Humid Subtropical Environment Research Articles

Intra-annual dynamic of opposite and compression wood formation of Pinus massoniana Lamb. in humid subtropical China

Radial growth of trees can result in opposite wood (OW) and compression wood (CW) due to the varying impact of stem mechanical stress, such as that caused by gravity or wind. Previous research has identified higher xylem production in CW compared to OW. Yet, it remains unclear whether the difference in the number of xylem cells between OW and CW results from differences in growth rate or the duration of xylem cells. In this study, we collected wood microcores on a weekly basis from March 2019 to January 2020 in Pinus massoniana Lamb. located on a steep slope. Our objective was to compare the dynamic of cambial activity and resulting cellular anatomical parameters between OW and CW in a humid subtropical environment. Our results showed that the xylem phenology of OW and CW was generally consistent with the xylem cell division process beginning in early March and ceasing in November. The last latewood cell completed its differentiation at the end of December. The response of wood formation dynamics to climate was consistent in both OW and CW. Moreover, both wood types exhibited a limited development of the enlargement phase due to the heat and drought during the summer. The rate of cell division was responsible for 90.7% of the variability in the number of xylem cells. The CW xylem obtained a larger number of cells by increasing the rate of cell division and displayed thinner earlywood cells with larger lumens than OW cells. Our findings showed that the xylem of conifer species responds to mechanical stress by accelerating the cell division rate. As a result, we suggest calculating the ratio between OW and CW widths to reconstruct wind stress changes rather than calculating the residuals used in the current study.

Analysis of mathematical models to estimate erosivity

The main cause of soil degradation in humid tropical and subtropical environments is water erosion, characterized by being the most important in Brazil. The main factors that determine soil losses by water erosion are erosivity, erodibility, topography, soil use and management and conservationist practices. Proper conservation planning requires knowledge of the factors that influence local erosion. The quantification of soil losses due to water erosion helps to define management techniques and conservation practices appropriate for each province. The municipality of Rio Largo - AL, is located in the metropolitan region of Maceió, within the physiographic region of the Coastal Tablelands. The objective of this work was to determine the erosivity of rainfall for the municipality of Rio Largo - AL, through rainfall data from 1963 to 2015. These data were tabulated to calculate rainfall, coefficient and its relationship with erosivity using six equations. The average annual rainfall calculated was 1800 mm for the observation period of 52 years, showing a wide variation in rainfall distribution, with the rainy season concentrated in the months of April to August. The computed average annual erosivity index was 3761 MJ mm ha-1 h-1 year-1, ranging from 312 to 7211 MJ mm ha-1 h-1 year-1. The months of May, June and July correspond to the most critical period in relation to the erosive potential of the rains and the months of October, November and December are the least critical.

Parametric calibration of Hargreaves–Samani (HS) reference evapotranspiration equation with different coefficient combinations under the humid environment

Evapotranspiration (ET) is a major hydrological component in irrigation system design, irrigation scheduling, and hydrologic and drainage design. Estimating crop ET requires accurate reference evapotranspiration (ET0) measurement. In this work, numerous modified Hargreaves models for ET0 were tested and calibrated against the standard FAO-56 Penman-Monteith eq. (F-56 PM) for further improvement in performance in the humid subtropical environment of Imphal West District, Manipur.The Martinez-Cob and Tejero-Juste (2004) equation resulted in best region-wide ET0 values of 3.536 mm d−1, mean absolute error (MAE) = 0.367 mm d−1, standard error of estimate (SEE) = 0.348 mm d−1, correlation coefficient (r) = 0.855, coefficient of determination (R2) =0.731, and index of agreement (d) = 0.891. Trajkovic (2007) equation has the second-best ET0 values of 3.383, MAE = 0.413 mm d−1, SEE = 0.3.77 mm d−1, r = 0.827, R2 = 0.685, and d = 0.852. The third-best equation, Ravazzani et al. (2012), with average ET0 values of 4.015 mm d−1, MAE = 0.506 mm d−1, SEE = 0.395 mm d−1, r = 0.855, R2 = 0.731, and d = 0.79.The observed wind speed data were sorted into five groups based on the average wind speed in different months in the region (1 m/s,2.5 m/s, 3.5 m/s, 4.5 m/s, and 5.5 m/s), and the estimated evapotranspiration was used to calibrate 14 selected combinations of the Hargreaves models. The calibration process significantly improved the performance of the different identified Hargreaves models.The analysis indicated that the improvement in estimation decreases with increasing wind speed. The revised coefficient predicted evapotranspiration is closer to F-56PM, with MAE (mm d−1) ranging from 0.125 at 1 m/s to 0.248 at 4.5 m/s and SEE(mm d−1) from 0.16 at 1 m/s to 0.245 at 5.5 m/s, as compared to the original Hargreaves equation, whose MAE is 0.543, and SEE is 0.400.More research must be conducted to extend the applicability of this equation to other regions of the State.

Evaluating geostatistical methods along with semi-destructive analysis for forensic provenancing organic-rich soils in humid subtropical climate

When no samples are available for direct comparisons during a criminal investigation, forensic scientists must resort to georeferenced soil databases in order to find the source of a single questioned evidence. To this end, several authors addressed many methods to infer the origin of soil samples, such as establishing search range intervals or defining statistical similarities. However, little is currently known about the efficiency of these methods when it comes to organic-rich and deep weathered subtropical soils. Therefore, this study attempts to contribute to this subject by evaluating the predictability of a soil database built in a 100 km² area in the Curitiba Metropolitan Region, Brazil, where 232 topsoil (<5 cm), 14 validation, and 38 subsoil samples (B horizon) were collected. To determine their physical, chemical, and colorimetric features, samples were subjected to magnetic susceptibility analysis, gamma-ray spectrometry, color analysis, pXRF, and ATR-FTIR. Two prediction methods were selected: search range intervals (SR) and n-dimensional Euclidean distances (ED). After the descriptive and multivariate statistical analyses, geostatistical models were generated for the 28 obtained variables using the empirical Bayesian kriging (EBK) with regression prediction method, where geological and airborne geophysical data were used as explanatory matrix. For the ED provenancing method, dissimilarity values were calculated and interpolated by applying the inverse distance weighting (IDW) approach. Findings, while preliminary, suggest that magnetic susceptibility, lightness, Fe, Mn, Cu, Ni, and the light elements group (LE) may be the most significant variables to discriminate parent rock and to correlate with subsurface data. The SR method managed to correctly predict the origin of 4 of 14 validation samples, reducing up to 97.5% of the original area. The ED method, on the other hand, accurately estimated the provenance of 8 out of 14 samples, excluding up to 63.4% of the area. Despite the limitations and errors inherent to semi-destructive analyses, the moderate chemical weathering, and the high organic matter content, overall soil provenancing results were suitable, demonstrating that spatial variability of topsoils developed under humid subtropical environments can be modeled and used in forensic contexts, as long as the right methods are applied.

Crop and water productivity and profitability of broccoli (Brassica oleracea L. var. italica) under gravity drip irrigation with mulching condition in a humid sub-tropical climate.

Strategic irrigation planning and soil water conservation measure can be rewarding for increasing agricultural productivity in a humid subtropical climatic environment. Field experiments were conducted to evaluate broccoli yield response to crop water productivity (CWP), irrigation water productivity (IWP) and economics under varied irrigation regimes and mulching. Four levels of irrigation: surface irrigation at 1.0 IW/CPE (irrigation water to cumulative pan evaporation, I1), drip irrigation at 0.6 (I2), 0.8 (I3) and 1.0 (I4) of crop evapotranspiration (ETc) and three mulches: none (M0), black polythene mulch (BPM, M1) and paddy straw mulch (PSM, M2) were examined. Among these treatments I3M1 produced the higher yield (19.17 t ha-1), CWP, IWP and maximum benefit-cost ratio (BCR), being almost competitive with I3M1. Under scarcity of water, I2M1 was an alternative. Drip irrigation could save 21.2–52.7% water over surface irrigation which accommodated 17.1 to 53.3% additional area under irrigation. Yield response factor and water-yield production function suggested the potential yield decrease in relation to increased deficit irrigation. However, a deficit drip irrigation scheduling with 0.8 ETc at a 3-day interval is optimum for increased curd yield, water productivity and economics of broccoli.

Organic soil fertility amendments enhance surface-dwelling beetle diversity in a sub-humid tropical environment under conservation agriculture

ABSTRACT Surface-dwelling beetles offer ecosystem services in agro-ecosystems including biological pest control and organic matter decomposition. This study was conducted to investigate beetle community response to six years of tillage, crop residue application, crop rotation and soil fertility amendments (low fertiliser, high fertiliser, manure, manure + low fertiliser and manure + 60 kg N ha−1) treatments. Reduced tillage increased beetle abundance by 4.6% relative to soil inversion tillage. Crop residue application increased the abundances of Platynus assimilis, Zophosis boei and total beetles by two to three times. Meanwhile, Renatiella reticulata increased by 628.6% in high fertiliser compared to manure + 60 kg N ha−1, manure + low fertiliser and the control. In crop rotation + crop residue retention plots, application of sole manure at 10 t ha−1 increased the Shannon index by 360–365% relative to manure + 60 kg N ha−1 and manure + low fertiliser. Based on the findings in this study, it can be concluded that reduced tillage, retention of crop residues on the soil surface and application of manure increase surface-dwelling beetle abundance and diversity.

Composição de elementos maiores de rochas fonte, solos e sedimentos derivados de rochas graníticas em clima subtropical úmido: contribuição aos estudos de proveniência sedimentar

O estudo dos processos sedimentares e da modificação da composição detrítica entre rocha, solo e sedimento é fundamental para compreender o fracionamento composicional nos primeiros estágios do ciclo sedimentar. Estudos em ambientes atuais são necessários para desvendar a inter-relação complexa entre os processos que geram todo o espectro composicional dos sedimentos detríticos. Neste trabalho, a influência dos processos sedimentares na composição dos sedimentos foi avaliada utilizando-se amostras de rochas fonte, solos e sedimentos detríticos em uma bacia hidrográfica na qual rochas graníticas estão expostas em clima subtropical úmido. As amostras foram separadas em oito intervalos granulométricos de seixo a lama. A composição geoquímica dessas amostras foi analisada por Inductively Coupled Emission Optical Spectroscopy — ICP-EOS. A relação entre a composição química e o tamanho de grão foi analisada por métodos estatísticos utilizando-se diagramas, gráficos de dispersão, análise dos componentes principais e avaliação da estrutura de covariância via análise biplot. Os resultados demonstram o controle do tamanho de grão na composição dos solos e sedimentos e têm implicação no entendimento da influência do intemperismo e do transporte no fracionamento geoquímico. A análise da relação entre a composição de rocha, solo e sedimento em ambientes atuais contribui para a construção e tem potencial para a construção de modelos quantitativos que permitam determinar o efeito dos processos sedimentares na composição das rochas siliciclásticas.

Diverse responses of vegetation to hydroclimate across temporal scales in a humid subtropical region

Study regionGuangdong Province, South China. Study focusWith evident climate and land use changes, concerns have arisen regarding the challenges for land and water management brought by alterations of the vegetation-hydroclimate relationships. Here we characterized the relationships under contrasting dryness conditions in Guangdong province of China during 2002–2015 based on multiple datasets, with a focus on forests and crops, to identify the controlling roles of water and energy in vegetation growth. New hydrological insightsAn increasing trend of annual vegetation and water availability, and diverse seasonal characteristics were revealed in dry and wet years. GPP was higher while NDVI and WUE were lower in dry years than wet years. Intra-annual NDVI and GPP were positively and WUE was negatively related to both water (TWS) and energy (ETp, Ta and Rs) factors. Linear regression shows that the correlation between TWSA and NDVI/GPP was stronger than that between atmospheric factors and NDVI/GPP at the annual scale, while the impact of the atmospheric factors on NDVI/GPP was stronger at the monthly scale. That is, water plays a dominant role in vegetation growth in the long term, while energy is more important in the short term. Different responses of NDVI and GPP to hydroclimate may lie in the GPP estimation algorithms. This study enhances our understanding of plant-water-energy interactions in the humid subtropical environment under contrasting dryness conditions.

Photostimulated changes in egg production and reproductive performance of the Guinea fowl in a sub-humid tropical environment.

The effect of photo-induced changes on egg production and reproductive performance of female guinea fowl was studied by exposing the birds to three photo-regimens, namely natural daylight all day for 12 weeks (NDL), 8 hours of light per day for 8 weeks (8L-16D) plus supplementary light for 16 hours per day for 4 weeks (16L-8D) (RSL), and provided natural daylight all day for 8 weeks plus supplementary light at 16 hours per day for 4 weeks (SL). Weight gain during the pre-laying period was similar (P&gt;0.05) in all the treatment groups between 20-36 weeks of age. The reverse was the case during the laying period between 36-52 weeks, which coincided with the age at sexual maturity. Feed intake was similar (P&gt;0.05) for the NDL and SL groups during the pre-laying period but the RSL group had significantly lower (P&lt;0.05) feed intake than the others. Overall laying mortality was lowest in the RSL birds. There was no significant difference (P&gt;0.05) in body weight for all the groups. Age at first egg was significantly lower (P&lt;0.05) in the RSL (207 d) than in the NDL (249 d) and SL (235 d) birds which were similar (P&gt;0.05). The guinea fowls which received 8 weeks of restricted light (RSL) responded more rapidly in terms of day-to-first-egg after exposure to 16 hours of light and achieved significantly higher (P&lt;0.05) level of egg production than the other two groups. The overall economy of production, in terms of cost, revealed that RSL birds performed better than the NDL and SL, in that it cost N36.58 and 127.05 more to produce each NDL and SL guinea fowl at point of lay respectively. The results indicate that different light regimes altered the time during which egg production response took place and apparently affected the genetic potentials of the groups with regard to egg mass and total number of eggs laid during the period covered by this trial.

Breeding Practices and Trait Preferences of Sheep Farmers in a Sub-Humid Tropical Environment

The present study was carried out to determine the livestock breeding practices and the trait preferences of sheep farmers in Nasarawa State, Nigeria. A total of 132 sheep keepers were randomly sampled out of which data from 120 farmers were utilized in the final analysis. Primary data were collected through individual semi-structured questionnaire administration. Categorical and continuous variables including production and breeding traits were statistically tested based on sex of the respondents. Age of respondents, educational status, primary occupation, access to credit, and type of landholding were significantly different between the male and female farmers. Flock size was higher in farms owned by male farmers (19.63±1.04 versus 15.16±1.00). However, both sexes did not differ (p&gt;0.05) in the ranking of meat, religion, income, hides, and skin and cultural purpose as reasons for keeping sheep. As regards management of sheep, control of breeding and access to veterinary services were low among female farmers. Apart from cultural/religious significance which was ranked higher by female farmers (63.38 versus 52.23; p≤0.05), other production traits such as disease resistance, survivability, growth rate, meat quality, fertility, body size, and prolificacy did not vary between sexes. Disease resistance, which the male farmers attached more importance (57.0 versus 70.52; p≤0.05), was the only significant breeding trait between sexes. Categorical principal component analysis (CATPCA) also revealed little influence of sex on the production and breeding traits investigated. The present findings could guide interventions such as the setting up of sustainable community-based breeding&nbsp;schemes to improve sheep production in the study area.

Simulation of the impacts of climate change on phenology, growth, and yield of various rice genotypes in humid sub-tropical environments using AquaCrop-Rice.

In the light of continuing anthropogenic climate change, it is important to gain a deep understanding of rice genotypic behavior under climate change. Most efforts on modeling rice performance under climate change focused on studying some aspects of climate change only such as CO2 concentration ([CO2]) or temperature. A comprehensive study on the role of genotypic variability in rice under diverse [CO2] × temperature × rainfall × representative concentration pathway (RCP) × environment is rare. The objective of the present study was to use AquaCrop-Rice model to study the impact of climate change on different rice cultivars in northern Iran. Three common improved and local rice cultivars were chosen, and their growth and yield behavior were simulated under three environments, three RCPs (2.6, 4.5 and 8.5), four temperature (+ 1 °C, + 2 °C, + 3 °C, + 4 °C), and two rainfall (± 20%) scenarios under two future timeframes (2020-2051 and 2052-2083). Results indicated different responses of rice cultivars under climate change. In general, improved cultivars acted better than the local cultivar although interaction with environment was also observed. Increase in [CO2] and temperature most often favored rice yield. However, RCP8.5 along with temperature scenario + 1 °C resulted in the highest aboveground biomass and yield. Rainfall variation was not of considerable importance. Phenology (flowering and physiological maturity) was accelerated especially by temperature. The length of the vegetative phase was more influenced by temperature than the length of the generative phase. Our simulations also indicated a potential for adaptation of improved cultivars under increasing [CO2] through their reduced stomatal conductance.

Legume silvopastoral systems enhance soil organic matter quality in a subhumid tropical environment

AbstractThe silvopastoral system avoids the degradation of tropical grasslands by providing essential nutrients to the soil while improving livestock diet and farmer's income by increasing the marketable wood supply. We hypothesize that intercropping shrub‐tree legumes into signalgrass increases microbial activity and soil organic matter (SOM) quality. We investigated silvopastoral system soils over 5 yr in a subhumid climate in northeastern Brazil to determine the total C and N contents and to estimate C‐microbial biomass and respiration, microbial and metabolic quotients, humic acid (HA), and fulvic acid (FA). The experimental design evaluated (a) signalgrass intercropped with gliricidia at 0, 4, and 8 m from the center of the double legume row; (b) signalgrass intercropped with sabia at 0, 4, and 8 m from the center of the double legume row; and (c) single signalgrass. Samples were obtained after 2, 3, 4, and 5 yr from silvopastoral system implementation. The shrub‐tree legumes soils had total C (39 g kg−1) and total N (3.8 g kg−1) contents significantly higher (30 and 72%, respectively) than single signalgrass soil only on the fifth year after establishment. Microbial biomass C at 0 and 4 m from the legume's rows was 700 mg kg−1, which was 75% higher than single signalgrass soils. There was strong microbial respiration (∼50 mg C‐CO2 kg−1 d−1) in legumes soils, but the metabolic quotient did not indicate disturbance in microbial activity. The microbial quotients were significantly higher in shrub‐tree legumes soil, and the HA/FA ratio was nearly 1, demonstrating greater efficiency in SOM decomposition by microbial activity. Overall, 5 yr after establishment, the silvopastoral system has improved SOM quality and contributed to grassland sustainability.

Modeling Hairy Vetch and Cereal Rye Cover Crop Decomposition and Nitrogen Release

Empirical models could help us to understand the process of plant residue decomposition and nutrient release into the soil. The objective of this study was to determine an appropriate model to describe the decomposition of hairy vetch (Vicia villosa Roth) and cereal rye (Secale cereale L.) cover crop (CC) residue and nitrogen (N) release. Data pertaining to above and belowground CC residue mass loss and N release for up to 2633 cumulative decomposition degree days (112 d) after litterbag installation were obtained from two cropping system experiments, a 1-yr study conducted in 2015 and a 2-yr study during 2017 to 2018 in the humid subtropical environment of southern IL, USA. Six exponential and two hyperbolic models were fit to percent mass and N remaining data to find the one with minimum Akaike information criterion (AIC) and residual sum of squares. Modified three-parameter single exponential and two- or three-parameter hyperbolic models best met the assumed criteria of selection for above and belowground CC residue, respectively. Fitting a double exponential model to combined data for percent mass and N remaining identified two mass and N pools, a fast and a slow pool with different rate constants. A five-parameter double exponential with an asymptote met the preset criteria and passed all tests for normally distributed population, constant variance, and independence of residuals at α = 0.05 when fit to combined data of hairy vetch shoot mass and N remaining. However, a two-parameter hyperbolic and three-parameter asymptotic hyperbolic model provided the best fit to a combined data of cereal rye shoot mass and N remaining, respectively. Both hyperbolic decay models showed a good fit for belowground mass decomposition and N release for both CCs. Cereal rye had a poorer fit than hairy vetch for mass and N remaining of both above and belowground mass. The best-selected decay models can be used to estimate the decomposition and N release rates of hairy vetch and cereal rye above and belowground residue in a similar environment.

Longitudinal retrospective study on the effect of season on milk production and composition in Rio Grande do Sul, Brazil

This longitudinal retrospective study evaluated production and composition of milk from dairy cows according to season on a rural property in Palmeira das Missões, Rio Grande do Sul, Brazil, between January 2009 and December 2016. Milk yield per hectare per month was the primary variable measured, along with chemical composition (total dry extract, defatted dry extract, fat, protein, and lactose), somatic cell count, and total bacterial count of milk. Production in summer (513.53 kg/ha/month) did not differ (p &gt; 0.05) from that in fall (504.69 kg/ha/month) or spring (564.63 kg/ha/month), but production in winter (639.20 kg/ha/month) was significantly higher than in summer (p &lt; 0.0057). The real price of milk did not differ (p &gt; 0.05) among seasons. The total dry extract content differed (p &lt; 0.0059) between seasons. However, the cooler fall and winter seasons favored the production of total solids. The defatted dry extract content was higher (p &lt; 0.0001) in winter (8.65%), compared to the other seasons of the year. Fat content did not differ (p &gt; 0.05) among seasons. Protein content differed (p &lt; 0.0200) between summer (3.01%) and winter (3.16%), but both seasons did not differ (p &gt; 0.05) from fall (3.13%) or spring (3.05%). Winter lactose levels (4.52%) were higher (p &lt; 0.0011) than during other seasons. The somatic cell count did not differ (p &gt; 0.05) among seasons, demonstrating that the evaluated herd possesses standard mammary gland health. The total bacterial count did not differ (p &gt; 0.05) among the seasons, demonstrating that the hygiene of the facilities remains constant. As expected, the temperature and humidity index varied (p &lt; 0.0001) with the seasons, and the deleterious effects were more pronounced in summer and spring, as they are the hottest seasons in humid subtropical environments. The results emphasize that the organized management of milk production reduces the variation in milk composition, making it easier to maintain a consistent high milk quality and also generating extra revenue.

Legume-based silvopastoral systems drive C and N soil stocks in a subhumid tropical environment

Silvopastoral systems include trees or shrubs and grasses and are considered a sustainable method of restoring degraded pastures and increasing carbon and nitrogen stocks in tropical soils. We hypothesize that establishing shrub-tree legumes in a signalgrass pasture has the potential to increase soil C and N stocks. Thus, we investigated a silvopastoral system over four years in a subhumid tropical zone in northeastern Brazil to determine the soil C and N stocks and the organic matter chemical fractions. The experimental design consisted of i-pure signalgrass (Brachiaria decumbens), ii-signalgrass intercropped with gliricidia (Gliricidia sepium) and iii-signalgrass intercropped with sabiá (Mimosa caesalpiniaefolia). Measurements were taken at 0, 4 and 8 m away from the legume rows and at random in the pure signalgrass pasture. Soil samples were obtained in the second and fourth years after silvopastoral system implementation at 0–10, 10–20, 20–40, 40–60 and 60–100 cm soil depths at each distance in triplicate to produce compound samples. These were used to determine the C and N contents and stocks, as well as the soil organic matter chemical fractions. Within two years, the gliricidia and sabiá soil C stocks directly below the legume row at 100 cm depth increased by 45% and 35%, respectively, while the soil N stock tripled at all distances. The soil organic matter increased over the two years, and the humin proportion in the soil organic matter (SOM) increased in the silvopastoral system soils. Overall, after four years of silvopastoral system establishment, this system showed the potential to store N and achieve soil C stock levels that are within the global average range for these systems.

The nitrogen nutrition potential of arable soils

Soils are an important source of nitrogen in many of the world’s cropping systems. Especially in low-input production systems, nitrogen release from soil organic matter turn-over is the major part of the crop’s nitrogen supply and research suggests that this process is significantly affected by changes in climate. The knowledge of the amount of nitrogen being accountable for crop nutrition is purely empirical in many production areas in the world and data as a foundation of global-scale climate change and food security assessments is scarce. Here we demonstrate that nitrogen mineralisation in general follows similar rules as for carbon, but with different implications for agricultural systems. We analysed 340 data sets from previously published incubation experiments for potential nitrogen mineralisation which covered a large range of soils and climate conditions. We find that under warm and all-year humid conditions the share of potentially mineralisable nitrogen in the soil’s total nitrogen is significantly smaller than in dry or temperate environments. We conclude that – despite relatively high soil nitrogen stocks – soil-borne nitrogen supply for crop production is very low in tropical and humid subtropical environments, which is a critical piece of information for global assessments of agricultural production and food security.

Nitrogen fertilization modifies maize yield response to tillage and stubble in a sub-humid tropical environment

Controversy around the benefits of NT and stubble retention, and weaknesses in the underpinning science arise from a limited understanding of the mechanisms that operate in these systems. Two experiments were conducted at the Kenya Agricultural and Livestock Research Organization research station in Embu (0.515°S and 37.273°E) over three seasons during the 2015 long rains, 2015/2016 short rains and 2016 long rains to explore the mechanisms that regulate crop growth, nitrogen uptake and yield in maize (Zea mays L.). In the first experiment, crops were grown in a factorial combination of conventional tillage (CT) and no-till (NT), three amounts of stubble (0, 3 and 5 t ha−1) and three N rates (0, 80 and 120 kg N ha−1). The second experiment investigated the interaction between tillage (CT, NT) and timing of N supply (80 kg N ha−1) that was supplied at sowing, six- (V6) and 12-leaf stage, with 5 t ha−1 of stubble. Grain yield ranged from 2.3 to 5.3 t ha−1, with small effects from tillage and stubble retention. Nitrogen had the largest impact on grain yield and influenced crop response to tillage and stubble by modifying crop growth rate (CGR) and nitrogen nutrition index (NNI). However, the effects of N timing on crop growth, yield and traits associated with N use efficiency were independent of tillage system. High CGR between V6 and flowering was associated with high NNI, which led to increased grain number. The value of stubble in water storage at sowing, and crop growth and yield was greater in a dry season (<300 mm rainfall) compared with wet seasons (>600 mm). Irrespective of tillage system, moderate amounts of stubble, higher N rates and better matching of N supply to the critical window for yield determination could improve maize yields in sub-humid tropical environments.

Cropping Systems and Climate Change in Humid Subtropical Environments

In the future, climate change will challenge food security by threatening crop production. Humid subtropical regions play an important role in global food security, with crop rotations often including wheat (winter crop) and soybean and maize (summer crops). Over the last 30 years, the humid subtropics in the Northern Hemisphere have experienced a stronger warming trend than in the Southern Hemisphere, and the trend is projected to continue throughout the mid- and end of century. Past rainfall trends range, from increases up to 4% per decade in Southeast China to −3% decadal decline in East Australia; a similar trend is projected in the future. Climate change impact studies suggest that by the middle and end of the century, wheat yields may not change, or they will increase up to 17%. Soybean yields will increase between 3% and 41%, while maize yields will increase by 30% or decline by −40%. These wide-ranging climate change impacts are partly due to the region-specific projections, but also due to different global climate models, climate change scenarios, single-model uncertainties, and cropping system assumptions, making it difficult to make conclusions from these impact studies and develop adaptation strategies. Additionally, most of the crop models used in these studies do not include major common stresses in this environment, such as heat, frost, excess water, pests, and diseases. Standard protocols and impact assessments across the humid subtropical regions are needed to understand climate change impacts and prepare for adaptation strategies.

Aeolian Erosion Processes in Humid Subtropical Ultisols in Southeastern United States

Aeolian Erosion Processes in Humid Subtropical Ultisols in Southeastern United States Jamie L. Kincheloe, Dr. Arpita Nandi, Dr. Ingrid Luffman Abstract Many aeolian erosion studies have been performed in arid and semi-arid environments, while few have been performed in humid subtropical environments. Since the primary erosional factor in humid environments is precipitation, aeolian erosion is often not accounted for. This study focuses on the role of wind and wind-driven rain erosion in humid subtropical environments on an east Tennessee hill slope, USA. Three years of wind data were aggregated to weekly soil erosion measurement periods using five wind and precipitation parameters: average wind speed, peak gust, average wind direction, high wind direction, and maximum precipitation intensity. Predictive statistical regression models were generated for aeolian erosion in gully interfluves and sidewalls. Principal Components Analysis was used to develop two independent factors for wind speed and direction. Ordinary Least Square regression models for erosion on interfluves and sidewalls using the two factors and wind-driven precipitation interaction variables explained 5.9% and 15%, respectively, of variability in erosion data. A comparison of erosion on lee and stoss sidewalls indicated no significant differences in the three-year lumped dataset, but differences at the weekly time scale were significant during winter months, likely related to freeze thaw events. Full Text: PDF DOI: 10.15640/jges.v6n1a3

Cassava Breeding II: Phenotypic Correlations through the Different Stages of Selection.

Breeding cassava relies on a phenotypic recurrent selection that takes advantage of the vegetative propagation of this crop. Successive stages of selection (single row trial–SRT; preliminary yield trial–PYT; advanced yield trial–AYT; and uniform yield trials UYT), gradually reduce the number of genotypes as the plot size, number of replications and locations increase. An important feature of this scheme is that, because of the clonal, reproduction of cassava, the same identical genotypes are evaluated throughout these four successive stages of selection. For this study data, from 14 years (more than 30,000 data points) of evaluation in a sub-humid tropical environment was consolidated for a meta-analysis. Correlation coefficients for fresh root yield (FRY), dry matter content (DMC), harvest index (HIN), and plant type score (PTS) along the different stages of selection were estimated. DMC and PTS measured in different trials showed the highest correlation coefficients, indicating a relatively good repeatability. HIN had an intermediate repeatability, whereas FRY had the lowest value. The association between HIN and FRY was lower than expected, suggesting that HIN in early stages was not reliable as indirect selection for FRY in later stages. There was a consistent decrease in the average performance of clones grown in PYTs compared with the earlier evaluation of the same genotypes at SRTs. A feasible explanation for this trend is the impact of the environment on the physiological and nutritional status of the planting material and/or epigenetic effects. The usefulness of HIN is questioned. Measuring this variable takes considerable efforts at harvest time. DMC and FRY showed a weak positive association in SRT (r = 0.21) but a clearly negative one at UYT (r = −0.42). The change in the relationship between these variables is the result of selection. In later stages of selection, the plant is forced to maximize productivity on a dry weight basis either by maximizing FRY or DMC, but not both. Alternatively, the plant may achieve high dry root yield by simultaneously attaining “acceptable” (but not maximum) levels of FRY and DMC.