Influence of Sampling Date on Soil Nitrogen Availability Indices

In spite of the great effort that has been devoted to the search for a chemical laboratory index to predict nitrogen (N) mineralization capability of soils, the results have not yet been fully satisfactory. A continued effort is still needed to increase the knowledge of the sources of variation that influence potentially available soil N. The time of sampling has received little attention, taking into account its potential to influence N-mineralization patterns. In this work, soil samples from three different agrosystems, consisting of a double-crop sequence of small grains and maize, an intensively grazed pasture, and a rainfed olive orchard, were collected at different dates. Several chemical extractions were performed, and the results were correlated with N uptake by turnip (Brassica campestris, L.) grown in a pot experiment. Kjeldahl N was the chemical test that best correlated (R ² = 0.621) with N uptake by turnip. Kjeldahl N showed great versatility relative to the origin of the soil samples. However, it was not very sensitive to the time of sampling. It did not detect changes occurring in the soil over a short period of time. Soil inorganic N showed the second highest coefficient of correlation (R ² = 0.483) with N uptake by turnip. In contrast to that observed with Kjeldahl N, soil inorganic N appeared as an index that can vary greatly over the short term. The hot saline potassium chloride (KCl) extractions gave generally fair results. The poorest, however, were obtained with the ultraviolet absorption of extracts of 0.01 mol L^?1 sodium bicarbonate (NaHCO₃) measured at 250- and 260-nm wavelengths.     

Change in Soil Microbial and Enzyme Activities in Response to the Addition of Rock-Phosphate-Enriched Compost

Phosphorus (P) is considered a nonrenewable resource that plays a key role in agriculture and such studies are needed to evaluate alternative sources of this element. In the current study, objectives were to evaluate soil microbial respiration and enzymatic activity resulting from the addition of rock-phosphate-enriched organic compost to soil under incubation conditions. An organic-mineral compost (OMC) was produced by aerobically composting a mixture of coffee grain trash (62%), bovine manure (7%), phosphate rock (28%), and gypsum (3%) for 3 months. Different amounts of OMC were added in a portion (100 g) of soil, and then this mixture was incubated for 28 days. After this time, soil microbial respiration (SMR), biochemical parameters, and available P were evaluated. The addition of OMC led to significant increase in SMR, dehydrogenase, fluorescein diacetate hydrolysis, β-glucosidase, and phosphatase activity, which were dependent on the added amounts of the compost. The values of available P in soil increased significantly (13 times) with the OMC addition when compared to the control.The assay showed that P-enriched OMC application impacted soil function and improved soil biochemical properties. These results suggest that this practice may be of great importance for soil fertilization.     

Nitrogen Availability Affects the Yield of Winter Wheat Subjected to Water Stress during Grain Filling

The effects of irrigation regimes (full irrigation and water-withholding at anthesis) and postanthesis nitrogen (N) supplies (LN, 0; MN 20; and HN, 40 kg N ha^?1) on grain yield and its components in winter wheat were studied, with attention to biomass gain by assimilation and its loss by respiration. Fully irrigated wheat responded to N fertilization with increased grain number (GN) and decreased grain weight (GW), whereas drought-stressed wheat responded with greater GN without significant changes in GW. Apparent whole-plant respiration (R_A) was not influenced by increased postanthesis N fertilizer. Thus, in drought-stressed wheat, the total biomass and stem reserves at maturity were increased by increasing N supply. These results suggest that high N supply at anthesis satisfied the grains’ increased demand for N by increasing postfloral assimilation, and the surplus assimilates not only compensated for the low-N-induced biomass loss by respiration but also may have increased the stem reserves.     

The determination of extractable plant available selenium from soils by electrothermal atomic absorption spectroscopy

Abstract

Plant available selenate was measured in a soil extract by electrothermal atomic absorption spectroscopy. Selenate in soil was first extracted with potassium sulfate then extracted into toluene fron an iodide‐sulfuric acid media. Aliquots of the toluene were injected into the graphite furnace for selenium determination. Quantities of extractable selenium measured using the electrothermal atomic absorption method compared favorably with the results of determinations using a fluorometric technique on aliquots of the soil extract. The simplicity of the procedure allowed for the precise determination of soil selenate in a brief period of time.     

Noncontinuous Development of Reducing Conditions in Wetland Soils

Abstract

Soil aeration status in relation to water table was analyzed by contour mapping in a forested wetland, an emergent marsh, and an irrigated rice field. Two soil aeration status indicators, oxygen (O₂) and redox potential (Eh), showed a significant correlation (P<0.01). Soil O₂ and Eh levels generally decreased with the water table rise in the forested wetland and marsh, but with a noncontinuous pattern. The results indicate that soil aeration status could be temporally improved at an optimum water table level, probably due to O₂ transport by wetland plants. The soil Eh in the rice fields clearly showed a seasonal pattern regardless of the water tables.     

新疆石灰性土壤锌有效性及其影响因素

为探讨新疆石灰性土壤锌的组分分布特征及锌有效性的影响因素,对南北疆3种最主要土壤类型农田土壤锌及其组分含量进行研究。结果表明:新疆石灰性土壤有效锌平均含量为潮土(0.69mg/kg)>棕漠土(0.57mg/kg)>灰漠土(0.51mg/kg),变异系数为灰漠土>潮土>棕漠土。在土壤锌组分中,松结有机态锌(WBO)、碳酸盐结合态锌(CARB)、氧化锰结合态锌(OxMn)、紧结有机态锌(SBO)、无定形铁结合态锌(AOFe)平均含量均为潮土>棕壤土>灰漠土。南北疆土壤锌背景值不同,南疆土壤全锌含量高于北疆土壤,而北疆土壤全锌变异较大。土壤碳酸钙含量和物理性粘粒含量与松结有机态、碳酸盐结合态、紧结有机态锌分配率高度相关。松结有机态锌、碳酸盐结合态锌及松结有机态锌分配率与土壤物理性粘粒含量呈(极)显著正相关。交换态锌与松结有机态锌呈显著正相关。松结有机态锌与碳酸盐结合态锌呈显著正相关。石灰性土壤有效锌含量与松结有机态锌、碳酸盐结合态锌含量呈显著正相关,可用方程Y=0.306+0.123WBO+0.116CARB(F=20.095,r2=0.801**)预测。     

Yield promotion and phosphorus solubilization by plant growth–promoting rhizobacteria in extensive wheat production in Turkey

Plant growth–promoting rhizobacteria (PGPR) have been reported to stimulate the growth and yield of grain crops, particularly when nutrient supply is poor. However, the mechanisms underlying stimulation of plant growth may vary depending not only on growth conditions and crop management but also on plant and bacterial species. The present study assessed the effect of an inoculation with single or multiple PGPR strains on phosphorus (P)‐solubilization processes in the soil and on grain yield in wheat. Single inoculation with Bacillus subtilis OSU‐142, Bacillus megaterium M3, or Azospirillum brasilense Sp245 increased grain yield by 24%, 19%, and 19%, respectively, while a mixed inoculation with OSU‐142, M3, and Sp245 increased grain yield by 33% relative to noninoculated plants. Single inoculations with Paenibacillus polymyxa RC05 or Bacillus megaterium RC07 were less effective. Single or mixed treatments with OSU‐142, M3, and Sp245 increased the concentrations of the labile and moderately labile P fractions in rhizosphere soil. The growth‐stimulating effect of OSU‐142, M3, and Sp245 was also reflected by higher P concentrations in most plant organs. Among all inocula tested, the highest plant P acquisition was obtained in the presence of M3 and accompanied by the highest microbial P levels and the highest phosphatase activities in the rhizosphere soil. In conclusion, seed inoculation with mixed PGPR strains may effectively substitute for a part of P‐fertilizer application in extensive wheat production, and in particular M3 appears to improve the solubilization of inorganic soil P.     

In vitro availability of iron from cereal meal with the addition of protein isolates and fenugreek leaves (Trigonella foenum-graecum)

In vitro iron availability was determined from a standard cereal meal (C) with and without the addition of protein isolates from bovine milk (BP), groundnut milk (GP) and soybean milk (SP). A second set of studies were done to investigate the potentially available iron from fenugreek leaves per se and the effect of their addition on the available iron from the cereal meal. The potentially available iron from the meal increased from 4.91% to 6.73% on the addition of BP. The next best enhancer was GP (4.91% to 6.17%). Although the addition of SP increased the total iron content of the cereal meal significantly, the percent available iron decreased compared to the other milk proteins. The addition of fenugreek leaves (100 g/meal) to the meal increased the total iron content of the meal significantly (3.24 mg to 9.12 mg) (p<.001), however, the available iron was observed to decrease (4.91% vs 4.34%).     

Effective use of a reservoir for paddy irrigation in tropical monsoon Asia—a case study of the Ngamoeyeik Project,Lower Myanmar

Irrigation projects with reservoirs have contributed to the stabilization of traditional rainfed rice and to the introduction of double-rice in monsoon Asia. This type of irrigation also has the capability of shifting the traditional rice-cropping season. This paper discusses the influences of the shifted cropping season on water resources and the effective use of the reservoir in the Ngamoeyeik Irrigation Project Area in Lower Myanmar. Synthesized streamflow data were applied to simulate water storage in the reservoir. The main results are as follows: (1) shifting the cropping season to avoid inundation problems can increase water availability, (2) the amount of evaporation loss in the reservoir water budget can be as high as 16%, which decreases water efficiency in the reservoir operation during the dry season, (3) a shifted cropping season is preferable under the special hydrological conditions found in Lower Myanmar.     

Effect of long-term changes in relative resource availability on dietary preference of grazing sheep for perennial ryegrass and white clover

Three replicate paddocks, each of 0·235 ha, containing adjacent monocultures of perennial ryegrass or white clover [50:50 by ground area, 6 cm sward surface height (SSH) at start of experiment] were continuously stocked with three yearling and four mature non-lactating, non-pregnant Scottish halfbred ewes for 12 weeks. Herbage intake, grazing behaviour and dietary selection were measured on seven occasions. Clover SSH declined rapidly over the first 5 weeks then stabilized at 1·2–1·6 cm, whereas perennial ryegrass SSH rose slightly initially, then declined gradually. Animals initially included proportionately c . 0·6 white clover in their diet but, by the end of the experiment, this had fallen to 0·3. Total daily herbage intake declined over the 12 weeks from 1·8 kg dry matter (DM) day^–1 at the start to 1·0 kg DM day^–1. Total grazing time increased from 561 min day^–1 to 649 min day^–1 at the end of the experiment. The results suggest that, despite overall herbage depletion and a greater depletion of white clover than perennial ryegrass as a result of the initial partial preference for white clover, the animals traded-off a reduced total intake and an increased grazing time in an attempt to maintain their initial preferred dietary composition.