Different Amounts Of Straw Research Articles

How do different amounts of straw as well as compost in the home pen affect the rooting motivation of growing-finishing pigs?

Rooting is a strongly motivated, species-specific behaviour of pigs. Most housing systems do not provide appropriate materials that enable the full expression of this behaviour, and it remains unclear whether straw is suitable to entirely fulfil the rooting motivation of pigs. We therefore investigated the suitability of small (minimal) and large (deep) amounts of straw as well as large amounts of compost to satisfy rooting motivation in pigs. Fifty-seven growing-finishing pigs were housed in three pens, each providing permanent access to one of the three treatment substrates. Eight pigs per group were tested individually in a classical preference test (PT) and another eight pigs in a conditioned place preference test (CPPT). In the tests, pigs could show their preference to consume freely available feed (“feed”) or feed hidden in sawdust (“root”). In the CPPT, feed was only present during training but not during testing. Pigs were exposed to the test situation twice, with approximately 72 kg and 115 kg BW. In both tests, the following variables were measured and used as outcome variables in linear mixed effect models: first decision to choose one of the two stimuli (“feed” or “root”), duration of time spent in proximity to “root”, number of changes between stimuli, and latency to the first decision. Overall, the pigs’ first decision (by tendency; P = 0.076) and the duration in proximity to “root” (P = 0.034) varied among treatments: Pigs housed with minimal straw tended to be more likely to choose “root” first (posthoc comparison; P = 0.090) and spent more time in proximity to “root” (P = 0.030) than pigs housed with compost, whereas pigs housed with deep straw were intermediate. Interestingly, the patterns of response to the treatment differed depending on the behavioural tests for both, first decision (interaction; P = 0.032) and duration in proximity to “root” (interaction; by tendency; P = 0.006). In addition, pigs in the PT changed more often between stimuli than pigs in the CPPT (P < 0.001). There was a tendency for an interactive effect between test and treatment for latency to first decision (interaction; P = 0.082), though pairwise comparisons did not reveal any differences. We concluded that in this study housing with permanent access to compost satisfied rooting motivation in pigs more than housing with minimal amounts of straw.

Effects of different amounts of straw return and nitrogen fertilizer application on soil CO2 emission from maize fields.

Understanding the effects of different amounts of straw returning and nitrogen fertilizer application on soil CO2 emission from maize field can provide theoretical support for carbon sequestration and CO2 emission reduction and the implementation of black soil region conservation plan. Three rates of straw returning were set up in the semi-arid area of northwest Liaoning Province, China, i.e. 3000 (S1), 6000 (S2) and 9000 kg·hm-2(S3, full amount of straw returned to the field); crossed with three nitrogen fertilizer application rates in the sub-region, respectively, i.e. 105 (N1), 210 (N2, conventional nitrogen application rate) and 420 kg N·hm-2(N3). In addition, there was a control treatment (CK) without nitrogen fertilizer and straw returning. Soil samples were collected after 4 years field experiment with maize plantation. The influence of different treatments on maize field soil CO2 emission and the relationship between CO2 emission and soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were investigated in an incubation experiment. The results showed that both of straw returning and nitrogen fertilizer application promoted soil CO2 emission in maize field, which were increased significantly with the increases of straw returning amount and nitrogen application amount. Nitrogen fertilizer application was the most important factor promoting soil CO2 emission in maize field. Straw returning combined with nitrogen fertilizer promoted soil CO2 emission by increasing microbial biomass and increasing DOC consumption. MBC and DOC stimulated soil CO2 emission significantly in maize field, and were mainly affected by their contents in the early stage of incubation. From the perspective of ensuring the fertilization of straw return to the field while reducing CO2 emissions, results from our experiment showed that 210 kg N·hm-2 conventional nitrogen application in combination with 6000 kg N·hm-2 straw returning (N2S2) was the most promising mode in the semi-arid area of northwest Liaoning Province.

Substituting nitrogen and phosphorus fertilizer with optimal amount of crop straw improves rice grain yield, nutrient use efficiency and soil carbon sequestration

Crop straw return after harvest is considered an important way to achieve both agronomic and environmental benefits. However, the appropriate amount of straw to substitute for fertilizer remains unclear. A field experiment was performed from 2016 to 2018 to explore the effect of different amounts of straw to substitute for fertilizer on soil properties, soil organic carbon (SOC) storage, grain yield, yield components, nitrogen (N) use efficiency, phosphorus (P) use efficiency, N surplus, and P surplus after rice harvesting. Relative to mineral fertilization alone, straw substitution at 5 t ha−1 improved the number of spikelets per panicle, effective panicle, seed setting rate, 1000-grain weight, and grain yield, and also increased the aboveground N and P uptake in rice. Straw substitution exceeding 2.5 t ha−1 increased the soil available N, P, and K concentrations as compared with mineral fertilization, and different amounts of straw substitution improved SOC storage compared with mineral fertilization. Furthermore, straw substitution at 5 t ha−1 decreased the N surplus and P surplus by up to 68.3 and 28.9%, respectively, compared to mineral fertilization. Rice aboveground N and P uptake and soil properties together contributed 19.3% to the variation in rice grain yield and yield components. Straw substitution at 5 t ha−1, an optimal fertilization regime, improved soil properties, SOC storage, grain yield, yield components, N use efficiency (NUE), and P use efficiency (PUE) while simultaneously decreasing the risk of environmental contamination.

Effects of Short-Term Rice Straw Return on the Soil Microbial Community

Rice straw is a byproduct of agricultural production and an important agricultural resource. However, rice straw has not yet been effectively used, and incorrect treatment methods (such as burning in the field) can cause serious damage to the environment. Studies have shown that straw returning is beneficial to soil, but there have been few studies focused on the effect of the amount of short-term straw returned on the soil microbial community. This study evaluates 0%, 50%, 75%, and 100% rice straw returned to the field on whether returning different amounts of straw in the short term would affect the diversity and composition of the soil microbial community and the correlation between bacteria and fungi. The results show that the amount of straw returned to the field is the main factor that triggers the changes in the abundance and composition of the microbial community in the paddy soil. A small amount of added straw (≤50% straw added) mainly affects the composition of the bacterial community, while a larger amount of added straw (&gt;50% straw added) mainly affects the composition of the fungal community. Returning a large amount of straw increases the microbial abundance related to carbon and iron cycles in the paddy soil, thus promoting the carbon and iron cycle processes to a certain extent. In addition, network analysis shows that returning a large amount of straw also increases the complexity of the microbial network, which may encourage more microbes to be niche-sharing and comprehensively improve the ecological environment of paddy soil. This study may provide some useful guidance for rice straw returning in northeast China.

Effects of straw returning levels on carbon footprint and net ecosystem economic benefits from rice-wheat rotation in central China.

Straw returning usually gives rise to greenhouse gas (GHG) emissions from the soil, and thus negatively affects carbon footprint (CF) of crop production. Numerous studies reported the effects of straw returning on the CF from single crop production. However, little is known about the integrated effects of different levels of straw returning on the CF and net ecosystem economic benefits (NEEB) from rice-wheat rotation. Here, we investigated the effects of different amounts of straw returning on soil CH4 and N2O emissions, GHG emissions from agricultural inputs (AIGHG), CF, and NEEB from a 2-year cycle of rice-wheat rotation. The CF was determined based on the total GHG emissions associated with crop production inputs and services. Overall, straw returning significantly increased annual CH4 emissions by 5.4-72.2% and reduced annual N2O emissions by 3.3-31.4% compared with straw removal. Straw returning remarkably increased rice grain yields by 8.1-9.9% and wheat grain yields by 10.2-21.1% compared with straw removal. The average annual AIGHG from rice-wheat rotation ranged from 3579 to 4987 kg CO2-eq ha-1. Diesel consumption played a dominant role in the AIGHG. The annual CF ranged from 0.96 to 1.31 kg CO2-eq kg-1 and increased with increasing straw returning amounts. The NEEB, which ranged from 14161 to 17413 CNY ha-1, was significantly affected by the levels of straw returning. The treatment with returning of 1/3 of preceding crop straw to the field (2.19-2.47 kg ha-1 year-1 of rice straw in the wheat season and 1.38-1.68 kg ha-1 year-1 of wheat straw in the rice season) resulted in relatively higher grain yield, the lowest CF, and the highest NEEB among all treatments, and thus can reduce CF, and increase grain yields and NEEB, and thus can be recommended as a sustainable approach to mitigate GHG emissions and increase economic benefits from rice-wheat rotation.

Thermal conductivity of two kinds of earthen building materials formerly used in Algeria

Traditional building materials based on earth offer the following advantages: easily accessible, inexpensive, and above all, environmentally friendly. This investigation is intended to determine the thermal conductivity of traditional building materials obtained by mixing two kinds of soil (agricultural and soil taken from a type of desert land (Hamada)), separately, with different amounts of straw, according to the expertise of the inhabitants of M'Sila (a province of Algeria). Then, find the best mass proportion (soil/straw), which gives the lowest thermal conductivity of the obtained earthen materials. Four samples were prepared for each soil, in addition to the reference one (without straw). The considered samples were obtained by sun-drying of the handy dough formed by soil, straw, and water. The hot wire method is the technique used to determine the thermal conductivity in longitudinal and transverse directions. All the tested samples display a thermal anisotropy as the thermal conductivity measured in the longitudinal direction is significantly different from that measured in the transverse direction (p < 0.05). The thermal conductivity of the tested samples is strongly affected by the quantity of the straw added (p < 0.05). All the samples tested with and without straw are within the range ([0.1, 2] W/m° C) recommended for construction materials. It was observed that adding a straw mass equivalent to one-twentieth of the mass of both soils (5% by mass) gives to the Adobe formed a minimum thermal conductivity. The thermal conductivity of the studied earthen based materials depends on their compositions.

A study of the thermal properties of an alternative straw-containing building material

Thermal comfort in buildings is usually achieved through sustainable materials obtained from natural sources, which justifies their use for developing building mixtures. Many natural materials were used as early as in ancient times to build homes that are warm in winter and cool in summer: a mixture of straw, clay and sand is an example of such a material. The objective of this article is to evaluate the effect of a mixture of clay, sand and straw on thermal comfort. For the purposes of this study, several types of sample plates were made from clay and sand mixture by adding different amounts of straw. The experiments were carried out and the thermal conductivity coefficient was determined using the method of infinite flat layer. The results indicate that the combination of different amounts of straw can be considered as good reinforcement of the sand and clay matrix and is characterized by a low thermal conductivity. Furthermore, 3D modelling was performed using Finite Element Analysis (FEA) software and a predictive model of the thermal behaviour of the samples from the different mixtures was developed. The thermal field distribution and the thermal conductivity coefficient thus determined were compared with the experimental data and showed consistency.

Microbial and Phenyl Acid Dynamics during the Start-up Phase of Anaerobic Straw Degradation in Meso- and Thermophilic Batch Reactors.

Aromatic compounds like phenyl acids derived from lignocellulose degradation have been suspected to negatively influence biogas production processes. However, results on this topic are still inconclusive. To study phenyl acid formation in batch reactors during the start-up phase of anaerobic degradation, different amounts of straw from grain were mixed with mesophilic and thermophilic sludge, respectively. Molecular biological parameters were assessed using next-generation sequencing and qPCR analyses. Metagenomic predictions were done via the program, piphillin. Methane production, concentrations of phenylacetate, phenylpropionate, phenylbutyrate, and volatile fatty acids were monitored chromatographically. Methanosarcina spp. was the dominant methanogen when high straw loads were effectively degraded, and thus confirmed its robustness towards overload conditions. Several microorganisms correlated negatively with phenyl acids; however, a negative effect, specifically on methanogens, could not be proven. A cascade-like increase/decrease from phenylacetate to phenylpropionate, and then to phenylbutyrate could be observed when methanogenesis was highly active. Due to these results, phenylacetate was shown to be an early sign for overload conditions, whereas an increase in phenylbutyrate possibly indicated a switch from degradation of easily available to more complex substrates. These dynamics during the start-up phase might be relevant for biogas plant operators using complex organic wastes for energy exploitation.

The release of macronutrients from second crop corn straw and their behaviour in a red-yellow latosol

Crop residues left on the soil function as a nutrient reservoir and as a ground cover in agricultural systems. The aim of the present study is to assess the chemical alterations in the soil after the decomposition of different amounts of straw from corn as second crop. The climate of the region is classified as hot tropical and the soil is categorized as Red-Yellow Latosol (Typic hapludox) in the cerrado-amazon ecotone. The experiment was set up in randomized blocks in September 2013 after harvesting the second crop corn, comprised of corn straw rates (0, 14.18 and 42.54 t ha-1) with six repetitions. The content of macronutrients, H+Al, pH and base saturation in the soil profile were assessed. The straw rates were added to litter bags and stored on the soil, where they were kept for 154 days throughout the rainy period. Subsequently, the soil characteristics were assessed in layers 0 to 0.05, 0.05 to 0.10, 0.10 to 0.15, 0.15 to 0.20 and 0.20 to 0.40 m. The Ca+2 and Mg+2 elements were only released by the straw on the first 0.05 m of soil. However, K circulated in the soil profile reaching depth of 0.40 m. There was reduction in K+ saturation in treatments without straw. No alterations were observed in the other nutrients and studied attributes. According to the results, it is important to distribute the cultural remains of maize homogeneously in the area during harvesting to avoid the appreciation of soil fertility spots, especially of K.

Exploring optimal soil mulching to enhance yield and water use efficiency in maize cropping in China: A meta-analysis

Global crop yields are limited by the shortage of water resources and nutrient availability. Mulching technology can effectively modify the crop growth environment and crop production due to differences in climatic conditions, spatial distribution characteristics, and cropping systems. Hence, we conducted a meta-analysis to evaluate the eff ;ects of plastic mulching (PM) and straw mulching (SM) on the yield and water use efficiency (WUE) of maize cropping in China using data obtained from 176 peer-reviewed publications. The results showed that plastic mulching significantly increased maize yield (29.24%) and WUE (29.45%). The eff ;ects of mulching on maize were also improved by 12.02% (yield) and 11.43% (WUE). At the regional scale, maize yield and WUE were influenced by diff ;erent planting regions and mulching management practices. Plastic mulching performed best in the North maize region and the Huanghuaihai maize region of China, while straw mulching performed better in the Southern hilly maize region of China. Plastic mulching was the best way to increase maize yield (59.56%) and WUE (29.91%) with mulching in fallow period, and straw mulching was the best way to increase maize yield (12.43%) and WUE (13.21%) with mulching in the growth period. Full plastic mulching could significantly increase maize yield (42.06%), and among different amounts of straw, mulching with 10-15 t ha−1 performed the best, boosting the maize yield by 13.35%. Transparent film and ridge row mulching were more favorable to maize growth and increased crop yield and WUE in the arid and low temperature areas of China. In conclusion, plastic mulching can significantly increase maize yield and WUE, the adoption of mulching practices and management practices has more application prospects.

The relative importance of influence factors to field soil respiration is shifted by straw incorporations: comprehensive analysis of the seasonal variability

Understanding the effects of agricultural managements (e.g., straw incorporation) on soil respiration (Rs) and its temperature sensitivity (Q10) is crucial for accurate estimation of the soil carbon sequestration potential under an increasing-temperature scenario in the future. However, how the influence drivers regulate Rs and whether their relative roles are changed under different agricultural practices remain unexplored. Static chambers were used to monitor field CO2 flux in one growing season for a straw return experiment, which had been amended with different amounts of straw (CK, no straw return; S4, straw amendment at 4000 kg ha−1; and S8, straw amendment at 8000 kg ha−1) for five consecutive years. Our monitoring showed that Rs was elevated with intensified use of straw and confirmed soil temperature, soil moisture, and rainfall were important seasonal drivers of Rs. Moreover, the lower coefficient of variations (CV) for each series of treatments of Rs was detected at the vigorous growth stage of the crop, implying the biotic factor of crop roots might also exert a role simultaneously. Straw addition tended to reduce Q10, probably due to the fact that the microbial degradation of SOC in S4 and S8 was less sensitive to temperature change. Interestingly, the Q10 of S4 but not S8 was significantly smaller (P < 0.05) than that of CK as the reduced magnitude of Q10 for S4 was more profound. This result corresponded with more proportional growth of crop root of S8 than S4. By comprehensively analyzing the seasonal variability of our data set, we inferred that for S8, the negative impact of straw incorporation on Q10 would be more offset by upregulated root metabolism. Although additional works were needed to corroborate and specify this explanation, present research highlighted the abiotic and biotic factors should both be incorporated to analyze the underlying mechanisms responsible for the seasonal dynamics of soil C emissions under agricultural managements.

Straw removal of sugarcane from soil and its impacts on yield and industrial quality ratoons

ABSTRACT: Mechanical harvesting leaves in its wake a considerable amount of straw in the field, which can be effectively utilized to improve the soil condition and sugarcane yield. However, there is no specific information as to the quantity of straw mulch required to achieve such effects and as to whether it can be used in other sectors for bioelectricity and ethanol production. The aim of this research was to evaluate the effect of removing different amounts of straw from the field and its impact on the yield and industrial quality of sugarcane ratoons. The experiment was carried out on Rhodic soil where six treatments were evaluated including 0 %, 25 % (5 Mg ha−1), 50 % (10 Mg ha−1), 75 % (15 Mg ha−1), 100 % (20 Mg ha−1) straw on the soil surface and burned sugarcane (where 100 % of the straw was burned). The influence on yield and industrial quality was calculated using total soluble solids, Pol (Apparent sucrose content), apparent purity, total sugars, reducing sugars and fiber. Shifting the harvesting system from burned cane to growing under straw mulch improved crop yield as well as favoring sugar contents during water deficit conditions. The straw left on the soil did not affect industrial quality in any way during the trials; however, under drought conditions, treatments with 50 and 75 % of straw resulted in a 76 % higher yield compared to burned sugarcane, and 29 % more than the 0 %, 25 % to 100 % treatments of straw mulch thus favoring higher sugar production. The removal of 50 % of the straw caused no damage to the sugarcane crop.

Abundance of microbial CO2-fixing genes during the late rice season in a long-term management paddy field amended with straw and straw-derived biochar

Straw return and biochar addition are promising approaches to enhance carbon sequestration and reduce greenhouse gas emission; however, their effect on CO2-fixing autotrophs remains unclear. Hence, quantitative PCR based on cbbL and cbbM, accC, and hcd, which are marker genes of the Calvin cycle, the 3-hydroxypropionate cycle, and the 4-hydroxybutyrate cycle, respectively, were used to determine the abundance of CO2-fixing autotrophs in paddy soil. Soils with chemical fertilizers receiving no exogenous carbon amendment, low and high amounts of rice straw, or low and high amounts of biochar were sampled at the tillering, milky, and ripening stages of late rice season. Results showed that both straw and biochar application increased the abundance of CO2-fixing microbes in paddy soil, whereas more abundant CO2-fixing microorganisms were observed in HS and LC rather than other treatments. The effects of different amounts of straw and biochar are attributable to the prominent differences in their properties. Redundancy analysis revealed that redox potential, C/N ratio of input fertilizer, and soil content were significantly correlated with the gene abundance of CO2-fixing microorganisms. Path analysis revealed that gene abundance was causally and indirectly driven by rice growth stage and exogenous C addition. Collectively, our study suggested that adding extra carbon affected the growth of CO2-fixing microorganisms, which provided novel insights into the effect of straw return and biochar addition in paddy soil.

Three-Year Soil Carbon and Nitrogen Responses to Sugarcane Straw Management

Green harvest sugarcane management has increased soil organic C and N stocks over time. However, emerging sugarcane straw removal to meet increasing bioenergy demands has raised concerns about soil C and N depletions. Thus, we conducted a field study in southeast Brazil over nearly three years (1100 days) for assessing soil C and N responses to increasing sugarcane straw removal rates. In order to detect the C input as a function of the different amounts of straw over three years, a field simulation was performed, where the original soil layer (0–0.30 m) was replaced by another from an adjacent area with low total C and δ13C. The treatments tested were as follows: (i) 0 Mg ha−1 year−1 (i.e., 100% removal), (ii) 3.5 Mg ha−1 year−1 (i.e., 75% removal), (iii) 7.0 Mg ha−1 year−1 (i.e., 50% removal), (iv) 14.0 Mg ha−1 year−1 (i.e., no removal), and (v) 21.0 Mg ha−1 year−1 (i.e., no removal + extra 50% of the straw left on the field). The results showed that sugarcane straw removal affected the soil C and total N pools. In the first 45 days of straw decomposition, a small but important straw-derived C portion enters into the soil as dissolved organic carbon (DOC). The lower the straw removal rate, the higher was straw-derived DOC content found into the soil, down to 0.50 m depth. After 3 years of management, keeping sugarcane straw on soil surface significantly increased C and N stocks within surface soil layer (0–0.025 m). Our findings suggest that under no straw removal management (i.e., 14 Mg ha−1), approximately 364 kg ha−1 of C and 23 kg ha−1 of N are annually stored into this low-C soil. The contribution of the straw-derived C (C-C4) to the total soil C increases over time, which accounted for about 60% under no straw removal rate. The greatest contribution of the C storage preferentially occurs into the fraction of organic matter (< 0.53 μm) associated with soil clay minerals. We concluded that indiscriminate sugarcane straw removal to produce cellulosic ethanol or bioelectricity depletes soil C stocks and reduces N cycling in sugarcane fields, impairing environmental gains associated with bioenergy production. Therefore, this information, linked with other agronomic and environmental issues, should be taken into account towards a more sustainable straw removal management for bioenergy production in Brazil.

Development and production of sugarcane under different levels straw after four years of cultivation

Environmental constraints, labour shortages and the search for greater efficiency have induced the mechanisation of sugarcane harvesting, providing a large amount of straw in the system, which provides benefits to the soil, the crop and the environment. The objective of this work was to evaluate the effect of the removal of different amounts of straw from the soil surface on the development and productivity of sugarcane in eutrophic Red Latosol. The experiment was conducted in an area belonging to the Usina in Bandeirantes, PR, using a randomised block design with four replications. The effects of six treatments (0, 25%, 50%, 75%, 100% of straw and sugarcane) were evaluated after four years of cultivation on the LAI (leaf area index), tillering, diameter, length and fresh mass of the stalks, in five periods: 60, 120, 180, 240 and 370 days after harvest (DAC). The results were submitted to analysis of variance and the means compared by Tukey’s test. The straw on the soil surface provided benefits to the development and productivity of sugarcane. The management of sugarcane burning, total removal of the straw (0% of soil cover) or 75% of straw resulted in a lower IAF and stalk diameter and a 37% decrease in final yield under conditions of water deficiency. The maintenance of 50% of straw is sufficient to favour the development and to provide greater productivity of the sugarcane, as it is possible to use the 50% surplus of the field for the production of ethanol of second generation or electric energy, without damage to the productivity of the culture.

Sugarcane straw management and its impact on production and development of ratoons

Due to mechanical harvesting large amount of straw is left in the field which implicates modification throughout the agriculture environment. This straw is beneficial for both soil and plant. However, there is no information about the sufficient quantity which can be used to achieve such effects and also whether it can be used in other sectors like electricity and ethanol production. Therefore, a research was designed with the objective to evaluate the effect of different amounts of straw on the development and productivity of sugarcane during the first and second ratoons. Treatments used in the experiment included: burned cane, 0%, 25%, 50%, 75% and 100% (20tha−1) of sugarcane straw left on the soil surface. The tested variables included leaf area index (LAI), number, diameter, length and production of stems. Plants were evaluated at 60, 120, 180, 240 and 370 days after harvest (DAH) for the first ratoon and at 60, 120, 180, 240 and 270 DAH for the second ratoon. Replacing burned cane harvest system for soil management with straw promotes the development and productivity of sugarcane ratoons. Field managements with burned cane, total removal of the straw, or keeping 25% of straw result in low number of tillers, leaf area index, stem diameter and productivity of sugarcane ratoons, under water stress conditions. Whereas keeping 50% of straw mulch is enough to improve the growth and yield of sugarcane with drought occurrences, while the remaining 50% can be used for second generation of ethanol production or electricity without damaging the crop yield.

The effects of closed circuit microbial fuel cells on methane emissions from paddy soil vary with straw amount

Straw return increases methane emissions from paddy fields due to carbon input. In closed circuit microbial fuel cells (CC-MFCs), because exoelectrogenic bacteria can compete with methanogens for soil organic carbon, CC-MFCs should reduce methane emissions. We aimed to study the effects of CC-MFCs on methane emissions from paddy soil that was amended with different amounts of straw. Paddy soil was packed into the CC-MFCs and flooded after amendments with 0.5%, 1% and 2% straw or without straw addition. The methane flux from the soil was assessed every seven days. Forty-five days after the CC-MFCs were put into operation, the dissolved oxygen concentration in the overlaying water was determined. Soil was collected from the CC-MFCs, the chemical properties of the soil were measured and DNA was extracted. This was followed by the quantification and sequencing of the methanogenic mcrA and methanotrophic pmoA genes. The results revealed that with 0.5% straw, CC-MFCs generated less methane than open circuit MFCs (OC-MFCs) which were set as references. However, the CC-MFCs generated more methane than the OC-MFCs under 1% and 2% straw conditions. The dissolved oxygen concentration, which was lower in CC-MFCs than in OC-MFCs, decreased as the straw amount increased. The abundance of methanotrophs in CC-MFCs was significantly lower than that in OC-MFCs with 2% straw. Methylococcaceae, which belong to type II methanotrophic bacteria, were more abundant in CC-MFCs than in OC-MFCs. Thus, we suggest that the effects of CC-MFCs on methane emissions vary with the straw amount. With 0.5% straw, the competition for organic carbon between methanogens and exoelectrogenic bacteria mitigated the production of methane. However, CC-MFCs with 2% straw decreased the concentration of dissolved oxygen, inhibiting the activity of methanotrophs and increasing the emissions of methane.

English

Change from the traditional harvesting system with burns to mechanized harvesting of sugarcane, as well as the amount of straw needed to remain in the field for sustainability of the production system and how much could be removed for sectors such as energy cogeneration and bioethanol production, are not clarified issues. The objective of this study was to evaluate the impact of harvest management with burning (traditional) and cultivatation with different amounts of straw on the industrial quality and productivity of sugarcane. The effect of six treatments were evaluated: cane burning, 0, 25, 50, 75 and100% (20 Mg ha-1) of straw on the industrial quality (soluble solids (&deg;Brix), Pol, apparent purity, total sugars (TS), reducing sugars (RS) and fiber) and productivity (Mg Pol ha-1) of sugarcane. At the end of the cycle, the straw decomposition rate for each treatment was also verified. The higher the percentage of straw, the higher the degradation rate. The change of burned cane harvesting system for sugarcane under straw results in improved productivity of sugarcane and favors the production of sugar. The straw and harvest system change do not affect the industrial quality of sugarcane. The harvest with burning, the total withdrawal or of 75% of the straw of the field result in lower productivity. The maintenance of 50% of the straw on the soil surface is sufficient to improve the productivity of sugarcane in dry period, and the remaining 50% can be used for second generation of ethanol production or electricity without damaging the crop productivity. Key words: Saccharum spp, soil cover technological quality, biomass, sucrose.

English

The amount of straw of sugarcane needed to remain in field for sustainability of the production system and quantity that could be used in sectors such as cogeneration and production of bioethanol for optimization of power generation by the sector are unclear issues. The aim of this study was to evaluate the effect of different amounts of straw on the development of the sugarcane root system and yield using the variety SP 801816 in a Rhodic Eutrudox in southern Brazil. Six treatments were evaluated: 0 (no straw), 25, 50, 75 and 100% (20 Mg ha-1) of straw and straw burned at 60, 180 and 270 days after planting in 150 m2 plots. Root samples were collected at 0.45 and 0.75 m from the planting line at depths of 0-0.10, 0.10-0.20, 0.20-0.40 and 0.40 to 0.60 m at harvest, and the stems of the plots were weighed to measure yield. In water stress period, the 50, 75 and 100% straw treatments promoted a greater root mass to 0.20 m deep, which was also reflected in the yield. The 50 and 75% straw treatments resulted in 25% greater yield than the 0 and 25% straw and straw burned, resulting in 28 Mg ha-1 more. The amount, 50% straw retention in the field is sufficient to increase the mass of the roots and, in turn, productivity, which is possible to remove the 50% surplus from the field for industrial processes for the production of energy, without the occurrence of damage to the crop. Key words: Green cane, biomass, mechanized harvesting, agricultural waste, Saccharum spp.

Effects of sugarcane straw on grass weeds emergence under field conditions

This study aimed to assess the effects of sugarcane straw soil cover on Brachiaria plantaginea , Panicum maximum and Digitaria nuda seedlings emergence. The experiment was carried out in a soil classified as Red Nitosol. Seven different amounts of sugarcane straw soil cover were assessed (0, 3, 6, 9, 12, 15 and 18 ha -1 ). SP83-2847 variety straw was used. The experiment was arranged in a randomized blocks design, with four replications. Each experimental unit contained three species, which were allocated in the center of each plot, sown at 1 cm depth in a demarcated area. Different amounts of straw were distributed in this area. The sowing rate was used in order to obtain 1200 plant m -2 . Two phases comprised the study. In the first phase, weeds emerged in sugarcane straw cover soil were assessed at 9, 12, 19, 34 and 43 days after sowing (DAS) and the second phase assessed plant emergence after straw removal, at 89, 130, 175, 196, 217 and 234 DAS. Seedlings that had over 1 cm shoot and were visible in all assessments were considered emerged. Soil cover sugarcane straw amount influenced the different species germination dynamics. In the first phase, species differential response was observed regarding used straw amount. In the second phase, after straw removal, there was higher germination for B. plantaginea and D. nuda , while P. maximum showed lower emergency, regardless of the used straw amount.