The effect of soil water status on fertiliser, topsoil and subsoil phosphorus utilisation by wheat

Background and aims

Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions.

Methods

An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm).

Results

The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P.

Conclusions

Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Identifying the critical period for waterlogging on yield and its components in wheat and barley

Background and aims

Crop tolerance to waterlogging depends on factors such as species sensitivity and the stage of development that waterlogging occurs. The aim of this study was to identify the critical period for waterlogging on grain yield and its components, when applied during different stages of crop development in wheat and barley.

Methods

Two experiments were carried out (E1: early sowing date, under greenhouse; E2: late sowing date, under natural conditions). Waterlogging was imposed during 15–20 days in 5 consecutive periods during the crop cycle (from Leaf 1 emergence to maturity).

Results

The greatest yield penalties occurred when waterlogging was applied from Leaf 7 appearance on the main stem to anthesis (from 34 to 92 % of losses in wheat, and from 40 to 79 % in barley for E1 and E2 respectively). Waterlogging during grain filling reduced yield to a lesser degree. In wheat, reductions in grain number were mostly explained by reduced grain number per spike while in barley, by variations in the number of spikes per plant.

Conclusions

The time around anthesis was identified as the most susceptible period to waterlogging in wheat and barley. Exposing the crop to more stressful conditions, e.g. delaying sowing date, magnified the negative responses to waterlogging, although the most sensitive stage (around anthesis) remained unchanged.     

Coupled response of soil carbon and nitrogen pools and enzyme activities to nitrogen and water addition in a semi-arid grassland of Inner Mongolia

Background and aims

Previous studies have demonstrated positive net primary production effects with increased nitrogen (N) and water availability in Inner Mongolian semi-arid grasslands. However, the responses of soil carbon (C) and N concentrations and soil enzyme activities as indicators of impacts of long-term N (urea) and water addition are still unclear. We tested the effect of 7 years of a N and water addition experiment on soil C, N, and specific soil-bound enzymes in a semi-arid grassland of Inner Mongolia.

Methods

We determined concentrations of soil organic carbon (SOC) and soil total nitrogen (TN) in both the 0–10 and 10–20 cm soil layers. Concentrations of labile carbon (LC) and inorganic nitrogen (nitrate and ammonium), and soil pH were measured. Additionally, soil dehydrogenase (DHA), β-glucosidase (BG) and acid and alkaline phosphomonoesterase (PME) enzyme activities were determined in the 0–10 cm soil layer.

Results

SOC concentration in the 0–10 cm soil layer showed no response to N addition or N plus water addition, but increased with water addition alone by 0.3–15.7 %. N addition significantly increased nitrate by 46.0–138.4 % and ammonium by 19.0–73.3 % in the 0–10 cm soil layer, whereas water addition did not affect them. The activities of DHA and alkaline PME enzymes, as well as soil pH, in the 0–10 cm layer decreased with N addition, however water addition alone caused these enzyme activities to increase. Unlike the surface soil (0–10 cm), the lower soil layer (10–20 cm), was responsive to N and water addition in that SOC and TN concentrations decreased with N addition and increased with water addition.

Conclusions

The accumulation of SOC and TN in N and water addition plots may be caused by the input of plant biomass exceeding SOC decomposition. Decrease in microbial activity, derived from decreased DHA and alkaline PME activities might result from suppression effects of lower pH and decreased microbial N supply. Water availability is proved to be more important than N availability for soil C and N accumulation in this semi-arid grassland.     

Differences in yield, Ellenberg N value, tissue chemistry and soil chemistry 15 years after the cessation of nitrogen addition

Background & Aims

The consequences of fertiliser addition to semi-natural grasslands are well understood, but much less is known about the consequences of cessation of nitrogen fertiliser regimes, including rates of recovery. This study aimed to investigate whether the effects of nitrogen (N) additions to a mesotrophic grassland were still apparent 15 years after the cessation of N inputs.

Methods

A long-term experiment at Tadham Moor, UK, received N additions at rates of 0, 25, 50, 100 and 200 kg N ha^?1 yr^?1 between 1986 and 1994. Fifteen years after the cessation of N additions soil chemistry, plant tissue chemistry, plant biomass and Ellenberg N values were assessed.

Results

KCl-extractable ammonium-N, total soil N, total organic carbon and microbial biomass N differed between the controls and the higher historic levels of N addition. Plant tissue chemistry showed no significant effects of previous N addition. Above-ground biomass was higher where N had been added, although this response was only weakly significant. The species composition of the vegetation showed effects of the N addition with mean Ellenberg N values significantly higher than the control in most treatments.

Conclusion

The effects of long-term N addition can be seen for many years.     

Localized application of NH4 +-N plus P at the seedling and later growth stages enhances nutrient uptake and maize yield by inducing lateral root proliferation

Background and aims

Localized supply of P plus ammonium improves root-proliferation and nutrient-uptake by maize (Zea mays L.) at seedling stage, but it is largely unknown how localized supply of nutrients at both early and late stages influences maize-growth, nutrient-uptake and grain-yield.

Methods

A 2-year field experimentation with maize was conducted with localized application of P plus ammonium as diammonium phosphate (LDAP) or ammonium sulfate plus P (LASP) at sowing or jointing stage, with broadcast urea and P (BURP) or no nitrogen (F0) as controls.

Results

Localized supply of P plus ammonium significantly increased root-proliferation, shoot dry-weight and nutrient-uptake at seedling stage. The positive effect disappeared at 53 days after sowing. However, plant-growth and nutrient-uptake increased again after the second localized application of P plus ammonium at jointing. The density and average length of the first-order lateral roots in local patches increased by 50 % in LDAP and LASP compared with F0 and BURP. Maize-yield increased by 8–10 % compared with BURP. Agronomic N efficiency and N-use efficiency increased by 41–48 % and 25–57 % compared with the BURP.

Conclusions

It is suggested that enhanced root-proliferation in the nutrient-rich patches with localized supply of ammonium and P at sowing and jointing stages is essential for improving nutrient-uptake and ultimately grain-yield.     

Improving fertiliser efficiency on calcareous and alkaline soils with fluid sources of P,N and Zn

Alkaline calcareous or sodic soils represent an important proportion of the world's arable soils and are important for cereal production. For calcareous soils in general, despite high applications of P fertiliser for many years, P deficiency in cereals is common. Field experiments were conducted to test the relative ability of granular (e.g. DAP, MAP and TSP) and fluid fertilisers to supply P to wheat on grey calcareous and red brown calcareous sandy loam soils (Calcixerollic xerochrepts). A pot experiment was also conducted with these soils and with two non-calcareous alkaline soils to investigate the effects of placement on the efficiency of fertiliser performance. In 1998, fluid and granular sources of P, N and Zn were compared in the field by banding below the seed at sowing. In 1999, MAP applied as granular, and technical grade MAP applied as fluid, were compared as sources of P in rate response experiments. First year results showed that fluid sources of P, N and Zn produced significantly more grain than the granular product. In the following year, fluid fertilisers were found to produce significantly higher response curves for shoot dry weight, grain yield and P uptake in grain. At a commercial rate of 8 kg P ha^–1, fluid fertiliser produced between 22% and 27% more grain than the granular product. Soil moisture and fertiliser placement effects are implicated in the higher efficiency of fluid fertilisers.     

Nitrogen release from incorporated 15N-labelled Chinese milk vetch (Astragalus sinicus L.) residue and its dynamics in a double rice cropping system

Background and aims

Chinese milk vetch (Astragalus sinicus L. CMV), a leguminous cover crop, has been shown to provide N benefits to rice crops, but little is known about the pathway of incorporated CMV and its N dynamics. In this study, effects of CMV under different application treatments (incorporated alone, applied in conjunction with urea fertilizer and applied with ryegrass (Lolium multiflorum Lam.)) on N dynamics, rice yields and N uptake were investigated and compared with those of chemical fertilizer (CF) and no fertilizer (NF) in a double rice cropping system.

Methods

Nitrogen release from incorporated CMV residue was quantified by using a bag method. Nitrogen dynamics of CMV were evaluated by using ¹⁵N-labelled fresh CMV tops and compared with those of CF (¹⁵N-labelled urea).

Results

CMV residue decomposition pattern and its N release pattern followed a single exponential decay model, with 87.8–89.5 % of the applied CMV decomposed and 95.1–96.1 % of the original N released in the double rice season (177 days after fertilizer application). CMV treatments had higher rice N uptake efficiency than CF (39.2–51.3 % vs. 29.9 %) at the sum of early and late rice seasons. Rice yield, N accumulation and mineral fertilizer efficiency in CMV treated treatments were higher than those in CF. After two consecutive rice seasons the amounts of residual N remained in the soil were higher in the CMV treated fields than in CF (29.4–33.2 % vs. 14.1 %).

Conclusions

CMV can be considered an efficient N source alternative to chemical fertilizer in double rice cropping systems.     

A multi-environmental study of recent breeding progress on nitrogen use efficiency in wheat (Triticum aestivum L.)

Key message

By comparing 195 varieties in eight trials, this study assesses nitrogen use efficiency improvement in high and low nitrogen conditions in European winter wheat over the last 25 years.

Abstract

In a context where European agriculture practices have to deal with environmental concerns and nitrogen (N) fertiliser cost, nitrogen use efficiency (NUE) has to be improved. This study assessed genetic progress in winter wheat (Triticum aestivum L.) NUE. Two hundred and twenty-five European elite varieties were tested in four environments under two levels of N. Global genetic progress was assessed on additive genetic values and on genotype × N interaction, covering 25 years of European breeding. To avoid sampling bias, quality, precocity and plant height were added as covariates in the analyses when needed. Genotype × environment interactions were highly significant for all the traits studied to such an extent that no additive genetic effect was detected on N uptake. Genotype × N interactions were significant for yield, grain protein content (GPC), N concentration in straw, N utilisation, and NUE. Grain yield improvement (+0.45 % year^?1) was independent of the N treatment. GPC was stable, thus grain nitrogen yield was improved (+0.39 % year^?1). Genetic progress on N harvest index (+0.12 % year^?1) and on N concentration in straw (?0.52 % year^?1) possibly revealed improvement in N remobilisation. There has been an improvement of NUE additive genetic value (+0.33 % year^?1) linked to better N utilisation (+0.20 % year^?1). Improved yield stability was detected as a significant improvement of NUE in low compared to high N conditions. The application of these results to breeding programs is discussed.     

Sharing N resources in the early growth of rapeseed intercropped with faba bean: does N transfer matter?

Background and aims

Legume-brassica intercrops may help to reduce N fertilizer input. We tested whether (i) intercropping with faba bean can improve N status of rapeseed, and (ii) root complementarity and/or N transfer is involved in such performance.

Methods

Pre-germinated rapeseed and faba bean were grown either together or in monospecific rhizotrons (2 plants per rhizotron). Root growth was recorded. N rhizodeposition of the crops and N transferred between species were assessed using a ¹⁵N stem-labelling method.

Results

Intercropped rapeseeds accumulated 20 % higher amounts of N per plant than monocultures. Up to 32 days after sowing, root distribution in the rhizotrons was favourable to physical sharing of the soil N: 64 % of faba bean root length was located in the upper part, as 70 % was in the lower part for rapeseed. At late flowering of the faba bean (52 days after sowing), N rhizodeposition of the two crops were similar and reached 8 to 9 % of the plant N. N transferred from the faba bean to the rapeseed was similar to that transferred from the rapeseed to the faba bean.

Conclusions

Niche complementarity benefits more intercropped rapeseed than net N fluxes between species in the early growth.     

Hyperaccumulation of thallium is population-specific and uncorrelated with caesium accumulation in the thallium hyperaccumulator, Biscutella laevigata

Purpose

This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO₂]).

Methods

Field pea (Pisum sativum L.) was labeled in situ with ¹⁵N (by absorption of a ¹⁵N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol^–1) [CO₂] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of ¹⁵N-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either ¹⁵N-labeled field pea residues (including ¹⁵N-labeled rhizodeposits) or ¹⁵N-labeled barley plus fertilizer ¹⁵N residues.

Results

Elevated [CO₂] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO₂] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO₂] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO₂], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO₂], but dropped to 11 % under elevated [CO₂], while that from fertilizer did not differ significantly between ambient [CO₂] (4 %) and elevated [CO₂] (5 %).

Conclusions

The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO₂]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO₂]) climates.     

Impact of plant growth-promoting bacteria on grain yield,protein content,and urea-<Superscript>15</Superscript> N recovery by maize in a Cerrado Oxisol

Background and aims

The inoculation of cereal crops with plant growth-promoting bacteria (PGPB) is a potential strategy to improve fertilizer-N acquisition by crops in soils with low capacity to supply N. A study was conducted to assess the impact of three inoculants on grain yield, protein content, and urea-¹⁵ N recovery in maize (Zea mays L.) under Cerrado soil and climate conditions.

Methods

The main treatments included inoculants containing (i) Azospirillum brasilense strain Sp245, (ii) A. brasilense strains AbV5 + AbV6, (iii) Herbaspirillum seropedicae strain ZAE94, and (iv) a non-inoculated control. The subtreatments were (i) urea-N fertilization (100 kg N ha^?1) at 30 days after sowing and (ii) no N addition at the stage. To determine fertilizer-N recovery, ¹⁵N–labelled urea was applied in microplots.

Results

Inoculants carrying A. brasilense improved urea-¹⁵ N acquisition efficiency in maize and also improved grain yield compared to the non-inoculated control, while urea-N fertilization enhanced grain quality by providing higher protein content.

Conclusion

Our results suggest that the inoculation of maize grains with PGPB represents a strategy to improve fertilizer-N recovery and maize yield in Cerrado soil with a low capacity to supply N.

     

Reducing methane on-farm by feeding diets high in fat may not always reduce life cycle greenhouse gas emissions

Purpose

To consider whether feed supplements that reduce methane emissions from dairy cows result in a net reduction in greenhouse gas (GHG) intensity when productivity changes and emissions associated with extra manufacturing and management are included.

Methods

A life cycle assessment was undertaken using a model farm based on dairy farms in Victoria, Australia. The system boundary included the creation of farm inputs and on-farm activities up to the farm gate where the functional unit was 1 L of fat and protein corrected milk (FPCM). Electricity and diesel (scaled per cow), and fertiliser inputs (scaled on farm size) to the model farm were based on average data from a survey of farms. Fertiliser applied to crops was calculated per area of crop. Animal characteristics were based on available data from farms and literature. Three methane-reducing diets (containing brewers grain, hominy or whole cotton seed) and a control diet (cereal grain) were modelled as being fed during summer, with the control diet being fed for the remainder of the year in all cases.

Results and discussion

Greenhouse gas intensity (kg CO₂-eq/L FPCM) was lower than the control diet when the hominy (97 % compared with control) and brewers grain (98 %) diets were used but increased when the whole cottonseed diet was used (104 %). On-farm GHG emissions (kg CO₂-eq) were lower than the control diet when any of the methane-reducing diets were used (98 to 99.5 % of emissions when control diet fed). Diesel use in production and transport of feed supplements accounted for a large portion (63 to 93 %) of their GHG intensity (kg CO₂-eq/t dry matter). Adjusting fertiliser application, changing transport method, changing transport fuel, and using nitrification inhibitors all had little effect on GHG emissions or GHG intensity.

Conclusions

Although feeding strategies that reduce methane emissions from dairy cows can lower the GHG emissions up to the farm gate, they may not result in lower GHG intensities (g CO₂-eq/L FPCM) when pre-farm emissions are included. Both transport distance and the effect of the feed on milk production have important impacts on the outcomes.     

Labeled nitrogen fertilizer research with urea in the semi-arid tropics

Summary As part of a research program to determine the fate of N fertilizers applied to dryland sorghum in the semi-arid tropics,¹⁵N balance studies were conducted with various N sources in the greenhouse. Two American soils, Houston Black clay (Udic Pellustert) and Windthorst sandy loam (Udic Paleustalf), similar in properties to the Vertisol and Alfisol in the semi-arid tropics of India, were employed. Experiments were conducted with large pots containing 20 or 60 kg of soil which was subjected to several watering regimes. The¹⁵N not accounted for in the plant and soil was presumably lost. Losses of N on calcareous Houston Black clay were greatest for broadcast urea, 16%–28%. Amendment of broadcast urea with 2% phenyl phosphorodiamidate, a urease inhibitor, reduced N losses only slightly to 15%–20%. Point placement of urea at a 6 cm soil depth reduced losses to 1%–11%. Granule size had no effect on N loss from point-placed urea. Ammonia volatilization was apparently the main N loss mechanism, since N losses from sodium nitrate were less than 7%, except when the soil surface was waterlogged. N losses on the Windthorst soil averaged 30% from urea and 11% from ammonium nitrate. Amendment of urea with urea phosphate to form a 27% N and 13% P product reduced fertilizer N losses but did not increase grain yield on Windthorst soil. N losses were also less from ammonium nitrophosphate than from urea. Band and point placement of urea 6 cm below the soil surface were equally effective in reducing N loss on Houston Black clay. The findings give credence to the recommendation of deep band placement for urea in the semi-arid tropics.     

Absorption of 15NH3 volatilized from urea by Citrus trees

Background and aims

Gaseous losses of ammonia (NH₃) have been observed in citrus orchards when urea is surface-applied to the soils, and this loss might significantly limit the effectiveness of the nitrogen (N) fertilizer. However, a portion of the volatilized NH₃ might be absorbed by the plants through the leaves. To quantify the contribution of the leaf absorption of ¹⁵NH₃, a study with sweet oranges was conducted in two field areas where trees were grown at standard (480 trees ha^?1) and high densities (617 trees ha^?1).

Methods

Plastic trays were filled with soil, covered with mown grass to simulate field management conditions, fertilized with ¹⁵N labeled urea (12 atom % excess) and placed under each of three trees in the orchards. This experimental procedure prevented the uptake of N from the labeled urea by the roots. Two weeks after ¹⁵N fertilization, the trays were removed from the field, and the soil was homogenized and sampled for chemical analyses. The citrus trees under which the trays were placed were destructively harvested, and the total N concentrations and ¹⁵N/¹⁴N ratios were determined.

Results

After urea application, the NH₃ losses peaked within three days and subsequently decreased to negligible amounts after 10 days. The total NH₃ losses accounted for 55–82 % of the applied N. Although the NH₃ absorption by the citrus leaves was proportional to the tree density in the field, only 3–7 % of the ¹⁵NH₃ volatilized from the soil was recovered by the citrus trees, and the NH₃ absorption was also influenced by the proximity of citrus trees to the site of urea application and the leaf areas of the trees.

Conclusions

The citrus trees can absorb the NH₃ volatilized from urea, even though, the amount recovered by the trees is small and does not represent a significant proportion of total gaseous N losses, what demonstrates the importance of enhanced N use efficiency practices in field to reduce losses of NH₃ when urea is applied to soil surfaces.     

Phosphorus accumulation in grains of japonica rice as affected by nitrogen fertilizer

Background and aims

This study aims to investigate the effect of nitrogen (N) on grain phosphorus (P) accumulation in japonica rice.

Methods

Six cultivars with contrasting agronomic traits were grown for 3 years (from 2008 to 2010) of field experiments under seven N treatments and 1 year (in 2010) of pot experiments with five N treatments to study the effect of N on grain phosphorus accumulation and to explore its physiological foundation.

Results

Grain total P and phytic acid concentration showed a clearly decreasing trend as N rate increased for both field and pot experiments. Pot experiment revealed that application of N increase plant biomass, but tended to lower plant P uptake, especially for the split topdressing treatments. Both harvest index (HI) and P harvest index (PHI) increased with N rate, but PHI was consistently higher than HI, indicating the larger proportion of P translocation to grain than that of dry matter by N. Further, ratio of PHI/HI differed significantly among genotypes, but was stable across contrasting N treatments.

Conclusions

The combination of decreased plant P uptake and dilution effect of increased grain yield by N is proposed as underlying mechanism of the decreased grain P concentration by high N.     

Effects of seed nickel reserves or externally supplied nickel on the growth,nitrogen metabolites and nitrogen use efficiency of urea- or nitrate-fed soybean

Background and aims

Nickel (Ni) has a critical role in the urea metabolism of plants. This study investigated the impact of seed Ni content along with external Ni supply on the growth, various nitrogen (N) metabolites and N use efficiency (NUE) of soybean plants.

Methods

Soybean plants raised from Ni-poor or Ni-rich seeds were grown in nutrient solution with or without external Ni supply and fed with either urea or nitrate as the sole N source. The changes in growth, leaf chlorophyll levels, Ni and N concentrations of different plant parts, tissue accumulation of various N metabolites and N uptake of soybean as well as NUE and its components were examined.

Results

Nickel starvation reduced the shoot biomass of urea-fed plants by 25 % and the leaf chlorophyll levels by up to 35 %, but nitrate-fed plants were unaffected. Visual toxicity symptoms were not observed in urea-fed plants. Under urea supply, Ni-deficient plants had lower levels of total N, protein and free amino acids in various organs. Root uptake of urea was severely depressed in Ni-deprived plants. Availability of Ni did not have any effect on the NUE of nitrate-fed plants, whereas its deficiency reduced the NUE of urea-fed plants by 30 %. The growth and N nutritional status of urea-fed soybean were significantly improved by high seed Ni reserves as well as external Ni supply.

Conclusion

Adequate Ni supply is required for maximizing the growth, root uptake of urea and NUE of urea-fed plants. Seed Ni reserves contribute significantly to the Ni and thus N nutritional status of soybean.     

Integrated effects of organic,inorganic and biological amendments on methane emission,soil quality and rice productivity in irrigated paddy ecosystem of Bangladesh: field study of two consecutive rice growing seasons

Aims

Effects of different soil amendments were investigated on methane (CH₄) emission, soil quality parameters and rice productivity in irrigated paddy field of Bangladesh.

Methods

The experiment was laid out in a randomized complete block design with five treatments and three replications. The experimental treatments were urea (220 kg ha^?1) + rice straw compost (2 t ha^?1) as a control, urea (170 kg ha^?1) + rice straw compost (2 t ha^?1) + silicate fertilizer, urea (170 kg ha^?1) + sesbania biomass (2 t ha^?1 ) + silicate fertilizer, urea (170 kg ha^?1) + azolla biomass (2 t ha^?1) + cyanobacterial mixture 15 kg ha^?1 silicate fertilizer, urea (170 kg ha^?1) + cattle manure compost (2 t ha^?1) + silicate fertilizer.

Results

The average of two growing seasons CH₄ flux 132 kg ha^?1 was recorded from the conventional urea (220 kg ha^?1) with rice straw compost incorporated field plot followed by 126.7 (4 % reduction), 130.7 (1.5 % reduction), 116 (12 % reduction) and 126 (5 % reduction) kg CH₄ flux ha^?1 respectively, with rice straw compost, sesbania biomass, azolla anabaena and cattle manure compost in combination urea and silicate fertilizer applied plots. Rice grain yield was increased by 15 % and 10 % over the control (4.95 Mg ha^?1) with silicate plus composted cattle manure and silicate plus azolla anabaena, respectively. Soil quality parameters such as soil organic carbon, total nitrogen, microbial biomass carbon, soil redox status and cations exchange capacity were improved with the added organic materials and azolla biofertilizer amendments with silicate slag and optimum urea application (170 kg ha^?1) in paddy field.

Conclusion

Integrated application of silicate fertilizer, well composted organic manures and azolla biofertilizer could be an effective strategy to minimize the use of conventional urea fertilizer, reducing CH₄ emissions, improving soil quality parameters and increasing rice productivity in subtropical countries like Bangladesh.     

Efficacy of zinc oxides as fertilisers

Background and aims

Human zinc (Zn) deficiency is prevalent in developing countries and Zn biofortification of grains is used to increase the Zn content of food staples. Agronomic interventions to biofortify grain involve fertiliser selection and management. The usefulness of a zinc compound as a fertiliser will depend on its solubility, bioavailability and the effect of its distribution in the soil profile.

Methods

Various sources of Zn oxide and Zn sulfate fertiliser were characterised for nutrient content, morphology, solubility, and fertiliser recovery when applied to the surface, banded near the seed or uniformly mixed.

Results

Compared with Zn sulfates, Zn oxide fertilisers had very low water solubility and slow dissolution rates, because of a higher dissolution pH. This did not translate to a diminished ability to supply Zn to plants when both sources of Zn were mixed through the soil, but there was significantly less fertiliser recovery from Zn oxides than from Zn sulfates when the fertiliser was banded near the seed.

Conclusions

All sources will be equally effective if uniformly mixed through the profile. In no-till systems where fertiliser is banded near seed, Zn sulfate is superior to Zn oxide.     

Increased plant density of winter wheat can enhance nitrogen–uptake from deep soil

Background and Aims

Increased plant density improves grain yield and nitrogen (N)–use efficiency in winter wheat (Triticum aestivum L.) by increasing the root length density (RLD) in the soil and aboveground N–uptake (AGN) at maturity. However, how the root distribution and N–uptake at different soil depths is affected by plant density is largely unknown.

Methods

A 2–year field study using the winter wheat cultivar Tainong 18 was conducted by injecting ¹⁵?N–labeled urea into soil at depths of 0.2, 0.6, and 1.0 m under four plant densities of 135 m^?2, 270 m^?2,405 m^?2, and 540 m^?2.

Results

We observed significant RLD and ¹⁵?N–uptake increases at each soil depth as the plant density increased from 135 to 405 m^?2. ¹⁵?N–uptake increased with plant density as the soil depth increased, although the corresponding RLD value fell with depth. The ¹⁵?N–uptake at each soil depth was positively related to the RLD at the same depth. The total AGN was positively related to RLD in deep soil, especially at 0.8–1.2 m.

Conclusions

Increasing the plant density from 135 m^?2 to the optimum increases AGN primarily by increasing the RLD in deep soil and therefore increasing the plant density of winter wheat can be used to efficiently recover N leached to deep soil. Moreover, the total root numbers per unit area and RLD still increased at supraoptimal density while shoot number and N uptake stagnated.