Sensitivity and requirement of improvements of four soybean crop simulation models for climate change studies in Southern Brazil

Crop growth models have many uncertainties that affect the yield response to climate change. Based on that, the aim of this study was to evaluate the sensitivity of crop models to systematic changes in climate for simulating soybean attainable yield in Southern Brazil. Four crop models were used to simulate yields: AQUACROP, MONICA, DSSAT, and APSIM, as well as their ensemble. The simulations were performed considering changes of air temperature (0, + 1.5, + 3.0, + 4.5, and + 6.0 °C), [CO2] (380, 480, 580, 680, and 780 ppm), rainfall (- 30, - 15, 0, + 15, and + 30%), and solar radiation (- 15, 0, + 15), applied to daily values. The baseline climate was from 1961 to 2014, totalizing 53 crop seasons. The crop models simulated a reduction of attainable yield with temperature increase, reaching 2000 kg ha-1 for the ensemble at + 6 °C, mainly due to shorter crop cycle. For rainfall, the yield had a higher rate of reduction when it was diminished than when rainfall was increased. The crop models increased yield variability when solar radiation was changed from - 15 to + 15%, whereas [CO2] rise resulted in yield gains, following an asymptotic response, with a mean increase of 31% from 380 to 680 ppm. The models used require further attention to improvements in optimal and maximum cardinal temperature for development rate; runoff, water infiltration, deep drainage, and dynamic of root growth; photosynthesis parameters related to soil water availability; and energy balance of soil-plant system to define leaf temperature under elevated CO2.

An assessment of yield gains under climate change due to genetic modification of pearl millet

Developing cultivars with traits that can enhance and sustain productivity under climate change will be an important climate smart adaptation option. The modified CSM-CERES-Pearl millet model was used to assess yield gains by modifying plant traits determining crop maturity duration, potential yield and tolerance to drought and heat in pearl millet cultivars grown at six locations in arid (Hisar, Jodhpur, Bikaner) and semi-arid (Jaipur, Aurangabad and Bijapur) tropical India and two locations in semi-arid tropical West Africa (Sadore in Niamey and Cinzana in Mali). In all the study locations the yields decreased when crop maturity duration was decreased by 10% both in current and future climate conditions; however, 10% increase in crop maturity significantly (p<0.05) increased yields at Aurangabad and Bijapur, but not at other locations. Increasing yield potential traits by 10% increased yields under both the climate situations in India and West Africa. Drought tolerance imparted the lowest yield gain at Aurangabad (6%), the highest at Sadore (30%) and intermediate at the other locations under current climate. Under climate change the contribution of drought tolerance to the yield of cultivars either increased or decreased depending upon changes in rainfall of the locations. Yield benefits of heat tolerance substantially increased under climate change at most locations, having the greatest effects at Bikaner (17%) in India and Sadore (13%) in West Africa. Aurangabad and Bijapur locations had no yield advantage from heat tolerance due to their low temperature regimes. Thus drought and heat tolerance in pearl millet increased yields under climate change in both the arid and semi-arid tropical climates with greater benefit in relatively hotter environments. This study will assists the plant breeders in evaluating new promising plant traits of pearl millet for adapting to climate change at the selected locations and other similar environments.

Genetics of promiscuous nodulation in soybean: nodule dry weight and leaf color score

The symbiotic relationship between the soybean plant and rhizobium results in fixation of atmospheric nitrogen (N(2)) in the root nodules, with the result that nitrogenous fertilization of the soybean is unnecessary. The effectiveness of nodule formation and N(2) fixation with rhizobial strains is under genetic control with two general categories identified: (1) promiscuous, which produces functional nodules with cowpea-type rhizobial strains; and (2) nonpromiscuous, which forms no or nonfunctional nodules with these strains. The segregation pattern of this promiscuity trait was studied using nodule dry weight (NDW) and leaf color score (LCS) as indicators of N(2) fixation effectiveness. Individual plants in each of six populations [P(1) = nonpromiscuous, P(2) = promiscuous, F(1) = P(1) x P(2) (and the reciprocal cross), BC(1)(P(1)) = F(1) (female) x P(1), BC(1)(P(2)) = F(1) (female) x P(2), F(2)] were scored for these characters after inoculation with a rhizobial strain that would distinguish between both types. For NDW, nonpromiscuity was found to be partially dominant (h/d = 0.37), controlled by four loci. For LCS, nonpromiscuity was shown to be almost completely dominant (h/d = 0.74), controlled by two loci. LCS was a more meaningful estimate of N(2) fixation because it represented the total effectiveness of nodulation to provide nitrogen for the plant.

Pollen morphology and in vitro germination characteristics of nodulating and nonnodulating soybean (Glycine max L.) genotypes

Artificial hybridization in highly self-pollinated crop species such as soybean (Glycine max L.) is important for both generating genetic variability and segregation for selection. In higher plants, pollen is an agent for transmission of genetic information over generations. The objective of this study was to measure and compare both morphological (length, width) and in vitro germination (germination percentage tube length) characteristics of pollen from the nodulating soybean cultivar, Bragg, and a nonnodulating Bragg mutant line, Nod 139, obtained following ethyl methanesulphonate treatment. Highly significant (P = 0.007) differences in pollen length were observed between these two genotypes. Similarly, in vitro germination percent (G%) indicated highly significant (P = 0.0001) differences between these genotypes, suggesting that the nodulation trait produces variation in in vitro germination capacity of the pollen. It appears the nonnodulation trait in soybean alters pollen grain length and G%.

Repeatability of Model Genetic Coefficients Derived from Soybean Performance Trials across Different States

Crop model testing in diverse environments is essential if modelers wish to make applications or extrapolations to those environments. A recent study demonstrated the effectiveness of optimization techniques for deriving cultivar coefficients for the CROPGRO-Soybean model from typical information provided by soybean performance tests. The objectives of this study were (i) to explore the extent to which cultivar coefficients developed by these approaches from crop performance tests are stable across different regions, (ii) to test the CROPGRO-Soybean model's ability to predict phenology and seed yield using cultivar coefficients that were developed in different regions, and (iii) to investigate whether 3 yr of crop performance data are adequate for developing stable genetic coefficients. A stepwise procedure was applied to derive cultivar coefficients for 10 common cultivars grown in different environments in Georgia and North Carolina. Regarding the transportability of cultivar coefficients across states, we found that the critical daylength coefficients were the most reliable cultivar traits. We found less stability of the cultivar traits that control genetic differences in seed yield potential. The estimated cultivar coefficients developed in Georgia enabled CROPGRO to predict yield and harvest maturity in North Carolina within 3.8% and 3.5 d, respectively, from the observed averages. Using the cultivar coefficients developed from North Carolina environments allowed us to simulate the actual mean yield and harvest maturity in Georgia to within 2.5% and 2.0 d. Furthermore, the model's ability to predict seed yield and maturity with cultivar coefficients developed from 3 yr of data was nearly as good as that derived from much larger data sets.

Fate of atrazine in sandy soil cropped with sorghum

A field study was conducted to determine the fate of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) within the root zone (0 to 90 cm) of a sandy soil cropped with sorghum [Sorghum bicolor (L.) Moench] in Gainesville, Florida. Atrazine was uniformly applied at a rate of 1.12 kg ai. ha(-1) to a sorghum crop under moderate irrigation, optimum irrigation, and no irrigation (rainfed), 2 d after crop emergence. Bromide as a tracer for water movement was applied to the soil as NaBr at a rate of 45 kg Br ha(-1), 3 d before atrazine application. Soil water content, atrazine, and Br concentrations were determined as a function of time using soil samples taken from the root zone. Atrazine sorption coefficients and degradation rates were determined by depth for the entire root zone in the laboratory. Atrazine was strongly adsorbed within the upper 30 cm of soil and most of the atrazine recovered from the soil during the growing season was in that depth. The estimated half-life for atrazine was 32 d in topsoil to 83 d in subsoil. Atrazine concentration within the root zone decreased from 0.44 kg ai. ha(-1) 2 days after application (DAA) to 0.1 kg a.i. ha(-1) 26 DAA. Negligible amounts of atrazine (approximately 5 microg kg(-1)) were detected below the 60-cm soil depth by 64 DAA. Most of the decrease in atrazine concentration in the root zone over time was attributed to degradation. In contrast, all applied bromide had leached past the 60-cm soil depth during the same time interval.

Changes in growth CO2 result in rapid adjustments of ribulose-1, 5-bisphosphate Carboxylase/Oxygenase small subunit gene expression in expanding and mature leaves of rice

The accumulation of soluble carbohydrates resulting from growth under elevated CO2 may potentially signal the repression of gene activity for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS). To test this hypothesis we grew rice (Oryza sativa L.) under ambient (350 &mgr;L L-1) and high (700 &mgr;L L-1) CO2 in outdoor, sunlit, environment-controlled chambers and performed a cross-switching of growth CO2 concentration at the late-vegetative phase. Within 24 h, plants switched to high CO2 showed a 15% and 23% decrease in rbcS mRNA, whereas plants switched to ambient CO2 increased 27% and 11% in expanding and mature leaves, respectively. Ribulose-1,5-bisphosphate carboxylase/oxygenase total activity and protein content 8 d after the switch increased up to 27% and 20%, respectively, in plants switched to ambient CO2, but changed very little in plants switched to high CO2. Plants maintained at high CO2 showed greater carbohydrate pool sizes and lower rbcS transcript levels than plants kept at ambient CO2. However, after switching growth CO2 concentration, there was not a simple correlation between carbohydrate and rbcS transcript levels. We conclude that although carbohydrates may be important in the regulation of rbcS expression, changes in total pool size alone could not predict the rapid changes in expression that we observed.

The Effect of Dry Pegging Zone Soil on Pod Formation of Florunner Peanut1

Peanut (Arachis hypogaea L.) fruit growth is sensitive to surface soil (0-5 cm) conditions due to its subterranean fruiting habit. This study was conducted to determine the effect of soil water content in the pegging zone (0-5 cm) on peanut pod growth rate and development. A pegging-pan-root-tube apparatus was used to separately control soil water content in the pegging and root zone for greenhouse trials. A field study also was conducted using portable rainout shelters to create a soil water deficit. Pod phenology, pod and seed growth rates, and final pod and seed dry weights were determined. In greenhouse studies, dry pegging zone soil delayed pod and seed development. In the field, soil water deficits in the pegging and root zone decreased pod and seed growth rates by approximately 30% and decreased weight per seed from 563 to 428 mg. Pegs initiating growth during drought stress demonstrated an ability to suspend development during the period of soil water deficit and to re-initiate pod development after the drought stress was relieved.

Leaf Nitrogen Content, Photosynthesis and Radiation Use Efficiency in Peanut1

It has been hypothesized that a close correlation exists between specific leaf nitrogen content (SLN, g N m-2 leaf area) and leaf carbon exchange rate (CER), and crop radiation use efficiency (RUE). This association has not been investigated previously in peanut (Arachis hypogaea L.) so the objective of this research was to obtain such data under greenhouse and field conditions. In the greenhouse study differing nitrogen fertilizer treatments for a non-nodulated cultivar resulted in leaves with a wide range of SLN and CER. A strong, positive association between SLN and CER was found. In the field little variation in either SLN or CER was observed through much of the growing season in four commercial cultivars. Consistent with the observation of stability in SLN and CER, RUE based on total, intercepted solar radiation was found to be constant at 1.00 g MJ-1 through the growing season. However, the observed RUE was 29% greater than a theoretical RUE calculated assuming a uniform distribution of SLN in the canopy. One possibility is that RUE of peanuts may be enhanced by a nonuniform SLN distribution within its leaf canopy. In any event, the results of both the greenhouse and field tests showed that peanut CO2 assimilation is closely linked to leaf SLN.

Single Leaf Carbon Exchange and Canopy Radiation Use Efficiency of Four Peanut Cultivars1

Knowledge of the interception of solar radiation by crop canopies and the use of that radiation for carbon assimilation is essential for understanding crop growth and yield as a function of the environment. A field experiment was conducted in 1990 at Gainesville, FL to determine if differences in single leaf carbon exchange rate (CER), canopy radiation interception, radiation use efficiency (g dry matter produced per unit of solar radiation intercepted), and increase in seed harvest index with time exist among several commonly grown peanut (Arachis hypogaea L.) cultivars. Four cultivars (Early Bunch, Florunner, Marc I, and Southern Runner) were grown in field plots on a Kendrick fine sand (a loamy, siliceous, hyperthermic Arenic Paleudult) under fully irrigated, intensive management. Total crop and seed dry matter accumulation were determined, and canopy radiation interception measured at weekly intervals. CER of uppermost, fully expanded sunlit leaves were determined at midday at 2-wk intervals. Single leaf CER's were similar among cultivars (25 to 35 μmol CO2 m-2 s-1) and relatively stable throughout most of the season, before declining during late seed filling. Although interception of radiation differed somewhat among cultivars during early canopy development, total crop dry matter accumulation was linearly related to the cumulative amount of radiation intercepted by all four cultivars (r2=≥0.99). Radiation use efficiency was similar among all cultivars with a mean of 1.00 g dry matter accumulated per MJ of intercepted solar radiation. The increase in seed harvest index with time was linear (r2≤0.94) and the rates of increase were similar among the Early Bunch, Florunner, and Marc I cultivars (0.0058 d-1), but lower (0.0043 d-1) for the later maturing Southern Runner cultivar. Results from this study indicated that the primary differences among these four cultivars were in early-season development of the leaf canopy and resultant radiation interception and the rate of seed growth, rather than the capacity to assimilate carbon dioxide.

Growth, Development, Yield, and Seed Quality of Florunner Peanut Affected by Late Leaf Spot1

Late leaf spot, induced by Cercosporidium personatum (Berk. & Curt.) Deighton, causes serious yield losses of peanut (Arachis hypogaea L.) in the southeastern United States. A two-year study was conducted to observe progress of late leaf spot and to evaluate subsequent effects of late leaf spot on accumulation of dry matter, leaf area index (LAI), and pod production of Florunner peanut in fungicide-treated and non-treated plots. Disease severity, which is an expression of both disease-induced defoliation and necrotic leaf area, was used as an indicator of disease progression in the field. The leaf dry weight, LAI, and the dry weight of the total biomass were significantly different at 93 days after planting (DAP) in 1986, and at 78 DAP in 1987 between fungicide-treated and non-treated plots. Late leaf spot reduced the potential yield (harvested and dropped pods) of Florunner peanut by 37% in 1986 and 46% in 1987. In non-treated plots, the abscission of pods was initiated later but progressed faster in 1986 than in 1987. The predictions of pod yield with the measures of healthy leaf area duration (HAD) and healthy area absorption (HAA) were adequate for fungicide-treated plots where pod losses were minimal. However, HAD and HAA were inadequate for predicting pod yield of a peanut crop severely infected by late leaf spot, primarily because this predictive approach does not account for losses of dropped pods.

Growth Stages of Peanut (Arachis hypogaea L.)1

Uniform growth stage descriptions were developed for peanut based on visually observable vegetative (V) and reproductive (R) events. The V stage was determined by counting the number of developed nodes on the main stem, beginning with the cotyledonary node as zero. The last node counted must have its tetrafoliolate leaf sufficiently expanded so the leaflets are unfolded and flat in appearance. The R stages proposed are R1 (beginning bloom), R2 (beginning peg), R3 (beginning pod), R4 (full pod), R5 (beginning seed), R6 (full seed), R7 (beginning maturity), R8 (harvest maturity), and R9 (over mature pod). The V and R stages can be measured separately and concurrently and apply to populations or single plants. For populations, a given stage is reached when 50% of the plants sampled have achieved the specified node number or have one or more flowers, pegs, pods, or seeds exhibiting the specified trait. The stages apply to both Spanish and Virginia type cultivars.

The proposed standard descriptions of peanut plant development should aid in peanut research planning and communication and should assist extension recommendation of timing of cultural practices.