Vertical distribution and population dynamics of Rotylenchulus reniformis under soybean and maize cultivation in a tropical no-till system

The phenological growth stages of various species of monocotyledonous and dicotyledonous plants can be uniformly coded using the Biologische Bundesanstalt, Bundessortenamt, und Chemische Industrie (BBCH) scale. The aim of the present study was to determine the duration of different phenological stages and the temperature requirements of the sugar-apple, Annona squamosa, during two crop cycles in the semiarid region of Brazil. Phenological stages were divided into eight of ten possible principal stages: (0) bud development, (1) leaf development, (3) shoot/branch development, (5) inflorescence emergence, (6) flowering, (7) fruit development, (8) fruit maturity and (9) senescence and the beginning of dormancy. The phenological cycle of the sugar-apple from having closed leaf buds to the fruit ripening stage lasted 149 and 164 days with temperature requirements of 1684.5 and 1786.7 degree days (DD) for the first and second crop cycles, respectively. The results provided important information that will inform the correct timing for crop management practices.

Performance of tissue-cultured versus sucker-derived East African highland banana (Musa AAA-EA) under high and low input systems in Uganda

Weeds are a major cause of production losses in arable lands, but the relative contributions of native and non‐native weeds vary considerably among countries. Understanding the factors that drive these differences could help improve biosecurity and weed management in arable lands by targeting measures to the unique agricultural contexts of different countries. However, global‐scale analyses aimed at understanding the variations in weed richness are rare. We examined the factors associated with native and non‐native weed richness in maize ( Zea mays ) fields worldwide. Using species records from 40 countries, we used random forest analysis to assess the importance of nine explanatory variables, selected a priori, on the richness of native and non‐native weed species in maize cultivation. We found that maize harvested area, arable land area and the number of scientific publications on weeds from the region were positively correlated with both native and non‐native weed richness. While the length of maize cultivation in a country was weakly positively correlated with both native and non‐native weed richness, the length of cereal cultivation was negatively correlated with non‐native weed richness. The length of cereal cultivation also had the strongest negative correlation with the percentage of non‐native weed species. Our findings suggest that most native weeds in maize fields probably result from ‘spillover’ from other cereal crops cultivated prior to maize cultivation in each country. Consequently, the percentage of non‐native weeds is relatively low in countries with a short history of maize cultivation but a long history of other cereal cultivation. In countries with a long history of cereal cultivation, native weeds of other cereal crops (e.g., sorghum and wheat) significantly shape weed assemblages of maize fields. These native weeds, originally associated with other cereal crops, have become introduced worldwide as contaminants of maize cultivation and now occur as non‐native weeds in countries with shorter cereal cultivation histories. This macroecological insight offers new opportunities for targeted weed management and potentially could inform strategies to mitigate the impacts of native and non‐native weeds in different agricultural contexts. In countries with long cereal cultivation histories, understanding the drivers of spillover from other crops could help identify specific high‐risk weed species that could facilitate targeted control measures to improve productivity. Conversely, in countries with shorter cereal cultivation histories, emphasis should be placed on preventing non‐native weeds from being introduced, particularly from seed contaminants.

Summary Worldwide, conservation agriculture practices involving minimal soil disturbances and retention of crop residue (>30%) have been practised increasingly and recognized to enhance soil health by optimizing key soil attributes. However, little information is available on the short‐term effects of conservation agriculture practices on soil properties under rainfed Vertisols of Central India. Thus, our aim was to study the short‐term effects of contrasting tillage treatments and cropping systems on soil aggregation, aggregate‐associated carbon (C), carbon pools and crop productivity. This study comprised three tillage systems (TS), reduced tillage (RT), no tillage (NT) with retention of crop residue and conventional tillage (CT), together with four cropping systems (CS), namely soya bean ( Glycine max L.) + pigeon pea ( Cajanus cajan L.) (2:1), soya bean–wheat ( Titricum durum L.), maize ( Zea mays L.) + pigeon pea (1:1), and maize–chickpea Cicer arietinum L.). The experiment was laid out in a split‐plot design with three replicates. Soil samples were collected at four depths: 0–5, 5–15, 15–30 and 30–45 cm from the experimental field after completion of four crop cycles. Results indicated that at depths 0–5 and 5–15 cm, tillage and cropping system had a significant effect on aggregate mean weight diameter (MWD). The MWDs of 0.97 and 0.94 mm were larger for NT than CT (0.77 and 0.83 mm) at 0–5‐ and 5–15‐cm depths, respectively. Water‐stable aggregates (WSAs) were also larger for NT (70.74%) and RT (70.09%) than CT (59.50%) at 0–5 cm. Tillage practice, cropping system and their interaction had a greater effect ( P < 0.05) on the content of aggregate‐associated C for large macroaggregates (LM). There was more aggregate‐associated C for NT and RT at 0–5‐cm depth than for CT. Cropping system also had a significant effect ( P < 0.05) on aggregate‐associated C at 0–5‐cm depth. Soil organic C (%) fractions were in the order of non‐labile >very labile >less labile >labile for 0–5‐ and 5–15‐cm depths after four crop cycles. Less labile and non‐labile C fractions contributed >50% of TOC, indicating a more recalcitrant form of carbon present in the soil. Tillage had no significant effect ( P > 0.05) on crop yields after four crop cycles. Conservation agriculture can have a positive effect on aggregate stability, aggregate‐associated C and different carbon pools in a Vertisol. Highlights Does conservation agriculture affect soil aggregation, aggregate stability and carbon pools more than conventional tillage? The SOC concentration increases with aggregate size and provides physical protection and stabilization of carbon (C). Aggregate‐associated C content was significantly affected by tillage practices and cropping system. Less labile and non‐labile C fractions contribute >50% TOC in the rainfed Vertisols of central India.

Dynamics and Availability of Different Pools of Manganese in Semiarid Soils as Affected by Cropping System and Fertilization

Potatoes are among the most profitable agricultural crops in arable farming in the Netherlands and consequently are grown as frequently as conditions allow. As a result Dutch farmers experienced huge problems with potato cyst nematodes during the last 50 years. In Chapter 1 an outline is presented of the situation of potato cyst nematode control in the 1980's, the problems, possible solutions and the research initiated, of which a part is presented in this thesis.In 1984 emphasis was put into research concerning the efficiency of soil fumigation on heavy marine clay soils where the majority of Dutch seed and consumption potatoes are grown. Both laboratory and field experiments were carried out to investigate the efficiency of 1,3 dichloropropene and metam-natrium. This required the processing of thousands of larvae suspensions. One of the most labourious and tedious occupations in nematological research is the counting of individuals of the pathogen.In Chapter 2 A GOP-302 image analysis system - Context Vision, Sweden - was used to automate the counting of large numbers of larvae-suspensions of Globodera rostochiensis and G. pallida . These suspensions originated from hatching tests, which were conducted to estimate percentage mortality in field and lab experiments of nematodes exposed to nematicides. The result is called ANECS ( A utomatic NE matode C ounting S ystem), a software program that can count up to 64 compartments with larvae suspensions successively without the aid of an operator. A special object carrier was developed. Images of up to eight object carriers (512 larvae suspensions) can be stored and image analysis can be suspended to off-office hours. The time needed to count one compartment was reduced by 80% to one minute compared to 'manual' labour while the time for probe preparation remained the same. The percentile error is highest at very low larvae densities (<20 per suspension) and is caused by pollution with small fibres carried by air during the handling of the larvae suspensions. This problem can be minimised by setting up clean-laboratory procedures. At least 95% of the larvae originating from hatching tests were recognized and counted. The program can and has been be adapted to count other nematode species or to suit more complicated problems like counting both larvae and eggs in one suspension.In Chapter 3 errors due to subsampling and laboratory procedures affecting the expected value and variance of cyst counts were investigated. Several fields, infested with potato cyst nematodes ( Globodera rostochiensis and G. pallida ) were sampled by collecting bulk samples of approximately 70 cores amounting to 1.8 or 2.5 kg soil from a number of square metre plots located in a regular grid pattern over a 0.33 ha area. Bulk samples from five fields, I-V, were thoroughly mixed and from one field, VI, lightly mixed, and subsequently divided into three subsamples of approximately equal weights. Two, sometimes three, subsamples were elutriated separately. Cysts were elutriated by two commercial laboratories, 1 and 2, and separated from the debris and counted at two research laboratories, 0 and 3.Random bulk samples from five fields, I-V, were divided into three portion after thoroughly mixing and taken to Laboratory 0, to compare elutriation precision and accuracy of commercial and scientific laboratories and to check the quality of mixing. To this purpose, pairs or triples were divided into classes. The expected value of the variance within pairs was estimated per class and could be described by a distribution function analogue to a negative binomial distribution, but with three in stead of two parameters. Cysts appeared to be randomly distributed in the well mixed samples, resulting in a binomial or trinomial distribution between pairs or triples. The expected values of the coefficient of variation associated with elutriation were 3.6, 9.6 and 5.5% in the Laboratories 0, 1 and 2, respectively. The upper 95% confidence limit,δ 0.95 , of coefficients of variation associated with elutriation in Laboratories 1 and 2, were estimated by the differences in 95% upper limits of coefficients of variation between the Laboratories 1 and 2 on the one hand and Laboratory 0 conversely. This difference,δ 0.95 , ranged from 73% to 42% for Laboratory 1 and from 43% to 19% for Laboratory 2 if 10 to 100 cysts were counted in samples. The consequences of these laboratory errors for the accuracy of sampling methods for both research and extension purposes are discussed.Nematicide trials require reliable results concerning the effect caused by the fumigant. The percentage mortality of potato cyst nematodes can be estimated by comparing the hatchability of untreated larvae with that of nematicide treated larvae. In Chapter 4 , research is described to improve the quality of hatching tests. Hatching tests using potato root diffusate are labourious and yield quite variable results. Sources of variability were identified and analysed, and solutions were presented. A method was developed to conduct hatching tests using inert materials so that the total variation at the end of the test is minimized.A number of hatching tests was carried out to increase reliability, optimize the method and limit the amount of work. Thus, it was possible to obtain a coefficient of variation ( cv ) of the hatching process which is in accordance with the combined errors expected when a certain number of cysts is treated and eggs are used in a hatching test. An Appendix is provided listing the different errors and ways to calculate and cope with them.The results indicate that the hatching process is no longer an important source of variation for the end result. All variation higher than expected could be explained by variation between replications of batches with the same treatment, indicating that small differences in nematicide application cause major differences in the end result. The treatment effect was more important in field experiments than in laboratory experiments.The hatching curve could be described adequately by a log-logistic curve with 3 parameters (λfinal number of hatched larvae,αtime,βslope parameter). Addition of a fourth parameter (γ, incubation time) improved the fit of the hatching curve significantly. Using the log-logistic model, final hatch can be predicted with a certain error before the actual hatching test ended, but in general final hatch is underestimated. When an error of 5% is accepted, the length of time required to perform a hatching test of a laboratory experiment can be reduced by 80% for untreated batches and by 40 to 80% for batches treated with nematicides. Acceptable reduction is negatively correlated with the concentration of the fumigant used.Hatching tests with cysts originating from field experiments are unsuitable for prediction using a time limited data set. In cyst batches from the field compound hatching curves could be distinguished in 4 out of 6 fields, indicating that the soil samples contained at least two fractions of cysts with different hatching responses. Prediction would cause a significant underestimation of final hatch and consequently an overestimation of mortality.Because of its high vapour pressure, 1,3-dichloropropene is primarily used on marine clay soils. In Chapter 5 a laboratory experiment is described investigating the two stereo-isomeres of 1,3-dichloropropene for their efficiency in killing nematodes. Batches of increasing numbers of Globodera rostochiensis cysts were exposed to a range of concentrations of the (E)- and (Z)-isomers of 1,3-dichloropropene. The cysts were of identical origin. Temperature during treatment was 10 oC, humidity 100% and time of exposure 8 days. The integrals of concentration time products ( CT ) created were 0, 3, 7, 14, 31, 60, 125, 242, and 437μg/ml·day for the (E)-isomer and 0, 3, 16, 59, 240, and 419μg/ml·day for the (Z)-isomer. Survival was estimated with hatching tests 1.5, 3, and 7 months after treatment.The relationship between dosage of (E)-isomer and numbers of hatchable nematodes followed a log-logistic equation at all hatching dates. Hatchability, and therefore lethal dosages, increased as hatching tests were more delayed. Seven months after treatment, practically all treated nematodes had recovered and hatchability of treated and untreated nematodes was the same. A log-logistic relationship was also found for dosage (Z)-isomer and numbers of hatchable nematodes 1.5 month after treatment. When hatching tests of nematodes treated with the (Z)-isomer were delayed till 3 and 7 months after treatment, the results were better explained by a compound model, assuming two independent log-logistic effects, one stimulating hatch at low dosages and one reducing hatch at all dosages. Only the (Z)-isomer of 1,3-dichloropropene was effective as a nematicide.Chapter 6 presents research concerning the efficiency of standard doses of 1,3 dichloropropene in fields with a high silt content. Three fields of marine clay soil were fumigated with 150 l/ha 1,3-dichloropropene (DD) (Teleone II TM, Shell 95 TM). On three dates after application, concentrations of Z- and E- 1,3-dichloropropene were measured per 5 cm layer of soil to a depth of 40 cm and integrals of concentration time products were calculated. When the fumigant was no longer detectable, a top soil treatment with either 150 l/ha metam-sodium or 180 kg/ha dazomet (active compound methyl isothiocyanate) was applied, followed immediately by autumn ploughing. Soil samples were taken before and after fumigation and after the top soil treatment to extract potato cyst nematodes (PCN). Survival was determined by means of hatching tests. Mortalities after the DD treatment, defined as 100 - % survival, were estimated per 5 cm layer of soil to a depth of 30 cm to construct dosage response curves. Fumigation with DD killed 48, 48 and 72% of the PCN per field, respectively. Accelerated breakdown of DD by microorganisms accounted for the two lower mortality rates.The additional top soil treatment with metam-sodium increased mortality to 90% or more. Dazomet, however, was less effective (53 and 80%) considering that twice as much of the active compound was applied as in the metam-sodium treatment. Multiplication of hatched larvae originating from the injection layer after the DD treatment was 25% less than that from untreated plots. This was caused by a lower fraction of larvae developing into cysts. PCN could be retrieved from soil layers as deep as 80 cm below the surface. Fumigation reached only a fraction of the infested soil, down to 25-30 cm. The infestation foci were so small compared to the standard minimum area fumigated (1 ha) that 90% of the active compound would be wasted on non-infested soil. Soil fumigation, whether or not combined with an additional top soil treatment, will seldom be profitable. Monitoring for infestation foci is recommended.As soil fumigation was not a viable option to keep potato cyst nematodes in check on heavy marine clay soils, another way of control had to be found. Research was focussed at the development of sampling methods for the detection of small infestation foci with high reliability (≥90% probability of detection). Precautionary soil fumigation can be avoided, the area where a control measure has to be applied can be minimized to the actual infestation, and detection occurs so early that (partially) resistant potato cultivars can be grown without significant yield reduction as population densities are still low.Research in the Flevopolders yielded promising results. Therefore, in 1990, a research program was initiated to develop new sampling methods for the detection of patchy infestations of potato cyst nematodes ( Globodera rostochiensis and G. pallida ) with known accuracy in all potato cropping areas of The Netherlands. Patchy infestations in cropping areas of the provinces of Zeeland, Friesland, Groningen and Drente were sampled to validate a model based on data from cropping areas in Flevoland and to determine whether one detection method could meet the requirements of all cropping areas in The Netherlands. The results are presented in Chapter 7 . Eighty two fields were presampled to locate patchy infestations using a coarse sampling grid (8 · 3 m). Parts of thirty seven fields, containing one or more foci, were sampled intensively by extracting at least 1.5 kg of soil per square metre (1.33 · 0.75 m). Forty foci were analysed for spatial distribution characteristics of cysts using Generalized Linear Models (GLM's) and classical Multiple Linear Regression Analysis, differing in assumptions about the distribution of the input variable (number of cysts per kg of soil).The results showed that the data from all investigated cropping areas fit well to an exponential model with two parameters, the length and width gradient parameters. Significant differences in these parameter values between cropping areas could not be demonstrated. As both parameters follow a normal distribution, the probability of any combination of these parameters can be described by a bivariate normal distribution. Gradient parameters were correlated but significant correlations between these parameters and certain variables, such as the nematode species involved ( G. pallida or G. rostochiensis ), the time interval between sampling and the last potato crop, soil type, cropping frequency and cyst density in the focus centre could not be demonstrated. It can be concluded that one detection method for small infestation foci suffices for all investigated cropping areas. Its expected accuracy is independent of soil type, potato cyst nematode species, cropping frequency or time interval between sampling and last potato crop.In Chapter 8 the model for infestation foci developed in the previous chapter was applied for practical usage. A computer program called SAMPLE was developed to evaluate existing and create new sampling methods for the detection of patchy infestations or 'foci' of the potato cyst nematode ( Globodera spp.). By combining a model for the medium scale distribution of cysts, which provides the expected population densities at each position within the focus, and a model for the small scale distribution within square metres (negative binomial distribution) SAMPLE allows to simulate sampling procedures.The importance of the parameters of the two distribution models - the length and width gradient parameters for the medium scale distribution and the aggregation factor k of the negative binomial distribution for the small scale distribution - was investigated by sensitivity analyses. The aggregation factor k proved to be less important when calculating the average detection probability of a focus than the length and width gradient parameters. Several existing versions of the statutory sampling method used in The Netherlands were tested for their performance on a standard infestation focus with a central population density of 50 cysts/kg soil.The standard focus is small enough to use resistant potato varieties as a control measure without noticeable yield reductions in a 1:3 potato crop rotation. As the statutory soil sampling methods did not perform with the desired average detection probability, set at 90%, the program was used to develop several new sampling methods for focus detection and to investigate their performance. SAMPLE is a tool to develop sampling methods on demand for every possible combination of characteristics required for use by seed and ware potato growers (recommendations for optimum control measures leading to maximum returns, Integrated Pest Management) and by governments (legislation, quarantine and export protection).For advisory purposes a model is required describing the relation between the number of potato cyst nematodes and tuber yield. A stochastic model with biologically relevant parameters was available. In Chapter 9 the direct relation between the number of potato cyst nematodes and plant growth is described and used to deduce the relation between nematode density and yield reduction of total plant weight and tuber yield. The relation between small and medium initial population densities and the relative total plant weight was derived as cross sections at right angles to the time axis of a growth model with three dimensions: time after planting t , relative total plant weight Y and relative growth rate r p /r 0 . The relative growth rate is the (constant) ratio between the growth rate r p of plants of a certain weight at a nematode density P and the growth rate r 0 of (younger) plants of the same weight without nematodes. Therefore, the ratio between the time after planting that plants need to reach a certain weight in the absence of nematodes and at nematode density P, t 0 /t p equals the ratio r p /r o (2).The relative growth rate r p /r o = k + (1 -k )0.95 P/T -1for P > T and = 1 for P ≤T (3). Formally, k is the minimum relative growth rate as P →∞. As a result the arbitrary equation y = m + (1- m )0.95 P/T- 1for P > T and = 1 for PT (6) also applies to the relation between small and medium initial population densities and relative total plant weight. T is the tolerance limit, below which growth and yield are not reduced by nematodes; m is the relative minimum yield.The relations between small and medium initial population densities of potato cyst nematodes and relative tuber weight of potatoes can be derived from the growth model in an analogous way. However, there is one complication: tuber initiation does not start at the same haulm weight in plants with and without nematodes, but at the smaller haulm weight the larger the nematode density. As a consequence, tuber weights of plants with a certain total weight at nematode density P are not equal to those of plants with the same total weight without nematodes, but r p Δ t units of weight larger,Δ t being the difference between the actual time of tuber initiation and the time total plant weight becomes the same as that of plants without nematodes at the initiation of tuber formation.Relative total and tuber weights of plants with 'early senescence' and at large nematode densities are smaller than estimated by the model and equation (2). This indicates that at large initial population densities growth reducing mechanism(s) become active that were not operating at smaller densities.In Chapter 10 an advisory system is presented for the management of potato cyst nematodes ( Globodera pallida) . It emphasizes the use of partially resistant potato cultivars, which provide the possibility of keeping population densities of potato cyst nematodes at a low level in short fixed rotations. Using stochastic models based on the population dynamics of potato cyst nematodes and the relation between pre-plant nematode densities and relative yield it is possible to calculate the probabilities of population development and the reductions in yield caused by these population densities. A simulation model is developed which integrates both models, using the frequency distributions of some of the most variable parameters relevant to a particular combination of potato cultivar and nematode population. Also, the natural decline in population density when non-hosts are grown is incorporated in the model.The model makes it possible to calculate the probability of a certain yield reduction, given a certain potato cultivar, nematode population and rotation. Therefore, it becomes feasible for a farmer to evaluate risks and the costs of different control measures in fixed rotations. The application of this model in the starch potato growing areas could lead to significant improvements in financial returns and a major reduction of the use of nematicides.In Chapter 11 we describe the 'Seinhorst research program' initiated by Dr J.W. Seinhorst, former head of the Nematology Department of the IPO-DLO. It consists of an empiric philosophy, the scientific methods applied, and the models developed at the IPO-DLO during the last 45 years of nematological research, including the 13 years in which the research described in this thesis was carried out. All theories of the Seinhorst research program are developed by searching for recurring regularities (patterns) in a collection of observations, named 'the empirical base'. To prevent " ghost theories from sloppy data " all assumptions underlying the empirical base are carefully described in theories with respect to methodology and technology, including statistics.The patterns to be recognized are summarized by mathematical equations, which must be connected with biological processes to bridge the gap between 'normal' language and mathematical language for the description of biological theories. Often, the patterns result from more than one biological process. If so, the basic patterns are disentangled from one another using a method of pattern analysis. The procedure is best carried out when only a limited number of more or less congruent patterns are involved. Therefore, attention must be given to the choice of the hierarchic level and the complexity of the investigated system. Investigations proceed from simple experimental systems to complex natural systems at a hierarchic level that is neither so high that manifesting processes are very dissimilar nor so low that one runs the risk of describing processes irrelevant for the purpose of the investigation.In the 'Seinhorst Research Program' this purpose is finding methods for improvement of financial returns of host crops attacked by plant-parasitic nematodes through calculating risks of nematode population development and subsequent yield reduction. Pattern analysis yields theories about causes of phenomena observed at the investigated hierarchic level and about properties of processes at the nearest lower hierarchic level. Predictions at the next higher hierarchic level are made by synthesizing several patterns in (stochastic) simulation models. Synthesis is also applied to compound patterns of processes in simple experimental systems, with the objective to explain complicated patterns in complex systems.In the Conclusions ( Chapter 12 ) an overview is presented of the practical results and aspects of the research effort described in this thesis. Some comments are made on the present state of affairs concerning potato cyst nematode control in the Dutch seed- and ware potato growing areas.

The albedo (alpha) of vegetated land surfaces is a key regulatory factor in atmospheric circulation and plays an important role in mechanistic accounting of many ecological processes. This paper examines the influence of the phenological stages of maize (Zea mays) and cowpea (Vigna unguiculata) fields on observed albedo at a tropical site in Ghana. The crops were studied for the first and second planting dates in the year 2002. Crop management was similar for both seasons and measurements were taken from 10 mx10-m plots within crop fields. Four phenological stages were distinguished: (1) emergence, (2) vegetative, (3) flowering, and (4) maturity. alpha measured from two reference surfaces, short grass and bare soil, were used to study the change over the growing seasons. Surface alpha was measured and simulated at sun angles of 15, 30, 45, 60, and 75 degrees . Leaf area index (LAI) and crop height (CH) were also monitored. Generally, alpha increases from emergence to maturity for both planting dates in the maize field but slightly decreases after flowering in the cowpea field. For maize, the correlation coefficient ( R) between alpha and LAI equals 0.970, and the R between alpha and CH equals 0.969. Similarly, for cowpea these Rs are 0.988 and 0.943, respectively. A modified albedo model adequately predicted the observed alphas with an overall R>0.860. The relative difference in surface alpha with respect to the alpha values measured from the two reference surfaces is discussed. Data presented are expected to be a valuable input in agricultural water management, crop production models, eco-hydrological models and in the study of climate effects of agricultural production, and for the parameterization of land-surface schemes in regional weather and climate models.

Our research team is participating in the ReCROP project, funded by the PRIMA-Med program, which focuses on developing and evaluating sustainable soil management practices. The project aims to reduce reliance on inorganic fertilizers and pesticides, prevent soil erosion, maintain or restore soil organic matter, and support the restoration of soil biodiversity.The temperate-humid zone of Spain is predominantly focused on livestock production, with forage maize being one of the main crops. An alternative practice proposed for this crop is its rotation with turnips (Brassica rapa L. var. rapa) as green manure. Turnips might offer multiple benefits: i) prevent the soil from remaining bare between harvest and sowing, ii) enrich the soil with minerals and organic matter, and iii) provide biofumigant properties through the release of thioisocyanates during the decomposition of the glucosinolates contained in their biomass.In 2021, a field experiment was established to assess the impact of turnip green manure on soil functioning and soil health. Six plots were established: three with conventional forage maize cultivation and three with maize planted after turnip green manure incorporation. The traditional crop rotation system of the region, consisting of one year of maize followed by three years of ley grassland, was followed. Soil properties were monitored over three years&amp;#8212;during maize cultivation in 2021 and ley grassland in 2022 and 2023. Soil samples (0-10 cm) were collected in late spring each year and analyzed for biochemical, physical, and chemical properties. This study presents the results on hydrolytic enzyme activities (C, N, P, and S cycles), dehydrogenase activity, and hot-water soluble carbon forms (carbohydrates and phenolic compounds).In the first year, when the soils were under maize cultivation, all biochemical properties showed higher values in the soil under conventional cultivation compared to the soil amended with green manure. Unexpectedly, the same was observed for organic matter content. However, over time, and as the soils transitioned to grassland cultivation, all biochemical properties tended to level out. When activities are expressed per unit of carbon, they initially follow the same pattern, being higher in conventionally managed soil than in soil amended with green manure (except for phosphomonoesterase and cellulase, which exhibit similar values in both soils). However, over time, this trend tends to reverse. This could reflect differences in agricultural practices resulting from the incorporation of green manure and the distinct practices between the maize and grassland cultivation phases, highlighting the sensitivity of the measured parameters to variations in agricultural soil use and management. However, to better understand the underlying causes of these differences, the study will continue into the next phase, when the soils will return to maize cultivation.Acknowledgements: The research was funded by the project PRIMA ReCROP Bioinocula and CROPping systems: an integrated biotechnological approach for improving crop yield, biodiversity and REsilience of Mediterranean agro-ecosystems. Ref PCI2021-121981/ AEI /10.13039/501100011033

Northeast China is the main production area of maize and soybean in China. In the present study, the rates of decomposition and replacement of soil organic carbon (SOC) were estimated using the soil inventory collected since 1991 from long-term maize and soybean cultivation plots in Heilongjiang Province, Northeast China, to evaluate the sustainability of the present cultivation system. The total carbon (C) content in soil was stable without any significant changes in the plots (approximately 28.5 g C kg−1). The δ13C value of soil organic matter under continuous maize cultivation increased linearly with an annual increment of 0.07 from −23.9 in 1991, which indicated that approximately 13% of the initial SOC was decomposed during the 13-year period of maize cultivation, with a half-life of 65 years. Slow decomposition of SOC was considered to result from the low annual mean temperature (1.5°C) and long freezing period (170–180 days year−1) in the study area. In contrast, the amount of organic C derived from maize increased in the soil with a very slow annual increment of 0.17 g C kg−1, probably because of the removal of all the plant residues from the plots. Based on the soil organic matter dynamics observed in the study plots, intentional recycling/maintenance of plant residues was proposed as a way of increasing soil fertility in maize or soybean cultivation.

The aim of the present research was to evaluate the efficiency of different vegetation indices (VI) obtained from satellites with varying spatial resolutions in discriminating the phenological stages of soybean crops. The experiment was carried out in a soybean cultivation area irrigated by central pivot, in Balsas, MA, Brazil, where weekly assessments of phenology and leaf area index were carried out. Throughout the crop cycle, spectral data from the study area were collected from sensors, onboard the Sentinel-2 and Amazônia-1 satellites. The images obtained were processed to obtain the VI based on NIR (NDVI, NDWI and SAVI) and RGB (VARI, IV GREEN and GLI), for the different phenological stages of the crop. The efficiency in identifying phenological stages by VI was determined through discriminant analysis and the Algorithm Neural Network-ANN, where the best classifications presented an Apparent Error Rate (APER) equal to zero. The APER for the discriminant analysis varied between 53.4% and 70.4% while, for the ANN, it was between 47.4% and 73.9%, making it not possible to identify which of the two analysis techniques is more appropriate. The study results demonstrated that the difference in sensors spatial resolution is not a determining factor in the correct identification of soybean phenological stages. Although no VI, obtained from the Amazônia-1 and Sentinel-2 sensor systems, was 100% effective in identifying all phenological stages, specific indices can be used to identify some key phenological stages of soybean crops, such as: flowering (R1 and R2); pod development (R4); grain development (R5.1); and plant physiological maturity (R8). Therefore, VI obtained from orbital sensors are effective in identifying soybean phenological stages quickly and cheaply.

The aim of the present research was to evaluate the efficiency of different vegetation indices (VI) obtained from satellites with varying spatial resolutions in discriminating the phenological stages of soybean crops. The experiment was carried out in a soybean cultivation area irrigated by central pivot, in Balsas, MA, Brazil, where weekly assessments of phenology and leaf area index were carried out. Throughout the crop cycle, spectral data from the study area were collected from sensors, onboard the Sentinel-2 and Amazônia-1 satellites. The images obtained were processed to obtain the VI based on NIR (NDVI, NDWI and SAVI) and RGB (VARI, IV GREEN and GLI), for the different phenological stages of the crop. The efficiency in identifying phenological stages by VI was determined through discriminant analysis and the Algorithm Neural Network–ANN, where the best classifications presented an Apparent Error Rate (APER) equal to zero. The APER for the discriminant analysis varied between 53.4% and 70.4% while, for the ANN, it was between 47.4% and 73.9%, making it not possible to identify which of the two analysis techniques is more appropriate. The study results demonstrated that the difference in sensors spatial resolution is not a determining factor in the correct identification of soybean phenological stages. Although no VI, obtained from the Amazônia-1 and Sentinel-2 sensor systems, was 100% effective in identifying all phenological stages, specific indices can be used to identify some key phenological stages of soybean crops, such as: flowering (R1 and R2); pod development (R4); grain development (R5.1); and plant physiological maturity (R8). Therefore, VI obtained from orbital sensors are effective in identifying soybean phenological stages quickly and cheaply.

Maize ( Zea mays L.), which is considered an important cereal everywhere, is widely cultivated in different agroecological conditions. Throughout their phenological stages, maize crops are attacked by pests and diseases, and in Ecuador these phytosanitary problems are usually counteracted with applications of pesticides. However, knowledge of beneficial entomofauna is fundamental to guide pest management programs. As part of this objective, the Coccinellidae species present in maize fields in localities (Santa Ana, Colon, and Danzarin) in Manabí province were identified. In each zone, maize plants were sampled from 2018–2019. A total of 2,654 specimens belonging to 14 taxa were collected in this study, of which Cheilomenes sexmaculata , Cycloneda sanguinea , Hippodamia convergens , Hyperaspis arida , and Psyllobora confluens were found in all the studied areas. Hyperaspis arida and Diomus apollonia are reported for the first time in Ecuador.

The effect of chamber placement site on N2O emission under different fertilizer regimes from maize field

AimsThe loss of soil organic matter (SOM) has widely been reported in the tropics after changing land use from shifting cultivation to continuous cropping. We tested whether continuous maize cultivation accelerates SOM loss compared to upland rice and forest fallow.MethodsBecause litter sources include C4 plants (maize in maize fields and Imperata grass in upland rice fields) in Thailand, C3-derived and C4-derived SOM can be traced using the differences in natural 13C abundance (δ13C) between C3 and C4 plants. We analyzed the effects of land use history (cultivation or forest fallow period) on C stocks in the surface soil. Soil C stocks decreased with the cultivation period in both upland rice and maize fields.ResultsThe rate of soil organic carbon loss was higher in maize fields than in upland rice fields. The decomposition rate constant (first order kinetics) of C3-plant-derived SOM was higher in the maize fields than in the upland rice fields and the C4-plant-derived SOM in the forest fallow. Soil surface exposure and low input of root-derived C in the maize fields are considered to accelerate SOM loss. Soil C stocks increased with the forest fallow period, consistent with the slow decomposition of C4-plant-derived SOM in the forest fallows.ConclusionsContinuous maize cultivation accelerates SOM loss, while forest fallow and upland rice cultivation could mitigate the SOM loss caused by continuous maize cultivation.

Bioenergy crop production is rapidly expanding in Europe, and the potential emissions of biogenic volatile organic compounds (BVOCs) might change the chemical composition of the atmosphere, influencing in turn air quality and regional climate. The environmental impacts of bioenergy crops on air chemistry are difficult to assess due to a lack of accurate field observations. Therefore, we studied BVOC fluxes from a bioenergy maize field in North‐Eastern Germany throughout the entire reproductive growth stage of the plants. Combining automated large chambers and proton transfer reaction mass spectrometry (PTR‐MS), we successfully measured fluxes of the highly reactive hydrocarbons monoterpenes (MTs) and sesquiterpenes (SQTs), together with several other BVOCs, including alcohols, aldehydes, ketones, benzenoids, and fatty acid derivatives. Emissions of MTs and SQTs were relatively high (17.0% and 3.6% of total mean molar BVOC emission, respectively) compared to methanol emissions (17.6%). Seasonal MT and SQT fluxes were clearly associated with the flowering phase, originating mainly from the flowering tissues as shown in additional laboratory experiments. From the observations of CO2 net ecosystem exchange and evapotranspiration rates, we could exclude heat and drought stress‐induced BVOC emissions. Standard emission factors calculated for all compounds, chemical groups, and growth stages, showed that the temperature dependency of volatile terpenoid fluxes decreased distinctively with proceeding development stage. The results indicate that emissions from large‐scale bioenergy maize fields should be better differentiated and considered in regional estimates of aerosol formation. For the implementation of such relation into biogeochemical modelling, it should be considered that not only seasonal weather development but also phenological growth stages are determining the BVOC patterns and emission potentials.