Phosphorus sorption capacity of low activity clay soils of South Western Nigeria and its usefulness in evaluating P requirement of rice

Field and laboratory experiments were conducted on 15 low activity clay soils in Ogun State of Nigeria to evaluate the relationships between P sorption capacity and some soil properties and the use of sorption indices in evaluating the P requirement of rice. Langmuir adsorption capacity (b) varied from 30.9 to 414.3 µg g^–1. Although adsorption capacity was related significantly to a number of soil properties, citrate dithinonite bicarbonate (CDB) extractable Fe was the most important variable accounting for 99% of the variation in adsorption capacity. The solution P concentration (SPC) required to achieve 95% maximum grain yield of rice varied from 0.03 in a sandy clay soil to 0.19 µg ml^–1 in a sandy soil, while the quantity of fertilizer P required to attain the solution P concentration (Standard Phosphate requirement, SPR) varied from 14.1 to 88.7 kg ha^–1. Highly significant power function relationships were obtained between SPC and b (r=0.93) and between SPR and b (r=0.93). The P buffering capacity (PBC) of the soils indicated that the soils are moderately buffered. However, SPR accounted best for the variation in grain yield of rice on the field (R²=0.90). The use of P sorption indices in estimating P needs of rice appears superior to the use of chemical extractants.     

An attempt to evaluate phosphorus fertilizer requirements of western Nigeria savannah soils

A greenhouse fertilizer trial was carried out on 60 surface soils of the western Nigeria savannah derived from basement complex rocks. Bray's P₁ available P in the soils varied between 1 and 112µg ml^–1. There was maize response to P addition and a critical P level of 12.7µg ml^–1 was calculated for the soils.For 22 of the soils, a laboratory incubation technique was used in evaluating changes in Bray's P₁ extractable P at various rates with time. The initial rapid decline in soil available P was completed between 28 and 84 days of incubation. A fertilizer factor, calculated from extracted P in treated and untreated soils varied between 1.5 and 16.7µg ml^–1 and was significantly correlated with soil pH and citrate-dithioniteextractable oxides of Fe and Al.Fertilizer rates based on critical soil P, available soil P and fertilizer factor, correlated significantly with greenhouse estimates for optimum yield obtained with the linear response plateau model (r = 0.91,p < 0.001). At ten field locations varying in available P content, response was only to P applications lower than 60 kg ha^–1 and the calculated P rates using a mean fertilizer factor of 3.0µg ml^–1 corresponded to P rates at which maximum yields were obtained in the sites.     

Relative agronomic merit of fused calcium phosphate

Three consecutive yields of dry matter (DM) and P in rye-grass and one of DM and P in barley sown after ryegrass were harvested from acid silt loam, clay, sandy loam and sandy clay soils that had been mixed with fused Ca phosphate (FP) or single superphosphate (SP) at the start of the trial. The relative agronomic merit (RAM) of FP was defined as an increase in the overall DM or P yield induced by FP and expressed as a percentage of the increase in overall DM or P yield induced by SP. The RAM values varied with soils and fertilizer rates. They were usually higher for DM yields than for the corresponding P yields. On average, RAM values were 56, 106 and 193% for DM yields and 31, 65 and 82% for P yields at P rates of 12, 36 and 108 mg P kg^–1 soil dry wt, respectively. Hence, FP was a better fertilizer than SP in terms of promoting plant growth, whereas SP was superior to FP at increasing P yields. Both barley DM and P yields were significantly and positively correlated (P = 0.05, n = 64) with soil levels of resin-P, inorganic NaHCO₃—P, organic and inorganic NaOH—P fractions extracted in sequence from samples taken before barley was sown.     

Very high applications of nitrogen fertilizer on grassland and residual effects in the following season

At very high nitrogen applications (480 and more kg N ha^–1 yr^–1) in field trials on all-grass swards the amount of N applied exceeded the amount of N harvested. In the humid temperate climate of the Netherlands in the subsequent spring approximately 25, 40, and 50% of this excess nitrogen was recovered as accumulated mineral nitrogen in the 0–100 cm layer of sandy, clay and heavy clay soil, respectively. The effect of this excess nitrogen on growth during the subsequent season was measured through the increase in DM and N yield over a reference treatment. In this season all treatments received a uniform application (40 kg N ha^–1 cut^–1). Residual effects were absent on sandy soil but distinct on the clay soils. On the clay soils each accumulated kg soil mineral nitrogen produced 15 kg DM. Assuming a relatively small contribution of residual nitrogen carried over in stubble, roots and organic matter, the accumulated soil mineral nitrogen would seem to be as effective as applied fertilizer nitrogen.     

Nitrogen movement and uptake by rice fertilized with urea supergranules in two contrasting Mollisols

In a glasshouse experiment, the periodic movement, loss and uptake of N by lowland rice fertilized with point-placed urea supergranule (USG) was studied in two soils differing in texture. Movement of urea-N, NH ₄ ⁺ -N and NO ₃ ^- -N was significantly faster in Patharchatta sandy loam (Typic Hapludoll) than in Beni silty clay loam (Aquic Hapludoll) and was mostly downward with peak concentration near the placement site.Nitrogen in leachate was higher in Patharchatta sandy loam than in Beni silty clay loam. About 60–70% of leaching of urea-N took place within 2 days of USG placement. The leaching of NH ₄ ⁺ -N and NO ₃ ^- -N increased till 14 and 21 days of USG placement in Patharchatta sandy loam and Beni silty clay loam, respectively. Nitrogen leached through urea, NH ₄ ⁺ and NO ₃ ^- forms was, respectively, 64, 25 and 25% higher from sandy loam. During 49 days, 49 and 32% of the applied N was recovered by rice plants from silty clay loam and sandy loam, respectively.     

Phosphorus status of soil and leaching losses: results from operating and dismantled lysimeters after 15 experimental years

The objectives of the present study were: (1) to evaluate the predicting value of the most important European soil P tests for P leaching losses; and (2) to investigate how these soil P tests reflect the development of P depth profiles in original homogeneous soils of lysimeters. The study included more than 100 lysimeters, located at the Lysimeter Station Falkenberg/Saxony-Anhalt, UFZ-Centre for Environmental Research Leipzig-Halle GmbH, Germany. Soil textures were sand, sandy loam, loam and silt. The management forms were arable land, grassland and fallow with various variation in fertilisation, crop rotation and irrigation. Samples were collected from the A-horizons and from the whole profiles of eight set-aside and dismantled lysimeters at 10-cm sections. The concentrations of total P were determined monthly in the leachates and evaluated for a three-year period. The concentrations of P extracted by ammonium acetate lactate (AL-P), double lactate (DL-P), sodium bicarbonate (Olsen-P) and ammonium oxalate (OX-P) as well as P_t were significantly correlated with each other (P<0.05–P<0.001) for arable soils. The relevant regression coefficients were strongly influenced by soil texture, soil use and management. The mean annual P concentrations of the leachates were in the range 0.4–1.2 mg l^–1 for sands and <0.001–0.1 mg l^–1 for the textures sandy loam, loam and silt. These corresponded to P leaching losses of 0.001–2846 g ha^–1 yr^–1. Mean annual and maximum P concentrations and leaching losses were significantly (r>0.954, P<0.001) predicted by the OX-P concentrations of arable topsoils in lysimeters filled with sand. For sandy loam under grass the agronomic soil P tests (AL-P, DL-P and Olsen-P) enabled reasonable predictions of P in leachate. Under arable use, factors such as fertilisation, management intensity, depth of tillage and irrigation resulted in weak correlations between soil P concentrations and P in leachate. It was shown for the first time that all P extractants reflected P enrichments in topsoils and subsoils and the development of distinct depth profiles. Influence of soil use on the depth distribution of P was more pronounced in the 0–20 cm layer than in the subsoils. Here, the original homogeneous substrate had oscillating P concentrations at 10-cm increments under all soil uses. These could not be explained by Al_ox and Fe_ox but were significantly correlated with the C_t contents and bulk density. This indicates that vertical movement of P containing organic matter along with differences in porosity contributed to the heterogeneous P distribution in the lysimeter subsoils. This new evidence must be considered if data sets from long-term lysimeter experiments are used to calibrate and validate P leaching models.     

Effects of gypsum on growth and mineral content of Brussels sprouts,and soil properties of Orthic Podzols

Studies of crop response to Ca fertilizers are generally few as well as information concerning the Ca nutrition of Brussels sprouts (Brassica oleracea var.gemmifera). Six field studies were conducted, over three years, to determine yield response of Brussels sprouts to soil applied gypsum (CaSO₄.2H₂O), lime (calcite), and elemental S on sandy loam to loamy sand Orthic Podzols in Prince Edward Island. Relative yield of marketable (0–32mm) Brussels sprouts were related to soil ammonium acetate extractable Ca (r = 0.71). The highest yields (11 to 13 t ha^–1) were associated with an extractable Ca of above 400µg g^–1 soil, while a Ca level below 400µg reduced yield by 20%. Highest marketable yields were associated with a Ca level in the leaf tissue (in upper mature leaves at sprout formation) of above 2.2% (w/w) (r = 0.55), this in turn was associated (r = 0.87) with an extractable soil Ca above 400µg g^–1 soil. Calcite and elemental S did not influence yield or mineral content. Gypsum, as expected increased leaf S content, but leaf tissue S levels were not related to marketable yield. Slight decreases in soil pH due to increasing gypsum rate (0.5–4.3 t ha^–1) were associated with changing accumulations of B, Mn, Fe, Ca, and Zn in the leaf tissue. Gypsum had little effect on soil porosity and structure indices, but changing pH (in both gypsum and lime treatments) significantly influenced soil microbial biomass.     

Uptake of NPK and yield of rainfed groundnut (Arachis hypogaea L.)

Experiments were conducted on sandy loam soils of Tirupati campus of Andhra Pradesh Agricultural University for two rainy seaons of 1980 and 1981 to study the effect of split application of NPK fertilizers on Spanish bunch groundnut. The fertilizer doses were 40 N, 20 P and 40 K kg ha^–1 in 1980 and 30 N, 10 P and 25 K kg ha^–1 in 1981.In 1980, uptake of N (48 kg ha^–1), P (7 kg ha^–1) and K (37 kg ha^–1) was maximum with the application of 10 N, 5 P and entire 40 K kg ha^–1 as basal and 30 N and 15 P kg ha^–1 at 30 days after sowing, leading to highest pod yield (0.76 t ha^–1). In 1981, application of 20 N, 10 P and 25 K kg ha^–1 as basal dose and 20 N kg ha^–1 at 30 days after seeding resulted in highest uptake of N (114 kg ha^–1), P (17 kg ha^–1) and K (58 kg ha^–1) and hence the pod yield (2.36 t ha^–1).Differences in the uptake of NPK and pod yield in 1980 and 1981 was due to variation in total rainfall and its distribution during the crop period. Rainfall was equally distributed throughout the crop period in 1981, whereas there were two prolonged dry spells of more than 40 days in 1980.     

Adsorption and desorption of phosphate in some semi-arid tropical Indian Vertisols

Adsorption and desorption of phosphorus in soils are among the key processes governing its availability to crops. There have been very few studies on the phosphorus adsorption and desorption characteristics of Vertisols. The P adsorption and desorption characteristics of four Vertisols belonging to three agriculturally important soil series were studied. The amounts of P adsorbed by the soils at 0.2µg ml^–1 equilibrium solution P concentration was low and ranged from 34.3 to 79.5µg g^–1 soil. The phosphate adsorption was very well described by Langmuir and Freundlich isotherms. The P adsorbed by a Vertisol (BR-1) fertilized with different rates of P in the previous season (0, 10, 20 and 40 kg P ha^–1) was similar (34.3–41.3µg g^–1 soil) indicating little effect of fertilization on P adsorption. The correlation studies indicated that the DTPA-extractable Fe was the most important factor accounting for P adsorption in these soils. Clay and CaCO₃ content were found to be relatively less important factors affecting P adsorption in the soils studied.The capacity of the two extractants and EUF (electro-ultrafiltration) to desorb the adsorbed P followed the order: EUF (400V, 80°C)>sodium bicarbonate>EUF (200V, 20°C)>calcium chloride. The average amounts of P desorbed from the four Vertisols using these methods were 74, 63, 50, and 3% respectively of the adsorbed P. In the Begamganj soil, the amount of P desorbed by EUF (400V, 80°C) exceeded 100%, indicating that all of the adsorbed P was desorbable including some native P.In conclusion the results of our study show that the Vertisols studied have low phosphate adsorption capacity and that the P they adsorbed is easily desorbable.Approved for publication as Journal Article No. 983 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT).     

Influence of soil organic carbon on the interpretation of soil test P for wheat grown on alkaline soils

Organic carbon is known to alter crop response to applied phosphorus (P) but that fact has not been incorporated in soil test interpretations. To achieve this objective, field experiments with wheat were conducted for four years on alkaline soils of Punjab, India. The experimental soils ranged from loamy sand to loam in texture, 7.4 to 9.6 in pH, 0.16 to 0.75% in organic carbon (OC) and 2 to 40 mg Olsen extractable P kg^–1 soil. Response of wheat to fertilizer phosphorus application was related to the combined effect of Olsen P and soil OC content. At a given Olsen P level, wheat yield was a function of soil OC content. Multiple regression analysis of the data showed that OC content <0.2% did not affect yield significantly. At values >0.6%, OC along with Olsen P accounted for 97% of the variation in yield and there was no response to applied fertilizer P. Yield isoquants for 4 and 5 tons grains ha^–1 showed that for a given Olsen P level, as OC content increased the amount of fertilizer P required to achieve a yield target decreased. It was shown that OC may be used to approximate the contribution of organic P mineralization to plant available soil P during a growing season. The reliability of fertilizer recommendations based on Olsen P may be improved on some alkaline soils by consideration of soil OC content.     

The interpretation of Olsen extractable P values in relation to recommendations for the fertilizer requirements of crops

A greenhouse experiment, with Okra (Abelmoschus esculentus L.) as the test crop, was conducted on twenty-one soils ranging in Olsen's extractable phosphorus from 1.8 to 15.5µg Pg^–1 soil. The experiment was conducted at Punjab Agricultural University, Ludhiana, India. The soils were nonsaline with pH ranging from 7.7 to 8.6. A critical level of 2.55µg Pg^–1 soil was predicted by Cate and Nelson's (1971) statistical procedure. Because of a wide range in relative yields, this value did not accurately predict response to applied P. An approach to compute minimum response to applied fertilizer, which is likely to be obtained at a particular Olsen P level, has been presented. It involves calculation of lower 60 percent confidence limits for relative yield and fitting log_e-linear regression to the transformed data. The regression was tested on a published data set and was found to hold well.     

Response of dryland wheat to fertilizer nitrogen in relation to stored water,rainfall and residual farm yard manure

Yield response of dryland wheat to fertilizer N application in relation to components of seasonal water (available soil moisture and rainfall) and residual farm yard manure (FYM) was studied for five years (1983–84 to 1987–88) on a maize-wheat sequence on sandy loam soils in Hoshiarpur district of Punjab, India. Four rates of N viz. 0, 40, 60 and 80 kg ha^–1 in wheat were superimposed on two residual FYM treatments viz. no FYM (F₀) and 15 t ha^–1 (F₁₅) to preceding maize. FYM application to maize increased the residual NO₃-N content by 19–30 kg ha^–1 in the 180 cm soil profile. For a given moisture distribution, F₁₅ increased attainable yields. Over the years, F₁₅ increased wheat yield by 230 to 520 kg ha^–1. Response to fertilizer N was lower in FYM amended plots than in unamended plots. Available soil moisture at wheat seeding and amount and distribution of rainfall during the vegetative and the reproductive phases of crop development affected N use efficiency by wheat. Available soil moisture at seeding alone accounted for 50% variation in yield. The residual effect of FYM on wheat yield could be accounted for by considering NO₃-N in 180 cm soil profile at seeding. The NO₃-N and available soil moisture at wheat seeding along with split rainfall for two main phases of crop development and fertilizer N accounted for 96% variation in wheat yield across years and FYM treatments.     

Greenhouse evaluation of phosphorus availability from compacted phosphate rocks with urea or with urea and triple superphosphate

The possible effect of urea hydrolysis on the availability of phosphorus (P) from phosphate rock (PR) was evaluated in two greenhouse experiments with maize, using two sources of PR — Pesca (Colombia) and Bayovar (Peru) — representing low and high chemical reactivity, respectively.In Experiment I, on a neutral Josephine silty clay loam (pH 6.2) (Typic Haplozerult), Bayovar PR compacted with urea (Bayovar PR + urea) performed better than Bayovar PR compacted with NH₄Cl (Bayovar PR + NH₄Cl) in increasing dry-matter yield at a rate of 100 mg P kg^–1 but not at rates of 50 and 200 mg P kg^–1. It was also found that the dry-matter yield obtained with compacted Bayovar PR products was significantly higher when the N ratios of urea: NH₄Cl were 1:1 or higher than when the ratios were below 1:1. Although Bray I–P can overestimate available P from PR with respect to that from TSP, a good relationship was observed between Bray I–P and dry-matter yield from various compacted Bayover PR products with a small particle size (–0.43 + 0.15 mm).In Experiment II an acid Bladen sandy loam (pH 4.5) (Typic Albaquult) was used. Finely ground Bayovar PR (– 0.07 mm) was about 66% as effective as TSP in increasing dry-matter yield, whereas Pesca PR was ineffective. When Pesca PR was partially acidulated with H₃PO₄ at 20% level (PAPR), it became 70% as effective as TSP. Granulated PAPR and Pesca PR compacted with TSP (Pesca PR + TSP) were found to be equally effective in increasing dry-matter yield when both products had the same particle size and the same water-soluble and citrate-soluble P as percent of total P, and when prilled urea was used as the N source. However, when urea was compacted with Pesca PR and TSP, the product's effectiveness was further increased by 30% and to the same level as TSP.In summary, the results tend to support the suggestion that urea hydrolysis can be beneficial in increasing the availability of P from PR to plants in soils having medium to high organic matter contents.     

Emissions of nitrous oxide from boreal agricultural clay and loamy sand soils

Long-term studies of greenhouse gas fluxes from agricultural soils in different climate regions are needed to improve the existing calculation models used in greenhouse gas inventories. The aim of this study was to obtain more information on nitrous oxide (N₂O) emissions from agricultural mineral soils in the boreal region. N₂O emissions were studied during 2000–2002 on two soil types in Finland, a loamy sand and a clay with plots of grass, barley and fallow. N₂O fluxes were measured with static chambers throughout the year. Other parameters measured were water filled pore space (WFPS), soil mineral nitrogen concentration, soil porosity, soil temperature and depth of soil frost. The annual fluxes from the clay soil ranged from 3.7 to 7.8 kg N ha^–1 and those from sandy loam from 1.5 to 7.5 kg N ha^–1. On average 60% of the annual fluxes occurred outside the growing season, from October to April. Increasing the number of freeze-thaw events was found to increase the fluxes during winter and during the thawing period in spring. The results suggest that N₂O fluxes from these boreal mineral soils do not vary much as a function of applied fertiliser N and could probably be better estimated from soil physical properties, including soil porosity.     

Critical Zn concentration for essential oil yield and menthol concentration of Japanese mint

The effect of different concentrations of Zn nutrient application on Japanese mint (Mentha arvensis L.) was studied under glasshouse conditions. Zn application stimulated the dry matter production, essential oil concentration and menthol concentration of Japanese mint. Zn supplies of 0.05µg ml^–1 were required for maximum responses in dry matter yield and oil concentration. Significantly positive interrelationships were observed among fresh herb yield, dry matter yield and menthol concentration in the oil. Graphical analyses of Cate and Nelson model indicated the critical Zn concentration in leaves to be 28µg g^–1 on a dry matter basis and in the solution culture 0.0475µg ml^–1 on the basis of Zn concentration in leaves.     

Effects of urea fertigation of apple trees on soil pH,exchangeable cations and extractable manganese in a sandy loam soil in New Zealand

Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha^–1 yr^–1 or 0, 16.9, 33.8 g N emitter^–1 yr^–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha^–1 yr^–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg^–1 and 78µg g^–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha^–1 yr^–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth.     

The effect of managing improved fallows of Mucuna pruriens on maize production and soil carbon and nitrogen dynamics in sub-humid Zimbabwe

Mucuna pruriens has emerged as a successful forage or green manure legume for use in the smallholder animal-livestock systems of Zimbabwe. The efficiency of N recovery from mucuna residues in subsequent maize crops can be low and the loss of nitrate nitrogen from the soil profile prior to maize N demand is proposed as a reason for this. An experiment was established in the 1999–2000 wet season at seven on-farm sites in a communal farming district of Zimbabwe (average rainfall 650–900 mm) on acidic (pH < 5), and inherently infertile soils with texture ranging from sandy/sandy loam (n = 5) to clay (n = 2). Improved fallows of mucuna grown for 19 weeks produced between 4.7 and 8.5 t/ha dry matter (DM) at the sandy/sandy loam sites and between 9.5 and 11.2 t/ha DM at the clay sites. This biomass was then either cut and removed as hay, or ploughed in as a green manure. Weedy fallow treatments, which represent typical farmer practice, produced 3.3–6.3 t/ha DM. A maize crop was then grown on these same sites in the following 2000–2001 wet season and the dynamics of soil N and C and maize production were investigated. Where mucuna was green manured, a positive linear response (r² = 0.72) in maize yield to increasing mucuna biomass (containing 101–348 kg N/ha) was found. On the sandy sites, and where no P fertiliser was applied to the previous mucuna phase, a maize grain yield of 2.3 t/ha was achieved following the mucuna green-manure system; this was 64% higher than the maize yield following the weedy fallow and 100% higher than the maize yield following the mucuna removed hay system. Apparent nitrogen recoveries in the range of 25 to 53% indicate that there are large quantities of nitrogen not utilised by the subsequent maize phase. The loss of 73 kg/ha of nitrate N from the soil profile (0–120 cm) early in the wet season and prior to maize N demand is proposed as a reason for low N recovery. No change in labile C (measured with 333 mM KMnO₄) was detected through the soil profile at this time and it is suggested that labile C movement occurred between the sampling times.     

Short-term carbon dioxide emissions and denitrification losses from soils amended with low-P manure from genetically modified pigs

Genetically modified pigs have been developed that are able to use phosphorus (P) in the feed more efficiently and thereby reduce the amount of P excreted in the manure. Improved digestibility would also change the chemical composition of the manure. The objective of this study was to determine how improved P digestibility affects the manure composition and the associated carbon dioxide (CO₂) emissions and nitrogen (N) loss through denitrification when the manure is applied to soil. Aerobic and anaerobic incubation studies were conducted to evaluate CO₂ emissions and denitrification losses from two soils (Brookston clay loam and Harrow sandy loam) amended with pig slurry (115 mg N kg⁻¹ soil) from transgenic pigs as well as from conventional pigs. In addition, both the transgenic and conventional pigs were fed either a low-P diet or a conventional P diet, and the effects of diet type on CO₂ emissions and denitrification losses were examined. Carbon dioxide emissions were 17% lower (P < 0.05) in treatments amended with transgenic pig manure compared with conventional pig manure in the clay loam soil. However, denitrification losses were increased by 37% (P < 0.05) in the clay loam soil amended with manure from transgenic pigs compared to manure from conventional pigs. Neither CO₂ emissions nor N loss through denitrification were affected by pig genotype when the manure was added to the sandy loam soil. The diet type (conventional P diet or low-P diet) did not affect either CO₂ emissions or N losses through denitrification in either the Brookston clay loam or Harrow sandy loam soils.     

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.     

Effect of excess boron fertilization on status and availability of boron in calcareous soils

Field experiments were conducted at Al-Qatif area in the eastern region of Saudi Arabia to study the status and availability of B under B fertilization regime in three types of calcareous soils and to evaluate the response of two alfalfa varieties, Hassawi (local variety) and Hyden (american variety), to increasing levels of added B.Boron was applied at 7 rates as Na₂B₄O₇.10H₂O. Four cuttings were taken from each site at different intervals. Data showed that extractable B by hot-water and NH₄HCO₃-DTPA (8 days after borax application) was significantly (p <0.001) affected by soil type and B applications. The amount of B recovered by hot-water from the three soils, 200 days after borax application, was in the following order: sandy loam > sandy clay loam > clay loam.Total dry matter of alfalfa (4 cuttings) was significantly (p <0.05) affected by soil type, borax application rates and alfalfa variety.The critical level of B in plant as determined by Cate and Nelson analysis, ranged from 148 to 652 mg kg^–1 dry matter for Hassawi cultivar and 138 to 521 mg kg^–1 for Hyden cultivar in the first harvest. However, the upper critical levels for the 2nd, 3rd and 4th harvests were 800, 875 and 935 mg B kg^–1 dry matter for Hassawi and 603, 723 and 812 mg B kg^–1 for Hyden varieties, respectively. Nevertheless, the lower critical levels for 2nd, 3rd and 4th harvests ranged from 148 to 153 mg B kg^–1 dry matter for Hassawi and 138 to 142 mg B kg^–1 for Hyden.