Assessing soil P fractions changes with long-term phosphorus fertilization related to crop yield of soybean and maize

Long-term P Fertiliser application increases soil phosphorus (P) labile fractions, which can be associated with crop P uptake and grain yield and are useful to improve fertilizer recommendations. Research aims were to evaluate in long-term experiments with different P Fertiliser application in a Mollisol and a Vertisol: (a) the changes of soil P fractions and (b) the relationship between soil P fractions with long-term P Fertiliser application, with accumulated apparent P budget, grain P, total P uptake, soybean (Glycine max L.Merr.) and maize (Zea mays L.) grain yield. Soil P fractions were measured after 1 and 9 year since the beginning of the long-term experiments. Experiments included an initial Fertiliser application rate of 200 kg P ha⁻¹ and annual P Fertiliser application rate of 36 kg P ha⁻¹. Bray1-P, total, organic, and inorganic P in fine (<53 μm) and coarse (>53 μm) (CF) soil fractions, and in NaHCO₃ extract were measured. Initial P Fertiliser application increased inorganic and total P fractions. However, Bray1-P, total P in NaHCO₃ extract and in the CF were the fractions that most increased with continuous long-term P Fertiliser application in both sites. In the Mollisol, maize grain yield was unrelated to long-term P Fertiliser application. In the Vertisol, total P in NaHCO₃ extract, and total and organic P in the CF were more closely related to soybean grain yield than Bray1-P. We proposed soil P indices of labile inorganic and organic P that showed close relationships with soybean grain yield and may be useful to improve the diagnosis of P soil fertility.     

The ability of the DGT soil phosphorus test to predict pasture response in Australian pasture soils – a preliminary assessment

Diffusive gradients in thin‐films (DGT) technology provides an alternative assessment of available phosphorus (P) for a range of crops, suggesting a preliminary examination of the performance of the new DGT‐P test, compared to existing bicarbonate extractable Olsen and Colwell P tests, for pastures is justified. This study utilized historic data from the Australian National Reactive Phosphate Rock (NRPR) study (1992–1994) that included 25 experimental sites representing a wide range of soil types and climates used for pasture production. Stored (~19 yr) soil samples were analysed for DGT‐P, Olsen P and a single point P buffering index (PBI) and re‐analysed for Colwell P. Results showed the traditional bicarbonate extractable Colwell (r² = 0.45, P < 0.001) and Olsen P (r² = 0.27, P < 0.001) methods predicted relative pasture P response more accurately, compared to the novel DGT‐P test (r² = 0.09, P = 0.03) when all 3 yr of data were examined. We hypothesize that the harsher bicarbonate extraction used for the Olsen and Colwell methods more accurately reflects the ability of perennial pasture roots to access less labile forms of P, in contrast to the DGT‐P test, which does not change the soil pH or dilute the soil and appears unable to fully account for a plants ability to solubilize P. Further studies are needed to compare the capacity of DGT‐P to measure P availability in perennial pasture systems and to better understand the soil chemical differences between pasture and cropping systems.     

生物碳对土壤磷素和棉花养分吸收的影响

通过两年温室盆栽试验,研究了不同磷肥用量下生物碳对土壤磷素含量、 棉花生长和养分吸收的影响。试验以棉花秸秆为原料制备生物碳,制成三种热解温度（450℃、 600℃和750℃）的生物碳,分别以BC450、 BC600和BC750表示,同时以空白土壤为对照（CK）; 磷肥（P2O5）用量设3个水平0、 0.25、 0.5 g/kg（分别以P0、 P1、 P2表示）。研究结果表明,施用生物碳可显著提高土壤磷素含量及其有效性,随着生物碳热解温度的升高,土壤水溶性磷、 速效磷及全磷含量均显著增加,且对三种磷素含量的影响表现为水溶性磷 全磷 速效磷。施用生物碳处理两年棉花的干物质重均显著高于对照,但不同热解生物碳处理对两年棉花干物质重的影响各异。施用生物碳可显著增加棉花养分吸收量,总体表现为750℃ 600℃ 450℃。因此,施用生物碳可显著提高土壤磷素含量,促进棉花生长和养分吸收; 热解温度是影响生物碳质量的重要因素,生物碳的热解温度越高（450~750℃）,其促进作用越好。     

Quantitative effects of soil depth and soil and fertilizer nitrogen on nitrogen uptake by tall fescue and switchgrass

Abstract

In semi‐arid regions, soil depth influences soil N uptake, but not ferilizer N uptake. How soil depth interacts with soil and fertilzer N to influence N uptake in humid regions is not known. The objective was to determine the relative importance of soil depth and soil and fertilizer N uptake, by forage grasses. Tall fescue (Festuca arundinacea Schreb.) and switchgrass (Panicum virgatum L.) were grown on soils of varying depths. Nitrogen rates are 0, 90, and 180 kgN/ha of ¹⁵N depleted (NH₄)SO₄ applied in a split application on fescue and in one aplication to switchgrass. Total N and fertilizer N uptake, were regressed against fertilizer N, variables related to soil depth (waterholding capacity (WC), water use (WU), water loss (WL), and total soil N (SN). Soil variables explained 28% of the accoutable variation in total N uptake by first cut fescue but only 10% by second cut fescue. Soil variables explained 11% of the accountable variation in fertilizer N uptake by first cut fescue and none by the seoond. Soil variables explained 40% of the accountable variation in the total N uptake, by switchgrass, but only 10% of the variation in the fertilizer N uptake. Only where soil depth was less than 90 cm did it have a significant effect on the fertilizer N uptake by first cut fescue. Soil depth had no significant effect on the uptake, of fertilizer N by second cut fescue or switchgrass.     

Phosphorus deficiency diagnosis and fertilization in mungbean grown in rainfed calcareous soils of Pakistan

Abstract

Mungbean [Vigna radiata (L). Wilczek] grown in rainfed calcareous soils suffers with phosphorus (P) deficiency. In view of high cost and low use efficiency of P fertilizer, greenhouse, incubation, and field experiments were carried out for determining P deficiency diagnostic criteria and efficient method of P fertilizer application in mungbean. In a pot culture experiment using a P‐deficient Typic Ustocherpt, maximum increase in grain yield with P was 686% over the control; and fertilizer requirement for near‐maximum (95%) grain yield was 30 mg P kg^‐1 soil where fertilizer was mixed with the whole soil volume (broadcast) and 14 mg P kg^‐1 where mixed with 1/4th soil volume (band placement). In a field experiment on a P‐deficient Typic Camborthid, however, maximum increase in grain yield was 262% over the control. Band placement resulted in 73% fertilizer saving as P requirement was 66 kg ha^‐1 by broadcast and only 18 kg ha^‐1 by band placement. Critical P concentration range appears to be 0.27–0.33% in young whole shoots (≤30 cm tall) and 0.25–0.30% in recently matured leaves. In an incubation study using the same Typic Ustochrept, P extracted by the sodium bicarbonate (NaHCO₃), the ammonium bicarbonate‐diethlylenetriaminepentaacetic acid (AB)‐DTPA), and the Mehlich 3 soil tests correlated closely with each other, P concentration of whole shoots, and total P uptake by mungbean plants. Critical soil test P levels for pot grown mungbean were NaHCO₃,9 mg kg^‐1; AB‐DTPA, 7 mg kg^‐1; and Mehlich 3, 23 mg dm^‐3 soil. The more efficient and economical ‘universal’ soil test, AB‐DTPA, is recommended for P fertility evaluation of calcareous soils.     

Effect of Enhanced Panicle Fertilization on Nitrogen Use Efficiency Traits of Rice (Oryza Sativa) with Different Planting Patterns

To evaluate the nitrogen (N) use efficiency of rice plants applied with enhanced panicle N fertilization (PN) on different planting patterns, field experiments were carried out with 5 nitrogen managements (two PN levels combined with two total N levels, and check, CK) under transplanting (TP) and direct seeded (DS). Our result showed that nitrogen use efficiency traits of physiological efficiency (PE), nitrogen use efficiency for grain (NUE_g), and recovery efficiency (RE) of DS rice were decreased compared with TP rice, and total nitrogen accumulation (TN_+N) were kept consistent between TP and DS. However, PN × PT interaction effect was significant in partial factor productive of applied N (PEP), agronomic efficiency (AE), nitrogen harvest index (NHI) and nitrogen translocation rate (NTR). High PN improved the AE value in DS system, but showed little effect in TP system. Oppositely, high PN decreased the PEP in TP system, while showed little effect in DS rice. The results indicated that improved PN applied in the TP system might affect the farmer's benefits without improving plant nitrogen utilization. For DS rice, though PEP was not significantly improved, but the N utilization efficiency of fertilizer uptake was enhanced. Furthermore, PE, AE, PEP, and NUE_g, which were related to the performance of yield production, were significantly correlated with each other with P value <0.01. RE was correlated with all traits but NTR and NUE_g with P value <0.01. NTR was correlated with NHI and NUE_g with P<0.01. Results showed that NUE_g was significantly correlated with PE, AE, PEP, and NTR. Considering most of the agronomic practice was carried out without zero N control, NUEg might be a practical option for farmers to evaluate the plant N fertilizer physiological use efficiency when soil texture is similar.     

Agronomic Efficiency of Indian Rock Phosphates in Acidic Soils Employing Radiotracer A‐Value Technique

Abstract

A greenhouse pot culture study was conducted to evaluate the agronomic efficiency of two rock phosphates from Mussoorie (MRP) and Purulia (PRP) in two acidic soils from Dapoli (Maharashtra) and Aruvanthklu (Karnataka), India, by growing maize (cv. Ganga) as the test crop and using ³²phosphorus (P) single superphosphate (³²P=SSP) as a tracer (A‐value technique). Dry‐matter yield and P uptake increased significantly with the application of P fertilizers compared to control treatment (without P) in both the soils. There was no significant difference with respect to dry‐matter yield among the P fertilizer treatments. However, P uptake by the shoots was found to be significantly higher in the PRP treatment in only Dapoli soil compared to other P fertilizer treatments. Phosphorus derived from fertilizer decreased in rock phosphate treatments compared to standard ³²P‐SSP treatment in both the soils, indicating an excess availability of P from the rock phosphates. A‐values of soil and rock phosphate indicate a relatively higher P availability from Aruvanthklu soil compared to Dapoli soil; A‐values for the rock phosphates were in the order PRP>MRP. The substitution ratio showed that the availability of P from both the rock phosphates were less than SSP in both the soils.     

The use of biologically based phosphorus fractions to evaluate soil P availability in reduced P‐input paddy soils

Chemical soil phosphorus (P) extraction has been widely used to characterize and understand changes in soil P fractions; however, it does not adequately capture rhizosphere processes. In this study, we used the biologically based phosphorus (BBP ) grading method to evaluate the availability and influencing factors of soil P under four P fertilizer regimes in a typical rice–wheat cropping rotation paddy field. Soil P was assessed after seven rice‐growth seasons at multiple growth stages: the seedling, the booting and the harvest stage. Soil CaCl₂‐P, citrate‐P and HC l‐P (inorganic P, Pi) as well as enzyme‐P (organic P, Po) were not significantly different between soil treated with P fertilizer during the wheat season only (PW ) and during the rice season only (PR ) compared with soil treated during both the rice and the wheat seasons (PR +W) at all three rice‐growth stages. No P fertilizer application during either season (Pzero) significantly reduced the concentration of soil citrate‐P and HC l‐P at the rice‐seedling and harvest stages. Significant correlations were observed between the HC l extraction and Olsen‐P (R ² = 0.823, P  <  0.001), followed by enzyme‐P (R ² = 0.712, P  <  0.001), citrate‐P (R ² = 0.591, P  <  0.001) and CaCl₂‐P (R ² = 0.133, P  <  0.05). Further redundancy analysis (RDA ) suggested that soil alkaline phosphatase (S‐ALP ) activity played a role in soil P speciation changes and was significantly correlated with enzyme‐P, citrate‐P and HC l‐P. These results may improve our ability to characterize and understand changes in soil P status while minimizing the overapplication of P fertilizer.     

Plant availability of isotopically exchangeable and isotopically nonexchangeable phosphate in soils

Isotopically exchangeable P (IEP) is usually considered to be completely plant‐available and the major source of P for plant uptake. The aim of the present study is to test whether plants can, besides IEP, also use non‐IEP and if part of the IEP has an equilibrium concentration in soil solution which is below the minimum concentration, C_Lmin, and can therefore not be taken up by plants. A pot experiment was carried out with maize for two years on two soils, an acid sandy and a neutral loamy soil, either without P fertilizer or fertilized with ten P sources of different solubility. Throughout both years of the study, pots were kept moist either without plants or planted twice with maize (Zea mays L., cv. Athletico). At the end of the experiment, plant P uptake, P concentration in the soil solution (C_L), and P accessible to isotopic exchange within 5 d (E_5d) were measured. Plant growth decreased the E_5d which was about equal to P uptake by maize for most treatments in the acid soil. But for some treatments, i.e., five in the acid and eight in the neutral soil, P uptake was up to 50% larger than the decrease of E_5d, indicating that plants had, besides IEP, also used P from non‐IEP sources. At adequate P supply, both soils had an E_5d of about 100 mg P (kg soil)^–1, but about 30 to 40 mg kg^–1 of this IEP had an equilibrium P concentration in the soil solution below C_Lmin of 0.1 μmol L^–1 at which P would actually not be plant‐available. This study shows that plants take up P mainly from IEP, but not the whole IEP is plant‐available. Furthermore, plants may also use P from non‐IEP sources.     

Availability of P from 32P-labelled endogenous soil P and 33P-labelled fertilizer in an alkaline soil producing cotton in Australia

Yield responses of irrigated, field‐grown cotton to phosphorus fertilizer application in Australia have been variable. In an attempt to understand better this variability, the distribution of fertilizer P within soil P fractions was identified using ³²P and ³³P radioisotopes. The soil chosen, an alkaline, grey, cracking clay (Vertosol), was representative of those used for growing cotton in Australia. Chang and Jackson fractionation of soil P from samples collected within 1 h of application indicated that 49, 7 and 13% of the P fertilizer was present as 0.5 m NH₄F, 0.1 m NaOH and 1 m H₂SO₄ extractable P, respectively. Over 89% of the P fertilizer was recovered as Colwell extractable P in these samples, suggesting that the majority of these reaction products was in a highly plant‐available form. Fertilizer‐P remained in an available form within the band 51 days after application, and 68% of the applied fertilizer‐P was recovered as Colwell‐P (1071 mg kg^?1). The Colwell‐P concentration in the band was 35 times that in the unfertilized soil. Thus, the variability in crop response to P fertilizer application in these soils is not a consequence of fertilizer‐P becoming unavailable to plants. These results confirm the suitability of the Colwell (1963) sodium bicarbonate extraction method for measuring available P in these soils.     

Phosphorus mineralization in subarctic agricultural and forest soils

Summary Potential P and C mineralization rates were determined in a 12-week laboratory incubation study on subarctic forest and agricultural soil samples with and without N fertilizer added. There was no significant difference in net inorganic P produced between N fertilized and unfertilized soils. The forest soil surface horizons had the highest net inorganic P mineralized, 32 mg P kg^-1 soil for the Oie and 17 mg P kg^-1 soil for the Oa. In the cropped soils net inorganic P immobilization started after 4 weeks and lasted through 12 weeks of incubation. Cumulative CO₂–C evolution rates differed significantly among soils, and between fertilizer treatments, with the N-fertilized soils evolving lower rates of CO₂–C than the unfertilized soils. Soils from the surface horizons in the forest evolved the highest rates of CO₂–C (127.6 and 89.4 mg g^-1 soil for the Oie and Oa horizons, respectively) followed by the cleared uncropped soil (42.8 mg g^-1 soil C), and the cropped soils (25.4 and 29.0 mg g^-1 soil C). In vitro soil respiration rates, or potential soil organic matter decomposition rates, decreased with increasing time after clearing and in accord with the degree of disturbance. Only soils with high potential C mineralization rates and high organic P to total P ratios, mineralized P by the end of the study. Mineralizable P appeared to be associated with readily mineralizable organic C.     

Changes in soil phosphorus pools of grasslands following 17 yrs of balanced application of manure and fertilizer

Limiting the use of phosphorous (P) in intensive agriculture is necessary to decrease losses to surface waters. Balanced fertilizer application (P supply equals P offtake by the crop) is a first step to limit the use of P. However, it is questioned whether this balance approach is sufficient to maintain soil fertility. A long‐term field experiment (17 yr), on grazed grassland, has been conducted on sandy soil, marine clay soil and peat soil to obtain insight into the effects of balanced P fertilizer application on soil test P values and to explain the results by changes in P pools in the soil. The balance approach led to a gradual decline in plant available P, measured as P‐AL, in the topsoil (<0.10 m deep). This decline was accompanied by a decline in oxalate extractable P, dithionite extractable P and inorganic P (0.5 m H₂SO₄). The decline in these mineral P pools in the topsoil was (partly) compensated by an increase in the amount of organic P. There was evidence for the accumulation of P in an occluded form, especially at one of sites which received P as Gafsa rock phosphate [Ca₃(PO₄)₂].     

Soil Colloidal P Release Potentials under Various Polyacrylamide Addition Levels

Anionic polyacrylamide (PAM) can prevent soil erosion, but its effect on fine particulate phosphorus (P), such as colloidal P, has not been thoroughly examined. The effects of PAM on the release potentials of water‐dispersible colloids (WDC) and total P, molybdenum‐reactive P (MRP), and molybdenum‐unreactive P (MUP) in the colloidal and truly dissolved phases (i.e., TP_coll, MRP_coll, MUP_coll, TP_truly, MRP_truly, and MUP_truly) from six soils across South China were tested in this study. The results showed that the release potentials of TP_coll in the control treatments were 6·9–46·1 mg kg⁻¹ and generally highest in sandy loam soil. Following low (12·5 kg ha⁻¹), middle (25 kg ha⁻¹), and high (50 kg ha⁻¹) levels of PAM application, the release potential of TP_coll decreased by 41·7, 63·2, and 77·4% compared to the control group, respectively. Additionally, PAM may trigger MRP_coll and TP_truly releases in sandy loam and/or silt soils, and for most soils, MRP_truly and MUP_truly showed the highest release potentials at middle or high PAM levels. A significant PAM application level by soil site interaction for the release potentials of WDC and colloidal P was observed. Multiple linear regression showed that the PAM rate combined with soil sand content can successfully predict the release potentials of WDC (R² = 0·552, p  < 0·001) and TP_coll (R² = 0·738, p  < 0·001). Our results suggest that PAM can effectively reduce the loss of soil colloids and colloidal P, while its effects are related to both application level and soil texture. Copyright © 2017 John Wiley & Sons, Ltd.     

Critical Olsen P and CaCl2‐P levels as related to soil properties: results from micropot experiments

The usefulness of soil phosphorus (P) tests used in routine soil analyses is limited by the fact that a single measurement cannot encompass all P‐related factors potentially affecting plant performance. In this work, we performed micropot (15 mL) experiments to test the hypothesis that the predictive value of two common soil P tests (Olsen P and CaCl₂‐P) can be improved by considering properties commonly measured in laboratory analyses. Forty‐nine sets of soils ranging widely in properties were used for this purpose, each set consisting of samples with similar properties but differing in P status. Ryegrass and turnip were grown in a chamber for 30 days in two separate experiments and their yields at harvest recorded. The critical Olsen P and CaCl₂‐P levels, which were taken to be those corresponding to 95% asymptotic yield as calculated from data fitted to a Mitscherlich equation, were greater for turnip than for ryegrass, probably as a result of the difference in yield (49 and 160 mg dry matter/micropot on average for ryegrass and turnip, respectively) and hence in P requirements between the two species. Critical Olsen P spanned narrower ranges than critical CaCl₂‐P in both crops and is therefore seemingly the more robust of the two tests. Both critical P values exhibited moderate correlations with soil properties. Thus, critical Olsen P was (a) lower in soils with a medium pH – which is consistent with the fact that the bicarbonate solution method tends to overestimate plant‐available P in strongly acid and calcareous soils; (b) positively correlated with pH and carbonate content in calcareous soils; and (c) uncorrelated with soil properties in noncalcareous soils. On the other hand, critical CaCl₂‐P in some soil groups was negatively correlated with some properties increasing the P buffering capacity of soil (e.g. Fe oxide content). Taken together, our results suggest that routinely measured soil properties help to predict critical Olsen P better than critical CaCl₂‐P.     

Relationship of Soil Phosphorus Pools with Bray 1 Phosphorus in Some Acid Soils of Central Southern Cameroon

We measured phosphorus (P) chemical pools of genetic horizons of five representative pedons from central southern Cameroon. Our objectives were to assess the relative abundance of P pools and to empirically model their interrelations and contributions to a P availability index. The fractionation scheme followed a modified Hedley sequential procedure with anion exchange resin, 0.5 M sodium bicarbonate (NaHCO₃; Pi and Po), 0.1 M sodium hydroxide (NaOH; Pi and Po), 0.5 M hydrochloric acid (HCl; Pi), and 2 M sulfuric acid (H₂SO₄) after soil ignition at 550 ^oC. Resin P, sodium bicarbonate (NaHCO₃-P; Pi and Po), and HCl-Pi–extractable pools accounted for 1.0, 5.7 and 0.7 % of total P (TP) respectively. The NaOH-P and residual P pools measured through 2 M H₂SO₄ emerged as the largest and most variable pools, accounting for 86.2% of TP. The relative abundance of extracted P pools decreased in the order resin P < NaHCO₃-P ≤ HCl-P < NaOH-P < H₂SO₄-P. Bray 1 P was significantly correlated with all P pools except NaHCO₃-Pi, NaOH-Pi, and residual pools.     

Fertilizer‐use efficiency of different inorganic polyphosphate sources: effects on soil P availability and plant P acquisition during early growth of corn

Polyphosphate‐based fertilizers are worldwide in use, and their effect on crop yield is often reported to be similar to orthophosphate products, although some studies showed higher yields with polyphosphate applications. However, information on how these fertilizers may influence plant P acquisition is very limited. A pot experiment was carried out under controlled conditions with corn (Zea mays L.) growing on a sandy soil (pH 4.9) and a silty‐loam soil (pH 6.9) differing in P‐sorption properties. The objective was to evaluate phosphorus fertilizer–use efficiency (PFUE) of several polyphosphate (poly‐P) compounds (pyrophosphate [PP], tripolyphosphate [TP], and trimetaphosphate [TMP]) using orthophosphate (OP) as a reference. Focus was put on evaluating plant parameters involved in plant P acquisition, i.e., root length and P uptake per unit of root length. Furthermore, soil P availability was characterized by measuring ortho‐P and poly‐P concentrations in soil solution as well as in CAL (calcium‐acetate‐lactate) extracts. The P availability was differentially influenced by the different P sources and the different soils. In the silty‐loam soil, the application of poly‐P resulted in higher ortho‐P concentrations in soil solution. In the same soil, CAL‐extractable ortho‐P was similar for all P sources, whereas in the sandy soil, this parameter was higher after OP application. In the silty‐loam soil, poly‐P concentrations were very low in soil solution or in CAL extracts, whereas in the sandy soil, poly‐P concentrations were significantly higher. Phosphorus fertilizer–use efficiency was significantly higher for poly‐P treatments in the silty‐loam soil and were related to a higher root length since no differences in the P uptake per unit of root length among poly‐P and OP treatments were found. However, in the sandy soil, no differences in PFUE between OP and poly‐P treatments were observed. Therefore, PFUE of poly‐P compounds could be explained by better root growth, thereby improving plant P acquisition.     

Phosphorus Uptake from Green Manures and Phosphate Fertilizers Applied in an Acid Tropical Soil

Abstract

Quantifying the relative contribution of different phosphorus (P) sources to P uptake can lead to greater understanding of the mechanisms that increase available P in integrated P management systems. The ³²P–³³P double isotope labeling technique was used to determine the relative contribution of green manures (GMs) and P fertilizers to P uptake by Setaria grass (Setaria sphacelata) grown in an amended tropical acid soil (Bungor series) in a glasshouse study. The amendments were factorial combinations of GMs (Calopogonium caeruleum, Gliricidia sepium and Imperata cylindrica) and P fertilizers [phosphate rocks (PRs) from North Carolina (NCPR), China (CPR) and Algeria (APR), and triple superphosphate (TSP)]. Dry matter yield, P uptake, and P utilization from the amendments were monitored at 4, 8, and 15 weeks after establishment (WAE). The GMs alone or in combination with P fertilizers contributed less than 5% to total P uptake in this soil, but total P uptake into Setaria plants in the GM treatments was three to four times that of the P fertilizers because the GMs mobilized more soil P. Also, the GMs markedly increased fertilizer P utilization in the combined treatments, from 3% to 39% with CPR, from 6–9% to 19–48% with reactive PRs, and from 6% to 37% with TSP in this soil. Both P_GM and the other decomposition products were probably involved in reducing soil P‐retention capacity. Mobilization of soil P was most likely the result of the action of the other decomposition products. These results demonstrate the high potential of integrating GMs and PRs for managing P in tropical soils and the importance of the soil P mobilization capacity of the organic components. Even the low‐quality Imperata GM enhanced the effectiveness of the reactive APR more than fourfold.     

Evaluation of the fertilizer value and nutrient release from corn and soybean residues under laboratory and greenhouse conditions

Abstract

Laboratory and greenhouse studies were conducted on a moderately fertile Taloka (fine, mixed, thermic mollic Albaqualf) silt loam and a low fertility Leadvale (fine‐silty, siliceous, thermic typic Fragiudult) silt loam to evaluate nutrient release and fertilizer value of soybean [Glycine max (L.) Herr.] and corn (Zea mays L.) residues as compared to the inorganic fertilizer 13–13–13–13 (N‐P₂O₅‐K₂O‐S). Residues and the inorganic fertilizer were applied at 50 mg N/kg in a incubation study and at 25 and 50 mg N/kg in a greenhouse study. The incubation study indicted that carbon dioxide (CO₂) evolution and nitrogen (N) mineralization followed a identical sequence: soybean > corn residues, similar to residue N concentration and carbon/nitrogen (C/N) ratio sequence. Application of corn residues produced N immobilization in both soils (‐20 mg N/kg soil), whereas soybean increased inorganic soil N in the Leadvale soil (3 mg N/kg soil) and particularly in the Taloka soil (17 mg N/kg soil). The greenhouse study showed the superiority of the inorganic fertilizer over corn and soybean residues for sorghum‐sudan yield, and N, phosphorus (P), potassium (K), and sulfur (S) total uptake. No significant differences were found among the residues and between residues and the control with the exception of the higher soybean rate for total N uptake in the Taloka soil, and the higher corn and soybean residue rate in the Leadvale soil for total K uptake. It also appeared that soybean residues provided a substantial amount of N and S to sorghum‐sudan. Higher rates of both soybean and corn residues constituted a prime source of K, particularly in the Landvale soil which had a low exchangeable soil K level.     

Characterizing phosphorus availability in waste products by chemical extractions and plant uptake

Background: The fertilizer value of phosphorus (P) in waste products relies heavily on its availability to the subsequent crop. Aim: We studied the link between extractable P in waste products and apparent P recovery (APR, i.e., difference in plant P uptake between P amended and un‐amended soils divided by the amount of P added) using spring barley grown on three sandy soils. Methods: The products included sewage sludge, biomass ash, struvite, compost, meat and bone meal, biochar from sewage sludge, and industrial sludge. Soft rock phosphate and triple‐superphosphate (TSP) were included for comparison. Availability of P was characterized by extraction with water and solutions of sodium bicarbonate, citric acid, oxalic acid, hydrochloric acid, ammonium acetate, ammonium fluoride and anion exchange resin membranes. TSP was used to establish mineral‐fertilizer‐equivalents (MFE). Water and bicarbonate extractions were also applied to products incubated with soil before extraction. Results: The APR ranged 26 to 31% for TSP and 0 to 30% for waste products. APR correlated most strongly with bicarbonate extractable P. The correlation increased when products were incubated with soil before extraction. Conclusions: We conclude that bicarbonate extraction is a good indicator of potential P availability. However, interactions between waste products and soil properties modify P availability.