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.     

Phosphorus release from cattle manure ash as soil amendment in laboratory-scale tests

ABSTRACT

Excessive application of animal manure to farmland leads to phosphorus (P) loss into the surrounding water. Manure is incinerated to convert it to P-rich ash as a slow-release P fertilizer. However, the potential P loss and P availability for plants from cattle manure ash (CMA) have not been fully understood. The aims of this study were to determine the P release mechanism from CMA and to propose appropriate application rates that mitigate P loss and increase available P to soil in Fukushima, where the soil is deficient in nutrients after the replacement of cesium-137-contaminated soil with sandy mountain soil. Different P fractions in CMA were sequentially extracted with H₂O, 0.5 M NaHCO₃, 0.1 M NaOH, and 1 M HCl. Phosphorus contents in different fractions of CMA were in the order of HCl–P > NaHCO₃–P > H₂O–P > NaOH–P. Water-soluble P release of CMA was also determined by kinetic experiments for 120 h. Results showed that total water-soluble P accounted for a maximum of 2.9% of total P in CMA over 120 h due to recalcitrant P compounds formed through incineration. The Fukushima sandy soil amended with CMA at three application rates, 94, 157, and 314 mg P kg^?1 (corresponding to 300, 500, 1000 kg P₂O₅ ha^?1) was incubated for 56 days. Cattle manure compost and KH₂PO₄ were applied at 157 mg P kg^?1 for comparison. Phosphorus release in water and CaCl₂ solution from ash-amended soil was significantly lower than those from compost and KH₂PO₄-amended soil at the same P application rate of 157 mg P kg^?1 (p < 0.05). Available P in ash-amended soil, determined by Fe-oxide impregnated strips, was not significantly different from those in compost-amended soil after day 7 and KH₂PO₄-amended soil on day 56 at the same P application rate. Thus, CMA reduces P losses from soil to the surrounding water while it increases P availability for plants. In comparison of different rates of CMA, P release in water or CaCl₂ was significantly greater at 314 mg P kg^?1 than at 94 or 157 mg P kg^?1, while the percentage of available P to total P was the lowest at the highest application rate (p < 0.05), suggesting that the best application rates were 94 and 157 mg P kg^?1 in this experiment.     

Wheat response to combined application of nitrogen and phosphorus in a saline sandy loam soil

Fertilization with nitrogen (N) or phosphorus (P) can improve plant growth in saline soils. This study was undertaken to determine wheat (Triticum aestivum L; cv Krichauff) response to the combined application of N and P fertilizers in the sandy loam under saline conditions. Salinity was induced using sodium (Na⁺) and calcium (Ca²⁺) salts to achieve four levels of electrical conductivity in the extract of the saturated soil paste (EC_e), 2.2, 6.7, 9.2 and 11.8?dS?m^?1, while maintaining a low sodium adsorption ratio (SAR; ≤1). Nitrogen was applied as Ca(NO₃)₂?·?4H₂O at 50 (N50), 100 (N100) and 200 (N200)?mg?N?kg^?1 soil. Phosphorus was applied at 0 (P0), 30 (P30) and 60 (P60)?mg?kg^?1?soil in the form of KH₂PO₄. Results showed that increasing soil salinity had no effect on shoot N or P concentrations, but increased shoot Na⁺ and chlorine ion (Cl^?) concentrations and reduced dry weights of shoot and root in all treatments of N and P. At each salinity and P level, increasing application of N reduced dry weight of shoot. At each salinity and N level P fertilization increased dry weights of shoot and root and shoot P concentration. Addition of greater than N50 contributed to the soil salinity limiting plant growth, but increasing P addition up to 60?mg?P?kg^?1 soil reduced Cl^? absorption and enhanced the plant salt tolerance and thus plant growth. The positive effect of the combined addition of N and P on wheat growth in the saline sandy loam is noticeable, but only to a certain level of soil salinity beyond which salinity effect is dominant.     

Eucalyptus growth and phosphorus nutritional efficiency as affected by soil compaction and phosphorus fertilization

ABSTRACT

Soil compaction interferes in soil nutrient transport and root growth. The aim of this work was to evaluate eucalypt growth and phosphorus (P) nutritional efficiency as affected by soil compaction and P rates. The treatments were composed of a 3 × 4 factorial scheme (soil bulk densities levels versus P fertilization rates) for two weathered tropical soils, a clayey Ferralsol (F_Clayey) and a sandy Ferralsol (F_Sandy). The soil bulk densities assessed were 0.90, 1.10 and 1.30 g cm^?3 for F_Clayey, and 1.35, 1.55 and 1.75 g cm^?3 for F_Sandy. The P rates were 0, 150, 300 and 600 mg kg^?1 for F_Clayey, and 0, 100, 200 and 400 mg kg^?1 for F_Sandy. Soil compaction reduced root growth, P content in the plant, P utilization efficiency and P recovery efficiency; and increased average root diameter. Phosphorus fertilization increased root length density, root surface area, dry matter, P content in the plant, P utilization efficiency and P uptake efficiency; and decreased P recovery efficiency. It was concluded that P fertilization is not effective to offset the deleterious effects of soil compaction on eucalypt growth and nutrition.

Abbreviations: F_Clayey: clayey Ferralsol; F_Sandy: sandy Ferralsol; R_Dens: root length density; R_Diam: root diameter; R_Surf: root surface area; R_DM: root dry matter; S_DM: shoot dry matter; WP_DM: whole-plant dry matter; R_P: root P content; S_P: shoot P content; WP_P: whole-plant P content; PU_tE: P utilization efficiency; PU_pE: P uptake efficiency; PRE: P recovery efficiency.     

Dairy manure treatment effects on manure phosphorus fractionation and changes in soil test phosphorus

In this research, a sequential fractionation procedure coupled with enzyme hydrolysis was used to categorize the phosphorus (P) forms of 18 manure samples collected from in-barn composted bedded pack (beef manure), anaerobic digestion with liquid–solid separation (dairy manure), and liquid–solid separation systems (dairy manure). This research also determined the effects of those P forms on the increase in soil test P (STP) of five soil series. The soils used had initial Bray-1 P ranging from 16 to 43 mg P kg^?1. Total dry-ash P (P_t) of the manures ranged from 1.4 to 15.0 g P kg^?1; total inorganic P (P_it) accounted for 20 to 81 % of P_t; and enzymatically hydrolysable P (P_et) accounted for 5 to 26 % of P_t. Liquid–solid separation tended to concentrate the manure P in the liquid fractions. In contrast, anaerobic digestion did not affect the manure P distribution compared with the undigested raw manure from the same system. No differences in P distribution were found for the compost bedded pack manure. In the soil incubation study, manure and fertilizer were applied at 40 mg total P kg^?1. Separated liquid manure from two systems tended to increase STP more than the separated solid manures from the same systems. Although anaerobic digestion modified some of the physical and chemical properties of the treated manures, it did not clearly impact how digested manure increased STP compared with the raw manures. Overall, the increase in STP after treated manure application was found to be a function of soil clay content and manure P_it?+?P_et applied.     

Phosphorus Nutrition of Upland Rice,Dry Bean,Soybean, and Corn Grown on an Oxisol

Rice, dry bean, corn, and soybean are important food crops. Phosphorus (P) deficiency is one of the most yield-limiting factors for these crops grown on highly weathered Brazilian Oxisols. Four greenhouse experiments were conducted to determine P requirements of these four crops. The P levels used were 0, 50, 100, 200, and 400 mg kg^?1. Growth, yield, and yield components evaluated of four crop species were significantly increased with the application of P fertilization. Most of the responses were quadratic in fashion when the P was applied in the range of 0 to 400 mg kg^?1. Maximum grain yield of upland rice was obtained with the application of 238 mg P kg^?1 of soil, maximum dry bean grain yield was obtained with the application of 227 mg P kg^?1 of soil, and maximum grain yield of soybean was obtained with the application of 224 mg P kg^?1 of soil. Maximum shoot growth of corn was obtained with the addition of 323 mg P kg^?1 of soil. Most of the growth and yield components had significant positive association with grain yield or shoot dry weight. Phosphorus concentration and uptake were greater in the grain compared to straw in upland rice and dry bean plants. Overall, P-use efficiencies decreased with increasing P rates.     

Efficiency of gypsum application to acid Andosols estimated using aluminum release rates and plant root growth

Abstract

A great deal of information on the efficiency of gypsum or phosphogypsum to ameliorate acidity in highly weathered soils is available, but only limited information is available on the efficiency in acid Andosols, which possess large amounts of active aluminum (Al). We examined the effectiveness of gypsum application to non-allophanic Andosols (one humus-rich A horizon and two B horizons poor in humus) using extractable soil Al analyses (batch and continuous extraction methods) and a cultivation test using burdock (Arctium lappa). With gypsum amendment, pH(H₂O) values of the soil decreased from 4.5–4.7 to 4.2–4.4, whereas the treatment made almost no difference to the values of pH(KCl). Total active Al (acid oxalate-extractable Al) was hardly affected by gypsum for all samples. Potassium chloride-extractable Al definitely decreased with the addition of gypsum in all soils; however, the decrease was small (0.1–1.4 cmol_c kg^?1) and the values still exceeded “the threshold of 2 cmol_c kg^?1” for inducing Al toxicity in sensitive plants (4.4–8.6 cmol_c Al kg^?1). The change in Al solubility with gypsum application represented by Al release rates from soils using continuous extraction methods with a dilute acetate buffer solution (10^?3 mol L^?1, pH 3.5) differed greatly among the soil samples: The release rate of one of the B horizon samples decreased by 71%, certainly showing the insolubilization of Al compounds, whereas the release rates of the A horizon sample showed almost no change. These changes in Al solubility were well correlated with the plant root growth. Root growth was improved with gypsum in the B horizon sample, whereas improvement was not observed in the A horizon soil. The decrease in the rate of Al release of another B horizon soil with gypsum treatment was smaller (by 20–34%), possibly because of lower pH values after gypsum application (pH[H₂O] of 4.2–4.3). In the B horizon soil, root growth improved only slightly. Thus, the effectiveness of gypsum application to acid Andosols appeared to be largely influenced by soil humus contents and slight differences in soil pH values, and corresponded to a decrease in Al release rates using the continuous extraction method.     

Contribution of Arbuscular Mycorrhizal and Saprobe Fungi to the Aluminum Resistance of Eucalyptus globulus

Aluminum in acidic conditions is toxic to plants. Aluminum tolerance in some plant species has been ascribed to arbuscular mycorrhizal fungal symbiosis. In this study, the application of aluminum was found to inhibit mycelia development of saprobe fungi Fusarium concolor and Trichoderma koningii and the hyphal length of the arbuscular mycorrhizal fungi Glomus mosseae and Glomus deserticola in vitro. Several levels of aluminum were applied to Eucalyptus globulus plants and inoculated with arbuscular mycorrhizal fungi alone or together with both saprobe fungi. The application of 1,500 mg kg^?1 decreased the shoot and root dry weight, chlorophyll content and total P, Mg, and Ca concentrations in the shoot of E. globulus. However, both mycorrhizal fungi G. mosseae and G. deserticola inoculated alone increased the shoot dry weight of Eucalyptus, compared with a non- arbuscular mycorrhizal inoculated control treated with 1,500 mg kg^?1 of aluminum. When 1,500 mg kg^?1 of aluminum was applied, T. koningii increased the effect of G. deserticola on the shoot weight of eucalyptus, whereas with 3,000 mg kg^?1, shoot weight and arbuscular mycorrhizal colonization decreased in all treatments. With 1,500 mg kg^?1, the highest accumulation of aluminum in the shoot was obtained when G. deserticola was inoculated together with T. koningii. The possibility of manipulating an arbuscular mycorrhizal inoculation together with a saprobe fungus confers a high aluminum resistance in E. globulus. The effect of such combined inoculation is particularly important in some Chilean volcanic acid soils, mainly those which have been intensively cropped and are without lime addition, which facilitates the increase of phytotoxic aluminum species and limits their agricultural use. Therefore, such dual inoculation in field conditions deserves further investigation. Overall, the arbuscular mycorrhizal and saprobe fungi contribute to the increase in resistance of E. globulus to aluminium.     

Maize Inbreds' Response to Riecito Phosphate Rock and Triple Superphosphate on an Acidic Soil

Abstract

Tropical acidic soils require large inputs of nitrogen (N) and phosphorus (P) fertilizers to sustain crop production. Attempts to use phosphate rock (PR) as a cheaper P source have shown limited success because of low rock solubility. The objective of this study was to evaluate growth and P nutrition of aluminum (Al)‐tolerant maize inbreds fertilized with PR. Twelve Al‐tolerant inbreds from CIMMYT were planted in 2‐kg pots filled with an acidic soil very low in available P and fertilized with 0, 40, or 100 mg kg^?1 of Riecito PR or triple superphosphate (SP). Plant shoots were harvested 35 days after planting, and biomass, root length, P uptake, and soil residual P were determined. Inbreds were able to sustain growth when fertilized with PR. There was indication that various mechanisms were involved in the responses to PR fertilization. Cultivars combining high uptake and conversion efficiencies should improve maize utilization of PR.     

Phosphorus Influx and Root‐Shoot Relations as Indicators of Phosphorus Efficiency of Different Crops

Abstract

The large variation in phosphorus acquisition efficiency of different crops provides opportunities for screening crop species that perform well on low phosphorus (P) soil. To explain the differences in P efficiency of winter maize (Zea mays L.), wheat (Triticum aestivum L.), and chickpea (Cicer arietinum L.), a green house pot experiment was conducted by using P‐deficient Typic ustochrept loamy sand soil (0.5 M NaHCO₃‐extractable P 4.9 mg kg^?1, pH 7.5, and organic carbon 2.7 g kg^?1) treated with 0, 30, and 60 mg P kg^?1 soil. Under P deficiency conditions, winter maize produced 76% of its maximum shoot dry weight (SDW) with 0.2% P in shoot, whereas chickpea and wheat produced about 30% of their maximum SDW with more than 0.25% P in shoot. Root length (RL) of winter maize, wheat, and chickpea were 83, 48, and 19% of their maximum RL, respectively. Considering relative shoot yield as a measure of efficiency, winter maize was more P efficient than wheat and chickpea. Winter maize had lower RL/SDW ratio than that of wheat, but it was more P efficient because it could maintain 2.2 times higher P influx even under P deficiency conditions. In addition, winter maize had low internal P requirement and 3.3 times higher shoot demand (i.e., higher amount of shoot produced per cm of root per second). Even though chickpea had 1.2 times higher P influx than winter maize, it was less P efficient because of few roots (i.e., less RL per unit SDW). Nutrient uptake model (NST 3.0) calculations satisfactorily predicted P influxes by all the three crops under sufficient P supply conditions (C_Li 48 µM), and the calculated values of P influx were 81–99% of the measured values. However, in no‐P treatment (C_Li 3.9 µM), under prediction of measured P influx indicated the importance of root exudates and/or mycorrhizae that increase P solubility in the rhizosphere. Sensitivity analysis showed that in low P soils, the initial soil solution P concentration (C_Li) was the most sensitive factor controlling P influx in all the three crops.     

Effect of cadmium toxicity on micronutrient concentration,uptake and partitioning in seven rice cultivars

Heavy metal uptake, translocation and partitioning differ greatly among plant cultivars and plant parts. A pot experiment was conducted to determine the effect of cadmium (Cd) levels (0, 45 and 90 mg kg^?1 soil) on dry matter yield, and concentration, uptake and translocation of Cd, Fe, Zn, Mn and Cu in seven rice cultivars. Application of 45 mg Cd kg^?1 soil decreased root and shoot dry weight. On average, shoot and root Cd concentrations and uptake increased in all cultivars, but micronutrients uptake decreased following the application of 45 mg Cd kg^?1. No significant differences were observed between 45 and 90 mg kg^?1 Cd levels. On average, Cd treatments resulted in a decrease in Zn, Fe and Mn concentrations in shoots and Zn, Cu and Mn concentrations in roots. Differences were observed in Cd and micronutrient concentrations and uptake among rice cultivars. Translocation factor, defined as the shoot/root concentration ratio indicated that Cu and Fe contents in roots were higher than in shoots. The Mn concentration was much higher in shoots. Zinc concentrations were almost similar in the two organs of rice at 0 and 45 mg Cd kg^?1. A higher Cd level, however, led to a decrease in the Zn concentration in shoots.     

Cadmium Uptake by Winter Wheat Seedlings in Response to Interactions Between Phosphorus and Zinc Supply in Soils

ABSTRACT

Effects of application of zinc (Zn) (0, 1, 5, 10 mg kg^?1 soil) and phosphorus (P) (0, 10, 50, 100 mg kg^?1 soil) on growth and cadmium (Cd) accumulations in shoots and roots of winter wheat (Triticum aestivum L.) seedlings were investigated in a pot experiment. All soils were supplied with a constant concentration of Cd (6 mg kg^?1 soil). Phosphorus application resulted in a pronounced increase in shoot and root biomass. Effects of Zn on plant growth were not as marked as those of P. High Zn (10 mg kg^?1) decreased the biomass of both shoots and roots; this result may be ascribed to Zn toxicity. Phosphorus and Zn showed complicated interactions in uptake by plants within the ranges of P and Zn levels used. Cadmium in shoots decreased significantly with increasing Zn (P < 0.001) except at P addition of 10 mg kg^?1. In contrast, root Cd concentrations increased significantly except at Zn addition of 5 mg kg^?1 (P < 0.001). These results indicated that Zn might inhibit Cd translocation from roots to shoots. Cadmium concentrations increased in shoots (P < 0.001) but decreased in roots (P < 0.001) with increasing P supply. The interactions between Zn and P had a significant effect on Cd accumulation in both shoots (p = 0.002) and roots (P < 0.001).     

Liming as an ameliorator of copper toxicity in black oat (Avena strigosa Schreb.)

This study aimed to assess the effect of liming as an ameliorator of copper (Cu) toxicity in black oats (Avena strigosa Schreb.) grown in soil with a sandy texture. The treatments were soil supplementation with increasing doses of lime (0.0, 0.5 and 1.0 g kg^?1) and two of Cu (0 and 50 mg kg^?1). Pre-germinated black oat seeds were sown for 30 days in the soil, subsequently, the plant height, root and shoot dry mass and concentration of total chlorophyll, chlorophylls a and b, carotenoids and total soluble carbohydrates and starch were analyzed. The dose of 50 mg kg^?1 soil Cu caused a toxic effect on black oat plant growth and development, affected the internal distribution of nutrients, decreased the leaf chlorophyll concentration and increased the leaf concentration of total soluble carbohydrates and starch. Increasing lime doses ameliorated the toxic effects of Cu.     

Assessing a suitable extractant and critical limits of nickel in soil and plant for predicting the response of barley (Hordeum vulgare L.) to nickel grown in Inceptisols

ABSTRACT

Nickel (Ni) is an essential element for plants. Abundant information exists on Ni toxicity in soil–plant system but not much is available on its critical level of deficiency (CLD) in soils and plants. Five chemical extractants were evaluated to find a suitable extractant for Ni in Inceptisol. Twenty-one soils having low to high levels of Ni were used to grow barley (Hordeum vulgare L). The amount of Ni extracted was correlated with Ni concentration and uptake by barley. The diethylene triamine penta acetic acid-calcium chloride (0.005 M DTPA-CaC1₂) was identified as the most promising soil extractant for Ni. The CLD of Ni for 0.005 M DTPA-CaC1₂ in soil was 0.22 mg kg^?1 whereas in barley plant it was 2.14 mg kg^?1. Application of 7.5 mg kg^?1 Ni in soil caused a significant increase in Ni concentration in the shoot of barley in all the soils irrespective of the initial Ni status.     

Inoculation of arbuscular mycorrhizal fungi can substantially reduce phosphate fertilizer application to Allium fistulosum L. and achieve marketable yield under field condition

The effects of inoculating arbuscular mycorrhizal (AM) fungi on the growth, phosphorus (P) uptake, and yield of Welsh onion (Allium fistulosum L.) were examined under the non-sterile field condition. Welsh onion was inoculated with the AM fungus, Glomus R-10, and grown in a glasshouse for 58?days. Non-inoculated plants were grown as control. Inoculated and non-inoculated seedlings were transplanted to a field with four available soil P levels (300, 600, 1,000, and 1,500?mg P₂O₅?kg^?1 soil) and grown for 109?days. AM fungus colonization, shoot P concentration, shoot dry weight, shoot length, and leaf sheath diameter were measured. Percentage AM fungus colonization of inoculated plants was 94% at transplant and ranged from 60% to 77% at harvest. Meanwhile, non-inoculated plants were colonized by indigenous AM fungi. Shoot length and leaf sheath diameter of inoculated plants were larger than those of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Shoot P content of inoculated plants was higher than that of non-inoculated plants grown in soil containing 300 and 600?mg P₂O₅?kg^?1 soil. Yield (shoot dry weight) was higher for non-inoculated plants grown in soil containing 1,000 and 1,500?mg P₂O₅?kg^?1 soil than for those grown in soil containing 300 and 600?mg?P₂O₅ kg^?1 soil. Meanwhile, the yields of inoculated plants (200?g plant^?1) grown in soils containing the four P levels were not significantly different. Yield of inoculated plants grown in soil containing 300?mg P₂O₅ kg^?1 soil was similar to that of non-inoculated plants grown in soil containing 1,000?mg P₂O₅?kg^?1 soil. The cost of AM fungal inoculum for inoculated plants was US$ 2,285?ha^?1 and lower than the cost of superphosphate (US$ 5,659?ha^?1) added to soil containing 1,000?mg P₂O₅ kg^?1 soil for non-inoculated plants. These results indicate that the inoculation of AM fungi can achieve marketable yield of A. fistulosum under the field condition with reduced application of P fertilizer.     

Effects of Source and Amount of Phosphorus on Sorption Kinetics in the Topsoil of a Highly Weathered Soil

Abstract

Soil chemical and physical reactions involving phosphorus (P) must be understood to predict the risk of P being transported from agricultural land to streams and lakes. The kinetics of P sorption by an Ultisols from West Virginia, USA, receiving P from fertilizers were compared to soils amended with turkey litter. Addition of 6.6 and 13.2 Mg turkey litter ha^?1 increased Bray 1P levels to about the same level as adding 53 and 115 kg P ha^?1, respectively. Phosphorus binding capacity decreased to a greater extent when P was added as fertilizer as compared to turkey litter. For example, P binding maximum was 360 mg P kg^?1 dry soil when soil was amended with 6.6 Mg turkey litter ha^?1 as compared to 260 mg P kg^?1 dry soil when amended with 53 kg P ha^?1. This study demonstrates that the decrease in P‐binding capacity with increasing soil P is less when P is added as turkey litter.     

Effect of nitrogen and phosphorus application on agricultural soil food webs

Aim of the present research is to investigate the effect of nitrogen (N) and phosphorus (P) on soil food webs (microbes, nematodes and microarthropods) trophic interactions in agriculture ecosystems. A complete randomized block design experiment of N and P fertilization was initiated in 2010 with four treatments: (1) P-addition, (2) N-addition, (3) NP-addition and (4) control. After 4 years of fertilization, compared with control, N-addition had a negative effect on microarthropods and clarify indirectly by significantly (P < 0.05) increasing soil total nitrogen (0.37 g kg^?1) and available nitrogen (20.03 mg kg^?1). The reduction in microarthropods resulted significant (P < 0.05) increase in bacterivores and fungivores feeding on bacteria and fungi, an example of top-down control. P-addition had indirect negative effects on microarthropods by means of significantly (P < 0.05) increasing soil total phosphorus (0.62 g kg^?1) and available phosphorus (24.17 mg kg^?1), aggravated fungivores feeding on fungi and strengthened top-down control. NP-addition significantly (P < 0.05) increased total microbial biomass, nematodes and microarthropods and resulted in bottom-up control. These results suggested that top-down effects were the dominant force in N- or P-addition treatments. NP-addition strengthened bottom-up control by enriching food resource. Unbalance fertilization could pose adverse on agricultural soil ecosystem and yield potential of crops.     

Combined Effect of Short-Term Water Deficit Stress and Aluminum Toxicity on Citrate Secretion from Soybean Roots

Abstract

In order to investigate the combined effect of drought stress and aluminum (Al) toxicity on citrate exudation in soybean, hydroponic cultivation with addition of Al and PEG-6000 was conducted to simulate Al-toxic dry soil. Results showed that 2-day exposure of soybeans to 5.5% (w/v) PEG-6000 or 100 µM AlCl₃ mainly hindered root growth, while combined exposure to PEG and Al (PEG/Al) reduced both root and shoot growth. Photosynthetic rate of first trifoliolate for the Al-tolerant genotype PI 416937 (PI) was not affected by imposition of 5.5% PEG/100 µM AlCl₃ (38–40 h), whereas photosynthetic rate for the Al-sensitive genotype YC was significantly reduced. Based on root fresh weight, Al-induced citrate exudation in the roots of soybean genotypes recovered from pre-treatment with 5.5 or 9% PEG was not altered, but was increased in the plants pretreated with 7% PEG without recovery. After 2 days of recovery from 2-day combined exposure to 5.5% PEG/100 µM AlCl₃, the Al-tolerant PI exuded more citrate than its control, but the Al-sensitive YC exuded significantly less citrate than its corresponding control. Split root experiment revealed that Al-induced citrate exudation in one half of the root system was significantly reduced by exposing the other half of the root system to 0.5 mM CaCl₂ solution containing 9% PEG or 9% PEG/50 µM AlCl₃. However, organic acid secretion was not observed in the half of the root system in the Ca solution when the other part of the root system was exposed to the Ca solution containing 50 µM AlCl₃, 9% PEG or 9% PEG/50 µM AlCl₃. This suggests that no Al- or drought-induced signals such as ABA are involved in the citrate secretion in soybean.     

Land Application of Aluminum Water Treatment Residual: Aluminum Phytoavailability and Forage Yield

Negative impacts of land‐applied aluminum (Al)–rich water treatment residuals (WTRs), which have been suggested to improve soil phosphorus (P) sorption, could include excessive immobilization of plant‐available P and Al phytotoxicity. We studied the impacts of an Al‐rich WTRs on agronomic returns and plant Al concentrations in glasshouse and field studies. The glasshouse study was a 4 × 2 × 3 factorial experiment with one control in a randomized complete block design and three replicates. Four sources of P were each applied at two agronomic rate [44 kg P ha^?1, P‐based rate; and 179 kg plant‐available nitrogen (PAN) ha^?1, N‐based rate] to topsoil (0–15 cm) of a sandy, siliceous, hyperthermic Arenic Alaquods. Three WTR rates (0, 10, and 25 g kg^?1 oven‐dry‐weight basis) were further applied, whereas the control received neither P source nor WTRs. Bahiagrass (Paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were continuously grown in succession for 18 months. Applied WTRs increased soil Al but not plant Al concentrations (22–80 mg Al kg^?1), which fell within the normal concentration range for pasture plants. In the glasshouse, when WTRs were incorporated with the soil, bahiagrass dry matter (DM) accumulation was reduced, but ryegrass DM was not affected even at 25 g kg^?1 WTR. A 2‐year field study, with same treatments but two rates of WTRs (0 and 10 g kg^?1 WTR) surface applied to established bahiagrass on the same soil type (Spodosols) showed neither reduced yields nor increased plant Al phytoavailability in the WTR treatments. The studies show no increase in plant Al is associated with Al‐WTRs applied to reduce excess soil‐soluble P and P losses but plant DM accumulation may be reduced.     

Differential Soil Acidity Tolerance of Tropical Legume Cover Crops

In tropical regions, soil acidity and low soil fertility are the most important yield‐limiting factors for sustainable crop production. Using legume cover crops as mulch is an important strategy not only to protect the soil loss from erosion but also to ameliorate soil fertility. Information is limited regarding tolerances of tropical legume cover crops to acid soils. A greenhouse experiment was conducted to determine the differential tolerance of 14 tropical legume cover crops to soil acidity. The acidity treatments were high (0 g lime kg^?1 soil), medium (3.3 g lime kg^?1 soil), and low (8.3 g lime kg^?1 soil). Shoot dry weight of cover crops were significantly affected by acidity treatments. Maximum shoot dry weight was produced at high acidity. Jack bean, black mucuna, and gray mucuna bean species were most tolerant to soil acidity, whereas Brazilian lucern and tropical kudzu were most susceptible to soil acidity. Overall, optimal soil acidity indices were pH 5.5, hydrogen (H)+ aluminum (Al) 6.8 cmol_c kg^?1, base saturation 25%, and acidity saturation 74.7%. Species with higher seed weight had higher tolerance to soil acidity than those with lower seed weight. Hence, seed weight was associated with acidity tolerance in tropical legume species.