lime and P inputs. Grain yield and secondary plant traits, including root and aboveground biomass, nutrient content and leaf development, were evaluated from 1996 to 2002 in field experiments on an Oxisol in order to identify maize characteristics useful in genetic improvement. Here we present the results of the 2002 trial and compare them with previous results. The aim of this experiment was to assess the effect of assimilate and nutrient partitioning on the growth and grain yield of two tropical cultivars having different Al tolerance (CMS36, tolerant, Spectral, moderately tolerant). The soil had an Al saturation of 36% in topsoil (pH 4.5) and >45% below 0.3 m depth (pH 4.2). Measurements made from emergence to grain filling included: root, stem and leaf biomass, P and N content, leaf area index (LAI), radiation use efficiency (RUE), soil available N and root profiles at anthesis. The experiments consisted of two P treatments, zero applied or 45 kg P ha⁻¹ (−P and +P). All the treatments received N and K fertilizers. In −P, root biomass and LAI at anthesis were twice as great in CMS36 as in Spectral. In +P the differences between cultivars were negligible. Roots were deeper in CMS36 due to its higher Al tolerance. Total biomass and grain yield were not strongly related to root biomass and LAI. Other factors such as the leaf biomass and the amount of nutrients per unit leaf area were highly correlated with RUE and biomass. In −P, Spectral had the same total biomass but a higher grain yield than CMS36 (2.1 Mg ha⁻¹ versus 1.5 Mg ha⁻¹). This was due to a higher leaf P content (+40%), a greater RUE (+74%), and a lower number of sterile plants. In +P, CMS36 had higher total biomass and grain yield (4.1 Mg ha⁻¹ versus 3.1 Mg ha⁻¹). This was due to its higher leaf P (+25%) and leaf N (+43%) contents, and an increased RUE (+130%) that were associated with higher P and N uptake. Our results indicated that although root tolerance to Al toxicity is necessary for good crop performance on acid soils, assimilate and nutrient partitioning in the aboveground organs play a major role in plant adaptation and may partially compensate for a lower root tolerance.     

Long-term effect of tillage systems on soil microbiological,chemical and physical parameters and the incidence of charcoal rot by Macrophomina phaseolina (Tassi) Goid in soybean

A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot (Macrophomina phaseolina) of soybean and crop yield. The tillage systems evaluated were direct seeding (DS), DS + scarifier (DS + S), minimum tillage (MT) and conventional tillage (CT). DS presented higher values than CT in culturable total fungi (26.33 × 10⁵ vs. 2.33 × 10⁵ CFU g⁻¹ dry soil), total bacteria (182 × 10⁷ vs. 64 × 10⁷ CFU g⁻¹ dry soil), microbial respiration (0.77 mg CO₂ g⁻¹ week⁻¹ vs. 0.45 mg CO₂ g⁻¹ week⁻¹) and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g⁻¹ h⁻¹ vs. 1.70 ug fluorescein g⁻¹ h⁻¹ in CT. Fungal and bacterial community fingerprints, by terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intergenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME (fatty acid methyl ester) profiles showed that microbial community structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results showed that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS. Soybean grown in high-quality soil was not affected by charcoal rot, however, under CT, disease incidence in soybean was 54%. These differences were correlated to the higher microbial abundance and activity under DS, the biological component being a key factor determining soil capacity to suppress the soilborne pathogen.     

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.     

Yield and agronomic traits of Khorasan wheat (Triticum turanicum Jakubz.)

The consumer's interest in natural, unconventional and nutritional foods led to the development of new specialty foods based on grain blends. Components of such foods are often so-called ‘ancient wheats’ which were never the subject of modern plant breeding programmes. Khorasan or Oriental wheat (Triticum turanicum) is a neglected and underutilised tetraploid wheat species, which probably survived over the centuries in subsistence farming systems in the Near East and Central Asia. In the present study the agronomic potential of Khorasan wheat was evaluated under eastern Austrian conditions.Fourteen accessions of Khorasan wheat were investigated together with check durum wheat cultivars over a period of 4 years in the Marchfeld region, north-east of Vienna. The crops were sown both in autumn and spring.The investigated material was inferior to modern durum wheats in most agronomic traits. No accession was found to tolerate soil temperatures below −5 °C. Tolerance to drought and fungal diseases was limited and/or modest, and grain yields were significantly lower. While the best performing turanicum accessions yielded in average 385.8 and 233.8 g m⁻² for autumn and spring sowing, respectively, the check winter durum yielded 466.5 g m⁻² and the check spring durums between 351.5 and 391.8 g m⁻². Several characteristic and interesting features were observed which permit successful marketing of pure Khorasan grain or as a component in grain blends, despite possible flour quality traits. The grain has an impressive kernel size and thousand kernel weight, in most cases greater than 50 g and often even greater than 60 g. The high thousand kernel weight might be a valuable trait to transfer into durum wheat to improve grain yield. Moreover, the grain has an amber colour and high vitreousness.Due to higher plant height, low lodging tolerance and high susceptibility against powdery mildew, Khorasan wheat is more suitable for organic farming systems. Although there is evidence that Khorasan wheat has low adaptation, it is of interest as an alternative cereal to increase diversity both in the field and on the consumer's table. However, further experiments are necessary: on the one hand to study the interactions between sowing rates, sowing dates, weed suppression, thousand kernel weight and kernel plumpness in order to find out optimal production procedures, and on the other hand to find out areas/fields with the best growth conditions for Khorasan wheat.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

Effect of growth regulators on yield and fiber quality in ramie (Boemheria nivea (L.) Gaud.), China grass

The effects of two mixtures of four plant growth regulators (choline chloride, gibberellin (GA₃), benzyladenine (6-BA) and NaHSO₃) at 20:9:5:800 mg kg⁻¹ (H1) and 20:42:43:2350 mg kg⁻¹ (H3) (active ingredients), respectively, were investigated on yield and fiber quality in ramie (Boehmeria nivea (L.) Gaud.). The mixtures were sprayed over the canopy at two growth stages (10 and 20 days after the previous cut) of field-grown ramie. The treatments increased raw fiber yield by 13–18%, and improved fiber fineness by 57–349 m g⁻¹, increased number of leaves per plant, and also improved all yield components. Treatment H1 resulted in a denser distribution, smaller diameters and greater quantity of fiber cells in stem cross-section. Physiological responses included improving leaf water status, increasing net photosynthetic rate, and decreasing electrolyte exosmosis rate.     

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.     

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.     

Soil fertility management in irrigated rice systems in the Sahel and Savanna regions of West Africa: Part I. Agronomic analysis

Yield, input use, productivity and profitability of irrigated rice systems were analyzed based on surveys in Senegal (Thiagar and Guédé), Mali (Office du Niger) and Burkina Faso (Kou Valley). The objective was to determine agronomic factors contributing to farmers' fertilizer-use efficiency and productivity, given current farmer practices. (A second paper addresses profitability and risk issues). Grain yields were highly variable, within and across sites. Minimum grain yield was 0.2 t ha⁻¹ (Thiagar), maximum recorded grain yield was 8.7 t ha⁻¹ (Office du Niger). The yield gap between actual farmers' yield and simulated potential or maximum attainable farmers' yield ranged from 0.6 to 5.7 t ha⁻¹ (Kou), 1.8 to 8.2 t ha⁻¹ (Thiagar), 0.3 to 6.3 t ha⁻¹ (Office du Niger), 0.8 to 5.7 t ha⁻¹ (Guédé), indicating considerable scope for improved yield. Physiological nitrogen efficiency (δ grain yield/δ N uptake) was mostly between 40 and 80 kg grain kg⁻¹ plant N. Apparent recovery of fertilizer N was highly variable (average: 30–40% of applied N). Timing of N fertilizer application by farmers was extremely variable and often did not coincide with critical growth stages of the rice plant. Other agronomic constraints included: use of relatively old (>40 days) seedlings at transplanting (Kou, Office du Niger), P and/or K deficiency (Office du Niger), unreliable irrigation water supply (Kou, dry season), delayed start of the wet growing season resulting in yield losses of up to 20% due to cold-induced spikelet sterility (Kou, Guédé, Office du Niger), weed problems (Thiagar), and late harvesting (Thiagar). Discussions during meetings with farmers at the survey sites revealed that farmers lacked knowledge on (i) optimal timing, dosage and mode of fertilizer application, (ii) optimal sowing dates to avoid yield loss due to cold- or heat-induced sterility, and (iii) the importance of N as the main limiting factor to yield. Possibilities to achieve a sustainable increase in rice productivity and profitability in West African irrigation systems are discussed.     

Leaf photosynthesis is enhanced in normal oil maize pollinated by high oil maize hybrids

The grain yield of normal oil maize (Zea mays L.) might increase when pollinated by high oil maize (HOM) hybrids because of heterosis. To testify that the grain yield increase might be a result of improved photosynthetic rate and related traits, the normal oil maize (NOM) hybrid, Nongda108, was cross-pollinated by three HOM hybrids, HOM202, HOM115 and HOM4515 (for short as ND108pHOM202, ND108pHOM115 and ND108pHOM4515). We found that the ND108pHOM202 and ND108pHOM115 exhibited higher net photosynthetic rate (P_n), accompanied by larger stomatal conductance (g_s) and transpiration rate (E). Moreover, delayed leaf senescence was observed in their leaves, including larger leaf area index (LAI) and higher Chl content and Chl a/b ratio. Apart from higher phosphoenolpyruvate carboxylase (PEPCase) activity, the soluble proteins were also higher in the two cross-pollinations. The higher leaf photosynthesis could explain the grain increase in ND108pHOM202 and ND108pHOM115. However, ND108pHOM4515 exhibited a decreased photosynthetic characteristic and yield performance. Significantly positive relation between grain yield and biomass (r² = 0.96, P < 0.05), P_n and biomass (r² = 0.74, P < 0.05) also suggested that the yield increase in the two cross-pollination treatments was generally owing to the higher photosynthetic rate and related photosynthetic traits.     

Predicting maize kernel sink capacity early in development

Development of maize (Zea mays L.) kernels follows a predictable pattern involving rapid increase in dry weight and large changes in water content (WC). We showed previously that final kernel weight (KW) was closely correlated with maximum WC achieved during rapid grain filling. The objectives of the current work were (i) to test if percent moisture content (MC, measured on a fresh weight basis) could be used to normalize genetic and environmental variations in kernel development shown to affect final KW and (ii) to determine whether final KW could be predicted from kernel WC prior to rapid grain filling. The data examined included results from five hybrids varying more than 2-fold in final KW grown in the field, and from previously published results. When KW and WC were expressed relative to their maximum values obtained during kernel development, a single model described the relationship between dry weight accumulation and MC for the larger seeded hybrids (199–352 mg kernel⁻¹) and published results (222–359 mg kernel⁻¹). Two smaller seeded yellow-flint popcorn hybrids, however, accumulated less dry matter per unit moisture than expected. Nonetheless, all genotypes exhibited a common developmental relationship between kernel WC (expressed as a percent of the maximum value) and MC under well-watered conditions. A new model was developed to couple this developmental relationship to final KW. This model accurately predicted final KW from kernel WC values measured prior to rapid grain filling (∼80% MC; root mean square error, RMSE, of 28.9 mg kernel⁻¹) for all hybrids examined and all published results for which KW and kernel WC data were available. The model also provided a simple means to determine whether final KW was limited by photosynthate supply during kernel development.