Effect of nitrogen,phosphorus and molybdenum application on growth and symbiotic N2-fixation of groundnut in an acid sandy soil in Niger

Two field experiments were conducted in 1988 and 1989 on an acid sandy soil in Niger, West Africa, to assess the effect of phosphorus (P), nitrogen (N) and micronutrient (MN) application on growth and symbiotic N₂-fixation of groundnut (Arachis hypogaea L.). Phosphorus fertilizer (16 kg P ha^–1) did not affect pod yields. Addition of MN fertilizer (100 kg Fetrilon Combi 1 ha^–1; P + MN) containing 0.1% molybdenum (Mo) increased pod yield by 37–86%. Nitrogen concentration in shoots at mid pod filling (72 days after planting) were higher in P + MN than in P – MN fertilizer treatment. Total N uptake increased from 53 (only P) to 108 kg N ha^–1 by additional MN application. Seed pelleting (P + MoSP) with 100 g Mo ha^–1 (MoO₃) increased nitrogenase activity (NA) by a factor of 2–4 compared to P treatment only. The increase in NA was mainly due to increase in nodule dry weight and to a lesser extent to increase in specific nitrogenase activity (SNA) per unit nodule dry weight. The higher NA of the P + MoSP treatment was associated with a higher total N uptake (55%) and pod yield (24%). Compared to P + MoSP or P + MN treatments application of N by mineral fertilizer (60 kg N ha^–1) or farmyard manure (130 kg N ha^–1) increased only yield of shoot dry matter but not pod dry matter. Plants supplied with N decreased soil water content more and were less drought tolerant than plants supplied with Mo. The data suggest that on the acid sandy soils in Niger N deficiency was a major constraint for groundnut production, and Mo availability in soils was insufficient to meet the Mo requirement for symbiotic N₂-fixation of groundnut.     

Effects of nitrogen on growth,and nitrogen and phosphorus uptake in tops and roots of sorghum grown in an Alfisol and a Vertisol

A greenhouse pot experiment was conducted to study the effects of added nitrogen (0, 10, 25, 50 and 100 mg N kg^–1 soil) on dry matter production, and N and P uptake in tops and roots of sorghum (cv CSH6) grown in a Vertisol and an Alfisol for 42 days at field capacity soil moisture content. More dry matter accumulated in the tops and roots of sorghum growing in the Alfisol than in the Vertisol. This resulted in higher N and P uptake. Top dry weight responded to N application up to 50 mg N kg^–1 soil, whereas the root weight increased at N application up to 25 mg N kg^–1. Ratios of root dry weight to total plant dry weight and N uptake in roots/total N uptake were similar in the two soils. Ratio of P uptake in roots to total P uptake was higher in Alfisol than in Vertisol. This result was attributed mainly to higher ratio of P content in roots compared to tops in the Alfisol.Approved for publication as ICRISAT Journal Article No. 709.     

Biological nitrogen fixation potential by soybeans in two low-P soils of southern Cameroon

Biological nitrogen fixation (BNF) potential of 12 soybean genotypes was evaluated in conditions of low and sufficient phosphorus (P) supply in two acid soils of southern Cameroon. The P sources were phosphate rock (PR) and triple superphosphate (TSP). The experiment was carried out during two consecutive years (2001 and 2002) at two locations with different soil types. Shoot dry matter, nodule dry matter, and nitrogen (N) and P uptake were assessed at flowering and the grain yield at maturity. Shoot dry matter, nodule dry matter, N and P uptake, and grain yield varied significantly with site and genotypes (P < 0.05). On Typic Kandiudult soil, nodule dry matter ranged from 0.3 to 99.3 mg plant^?1 and increased significantly with P application (P < 0.05). Total N uptake of soybean ranged from 38.3 to 60.1 kg N ha^?1 on Typic Kandiudult and from 18 to 33 kg N ha^?1 on Rhodic Kandiudult soil. Under P-limiting conditions, BNF ranged from ?5.8 to 16 kg N ha^?1 with significantly higher values for genotype TGm 1511 irrespective of soil type. Genotype TGm 1511 can be considered as an important companion crop for the development of smallholder agriculture in southern Cameroon.     

Greenhouse evaluation of agronomic potential of different sources of phosphate fertilizer in a typical concretionary soil of Northern Ghana

The concretionary soils of Northern Ghana, which are near neutral with respect to pH and which comprise mostly lateritic ferruginous nodules are known to sorb significant amounts of phosphate. Instead of imported superphosphate, the use of less expensive indigenous Togo rock phosphate (PR) or partially acidulated (50%) Togo rock phosphate (PAPR-50), are possible alternative phosphate fertilizer options for these soils. The objective of this research was to evaluate the effectiveness of freshly-applied SSP, PR and PAPR-50, and the effectiveness of the residues of these fertilizers in a glasshouse pot study. Laboratory studies were also undertaken to study the transformation of these fertilizers after their application to the concretionary ferruginous soils. In the greenhouse study, yield of dried tops and the P uptake by the tops of maize var. Dobidi (Zea mays) was used to measure fertilizer effectiveness. One level of P was applied for each fertilizer (26.4 kg P ha^–1). Plants were grown for 28 days. After harvesting the first crop, subsequent cropping was carried out to evaluate the effects of the residual P in the pots. The results showed that increases in dry matter yield of shoot and total P uptake followed the trend SSP > PAPR-50 > PR > control. The relative agronomic effciency (RAE) of PAPR-50 was 58% that of commercial SSP in increasing growth of the crop, while that of PR was only 23%. The residual effect of either PAPR-50 or PR on dry matter yield and total P uptake was found to be negligible compared with SSP, suggesting that apatitic P was poorly effective relative to SSP in the used soils. The P fractionation results confirmed that PR and PAPR-50 did not significantly increase any of the P fractions in either the soil fines or nodules after the first crop. By contrast, application of SSP increased all extractable Pi fractions, most of the P added being recovered from the nodules in forms associated with Fe (hydroxide and residual Pi).It is concluded that, relative to SSP, the P from residues of PAPR-50 and PR are poorly effective in the soils studied for sustainable plant production.     

Phosphorus and mycorrhizal interaction on uptake of P and trace elements by maize

Vesicular arbuscular mycorrhizal fungi (VAM) when applied to soils can result in marked increases in plant growth and P uptake. Application of molybdenum can also result in a synergistic interaction with phosphorus, with reslutant increases in plant dry matter production. The current investigation was designed to evaluate P X Mo X VAM interactions on yield and P uptake of sweet corn (Zea mays L.) The experiment was conducted in the greenhouse using soils from Missouri and Jamaica (West Indies) which were very low in available soil P. Corn was grown in pots amended with P and VAM, with and without Mo. Colonizing Jamaican soil amended with P withGlomus etunicatum increased shoot dry matter weights significantly. Greatest P uptake occured in treatments receiving the highest application of P and mycorrhizal inoculation. There was a significant difference between the two soils with respect to treatment effects on micronutrient accumulation of the test crop. The decreases in Cu, Zn, Mn, and Mo concentration of corn leaves between control and the treated pots, is attributed to dry matter dilution effect. The results indicated that mycorrhizal inoculation increased the dry matter significantly in Jamaican soil amended with P, however not in Missouri soil.Contribution No. A6-202-88, Cooperative Research, Lincoln University, Jeffeson City, MO 65101 USA     

Alfalfa response to lime,phosphorus, potassium,magnesium, and molybdenum on acid ultisols

Alfalfa (Medicago sativa L.) is a high protein forage, cultivated widely in young, fertile soils. There is considerable potential for alfalfa production in areas with acidic, highly weathered soils, but few field studies on fertility requirements under these conditions have been published.Two field trials were conducted on ultisols to study the effects of lime, P, K, Mg and Mo on alfalfa growth and tissue composition. A trial with three rates of calcitic lime (0, 2400, and 3800 kg ha^–1) and P (0, 25, and 50 kg ha^–1) and two rates each of K (20 and 200 kg ha^–1 the first year, 250 and 500 kg ha^–1 in subsequent years), Mg (36 and 106 kg ha^–1) and Mo (0 and 0.25 kg ha^–1) was conducted on an Appling coarse sandy loam (Typic Hapludult). Another factorial experiment with three levels each of lime (0, 2000, and 4,000 kg ha^–1), P (0, 100, and 200 kg ha^–1), and K (0, 150, 300 kg ha^–1) was conducted on a Davidson sandy clay loam (Rhodic Paleudult).Application of lime or P resulted in increased dry matter (DM) production at both locations. Liming also raised plant tissue N concentration. Addition of Mo had no effect on DM production or on foliar composition. Addition of K depressed soil Mg, plant tissue Mg, and plant Mg uptake at both locations. On the Davidson soil DM increased when K was applied, but on the Appling soil K increased DM production only where Mg was also added. Addition of Mg decreased K uptake and depressed DM production unless K was also added.The observed antagonism between K and Mg is of importance for alfalfa production in highly weathered soils. Successful alfalfa production in these soils is unlikely unless attention is paid to the balance between these two nutrients. Raising soil pH increased foliar N concentration affecting forage quality as well as DM production.Contribution from the Dept. of Agronomy, Univ. of Georgia, Athens, GA 30602.     

Transformations and plant uptake of urine N and S in long and short-term pastures

A field trial was carried out to compare the transformations and plant uptake of urine N and S in a short-term pasture from within an arable/pasture ley rotation and a long-term pasture. Animal urine labelled with ¹⁵N and ³⁵S was applied to microplots at both sites. These microplots were destructively sampled at various time intervals over 12 months and analysed for ¹⁵N and ³⁵S. It is known that soil organic matter accumulates under short-term pastures compared with a long-term pasture in which accumulation and degradation are in balance. Consequently, it was hypothesised that immobilization of urine N and S is more intense in the short-term. However, in this study there was considerably less immobilization of ¹⁵N and ³⁵S into soil organic forms under short-term pasture than long-term pasture. This was attributable to a greater pasture dry matter response to urine application under the short-term pasture (due to its inherently low N fertility) resulting in a greater plant uptake of ¹⁵N and ³⁵S with less ¹⁵N and ³⁵S consequently being available for immobilization. At both sites, all of the applied ³⁵S was accounted for through plant uptake and recovery in the soil, but 21–48% of the ¹⁵N was unaccounted for and presumed to have been lost through gaseous emissions. It was concluded that accumulation of soil organic N and S under short-term pastures is likely to be attributable to turnover of plant residues (particularly root material) and does not appear to be related to immobilization in urine patches.     

Variable grain legume yields,responses to phosphorus and rotational effects on maize across soil fertility gradients on African smallholder farms

Promiscuous soyabean varieties have potential to contribute significantly to income generation, food security and soil N budgets on smallholder farms. One of the major factors limiting this potential is farmers’ preference to allocate nutrient resources to food security cereal crops on the most fertile fields, leaving grain legumes to grow on residual fertility on infertile fields. Two experiments were conducted to: (i) compare the current farmer practice with targeting manure and single super phosphate (SSP) to soyabean in a three-year rotation cycle on two fields with different soil fertility: an infertile sandy soil and a more fertile clay soil; and (ii) assess the effects of variability of soil fertility within and across farms on productivity of soyabean and groundnut. In the first experiment, soyabean (<0.2 t ha⁻¹) and maize yields (<0.7 t ha⁻¹) without fertilizer were poor on a degraded sandy soil. Both crops responded poorly to SSP due to deficiency of other nutrients. Manure application significantly increased soyabean and maize yields, led to yield stabilization over three seasons and also significantly increased the proportion of N₂ fixed by soyabean (measured using ¹⁵N natural abundance) from 60% to 83%. On the sandy soil, P was used more efficiently and gross margins were greater when SSP and manure were applied to maize in a maize–soyabean rotation. Soyabean and maize yields without fertilizer inputs were larger on clay soil with moderate fertility (0.4–0.7 t ha⁻¹ and 2.0–2.3 t ha⁻¹ respectively) and were significantly increased by application of SSP and manure. Within rotations, P recovery was higher when manure and SSP were applied to maize (43 and 25%) than when applied to soyabean (20 and 19%). However, application of manure to soyabean on the clay was more profitable than application to maize for individual crops and within rotations. In the second experiment, soyabean and groundnut yields were largest (∼1 and ∼0.8 t ha⁻¹ respectively) on plots closest to homesteads on wealthy farms, which were more fertile due to good past management. Yields were poor (< 0.5 t ha⁻¹) on other fields which previously had received little nutrient inputs. Soyabean and groundnut yields correlated well with available P (R ² = 0.5–0.7) and soil organic C (SOC) contents (R ² = 0.4–0.6). For smallholder farmers to maximise benefits from legume production they need to focus attention on the more fertile plots, although production should be optimized in relation to maize. Targeting nutrients to maize as currently practiced by farmers was more efficient and economic under poor soil fertility conditions, whilst potential exists to increase income by targeting manure to soyabean on the more fertile soils.     

Response of promiscuously nodulating soybean to N and P fertilization andBradyrhizobium inoculation in a ferruginous tropical soil (Haplustalf)

Field trials were conducted at Samaru, Nigeria over a three-year period (1986–88) to study the effects of N and P fertilization on the response of promiscuously nodulating soybean toBradyrhizobium japonicum inoculation in a ferruginous tropical soil. Phosphorus fertilization enhanced nodulation, while N fertilization had no consistent effect on nodulation. Both N and P increased dry matter production. Seed yields were not influenced by the application of N. However, P increased seed yields in two out of three years. Response of seed yield to P fertilization was significant up to 26.4 kg P ha^–1.Bradyrhizobium inoculation consistently enhanced nodulation while it increased seed yield in only one out of three years. Results demonstrate that P is an important nutrient for soybean production in ferruginous tropical soils. The roles of promiscuously nodulating soybean in the maintenance of tropical soil fertility are discussed.     

Nitrogen-15 and sulfur-35 balances for fertilizers applied to transplanted rainfed lowland rice

A field experiment was conducted on a poorly-drained Aeric Paleaquult in northeastern Thailand to determine the effect of N and S fertilizers on yield of rainfed lowland rice (Oryza sativa L.) and to determine the fate of applied¹⁵N- and³⁵S-labeled fertilizers. Rice yield and N uptake increased with applied N but not with applied S in either sulfate or elemental S (ES) form. Rice yield was statistically greater for deep placement of urea as urea supergranules (USG) than for all other N fertilizer treatments that included prilled urea (PU), urea amended with a urease inhibitor (phenyl phosphorodiamidate), and ammonium phosphate sulfate (16% N, 8.6% P).The applied¹⁵N-labeled urea (37 kg N ha^–1) not recovered in the soil/plant system at crop maturity was 85% for basal incorporation, 53% for broadcast at 12 days after transplanting (DT), 27% for broadcast at 5–7 days before panicle initiation (DBPI), and 49% for broadcast at panicle initiation (PI). The basal incorporated S (30 kg ha^–1) not recovered in the soil/plant system at crop maturity was 37% for sulfate applied as single superphosphate (SSP) and 34% for ES applied as granulated triple superphosphate fortified with S (S/GTSP). Some basal incorporated¹⁵N and³⁵S and some broadcast¹⁵N at PI was lost by runoff. Heavy rainfall at 3–4 days after basal N incorporation and at 1 day after PI resulted in water flow from rice fields at higher elevation and total inundation of the 0.15-m-high¹⁵N and³⁵S microplot borders. Unrecovered¹⁵N was only 14% for 75 kg urea-N ha^–1 deep placed as USG at transplanting. This low N loss from USG indicated that leaching was not a major N loss mechanism and that deep placement was relatively effective in preventing runoff loss.In order to assess the susceptibility of fertilizer-S to runoff loss, a subsequent field experiment was conducted to monitor³⁵S activity in floodwater for 42 days after basal incorporation of SSP and S/GTSP. Maximum³⁵S recoveries in the floodwater were 19% for SSP after 7 days and 7% for S/GTSP after 1 day. Recovery of³⁵S in floodwater after 14 days was 12% for SSP and 3% for S/GTSP.This research suggests that on poorly drained soils with a low sorption capacity, a sizeable fraction of the fertilizer S and N remains in the floodwater following application. Runoff could then be an important mechanism of nutrient loss in areas with high probability for inundation following intense rainfall.     

Effect of Straw Application on Rice Yields and Nutrient Availability on an Alkaline and a pH-neutral Soil in a Sahelian Irrigation Scheme

Like elsewhere in the Sahel, actual rice yields (3–5 t ha⁻¹) are far below yield potential (±8 t ha⁻¹) in an irrigation scheme in central southern Mauritania. Earlier studies showed that yields are especially low on alkaline soils due to N and P deficiency. We investigated the potential of rice straw application as a mean to improve yields and fertilizer efficiency on an alkaline soil (pH 8.2) and a pH-neutral soil (pH 6.2). Application of 5 t straw ha⁻¹ increased yields by 1.1 t ha⁻¹ on average, independent of soil type and fertilizer dose. Contrary to our study, similar studies in Asia showed little short-term effects of straw on yield and N uptake. Straw application improved N availability, but not P availability. The improved N availability was attributed to N mineralized from the straw, from increased mineralization of soil organic matter (SOM) with a low C:N ratio (< 7.2) and from increased mineral fertilizer N (urea) recovery efficiency. We deduced that improved N fertilizer recovery upon straw application was due to reduced nitrification–denitrification losses. On the alkaline soil, volatilization was important, but that process seemed unaffected by straw application. We hypothesize that the positive effects of straw application at our study site are due to low soil C content (< 43 g kg⁻¹) and low C:N ratio compared to most lowland rice soils in Asia.     

Impact of vesicular arbuscular mycorrhizal fungi andRhizobium on the growth and P, N and Fe uptake by faba-bean

The effect of rhizobial inoculation, vesicular arbuscular mycorrhizal (VAM) fungi on the growth, P, N and Fe uptake by faba-bean plants (Vicia faba L.V. Giza 2) grown in virgin sandy soil, treated with super or rock-P were studied under green-house conditions. The earthern pots received a half of the recommended rate of P either as single super phosphate or rock-P in the rate of 20 mg P/kg soil, and calcium ammonium nitrate was added in the rate of 10 mg N/kg soil. Iron was applied in two levels 0 and 5 mg Fe/kg soil, in the form of iron sulphate (FeSO₄·7H₂O). Dry matter yield, as well as P, N and Fe-uptake were determined. Nodule numbers and their dry weights, spore numbers and mycorrhizal root infection were determined. Results indicated that, fungal infection and rhizobial inoculation either alone or in combination increased dry matter yield as compared to uninoculated plants, whereas the percentages increase in dry matter were 34, 26 and 57% in case of super-P application, while they were 56, 47 and 89% in case of rock-P when inoculated withRhizobium, VAM and dual inoculation respectively. Also P, N and Fe uptake were significantly increased due to inoculation, and dual inoculation resulted the highest effect. Generally, inoculation withRhizobium and/or mycorrhizae can remove the deficient effect of P and Fe on N₂-fixation and plant growth in the soil of low nutrients content.     

Differential availability of partially sulphuric and phosphoric acidulated phosphate rocks I. Plant response

A glasshouse study was conducted to determine the influence of soil pH on the agronomic effectiveness of partially phosphoric (Phos-PAPR) and partially sulphuric (SA-PAPR) acidulated phosphate rocks (PR). For Phos-PAPR ground North Carolina PR (NCPR) was acidulated with 10, 30 and 50% of acid needed for complete acidulation. For SA-PAPR a blend of NCPR, Arad and Khouribga PRs were acidulated with 60% of the acid needed. The relative agronomic effectiveness of these PAPRs were compared with superphosphate (SSP) and ground NCPR. A highly phosphate (P) retentive and P deficient pasture soil was used. Prior to addition of fertilizers to soil, the pH of soil was adjusted to 5.1 (initial soil pH) 5.4, 5.7 and 6.1 by applying varying amounts of Ca(OH)₂. Ryegrass (Lolium perenne) was grown as the test plant over a period of eight months. Fertilizers were applied at three rates plus control. Soil pH was monitored and continuously adjusted to the desired levels throughout the experimental period.The dry matter yields and P uptake in SSP treated pots were not influenced by soil pH. With increasing soil pH, agronomic performance of Phos-PAPRs and NCPR significantly (P<0.01) decreased but that of SA-PAPR was not affected. On the basis of per unit water-soluble P applied, uptake of P by plants was greater from PAPRs than SSP. Using the P uptake values of SSP and NCPR (which was used to prepare the PAPRs), the dissolution of P from the residual PR component of the PAPRs were calculated. The residual PR component of the Phos-PAPRs apparently dissolved in greater quantities than unacidulated NCPR. Dissolution of the residual PR was enhanced with increasing degree of acidulation. However, in the case of SA-PAPR, the agronomic performance of the PAPR was mostly dependent on the water-soluble P component of the PAPR. The uptake of P from the residual PR component of the SA-PAPR was insignificant.     

Crop yield and the fate of nitrogen and phosphorus following application of plant material and feces to soil

Organic materials are the most important sources of nutrients for agricultural production in farming systems of semi-arid West Africa. However, reliance on locally available organic nutrient sources for both crop and livestock production is rapidly becoming unsustainable. A series of feeding and agronomic trials have been conducted to address the role of livestock in sustainable nutrient cycling. This paper reports results of a greenhouse study that evaluated the effects of applying crop residue and browse leaves, or feces derived from these feeds, at equal organic-N application rates (150 kg ha^-1), alone or with fertilizer-N (60 kg ha^-1), on pearl millet (Pennisetum glaucum [L.] R.Br.) dry matter (DM) yield, nitrogen (N) and phosphorus (P) uptake, on soil nutrients, and on total, labile and recalcitrant fractions of soil organic matter (SOM). Millet DM and cumulative N uptake were most affected by fertilizer-N, followed by plant species and amendment type, although various interactions among these treatments were noted due to variations in the composition of the applied amendments. Fertilizer-N increased total millet DM by 39%, N uptake by 58% and P uptake by 17%, and enhanced N mineralization from most organic amendments, but was applied insufficiently to totally offset N and P immobilization in pots containing leaves of low initial N and P content. Feces alone appeared to supply sufficient N to meet millet-N demands. Nitrogen use efficiency was, in most cases, higher in pots amended with feces than with leaves. Nitrogen in feces apparently mineralized more in synchrony with millet-N demands. Also, the relatively high cell wall content of feces may have provided an effective, temporary sink for fertilizer-N, which upon remineralization provided more N to millet than pots amended with leaves. Whereas most of the P contained in feces mineralized and was taken up by millet, most leaves immobilized P. Assessing the costs and benefits associated with the direct land application of biomass as a soil fertility amendment versus feeding biomass first to livestock then using feces (and urine) to fertilize the soil requires information on both crop and livestock production and associated impacts on nutrient cycling.     

Growth,grain yield and nitrogen use efficiency of Mediterranean wheat in soils amended with municipal sewage sludge

The application of sewage sludge (SS) to agricultural land can improve soil fertility and physical properties, and enhance crop production. This field study was conducted for two consecutive growing seasons to investigate the influence of SS application on winter wheat growth, grain yield, N accumulation, translocation and use, and on trace elements concentrations in soil and wheat plants under Mediterranean conditions. Treatments consisted of three rates of SS, i.e. 20, 40, and 60 Mg dry weight ha^?1 year^?1, one rate of inorganic fertilizer (IF, 120 kg N ha^?1 year^?1 plus 80 kg P₂O₅ ha^?1 year^?1), and an unamended control. The application of SS resulted in tall plants with high early dry matter and N accumulation similar to or significantly higher than those obtained with IF. The lowest SS application rate resulted in grain yield similar to that obtained with IF. Nitrogen use efficiency (NUE) in SS treatments was mainly determined by uptake efficiency, which decreased with increasing SS application rate. Values of NUE and biomass production efficiency with the lowest SS rate were similar to those obtained with IF. SS application resulted in increased concentrations of total and DTPA-extractable trace elements in the soil after the first year, but concentrations were much lower than the regulation limits. Concentrations of Cu, Mn and Zn in wheat plants did not exceed those obtained with IF. Overall, SS could be considered for use as a fertilizer in wheat production systems in the area, serving also as an alternative method of SS disposal.     

Critical levels of Mn in coarse textured rice soils in India for predicting response of barley to Mn application

Green house studies of 20 soils, having a range in DTPA extractable Mn, were made to determine the critical deficiency level of Mn for predicting response of barley to Mn application. Soil Mn was significantly related with both Bray's per cent dry matter yeild (r = 0.70^**) and Mn uptake (r = 0.65^**). Soil application of 25 mg Mn kg^–1 soil significantly increased yield. Both graphical and statistical models of Cate and Nelson indicated the critical level to be 2.05 mg kg^–1 soil of DTPA extractable Mn. The critical Mn deficiency level in 45 day barley plants was 18.6 mg kg^–1 dry matter. The predictability of soil and plant critical Mn level was 91 and 80 per cent respectively.     

Response of irrigated maize to urea-ammonium nitrate and ammonium thiosulphate solutions on a sulphur deficient soil

Ammonium thiosulphate solution, (ATS, (NH₄)₂S₂O₃, 12% NH₄-N and 26% S), is a nitrogen-sulphur fertiliser which can also inhibit nitrification, inhibit area hydrolysis and also solubilize micronutrients in alkaline soils. A three year field study was conducted in northeastern Italy to compare the growth, yield, and nutrient uptake of irrigated maize (Zea mays L.) fertilised with 250 kg N ha^-1 urea-ammonium nitrate solution (UAN, 30-0-0) or UAN plus ATS. Dry matter (DM) yield, sulphur (S) and nitrogen (N) uptake were measured at several growth stages. Grain was measured and analyzed at maturity. Maize grain yield and N uptake were increased respectively 30.6% and 42.2% in the first year by adding ATS to UAN. Adding 10% by weight ATS to UAN (22.8 kg S ha^-1) increased grain yields by 1.9, 1.7 and 1.6t ha^-1 for the three years of the study. To distinguish whether the response was due to S or other ATS attributes, ATS was compared to an equivalent amount of S from single superphosphate (SSP). Plots fertilised with ATS gave grain yields 0.5 and 1.2 t ha^-1 greater than plots fertilised with equal rates of S from SSP in the last two years of the study. This added yield from ATS over SSP may have been due to beneficial effects of ATS on N or micronutrient availability or to the split application of the S from ATS.     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.     

Response of rice cultivars to phosphorus supply on an oxisol

Genotypic differences in absorption or utilization of P might be exploited to improve efficiency of fertilizer use or to obtain higher productivity on P-deficient soils. The objective of this study was to evaluate responses by 75 genotypes of upland rice (Oryza sativa L.) to two soil P levels in two field experiments. In the first experiment, soil P levels (Mehlich 1) were 1.5 mg kg^–1 and 5 mg kg^–1, and in the second experiment, 3 mg kg^–1 and 4.7 mg kg^–1 of soil, respectively. Rice cultivars differed significantly in shoot dry matter production at flowering, grain yield, and plant P status. Based on a grain yield efficiency index, cultivars were classified as P-efficient or P-inefficient. Shoot dry matter was more sensitive to P-deficiency but was not related to grain yield. Phosphorus use efficiency was higher under the low P treatment. Phosphorus uptake was significantly correlated with dry matter, P concentration and P-efficiency ratio. Results of this study indicate that genetic differences in P-use efficiency exist among upland rice cultivars and may be exploited in breeding programs.Contribution from National Rice and Bean Research Center of EMBRAPA, Goiania, Goias, Brazil and Appalachian Soil and Water Conservation Research Laboratoy, Beckley, WV, USA.     

The relative effectiveness of superphosphate and rock phosphate for soils where vertical and lateral leaching of phosphate occurs

Laboratory studies have shown that up to 70% reactive rock phosphate dissolves in three soil types found in the high rainfall (> 800 mm annual average) area of south-western Australia. Three field experiments were undertaken on these soils to compare reactive apatite rock phosphate from North Carolina (NCRP) with single superphosphate (SSP) as fertilizers for subterranean clover (Trifolium subterraneum) pasture. Vertical leaching of phosphorus (P) occurs in one soil, a deep, very sandy, acid peaty sand. Lateral leaching of P occurs in the second soil, a shallow (3 cm) sand over a slowly permeable sandy clay loam. No leaching of P occurs in the third soil, a uniform, permeable red sandy loam with a moderate capacity to sorb P. All the soils remained moist to very wet for the 6 to 8 month growing season. Fertilizers were applied once only to different plots over a four-year period (1992 to 1995). Each year fertilizer effectiveness was determined relative to the effectiveness of freshly-applied (current) SSP using yield and P content of dried clover herbage and bicarbonate-soluble P extracted from the soil (soil test P) as indices of effectiveness.For the two P leaching soils, NCRP was less, equally, or more effective than current SSP in different years. This variation is attributed to the different extents of leaching of P from current SSP in different years which experienced different amounts of rainfall and associated leaching. For the non-P leaching soil, the effectiveness of current NCRP and the residual effectiveness of NCRP were from 5 to 80% the values for current SSP. When measured using soil test P, current NCRP and residual NCRP varied from 40% as effective, to equally or 30% more effective as current SSP at one site, but were about 20% as effective at the other two sites. For the two P leaching soils in some years, the residual value of RP was higher than that of current SSP, presumably due to the rapid leaching of water-soluble P from the SSP. As measured using yield, P content and soil test P, the relative effectiveness of SSP consistently decreased with increasing time from application; the decreases were much less obvious for NCRP.