Effects of temperature,algae biomass and ambient nutrient on the absorption of dissolved nitrogen and phosphate by Rhodophyte Gracilaria asiatica

Gracilaria asiatica, being highly efficient in nutrient absorption, is cultivated in sea cucumber ponds to remove nutrients such as nitrogen and phosphate. It was cultured in a laboratory simulating field conditions, and its nutrient absorption was measured to evaluate effects of environmental conditions. Ammonia nitrogen （AN）, nitrate nitrogen （NN）, total inorganic nitrogen （TIN）, and soluble reactive phosphorus （SRP） uptake rate and removal efficiency were determined in a 4~2 factorial design experiment in water temperatures （T） at 15~C and 25~C, algae biomass （AB） at 0.5 g/L and 1.0 g/L, total inorganic nitrogen （TIN） at 30 ~tmol/L and 60 ~tmol/L, and soluble reactive phosphorus （SRP） at 3 and 6 ~tmol/L. AB and ambient TIN or SRP levels significantly affected uptake rate and removal efficiency of AN, NN, TIN, and SRP （P〈0.001）. G. asiatica in AB of 0.5 g/L showed higher uptake rate and lower removal efficiency relative to that with AB of 1.0 g/L. Nitrogen and phosphorus uptake rate rose with increasing ambient nutrient concentrations; nutrient removal efficiency decreased at higher environmental nutrient concentrations. The algae preferred to absorb AN to NN. Uptake rates of AN, NN, and SRP were significantly affected by temperature （P〈0.001）; uptake rate was higher for the 25~C group than for the 15~C group at the initial experiment stage. Only the removal efficiency of AN and SRP showed a significant difference between the two temperature groups （P〈0.01）. The four factors had significant interactive effects on absorption of N and P, implying that G. asiatica has great bioremedial potential in sea cucumber culture ponds.

Association of Organic and Mineral Fertilization on Crop Yield and Theoretical Cachaqa in Sugarcane

We evaluated several organic fertilizers associated or not to mineral fertilizers, in the cane yield and theoretical sugarcane brandy in plant cane. The experimental design was randomized blocks, with nine treatments and four replications, constituted of： TI： Liming （ 1 ） ＋ reactive rock phosphate （2） ＋ chemical fertilizer （3）; T2：2 ＋ 3; T3：1 ＋ 3 （control）; T4：1 ＋ 2 ＋ 3 ＋ cattle manure （4）; T5： 1 ＋ 2 ＋ 4; T6：1 ＋ 2 ＋ 3 ＋ chicken manure （5）; T7：1 ＋ 2 ＋ 5; T8：1 ＋ 2 ＋ 3 ＋ cane bagasse （6）; T9：1 ＋ 2 ＋ 6. It was applied the fertilizers in the following doses： cattle manure, 30 t hal; chicken manure, 3.5 t hal; cane bagasse, 24 t ha-1; reactive rock phosphate, 400 kg ha-1 and 120 kg ha-1 of K20 and P205, in the planting furrow. The limestone was distributed in the dose of 2.5 t ha-1 The variety was used SP 79-1011. The cattle manure substituted the chemical fertilization of plant cane. The cane bagasse, when used as organic source should always be complemented with the chemical fertilization; there were no effect of treatments in the principal technological characteristics of the cane.

Organomineral Phosphorus Fertilization in the Production of Corn,Soybean and Bean Cultivated in Succession

The use of organic waste in agriculture has been used aiming at greater productivity, decrease in the cost of production and sustainable use of resources. The present study aimed at evaluating the effect of phosphate fertilization with the maintenance of organomineral fertilizers, combining poultry manure and soluble or reactive phosphate, in the production of grains in corn culture and the residual effect for subsequent crops of beans and soybeans. The experiment was conducted in Sete Lagoas, MG, in 2015, using three fertilizers with sources of different phosphorus sources (triple super phosphate—STP, organomineral with STP and organomineral with Bayovar phosphate) applied at the doses of 65, 130, 195 and 260 kg·ha¯1 of P2O5 total, and compared to the control without phosphate fertilization. We evaluated the contents of foliar P, P accumulation in the grains, yields of corn grains, beans and soy, accumulated productivity and export of accumulated P of the three cultures. The three cultures assessed presented higher productivity when compared to the average of the factorial treatments that received phosphate fertilization relative to the control. Organomineral fertilizers increased grain production, obtaining average productivity equal to or greater than those obtained with the exclusive use of STP.

Investigation of potential interferences on the measurement of dissolved reactive phosphate using zirconium oxide-based DGT technique

A diffusive gradients in thin films （DGT） technique based on hydrous zirconium oxide （Zr-oxide） has been recently developed for the measurement of dissolved reactive phosphate （DRP）. In this study, the detailed performance of the DGT technique is reported. Spiking experiments revealed that several orthophosphate monoester compounds contributed to the Zr-oxide DGT measurements of DRP. However, such a phenomenon is unlikely to occur during field conditions due to the low concentration of organic P in typical natural waters. The presence of Cl- （up to 106 g/L）, SO42- （up to 16 g/L）, HCO3- （up to 817 g/L）, and AsO2- and AsO 3 4 （both up to 1 mg As/L） in solutions had negligible effects on the measurement of DRP. The threshold concentrations of Cl-, SO42- and HCO3- have been increased from previous reports for the measurements of DRP using other adsorbent-based DGT techniques. The capacity for DGT measurements of DRP decreased with increasing solution pH （4.2-9.2）. The lowest capacity （95 μg P/m2 at pH 9.2） was still greater than that of other DGT techniques that are usually used for the measurement of DRP （2-12 μg P/cm2 ）. The Zr-oxide binding gel could be stored for up to 2 years without any aging effect. This period of validity was considerably longer than the ferrihydrite binding gel that is commonly used in present DGT devices （6 months）. The field application revealed that the concentrations of DRP measured in three fresh water samples using the Zr-oxide DGT technique were in agreement with those of the traditional colorimetric method.

Simulation on phosphorus release characteristics of Poyang Lake sediments under variable water levels and velocities

Since the construction of the Three Gorges Dam, the Poyang Lake hydrological characteristics obviously changed. During the impoundment period of the Three Gorges Reservoir, the hydrodynamic factors of Poyang Lake varied. Water level dropped, the velocity decreased and water exchange time lengthened, which changed the release of phosphorous from sediments. In order to investigate how the hydrodynamic factors influence the release of phosphorous from sediments, we used a two-way annular flume device to simulate the release characteristics of phosphorous from sediments under variable water levels and velocities. We found that both water level rising and velocity increasing could enhance the distur- bance intensity to sediments, which caused the increase of suspended solids （SS） concentration, total phosphorus （TP） concentration in the overlying water, and the ability that phosphorus released to overlying water from sediments enhanced as well： when overlying water velocity maintained 0.3 m/s, SS concentration increased to 4035.85 mg/L at the water level 25 cm which was about 25 times compared to the minimum value and TP concentration in the overlying water also reached the maximum value at the water level 25 cm which was 1.2 times that of the value at 10 cm; when water level maintained 15 cm, SS concentration increased to 4363.35 mg/L at the velocity of 0.5 m/s which was about 28 times compared to the value of 0 m/s, and TP concentration in the overlying water increased from 0.11 mg/L to 0.44 mg/L. When the water level maintained 15 cm, the phosphorous release rate reached the maximum value of 4,86 mg/（md） at 0.4 m/s. The concentration of total dissolved phosphorous （TDP） and soluble reactive phosphate （SRP） both in overlying water and sediment-water interface were negatively correlated with pH. Using the parabolic equation, the optimum water level at a velocity of 0.3 m/s was calculated to be 0.57 cm, and the optimum velocity at water level of 15 cm was found to be 0.2 m/s.