Calibration of Hargreaves-Samani Equation for Estimating Reference Evapotranspiration in Sub-Humid Region of Brazil

Reference evapotranspiration (ETo) is an important parameter used in numerous applications, such as climatological and hydrological studies, as well as for water resources planning and management. There are several methods to estimate ETo, being that the FAO Penman-Monteith (EToPM) method is considered standard. This method needs many parameters (solar radiation, air temperature, humidity and wind speed), however there are still many uncovered areas, suggesting the need for methods of calculating evapotranspiration based on few meteorological elements, such as air temperature. Therefore, this study aimed to determine the ETo by Hargreaves-Samani method in the experimental watershed of the “Riacho do Papagaio” farm, in county of Sao Joao, in north-eastern Brazil, using data of 2011 and 2012. Reference evapotranspiration estimated by non-calibrated Hargreaves-Samani method (EToHS) was overestimated in all months (RMSE = 1.43 mm·d-1), mainly in months of lower evaporative demand (from May to July). Because of these tendencies, this method cannot be used in its original form to estimate ET for this region;therefore, a calibration of radiation adjustment coefficient (kRs) was performed. The calibrated Hargreaves-Samani method (EToHSc) had better performance (RMSE = 0.52 mm·d-1), being suitable for predicting ETo in this region.

Maize Cannot Be Grown in Xiengkhouang Province?

During a 2005 visit with National Agricultural and Forestry Institute (NAFRI) Director, Dr. Kouang Doungsila issued a challenge to these authors to determine if it was true that crops could not be grown in the extensive uplands of Xiengkhouang Province, Laos PDR. In response, a two-phase series of experiments was proposed and implemented. The Phase I experiment was to bring soil from the Xiengkhouang province uplands to a NAFRI greenhouse near Vientiane to assess possible nutrient requirements using a nutrient omission experiment. Simultaneously, soils were collected and analyzed from seven recognized agricultural regions of Laos. The initial Vientiane greenhouse experiment indicated that maize did grow, but there were multiple issues of extreme soil acidity and clear deficiencies of phosphorus and other nutrients. Phase II of the study included field studies on the site of soil selected for the greenhouse study. Field experiments were carried out for two years at the site with yields of maize exceeding 5500 kg⋅ha−1 in the first year and exceeding 6250 kg⋅ha−1 in a subsequent year. Intense symptoms of nutrient zinc (Zn) deficiency were observed, however. In 2008 another experiment was designed and carried out that included a Zn variable. The results from that experiment confirmed that maize yields nearing 6000 kg⋅ha−1 were indeed possible. Substantial amounts of lime were needed to correct the strong soil acidity, and a series of other nutrients including N, P, K, and Zn were also required. Ongoing issues are where to obtain the extensive amounts of limestone needed as well as an evaluation of the residual effect of the limestone The finely ground, very reactive burnt lime residual effect was, as expected, short-lived. The results clearly demonstrated that, indeed, it was possible for maize to be produced in the extensive uplands of Xiengkhouang province, in answer to Director Khouang’s challenging question.

Effects of Biochars and Other Organic Soil Amendments on Plant Nutrient Availability in an Ustoxic Quartzipsamment

A sandy soil, Nampong soil(classified as Ustoxic Quartzipsamment), was incubated under controlled condition i) to compare the mineralization of major plant nutrients derived from different types of biochars and other organic soil amendments; ii) to examine their effects on soil properties and plant nutrient availability; and iii) to evaluate the plant nutrient losses in leachate from the rooting zone of soil incorporated with the different amendments. The experiment was arranged in a completely randomized design with 3 replications.Five treatments of soil amendments used were cassava stem base biochar(CSB), rice husk biochar(RHB), chicken manure(CM),compost(CP), and no amendment application(control). The RHB treatment released the highest amounts of mineralized NO-3-N,available P and K(2.30–17.26, 5.50–42.90 and 43.00–187.63 mg kg-1, respectively) while the CM treatment releasing the highest NH+4-N in the range of 1.86–53.67 mg kg-1. The CSB and RHB treatments showed better continuity of mineralization of nutrients than the treatments of CM and CP, particularly in the case of the CSB treatment. In the soil column incubation experiment, the amounts of NH+4-N and NO-3-N in all treatments barely changed on Day 1 to Day 30 of incubation and then the amounts increased markedly on Day 60. On Day 60, the RHB treatment contained a very high amount of NO-3-N(> 250 mg kg-1). This suggests that N would become more available 30 d after the incorporation. The CM treatment gave the highest amounts of organic matter and available P in the ranges of 4.64–8.94 g kg-1and 14.41–36.33 mg kg-1, respectively, during the 60-d column incubation. The CSB treatment tended to have higher available K throughout the measuring period. The NO-3-N was leached from the soil column quite quickly on Day 1 of incubation while the loss of NH+4-N decreased slightly from Day 1 until the end of the measurement. The amounts of P and K losses varied with the type of soil amendments, and the pattern of the loss was irregular.

Silicate minerals control the potential uses of phosphorus-laden mineral-engineered biochar as phosphorus fertilizers

Silicate minerals constitute the main components in silicon(Si)-rich biomass,affecting the phosphorus(P)adsorption and release competencies of mineral-engineered biochar;however,the mechanisms underlying their differences remain largely unresolved.To examine these interactions,we investigated the mineralogical compositions and quantified the P-adsorption capacities of Al-,Fe-,Mn-,Zn-,and Mg-engineered biochars from Si-rich rice husk material.The potential uses of P-laden mineral-engineered biochar for P fertilizers were assessed using citric acid extraction.The results from X-ray diffraction,scanning electron microscopy,and Fourier transform infrared spectrometry revealed that mixed metal(oxyhydr)oxides and metal-silicate compounds precipitated in the biochar structure and acted as the main P adsorbents.Micro-crystalline silicates derived from the biomass-induced metal-silicate precipitates in all engineered biochars,which effectively retained the aqueous P with varying excellent capacities(25.6-46.5 mg/g)but relatively slow kinetics(48 h).The suitability of the Zn-,Mg-,Mn-,and Fe-biochars as P-recycled fertilizers was confirmed by the high amounts of citric acid extractable P(19-69%of the total P).Varying amounts of Zn,Mg,and Mn(34-47%of the total host metals)were also released from the engineered biochar through ligand-promoted dissolution.Our data shed light on the novel potential utilization of Mn-,Mg-and Zn-biochars from Si-rich biomass for P retrieval and their use for P,Mg,and micronutrient(Mn and Zn)fertilizers.Regarding the P removal capacity,the mineral-engineered biochar needed a longer adsorption period than conventional metal-engineered biochar.

The effect of reforestation on stream flow in Upper Nan river basin using Soil and Water Assessment Tool(SWAT)model

Forests are an important natural resource,vital to all life.Forests are an important source of food,clothing,and medicines,as well as a place to live.Water released from forests drains into the soil causing groundwater to emerge as stream flow throughout the year.In Thailand,most forests have been encroached by logging,paper production,and housing construction.Population growth and the need for farming area for crop and livestock production have also caused forest encroachment.Technical tools are needed to support the decision makers and planners if they are to achieve objectives of water conservation,and development.These technical tools are needed for assistance in the engineering,socio-economic,and environmental planning.The Soil and Water Assessment Tool(SWAT)was used in the hydrological modeling in this study of the complex and dynamic problems of The Upper Nan river basin.This was a case study to evaluate the impact of changing conditions in the river basin affected by the stream flow due to reforestation.The watershed area was delineated into 5 sub-watersheds based on surface topography provided by the Digital Elevation Model(DEM)and the parameters of each of these watersheds were calculated.The land use data was processed and reclassified to match with the SWAT model land use code.Ten different categories of land use in the study area were used for SWAT processing.Types of land use consist of:mixed forest(33.7%),disturbed forest(30.2%),evergreen forest(17.7%),paddy field(7.1%),orchard(3.7%),range brush(2.7%),field crop(1.7%),planted forest(1.7%),urban(1.4%)and water resources(0.4%).Twenty-two types of soil were found in the basin.The initial curve number values were assigned based on the land use type and soil hydrologic group for the average antecedent moisture condition of the curve number method.The potential evapotranspiration was computed using the Penman-Monteith method.The simulation was performed using three reforestation scenarios to assess stream flow:(1)improved disturbed forest,(2)field crops and range grass,and(3)both disturbed forest and field crops.The results of reforestation from scenarios 1 and 3 can increase stream flow in the drought season and can also reduce the flow in the wet season in the main stream and its tributaries.For scenario 2 Reforestation had no significant effect on the main stream.