Bray and Kurtz phosphorus (p1), 1m potassium chloride,and saturated calcium oxide extraction of soil nitrate comparison to 2m potassium chloride

Abstract

Labor and laboratory expense could be reduce if soil extractable nitrate (NO₃) was extracted simultaneously with other routinely used soil extractants. This study was conducted to compare 1M potassium chloride (KCl), saturated calcium oxide (CaO), and Bray and Kurtz P1‐extractable soil NO₃, the proposed new method to 2M KCl. Nitrate was extracted from 140 selected soils with 1M KCl, saturated CaO, Bray and Kurtz P1, and 2M KCl extractants and analysed by cadmium reduction with a flow injection analyser. Nitrate extracted with 2M KCl was used as the standard. When 1M KCl, saturated CaO, and Bray and Kurtz P1 was regressed against 2M KCl, the slopes were equal to 1.0 and the intercepts were equal to 0.0 with r²>0.99. No detectable differences in extractable NO₃ were measured between 1M KCl, saturated CaO, Bray and Kurtz Pl, and 2M KCl extraction procedures. Bray and Kurtz P1 can be used to simultaneously extract phosphorus (P) and NO₃.     

Application of low‐phosphorus‐containing legume residues reduces extractable phosphorus in a tropical Ultisol

Application of legume green manure (GM) is suggested to be effective in increasing the availability of native soil phosphorus (P) and the dissolution and utilization of phosphate rock (PR)‐P by food crops. Experiments were conducted to study the dynamics of extractable P (P extracted by Bray‐1‐extracting solution) of an Ultisol amended with or without GM residues of contrasting P concentrations in the absence of growing plants. In two separate experiments, GM residues of Aschynomene afraspera (a flood‐tolerant legume) and of Crotalaria micans (upland) with varying P concentrations were added to an acidic soil amended with PR‐P or triple superphosphate (TSP) in plastic bottles. Soil moisture was brought to field capacity of the soil in the upland experiment and saturated with distilled water in the lowland setup. This was done to simulate aerobic upland and anaerobic lowland soil conditions in the relevant plastic bottles. Only P concentration of the residues added varied, while lignin and C : N ratios were similar. A temperature of 25°C was maintained throughout the experiment. Changes in soil extractable Bray‐1‐P were measured at the end of the incubation period (60 or 80 d). In the aerobic soils, extractable P in the combined PR+GM or TSP+GM treatments was significantly lower than in the PR‐ or TSP‐ treated soils. The amendment with GM residues alone significantly increased Bray‐1‐P over the unamended control in the case of the inorganic P‐fertilized GM residues. The trend in extractable P was similar in the soils incubated under anaerobic conditions. However, in the case of PR, concentrations of P extracted by Bray‐1 solution did not significantly change in the presence or absence of GM. The results suggest that the incorporation of GM residues with low P concentration does not lead to a net P release in upland or lowland soils. These results have implications for nutrient cycling in farming systems in W Africa as most of the soils are poor and very low in available P.     

Modified Soil‐Test Methods for Extractable Phosphorus in Acidic,Neutral, and Alkaline Soils

Abstract

Although numerous soil‐test methods for estimating extractable phosphorus (P) have been developed around the world, their results are difficult to compare because of the very different scale levels used. In the present study, the Bray–Kurtz method (Bray‐P) is used as a reference value. Two other methods [lactate‐P and sodium bicarbonate (NaHCO₃)‐P] were modified to facilitate the comparison of extractable‐P determinations, mainly by adjusting the shaking time. These three methods were applied to 101 soil samples from an extensive region of Argentina with soil pH values ranging from 5.5 to 8.5. The results confirm that the Bray‐P and the two modified methods (lactate‐P and NaHCO₃‐P) determine similar contents of extractable P but are not applicable to all types of soils and conditions. Equations that minimize the statistical error were selected for soil properties such as organic carbon (OC) content, pH, soluble salts, and calcium carbonate content. Correlation coefficients between Bray‐P and NaHCO₃‐P increased to 0.91 and 0.95 in soils with high and low OC levels, respectively. It was also demonstrated that the lactate‐P test is not suitable for soils rich in calcium carbonate or soluble salts. These two modified methods are expected to be useful for testing P values that impact agricultural production.     

Mild drying of sandy soil can physically limit the uptake of phosphorus by rainfed lowland rice in northeast Thailand

ABSTRACT

Poor response of rice to phosphorus (P) fertilization and low phytoavailability of soil P have been reported in sandy rainfed fields in northeast Thailand. In order to evaluate the effects of mild soil drying on the uptake of P by rainfed lowland rice, we carried out nutrient omission trials for nitrogen (N) and P at Ubon Ratchathani Rice Research Center under rainfed and flooded conditions. The surface soil was classified as sandy loam. To avoid severe soil drying and drought stress in the rainfed field, soil water potential at a depth of 20 cm was maintained at the field capacity (> ?20 kPa) by flush irrigation. The effects of flooding and drying on the soil properties were also evaluated in the laboratory using soils with diverse textures in and around the center. In the field experiments, the above-ground biomass of rice plants (RD6) did not respond significantly to P fertilization in the rainfed field, although it responded positively to N fertilization. Root length in the surface 10 cm under the rainfed condition was significantly smaller than that under the flooded condition due partly to the increased soil hardness upon drying, but this could not quantitatively explain the large discrepancy of P uptake observed between the rainfed and flooded conditions. Under the rainfed condition, the P uptake did not increase significantly, even when the concentration of soil Bray P was tripled by transferring the surface soil from the flooded to the rainfed field. From the laboratory experiments, it was further suggested that soil P was supplied mainly by diffusion and that the effective diffusion coefficient for P can become less than one-tenth of the value in the flooded field when the sandy soil with clay at around 10% dried to ?100 kPa. Our results suggest that the uptake of P by the rainfed lowland rice grown in sandy soil can be limited physically by mild soil drying that reduces the supply of P to roots by diffusion rather than the chemical extractability of soil P.     

Assessing extractable soil phosphorus methods in estimating phosphorus concentrations in surface run‐off from Calcic Hapludolls

Understanding soil test phosphorus (STP) and surface run‐off phosphorus (P) relationships for soils is necessary for P management. The objective of the study was to evaluate the efficacy of various soil test indices to predict P losses in surface run‐off. Selected sites were subjected to in situ rainfall simulations according to the protocol of the National Phosphorus Research Project ( NPRP, 2001 ). P from a composite of twenty‐four 2.0‐cm‐diameter core soil samples (0–5 cm) was extracted using the Olsen, Bray–Kurtz, Mehlich III, distilled water and 0.01 m calcium chloride procedures. All of these P extraction methods explained a significant amount of variability in surface run‐off total dissolved P [TP (<0.45)] (r² ≥ 0.67; P ≤ 0.01), where 0.45 is the filter pore diameter in microns. Multiple regression models showed extractable P to be the best soil predictor of surface run‐off TP (<0.45) among the studied soils. Despite extraction method or soil type, extractable P was the best soil predictor of surface run‐off TP (<0.45). Either agronomic (0.92 ≤ r² ≤ 0.96) or environmental (0.94 ≤ r² ≤ 0.96) soil tests were effective in estimating surface run‐off TP (<0.45) in select Mollisols.     

Repeated Bray‐2 extractions of an Inceptisol and an Andisol

Abstract

Bray‐2 extractable phosphorus (Bray2‐P) is commonly used to measure plant‐available P in soil. The pool size of extractable P in the residual soil should be reduced after extraction. Phosphorus, once released with the Bray‐2 solution, is resorbed by the soil during the extraction‐filtration period. If P resorption is large, the Bray2‐P concentration is underestimated. The P absorption coefficient and composition of inorganic P [calcium (Ca)‐P, aluminum (Al)‐P, and iron (Fe)‐P] probably affect the Bray2‐P concentration. We investigated the effect of repeated Bray‐2 extractions on the Bray2‐P concentrations in relation to the P absorption coefficient and Ca‐P, Al‐P, and Fe‐P concentrations in two soils (an Inceptisol and an Andisol), which markedly differ in the P absorption coefficient. Test soil samples were the initial soil (S0) and soils after the 1st to 4th extractions (S1‐S4) for the Inceptisol, and S0, S1‐S4, and S7 for the Andisol. The Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S0 were 260, 75, 338, and 536 mg kg^‐1 in the Inceptisol, and 217, 31, 972, and 354 mg kg^‐1 in the Andisol, respectively. All of the extractable P concentrations in the Inceptisol decreased with increasing numbers of extractions, and the Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S4 were 5.3, 21, 5.7, and 30% of those in the S0, respectively. On the other hand in the Andisol, the Bray2‐P, Ca‐P, and Fe‐P concentrations did not decrease in the S1 and S2 compared with those in the S0, although the Al‐P concentration decreased with increasing numbers of extractions. The Bray2‐P, Ca‐P, Al‐P, and Fe‐P concentrations in the S7 were 23, 71, 16, and 79% of those in the S0, respectively. The P absorption coefficient in the S0 was higher in the Andisol (7,703 mg kg^‐1) than in the Inceptisol (1,582 mg kg^‐1), and it decreased with increasing numbers of extractions in both soils. The P absorption coefficient in the S7 Andisol was 51% of that in the S0, while the P absorption coefficient in the S4 Inceptisol was 24% of that in the S0. The results suggest that Presorption affects the efficiency of extraction with the Bray‐2 solution, and the composition of Ca‐P, Al‐P, and Fe‐P fractions. The Bray2‐P concentration in soil with high P absorption coefficient is underestimated due to P resorption.     

Comparison of phosphorus impregnation and bray 1 soil tests for evaluating plant available phosphorus

Abstract

The relationship between soil test phosphorus and crop response has not been studied for maize (Zea mays L.) in some major benchmark soils of Zambia. The suitable soil test procedure for estimating available P needs to be identified. The objective of this study was to compare two soil test methods, impregnation of phosphorus (Pi) and Bray 1, in predicting P requirement of maize grown in Makeni (fine, mixed Isohyperthermic Udic Paleustalf), Maheba (clayey, kaolinitic, isohyperthermic Haplic Acrustox), and Konkola soil series (fine, oxidic, isohyperthermic oxic, Rhodustalf). The three soil series were treated with 0, 262, 524, and 1,048 mg P per pot as triple superphosphate (TSP). Maize was grown in pots, and after 8 weeks the plants were harvested and analyzed for total P concentration. Phosphorus uptake (P uptake) was calculated as a product of P concentration in the plant and maize dry matter yield. The soil was dried, sieved and analyzed for available P. The available P content estimated by Bray 1, and Pi soil tests was correlated with maize dry matter yield, and P uptake. The P which was extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and more significant (r=0.991 * *), than correlation with P extracted by Pi soil test (r=0.958*). The P extracted from Makeni soil series by Pi soil test correlated highly significantly (r=0.996**) with maize dry matter yield, but the correlation of maize dry matter yield and P extracted by Bray 1 soil test was not significant (r=0.908 ns), Correlation of P uptake with P extracted by Bray 1 soil test was high and significant (r=0.990**), as well as correlation with P extracted by Pi soil test (r=0.958**). The correlation of P extracted from Maheba soil series by Pi soil test and maize dry matter yield followed the same trend as for Makeni series with correlation of r=0.990**. The correlation of P uptake and P extracted by Pi soil test was high but less significant (r=0.955*) than that for Makeni soil series. The correlation of P extracted by Bray 1 soil test with maize dry matter yield was high (r=0.973 *) and significant, but the correlation with P uptake was low and not significant (r=0.879 ns). The available P extracted from Konkola soil series by both Bray 1 and Pi soil tests produced poor and not significant correlation with maize dry matter yield, as well as P uptake. The results show that Bray 1 soil test extracted larger amounts of P from all the three soil series than P impregnation (Pi) soil test. The results further demonstrated that Pi soil test was consistently more closely related to P uptake and dry matter yield of maize grown in Makeni and Maheba soil series. Therefore, Pi soil test was more effective than Bray 1 soil test in evaluating soil solution P that the plant usually takes up.     

A preliminary comparison of the ammonium acetate‐edta soil phosphorus extraction method to the bray‐1 and olsen soil phosphorus extraction methods

Abstract

The ammonium acetate (NH₄OAc)‐EDTA soil phosphorus (P) extraction method was compared to either the Bray‐1 soil P extraction method for non‐calcareous soils or the Olsen soil P extraction method for calcareous soils to predict com and wheat plant tissue P concentration and grain yield responses. The NH₄OAc‐EDTA method predicted yield and tissue P concentration responses to P fertilizer applications more accurately than the Olsen method at three of five sites. Both the Bray‐1 and NH₄OAc‐EDTA methods were successful in predicting corn and wheat yield responses to P fertilizer applications in non‐ calcareous soils in many locations. However, a direct comparison of extracted soil P levels showed that the NH₄OAc‐EDTA method extracted soil P at levels which were more closely related to the Bray‐1 method than the Olsen method.     

Soil tests for predicting plant available phosphorus in newly reclaimed alkaline minespoil

Abstract

Four selected soil tests (Olson's bicarbonate, Bray P‐l, Bray P‐2, and a modified Bray P‐l test) were compared over a four year period as methods for predicting plant available‐P in a slightly alkaline (pH 7.25) minespoil from a west‐central coal field in Illinois. Phosphorus recovery by hybrid corn, measured under both greenhouse and field conditions, showed that the minespoil was extremely P deficient. Extractable Olson's bicarbonate P and standard Bray P‐l phosphorus were highly correlated with total‐P recovery by corn, with respective coefficients of r =0.973 and r =0.957 in the greenhouse; and r =0.998 and r =0.983 respectively, under field conditions. Consistent Mitscherlich‐Bray proportionality constants were calculated from corn grain yields under field conditions in three of four years, after adjustments for annual differences in plant population density. Minespoil was found to require about twice as much extractable‐P (about 40 mg/kg Olson‐bicarbonate or Bray P‐l) as topsoil to support maxiumum corn productivity. It was estimated that more than 500 kg/ha fertilizer‐P will be required to achieve maximum corn grain production in spoil.     

Comparisons of soil test phosphorus by Olsen,Bray P1, Mehlich I and Mehlich III methods

Abstract

A study was undertaken to evaluate the agreement among different university laboratories performing the Olsen, Bray P1, and Mehlich I tests for P on a diverse group of noncalcareous agricultural soils and to develop relationships among the Olsen, Bray P1, Mehlich I, and Mehlich III soil tests. For each test, the results from the individual laboratories were highly correlated (r² ≥ 0.90) and in almost all instances the slopes of the equations describing the relationships among laboratories approached one, The results indicate that the Olsen, Bray P1 and Mehlich I soil tests may be performed with a high degree of precision when standard soil test procedures are followed.

Of the three most commonly performed tests in the U.S. (Olsen, Bray P1, and Mehlich I), the Olsen and Mehlich I tests were the most highly correlated (r² = 0.87) although the Mehlich I test removed approximately one and one half times more P than did the Olsen test. Bray P1 and Olsen and Mehlich I P were less highly correlated (r² ≤ 0.72) and the relationships between these variables were influenced by the texture of the soils. The quantity of P removed by the Bray P1 test was on the order of two and three times greater than that removed by the Olsen and Mehlich I tests, respectively. The Bray P1 and Mehlich III soil tests were highly correlated (r² = 0.97) and similar quantities of P were extracted from the soil by the two tests.     

Can tropical grasses grown as cover crops improve soil phosphorus availability?

Tropical grasses grown as cover crops can mobilize phosphorus (P) in soil and have been suggested as a tool to increase soil P cycling and bioavailability. The objective of this study was to evaluate the effect of tropical grasses on soil P dynamics, lability, desorption kinetics and bioavailability to soya bean, specifically to test the hypothesis that introducing grass species in the cropping system may affect soil P availability and soya bean development according to soil P concentration. Three grass species, ruzi grass (Urochloa ruziziensis ), palisade grass (Urochloa brizantha ) and Guinea grass (Megathyrsus maximus ), were grown in soils with contrasting P status. Soya bean was grown after grasses to assess soil P bioavailability. Hedley P fractionation, microbial biomass P, phytase‐labile P and the diffusive gradient in thin films were determined, before and after cultivation. It was found that grasses remobilized soil P, reducing the concentration of recalcitrant P forms. The effect of grasses on changing the P desorption kinetics parameters did not directly explain the observed variation on P bioavailability to soya bean. Grasses and microorganisms solubilize recalcitrant organic P (P_o) forms and tropical grasses grown as cover crops increased P bioavailability to soya bean mainly due to the supply of P by decomposition of grass residues in low‐P soil. However, no clear advantages in soya bean P nutrition were observed when in rotation with these grasses in high‐P soil. This study indicates that further advantages in soya bean P nutrition after tropical grasses may be impeded by phytate, which is not readily available to plants.     

Effect of seed zinc content on grain yield and zinc concentration of wheat grown in zinc‐deficient calcareous soils

Field experiments were carried out to study the effect of different seed‐zinc (Zn) content on grain yield and grain Zn concentration in a bread wheat cultivar Atay 85 grown in a severely Zn‐deficient soil under rainfed and irrigated conditions for two years. Three groups of seeds with Zn contents of 355, 800, and 1,465 ng Zn seed^‐1 were obtained through different number of foliar applications of ZnSO₄.7H₂O in the previous crop year. Experiments were carried out with 23 kg Zn ha^‐1 (as ZnSO₄.7H₂O) and without Zn fertilization to the soil. Grain yield from seeds with 800 and 1,465 ng Zn seed^‐1 content was significantly higher than that from low seed‐Zn, especially under rainfed conditions. In the first year, under rainfed and Zn‐deficient conditions, yield of plants grown from the highest seed‐Zn content was 116% higher than the yield of plants grown from the low seed‐Zn content. However, in the first year soil‐Zn application combined with low‐Zn seed resulted in a yield increase of 466% compared to nill Zn treatment with low‐Zn seed, indicating that higher seed‐Zn contents could not compensate for the effects of soil Zn application. Soil Zn application significantly increased Zn concentrations in shoot and grain. However, the effect of different seed Zn contents on Zn concentrations of plants was not significant, probably due to the dilution of Zn in tissues resulting from enhanced dry matter production. The results presented show that wheat plants grown from seed with high Zn content can achieve higher grain yields than those grown from the low‐Zn seed when Zn was not applied to the soil. Therefore, sowing seeds with higher Zn contents can be considered a practical solution to alleviate Zn deficiency problem, especially under rainfed conditions in spite of it being insufficient to completely overcome the problem.     

Effects of arbuscular mycorrhizal inoculation on growth,yield, nitrogen,and phosphorus nutrition of nodulating bean varieties in two soil substrates of contrasting fertility

A pot experiment was conducted to study the response of nodulated bean (Phaseolus vulgaris L.), vars. Ceca and Montalbán, to inoculation with the arbuscular‐mycorrhizae (AM) Glomus spurcum strain IES‐3 and G. mosseae strain IES‐8 in two non‐sterilized non‐amended soil substrates (S‐l and S‐2) of contrasting fertility. S‐l was an acid soil (pH 5.0) with 77% exchangeable aluminum (Al), low available phosphorus (P) (3.5 ug g^‐1 dry soil) and 1.8% organic matter. S‐2 was a soil with pH 7.0, 7.9 μg P g^‐1 dry soil, 9.6% organic matter and no exchangeable Al. Plants growing in S‐1 (S‐1 plants) and S‐2 (S‐2 plants) soils were sampled at the beginning of the flowering stage. S‐1 and S‐2 plants were nodulated by the rhizobial populations native of each soil. S‐1 plants of both varieties did not respond to AM inoculation in term of shoot and root mass, P content, relative abundance of ureides (RAU) and seed yields. Only the total chlorophyll, chlorophyll‐a, chlrophyll‐a/b ratio and nodule mass were significantly enhanced in AM‐inoculated plants. Increased total reducing sugars concentration was detected in roots of S‐1 plants inoculated with G. mosseae. S‐2 plants displayed significantly higher shoot and nodule mass as well as increased total chlorophyll, chlorophyll‐a, chlorophyll‐a/b ratio and P content than S‐1 plants, regardless of the variety and AM inoculation. S‐2 plants of the var Ceca showed a two fold increase in seed yields but similar RAU values (>60%) when compared to S‐1 plants of the same variety. In contrast, the significant increase in RAU detected in S‐2 plants of the var Montalban was not translated into higher seed yields. In S‐2, the productivity of plants of the var Ceca doubled that of the var Montalban. For both bean varieties the highest significant P content and seed yield were observed exclusively in S‐2 plants inoculated with G. mosseae. This Glomelean strain enhanced the sink‐source ratio of the S‐2 plants as evidenced by the higher total reducing sugar concentration in the root mass. Arbuscular‐mycorrhizae inoculation significantly decreased the acid phosphatase activity in the rhizosphere of S‐1 and S‐2 plants, respectively, pointing toward a negative effect of foreign AM on the native microbial biomass. The effectiveness of the rhizobial populations native of each soil type and the weak response elicited by G. mosseae in S‐2 plants do not justify, at present, the inclusion of foreign inocula in the bean crops carried out at S‐1 and S‐2 soils of the Sucre State of Venezuela. Results also indicated the higher adaptability of var Ceca to conditions prevailing in S‐1 and S‐2.     

Evaluation of soil test methods for estimation of available phosphorus in some Portuguese soils: A greenhouse study

Abstract

The Egnér‐Riehm method for estimating plant‐available soil phosphorus (P) has been used as the standard soil testing method in Portugal for making fertilizer recommendations. However, this method does not accurately reflect the available P status for wheat in some representative soils from the South Region of the country. Therefore, a pot experiment was established with four Luvisols (LVx, LVv, and two different LVh soils) from the South Region of Portugal in order to evaluate the Egnér‐Riehm, Bray I, Bray II, Olsen, and Anion Exchange Resin (AER) methods for their ability to estimate available P in those soils. Wheat (Triticum aestivum L., cv. Panda) was used as test the crop. The experiment was arranged into a randomized complete block design with three replications and five rates (0, 50, 100,150, and 200 mg kg^‐1) of P added to each soil. Critical soil P levels for LVx were established in case for Bray I (27.9 mg kg^‐1), Bray II (33.5 mg kg^‐1), Egnér‐Riehm (25.4 mg kg^‐1), and AER (14.7 mg kg^‐1) soil test procedures. Regarding the other soils, the critical soil P levels could not be estimated. The obtained results confirm that the development of an universal soil test P exti action is of great importance, and that further research should be conducted in order to evaluate routine soil fertility tests in different pedoclimatic environments.     

Correlation of Mehlich 3, bray 1, and ammonium acetate extractable P,K, Ca,and Mg for Alaska agricultural soils

Abstract

Soil test recommendations currently used in Alaska are based on a limited amount of in‐state data along with consideration of data from other states. Recently, Mehlich 3 extractable P has been found to be highly correlated to yield on representative agricultural soils in Alaska. To fully use its multi‐element capability, a study was conducted to correlate Mehlich 3 extractable P and cations (K, Ca, and Mg) with the P and cations extracted by the Bray 1 and ammonium acetate methods respectively.

When Mehlich 3 extractable K and Mg were regressed with ammonium acetate extractable K and Mg respectively, the relationship was essentially one‐to‐one and the relationship held across all soils tested. Significant variation was observed among soils in the extraction of Mehlich 3‐P and Ca relative to Bray 1‐P and ammonium acetate‐Ca. Individual soil character appeared to affect the regressions for extractable P and Ca, even though the R² values were generally high. The regression slopes for Mehlich 3‐P versus Bray 1‐P ranged from 1.01 to 1.88 with Mehlich 3 extracting an average of 66% more P than Bray 1 in the volcanic ash soils, and 12% more in the loess soils. The regression slopes for Mehlich 3‐Ca versus ammonium acetate‐Ca ranged from 0.95 to 1.33, and the former extracted an average of 17% more Ca than the latter. It is suggested that the regression data of P and Ca can be extrapolated to other soils based on soil classification; to extend the soil test data over a geographic base.     

Interactive effects of phosphorus,nitrogen, and thiourea on clusterbean (Cyamopsis tetragonoloba L.) under rainfed conditions of the Indian arid zone

A two‐year field study was undertaken with clusterbean (Cyamopsis tetragonoloba L. Taub. cv. RGC‐936) under rainfed conditions. The experiments were set up in a split‐split‐plot design with three levels of phosphorus (0, 20, and 40 kg ha^–1) and two levels of nitrogen (0 and 20 kg ha^–1) with and without thiourea application (seed treatment with 500 mg kg^–1 followed by two foliar sprays of 1000 mg kg^–1 each at 25 and 40 d after sowing). The years varied in their pattern of precipitation and, consequently, in the available soil moisture at different growth stages. Phosphorous (P) and nitrogen (N) application either alone or in combination with thiourea resulted in significantly higher net photosynthetic rates and concentrations of chlorophyll, starch, soluble protein, and total free amino acids as well as nitrate reductase activity compared to control plants at both vegetative and flowering stages. However, the magnitude of favorable changes varied with soil moisture due to varying rainfall, and the effects of N, P, and thiourea were generally more pronounced in the vegetative stage. Seed yield, dry‐matter production, harvest index, and water‐use efficiency were significantly enhanced by the above mentioned treatments. The favorable effects of the treatments were realized through significant improvements of metabolic efficiency and maintenance of higher photosynthesis and nitrate reductase activity for more efficient N utilization. It is concluded that the improvement of P and N status of arid‐zone soils coupled with thiourea application can significantly improve the yield of clusterbean under rainfed conditions, though the potential gains may vary with soil‐moisture availability.     

Predicting Maize Yield,Nutrient Concentration,and Uptake in Phosphorus- and Potassium-Fertilized Soils: Pressurized Hot Water and Other Alternatives to Mehlich I Extraction in Guatemala Soils

Abstract

Poor accessibility and cost of soil testing reduce effectiveness of fertilizer use on small‐scale subsistence farms, and inadequate funding promotes adoption of soil tests in developing countries with minimal validation. For example, Mehlich I extraction of phosphorus (P) currently used extensively in Guatemala may not be suitable for Guatemala's broad range of soils. At least four alternatives are available but relatively untested [Bray 1, Mehlich III, Olsen, and pressurized hot water (PHW)]. Pressurized hot water is relatively simple and inexpensive but is not yet tested against other extraction methods under variable P or potassium (K) fertilization levels. To determine whether PHW‐extracted nutrients could be used to predict maize yield and nutrient concentration and uptake, soil, plant tissue and grain samples were obtained from a multiple‐site field study, and calibration studies were conducted using five rates of P and three rates of K on soils incubated without plants or cropped with maize in greenhouse and field conditions. In the multiple‐site field study, maize yield related significantly to PHW‐extractable P (r²=0.36) and to leaf P concentration (r²=0.23), but Mehlich I–extractable P did not. In the two soils used in the greenhouse study, maize yield, vegetative P concentration, and total P uptake by maize were predicted by PHW‐extractable P (R²=0.72, 0.75, and 0.90, respectively). In the field experiment, grain yield was not improved by P or K application, but P concentration of maize leaf tissue did relate significantly with PHW‐extracted P (R²=0.40). Mehlich I did not. There were no yield responses to K application in any experiment, but relationships defined between extractable K for all five K‐extraction procedures and soil‐applied K were similarly significant. In comparison, PHW was as good as or better than Olsen whereas Bray 1 and Mehlich III were less consistent. Mehlich I was overall the poorest P extractant. Mehlich I extraction of P should be replaced by one of the four alternatives tested. PHW is the least expensive and, therefore, most viable for use in Guatemala soils.     

Soil test calibration studies for formulation of phosphorus fertilizer recommendations for maize in Morogoro district,Tanzania. I. evaluation of soil test methods

Abstract

Optimum crop production depends, among other things, on the maintenance of adequate plant nutrients in the root zone. The objective of this study was to find a reliable index for assessing needs for supplemental phosphorus (P) in soils of Morogoro District, Tanzania. Six indices of P availability, namely: Bray and Kurtz No. 1 (BK1), Bray and KurtzNo.2 (BK2), Mehlich 1, Mehlich 3, Olsen and ammonium bicarbonate‐DTPA (AB‐DTPA), were evaluated. Evaluation of the P indices involved relating extractable P contents by different methods with crop response data expressed as relative yields. The response data was obtained from pot trials with soil samples from ten repesentative soils designated as benchmark soils of the district. Treatments were absolute control, 0, 10, 20, and 30 mg P kg^‐1 of soil. Correlation of maize relative yields with soil test values by the six indices of P availability resulted in correlation coefficients ranging from 0.65 to 0.90. The Olsen method gave the highest r value suggesting that it was superior to the others. However, using the Cate and Nelson approach, the Olsen and ammonium bicarbonate‐DTPA methods were found to be at par and superior to the others. They each accounted for 76% of the variations observed in maize relative yields, respectively. The critical P levels for the indices were 10.50 mg P kg^‐1 for Olsen and 2.80 mg P kg^‐1 for the AB‐DTPA method. Phosphorus fertility categories were delineated in relation to Olsen extractable P as: low (<6.50 mg P kg^‐1), medium (6.50 to 23.0 mg P kg^‐1), and high (>23.0 mg P kg^‐1). Based on this classification it was determined that 16%, 25 %, and 59% of the surveyed area had low, medium, and high P levels, respectively. About 40% of the surveyed area may, therefore, require fertilization with P for optimum yields.     

Phosphate fertilizer compounds in soils: Their influence on the relationship between plant yield and soil test value

Abstract

A pot experiment with a lateritic soil measured the relative effectiveness of monocalcium phosphate (MCP) fertilizers and six phosphate (P) compounds which were used to represent fertilizer compounds that may be present in soils. The P compounds were added at various rates, wheat was grown, and the treated soils were extracted with eight standard soil P‐test reagents. The relative effectiveness (RE) values for the fertilizer compounds based on plant yield were 1.00, 0.33, 0.32, 0.20, 0.16, 0.15, and 0.09 for MCP, P sorbed on gibbsite (Gi‐P), P sorbed on goethite (Go‐P), P sorbed on calcite (Ca‐P), AlPO₄ (Al‐P), Apatite (Ap‐P) and FePO₄ (Fe‐P), respectively. For soil treated with Ap‐P, Gi‐P, Go‐P, Ca‐P, and MCP, soil test values were significantly related to the yield of wheat. Only Bray 1, Bray 2, ammonium oxalate, and Colwell soil tests adequately predicted yield for Al‐P treated soil, and no soil test was suitable for soil treated with Fe‐P. Where soil tests were predictive of yield, separate calibrations were required for the different P compounds. For example, in order to obtain 100 mg of wheat per pot from soil that was treated with Al‐P, Fe‐P, Ap‐P, Gi‐P, Go‐P, Ca‐P, and Bray 2 soil test values of 122, 8, 387, 112, 9, 202, and 50 ug/g, respectively, were required.     

Zinc‐efficient wild grasses enhance release of phytosiderophores under zinc deficiency

The effect of the zinc (Zn) nutritional status on the rate of phyto‐siderophore release was studied in three wild grass species (Hordeum murinum, Agropyron orientale, and Secale cereale) grown in nutrient solution under co‐trolled environmental conditions. These wild grasses are highly “Zn‐efficient”; and grow well on severely Zn‐deficient calcareous soils in Turkey (DTPA‐extractable Zn was 0.12 mg/kg soil and CaCO₃ was 37%). In all wild grasses studied, Zn deficiency reduced shoot growth but had no effect on root growth. Low amounts of phytosiderophores were released from roots of all wild grasses adequately supplied with Zn. In plants grown without Zn, release of phytosiderophores progressively increased with the onset of visual Zn deficiency symptoms, such as inhibition of shoot elongation and appearance of chlorotic and necrotic patches on leaves. Compared to Zn‐sufficient plants, phytosiderophore release increased 18–20‐fold in deficient plants. HPLC analysis of root exudates showed that the dominating phytosiderophore in Zn‐deficient Agropyron and Hordeum was 3‐epi‐hydro‐xymugineic acid (epi‐HMA) and was 3‐hydroxy‐mugineic acid (HMA) in Secale. Besides HMA, epi‐HMA and mugineic acid (MA) were also detected in exudates of Zn‐deficient Secale. The results indicate the importance of phytosiderophores in adaptation of wild grasses to Zn‐deficient calcareous soils. Phytosiderophores might enhance mobilization of Zn from sparingly soluble Zn pools and from adsorption sites, both in the rhizosphere and within the plants.