Transformation of inorganic phosphorus in flooded soils under rice cropping

Summary The concentrations of water soluble and ammonium acetate extractable phosphorus in all the soils under investigation first increased and then decreased with time of submergence under rice cropping. The increase in soluble phosphorus in the three acid soils of Luisiana, Casiguran and Guadalupe was related to decrease in the concentration of iron, calcium and reductant soluble phosphates, while in slightly acidic Maahas clay, the increase was associated with decrease in iron and aluminium phosphates. But in the calcareous soil, the increase was due to decrease in the concentration of aluminium and reductant soluble phosphates. The decrease was due to the re-formation of insoluble aluminium, iron and calcium phosphates in Luisiana and Guadalupe clays, to the formation of aluminium and calcium phosphates in Maahas and to the formation of calcium phosphate only in Casiguran fine sand. The application of phosphorus at the rate of 100 pounds per acre produced better tillering, more penicles and higher straw and grain productions in Luisiana, Casiguran and Guadalupe only where the level of soluble phosphate was very low in pots where no phosphorus was applied. This study, thus, indicated the necessity of phosphorus fertilization in low land rice for soils which are low in phosphorus and high in active iron and aluminium.     

Seasonal variation in organic and inorganic phosphorus fractions of temperate-climate sandy soils

Soils from an arable plot, a grassland plot and pasture plot were sampled over an 18-month period. Inorganic (P_i) and organic (P_o) soil phosphorus fractions were extracted sequentially with resin, NaHCO₃, and NaOH. Soil solution was sampled on the arable plot and pasture plot during 12 months with teflon suction cups, and the contents of P_i and P_o were determined.The patterns of the variation for all soil fractions were similar for the three plots. All soil P_i fractions were at minimum in the cool moist winter period. The soil P_o fractions varied less systematically than P_i fractions. The sum of P_o fractions had a winter maximum and a spring minimum. For all soil P fractions temporal variation was highly significant (p<0.0001). The magnitude of change in P_i and P_o soil fractions was 4–40 times greater than what would be expected from the magnitude of new N mineralization.The content of P in the inorganic soil P fractions was negatively correlated with soil moisture. The variation in organic soil P could not be explained by any single factor, but it is suggested that the variation is caused by changes in solubility rather than by biological transformations. Thus, physicochemical processes masked the impact of biological transformations on the temporal variation of soil phosphorus fractions.Both soil solution P_i and P_o varied significantly with time on field scale. In contrast to soil P_i fractions, solution P_i was initially low in the early autumn, increased by a factor 4 during the following 6 weeks, and thereafter decreased to a low level by the end of the sampling period. Soil solution P_o had several fluctuations during the sampling period.     

Phytotoxicity of soilborne glyphosate residues is influenced by the method of phosphorus fertiliser application

Plant and Soil - Glyphosate use has increased in recent decades with the adoption of minimum tillage techniques and the emergence of glyphosate-tolerant crop cultivars. There is evidence that...     

Growth and survival of cowpea rhizobia in bauxitic silt loam and sandy clay loam soils

Survival of 4 cowpea Rhizobium strains, IRC291, MI-50A, JRW3 and JRC29, in two soil types (bauxitic silt loam and sandy clay loam) undergoing drying at 30°C and 37°C was examined. While all strains except JRW3 showed a general pattern of increase in their numbers during the first 3 weeks in sterile soils, none of the strains showed any increase in their population in non-sterile soils. Cowpea rhizobia showed better survival in non-sterile bauxitic silt loam than in clay loam soils at 30°C. However, the long-term survival (examined up to 6 months) of rhizobia in both soils was poor at 37°C as compared to 30°C. We also found that cowpea rhizobia survived better in soils undergoing drying than in moist soils at 30°C. Our results suggest that (a) cowpea rhizobia survived better in bauxitic silt loam than in clay loam soil and (b) the low indigenous cowpea rhizobial population in Jamaican soils may be due to their poor long-term survival and weak saprophytic competence.     

Soil physical behaviour and crop responses to tillage in lowland rice soils of varying clay content

The influence of various tillage methods on two wetland rice soils in the Philippines is reported. The soils differed principally in clay content, 38% for the clay loam (clayey, mixed isohyperthermic Entic Hapludoll) while 56% for the clay (clayey, mixed noncalcareous, isohyperthermic Andaqueptic Haplaquoll). This had a marked effect on their response to tillage and varying water regime. The clay soil, under field conditions, showed little change in pore size distribution or soil water behaviour with different tillage methods. Crop (Rice, Oryza sativa L., var. IR20) yields were unaffected by tillage.In contrast, tillage effects were very marked in the clay loam soil, which consisted of a greenhouse and a field trial. In the greenhouse, which experienced severe dry periods, wet tillage not only increased the moisture retentivity but also the soil impedance at soil matric potential ()<–0.01 MPa. Seasonal average was <–1 MPa. Root length density decreased by 39% with dry tillage and by 56% with wet tillage compared with zero tillage. Grain yield however, did not vary with soil treatment. In the field, which experienced moderate dry spells, varied between –0.13 and –0.48 MPa. Root length density was significantly reduced at soil impedance >0.75 MPa. Wet tillage increased soil moisture storage which minimized the soil impedance during the dry cycle more effectively than did dry tillage. The crop performed best under wet tillage and least under zero tillage. Wet tillage in this soil was more effective under moderate than under severe water stress conditions.     

Estimation of the increase in CH4 emission from paddy soils by rice straw application

The relationship between the amount of CH₄ emission to the atmosphere from submerged paddy soils with rice plants and the application level (0–8 g kg^-1) of rice straw (RS) in soil was investigated in a pot experiment. Amounts of CH₄ emitted from pots with respective RS levels differed between a clayey yellow soil and a silty gray lowland soil. However, the increase in cumulative amounts of CH₄ emission with the increase in the application level of RS was similar in pattern between the two soils, and the increase (Y) was formulated with a logistic curve: x, application level of RS; k, a coefficient for relative CH₄ emission.Since the seasonal variations in coefficients a, b, and c in the logistic equation were also formulated as the function of the sum of effective temperature (E, (T–15); T, daily average temperature), the increase in cumulative amounts of CH₄ emission from any paddy soil by any level of RS application was known to be estimated by the following equation:     

Iron plaque enhances phosphorus uptake by rice (Oryza sativa) growing under varying phosphorus and iron concentrations

Both solution culture and pot experiments were performed to investigate (a) the effects of external Fe (II) concentrations and forms on the formation of iron plaque on the roots of rice (Oryza sativa) and subsequent P adsorption on iron plaque and shoot P concentrations and (b) the effects of soil moisture regimes on the formation of iron plaque and P adsorption on root surfaces and P accumulation in shoots. The results showed that iron plaque was significantly increased with increasing Fe²⁺ concentrations in the solution culture. The amounts of P adsorbed on the iron plaque were increased significantly with external Fe²⁺ concentrations. Although shoot P concentration was not significantly affected by Fe²⁺ treatment after incubation for 2 days, it was significantly increased in the Fe‐treated plants compared with Fe‐deprived ones after incubation for 4 days. Soil culture experiment showed that the formation of iron plaque on root surfaces was promoted by exogenous iron, with greater amount of iron plaque being formed by addition of ferric hydroxide than of ferric oxide. Phosphorus adsorption on iron plaque also increased with the addition of iron oxides, and increasing soil P increased the amounts of P associated with the iron plaque and shoot P concentration. The amounts of iron plaque were almost sixfold higher under flooding condition than under field capacity condition. Plants pretreated under flooding condition generally had higher shoot P concentrations when they were transplanted to solutions with varying P levels, and this was most pronounced in the treatment with highest solution P concentration. The results suggest that iron plaque acts as a nutrient reservoir for phosphorus in the rhizosphere and helps enhance P acquisition by rice.     

Effect of algal growth on the availability of phosphorus,iron and manganese in rice soils

Summary Laboratory experiments were conducted to study the effect of algal growth on the change of (I) pH, (II) available phosphorus and (III) solubility of iron and manganese content in five waterlogged alluvial rice soils of West Bengal, India. The results showed that the algal growth initially caused an increase in the soil pH, which later declined to the original value in some of the soils. The available phosphorus content decreased upto 90 days of their growth and began to increase towards the later period of incubation. The drastic fall of water soluble plus exchaneable manganese content of the soils due to algal growth was accompanied by similar increase in reducible manganese content. No appreciable change in water soluble plus exchangeable ferrous iron content was encountered but theN-NH₄OAC(pH 3) extractable iron due to algal growth progressively decreased with the progress of the incubation period.     

The effect of limestone application on the availability and form of phosphorus in Davidson clay loam

Summary The effect of limestone application on the P supplying power of Davidson clay loam, a soil high in free iron, was investigated by laboratory and greenhouse procedures. The soil under study did not receive fertilization for a 17-year period prior to the investigation. Application of dolomitic limestone to the soil increased both yield and P uptake of 3 successive cuttings of alfalfa. A comparison of inorganic P fractions in the soil before and after growth of each alfalfa crop showed that mineralized organic P and Ca-P supplied P to the first cutting of alfalfa and that Fe-P supplied P to the second and third cuttings. Application of limestone increased the availability of the Fe-P fraction to the second and third crops of alfalfa. The P availability of the inorganic P fractions was explained on the basis of chemical properties of the soil.     

秸秆覆盖与施磷对四川丘陵旱地土壤磷形态及有效性的影响

为揭示秸秆覆盖配施磷肥下土壤无机磷形态变化规律及磷的有效性,本研究采用二因素裂区设计,主区为秸秆覆盖和不覆盖,副区为3个施磷量(0、75和120 kg·hm^-2),分析秸秆覆盖与施磷条件下四川丘陵旱地紫色土磷吸附-解吸特征、无机磷组分含量及其与有效磷的关系。结果表明: 2018—2020年两个试验年度秸秆覆盖处理比不覆盖处理土壤磷最大吸附量分别显著降低7.7%和7.4%,磷吸附饱和度分别显著增加35.4%和18.6%,土壤易解吸磷分别显著提高21.6%和35.2%,磷最大缓冲容量无显著差异;施磷与不施磷相比,磷最大吸附量和最大缓冲容量显著降低,吸附饱和度显著增加,易解吸磷则随施磷量的增加而增加。两个试验年度秸秆覆盖处理比不覆盖处理磷酸二钙(Ca₂-P)、磷酸八钙(Ca₈-P)和铁磷(Fe-P)含量显著增加,铝磷(Al-P)含量显著降低,闭蓄态磷(O-P)和磷灰石(Ca₁₀-P)含量有降低的趋势;与不施磷相比,施磷则提高了不同无机磷组分含量。与不覆盖处理相比,两个试验年度秸秆覆盖处理土壤有效磷含量分别显著增加23.2%和9.6%,磷活化系数分别显著提高21.3%和8.9%,且土壤有效磷含量和磷活化系数均随施磷量的增加而提高。回归分析表明,无机磷各组分对紫色土有效磷有效性的贡献为Ca₂-P>Fe-P>Al-P>Ca₈-P>Ca₁₀-P>O-P。因此,秸秆覆盖配施磷肥促进了土壤难溶性磷向中等活性或易于作物吸收的磷形态分解和转化,降低土壤对磷素的吸附,促进土壤磷素的解吸,最终提高土壤磷素有效性。综合考虑经济效益,推荐四川丘陵旱地秸秆覆盖配施75 kg·hm^-2磷肥更有利于提高土壤磷素有效性。     

Effect of moisture and oxidation status of alkaline rice soils on the adsorption of soil phosphorus by an anion resin

Summary Considerable effort was devoted to experimentally explaining the greater amount of anion resin-adsorbable P (ARAP) in water-saturated alkaline soils relative to moist soils with the purpose of explaining the phenomenon of increased P availability in flooded rice soils. ARAP increased when waterlogged conditions were imposed on soils, but the increase in ARAP occurred before reducing conditions were obtained. Reducing conditions did not increase ARAP. The increase in ARAP in the water-saturated alkaline soils was attributed to the enhanced P diffusion resulting from a decrease in tortuosity, thus indicating that increased P availability upon flooding could be due to increased P diffusion.Paper number 4533 of the Journal Series of the North Carolina Agricultural Experiment Station.Paper number 4533 of the Journal Series of the North Carolina Agricultural Experiment Station.     

Transformation of iron and manganese in rice soils under different moisture regimes and organic matter applications

Summary Transformation of iron and manganese under three different moisture regimes,viz continuous waterlogged (W₁), continuous saturated (W₂) and alternate waterlogged and saturated (W₃) and three levels of organic matterviz 0, 0.5 and 1.0% in all possible combinations was studied in four soils. The results showed that under waterlogged moisture regime there was a sharp increase in the content of water soluble plus exchangeable manganese accompanied by significant decrease in the content of reducible manganese in all the soils excepting the acidic soil which was very poor in active manganese content. The increase in respect of iron in similar form was, however, very small. The increase in the content of water soluble plus exchangeable manganese as well as iron under the continuous saturated and alternate waterlogged and saturated moisture regimes was always much lower as compared to that under the continuous waterlogged condition. Application of organic matter brought about an increase in the content of water soluble plus exchangeable manganese in all the soils excepting the lateritic one irrespective of moisture regimes but did not cause any change in the content of iron and manganese in insoluble complex. The content of water soluble plus exchangeable iron and of insoluble ferrous iron although recorded some increase due to organic matter application, the increase was not so marked in any of the soils.     

Uptake of zinc and phosphorus by plants is affected by zinc fertiliser material and arbuscular mycorrhizas

Background and Aims

Water solubility of zinc (Zn) fertilisers affects their plant availability. Further, simultaneous application of Zn and phosphorus (P) fertiliser can have antagonistic effects on plant Zn uptake. Arbuscular mycorrhizas (AM) can improve plant Zn and P uptake. We conducted a glasshouse experiment to test the effect of different Zn fertiliser materials, in conjunction with P fertiliser application, and colonisation by AM, on plant nutrition and biomass.

Methods

We grew a mycorrhiza-defective tomato genotype (rmc) and its mycorrhizal wild-type progenitor (76R) in soil with six different Zn fertilisers ranging in water solubility (Zn sulphate, Zn oxide, Zn oxide (nano), Zn phosphate, Zn carbonate, Zn phosphate carbonate), and supplemental P. We measured plant biomass, Zn and P contents, mycorrhizal colonisation and water use efficiency.

Results

Whereas water solubility of the Zn fertilisers was not correlated with plant biomass or Zn uptake, plant Zn and P contents differed among Zn fertiliser treatments. Plant Zn and P uptake was enhanced when supplied as Zn phosphate carbonate. Mycorrhizal plants took up more P than non-mycorrhizal plants; the reverse was true for Zn.

Conclusions

Zinc fertiliser composition and AM have a profound effect on plant Zn and P uptake.     

Nitrogen mineralisation in soils of varying texture,moisture and organic matter

Summary Estimates of nitrogen availability based on the nitrogen mineralisation potential,N ₀, and the mineralisation rate constant,k, increased within the sequence, loamy sand, coarse sandy loam and loam, and were consistently higher in the high labile organic matter counterparts of the soils. There was a similar trend in the production of inorganic nitrogen at ambient temperatures. Under these conditions, an increase between mid-April and the end of May was followed by a trough in June and July and a second increase from early August to the end of September. Nitrogen production was generally higher where soil moisture was allowed to fluctuate widely in the available range, compared with a moisture regime near field capacity. Results of short-term incubations indicated that net mineralisation was minimal or negative in June and July.There was a significant relationship between values calculated fromN ₀ andk and those obtained near field capacity in the second period of mineralisation when soil temperature was relatively constant, but not in the first period when soil temperature was rising.The time required for mineralisation of 50% ofN ₀ indicated that less than half the potential value would become available in a normal temperature growing season.     

Effects of soil moisture content and temperature on methane uptake by grasslands on sandy soils

Aerobic grasslands may consume significant amounts of atmospheric methane (CH4). We aimed (i) to assess the spatial and temporal variability of net CH4 fluxes from grasslands on aerobic sandy soils, and (ii) to explain the variability in net CH4 fluxes by differences in soil moisture content and temperature. Net CH4 fluxes were measured with vented closed flux chambers at two sites with low N input on sandy soils in the Netherlands: (i) Wolfheze, a heather grassland, and (ii) Bovenbuurtse Weilanden, a grassland which is mown twice a year. Spatial variability of net CH4 fluxes was analysed using geostatistics. In incubation experiments, the effects of soil moisture content and temperature on CH4 uptake capacity were assessed. Temporal variability of net CH4 fluxes at Wolfheze was related to differences in soil temperature (r2 of 0.57) and soil moisture content (r2 of 0.73). Atmospheric CH4 uptake was highest at high soil temperatures and intermediate soil moisture contents. Spatial variability of net CH4 fluxes was high, both at Wolfheze and at Bovenbuurtse Weilanden. Incubation experiments showed that, at soil moisture contents lower than 5% (w/w), CH4 uptake was completely inhibited, probably due to physiological water stress of methanotrophs. At soil moisture contents higher than 50% (w/w), CH4 uptake was greatly reduced, probably due to the slow down of diffusive CH4 and O2 transport in the soil, which may have resulted in reduced CH4 oxidation and possibly some CH4 production. Optimum soil moisture contents for CH4 uptake were in the range of 20 – 35% (w/w), as prevailing in the field. The sensitivity of CH4 uptake to soil moisture content may result in short-term variability of net atmospheric CH4 uptake in response to precipitation and evapotranspiration, as well as in long-term variability due to changing precipitation patterns as a result of climate change.     

Re-assessment of phosphorus availability in fens with varying contents of iron and calcium

Aim

To further unravel P availability in mineral-rich fens, and test whether high Fe in the soil would lead to low P availability to the vegetation.

Methods

Mesotrophic fens were selected over gradients in Ca and Fe in central Sweden and the Netherlands, to study characteristics of vegetation, pore water and peat soil, including inorganic and organic forms of P, Fe and Al.

Results

Soil Fe was more important than region or soil Ca, and P availability to the vegetation increased from Fe-poor to Fe-rich fens. Contrary to expectations, precipitation of iron phosphates played a minor role in Fe-rich fens. Fe-rich fens were P-rich for three reasons: (1) high P sorption capacity, (2) relatively weak sorption to Fe-OM complexes and (3) high amounts of sorbed organic P, which probably consists of labile P. Also, nonmycorrhizal wetland plants probably especially take up weakly sorbed (organic) P. However, high P did not lead to high biomass or low plant diversity. Fe-rich fens were limited by other nutrients, and high P may help protect the vegetation against Fe-toxicity.

Conclusions

Fe-poor fens are P-poor, irrespective of Ca, and Fe-rich fens P-rich even under mesotrophic conditions. However, high P itself does not endanger Fe-rich fens.

     

Aluminium,boron and molybdenum availability and uptake by rice in acid sulfate soils

Although Al toxicity is believed to be a problem in acid sulfate soils cropped to rice (Oryza, sativa L.), little is known about the behavior of other trace metals such as B and Mo in these soils. The objectives of this study were to measure the availability of Al, B, and Mo in these soils, to determine what governs the availability of these metals and to investigate the relationships between metal availability and uptake by rice. Metal availability and uptake by rice were evaluated in 134 flooded acid sulfate soils in the Central Plains region of Thailand and in a growth chamber study using 50 of the same soils. Soil and plant metal analyses were conducted at the panicle differentiation stage of growth in both studies and in the soil prior to transplanting in the growth chamber study. Metal activities were determined with GEOCHEM. The mineral phases believed to be governing Al³⁺ activities were jurbanite under low pH conditions and amorphous Al(OH)₃ at high pH. The Al chemistry is believed to be intimately linked to the redox-pH cycle, which is driven by the monsoonal climate. Mortality of rice associated with Al toxicity was observed under field and growth chamber conditions. Interference in P uptake and/or assimilation was believed to be the mechanism of Al toxicity. Activities of B(OH) ₄ ^– and B(OH) ₃ ⁰ were found to be highly correlated to pH and ionic strength, respectively, with the latter being the dominant B ion found in these soils. Activities of MoO ₄ ^2– were positively correlated to pH and appeared to be controlled by wulfenite. Leaf Mo contents were found to be positively correlated with MoO ₄ ^2– activity.     

Transformation of zinc in soils under submerged condition and its relation with zinc nutrition of rice

Laboratory and greenhouse experiments were conducted with two soilsviz., laterite and alluvial to study the transformation of applied Zn in soil fractions under submerged condition in the presence and absence of added organic matter and its relationship with Zn nutrition of rice plants. The results showed that application of organic matter caused a decrease in the concentration of Zn in shoot and root of rice plants and helped in translocating the element from root to shoot. The per cent utilization of applied Zn by plants was also found to increase by the application of organic matter. The transformation of applied Zn in different fractions in soils showed that a major portion (53.6–72.6%) of it found its way to mineral fractions leaving only 1.0–3.3, 6.6–18.9, 11.0–21.6 and 2.3–8.8% of the applied amounts in water soluble plus exchangeable, organic complexed, amorphous sesquioxides and crystalline sesquioxides bound fractions respectively. Application of organic matter favoured such transformation of applied Zn into these fractions except the mineral and crystalline sesquioxides bound ones. Simple correlation and multiple regression analyses between applied Zn in different soil fractions and fertilizer Zn content in plants showed that organic matter application increased the predictability of fertilizer Zn content in plants which has been attributed to the higher per cent recovery of applied Zn in plant available fractions in soils in presence of added organic matter.     

Growth and dry-mass partitioning in tomato as affected by phosphorus nutrition and light

We studied the effects of phosphorus (P) and light on the physiological and morphological components of growth of young tomato plants (Lycopersicon esculentum Mill. cv. Capita). The importance of dry‐mass partitioning and starch accumulation in explaining the effects of P limitation on growth was examined more closely. Plants were grown at a wide range of exponential P supply rates (between 70 and 320 mg g^?1 d^?1) and one free‐access treatment (1 mm ). Two light levels (70 and 300 µmol m^?2 s^?1) were applied. Growth response coefficients (GRCs) were calculated to address the importance of different growth parameters in explaining relative growth rate (RGR). At both light levels, net assimilation rate (NAR) was more important than leaf area ratio (LAR) in explaining the effects of P on growth as indicated by GRCs. At less severe P limitation, LAR became more important and NAR less important. Dry‐mass partitioning to both roots and leaves played a minor role in determining the effects of P limitation on growth as indicated by low GRCs. The increase in starch at mild P limitation showed that the assimilate supply was not limiting. At severe P limitation, the rate of photosynthesis was decreased, as suggested by the decrease in starch accumulation.