Surface Mulch Research Articles

Effect of Straw Mulch on Soil Evaporation during Freeze–Thaw Periods

Reducing soil evaporation is important to alleviate water shortages in arid and semi-arid regions. The objective of this work was to reveal the effect of straw mulch on soil evaporation based on field experiments during a freeze–thaw period in Northern China. Four soil surface mulch treatment modes were investigated: Bare soil (BS), 1 cm thick straw mulch with 100% coverage rate (J1), 2 cm thick straw mulch with 100% coverage rate (J2), and 2 cm thick straw mulch with 50% coverage rate (J3). Principal component analysis was used to analyze the major factors influencing soil evaporation in three freeze–thaw stages. The results show that cumulative soil evaporation decreased with increased straw mulch thickness and coverage rate. The effect of straw mulching on soil evaporation was obvious during the stable freezing period, and soil evaporation with straw mulch treatments was reduced by 49.0% to 58.8% compared to BS treatment, while there was little difference for straw mulch treatments in the thawing stage. The relationship between cumulative soil evaporation under different straw mulch modes and time was well fitted by the power function. In the unstable freezing stage, the major factors for all treatments influencing soil evaporation were surface soil temperature and water surface evaporation; in the stable stage, they were solar radiation and relative humidity, and in the thawing stage, they were solar radiation and air temperature. The research results can provide a basis for addressing soil water storage and moisture conservation and restraining ineffective soil evaporation in arid and semi-arid areas.

Integrated influence of soil tillage, nitrogen–potassium fertiliser and mulching on pineapple (Ananas comosus (L.) Merr.) growth and yield

Pineapple is one of the most important fruit in the world and its production requires appropiate cultural practices. This work aimed to investigate the influences of soil tillage, nitrogen–potassium (N-K) fertiliser and mulching on pineapple growth and yield. The experimental design was a split-split plot with four replications. The main factor was soil tillage (at two levels: flat tillage and ridging), the subplot factor was N-K fertilisation (at five levels: 1.6 N and 1.6 K, 5.8 N and 6.6 K, 10 N and 11.6 K, 1.6 N and 11.6 K, and 10 N and 1.6 K, in g plant−1) and the sub-subplot factor was use of fresh pineapple residues (at three levels: surface mulching (at 10 t ha−1), 10 t ha−1 buried residues at 10 cm depth, and no mulching). Growth and yield parameters were recorded. A mixed ANOVA model was performed on ‘D’ leaf characteristics, biomass production and yield. The results suggested that soil ridging and burying of 1 kg m−2 of crop residues improved pineapple growth and yield. Nitrogen–potassium combinations 10 N and 11.6 K, 1.6 N and 11.6 K, and 5.8 N and 6.6 K (in g plant−1) resulted in better plant development and higher yield.

Impact of organic matter amendments on soil and tree water status in a California orchard

Permanent crops like almond (Prunus dulcis) require significant water inputs for economic yields and long-term productivity. This demand creates a challenge in drought-prone regions like California. Use of organic matter amendments (OMA) can improve water use efficiency by conserving soil moisture and reducing tree water stress. The majority of almond orchards in California are no-till with irrigation targeted on a narrow tree berm where OMA is applied as surface mulch. We examined the effects of composted dairy manure (CM) and the timing of its application on soil moisture, soil water retention and tree water status in a young orchard planted in 2014. Treatments including Fall-applied CM (October 2015 and 2016), Spring-applied CM (April 2016 and 2017) and an unamended control were monitored during the 2016 and 2017 growing seasons. Fall-applied CM was more readily incorporated in soil organic matter of the 0–60 cm rooting zone as evidenced by significantly greater soil organic carbon (SOC) for Fall versus Spring-applied CM in 2016 (p < 0.05). Fall-applied CM significantly increased soil volumetric water content (VWC) by 22% from 0 to 150 cm depth during the driest period of year one and tended to make midday stem water potential (SWP) less negative relative to the control. Fall-applied CM tended to increase VWC in 2017, but treatment differences were no longer significant. Differences in VWC and SWP between Fall-applied CM and the control were most apparent at low VWC (<10%). Two years of Fall-applied CM increased soil water retention between 0 to ˜100 kPa at 0–10 cm depth by 13% compared to the control. These results demonstrate Fall-applied CM was more effective at enhancing soil moisture retention and reducing tree water stress compared to Spring-applied CM. We also conclude OMA use may buffer against periods of limited water supply for young trees.

Effects of Organic Mulching on Soil Water Potential and SPAD Values as Factors on Yield of Potatoes (Solanum tuberosum L.)

In the present study, Finka and Katka potato (Solanum tuberosum L.) varieties were used at two localities (Leškovice and Uhříněves) and the effects of the surface mulching on chlorophyll content (SPAD values), soil water potential (SWP) a nd tuber yield of potato (YWP) were observed. Two mulching treatments (chopped grass and black polypropylene mulch) were used in the study. The results showed that plastic mulch can be an important factor for potato cultivation on localities with dystric cambisol soil type currently facing lack of precipitation. Organic mulching (with chopped grass) significantly influenced YWP. It favorably increased the fresh weight of tubers (over 60 mm) per plant by 81.4% in comparison with control. Additionally, it has been found that the type of mulching or varieties can be expressed by different SPAD-yield relationship. Whereas the values of SWP and SPAD values too were not significantly affected by organic mulch, they were significantly correlated with the YWP (r2= 42.4%, P<0.0001 and r2= 28.8%, P<0.0023). SPAD value can predict the level of tuber yield if the value was calibrated for particular potato variety. However, the highest SPAD reading value did not guarantee the highest tuber yield.

The influence of the methods of the main tillage and fertilizers on the agrochemical properties of chernozem

In experiments carried out on ordinary and leached chernozem, the effect of minimizing the methods of basic tillage and biologization on the fertility of these soils was analyzed. The studies were carried out in stationary and short-term experiments from 1984 to 2017. The effect of various methods and depths of the main tillage, autumn tillage systems, and fertilizers (mineral and organic) on the agrophysical, biological and agrochemical indicators of chernozem was studied. Refusal to carry out farewell processing in grain cultivating crop rotation leads to an increase in the differentiation of the arable layer, a decrease in the fertility of its lower part. The use of annual tillage in the crop rotation resulted in a decrease in the humus content in the soil layer of 0–40 cm by 0.17% (after fertilizers application) and by 0.22% (without fertilizers) compared to the dump processing by 20–22 cm. Organic fertilizers in a complex with minerals during farewell processing promotes an increase in the content of humus in comparison with the surface distribution during surface mulch tillage. A decrease in soil fertility and yield of cultivated crops without dump processing is proved.&#x0D;

Playground lead levels in rubber, soil, sand, and mulch surfaces in Boston.

Rubber surfacing is often used in playgrounds due to its potential injury prevention benefits and as a way to recycle waste tires. Available research on chemicals in recycled rubber has focused on synthetic turf applications, but is limited for playground rubber surfacing. Potential lead contamination from vulcanizing agents used in rubber surfacing are a possible concern; however this has not been researched. We examined levels of lead in poured-in-place rubber and compared them to levels in soil, sand, and wood mulch materials from 28 randomly selected playgrounds in Boston, MA, USA using X-ray fluorescence. To evaluate the association between material type and lead concentrations, we conducted a two-way ANOVA with repeated measures and built a linear regression model controlling for distance to major roadway, neighborhood-level status as an environmental justice area, peeling paint on the playground, and rubber condition. Average lead levels were 65.7 μg/g for soil, 22.0 μg/g for rubber, 8.5 μg/g for sand, and 9.0 μg/g for mulch. Our finding of lower concentrations of lead in sand and mulch compared to rubber and soil should be used to inform playground design to optimize children’s health, alongside other chemical and safety considerations.

Impact of farmland mulching practices on the soil bacterial community structure in the semiarid area of the loess plateau in China

Farmland mulching is widely used to preserve soil moisture and increase crop yield in the semiarid region of the Loess Plateau. However, the effect of different farmland mulching on soil bacterial communities is not clear. Therefore, the impact of a 5-year field management practice (surface mulching) on the soil bacterial communities was studied in dryland farmland of the Loess Plateau by using Illumina sequencing of the 16S rRNA gene. The following treatments were investigated: (1) ridge-furrow mulching pattern; (2) flat plastic film mulching; (3) flat biodegradable film mulching; (4) flat straw mulching; and (5) control (CK), conventional flat planting without mulch. All farmland mulching increased the diversity of soil bacteria and the diversity was greatest under the plastic film treatment. The dominant phyla across all soil samples were Proteobacteria, Acidobacteria, and Actinobacteria. Cluster analyses showed that bacterial communities under mulching treatments were different from that of CK. The bacterial community composition of plastic film and straw mulching treatments, biodegradable film and ridge-furrow mulching treatments were similar at the phylum level. Spearman correlation analysis indicated that the response of bacterial alpha-diversity was mainly negatively associated with the soil organic carbon and total nitrogen. The Mantel test showed that the beta-diversity depended primarily on the soil total nitrogen and soil temperature. The changes of the bacterial community distribution were significantly related to the soil moisture, which varied significantly with a range of 9.8–17.3 between treatments. These results indicated that soil properties changed after long-term farmland mulching, and these changes were related to soil bacterial diversity and community structure. According to this study, flat plastic firm mulching was found to being a good option for increasing soil bacterial diversity and richness and thereby potentially stabilize functional stability of soil biological processes.

Temporal changes in biochemical indicators of soil quality in response to tillage, crop residue and green manure management in a rice-wheat system

Abstract Soil quality degradation in the last four decades is threatening the sustainability of puddled transplanted rice (Oryza sativa L.) – wheat (Triticum aestivum L.) (RW) system in north-western region of India. Hence comprehensive information on the influence of soil and crop management practices in intensive and nutrient exhausting RW system on soil quality is urgently needed. The present study evaluated the effects of crop residues, green manure and tillage on the changes in soil biochemical properties at different growth stages of wheat after five cycles of RW system. Four main plot treatments in rice included combinations of wheat straw and Sesbania green manure management: (1) PTRWS0, puddled transplanted rice (PTR) with no wheat straw (2) PTRWS25, puddled transplanted rice with 25% anchored wheat stubbles retained (3) PTRWS0 plus green manure (GM), and (4) PTRWS25 plus GM. Three sub-plots treatments in subsequent wheat included (1) CTWRS0, conventional tillage wheat without rice straw (2) ZTWRS0, zero tillage wheat without rice straw and (3) ZTWRS100, ZTW with 100% rice straw retained as surface mulch. The results showed that PTRWS25 plus GM and ZTWRS100 increased significantly all the soil biochemical properties (enzyme activities and glomalin related soil protein concentration) except phenol oxidase and peroxidase activities. The activities of dehydrogenase, β-glucosidase and concentration of easily extractable glomalin and total carbohydrate carbon under ZTWRS100 were 36.8, 24.6, 25.9 and 23.3% higher than CTWRS0. Application of GM and wheat straw retention in previous rice significantly increased grain yield of subsequent wheat crop by 26.5%. The majority of the increases in biochemical properties were higher at vegetative growth (at 40–45 days after sowing) and flowering (at 80–85 days after sowing) stages compared to the initial and at maturity. Principal component analysis identified β-glucosidase, cellulase and phenol oxidase activities as the most sensitive and reliable indicators for assessing soil quality for conservation agriculture based RW system.

Effects of litter decomposition on contents and three-dimensional fluorescence spectroscopy characteristics of soil labile organic carbon in coastal wetlands of Jiaozhou Bay, China

Litter of Suaeda glauca, Phragmites australis, and Spartina alterniflora from coastal wetland of Jiaozhou Bay was decomposed in a laboratory experiment. The contents of soil labile organic carbon including dissolved organic carbon (DOC) and microbial biomass carbon (MBC) were determined, with the spectra characteristics of which being investigated by three-dimensional fluorescence spectroscopy. The results showed that the contents of soil labile organic carbon during litter decomposition increased first, then decreased, and finally tended to be stable. Different litter types and adding ways had different effects on soil labile organic carbon. The contents of soil DOC and MBC decreased in the order of Suaeda glauca, Spartina alterniflora and Phragmites australis. Soil mixed with bulk leaf litter had more soil labile organic carbon than surface mulch. The number and position of fluorescence peak, and fluorescence intensity changed during litter decomposition. No tyrosine-like peaks appeared in the soil with litter addition. Many factors drove litter decomposition, with microbial decomposition being the dominant factor and litter nature as the essential factor. Litter decomposition could improve the content of soil active organic carbon and enhance the stability of soil carbon pool. Litter decomposition changed the structure and chemical composition of soil DOC, which improved its ability of migration and transformation in soil. Moreover, this process enhanced its biodegradability and microbial bioavailability, promoted the production of endogenous DOC by microorganisms, and consequently stimulated carbon cycling of wetland soil.

Rice–wheat productivity and profitability with residue, tillage and green manure management

The rice–wheat system (RWS) practiced in northwestern parts of the Indo-Gangetic plains of India is highly productive, but conventional practices are resource (water, labour and energy) and cost intensive. A 4-year field study evaluated the effects of green manure (GM), crop residue and tillage on crop yields, economic profitability and soil fertility in a RWS. Four main plot treatments in rice included combinations of wheat stubble and Sesbania aculeata GM management: (1) puddled transplanted rice (PTR) with no wheat stubble, (2) PTR with 25% wheat stubbles (15–20 cm high) retained, (3) PTR with no wheat stubble plus GM, and (4) PTR with wheat stubble splus GM. Three sub-plots treatments in subsequent wheat included (1) conventional till wheat with rice straw removed (CTWR0), (2) zero till wheat with rice straw removed (ZTWR0) and (3) zero till wheat with 100% rice straw retained as surface mulch (ZTWR100). The results showed that main rice yield was significantly higher (8.0%) with 50% less fertilizer N application in GM compared with conventional PTR with no GM. Rice treatments did not affect the grain yield of subsequent wheat. ZTWR100 produced significantly higher mean wheat grain yield by 7.3% and 17.5% compared with CTWR0 and ZTWR0, respectively. System productivity was 11.5% higher in PTR with wheat stubble + GM followed by ZTWR100 compared with the conventional RWS and resulted in Rs 24,075 ha−1 more net returns. Significant increases in soil organic carbon, available P and available K contents were recorded in ZTWR100 over CTWR0. Recycling rice and wheat stubble in the field in RWS is also environment friendly as it avoids ill effects of straw burning.

Decomposition of maize stover varies with maize type and stover management strategies: A microcosm study on a Black soil (Mollisol) in northeast China

Crop residue decomposition has an important impact on soil organic carbon (SOC) sequestration and CO2 emission. Residue quality and management strategies are two important factors regulating decomposition process and SOC mineralization and greenhouse gas emission. In this study, a microcosm experiment in field condition was conducted on a silty loam (a Black soil) in Northeast China to investigate stover decomposition and soil CO2 emission characteristics as influenced by different crop cultivars and stover field incorporation methods. Stover from two popular maize cultivars Xianyu335 (XY) and Liangyu99 (LY) were applied in two modes (soil surface application vs soil incorporation) at a rate of 11 t ha−1, and CO2 efflux was monitored during the decomposition duration of 144 days. The structural transformation of carbon functional groups in maize stover were evaluated using solid state 13C-CPMAS NMR and elemental analysis techniques. Results showed that up to 71.7%∼86.9% (weight basis) of C and N in soil-incorporated stover was decomposed during the study period, which was significantly greater than the losses (32.8%∼55.3%) of C or N from the surface-applied stover for both maize cultivars; decomposition rates of main C functional groups were significantly higher in soil incorporation (71.1%∼88.8%) than in surface application (20.9%∼60.2%) systems. The concentrations of SOC, total N, available N, and microbial biomass C and N in soil were also higher with stover incorporation than surface application. Stover incorporation resulted in a notably lower CO2 emission rate and accumulative CO2 efflux (53.9–55.4 mol m−2) during the stover decomposition compared with surface application (57.4–67.0 mol m−2). Between the two maize cultivars, the LY stover showed a higher decomposition rate and greater capacity for SOC sequestration when incorporated into soil. The LY stover induced higher (16.8%) CO2 emission than XY when applied on soil surface, but no significant difference was found between the two cultivars when incorporated into soil. The results suggested that cultivar selection and stover management strategies have great potential in reducing soil CO2 emission while improving soil biochemical properties. Incorporating the LY stover into soil rather than surface mulching could enhance SOC sequestration and reduce CO2 emission.

Nutrient Mass Balance and Fate in Dairy Cattle Lots with Different Surface Materials

Abstract.On dairy farms, outdoor lots where cows spend substantial time can be areas of high nutrient deposition in manure. This represents an inefficient use of farm nutrients, if the nutrients are not recovered, and a potential for nutrient loss to the environment. Management of barnyards to recover nutrients can have environmental and production benefits. We monitored nitrogen (N) and phosphorus (P) fate for five years in dairy heifer barnyard plots constructed with soil, sand, or bark mulch surfaces. The plots were stocked with heifers several times per year for about a week at a time. We monitored N and P loss in runoff (soil plots only), leachate, and gas emissions. Of the total N inputs to the plots through heifer excretion, 6% to 8% of inputs were lost in runoff (~2%), leachate (~3% to 4%), and gas emissions (~3% to 4%) from the soil and mulch plots. Most of the N inputs remained in the surface materials. For the sand plots, more N inputs were lost in leachate (~13%) and gas emissions (~6%), but most of the N remained in the surface material. Of total P inputs to the plots through heifer excretion, 4% to 6% of inputs were lost in runoff and leachate, with most of the P remaining in the surface materials. The results suggest that most of the nutrients deposited by heifers onto barnyards could be recovered and used as fertilizer for crop growth by excavating the surface materials and spreading them on cropland, by including animal holding areas in land used for crop rotation so crops can recover nutrients , or by corralling animals directly on cropland. Keywords: Barnyards, Cattle, Leaching, Nutrients, Runoff.

Tobacco growth, yield and quality affected by soil constraints on steeplands

Soil tillage/management systems with minimum tillage and mulch are predominant in agriculture of southern of Brazil, but little is known for tobacco crop under conservation agriculture. Objective of this study was to evaluate soil tillage systems for tobacco crop and possibilities of changing the traditional system of tobacco cropping to improve the soil physical conditions and maintain high yield. In a randomized compete block design with three replicates, six tillage/management systems were studied: inverting tillage (IT); minimum tillage after fallow (MTf); minimum tillage after oat as cover crop (MTo); no-tillage without ridge (NT); no-tillage with ridge (NTr); and no-tillage with consolidated ridge (NTrc). The experiment was installed in a small, hilly watershed, located in southern Brazil, on a soil classified as Leptosol. The main physical properties evaluated were soil moisture measured with a time domain reflectometer in 0.00–0.06, 0.06–0.12 and 0.12–0.18 m soil layers, and soil temperature at 0.05 m depth measured with termopars, both during 87 days in the growth cycle; total porosity, macroporosity, microporosity, bulk density and soil water retention curve (WRC), in 0.00–0.06, 0.06–0.12, 0.12–0.18 and 0.18–0.24 m soil layers, 30 days after transplanting (DAT) and on 135 DAT, except for WRC, in 0.00–0.06 and 0.06–0.12 m soil layers; soil mechanical resistance to penetration; root distribution; nutrient availability in root zone; crop parameters leaf area, plant height, number of leaves and yield. Soil water retention was similar among tillage/management systems and soil layers, and decreased, approximately 50%, from soil saturation up to 33 kPa water tension. Soil moisture was longest within the range of available water of no-tillage (NTrc) and minimum (MTf and MTo) systems. Soil air-space was above the critical value (0.15 m3 m−3) during most days throughout the tobacco cycle in the surface soil layer for all systems. NTrc, MTo, NT and NTr provided longest consecutive period (30, 20, 13 and 11 days, respectively) with airspace below the critical in deepest soil layer. Soil temperature amplitude during tobacco crop cycle was highest for MTo and lowest for NT. Soil temperature had greater variations in the first 55 DAT, while from 55 to 75 DAT, there was a reduction in thermal amplitude and daily temperature average for most systems, with the increase in soil moisture and crop shading. The tillage/management systems did not show differences in bulk density in the surface, but differed in subsurface soil layers, being higher in no-tillage systems, but not reach critical values. Macroporosity behaved similar to total porosity and inverse to bulk density. Soil penetration resistance increased with depth in no-tillage systems, down to approximately 0.20 m and reaching 3 MPa. In NT, soil PR of 3 MPa was reached before 0.15 m depth; in IT and MTf, soil RP was less than 2 MPa down to 0.15 m depth and close to 3 MPa in deeper depths. No-tillage systems had the shallowest root development, not exceeding the 0.18-m soil depth. Contents of K and P in the tobacco rhizosphere were high, but there was no clear relationship between plant size (small vs. large) with the nutrient content in the root zone. The MTo and no-tillage systems, except NTrc, had higher leaf area index compared with IT and MTf. At 63 DAT, NTrc had significantly lowest leaf area index. The systems with higher dry-mass (NTr) and stem length (MTo) also showed higher productivity. The greatest productivity per area was observed in tilled soil (IT, MTf and MTo), while lower productivity was observed for NT. Less tillage and more surface mulch contributed to soil physical quality improvement, while no-tillage system reached some critical physical values, particularly in the deepest soil layer. Furthermore, tillage and ridging for tobacco cropping in shallow soil reduced the effect of some soil physical stressors to tobacco growth and development. Consequently, soil management systems with winter cover crop, ridging and reduced soil tillage increased flue-cured tobacco yield, even low effect of tillage and ridging occurred for leaves qualitative classification, cropped on shallow soils on steeplands.

Long-term effects of different surface mulching techniques on soil water and fruit yield in an apple orchard on the Loess Plateau of China

Surface mulching has been extensively used for water conservation in dryland orchards. It is critical to choose an appropriate mulching technique for high yield and sustainable development of fruit crops. To solve the impact of water shortage on the production and growth of fruit trees on the Loess Plateau (China), the effects of different surface mulching techniques on an orchard ecosystem were monitored from 2008 to 2015. Different mulching methods, including grass cover (GC), film mulching (FM), straw mulching (SM), and gravel mulching (GM), effectively enhanced the regulatory capacity of soil water reservoir. The soil water content of SM and FM treatments was higher compared with other treatments. With the increase of planting age, the use of deep soil water increased, soil water content showed a decreasing trend, and soil desiccation was partially alleviated. Different mulching treatments improved water use efficiency and apple yield, with the best effect being achieved with GM and SM. GM resulted in lower soil water content, while it increased the proportion of short and medium branches, thus increasing the yield of apples. The water use efficiency was higher and the effect was better for the GM treatment during 2008–2012; thereafter, the benefits decreased due to a mixture of gravel and topsoil. SM produced higher soil water content and apple yield, and its regulation effect on temperature was better than other treatments. Although the soil water content of FM was relatively high, the corresponding yield and water use efficiency were low. The root growth of fruit trees was affected by high summer heat in the FM treatment. Given the high cost of labor required for GM, SM was an appropriate technique to improve the hydrological status and fruit yield of apple orchard soil in the gully region of the Loess Plateau.

Bicarbonates dissolved in irrigation water contribute to soil CO2 efflux

Understanding the processes that drive the release of carbon dioxide (CO2) from soil is essential to combat rising atmospheric greenhouse gases. Whilst significant research has focused on soil organic carbon (C) dynamics, soil inorganic C has received much less attention. In arid and semi-arid regions, crops are often irrigated with water containing inorganic (bicarbonate) C, which can be a source of CO2 emissions. CO2 released from dissolved bicarbonates is 13C enriched compared to that from organic sources in the soil (e.g., organic matter and respiring roots). Measurement of δ13CO2 at the soil surface can therefore be used to trace CO2 sources. Using on-line 13C analysis, we monitored δ13CO2 and rate of soil CO2 emissions in an apple orchard in British Columbia, Canada, irrigated with bicarbonate-containing irrigation water drawn from Okanagan Lake. In Experiment 1, we applied deionised or irrigation water to wet and dry soils; in Experiment 2, we applied irrigation water from Okanagan Lake to soils with and without a surface mulch. In both experiments, soil efflux responded within seconds to application of water. In Experiment 1, a 6‰ enrichment of 13CO2 followed the application of irrigation water, confirming the contribution of bicarbonate-C to soil surface efflux, whereas a 4‰ depletion of 13CO2 followed the application of deionised water, suggesting a stimulation of labile organic C mineralisation. Experiment 2 confirmed that bicarbonates in irrigation water contribute to soil CO2 efflux; surface mulch had no effect on the response of CO2 release following irrigation. Using an isotopic mass balance model, we calculated that bicarbonates dissolved in irrigation water accounted for between 9 and 15% of total soil surface efflux, and estimate that irrigation with Okanagan Lake water generates on average >45,000 kg bicarbonate-derived CO2 each year.

Urban sediment supply to streams from hillslope sources

Coarse-grained sediments supplied to a stream, in concert with the flow regime, play an important role in channel form and functioning, but are poorly understood in urban catchments. Improved knowledge of coarse-grained (>0.5 mm) sediment sources and supply rates will underpin strategies to mitigate impacts of urbanization on streams. We quantified key hillslope (i.e. non-channel) sources of sediment in urban areas by monitoring coarse-grained sediment yields from nine street-scale stormwater catchments over one year. From our observations, we developed a suburban hillslope sediment budget and a conceptual model of the response of hillslope coarse-grained sediment supply to different levels of urbanization. Coarse-grained sediment supply from the urban land surface was substantial. The highest unit-area yields came from infill construction sites (2800 kg/ha/yr), followed by gravel surfaces (740 kg/ha/yr), grass/mulch surfaces (84 kg/ha/yr), then impervious surfaces (21 kg/ha/yr), with the latter still producing yields far above background conditions. In typical suburban catchments grass and mulch surfaces and construction areas were key sources, with gravel and impervious surfaces making smaller contributions. Small source areas were important, for example construction produced 32% of sediment from 0.5% of the area. Connectivity of sediment sources to impervious surfaces, and hence to drainage systems, was important in driving sediment yields. Our conceptual model indicates that hillslope coarse-grained sediment supply increases with urbanization from natural to suburban conditions as connectivity increases, then declines with higher levels of urbanization as sources become scarcer. Impervious surfaces provide sources and supply pathways of coarse sediment, but also increase sediment transport capacity, causing severely supply-limited conditions and reducing the persistence of bed sediments in streams. When reducing hydrological connectivity to address the urban flow regime, consideration should be given to maintaining coarse-grained sediment supply through bypass or replenishment arrangements, to help reduce stream degradation and maintain form and functioning.

Evaluation of total greenhouse gas emissions during sewage sludge composting by the different dicyandiamide added forms: Mixing, surface broadcasting, and their combination

The aim of this work was to compare the impact of different adding forms of dicyandiamide (DCD) on NH3 and greenhouse gas (GHG) emissions during sewage sludge (SS) composting. Four treatments were set up using SS mixed with sawdust, to which DCD was then added by mixing (M), surface broadcasting (B), and a combination of the two (M+B). The treatment without DCD applied was used as the control. The results indicate that the addition of DCD slightly inhibited the organic matter (OM) degradation, but that it had no significant effect on CO2 emission. The surface mulching of DCD has no significant effect on NH3, N2O, and CH4 emissions. The mixing addition of DCD significantly increased the NH3 emission by 32.5% compared to that of the control. The N2O emission for the M and M+B treatments significantly decreased by 35.1% and 51.8%, respectively. The CH4 emission for the M and M+B treatments decreased by 33.9% and 31.8%, respectively. In addition, the total GHG emissions for the M and M+B treatments were significantly reduced by 16.7–25.7% (P < 0.05) compared to those of the control. Therefore, to reduce the total GHG emissions of the SS composting process, the addition of DCD by a combination of mixing and surface mulching is strongly recommended as a highly efficient solution.

Types of Stover Layers Used for Salt Management Influence Sunflower Production in Saline Soils

Three field experiments were conducted in Inner Mongolia, China, to evaluate the effects on soil water and salt distribution of maize (Zea mays L.) stover (MS), wheat (Triticum aestivum L.) stover (WS) and sunflower (Helianthus annuus L.) stover (SS) layers used alone (Exp. 1) and in combination with plastic film surface mulching (PM) (Exp. 2); their effects on sunflower yield were also examined (Exp. 3). All stover layer treatments retained more water at 0‐ to 40‐cm soil depths than was retained by the no‐stover controls in the first month, but a reverse trend occurred thereafter. The addition of PM helped maintain this advantage for 3 mo, but the advantage disappeared when PM was applied to the sunflower crop. However, stover layer treatments were consistently associated with lower soil salt contents throughout the experimental period, regardless of whether mulching or planting was applied. In addition, higher water storage and lower salt accumulation were observed in the stover layer treatments than those in the no‐stover controls in the 0‐ to 40‐cm soil layer. Reduced soluble salt concentrations were observed throughout all the stover layer treatments, except in the late growth period of sunflowers (Exp. 3). Generally, MS was more beneficial than WS or SS for resolving soil water‐ and salt‐related problems. As a result, MS+PM provided seed and biomass yields that were 13 and 23% higher than those in SS+PM, respectively, but were similar to those in WS+PM. These results suggest that MS is a top‐priority capillary cut material for sunflower production in the Hetao Irrigation District of China and similar ecological regions.

Changes in soil biochemical indicators at different wheat growth stages under conservation-based sustainable intensification of rice-wheat system

Soil microbes play critical roles in soil biogeochemistry, soil biological health and crop productivity. The current study evaluated the effects of tillage and residue management on changes in soil biochemical indicators at different growth stages of wheat after 5 years of rice-wheat system. Nine treatment combinations of tillage, crop establishment and crop residue management included three main plot treatments applied to rice: (1) conventional till direct dry seeded rice (CTDSR), (2) zero till direct dry seeded rice (ZTDSR), and (3) conventional puddled manual transplanted rice (CTPTR) and three subplot treatments in subsequent wheat: (1) conventional tillage with rice residue removed (CTW-R), (2) zero tillage with rice residue removed (ZTW-R) and (3) zero tillage with rice residue retained as surface mulch (ZTW+R). Irrespective of rice treatments, ZTW+R treatment had higher soil biochemical indicators compared with ZTW-R and CTW-R at all the growth stages of wheat. Generally, all the biochemical indicators were the highest at the flowering stage of wheat. Residual effect of rice treatments was also significant on biochemical quotients in wheat, which were the highest under ZTDSR followed by CTDSR and CTPTR. The present study provided three sensitive and reliable biochemical indicators (microbial biomass, basal soil respiration and microbial quotient) which respond rapidly to change in tillage and residue management practices in RWS of South Asia.

Organic Mulch Effects on High Tunnel Lettuce in Southern New England

Lettuce (Lactuca sativa L.) is a popular crop for spring and fall high tunnels among direct-market vegetable producers. Common practices include the use of compost as a soil amendment, and reliance on cultivation for weed control. This study examined the impacts of using compost as a surface mulch to control weeds in spring and fall romaine lettuce, with data collected on soil temperature, weed suppression, and lettuce yields. Costs of all inputs, including labor, were tracked to assess economic feasibility of using mulch. Compost mulch was compared with bare ground with cultivation across four cultivars of romaine lettuce: Ridgeline, Coastal Star, Green Forest, and Shushan. In the fall experiment, mulching increased average soil temperature by 1 °C and canopy cover, leaf area index (LAI), and fresh and dry weights were significantly higher in mulched plots. Mulching decreased daily variation in soil temperature in the spring experiment but had no effect on average soil temperature. Canopy cover, LAI, and fresh and dry weights were not significantly affected by mulching in the spring experiment. Compost mulch affected all cultivars similarly in both experiments, with no significant interaction effects. Yields were greater and leaves were larger in the spring experiment than in the fall for all cultivars. Fresh weight yields in the spring experiment averaged 3.22 kg·m−2 and heads had a LAI of 7.9 as compared with 1.02 kg·m−2 and 1.6 for the fall experiment. Dry matter content (DMC) was significantly higher in the fall lettuce (113 g·kg−1) than in the spring lettuce (43 g·kg−1). Cultivar rank order was consistent across experiments, with ‘Ridgeline’ having the best performance and ‘Green Forest’ the worst. ‘Coastal Star’ and ‘Shoshone’ were intermediate and very similar to each other. Although the use of compost as a mulch increased yields of all cultivars in the fall experiment, only the top cultivar, Ridgeline, produced enough additional yield to offset the increased costs of the compost mulch used in this study. The use of a less-expensive compost or a higher retail price for romaine lettuce would have made the economics more favorable for the other cultivars.