Effects of the nitrification inhibitor nitrapyrin and the plant growth regulator gibberellic acid on yield-scale nitrous oxide emission in maize fields under hot climatic conditions

Nitrification inhibitors are widely used in agriculture to mitigate nitrous oxide(N₂O)emission and increase crop yield.However,no concrete information on their mitigation of N₂O emission is available under soil and environmental conditions as in Pakistan.A field experiment was established using a silt clay loam soil from Peshawar,Pakistan,to study the effect of urea applied in combination with a nitrification inhibitor,nitrapyrin(2-chloro-6-tri-chloromethyl pyridine),and/or a plant growth regulator,gibberellic acid(GA_3),on N₂O emission and the nitrogen(N)uptake efficiency of maize.The experimental design was a randomized complete block with five treatments in four replicates:control with no N(CK),urea(200 kg N ha^-1)alone,urea in combination with nitrapyrin(700 g ha^-1),urea in combination with GA_3(60 g ha^-1),and urea in combination with nitrapyrin and GA_3.The N₂O emission,yield,N response efficiency,and total N uptake were measured during the experimental period.The treatment with urea and nitrapyrin reduced total N₂O emission by 39%–43%and decreased yield-scaled N₂O emission by 47%–52%,relative to the treatment with urea alone.The maize plant biomass,grain yield,and total N uptake increased significantly by 23%,17%,and 15%,respectively,in the treatment with urea and nitrapyrin,relative to the treatment with urea alone,which was possibly due to N saving,lower N loss,and increased N uptake in the form of ammonium;they were further enhanced in the treatment with urea,nitrapyrin,and GA_3 by 27%,36%,and 25%,respectively,probably because of the stimulating effect of GA_3 on plant growth and development and the reduction in biotic and abiotic stresses.These results suggest that applying urea in combination with nitrapyrin and GA_3 has the potential to mitigate N₂O emission,improve N response efficiency,and increase maize yield.     

Nutrient cycling and greenhouse gas emissions from soil amended with biochar-manure mixtures

Integrating biochar into cattle diets has recently emerged as a potential management practice for improving on-farm productivity.Yet,information concerning the cycling of biochar-manure mixtures is scarce.A 70-d incubation experiment was conducted within two surface(0–15 cm)Mollisols with contrasting textures,i.e.,sandy clay loam(Raymond)and clayey(Lethbridge),to evaluate the effects of biochar(3 Mg ha^-1)on cumulative greenhouse gas(GHG)emissions and related fertility attributes in the presence or absence of cattle manure(120 Mg ha^-1).Five treatments were included:i)non-amended soil(control,CK),ii)soil amended with pinewood biochar(B),iii)soil amended with beef cattle manure(M)(manure from cattle on a control diet),iv)soil amended with biochar-manure(BM)(manure from cattle on a control diet,with pinewood biochar added at 20 g kg^-1of diet dry matter),and v)soil amended with B and M at the aforementioned rates(B+M).A total of 40 soil columns were prepared and incubated at 21℃and 60%–80%water-holding capacity.On average,total CO₂fluxes increased by 2.2-and 3.8-fold under manure treatments(i.e.,M,BM,and B+M),within Raymond and Lethbridge soils,respectively,relative to CK and B.Similarly,total CH4 fluxes were the highest(P<0.05)in Raymond soil under B+M and BM relative to CK and B,and in Lethbridge soil under M and BM relative to CK and B.In Lethbridge soil,application of BM increased cumulative N₂O emissions by 1.8-fold relative to CK.After 70-d incubation,amendment with BM increased(P<0.05)PO_4-P and NO_3-N+NH_4-N availability in Raymond and Lethbridge soils compared with B.A similar pattern was observed for water-extractable organic carbon in both soils,with BM augmenting(P<0.05)the occurrence of labile carbon over CK and B.It can be concluded that biochar,manure,and/or biochar-manure have contrasting short-term effects on the biogeochemistry of Mollisols.At relatively low application rates,biochar does not necessarily counterbalance manure-derived inputs.Although BM did not mitigate the flux of GHGs over M,biochar-manure has the potential to recycle soil nutrients in semiarid drylands.     

Nitrification inhibitor nitrapyrin does not affect yield-scaled nitrous oxide emissions in a tropical grassland

Urea is the most common nitrogen(N)fertilizer used in the tropics but it has the risk of high gaseous nitrogen(N)losses.Use of nitrification inhibitor has been suggested as a potential mitigation measure for gaseous N losses in N fertilizer-applied fields.In a field trial on a tropical Andosol pastureland in Costa Rica,gaseous emissions of ammonia(NH₃)and nitrous oxide(N₂O)and grass yield were quantified from plots treated with urea(U;41.7 kg N ha^-1application^-1)and urea plus the nitrification inhibitor nitrapyrin(U+NI;41.7 kg N ha^-1application^-1and 350 g of nitrapyrin for each 100 kg of N applied)and control plots(without U and NI)over a six-month period(rainy season).Volatilization of NH₃(August to November)in U(7.4%±1.3%of N applied)and U+NI(8.1%±0.9%of N applied)were not significantly different(P>0.05).Emissions of N₂O in U and U+NI from June to November were significantly different(P<0.05)only in October,when N₂O emission in U+NI was higher than that in U.Yield and crude protein production of grass were significantly higher(P<0.05)in U and U+NI than in the control plots,but they were not significantly different between U and U+NI.There was no significant difference in yield-scaled N₂O emission between U(0.31±0.10 g N kg^-1dry matter)and U+NI(0.47±0.10 g N kg^-1dry matter).The results suggest that nitrapyrin is not a viable mitigation option for gaseous N losses under typical N fertilizer application practices of pasturelands at the study site.     

A Hybrid Artificial Intelligence Model for Aeneolamia varia (Hemiptera: Cercopidae) Populations in Sugarcane Crops

Sugarcane spittlebugs are considered important pests in sugarcane crops ranging from the southeastern United States to northern Argentina. To evaluate the effects of climate variables on adult populations of Aeneolamia varia (Fabricius) (Hemiptera: Cercopidae), a 3-yr monitoring study was carried out in sugarcane fields at week-long intervals during the rainy season (May to November 2005–2007). The resulting data were analyzed using the univariate Forest-Genetic method. The best predictive model explained 75.8% variability in physiological damage threshold. It predicted that the main climatic factors influencing the adult population would be, in order of importance, evaporation; evapotranspiration by 0.5; evapotranspiration, cloudiness at 2:00 p.m.; average sunshine and relative humidity at 8:00 a.m. The optimization of the predictive model established that the lower and upper limits of the climatic variables produced a threshold in the population development rate of 184 to 267 adult insects under the agroecological conditions of the study area. These results provide a new perspective on decision-making in the preventive management of A. varia adults in sugarcane crops.     

Biomonitoring and Sourcing Toxic Elements Using Vascular Epiphytes of the Tillandsia Genus in the Mining Region of Taxco de Alarcón,Guerrero, Southern Mexico

Water, Air, &; Soil Pollution - The concentration of As, Pb, Cd, Zn, Fe, Mn, and Cu and the Sr and Pb isotopic compositions were determined in four species of the vascular epiphyte Tillandsia...     

Characterization of the Wx gene in diploid Aegilops species and its potential use in wheat breeding

Wx gene encodes for the granule-bound starch synthase I or waxy protein, which is the sole enzyme responsible for amylose synthesis in wheat seeds. The Aegilops species, which are related to wheat, could be important sources of variation in this gene. In addition to its role in starch quality, this gene has been used in phylogenetic studies of wheat. The current study evaluated the variability of Wx gene in seven diploid species of Aegilops genus and compared their nucleotide sequences with the wheat homeologous genes. Nineteen new Wx alleles were found in the seven species evaluated. The alleles detected in two species of the Sitopsis section, Ae. searsii and Ae. speltoides, were related to the Wx-B1 gene of wheat. Two more of the Sitopsis species did not appear to be associated with this genome, whereas the remaining species were related to the Wx-D1 gene of wheat. The results showed an important variation of the Wx gene present in the Aegilops genus, and the 19 new Wx alleles detected could enlarge the genetic pool of wheat.     

Genetic diversity assessment for Eugenia uniflora L., E. pyriformis Cambess., E. brasiliensis Lam. and E. francavilleana O. Berg neotropical tree species (Myrtaceae) with heterologous SSR markers

In this study, a set of nuclear microsatellite markers were transferred and characterized from two Myrtaceae sub-families to four neotropical Eugenia fruit tree species (E. uniflora L., E. pyriformis Cambess., E. brasiliensis Lam. and E. francavilleana O. Berg), which are neglected and underutilized foods of great ecological and potential economic value found in the Atlantic forest regions of South America. Leaf samples of mature E. uniflora, E. pyriformis, E. brasiliensis and E. francavilleana trees, which are popularly termed “pitanga”, “uvaia”, “grumixama” and “guamirim”, respectively, were collected from two areas greatly impacted by the agricultural practices of the sugar cane industry in the state of São Paulo in the southeastern region of Brazil. A total of 19 simple sequence repeat (SSR) markers from the Myrtaceae sub-families Leptospermoideae and Myrtoideae were tested, and 15 polymorphic heterologous SSR markers were identified. The expected heterozygosities for E. uniflora, E. pyriformis, E. brasiliensis and E. francavilleana were 0.64, 0.75, 0.54 and 0.71, respectively. These results suggest that these SSR markers may be useful for population genetic studies. A total of 4, 9, 11 and 4 heterologous SSR polymorphic markers for E. uniflora, E. pyriformis, E. brasiliensis and E. francavilleana, respectively, are now available for genetic diversity, gene flow and mating system analyses in these species.     

Connectivity of sediment transport in a semiarid environment: a synthesis for the Upper Jaguaribe Basin,Brazil

Purpose

Hydrosedimentological studies conducted in the semiarid Upper Jaguaribe Basin, Brazil, enabled the identification of the key processes controlling sediment connectivity at different spatial scales (10⁰–10⁴ km²).

Materials and methods

Water and sediment fluxes were assessed from discharge, sediment concentrations and reservoir siltation measurements. Additionally, mathematical modelling (WASA-SED model) was used to quantify water and sediment transfer within the watershed.

Results and discussion

Rainfall erosivity in the study area was moderate (4600 MJ mm ha^?1 h^?1 year^?1), whereas runoff depths (16–60 mm year^?1), and therefore the sediment transport capacity, were low. Consequently, ～60 % of the eroded sediment was deposited along the landscape, regardless of the spatial scale. The existing high-density reservoir network (contributing area of 6 km² per reservoir) also limits sediment propagation, retaining up to 47 % of the sediment at the large basin scale. The sediment delivery ratio (SDR) decreased with the spatial scale; on average, 41 % of the eroded sediment was yielded from the hillslopes, while for the whole 24,600-km² basin, the SDR was reduced to 1 % downstream of a large reservoir (1940-hm³ capacity).

Conclusions

Hydrological behaviour in the Upper Jaguaribe Basin represents a constraint on sediment propagation; low runoff depth is the main feature breaking sediment connectivity, which limits sediment transference from the hillslopes to the drainage system. Surface reservoirs are also important barriers, but their relative importance to sediment retention increases with scale, since larger contributing areas are more suitable for the construction of dams due to higher hydrological potential.