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.     

Effects of N application on agronomic and environmental parameters in silage maize production on sandy soils

The current nitrogen (N) use in silage maize production can lead to considerable N losses to the environment. Maize growers fear that a reduction of N inputs needed to minimize N losses might depress yields. The objective of this study was therefore to quantify: (1) the response of silage maize dry matter (DM) yields to N, (2) the economically optimal N reserve, and (3) the trade-off between silage maize DM yield and N losses. The indicators of N losses used in this study were the difference between N input and N uptake and the post-harvest residual soil mineral N. Regression models were used to fit DM yields and N uptakes of silage maize measured in 25 experiments on sandy soils in the Netherlands to the sum (SUMN) of the soil mineral N reserve (SMN_early) in March–April, plus mineral N in fertilizer, plus ammonium N in spring-applied slurry. The values obtained for the economically optimal SUMN in the upper 30 and 60 cm of soil were, respectively, 173 and 195 kg N ha⁻¹, when we assumed that the value of 1 kg fertilizer N equals the value of 5 kg silage DM. The economically optimal SUMN was not significantly related to the attainable DM yield. The apparent N recovery (ANR) of maize averaged 53% at the economically optimal SUMN. The ANR rose considerably, however, when N was applied at lower rates, indicating that N losses may be considerably smaller in less intensive maize cropping. When maize was fertilized at 100 kg N ha⁻¹ below the economic optimum, the ANR was 73%, the difference between the mineral N input and the N crop uptake decreased by 57 kg N ha⁻¹ and the soil mineral N residue at the end of the growing season (0–60 cm) decreased by 24 kg N ha⁻¹. The associated reduction in DM yield averaged 16%. Fertilizer prices would have to be as much as four times higher to make maize growers spontaneously reduce the application rates by a 100 kg N ha⁻¹, however. It is concluded that adjusting the N input to a level below the economically optimal rate can reduce the risks for N losses to the environment associated with conventional maize production, with a limited effect on silage yields.     

Population density and row spacing effects on dry matter yield and bark content of kenaf (Hibiscus cannabinus L.)

Efforts to bring kenaf from experimental crop status to an accepted alternative in established cropping systems have been ongoing for years. To compete with existing crops and maximize monetary returns, the effects of agronomic practices on yield and crop quality must be better understood. Row spacing and population density are implicated in dry matter yield, and therefore, bast fiber production. Four row spacings, four population densities, and two cultivars were examined to determine these effects on dry matter accumulation and bark content. Of all factors evaluated, only row spacing significantly affected dry matter yield. Yield was greatest at the 35.5-cm row spacing, and lowest at the 71- and 101.6-cm row spacings. With regard to bast yield, calculated as a percentage of total sample dry weight, a significant cultivar × row spacing interaction occurred. However, data indicate that manipulating row spacing to maximize total stalk yield per hectare resulted in the highest bast fiber yield for the two cultivars tested. The narrowest row spacing of 35.5 cm, gave the greatest biomass yield as well as the highest bark yield per hectare.     

Submergence tolerance and yield performance of lowland rice as affected by agronomic management practices in eastern India

Rice is subjected to excessive waterlogging and flash-flooding on large areas in south and south-east Asia. Besides cultivars, submergence tolerance of plants is influenced by various agronomic practices. A field experiment was conducted at Cuttack, India during 1994–1995 to study the effect of method of stand establishment (direct seeding and transplanting), vigour of seed (low and high-density) or seedlings (N-fertilized and unfertilized), plant population (normal and 50% more) and N fertilizer (single basal and split application) on yield performance of lowland rice under conditions of natural submergence and simulated flash-flooding (impounding up to 90 ± 3 cm depth for 10 days at vegetative stage). Flooding reached a maximum depth of 80 cm in 1994 and 52 cm in 1995 under natural submergence. The crop performance was better in 1994 due to timely sowing in dry soil and delayed accumulation of water (43 days after sowing) than in 1995 when sowing was done late in saturated soil followed by early water accumulation (28 days after sowing). Grain yield of rice decreased by 30.0–33.6% due to simulated flash-flooding compared with natural submergence, and by 21.4–33.1% due to transplanting in July compared with direct seeding in May-end/early June. The yield of direct-sown crop increased by using high-density seed of 22.9–23.0 mg weight (5.2–9.0%), higher seed rate of 600 m⁻² (2.2–2.3%) and basal fertilization at 40 kg N ha⁻¹ (19.4–25.7%) compared with low-density seed (19.4–20.1 mg), 400 seed m⁻² and no N, respectively. The yield of transplanted crop increased by using N-fertilized seedlings of 0.49–1.65 g weight (29.5–38.5%), higher number of seedlings at 155 m⁻² (3.5–16.7%) and basal fertilization at 40 kg N ha⁻¹ (31.9–32.5%) compared with unfertilized seedlings (0.19–0.79 g), 115 seedlings m⁻² and no N. Split application of 40 kg N ha⁻¹ — 50% each at basal and top dressing (105–115 days of growth after flash-flooding) — improved yield significantly (10.1–13.1%) over single basal application under simulated flash-flooding, but not under natural submergence conditions. Regression analysis indicated that relative contribution of various factors in increasing grain yield was in order: N fertilizer > seed density > seed m⁻² in direct-sown rice, and N fertilizer > seedlings m⁻² > seedling dry weight in transplanted rice. It was concluded that grain yield of flood-prone lowland rice can be increased by establishing the crop early through direct seeding using high-density seed and basal N fertilization.     

Effect of sulphur fertilisation on the growth and metabolism of sugar beet grown on soils of differing sulphur status

Field experiments were conducted at high- and low-S status sites in the 1998 and 1999 seasons to investigate the effect of sulphur application on the growth and metabolism of sugar beet. Application of sulphur (25 kg ha⁻¹) resulted in a 25% increase in root yield together with significant increases in root and shoot dry matter accumulation at the low-S site only in the 1998 season. Beet quality was also increased through a reduction in α-amino N concentration. Crop S uptake was shown to be as much as 35 kg S ha⁻¹ per year but with most S being returned to the soil removal of S is likely to be <15 kg ha⁻¹ per year. The use of diagnostic plant indicators to predict sulphur deficiency in this crop was limited by the potential of the crop to access subsoil S through an extensive rooting depth. Application of sulphur to high-S status sites had no effect on the growth or metabolism of sugar beet.     

Grain yield,zinc efficiency and zinc concentration of wheat cultivars grown in a zinc-deficient calcareous soil in field and greenhouse

Field experiments were carried out to study grain yield, zinc (Zn) efficiency and concentrations of Zn in shoot and grain of 37 bread wheat (Triticum aestivum) and three durum wheat (Triticum durum) cultivars grown in a Zn-deficient calcareous soil with (23 kg Zn ha⁻¹), and without, Zn fertilization in 1993–1994 and 1994–1995. The same Zn-deficient soil was used in greenhouse experiments to study shoot dry weight, Zn efficiency and shoot Zn concentrations of 21 bread and three durum wheat cultivars (same cultivars used in the field experiments). Zinc fertilization of cultivars in the field enhanced grain yield on average by 30% in both years. Increases in grain yield to Zn fertilization varied substantially between cultivars from 8% to 76%. Accordingly, there was large variability in Zn efficiency of cultivars, expressed as the ratio of grain yield or shoot dry-matter yield produced under Zn deficiency compared to that under Zn fertilization. On average, Zn efficiency values ranged from 57% to 92% for grain yield in field experiments and from 47% to 83% for shoot dry weight in greenhouse experiments. Most of the cultivars behaved similarly in their response to Zn deficiency in the field and greenhouse. The cultivars selected from local landraces had both, a high Zn efficiency and high yield under Zn-deficient conditions. The bread wheat cultivars, improved for irrigated conditions, had generally low Zn efficiency and low yield, both in the field and greenhouse. All durum wheat cultivars in this study also showed low levels of Zn efficiency, grain yield and shoot dry weight under Zn deficiency. Overall, there was no relation between Zn efficiency values and Zn concentrations in grain or shoot dry matter. The results presented here demonstrate the existence of substantial variation in Zn efficiency among wheat cultivars, particularly bread wheat cultivars, and suggest that wheat landrace populations are a valuable source of genes to improve high Zn efficiency of wheat for Zn-deficient soils.     

Simulation of seasonal stalk water content and fresh weight yield of sugarcane

Stalk water content is an important variable for a sugarcane simulation model as sugar industries in many countries use cane yield and sucrose content on a wet mass basis for payment and yield reports. The prime objective was to develop a stalk water content module (SWCM) that can be incorporated into a sugarcane simulation model. SWCM starts from consideration of the dynamics of water concentration (ρ, g water g⁻¹ dry matter) along stalks and through seasons. The quantities of stalk water were modelled separately for the top and basal sections of the millable stalks. Field observations showed that the stalk water concentration (ρ) declined from 7.8 to 11.8 in the top internodes to 1.6–2.9 g water g⁻¹ dry matter in bottom internodes. In the basal section, ρ ranged from 1.98 in winter to 2.83 g water g⁻¹ stalk dry matter in summer. A two-parameter equation was used to model ρ and resulted in a range of coefficients of determination from 0.8 to 0.97 for six varieties. The SWCM was developed to simulate both the effects of seasonal variation and the age of internodes on the quantity of stalk water. The module was incorporated into a process oriented model of sugarcane growth for validation against field observations in tropical and subtropical areas of Australia and Hawaii, USA. Comparison of observed yields with cane yield simulated by the model that included the SWCM, gave an average of R² of 0.95, compared with the average of R² of 0.97 for simulation of stalk dry matter. The average relative root mean squared error (RMSE) was 15.2% in simulation of cane yield and 15.1% for simulation of cane dry weight. The module can be readily incorporated into a model that simulates sugarcane dry matter so that commercial crop yield can be estimated.     

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.     

The response of autumn and spring sown sugar beet (Beta vulgaris L.) to irrigation in Southern Italy: Water and radiation use efficiency

The Apulia region in Southern Italy is an important area for sugar beet cultivation. It is characterised by clay soils and a hot-arid and winter-temperate climate. The capability of sugar beet to exploit solar radiation, water use and irrigation supply in root yield, total dry matter and sucrose production was studied and analysed in relation to two experimental factors: sowing date – autumn (October–December) and spring (March) – and irrigation regime – optimal and reduced (respectively with 100 and 60% of actual evapotranspiration). Data sets from three experiments of spring sowing and three of autumn sowing were used to calculate: (1) water use efficiency in the conversion in dry matter (WUE_dm, plant dry matter at harvest versus seasonal water use ratio), in sucrose (WUE_suc, sucrose yield versus seasonal water use ratio); (2) irrigation water use efficiency in the conversion in dry matter (IRRWUE_dm), in sucrose (IRRWUE_suc) and fresh root yield (IRRWUE_fr); and (3) radiation use efficiency (RUE, plant dry matter during the crop cycle and at harvest versus intercepted solar radiation ratio).Autumnal beet was more productive than spring for fresh root, plant total dry matter, sucrose yield and concentration; also WUE_suc and IRRWUE_s were higher in the autumnal sugar beet, but no difference was observed in WUE_dm (on average, 2.83 g of dry matter kg⁻¹ of water used). An average saving of about 26% of seasonal irrigation supply (equivalent to about 100 mm) was measured in the three years with the earliest sowing time. The optimal irrigation regime produced higher root yield, plant total dry matter and sucrose yield than the reduced one; on the contrary the IRRWUE_fr and IRRWUE_dm were higher in the reduced irrigation strategy. WUE_s and IRRUWE_s correlated positively with the length of crop cycle, expressed in growth degree days and, in particular, to the length of the period from full soil cover canopy to crop harvest, the period when plant photosynthetic activity and sucrose accumulation are at maximum rates. Seasonal RUE was higher in the spring than in the autumn sowing (1.14 μg J⁻¹ versus 1.00 μg J⁻¹). The RUE values during the crop cycle reached the maximum in the period around complete canopy soil cover. The results showed the importance for better use of water and radiation resources of autumnal sowing time and of reduced irrigation regime in sugar beet cropped in a Mediterranean environment.     

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.     

Variability of root length density and its contributions to seed yield in chickpea (Cicer arietinum L.) under terminal drought stress

The importance of root systems in acquiring water has long been recognized as crucial to cope with drought conditions. This investigation was conducted to: (i) evaluate the variability on root length density (RLD) of chickpea in the vegetative growth stage; (ii) estimate the effect of RLD on seed yield under terminal drought conditions; and (iii) set up a procedure to facilitate the screening of chickpea genotypes with large RLD. Twelve diverse chickpea genotypes were grown in tall PVC cylinders with two different soil water treatments in 2000 and 2001, and in field under water deficit conditions during 2000/2001 and 2001/2002. In field trials, the mean RLD at 35 days after sowing showed a significant positive correlation with seed yield in both years. Similarly, the RLD in the 15–30 cm soil depth had significant positive effects to the seed yield in both years. The importance of the root trait was particularly relevant in 2001/2002, a more severe drought year, when the RLD in deeper soil layer, 30–60 cm depth, showed a significant positive relationship with seed yield. Also, the RLD at deeper soil layer, 30–60 cm depth, was higher in 2001/2002 than in 2000/2001, in particular in tolerant genotypes. The PVC cylinder trials were set up to facilitate the screening of chickpea genotypes with large RLD. RLD of plants grown in cylinders with 70% field capacity was correlated with RLD in the field trials (r = 0.731; p = 0.01). This work highlights the importance of roots in coping with terminal drought in chickpea. The cylinder system offers a much easier procedure to screen chickpea genotypes with large RLD.     

Pig slurry applications to alfalfa: Productivity,solar radiation utilization,N and P removal

A field study was carried out over 4 years at one site in the Low Po Valley, Northern Italy, to examine the effect of various levels of pig slurry applications on alfalfa (Medicago sativa L.) productivity, solar radiation utilization, and nutrient removal. Treatments consisted of three liquid pig manure rates, estimated to provide in total 300, 450 and 600 kg N ha⁻¹ year⁻¹ (PS300, PS450, PS600, respectively), and one unfertilized control (named as Control). Treatments were applied on the second and third year of crop stand (1994 and 1995), whilst during the subsequent fourth and fifth years of crop stand (1996 and 1997) the residual effects of previous treatments were investigated. Regardless of crop age and year-to-year variability, pig slurry tended to increase annual forage production during the 2 years of fertilization and the subsequent biennium of stand duration. Overall, the forage dry matter production, accumulated over four growing seasons and 17 cuts, was 39 000 kg ha⁻¹ for the Control, 44 500 kg ha⁻¹ (+14%) for PS300, to 49 800 kg ha⁻¹ (+28%) for PS450 and 45 800 kg ha⁻¹ (+17%) for PS600. Nitrogen concentration in shoot dry matter was not influenced by the treatment applied. P concentration, on the other hand, was substantially increased by all three rates of pig slurry application, with an evident residual effect observed during the last 2 years of crop stand. However, the evident increase of P availability, assured by pig slurry fertilization, resulted in most of cases in luxury consumption of P by the crop plant. A strong linear relationship was found between cumulative forage dry matter and accumulated incident global solar radiation. Pig slurry fertilization increased significantly the slope of the regressions with respect to the Control. Since enhanced N and P availability may reduce the carbon costs for sustaining root nodules and symbiotic organisms, it seems likely that the crop plant must gain advantage in terms of dry matter produced per unit of radiation intercepted. However, further research is needed to clarify whether the effect of manure is attributable to improved alfalfa efficiency in converting intercepted solar energy into forage dry matter, to enhanced canopy cover thus higher radiation capture per unit of soil area, or to a combination of both mechanisms.     

Weed control in a pigeon pea–wheat cropping system

Pigeon pea (Cajanus cajan (L.) Millsp.) seedlings compete poorly against the rapid growth of warm-season annual weeds. Weed control is required before this heat and drought-tolerant legume can be reliably grown in the U.S. southern Great Plains as a potential source of livestock hay between annual plantings of winter wheat (Triticum aestivum L.). Currently, no herbicides are labeled for use on pigeon pea grown in the U.S. Three years of replicated field experiments were conducted to determine the effects of applications (1× and 2× rates) of herbicides (pre-emergence, sulfentrazone + chlorimuron and metribuzin; post-emergence, imazapic and sethoxydim) on weed suppression, pigeon pea dry matter, and carry-over effects on a winter wheat crop. The most abundant summer weeds were broadleaf, and all herbicide treatments, except sethoxydim (grass herbicide), reduced weed densities compared to untreated plots without adversely affecting pigeon pea stands. Imazapic treatments provided the most effective weed control. Overall average pigeon pea dry matter ranged from 75 to 256 g m⁻² with sethoxydim and the untreated control ≤ metribuzin ≤ sulfentrazone + chlorimuron ≤ hand weeded control ≤ imazapic. Compared to the hand-weeded control, imazapic treatments greatly reduced wheat dry matter (1×, 65% and 2×, 91%) and grain yield (1×, 59% and 2×, 93%). Imazapic should not be used unless nontransgenic imidazolinone herbicide tolerant wheat cultivars are planted. While the other herbicides decreased negative effects of weeds on pigeon pea dry matter without greatly affecting productivity of a following wheat crop, appropriate labels for each of these herbicides will be required prior to their use by southern Great Plains pigeon pea producers.     

Differences in tolerance to infertile acid soil stress among germplasm accessions and genetic recombinants of the tropical forage grass genus,Brachiaria

Several Brachiaria species are the most widely grown forages in tropical America. A field study was conducted during two seasons (1994, wet and 1995, dry) in a medium-textured Oxisol at Carimagua, Colombia. The main objective of the study was to evaluate genotypic variation in plant attributes for tolerance to low fertility, acid soil stress conditions (pH 4.9) among germplasm accessions and genetic recombinants of Brachiaria. The entries included 43 genetic recombinants selected from a breeding population, four parental accessions and an additional eight germplasm accessions. Small amounts of fertilizer were applied at establishment (kg ha⁻¹: 40 N, 20 P, 20 K, 14 Ca, 12 Mg and 12 S). A number of plant attributes including forage yield, leaf area, shoot nutrient composition and shoot nutrient uptake were measured during both seasons. Significant genetic variation was observed in several plant attributes such as leaf area, shoot nutrient content, nutrient partitioning to leaves, shoot nutrient uptake, and forage yield in both seasons. Forage yield ranged from 59 to 343 g plant⁻¹ in the wet season and 5 to 174 g plant⁻¹ in the dry season. Correlation between forage yield and shoot nutrient uptake indicated the importance of nutrient acquisition, particularly of phosphorus (r=0.90; P<0.0001), for adaptation to infertile acid soil stress. Two genetic recombinants (BRN093/3009, FM9201/1873) were productive when grown under infertile acid soil stress in both wet and dry seasons. But, neither of these two recombinants is highly resistant to xylem-feeding insects known as spittlebugs (Homoptera: Cercopidae). One spittlebug-resistant genetic recombinant (BRN093/1371) exhibited several desirable attributes such as superior leaf area and leaf biomass, greater N content in leaves, and greater partitioning of N and P to leaves that could contribute to adaptation and persistence in these soils. This recombinant is being utilized in a breeding program to develop superior Brachiaria lines.     

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.     

Root growth,soil water content and yield of barley under different tillage systems on two soils in semiarid conditions

An experiment was conducted on two soils in a semiarid area in the Spain’s Ebro valley. Soil A was a Fluventic Xerochrept of 120 cm depth and Soil B was a Lithic Xeric Torriorthent of 30 cm depth. Three tillage systems were compared in Soil A: subsoiler tillage, minimum tillage and no-tillage, and two (minimum tillage and no-tillage) in Soil B. The experiment was repeated for 5 years on Soil A and 3 years on Soil B. Root length density, volumetric water content and dry matter were measured at important developmental stages. Yield was determined at harvest. In Soil A, root length density and volumetric water content were significantly greater for no-tillage than for subsoiler or minimum tillage (up to 1.4 cm cm⁻³ and 5%, respectively), mainly in the upper part of the soil profile. At lower depths, differences as great as 0.8 cm cm⁻³ and 6% were also found. Mean yield (4 years) was similar between no-tillage (3608 kg ha⁻¹) and minimum tillage (3508 kg ha⁻¹), and significantly smaller for subsoiler tillage (3371 kg ha⁻¹). In Soil B, no differences were observed between tillage systems for volumetric water content. Significant interactions between tillage and year were found for root length density, dry matter and yield. Mean yield (3 years) was not significantly different for minimum tillage (1806 kg ha⁻¹) and no-tillage (1867 kg ha⁻¹). The results in Soil A showed that surface conditions are of major importance in the water content of the soil and determined the differences among tillage systems. No-tillage favoured greater and deeper water accumulation in the soil profile and greater root growth. This makes this system potentially better for years of low rainfall. In Soil B no tillage system proved to be better because of the low water-holding capacity of this soil (56 mm).     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: II. Residual effects on rice

Field experiments were conducted over the period 1994–1996 to investigate the residual effect on rice of a wide range of temperate legume species, grown during the preceding winter season in a warm-temperate environment in Nepal. The incorporation of large quantities of above- and below-ground legume biomass (roots and foliage) resulted in substantial residual effects on the subsequent upland rice crop. The effects on rice yield in terms of percent increase over the control were more pronounced at a site of comparatively lower inherent soil fertility where grain yields of rice grown after high yielding legume crops such as bitter lupin (Lupinus mutabilis) and Persian clover (Trifolium resupinatum) were almost twice as high (up to 7.6 t DM ha⁻¹) than those of the control treatment (rice after wheat). In contrast, the residual effects of below-ground biomass (roots, nodules) on the following rice crop were not very pronounced and resulted in similar residual effects as rice, after fallow. Although up to 480 kg ha⁻¹ of legume foliage N had been applied to rice, only a small proportion of the legume N (up to 70 kg N ha⁻¹) was recovered by the following rice crop. Total rice dry matter yields were highly correlated with the amount of legume N applied, yet other factors such as residue quality and residue management practices appeared to also affect the magnitude of the residual effects. Future work should aim at investigating the effect of residue quality as affected by legume species and residue management practice on decomposition and N mineralisation processes in rice soils.     

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha⁻¹ in 2002, 310 kg ha⁻¹ in 2003, and 360 kg ha⁻¹ in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha⁻¹ of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: I. Legume biomass production and N fixation

Field experiments were conducted to investigate the performance of temperate legume species in rice-based cropping systems in a warm-temperate environment in Nepal. Over the period 1994–1996, various legume species were grown during the winter season (October–May) in the Kathmandu valley (27° N, 1350 m asl) with the aim of evaluating their biomass production and N fixation. A wide range of legume species including food, feed and green manure crops proved to be very well adapted to the winter growing conditions in this environment. The cultivation of temperate legume crops therefore, constitutes an alternative to traditional cropping practices such as growing wheat or leaving the land fallow. The temperate species appeared to capitalise on generally favourable growing conditions such as long growing season, low pest and disease pressure, high radiant energy receipt and cool night temperatures. However, performance varied greatly between species and years. Total dry matter yields ranged from 2 to 20 t ha⁻¹ obtained with lentil (Lens culinaris Medic) and bitter lupin (Lupinus mutabilis), respectively. Highest seed yields were produced by fababean (Vicia faba) (5 t ha⁻¹) and field pea (Pisum sativum var. arvense) (3 t ha⁻¹) in the first season. Nitrogen yields and quantities of N fixed ranged from 18 to 481 kg ha⁻¹ and from 0 to 463 kg ha⁻¹, respectively. Large amounts of N were fixed by species such as fababean, Persian clover (Trifolium resupinatum) and bitter lupin. Early sowing in autumn was shown to be beneficial for some crops such as fababean, vetch (Vicia benghalensis) and Persian clover. In these cases, it is, therefore, important to reduce the turn-around interval after rice. Further research is required to fully determine the potential of temperate legume species in these environments with particular emphasis given to the identification of the most adapted cultivars and to reduce the need for irrigation of these winter crops.     

The effect of increasing NaCl in irrigation water on growth,gas exchange and yield of tobacco Burley type

Despite the economic importance of tobacco, there is limited field study on the quantitative response of growth and yield to increasing soil salinity. The effects of irrigation with saline water on yield components of field-grown tobacco (Nicotiana tabacum L.) “Burley” type plants were studied over two growing seasons. Growth, dry matter partitioning and gas exchange were measured either in rainfed or fully irrigated plants growing in a clayey–sandy–loam soil. The four fully irrigated treatments received amounts of saline waters at 0.54, 2.5, 5.0 or 10 dS m⁻¹ electrical conductivity (EC_w) equal to crop evapotranspiration. In both years, the electrical conductivity of the saturation phase (EC_e) across the 0.6 m topsoil profile increased with increasing salinity of the irrigation water. Soil moisture was markedly lower in the rainfed treatment than in fully irrigated treatments. Different saline concentrations of irrigation water had virtually no effect on soil moisture. Carbon assimilation rate, stomatal conductance and water use efficiency of the saline treatments were lower than the fully irrigated plants at 0.54 dS m⁻¹ (NW treatment) in 1996, but not in 1997. Transpiration rates were unaffected by salinity in both years. The highest yield was produced by plants irrigated with good quality water. The number of leaves per unit land area was greater for the NW plants, whereas there were no differences between the other four treatments. Salinity decreased plant dry matter and height at harvest, increased dry matter partitioning into leaves and decreased that into stems in both years. Dry matter partitioning to leaves was also greater for the rainfed plants than for the NW plants. Tobacco plants grown under field conditions showed a maximum reduction of relative yield at the highest salinity level of only 31%. The threshold values (0.56 and 0.96 dS m⁻¹) and the EC_e at which a 10% yield reduction was obtained (3.12 and 2.55 dS m⁻¹) calculated from the linear model of response of relative yield to increasing EC_e were typical of moderately sensitive crops. The EC_e values at which 50% yield was reduced (13.34 and 8.91 dS m⁻¹) were indicative of moderate tolerance to salinity.