The benefits of reduced and zero-tillage systems have been presented as reducing runoff, enhancing water retention and preventing soil erosion. There is also general agreement that the practice can conserve and enhance soil organic carbon (C) levels to some extent. However, their applicability in mitigating climate change has been debated extensively, especially when the whole profile of C in the soil is considered, along with a reported risk of enhanced nitrous oxide (N2O) emissions. The current paper presents a meta-analysis of existing literature to ascertain the climate change mitigation opportunities offered by minimizing tillage operations. Research suggests zero tillage is effective in sequestering C in both soil surface and sub-soil layers in tropical and temperate conditions. The C sequestration rate in tropical soils can be about five times higher than in temperate soils. In tropical soils, C accumulation is generally correlated with the duration of tillage. Reduced N2O emissions under long-term zero tillage have been reported in the literature but significant variability exists in the N2O flux information. Long-term, location-specific studies are needed urgently to determine the precise role of zero tillage in driving N2O fluxes. Considering the wide variety of crops utilized in zero-tillage studies, for example maize, barley, soybean and winter wheat, only soybean has been reported to show an increase in yield with zero tillage (7·7% over 10 years). In several cases yield reductions have been recorded e.g. c. 1–8% over 10 years under winter wheat and barley, respectively, suggesting zero tillage does not bring appreciable changes in yield but that the difference between the two approaches may be small. A key question that remains to be answered is: are any potential reductions in yield acceptable in the quest to mitigate climate change, given the importance of global food security?

The introduction of cover crops in the intercrop period may provide a broad range of ecosystem services derived from the multiple functions they can perform, such as erosion control, recycling of nutrients or forage source. However, the achievement of these services in a particular agrosystem is not always required at the same time or to the same degree. Thus, species selection and definition of targeted objectives is critical when growing cover crops. The goal of the current work was to describe the traits that determine the suitability of five species (barley, rye, triticale, mustard and vetch) for cover cropping. A field trial was established during two seasons (October to April) in Madrid (central Spain). Ground cover and biomass were monitored at regular intervals during each growing season. A Gompertz model characterized ground cover until the decay observed after frosts, while biomass was fitted to Gompertz, logistic and linear-exponential equations. At the end of the experiment, carbon (C), nitrogen (N), and fibre (neutral detergent, acid and lignin) contents, and the N fixed by the legume were determined. The grasses reached the highest ground cover (83–99%) and biomass (1226–1928 g/m2) at the end of the experiment. With the highest C:N ratio (27–39) and dietary fibre (527–600 mg/g) and the lowest residue quality (~680 mg/g), grasses were suitable for erosion control, catch crop and fodder. The vetch presented the lowest N uptake (2·4 and 0·7 g N/m2) due to N fixation (9·8 and 1·6 g N/m2) and low biomass accumulation. The mustard presented high N uptake in the warm year and could act as a catch crop, but low fodder capability in both years. The thermal time before reaching 30% ground cover was a good indicator of early coverage species. Variable quantification allowed finding variability among the species and provided information for further decisions involving cover crop selection and management.

The classical analysis model for agricultural field trials is based on the principles of experimental design – randomization, replication and blocking – and it assumes independent residual effects. Accounting for any existent spatial correlation as an add-on component may be beneficial, but it requires selection of a suitable spatial model and modification of classical tests of treatment contrasts. Using a sugar beet trial laid out in complete blocks for illustration, it is shown that tests obtained with different modifications yield diverging results. Simulations were performed to decide whether different test modifications lead to valid statistical inferences. For the spherical, power and Gaussian models, each with six different values of the range parameter and without a nugget effect, the suitability of the following modifications was studied: a generalization of the Satterthwaite method (1941), the method of Kenward and Roger (1997), and the first-order corrected method described by Kenward and Roger (2009). A second-order method described by Kenward and Roger (2009) is also discussed and detailed results are provided as Supplemental Material (available at: http://journals.cambridge.org/AGS). Simulations were done for experiments with 10 or 30 treatments in complete and incomplete block designs. Model selection was performed using the corrected Akaike information criterion and likelihood-ratio tests. When simulation and analysis models were identical, at least one of the modifications for the t-test guaranteed control of the nominal Type I error rate in most cases. When the first-order method of Kenward and Roger was used, control of the t-test Type I error rate was poor for 10 treatments but on average very good for 30 treatments, when considering the best-fitting models for a given simulation setting. Results were not satisfactory for the F-test. The more pronounced the spatial correlation, the more substantial was the gain in power compared to classical analysis. For experiments with 20 treatments or more, the recommendation is to select the best-fitting model and then use the first-order method for t-tests. For F-tests, a randomization-based model with independent error effects should be used.

Maize (Zea mays L.) is the major staple crop in Timor-Leste, but yields are low, averaging 1·0–1·7 t/ha, and losses during storage are high from maize weevil (Sitophilus zeamais Motschulsky) damage. The current research, assessing both weevil damage and management options, studied household storage of traditional and introduced maize varieties in 18 farmer groups for 33 weeks, and then evaluated the weevil damage in cobs stored for 9 months of 19 populations from different multi-location yield trials in 2007 and 2010. Storage of shelled grain in airtight containers for 33 weeks had no weevil damage on-farm. In contrast, storing shelled maize in a woven sack was the worst storage method with an average of 0·96 of grain attacked by weevils by Week 33, with local and introduced varieties damaged similarly. Shelled grain stored in a woven sack were infested significantly more than in traditional storage methods husked on the cob – above a fireplace, in a tree or an elevated house. Importantly, modern varieties were damaged more extensively by weevils than local maize types when the husked maize was stored using traditional methods. In the yield trials, grain weevil damage averaged 0·39 in both years after storage in the husk for 9 months. Varietal and location effects were significant for proportion of weevil damage, but the interaction effect was not significant in either year. The broadsense heritabilities were intermediate/high for proportion of weevil-damaged grain (H2=0·81 in 2007 and 0·59 in 2010), and there is potential that populations can be found combining a substantial yield increase with no increase in weevil susceptibility for households using traditional storage methods. For those households with access to airtight storage systems, the results emphasize the need to exploit the interaction of variety with storage method to benefit from the yield advantage of introduced varieties through the concurrent dissemination of improved seed with subsidized, airtight storage drums.

Most crop models make use of a nutrient-balance approach for modelling crop response to soil fertility. To counter the vast input data requirements that are typical of these models, the crop water productivity model AquaCrop adopts a semi-quantitative approach. Instead of providing nutrient levels, users of the model provide the soil fertility level as a model input. This level is expressed in terms of the expected impact on crop biomass production, which can be observed in the field or obtained from statistics of agricultural production. The present study is the first to describe extensively, and to calibrate and evaluate, the semi-quantitative approach of the AquaCrop model, which simulates the effect of soil fertility stress on crop production as a combination of slower canopy expansion, reduced maximum canopy cover, early decline in canopy cover and lower biomass water productivity. AquaCrop's fertility response algorithms are evaluated here against field experiments with tef (Eragrostis tef (Zucc.) Trotter) in Ethiopia, with maize (Zea mays L.) and wheat (Triticum aestivum L.) in Nepal, and with quinoa (Chenopodium quinoa Willd.) in Bolivia. It is demonstrated that AquaCrop is able to simulate the soil water content in the root zone, and the crop's canopy development, dry above-ground biomass development, final biomass and grain yield, under different soil fertility levels, for all four crops. Under combined soil water stress and soil fertility stress, the model predicts final grain yield with a relative root-mean-square error of only 11–13% for maize, wheat and quinoa, and 34% for tef. The present study shows that the semi-quantitative soil fertility approach of the AquaCrop model performs well and that the model can be applied, after case-specific calibration, to the simulation of crop production under different levels of soil fertility stress for various environmental conditions, without requiring detailed field observations on soil nutrient content.

Delayed senescence, or stay-green, contributes to a longer grain-filling period and has been regarded as a desirable characteristic for the production of a number of crops including wheat. In the present study, in order to identify quantitative trait loci (QTLs) for traits related to the progression of wheat flag leaf senescence, green leaf area duration (GLAD) of a doubled haploid (DH) population, derived from two winter wheat varieties Hanxuan10 and Lumai14, was visually estimated under two water conditions and was recorded at 3-day intervals from 10 days after anthesis to physiological maturity using a 0–9 scale. According to GLAD, parameters related to the progression of senescence of DH lines and their parents were estimated by the Gompertz statistical model. Based on the model parameters, DH lines were categorized into three groups under drought stress and four groups under well-watered conditions. A total of 24 additive QTLs and 23 pairs of epistatic QTLs for parameters related to the progression of senescence were identified on 18 chromosomes, except for 3B, 1D and 6D. Of the QTLs detected, 14 and 10 additive QTLs were associated with the investigated traits under drought stress and well-watered conditions, respectively. Furthermore, 4, 7, 6, 2 and 2 additive QTLs for traits related to progression of senescence were clustered around the same or similar regions of chromosomes 1A, 1B, 5A, 5B and 7A, respectively. The present data provided the genetic basis for high phenotypic correlations among traits related to the progression of wheat flag leaf senescence. In addition, 17 loci were co-located or linked with previously reported QTLs regulating chlorophyll fluorescence, high-light-induced photo-oxidation, or heat stress and dark-induced senescence. The marker Xwmc336 on chromosome 1A, responsible for the onset and end times of leaf senescence, the time to maximum rate of senescence, the time to reach 75% senescence and chlorophyll content under drought stress may be helpful for marker-assisted selection breeding of wheat.

Predictive models for the accumulation of available phosphorus (Olsen-P, extracted with 0·5 mol/l sodium bicarbonate (NaHCO3) at pH 8·5) in the north-western arid areas of China, especially in Xinjiang, are essential for the improved management of phosphorus (P) fertilizers. In the present study, an accumulation model for Olsen-P in grey desert soil (Calcaric Cambisol) was developed using the data for initial Olsen-P in soil, P fertilizer application rate (organic and inorganic P), crop yields, and soil pH from a 22-year long-term experiment (1990–2011) with 3-year rotation of wheat (Triticum aestivum L.), maize (Zea mays L.) and cotton (Gossypium spp.). The model was also validated independently using previously published data from the literature. The results indicated an average net accumulation of Olsen-P in the plough layer (0–200 mm) of 0·36 mg/kg/year (from 0·083 to 0·47 mg/kg/year) when P fertilizer was applied, while an average net Olsen-P loss of 0·12 mg/kg/year (from 0·067 to 0·26 mg/kg/year) was observed without P fertilization in the soil. For target yields of wheat, maize and cotton at 5, 6 and 6 tonne/ha (t/ha), respectively, in soil with pH 8, the rates of Olsen-P increase in the soil as estimated by the model were 0·11, 0·24, 0·36, 0·49 and 0·61 mg/kg/year when P application rates were 60, 70, 80, 90 and 100 kg P/ha per 3-year period, respectively. For every 100 kg/ha of P surplus, Olsen-P increased by 1·1 mg/kg in Xinjiang grey desert soil. This Olsen-P accumulation model was valuable for the management of soil P in agricultural production and environmental protection in north-western China and other arid areas planted with a yearly rotation of wheat, maize or cotton.

Pythium damping-off caused by Pythium aphanidermatum usually occurs in commercial nurseries of cucumber seedlings. The purpose of the present study was to develop a container medium for effectively suppressing Pythium damping-off of cucumber seedlings. Seven agricultural materials were tested for their suitability as substrates for the growth of cucumber seedlings. Bas Van Burren No. 4 peat moss (BVB) was able to promote the growth of cucumber seedlings, but it was ineffective against Pythium damping-off. Spent blewit mushroom compost (SBMC) was an available substrate that could inhibit P. aphanidermatum, but it also inhibited the growth of cucumber seedlings slightly. A cultural medium, spent blewit peat compost (SBPC), containing 50% (v/v) SBMC, 50% (v/v) BVB and 0·3% (w/v) lime was consequently formulated. The SBPC was able to promote the growth of cucumber seedlings and reduce the incidence of Pythium damping-off. A total of 20 micro-organisms were isolated from SBMC compost and screened in steamed SBPC medium for their ability to inhibit the growth of P. aphanidermatum. Among these, Bacillus aryabhattai isolate number CB13 was able to suppress P. aphanidermatum significantly in the steamed SBPC medium. Thus, bio-formulation of SBPC medium with the beneficial microbe B. aryabhattai CB13 was carried out. The incidence of Pythium damping-off was reduced from 58% in steamed SBPC medium to 4% in the bio-formulated container medium. The novel bio-formulation has high potential for controlling Pythium damping-off in commercial nurseries.

Cassava (Manihot esculenta Crantz) is an important storage root crop with largely unexplored and unexplained potentially valuable genetic variability. Genetic variability is important in selecting suitable genotypes for crop improvement. The present study was aimed at assessing the extent of variability in cassava storage root bulking, based on fresh storage root yield accumulated over time. Twelve cassava genotypes were evaluated in a randomized complete block design at three contrasting locations in Uganda. Assessments were done from 5 to 13 months after planting at intervals of 2 months. Genotype, harvest time, location and their interactions were significantly different for fresh storage root yield and most of the other traits assessed. Estimates of variance components revealed that a large portion of the phenotypic variance was accounted for by the genotypic component for all traits assessed indicative of substantial genetic variability among the genotypes evaluated. This genetic variability is important in a hybridization and/or selection programme because it implies that significant genetic gain through phenotypic selection is possible for the traits assessed. Fresh storage root yield was positively and significantly correlated with storage root girth, harvest index, shoot mass and storage root number. The information generated will inform future breeding initiatives to develop early-bulking cassava genotypes with farmer-preferred traits in Uganda.

Crop nitrogen (N) status is an important indicator of crop health and predictor of subsequent crop yield. The present study was conducted to analyse the relationships between nitrogen nutrition index (NNI), nitrogen biomass difference (ΔNB) and spectral indices in wheat, and then attempt to improve field N management. Spectral indices and concurrent sample N and biomass parameters were obtained from the Shihezi University experimental site in Xinjiang, China during 2009 and 2010. The results showed that all spectral indices were significantly correlated with NNI. Regression functions with the highest determination coefficient (R2) and the lowest root mean square error (RMSE) were used to improve prediction of NNI, and then the selected spectral index was used to estimate NNI and ΔNB. The strongest relationships were observed for the products of modified normalized difference 705 × biomass dry weight (BND705) and the enhanced vegetation index 2 (EVI2) for estimating NNI. There were also strong relationships between the NNI and the normalized NNI (ΔNNI) as well as between ΔNNI and ΔNB, with a linear relationship between ΔNB and the spectral index BND705 and a linear relationship between ΔNB and the spectral index EVI2. These results indicated that BND705 and EVI2 can be used to improve the accuracy of NNI estimation, and the correlations of ΔNB and NNI with BND705 and EVI2 can be used to further improve field N management in wheat.

In most regions, sugar beet is normally sown as a spring crop. If sown in autumn the crop remains on the field over winter and may achieve fast re-growth in spring from assimilates stored within the beet, allowing earlier leaf growth and light interception in spring. The specific leaf area (SLA) (ratio between leaf surface and leaf mass) is mainly affected by leaf area expansion and consequently affects productivity in early growth stages. The aim of the present study was (i) to examine the SLA dynamics of autumn-sown sugar beet before and after winter and (ii) to develop an empiric approach describing SLA changes during the growth period. A field trial in northern Germany with three different sowing times (mid-April, mid-June and mid-August) and varying plant densities (148 000, 246 000 and 370 000 plants/ha) was carried out in 2009/10 to 2011/12. The average SLA of the canopy was the highest (>25 m2/kg) directly after emergence, then decreased until autumn (<13 m2/kg) and increased again up to 20 m2/kg during re-growth of winter sugar beet in spring. A stepwise multiple regression analysis revealed mean photosynthetically active radiation over 10 days before measurement (PARmean), leaf area index (LAI), mean temperature over 10 days before measurement (Tmean) and temperature sum since sowing (Tsum) as the main influences on SLA dynamics. The strongest correlation to SLA was shown by Tmean (r = 0·69) and the weakest by Tsum (r = −0·28). A multiple linear regression model was fitted to the dataset with Tmean, PARmean and log (Tsum) achieving an adjusted R2 of 0·64. This empirical equation is suitable for use in a crop growth model for winter sugar beet.

Improvements of a home-made mobile open-circuit respirometry system for the rapid determination of methane (CH4) and carbon dioxide (CO2) production, oxygen (O2) consumption and, thereafter, heat production (HP) for small ruminants are described and validated. Upgrades consisted of three main features: utilization of a head hood (replacing the previous face mask); use of a computerized control system, data acquisition and recording for gases and air flux (replacing collecting bags for air sampling); and use of a gas cooler to remove the air sample moisture (replacing the chemical drier (silica gel) approach). Calibration factors were established by injecting nitrogen (N2) and CO2 in the system into the head hood. Repetitive and consistent values for the calibration factor were obtained for O2 and CO2 which confirmed the absence of leaks and the good performance of the system. In addition, an experimental test with 12 Manchega female dry sheep was conducted to validate the system. Three diets based on cereal grain, fibrous by-products and alfalfa hay (ALH) were used with four sheep per diet. Metabolizable energy intake was close to metabolizable energy for maintenance. Average HP measured by indirect calorimetry (respiratory quotient (RQ) method) was close to the average HP determined from Carbon–Nitrogen balance (CN method) accounting for 443 and 426 kJ/kg0·75 body weight (BW) per day, respectively. Fasting HP was determined by the RQ method with two sheep from the ALH diet accounting for 269 kJ/kg0·75 BW per day. The head hood and computerized control, data acquisition and recording as well as the gas cooler improved the system by reducing the labour input without loss of functionality for measuring gas exchange and energy metabolism in small ruminants.

Lignification-associated phenolic acids are widely distributed in graminaceous plant cell walls. Nylon bags containing maize bran, wheat bran, millet husk and rice husk were incubated in the rumens of five Charolais (♂) × Nanyang (♀) crossbred steers for 6, 12, 24, 36, 48 and 72 h. The in situ ruminal disappearance of ester-linked phenolic acids linearly increased in the brans with increasing incubation time, and the disappearance was greater for ester-linked ferulic acid (FAest) than for ester-linked p-coumaric acid (PCAest). The disappearances of FAest and PCAest were positively correlated with disappearances of neutral detergent fibre (NDF), cellulose and hemicellulose. The effective degradabilities of NDF, cellulose and hemicellulose in the brans were markedly greater than the effective degradabilities of these components in the husks, and were negatively correlated with the contents of Lignin (sa), ether-linked ferulic acid, PCAest and ether-linked p-coumaric acid in both the cereal brans and husks. These findings suggested that breeding forage crops with modified phenolic acid contents could represent an alternative strategy to promote further increases in fibre digestibility of cereal residue feeds for ruminant animals.

The goal of the present study was to characterize the growth of body parts and composition of the growing empty body to infer how these aspects relate to the long-term growth of goat wethers from dairy breeds. Animals were slaughtered at several ages from birth to maturity (≅900 days old). All body parts were weighed and sampled to determine chemical constituent dry matter, crude protein, crude fat, ash and specific energy. The monomolecular (Brody), Gompertz, and Richards models, a biphasic model formed by the combined Brody and Gompertz functions, and a simple linear model were fitted to the growth profiles with different variance functions and were all evaluated using likelihood-information criteria. The effect of breed (genotype) was accounted for in all models but the resulting models were not more likely than the models without the breed effect. Remarkable differences were observed regarding inflection points, growth rates and trends for all body parts and chemical constituents of the body. The biphasic model did not supplant the monomolecular, Gompertz, Richards or the linear model in terms of likelihood-information criteria. Therefore, body parts and chemical constituents of the empty body presented monomolecular, sigmoid and linear time-trends. The growth profiles of fat, protein and energy of the empty body did not scale isometrically with the empty body proper. In addition, the variance was heteroscedastic along the time scale and was better represented by both an exponential variance over time or by a power function of the mean.