Influence of cover crops on potential nitrogen availability to succeeding crops in a Southern Piedmont soil

Winter cover crops are essential in conservation tillage systems to protect soils from erosion and for improving soil productivity. Black oat (Avena strigosa Schreb) and oilseed radish (Raphanus sativus L.) could be useful cover crops in the southeastern USA, but successful adoption requires understanding their influence on N availability in conservation tillage systems. Black oat and oilseed radish were compared to crimson clover (Trifolium incarnatum L.) and rye (Secale cereale L.) for biomass production and effects on N mineralization during the summer crop growing season from fall 1998 through summer 2002 near Watkinsville, GA. Rye produced 40 to 60% more biomass, although N contents were less than the other cover crops. Oilseed radish and black oat N contents were similar to crimson clover. Black oat, oilseed radish, and crimson clover C/N ratios were less than 30, whereas rye averaged 39. Amount of N mineralized in 90 days (N _min90) measured with in situ soil cores was 1.3 to 2.2 times greater following black oat, crimson clover, and oilseed radish than following rye. No differences in N _min90 were found between black oats, crimson clover, and oilseed radish in 1999 and 2000. The amount of potentially mineralizable N (N ₀) was not different due to cover crop, but was 1.5 times greater in 2000 and 2002 than in 1999. The rate of N mineralization (k) was 20 to 50% slower following rye than the other three cover crops. Black oat and oilseed radish biomass production and soil N mineralization dynamics were more similar to crimson clover than to rye, which indicates that they could be used as cover crops in the southeast without significant changes in N recommendations for most crops.

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Enhanced biological cycling of phosphorus increases its availability to crops in low-input sub-Saharan farming systems

Many soils in sub-Saharan Africa, which are farmed by smallholders, are P deficient and highly P fixing. Furthermore, P inputs supplied as farmyard manure (FYM) or inorganic P fertilizer are normally too small to replace P offtakes by crops. Consequently most soils are in a negative P balance, which is reflected in small, and often declining, crop yields. The obvious solution of simply applying adequate P is seldom an option due to shortages of manure, which is usually low in nutrients in any case, and the high cost of inorganic P fertilizer relative to the likely cash value of the harvest. Our aim was to see if we could devise practical methods to increase soil P availability in this situation and to investigate the mechanisms involved. Two approaches were adopted. Firstly, to attempt to saturate the P-fixing sites in the soils by applying a large annual application of P (75 kg P ha⁻¹), which should serve for several seasons. Secondly, to attempt to keep the fertilizer P in biological forms by supplying fertilizer P and cattle manure (FYM) in combination. Here, the aim was to promote the cycling of P through the soil microbial biomass and associated metabolite pools, with the expected result of decreasing P fixation and increased plant availability of this P. These treatments were investigated using two field sites on smallholder farms in Kenya: one, considered a ‘high P fixing’ soil at Malava (Kakamega District) and one considered a ‘low P fixing’ soil at Mau Summit (Nakuru District). The following treatments were applied in 1997 and 1998: nil; 75 kg P ha⁻¹ as super phosphate (P); 25 kg P ha⁻¹; FYM at 1.9 t ha⁻¹ dry matter; FYM+25 kg P ha⁻¹. All treatments also received 100 kg inorganic N ha⁻¹. Maize was the test crop. There was no significant correlation in either year at either site between soil P, measured as NaHCO₃-extractable P, resin P or NaOH-extractable P and maize yield. However, the different soil P fractions were closely correlated with each other. Yields at the high P rate (75 kg ha⁻¹y⁻¹) were often little better than the control. There was, however, a significant positive relationship (P<0.05) between soil microbial biomass P and crop yield, again at both sites and in both years. The treatment giving the best yield and the largest biomass P was always FYM+P. Our results indicate that the combined use of organic and inorganic fertilizers in these low input systems may promote increased biological cycling, enhanced availability and consequently improved plant uptake of soil and fertiliser P, to the advantage of the small scale farmer. The results also indicate that biomass P measurements may provide a better indicator of soil P availability in these soils than some more conventional chemical extractants. However, both findings require further evaluation.     

Sulfuric acid effects on iron and phosphorus availability in two calcareous soils

An attempt was made to study the effects of sulfuric acid additions to iron (Fe)‐ and phosphorus (P)‐deficient calcareous soils. Several greenhouse experiments were conducted with sorghum (Sorghum bicolor L.) grown in two calcareous soils. Addition of sulfuric acid to soils increased soil acidity, salinity, DTPA‐extractable Fe, available P (NaHCO₃‐extractable), and crop yield. The change in soil pH is the primary cause of increased nutrient availability and thus crop yield. Leaching after acid application is highly beneficial in decreasing salinity during germination and seedling stages and therefore has a direct impact on the yield. The beneficial effects of acid carried over for at least two greenhouse cropping seasons (approximately 4.5 months).     

Influence of bacteria on growth and phosphorus nutrition of mycorrhizal corn

Com plants were grown in a non‐sterile soil in a greenhouse or in hydroponic culture in a growth chamber. We studied the influence of chitinolytic, pectinolytic, P‐solubilizing bacterial isolates, and a collection of bacterial strains on the development of native vesicular‐arbuscular mycorrhizal (VAM) populations, colonization of roots by the VAM fungus Glomus fasciculatum and their influence on the phosphorus (P) nutrition and growth of plants. As compared with VAM native control, the most potent stimulants for root colonization of soil‐grown plants by the VAM native population was a strain of Agrobacterium radiobacter and isolate H30. All bacteria used significantly supressed shoot fresh weight of mycorrhizal plants (‐13% up to ‐37%), with the exception of Agrobacterium. Under hydroponic conditions, the P‐solubilizing isolate F27 significantly stimulated the intensity of mycorrhiza, the number of arbuscules in roots, and increased both the P concentration and P content in corn shoots (+30% and +35%), than did the VAM fungus alone. Isolate F27 significantly increased shoot dry weight as compared with the mycorrhizal control. The other bacteria did not influence biomass production of corn.     

中国亚热带地区酸性土壤上部分酸化的磷矿石的农学潜力

A glasshouse experiment was conducted to evaluate the agronomic potential of four partially acidulated rock phosphates(PARP) in three representative solis sampled from subtripical China.The PARPs were manufactured by attacking a moderately reactive phosphate rock either with sulfuric acid alone or with combination of sulfuric and phosphoric acids at 30 or 60 percent of acidulation.Shoot dry weight and P accumulation of six successive cuttings of ryegrass were used to compare the agronomic potential of these fertilizers with that of the raw rock phosphate(RP) and monocalcium phosphate (MCP).Results indicated that the effectiveness of various phosphates was determined both by the solubility of the phosphates and by the acidity and P-fixing capacity of the soils.The higher the watersoluble P contained,the better the effectiveness of the fertilizer was.Although plant P accumulation of PARP treatments was constantly lower than that of MCP treatment,some PARPs could still get a dry matter production similar to that of MCP treatment.PARP SP60,which was acidulated with a mixture of sulfuric acid and phosphoric acid at 60 percent of acidulation and contained the highest soluble,P,was as effective as MCP in terms of dry matter production on all the soils.S60 and C1 which were both acidulated with sulfuric acid with the former at 60 percent of acidulation and the latter at 30 percent but with a further addition of monoammonium phosphate,were more than 80 percent as efective as MCP,Raw RP also showed a reasonable effectiveness which increased with soil acidity.It was suggested from the study that some of these APRPs could be expected to have a comparable field performance as soluble P fertilizers in the acid soil regions.     

Response of corn seedlings to high concentrations of ammonium phosphates

Abstract

When in‐row subsoilers are used to plant crops in no‐tillage systems, starter fertilizers are often applied in the in‐row subsoil track. Although rates applied are small, the actual concentration within the rooting zone can be excessive, and injury to germinating seed and young plants can be severe. The purpose of this greenhouse study was to determine the effect of starter fertilizer placement, rate, and source on germination, growth, and nutrient uptake ef corn (Zea mays L.) seedlings. Fertilizers were surface applied, mixed with the upper 7.5‐cm, 7.5‐ to 15‐cm and the 0‐ to 15‐cm soil depths. Fertilizer rates were equivalent to 15 and 30 kg/ha of field applied P. Sources were diammonium phosphate (DAP, 18–46–0) and ammonium polyphosphate (APP, 10–34–0). Treatments did not affect germination, but the surface application resulted in severe crust formation which had to be mechanically broken. Plant heights and weights and root weights were increased by fertilizer. Nitrogen was primarily responsible for increased plant growth 2 weeks after emergence, but P appeared to have the greatest effect at 4 and 6 weeks. Although seedling death or severe damage to plants did not result from any source, rate, or application zone, some damage did occur. Optimum treatments varied with sampling dates, but after 6 weeks, optimum treatments in terms of greatest root and shoot weights and plant heights were the low rate of APP mixed with the 0‐ to 7.5‐ or the 0‐ to 15‐cm soil depths.     

Specific activity of phosphorus in mycorrhizal and non-mycorrhizal plants in relation to the availability of phosphorus to plants

Phosphate was allowed to react with a soil to which iron hydroxide had been added. The P was then labelled by a subsequent addition of ³²P. Soil P was extracted by 10 mm CaCl₂, 0.5 m NaHCO₃, and acid NH₄F solutions and the specific activity of P in the extracts was measured. Subterranean clover plants were grown both with and without a mycorrhizal fungus. Phosphorus contents and the specific activities of P in the plant shoots were determined.For mycorrhizal plants, adding iron hydroxide had no effect on the amount of P taken up, but for non-mycorrhizal plants it decreased the uptake. However there was no effect of iron hydroxide or of mycorrhizal infection on the specific activity of P in the plants. Adding iron hydroxide had no effect on the amount of P extracted by acid NH₄F, but decreased the P extracted by 10mm CaCl₂ and by 0.5 m NaHCO₃. The specific activity of P in the extracts was not affected by the addition of iron hydroxide and was the same for the three extractants. Further, the specific activity of P in all extractants was similar to that of P in both mycorrhizal and non-mycorrhizal plants. Thus differences in the availability of soil P to mycorrhizal and non-mycorrhizal plants and to the extractants were not reflected by differences in labelling. It therefore follows that lack of difference in specific activity between mycorrhizal and non-mycorrhizal plants does not eliminate the possibility that mycorrhizal plants can obtain P that was unavailable to non-mycorrhizal plants.     

土壤磷素形态及其生物有效性研究进展

土壤磷素形态及其生物有效性的研究对解决农业生产中所引起的经济、环境和资源问题有很重要的作用。结合国内外已有成果和最新研究进展,从土壤的形态、磷的分组以及测定方法,土壤各形态磷的生物有效性等几个方面综述了国内外土壤磷的研究现状,并提出了目前在土壤磷研究中存在的一些问题以及今后研究的热点。     

Increased phosphorus availability to corn resulting from the simultaneous applications of phosphate rock, calcareous rock, and biochar to an acid sandy soil

Phosphorus (P) deficiency is one of the main constraints on crop production in Arenosols (acid sandy soil). The high cost of P fertilizers may represent an insurmountable obstacle in many poor countries, leaving the exploitation of their own calcareous and phosphate rocks as the only low-cost and long-term alternative. Biochar is suggested to have positive effects on soil properties; however, there is no published research on the synergistic effects of biochar and rocky materials in modifying soil properties. The aim of this study was to investigate the chemical and biochemical responses of an acid Arenosol treated with phosphate rock (PR), calcareous rock (CR), and biochar (BC), and the implications for corn yield. A soil from Marracuene District, Mozambique was used, where corn was grown for 90 d with the soil treated with:no addition (control), water-soluble zinc phosphite fertilizer (WSP), PR, WSP+CR, WSP+BC, WSP+CR+BC, PR+BC, and PR+CR+BC. Biochar was produced by pyrolysis of babycorn peels for 4 h at 450℃ and applied at 11 g kg^-1. The soil pH_H2O increased from about 4.54 in the control to 7.38 in the PR+CR+BC treatment. Easily oxidizable organic carbon, cation exchange capacity, and available P were higher in the treatments containing BC than in the control. The treatments containing CR and/or BC led to the highest activities of alkaline phosphomonoesterase, phosphodiesterase, and α-glucosidase, which increased P availability and gave the greatest biomass and yields. We suggest that biochar provides additional soluble P and supplies adsorption sites for phosphate, preventing its evolution to unavailable forms. Thus, PR applied together with BC contributed to an 840% yield increase compared to the control. The treatments containing WSP and BC facilitated phosphite oxidation to phosphate and increased crop yield.     

Effect of liming and phosphate application on sudangrass growth and phosphorus availability in two temperate acid soils

Abstract

A pot experiment was carried out in the greenhouse with two loamy sand Dystric Cambisols derived from schist to investigate the effect of liming and phosphorus (P) application on plant growth and P availability and its assessment by four soil test methods: 0.01M calcium chloride (CaCl₂), cation anion exchange membrane (CAEM), Egnér‐Riehm, and Olsen procedures. Soils were first incubated for two weeks with lime at four levels, depending on their content of exchangeable aluminum (Al). Phosphorus was added at two rates (75 and 150 mg P kg^‐1) and the incubation proceeded for an additional two‐week period. Sudangrass (Sorghum sudanenses cv. Tama) was then planted and harvested four weeks later. During incubation and plant growth, soils were maintained at 70% of field moisture capacity. Although pH value and soil extractable P in original soils were similar, the results showed a significant difference on the effect of liming and P application. Acidity was the major limitation for DM yield in the soil with the highest amount of exchangeable Al, while P availability was the main constraint in the other soil. Liming above pH (0.01M CaCl₂) 5.3–5.5 did not increase DM yield in either soil and showed a negative effect on one soil (9.7 to 6.9 and 10.2 to 7.8 g pot^‐1). Phosphorus content and uptake by sudangrass increased with liming, revealing a positive effect of lime on the availability of P to plants. Added P showed a lower efficiency in the soil with highest amounts of Al compounds. Soil tests performed after the execution of the pot experiment showed variable tendencies to predict P availability, according to the nature of the procedures and soils. Soluble‐P in 0.01M CaCl₂ increased with the rise of soil pH. Extractable CAEM‐P and Egnér‐Riehm‐P also increased with liming, but reflected the soil depletion caused by plant uptake. Extractable Olsen‐P presented the most inconclusive results, suggesting the limitation of this method for acid soils which have been limed.     

Effect of phosphorus status of the soil on selenium availability

Due to its importance for human and animal health, low bioavailability of selenium (Se) is of concern in large parts of the world. Among the factors determining Se availability is competition for binding sites by other anions. In order to evaluate the effect of different soil P status on Se availability from fertilizer, adsorption studies were conducted with soils ranging from low to very high available P as measured in ammonium lactate (P‐AL) and addition of Se as either selenate or selenite. Generally selenite, and to some extent also selenate, adsorption decreased with increasing P‐AL status of the soil. However, in a silt loam, the increase in P‐AL from 140 (high) to 210 mg P kg^–1 (very high) did not result in a corresponding decrease in Se adsorption. Phosphorus saturation, on the other hand, was found to be lower in the sample that was very high in available P, suggesting that both the total amount of P on binding sites and the amount of plant‐available P influence Se availability. Selenate addition caused an increase in P availability, especially when added together with phosphate to a silt loam with very high P‐AL status.     

Studies on the effect of humic acid on availability of phosphorus

It is believed that some organic compounds form complexes with iron and aluminum and prevent the fixation of phosphate applied to soils.     

Evaluation of phosphorus availability from three phosphorus sources in Nigerian soils

Abstract

In an attempt to search for a cheaper source of phosphorus (P), both for direct application and industrial use, three P fertilizers were evaluated in incubation and greenhouse studies. Indigenous Sokoto rock phosphate (SRP) imported, Togo rock phosphate (TRP), and conventional single superphosphate (SSP) were applied on three soil types namely Oxisol, Ultisol, and Alfisol at rates ranging from 0–800 mg P kg^‐1 soil. Evaluation of the P sources was conducted for 12 weeks in incubation study, and five weeks in the greenhouse using maize as test crop. Evaluation of direct application of SSP and SRP on an oxic paleudult was carried out in the field for three years. The results of incubation studies revealed in general, that P availability increased as fertilizer rates increased. The P availability was, however, greater when SSP was applied on the Alfisol than on the Oxisol and Ultisol. The rock phosphates on the other hand were more efficient on acid soils than on soils neutral in pH. Optimum P availability from the fertilizers was observed to occur predominantly between four and eight weeks of incubation. In the greenhouse study, SSP gave the highest cumulative P uptake and optimum rate of application was 200 mg P kg^‐1 soil, while optimum rate for rock phosphate was 400 mg P kg^‐1 soil. The agronomic effectiveness (EA) of the rock phosphates was about 40% relative to SSP on the Alfisol. The EA, however, for TRP and SRP was 120% and 160%, respectively, on the Oxisol, while on the Ultisol, SRP was equally effective as SSP and TRP had 65% effectiveness. The results of the field trial indicated that the SRP had 54%, 83%, and 107% agronomic effectiveness of SSP, respectively, in the first, second, and third year of cropping. Optimum rate for SSP and SRP application was considered to be 50 and 75 kg P₂O₅ ha^‐1, respectively.     

施磷对不同质地棉田土壤磷素有效性及磷肥利用率的影响

为阐明施磷对不同质地棉田土壤磷素有效性及磷肥利用率的影响,以盆栽试验为基础,在不同质地(粘土、壤土、砂土)上设计5个磷素水平(P0、P150、P300、P600、P1200)研究棉田磷素状况和棉花磷素积累及磷肥利用率。结果表明:不同质地棉田土壤有效磷含量在苗期和蕾期均随施磷量的增加而增加,苗期时粘土、壤土、砂土的土壤有效磷含量在P1200处理下与对照相比分别增加了80.94%、85.78%、94.41%,蕾期则分别增加了76.82%、85.10%、94.20%。苗期时,土壤全磷含量分别在粘土P600、壤土P1200、砂土P600处理下达到最大值;蕾期时粘土、壤土和砂土的全磷含量均在P1200处理达到最大值,土壤磷素活化系数在苗期时表现为粘土砂土壤土,蕾期磷素活化系数在粘土和砂土基本呈持续递增状态,最大值与对照(P0)相比分别增加了34.22%、85.71%。植物整株干物质积累在不同土壤质地表现为粘土砂土壤土。植物全磷含量则是壤土略低于粘土,砂土最低。棉花整株磷素积累量在不同土质上表现为粘土最高,壤土次之,砂土最低,且分别在P600、P300、P600处理时达到最大值。不同磷水平下,磷肥表观利用率在3种土壤质地上表现不同,粘土、壤土、砂土分别在P150、P300、P600时达到最大值,与P0相比分别提高了16.84%、29.19%、10.68%。同一磷水平下不同土壤质地磷素生理利用率表现为砂土壤土粘土。因此,在生产中应针对土壤质地合理施磷,粘土土质下棉田施磷量应控制在约150 kg/hm~2,壤土土质应控制在150～300 kg/hm~2,砂土土质施磷量总体应控制在300～600 kg/hm~2,才能促进土壤中磷的有效性和棉花磷素吸收,从而提高磷肥利用率。     

土壤磷素的化学组分及其植物有效性

本文主要论述了土壤磷素分级方法、土壤不同磷素组分的转化与植物有效性的关系及影响因子等方面的研究进展,对不同分级方法的优缺点给予了评价,并提出了该领域今后的重点研究方向。     

Plant availability of phosphorus sorbed to potential wastewater treatment materials

Ecologically engineered wastewater treatment facilities, such as constructed wetlands and infiltration plants, can be further improved in their P retention by using reactive media with a high P-retention capacity. In a sustainable system, the sorbed P should be recycled in agricultural production. The objective of the present study was to determine the plant availability of P sorbed to different P-retention media. The studied media were: crystalline and amorphous blast furnace slag, natural and burned opoka (a bedrock from Poland), limestone, burned lime, soil from a spodic B horizon, and light expanded clay aggregates (LECA). They were soaked in a P solution, rinsed and dried before incorporation into soil. An additional aim was to compare P taken up by barley with amounts chemically extracted for the estimation of plant-available soil P. P sorbed to the crystalline slag was delivered to the barley plants more efficiently than P added in K₂HPO₄ fertiliser. Soil extraction with acid ammonium lactate correlated well with P taken up by barley and indicated that P bound to Ca is more available to plants than P bound to Al and Fe. The Mg content of the used slag may replace Mg fertilisation in certain soils. It was concluded that among the investigated filter materials, crystalline slag was the most suitable sorbent from an agricultural point of view, since it possessed a large P-sorption capacity and the sorbed P was largely plant available. The heavy metal content of sorption materials must be examined carefully before their application to agricultural soils.     

腐植酸钾与速效磷肥结合形态对磷的有效性影响

本文研究了速效磷肥及其与腐植酸钾的混合物和反应产物在土壤中培养60天中磷的有效性.结果表明,反应产物的效果最好.其施入土壤后10～15天磷就几乎不再被固定,60天中有效磷含量基本保持平稳状态,60天后比单施磷肥多14.6%,比混合物多12.7%,抑制磷的固定率是混合物的8.4倍,相对提高了磷肥的有效性.化学研究表明,反应产物水溶磷减少,枸溶磷增加,但这种枸溶磷不是简单的CaHPO4,而是以腐植酸-磷酸盐复合物的形式存在,这可能是反应产物在土壤中有效磷能够维持平稳状态的主要原因之一.     

三种一年两熟地区小麦免耕播种机适应性试验与分析

免耕播种是保护性耕作技术最重要的作业环节之一,为了在一年两熟旱作区选择适合的播种机来实施保护性耕作技术,对国内目前可选用的JOHN DEERE 1590型小麦免耕播种机、2BMD-12型小麦对行免耕播种机、2BMFS-6/12型带状浅旋免耕播种机在3种地表覆盖状况下进行田间播种适应性试验,结果表明：参照播种机国家标准和农业部农机试验鉴定总站对小麦免耕播种机播种质量的检测指标,3种免耕播种机在秸秆粉碎覆盖地面条件下基本上都能满足播种要求。JOHN DEERE 1590型小麦免耕播种机不适合于在直立秸秆情况下