1. Conservation tillage of rainfed maize in semi-arid Zimbabwe: A review

• Authors:
  • Stroosnijder, L.
  • Nyakudya, I. W.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 145
• Year: 2015
• Summary: Food security in Sub-Saharan Africa, particularly in semi-arid tropics (41% of the region; 6 months of dry season) is threatened by droughts, dry spells and infertile soils. In Zimbabwe, 74% of smallholder farming areas are located in semi-arid areas mostly in areas with soils of low fertility and water holding capacity. The dominant crop in these areas, maize (Zea mays L.), is susceptible to drought. Under smallholder farming in Zimbabwe, conventional tillage entails cutting and turning the soil with a mouldboard plough thereby burying weeds and crop residues. Seed is planted by hand into a furrow made by the plough, ensuring that crops germinate in relatively weed free seedbeds. Inter-row weed control is performed using the plough or ox-drawn cultivators and hand hoes. Conventional tillage has been criticised for failure to alleviate negative effects of long dry spells on crops and to combat soil loss caused by water erosion estimated at 50 to 80tha-1yr-1. Therefore, conservation tillage has been explored for improving soil and water conservation and crop yields. Our objective was to determine the maize yield advantage of the introduced technology (conservation tillage) over conventional tillage (farmers' practice) based on a review of experiments in semi-arid Zimbabwe. We use a broad definition of conservation tillage instead of the common definition of =30% cover after planting. Eight tillage experiments conducted between 1984 and 2008 were evaluated. Conventional tillage included ploughing using the mouldboard plough and digging using a hand hoe. Conservation tillage included tied ridging (furrow diking), mulch ripping, clean ripping and planting pits. Field-edge methods included bench terraces (fanya juus) and infiltration pits. Results showed small yield advantages of conservation tillage methods below 500mm rainfall. For grain yields =2.5tha-1 and rainfall =500mm, 1.0m tied ridging produced 144kgha-1 and mulch ripping 344kgha-1 more than conventional tillage. Above 2.5tha-1 and for rainfall >500mm, conventional tillage had =640kgha-1 yield advantage. Planting pits had similar performance to ripping and conventional tillage but faced digging labour constraints. Experiments and modelling are required to test conservation tillage seasonal rainfall thresholds. Constraints to adoption of conservation tillage by smallholder farmers necessitate best agronomic practices under conventional tillage while work on adoption of alternative tillage methods continues.

2. Nitrogen and carbon transformations, water use efficiency and ecosystem productivity in monocultures and wheat-bean intercropping systems

• Authors:
  • Riseman, A.
  • Chapagain, T.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 1
• Year: 2015
• Summary: Enhancing soil organic carbon (SOC), nitrogen (N) and water use efficiency (WUE) are significant challenges in intensive wheat production. An intercropping system combining wheat and grain legumes may help maintain SOC, soil mineral N and WUE while also providing an opportunity to sequester carbon (C) in low input organic systems. We grew wheat (Triticum aestivum cv. 'Scarlet') as a monoculture and intercropped with either common bean (Phaseolus vulgaris cv. 'Red Kidney', or cv. 'Black Turtle'), or fava bean (Vicia faba cv. 'Bell') in rows of 1:1, 2 wheat: 1 bean or broadcast arrangement without fertilizers for 2 years to assess the effects of genotype and spatial arrangement on biological nitrogen fixation and seasonal transfer, WUE, gross ecosystem photosynthesis (GEP), and net ecosystem productivity (NEP). Stable isotope methods (C-13 and N-15 natural abundance) were used to quantify C and N within the plant and soil system. Field CO2 exchange measurements used a dynamic closed transparent chamber connected to a portable CO2 analyzer. Intercropped plots had higher percent N derived from symbiotic N-2 fixation, and increased C and N accumulation compared to monocultured wheat. The fava bean cv. Bell intercrops showed increased nodulation (60-80 % more nodules) and percent N derived from symbiotic N-2 fixation (10-12 % higher) compared to common beans resulting in the fixation of 74 kg N ha(-1) biologically from the 1:1 arrangement. The highest rate of N-transfer (13 %) was observed in the wheat-fava bean cv. Bell combination when planted in the 1:1 arrangement. All intercrops accumulated more N in shoot biomass compared to monoculture wheat with wheat-fava bean cv. Bell (1:1 arrangement) accumulating the highest N (34 kg N ha(-1), i.e., 176 % higher) and C (214 g C m(-2) year(-1), i.e., 26 % higher). All plots fixed the most CO2 (i.e., greatest GEP) during mid-growth stage (50 days after seeding i.e., prior to flowering) however, wheat-fava bean cv. Bell in the 1:1 arrangement displayed the greatest NEP sequestering C at the seasonal daytime average rate of 208 mg C m(-2) h(-1) (i.e., 7 % higher than wheat monoculture plots). Intrinsic WUE of wheat, as indicated by delta C-13, was also improved when grown with fava bean cv. Bell or common bean cv. Red Kidney. This study demonstrated that intercropping wheat and fava bean is an effective strategy to achieve greater nitrogen fixation and transfer to the wheat counterparts, higher WUE, and ecosystem productivity than wheat monocultures in areas with low soil N and C. Furthermore, the wheat-fava bean cv. Bell (1:1 arrangement) was more productive than either the 2:1 or mixed planting arrangements.

3. NO, N2O and CO2 soil emissions from Venezuelan corn fields under tillage and no-tillage agriculture

• Authors:
  • Herrera, F.
  • Rasse, R.
  • Giuliante, A.
  • Donoso, L.
  • Perez, T.
  • Marquina, S.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 1
• Year: 2015
• Summary: The largest share of Latin American and Caribbean (LAC) anthropogenic greenhouse gases is derived from land use changes as well as forestry and agriculture, representing up to 67 % of the relative contribution from all sources. However, in spite of the rapid expansion of LAC tropical agriculture, little is known about its impact on atmospheric trace gases emissions, such as nitrogen oxides (NO (x) ), nitrous oxide (N2O) and carbon dioxide (CO2), which are produced in soils by microbial processes and also accelerated in tropical climates. This information is crucial for assessing mitigation strategies linked to agricultural practices to satisfy food demands for the region's future. We measured NO, N2O and CO2 soil emissions along with soil variables from corn fields under tillage (T) and no-tillage (NT) agriculture at two of the largest cereal-producing regions in Venezuela during the crop-growing season. We found statistically significant positive correlations between the logarithms of nitrogen gas emissions and soil inorganic nitrogen concentrations, soil water and clay contents. Average emissions of NO and CO2 were larger in T than NT sites, while N2O fluxes showed the opposite. CO2 emissions from T were 1.6 as much as those found in NT, whereas N2O was 0.5 of that found in NT. These results imply that NT practices more effectively mitigate climate change from these monoculture systems mainly because of CO2 emission reduction. We suggest then that agricultural mitigation actions for tropical monoculture systems should aim for the enhancement of NT management practices along with N fertilization rate reduction to compensate for the larger N2O emissions.

4. Carbon and nitrogen dynamics in bioenergy ecosystems: 2. Potential greenhouse gas emissions and global warming intensity in the conterminous United States.

• Authors:
  • Zhu, X. D.
  • Zhuang, Q. L.
  • Qin, Z. C.
• Source: GLOBAL CHANGE BIOLOGY BIOENERGY Volume: 7 Issue: 1 Pages: 25-39 DOI:
• Volume: 7
• Issue: 1
• Year: 2015
• Summary: This study estimated the potential emissions of greenhouse gases (GHG) from bioenergy ecosystems with a biogeochemical model AgTEM, assuming maize ( Zea mays L.), switchgrass ( Panicum virgatum L.), and Miscanthus ( Miscanthus * giganteus) will be grown on the current maize-producing areas in the conterminous United States. We found that the maize ecosystem acts as a mild net carbon source while cellulosic ecosystems (i.e., switchgrass and Miscanthus) act as mild sinks. Nitrogen fertilizer use is an important factor affecting biomass production and N 2O emissions, especially in the maize ecosystem. To maintain high biomass productivity, the maize ecosystem emits much more GHG, including CO 2 and N 2O, than switchgrass and Miscanthus ecosystems, when high-rate nitrogen fertilizers are applied. For maize, the global warming potential (GWP) amounts to 1-2 Mg CO 2eq ha -1 yr -1, with a dominant contribution of over 90% from N 2O emissions. Cellulosic crops contribute to the GWP of less than 0.3 Mg CO 2eq ha -1 yr -1. Among all three bioenergy crops, Miscanthus is the most biofuel productive and the least GHG intensive at a given cropland. Regional model simulations suggested that substituting Miscanthus for maize to produce biofuel could potentially save land and reduce GHG emissions.

5. The economic and environmental impacts of precision agriculture and interactions with agro-environmental policy

• Authors:
  • Schieffer, J.
  • Dillon, C.
• Source: PRECISION AGRICULTURE
• Volume: 16
• Issue: 1
• Year: 2015
• Summary: A whole-farm model was used to investigate the interacting effects of precision agriculture technology and agro-environmental policy on the production choices of a representative grain farm. Although some precision agriculture technologies did increase efficiency of resource use, they also decreased the effectiveness of policy, especially policies that rely on economic incentives (e.g., emission taxes). Precision agriculture can lead to higher marginal abatement costs in the form of forgone profits, decreasing producers' responsiveness to those policies. Policy-makers targeting pollution reductions from agriculture should take into account the increasing use of precision agriculture techniques and their varying effects on agro-environmental policy.

6. Yield response of maize (Zea mays L.) to conservation agriculture cropping system in Southern Africa

• Authors:
  • Rusinamhodzi, L.
  • Matemba-Mutasa, R.
  • Thierfelder, C.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 146
• Issue: Pt. B
• Year: 2015
• Summary: The effect of different conservation agriculture (CA) systems on maize grain yield was studied across four countries in southern Africa. Maize yield data was obtained from plots under no-tillage as well as from conventionally tilled plots. Crop residues were retained in no-till plots, whereas they were removed from conventional tillage plots in line with current farmer practices. Rotations or intercropping systems with grain legumes were introduced at all sites. Fertiliser treatments were uniform across tillage treatments at each trial location but varied across countries, based on local fertilizer recommendations. Focus group discussions were conducted with farmers in the study sites to understand the constraints related to the successful integration of CA into the farming systems and to document farmers' perceptions about CA. In the majority of cases (80%), yield responses from a range of CA systems were greater than those of the conventional control plot at the respective site. In 20% of the cases there was a negative response to CA, due to lack of experience by farmers in the initial year, slow increase in soil fertility at the respective site and waterlogging in some years with too much rainfall. Yield advantages on two manual CA systems, planted with a dibble stick with sole maize and maize-legume intercropping in Malawi were 1152kgha-1 and 1172kgha-1, respectively. Animal traction CA systems had slightly smaller yield benefits (458kgha-1 on a ripline seeded system and 761kgha-1 on an animal traction direct seeding systems) as compared to a ploughed control treatment. Yield benefits increased with increasing years of practicing CA, highlighting the need to gain experience to master critical management steps such as timely planting, weeding, fertiliser application and crop harvest residue management. Yields from CA system responded better to increasing clay and silt content in the top soil and were more resilient to seasonal rainfall variability than conventional control treatments. Results suggest that the niche for CA in southern Africa is larger than expected although rainfalls regimes below 600mm are challenging to sustain large maize biomass production to provide effective soil cover in CA systems. The success of CA implementation will largely depend on addressing critical challenges observed in the field, which will need adaptation of CA system to the site and farmer circumstances.

7. Methane and nitrous oxide emissions from rice and maize production in diversified rice cropping systems

• Authors:
  • Butterbach-Bahl, K.
  • Alberto, M. C. R.
  • Wassmann, R.
  • Ayag, K. R. P.
  • Kraus, D.
  • Weller, S.
  • Kiese, R.
• Source: NUTRIENT CYCLING IN AGROECOSYSTEMS
• Volume: 101
• Issue: 1
• Year: 2015
• Summary: Traditional irrigated double-rice cropping systems have to cope with reduced water availability due to changes of climate and economic conditions. To quantify the shift in CH4 and N2O emissions when changing from traditional to diversified double cropping-systems, an experiment including flooded rice, non-flooded "aerobic" rice and maize was conducted during the dry season (February-June 2012) in the Philippines. Two automated static chamber-GC systems were used to continuously measure CH4 and N2O emissions in the three cropping systems of which each included three different nitrogen fertilization regimes. Turning away from flooded cropping systems leads to shifts in greenhouse gas emissions from CH4 under wet soil to N2O emissions under drier soil conditions. The global warming potential (GWP) of the non-flooded crops was lower compared to flooded rice, whereas high CH4 emissions under flooded conditions still override enhanced N2O emissions in the upland systems. The yield-scaled GWP favored maize over aerobic rice, due to lower yields of aerobic rice. However, the lower GHG emissions of upland systems are only beneficial if they are not overwhelmed by enhanced losses of soil organic carbon.

8. Land cover change from cotton to corn in the USA relieves freshwater ecotoxicity impact but may aggravate other regional environmental impacts

• Authors:
  • Suh, Sangwon
  • Yang, Yi
• Source: INTERNATIONAL JOURNAL OF LIFE CYCLE ASSESSMENT
• Volume: 20
• Issue: 2
• Year: 2015
• Summary: Purpose Rising corn prices in the USA due partly to increasing ethanol demands have led to a significant expansion of corn areas displacing natural vegetation and crops including cotton. From 2005 to 2009, cotton area harvested in the USA nearly halved with a reduction of 2.5 million hectares, while that of corn increased by 1.8 million hectares. However, environmental impacts of land shifts from cotton and corn have been largely neglected in literature. Methods In this study, we evaluate the environmental properties of US corn and cotton production and implications of land cover change from cotton to corn using state-specific data and life cycle impact assessment. Focusing on regional environmental issues, we cover both on-farm direct emissions such as different types of volatile organic compounds and pesticides and indirect emissions embodied in input materials such as fertilizers. TRACI 2.0 is used to evaluate the environmental impacts of these emissions. Results and discussion The results show that US cotton and corn productions per hectare on average generate roughly similar impacts for most impact categories such as eutrophication and smog formation. For water use and freshwater ecotoxicity, corn shows a smaller impact. When land shifts from cotton to corn in cotton-growing states, however, the process may aggravate most of the regional environmental impacts while relieving freshwater ecotoxicity impact. The differences in the two estimates are due mainly to underlying regional disparities in crop suitability that affects input structure and environmental emissions. Conclusions Our results highlight the importance of potential, unintended environmental impacts that cannot be adequately captured when average data are employed. Understanding the actual mechanisms under which certain policy induces marginal changes at a regional and local level is crucial for evaluating its net impact. Further, our study calls for an attention to biofuel-induced land cover change between crops and associated regional environmental impacts.

9. Long-term effects of different organic and inorganic fertilizer treatments on soil organic carbon sequestration and crop yields on the North China Plain

• Authors:
  • Lv, Y. Z.
  • Huang, F.
  • Zhao, N.
  • Yang, Z. C.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 146
• Issue: Pt. A
• Year: 2015
• Summary: The aim of the study is to analyze the effects of different fertilization of organic and inorganic fertilizers on soil organic carbon (SOC) sequestration and crop yields after a 22 years long-term field experiment. The crop yields and SOC were investigated from 1981 to 2003 in Dry-Land Farming Research Institute of Hebei Academy of Agricultural and Forestry Sciences, Hebei Province, China. The dominant cropping systems are winter wheat-summer corn rotation. There were totally sixteen treatments applied to both wheat and corn seasons: inorganic fertilizers as main plots and corn stalks as subplots and the main plots and subplots all have four levels. The results revealed: after 22 years, mixed application of inorganic fertilizers and crop residuals, the SOC and crop yields substantially increased. Higher fertilizer application rates resulted in greater crop yields improvement. In 2002-2003, wheat and corn for the highest fertilizer inputs had the highest yield level, 6400kgha-1 and 8600kgha-1, respectively. However, the SOC decreased as the excessive inorganic fertilizer input and increased with the rising application of corn stalks. The treatment of the second-highest inorganic fertilizer and the highest corn stalks had the highest SOC concentration (8.64gCkg-1). Pearson correlation analysis shows that corn and winter wheat yields and the mineralization amount of SOC have significant correlation with SOC at p<0.05 level.

10. Greenhouse gas emissions dynamics as influenced by corn residue removal in continuous corn system

• Authors:
  • Al-Kaisi, M.
  • Guzman, J.
  • Parkin, T.
• Source: SOIL SCIENCE SOCIETY OF AMERICA JOURNAL
• Volume: 79
• Issue: 2
• Year: 2015
• Summary: The removal of corn residue for bioethanol may require changes in current tillage and fertilization practices to minimize potential alterations to the soil environment that may lead to increase in greenhouse gas (GHG) emission. The objectives of this study were to examine how tillage, N fertilization rates, residue removal, and their interactions affect CO2, and N2O soil surface emissions. Greater CO2 emission coincided with higher soil temperatures typically observed with conventional tillage (CT) compared with no-tillage (NT), resulting in greater annual cumulative CO2 emission in CT (18.1 CO2 Mg ha-1 yr-1) compared with NT (16.2 CO2 Mg ha-1 yr-1) in 2009 and 2010 across sites. However, drier soil conditions during the growing season in 2011 lead to higher soil temperatures compared with 2009 and 2010. Consequently, annual cumulative CO2 emission from NT with 50 and 100% residue removal was (19.5 CO2 Mg ha-1 yr-1) greater than that from CT (17.8 CO2 Mg ha-1 yr-1) across all residue removal rates and from NT (17.5 CO2 Mg ha-1 yr-1) with no residue removal, respectively across all N rates in the Ames central site (AC) in 2011. In the Armstrong southwest site (ASW) site, there were no significant differences between tillage or residue removal rates for annual cumulative CO2 emission (19.9 CO2 Mg ha-1 yr-1) in 2011. Although N2O emission was considerably lower than CO2 emission, differences in N fertilization rates did have a significant impact on global warming potential once these gases were converted on the basis of their radiative forcing of the atmosphere.