Variability in growth and nutrient accumulation in sorghum grown in waterlogged soils

Abstract

Sorghum [Sorghum bicolor (L.) Moench] is a potential crop for use in lowland paddy soils following rice in the Philippines. Little is known about the variability in sorghum germplasm with respect to yield potential in these soils, or the alterations in mineral uptake which might occur if late season rains resulted in waterlogging. Eight sorghum cultivars including the most widely used Philippine cultivar were grown after rice under flooded or non‐flooded conditions. Flooding was initiated 30 days after seeding and terminated when most cultivars were at or near the boot growth stage. Flooding markedly reduced dry matter production, and delayed bloom date on the average of 5.5 days. Grain yield was reduced about 57% over all cultivars. Early maturing cultivars were not reduced in days to bloom as much as the late maturing types, and there was a significant cultivar x treatment interaction for both bloom date and grain yield. Later maturing cultivars outyielded the other cultivars at physiological maturity in both flooded and non‐flooded conditions. Concentrations of the major nutrients N, P, K, Ca, Mg, and S were decreased in foliage at the boot stage due to flooding. The only nutrient to fall below published “critical” levels in leaf tissue, however, was N, and plants growing in these conditions showed classical N deficiency symptoms. Iron and Mn concentrations were significantly higher in foliage at the boot stage with flooding, but not high enough to be considered toxic. Most differences observed at boot still existed at maturity, but of less magnitude. Marked variability existed in the response among cultivars to waterlogging. It would appear that flooding tolerant genotypes could be selected which would improve existing cultivar choices for use in these difficult soils.     

Dry matter and primary nutrient accumulation in soybeans as affected by combined Nitrogen levels

Nodulating and non‐nodulating soybeans were grown on a Alfic Udipsamment and a Typic Hapludoll amended with 10 or 100 kg N/ha. Tissue and grain samples were analyzed to determine N₂‐fixation, dry matter, and N, P, and K accumulation. Highest grain yields were associated with the highest levels of N₂‐fixation and N and K accumulation in grain. The largest dry matter production was by nodulating plants grown on a high soil N regime. Nodulating plants accumulated more grain and tissue N, P, and K than non‐nodulating plants. Nitrogen stress increased P concentrations in both grain and tissue and decreased harvest indices.     

Variation of nitrogen accumulation and yield in response to phosphorus nutrition of soybean (Glycine max L. Merr.)

Phosphorus (P) is essential macronutrient for soybean [Glycine max (L.) Merr.] growth and function. The objective of this study was to determine effect of phosphorus nutrition (including phosphorus nutrition level and interruption of phosphorus supply) on nitrogen accumulation, nodule nitrogen fixation and yield of soybean plants by ¹⁵N labeling with sand culture. The results showed that they all presented a single peak curve with improvement of phosphorus nutrition level, when phosphorus concentration of nutrient solution was about 31 mg/L, they all reached the maximum and effect of phosphorus nutrition level on nodule nitrogen fixation was lower than that on yield formation level. Interruption of phosphorus supply during soybean growth period, nitrogen accumulation and nodule nitrogen fixation were seriously inhibited, and yield was decreased significantly when interruption of phosphorus supply during V₃-R₁ and R₁-R₅ period, while interruption of phosphorus supply during R₅-R₇ period had no significant effect on nitrogen accumulation, nodule nitrogen fixation and yield. So soybean nitrogen metabolism and yield were sensitive to phosphorus nutrition in the V₃-R₅ period, those were not sensitive to phosphorus nutrition after R₅ period.     

Influence of temporary flooding at three growth stages on soybeans grown on a clayey soil

Abstract

Knowledge of crop response to temporary waterlogging is important in the development of effective water management practices. A field study was conducted to determine the response of soybean [Glvcine max. (L.) Merr] grown on a poorly drained, clayey soil to temporary flooding at three growth stages. The four treatments were soybean flooded for seven consecutive days at either VI, V4 or R2 growth stages at a flood height of 0.03 m above the soil surface and a well‐watered control. Flooding for seven consecutive days wetted but did not saturate the lower parts of the soil profile. This was attributed to the swelling by the montmorillonitic clay and subsequent sealing of the soil near the surface. In general, Eh and ODR decreased gradually during the flood, but increased as the soil dried upon removal of the flood. Canopy heights and dry weights of the flooded soybeans were dependent on plant growth stage at flooding and time of measurement but were lower than the control. When flooded at the VI or V4 growth stages, concentrations of N and K in the above‐ground plants were lower than the control after the flood. Three weeks after the flood was removed higher concentrations of these elements were found. When flooded at R2, concentrations of N and K were lower than in the control. Few differences were found in the plant concentrations of Ca, Mg, Mn, Fe, Al, and Na in the plant due to the flood, but by the end of the growing season, concentrations of Mn, Fe and Al were higher in the R2 flooded soybeans than in the other treatments. Seed yield response of the soybeans depended upon plant growth stage at flooding. The soybeans were particularly sensitive to the seven days of continuous flood at the R2 growth stage. Values of relative seed yield were 88, 83, and 44 % of the well watered‐control for the VI, V4 and R2 growth stages, respectively. Differences in seed yield were found with cultivar and with cultivar?flood treatment.     

The effect of soil flooding on the transformation of Fe oxides and the adsorption/desorption behavior of phosphate

As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N₂ atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Fe_ox), mainly at the expense of dithionite‐soluble Fe (Fe_DCB), as well as oxalate‐extractable P (P_ox), but decreased the ratio of P_ox/Fe_ox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was P_ox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Fe_ox and P_ox fractions under non‐flooded and flooded conditions. The degree of the changes in Fe_ox, P_ox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed.     

Concentration Profile of Nitrogen and Phosphorus in Leachate of a Paddy Plot during the Rice Cultivation Period in Southern Korea

Abstract

The relationships between nitrogen (N) and phosphorus (P) concentrations in surface flooding water and those in the leachate of various soil depths were monitored, and temporal variation of leaching losses of N and P from a paddy plot during rice cultivation was estimated under the conditions of southern Korea. Even flooded conditions nitrification in subsurface soil was identified, but nitrate concentrations in leachate were less than 10 mg/L, the standard drinking water nitrate concentration set by the World Health Organization (WHO). The NO₃‐N and ortho‐P concentrations in the leachate were generally higher than those in the surface flooding water. Field data implied that leaching losses would not be accurately estimated under the flooded conditions of the paddy field when using the N and P concentrations of surface flooding water and infiltration depth. The leaching losses of NO₃‐N from paddy fields were high immediately after fertilization. The study results suggested that proper fertilization and irrigation strategies are required to reduce leaching losses of NO₃‐N from paddy fields.     

Effect of Lime and Flooding on Phosphorus Availability and Rice Growth on Two Acidic Lowland Soils

Abstract

Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg^?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r²=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO₃ [to establish pH (CaCl₂) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg^?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed.     

Effects of soil flooding and organic matter addition on plant accessible phosphorus in a tropical paddy soil: an isotope dilution study

Plant growth experiments were conducted to reveal the mechanism by which organic matter (OM) and soil flooding enhance phosphorus (P) bioavailability for rice. It was postulated that reductive dissolution of iron‐(III) [Fe(III)] oxyhydroxides in soil releases occluded phosphate ions (PO₄), i.e., PO₄ that is not isotopically exchangeable in the original soil prior to flooding. Rice was grown in P‐deficient soil treated with factorial combinations of addition of mineral P (0, 50 mg P kg^?1), OM (0, ≈ 20.5 g OM kg^?1 as cattle manure +/– rice straw) and water treatments (flooded vs. non‐flooded). The OM was either freshly added just before flooding or incubated moist in soil for 6 months prior to flooding; nitrogen and potassium were added in all treatments. The soil exchangeable P was labeled with ³³PO₄ prior to flooding. The plant accessible P in soil, the so‐called L‐value, was determined from the ³³P/³¹P ratio in the plants. The L‐values were inconsistently affected by flooding in contrast with the starting hypothesis. The OM and P addition to soil clearly increased the L‐value and, surprisingly, the increase due to OM application was larger than the total P addition to soil. An additional isotope exchange study in a soil extract (E‐value) at the end of the experiment showed that the E‐value increased less than the total P addition with OM. This suggests that plants preferentially take up unlabeled P from the OM in the rhizosphere compared to labeled labile inorganic P. The effects of soil flooding on P bioavailability is unlikely related to an increase of the quantity of bio‐accessible P in soil (L‐value) but is likely explained by differences in P mobility in soil.     

不同磷肥水平对大豆磷营养状况和产量品质性状的影响

本试验选用近年来黑龙江省推广面积较大并具有代表性的3个基因型大豆品种作为试验材料,采用盆栽试验,利用钼锑抗比色法测定了大豆生育期各器官磷素含量,并测定了单株产量及成熟子粒蛋白质和脂肪含量,结果表明:施磷量对不同大豆品种植株及各器官磷素含量有较大影响;不同品种不同处理全株及各器官磷素含量从分枝期逐渐增加,开花期达到高峰,随后下降至成熟期;同一品种不同处理间高蛋白品种和中间型品种是P150处理全株磷积累量最高,高油品种是P225处理全株磷素积累最高;生育期内只有适宜施磷才能促进磷素含量达到最高峰;同一处理不同品种间是高油品种磷素积累量大于中间型品种和高蛋白品种,说明高油品种需磷量多于中间型品种和高蛋白品种。高蛋白品种和中间型品种P150处理单株产量和子粒蛋白质含量最高,高油品种P75处理单株产量和子粒蛋白质含量最高。3个品种脂肪含量均以P225处理最高。     

OIL BIOREMEDIATION IN SALT MARSH MESOCOSMS AS INFLUENCED BY N AND P FERTILIZATION,FLOODING, AND SEASON

Bioremediation of crude oil in salt marsh mesocosms growing Spartina alterniflora was investigated during winter and summer to determine the influence of nitrogen (N) and phosphorus (P) fertilization, flooding, and season. Fertilization with urea and ammonium (NH₄ ⁺) applied at 75 or 150 kg N ha^-1 with or without P did not significantly (p = 0.05) increase oil or hydrocarbon degradation in continuously flooded mesocosms over an 82 day period during winter (temperature range of 17 to 30 °C). Phosphorus applied at 40 kg P ha^-1 significantly (p = 0.05) increased oil and hydrocarbon degradation. Nitrate (NO₃ ^-) added alone did not increase oil or hydrocarbon degradation, but when added with P, it significantly (p = 0.05) increased degradation above that for P alone. Up to 70% of applied oil and 75% of applied hydrocarbons were degraded in P supplemented treatments. Inipol, an oleophilic fertilizer containing N, P, and a dispersant, significantly increased oil and hydrocarbon degradation. During a 40 day summer experiment (temperature range of 27–42 °C), N and P fertilization did not increase oil or hydrocarbon degradation. For continuously flooded treatments, 72% of applied hydrocarbons were degraded while 51% were degraded in alternately flooded treatments. Mesocosms provided conditions suitable for quantitative recovery of oil and results indicated that N and P fertilization, flooding, and season interacted to influence oil bioremediation. Even under the most favorable conditions, more than 1 month was required for most of the oil to disappear.     

Dinitrogen fixation and soil n uptake by soybean as affected by phosphorus availability

The effects of phosphorus supply (0, 30, and 90 mg P kg^‐1) on growth, N₂ fixation, and soil N uptake by soybean (Glycine max (L.) Merr.) were studied in a pot experiment using the ¹⁵N isotope technique. Phosphorus supply increased the top dry matter production at flowering and the dry matter production of seeds, straw, pod shells, and roots at late pod filling of inoculated soybeans. Phosphorus supply reduced the N concentration of plant tops at flowering, but increased the amount of N accumulated at both flowering and late pod filling. In inoculated soybeans total N accumulation paralleled the dry matter production. The P concentration in above‐ground plant parts of nodulated soybeans was not affected by P application. At flowering only 18 to 34% of total N was derived from N₂ fixation, whereas as much as 74% was derived from N₂ fixation at late pod filling. Only the addition of 90 mg P kg^‐1 soil significantly increased the amount of N₂ fixed at the late pod filling stage. Phosphorus supply did not influence the uptake of fertilizer or soil N in soybeans, even if the root mass was increased up to 60% by the P supply.     

N2 fixation of nodules and N absorption by soybean roots associated with ridge tillage on poorly drained upland fields converted from rice paddy fields

Abstract

Sowing on elevated ridges is effective in reducing wet injury of soybean plants cultivated in upland fields converted from rice paddy fields. Therefore, we investigated the effect of ridge tillage (RT) on soybean N accumulation properties. We compared the amounts of plant N associated with N₂ fixation of nodules and from soil and fertilizer in the RT treatment with amounts in conventional tillage (CT) in two fields in 2002–2003. Both fields were upland fields converted from rice paddy fields (Typic Hydraquents). The main difference between the fields was the presence of a field underdrain. The amounts of Rb and K accumulated in the shoots were also determined to estimate soybean root distribution. The grain yields with RT increased in both fields from 106% to 129% compared with CT. Increased pod number and seed weight were the major factors responsible for the yield increase. anova indicated that RT significantly increased the activities of both N₂ fixation of nodules and N absorption by roots until R1 (flowering stage). The ratio of Rb and K accumulated in the shoots indicated that with RT, the root distribution was more abundant in the superficial layers compared with CT. Thus, RT reduced wet injury during the rainy season that overlapped the flowering stage. Nitrogen accumulation from N₂ fixation until the R7 stage with RT was significantly higher than that with CT. We concluded that RT was effective in increasing N₂ fixation of nodules in poorly drained upland fields converted from rice paddy fields.     

Changes in soil chemistry and aggregate stability induced by fertilizer applications, burning and trash retention on a long-term sugarcane experiment in South Africa

Throughout the world there is a trend towards retaining crop residues rather than burning them. For this reason, changes in soil chemistry and aggregation in a Vertisol induced by 59 years of burning or green cane harvesting with or without annual fertilizer applications were investigated. Crop residues were either burnt prior to harvest with the harvest residues raked off (R₁), burnt prior to harvest with the harvest residues left on the soil surface (R₂), or left unburnt with all the trash left on the soil surface (R₃). Concentrations of organic C in the surface 10 cm of soil increased with fertilizer applications and with increasing amounts of crop residue returned in the order R₁ < R₂ < R₃. Fertilizer applications caused an accumulation of residual P in both inorganic (Pi) and organic (Po) forms. A sequential P fractionation showed that fertilizer P accumulated in both labile and recalcitrant Pi and Po forms, and trash retention caused an accumulation of recalcitrant Po. Concentrations of K decreased in the unfertilized R₁ and R₂ treatments because K reserves were depleted. By contrast, there was an increase in the concentrations of K in the fertilized R₃ treatment. The soil became more acid on the fertilized and, to a lesser extent, trash retention plots. We attribute this to nitrification and subsequent nitrate leaching. Acidification resulted in a loss of exchangeable Ca and Mg, a decrease in ECEC, and an increase in the concentrations of total and monomeric Al in soil solution, in exchangeable Al³⁺ and in the buffering reserve of non‐exchangeable Al associated with organic matter. Aggregate stability was increased by increasing crop residues but decreased by fertilizer applications. The decrease was attributed to an increase in the proportion of exchangeable cations present in monovalent form due to applications of fertilizer K and leaching of Ca and Mg. We conclude that trash retention and annual fertilizer applications have substantial long‐term effects on both organic matter status and soil pH and therefore on other soil chemical and physical properties.     

Diffusion of ammonium and nitrate ions in flooded soil and nitrogen use efficiency of an irrigated rice system

Abstract

A laboratory study was used to simulate the pattern of diffusion of ammonium and nitrate ions in flooded soil. Ammonium, deep incorporated in a submerged irrigation system, diffused upward from the anaerobic to the aerobic layer where biochemical oxidation nitrified it to NO₂ and NO₃. These oxidized N species diffused downward from the aerobic layer to the anaerobic layer where most or at least partly, was lost as gaseous end products. Three crops of rice were grown in a glasshouse experiment to estimate N use efficiency under various combinations of irrigation and N management practices. Overall N use efficiency averaged 45%. Under continuous flooding, almost two thirds of the applied fertilizer N (647% use efficiency) was recovered by the rice crop. Under alternate flooding and drying, the response was very poor, with only about one fourth (26% use efficiency) of the applied fertilizer N being recovered by the crop. This demonstrated importance of the proper combination of irrigation and fertilizer management in paddy soils to maximize N utilization.     

Crop residues exacerbate the negative effects of extreme flooding on soil quality

Extreme flood events are predicted to have a negative impact on soil quality. Currently, there is a lack of information about the effect of agricultural practices on soil functioning and microbial processes under these events. We hypothesized that the impact of flooding on soil quality will be exacerbated when crop residues are present in the soil as they will induce more extreme anaerobicity. A spring extreme flood event (10 °C, 9 weeks) was simulated in mesocosms containing an arable sandy-loam soil low in nutrients. The main treatments were (1) with and without flooding and (2) with and without maize residue addition (8 Mg ha^?1). We monitored changes in soil chemical quality indicators (e.g. pH, salinity, Fe³⁺, P, C, NH₄ ⁺, NO₃ ^? and organic N), greenhouse gas (GHG) emissions (CO₂, CH₄, N₂O) and soil microbial community composition (PLFAs) during a prolonged flood period (9 weeks) and an 8-week “recovery” period after flooding. In comparison to the other treatments, flooding in the presence of crop residues resulted in a dramatic drop in soil redox potential. This was associated with the enhanced release of Fe and C into solution and an increase in CH₄ emissions. In contrast, maize residues reduced potential nitrate losses and N₂O emissions, possibly due to complete denitrification and microbial N immobilization. Both flooding and maize residues stimulated microbial growth and promoted a shift in microbial community composition. Following floodwater removal, most of the soil quality indicators returned to the levels of the control treatment within 5 weeks. After this short recovery phase, no major impact of flooding could be observed on plant growth (maize pot-grown). Overall, we conclude that both extreme flooding and management regime negatively impact upon a range of soil quality indicators (e.g. redox, GHG emissions); however, the soil showed high resilience and recovered quickly after floodwater removal. Further work is required to investigate the impact of repeated extreme flood events on soil quality and function over longer timescales.     

Influence of sulfur and nitrogen fertilzer on the uptake of iron,manganese, and zinc by corn plants grown in calcareous soil

Abstract

A pot experiment was conducted with a coarse‐textured calcareous soil (pH‐H₂O 8.3) to study the effect of single and combined application of N and S fertilizers on soil pH, Fe, Mn, Zn, and P mobilization, and on growth and micronutrient uptake by com (Zea mays L.). Increasing amounts of elemental sulfur were mixed with the soil. To stimulate S oxidation, the treated soils were incubated for six weeks at field capacity. Nitrogen was applied as NH₄NO₃ (100, 200, and 400 mg N/kg). After six weeks, dry matter yields were recorded and shoots were analyzed for Fe, Mn, Zn, and P. At the end of the experiment, soil pH and the DTPA‐extractable micronutrients were determined. The results showed that: a. Soil pH was decreased by 0.2, 0.5, and 0.9 unit as a result of increasing S applications.

b. Applied sulfur and N fertilizer had increased the availability of micronutrients to following crops.

c. Application of N and/or S resulted in increased dry matter yields.

d. Manganese uptake tended to be higher as amounts of N applied increased; this was most evident at the higher S application rates. This effect was, however, reversed for Fe, Zn, and P uptake.

e. Under our experimental conditions, promising results were achieved on improving micronutrient availability and uptake when 400 mg N/kg was combined with 3 g S/kg.

     

Effect of inoculum,variety, nitrogen,phosphorus, and potassium on yield,protein and oil content of soybeans at jabalpur,M.P. India

Abstract

Regardless of inoculum or fertility rate Bragg outyielded Clark 63 soybeans. Yields of Bragg and Clark 63 were increased about 1000 kg per ha by treatment with inoculum at the rate of approximately 313, 000 bacteria per seed. At the highest rate of applied N, yields of uninoculated soybeans, were lower than the inoculated soybeans at the lowest applied N rate. Phosphorus fertilizer increased yields at a decreasing rate and yields were decreased at the highest rate of applied P. Potassium fertilizer had a negative effect on soybean yields and did not significantly effect the protein or oil content of soybean seed. With increasing P fertilizer rates, there was a decrease in oil content and in increase in protein content of soybean seed.     

Effects of rice‐straw and phosphorus application on production and emission of methane from tropical rice soil

Rice‐straw amendment increased methane production by 3‐fold over that of unamended control. Application of P as single superphosphate at 100 μg (g soil)^–1 inhibited methane (CH₄) production distinctly in flooded alluvial rice soil, in the absence more than in the presence of rice straw. CH₄ emission from rice plants (cv. IR72) from alluvial soil treated with single superphosphate as basal application, in the presence and absence of rice straw, and held under non‐flooded and flooded conditions showed distinct variations. CH₄ emission from non‐flooded soil amended with rice straw was high and almost similar to that of flooded soil without rice‐straw amendment. The cumulative CH₄ efflux was highest (1041 mg pot^–1) in rice‐straw‐amended flooded soil. Appreciable methanogenic reactions in rice‐straw‐amended soils were evident under both flooded and non‐flooded conditions. Rice‐straw application substantially altered the balance between total aerobic and anaerobic microorganisms even in non‐flooded soil. The mitigating effects of single‐superphosphate application or low‐moisture regime on CH₄ production and emission were almost nullified due to enhanced activities of methanogenic archaea in the presence of rice straw.     

Nitrogen mineralization in histosols of the everglades agricultural area

Abstract

A long‐term soil incubation and column nutrient leaching study was conducted to determine nitrogen (N)‐mineralization rates of selected Florida Histosols with drained and intermittent‐flooded conditions. Five surface soils from the Everglades Agricultural Area (EAA) were packed in columns (5‐cm i.d. containing the 0‐ to 15‐cm depth of each soil) and leached with 0.01M CaC12 followed by distilled water every 25 d for 1 yr. Drained columns were treated with a minus‐nitrogen‐phosphorus (NP) solution followed by applying ‐0.97 MPa tension to remove excess solution. Flooded columns received the same minus‐NP solution, but were flooded to a depth of 3 cm. Both treatments were incubated for 25‐d periods, solution sampled, and treatments reapplied. Because flooding conditions could not be maintained during the sampling period, this treatment is referred to as intermittent flooded. The ammonium‐nitrogen (NH₄ ⁺‐N) released from drained soils accounted for less than 6% of the total soluble N released from all soils, compared to more than 30% released from flooded soils. There were no differences in the amounts of soluble organic N from drained and intermittent flooded soils. Total soluble N from the surface 15‐cm of drained soils ranged from 217 to 509 kg‐ha^‐1yr^‐1, with 50 to 67% released as nitrate‐nitrogen (NO₃ ^‐‐N). In contrast, total soluble N released from flooded soils ranged from 168 to 345 kg‐ha^‐1yr^‐1, with less than 3% released as NO₃ ^‐‐N.