1. Long-term effect of sediment laden Yellow River irrigation water on soil organic carbon stocks in Ningxia, China

• Authors:
  • Shi, X.
  • Liu, Y.
  • Jin, W.
  • Zhang, M.
  • Zhang, H.
  • Yu, D.
  • Dong, L.
• Source: SOIL & TILLAGE RESEARCH
• Volume: 145
• Year: 2015
• Summary: Given the positive effects of mediating the growth of greenhouse gases in the atmosphere, interest in soil carbon stock dynamics has greatly increased. Several questions still exist as to whether irrigation with sediment laden water benefits carbon sequestration in soil profiles. This case study documented how long-term irrigation with sediment laden water from the Yellow River affected soil carbon sequestration in the Ningxia Irrigation Zone, China. The study included eight durations of irrigation management (10, 20, 30, 50, 280, 1300, 2100, and 2200 years) and five soil types. Soil samples from 44 profiles were collected to a depth of 100. cm, divided into four layers (0-20, 20-30, 30-60, 60-100 cm), and analyzed for soil organic carbon (SOC). SOC stocks both of soil profiles (0-100 cm) and irrigation-silted soil (ISS) layer, were 28.2 Tg C and 24.1 Tg C, respectively. The ISS layer was formed by the overlapping actions of irrigation and tillage, manure addition, and sediment silting as a result of long-term irrigation from the sediment laden water of the Yellow River. Compared to non-irrigated and non-cultivated control soils of similar depths and thicknesses, SOC stocks of the ISS layer increased 16.9. Tg C, and accounted for 89.9% of a total increment of 18.8 Tg C in the 0-100 cm layer of irrigated cropland soils. A significant correlation was found between the SOC density increment of the ISS layer and the number of irrigation years. Long-term irrigation with sediment laden Yellow River water greatly influenced SOC stocks, especially in the ISS layer, which plays an important role in soil carbon sequestration.

2. Climate change mitigation.

• Authors:
  • Paustian, K.
  • Bernoux, M.
• Source: Soil Carbon: Science, Management and Policy for Multiple Benefits
• Year: 2015
• Summary: Terrestrial ecosystems play a major role in regulating the concentrations of three greenhouse gases (CO 2, CH 4 and N 2O), of which CO 2 is the most important in terms of the impact on the global radiative balance. Soils play a major role in the global carbon (C) cycle and CO 2 dynamics; thus, management of soil carbon appears essential and more and more inevitable. The capacity of natural and managed agroecosystems to remove carbon dioxide from the atmosphere in a manner that is not immediately re-emitted into the atmosphere is known as carbon sequestration: carbon dioxide is absorbed by vegetation through photosynthesis and stored as carbon in biomass and soils, and released through autotrophic and heterotrophic respiration. Forests, croplands and grasslands can store large amounts of carbon in soils for relatively long periods. Soils are the larger terrestrial pool of organic carbon. Moreover, soil carbon sequestration is beneficial for soil quality, both over the short term and long term, and can be achieved through land management practices adapted to the specific site characteristics. The ability of soils to sequester carbon depends on climate, soil type, vegetation cover and land management practices. According to the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), the total technical greenhouse gas (GHG) mitigation potential of agriculture (considering all gases and sources) is estimated to be in the range 4.5-6 Gt CO 2-equivalent year -1 by 2030. Estimates indicate that many of these options are of relatively low cost and generate significant co-benefits in the form of improved agricultural production systems, resilience and other ecosystem services. Moreover, many of the technical options are readily available and could be deployed immediately. About 90% of this potential can be achieved by soil C sequestration through cropland management, grazing land management, restoration of organic soils and degraded lands, and water management in rainfed and irrigated croplands. In most cases, such management practices include the management of organic residues produced on site or coming from outside the field or the farm. It has been estimated that the global world production of residues in the agriculture sector is about 3.8 Pg C and, to date, the use of this resource has not been optimized; a large part is still being burned. Over the past two decades, other practices have been tested and are still controversial, such as biochar or chipped ramial wood application in cultivated fields. Biochar is a stabile carbon amendment, produced from pyrolysis of biomass, which may increase biomass productivity as well as sequester C from the source biomass. The scientific validation of these practices is still incomplete. Full participation of the agricultural sector in GHG mitigation still faces some challenges and barriers related to measurement, monitoring and reporting requirements in C offset markets. Further improvements are needed in methodologies and approaches that would help project designers and policy makers to integrate significant mitigation effects in agriculture development projects.

3. Metabolic responses of two contrasting sorghums to water-deficit stress.

• Authors:
  • Burow, G.
  • Xin, Z. Q.
  • Chen, J. P.
  • Payton, P.
  • Burke, J. J.
  • Hayes, C.
• Source: Crop Science
• Volume: 55
• Issue: 1
• Year: 2015
• Summary: Water-deficit stress responses in sorghum [Sorghum bicolor (L.) Moench] have been described in the literature as preflowering drought tolerant (postflowering senescent) or postflowering drought tolerant (preflowering drought sensitive). The underlying physiological mechanisms associated with these drought traits remain unclear. It was hypothesized that the preflowering drought sensitivity of stay-green lines could be related to reported differences in osmotic potential among stay-green and senescent lines resulting in an inability of the cultivars to either sense or respond the soil drying until the rate of drying is too great for the stay-green lines to compensate. The objective of this study was to measure stress-induced changes in relative water content, abscisic acid (ABA), proline, dhurrin, sucrose, and carbon assimilation during the onset of water-deficit stress in the preflowering drought-tolerant line SC1211-11E and the postflowering drought-tolerant line BTx642 to determine if there were differential responses to the onset of soil drying. In both greenhouse and field studies, it was found that SC1211-11E had lower relative water contents and accumulated higher levels of ABA and proline than the BTx642. The SC1211-11E also showed increases in carbon assimilation shortly after the cessation of irrigation that declined with prolonged stress. These results provide new insights into the differential responses of pre and postflowering drought-tolerant sorghum lines.

4. Splitting the application of 3,4-dimethylpyrazole phosphate (DMPP): Influence on greenhouse gases emissions and wheat yield and quality under humid Mediterranean conditions

• Authors:
  • Menendez, S.
  • Maria Estavillo, J.
  • Gonzalez-Murua, C.
  • Dunabeitia, M. K.
  • Fuertes-Mendizabal, T.
  • Huerfano, X.
• Source: EUROPEAN JOURNAL OF AGRONOMY
• Volume: 64
• Year: 2015
• Summary: Wheat is among the most widely grown cereals in the world. In order to enhance its production, its management is based on the addition of nitrogen (N) fertilizers. Nevertheless, its application could increase nitrous oxide (N2O) emissions, which effects are very pernicious to the environment, being a strong greenhouse gas (GHG). Regarding GHG, soil processes can also produce or consume carbon dioxide (CO2) and methane (CH4). Nitrification inhibitors (NI) have been developed with the aim of decreasing fertilizer-induced N losses and increase N efficiency. The fact that the application of a NI enhances N use efficiency is a good reason to think that more N should be also available for increasing the grain N concentration of wheat plants. If the application of NI means an increase in N use efficiency, it is plausible to consider that more N would be available, hence, increasing the grain N concentration of wheat. We present a two-year field-experiment to evaluate the influence of the NI 3,4-dimethylpyrazol phosphate (DMPP) on grain yield, grain quality and GHG emissions. Fertilizer dose, with and without DMPP, was 180 kg N ha(-1) applied as ammonium sulfate nitrate (ASN) splitted in two applications of 60 kg N ha(-1) and 120 kg N ha(-1), respectively. A treatment with a non-splitted application of ASN with DMPP and an unfertilized treatment were also included. The splitted application of ASN with DMPP was able to reduce N2O emissions, without affecting yield and its components. The alternative management of a non-splitted application of DMPP was more efficient mitigating N2O emissions, whilst keeping yield and slightly reducing grain protein content. In consequence of the low N2O fluxes from our soils, the EF applied in our region should be lower than the default value of 1% proposed by IPCC.

5. Long-rotation sugarcane in Hawaii sustains high carbon accumulation and radiation use efficiency in 2nd year of growth.

• Authors:
  • Wang, D.
  • Tirado-Corbala, R.
  • Anderson, R. G.
  • Ayars, J. E.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 199
• Year: 2015
• Summary: Sugarcane has been a major agronomic crop in Hawaii with an unique, high-yield, two-year production system. However, parameters relevant to advanced, cellulosic biofuel production, such as net ecosystem productivity (NEP) and radiation use efficiency (RUE), have not been evaluated in Hawaii under commercial production. Recent demand potential has rekindled interest in Hawaiian grown biofuels; as such, there is a need to understand productivity under changing climate and agronomic practices. To this end, we established two eddy covariance towers in commercial sugarcane fields in Maui, Hawaii to evaluate the carbon balance and RUE of sugarcane under contrasting elevations and soil types. We combined the tower observations with biometric and satellite data to assess RUE in terms of net biomass accumulation and daily gross primary production. High, sustained net NEP was found in both fields (cumulative NEP 4.23-5.37*10 3 g C m -2 over the course of the measurement period). Biomass RUE was statistically similar for both fields (1.15-1.24 g above ground biomass per MJ intercepted solar irradiance). Carbon accumulated in both fields at nearly the same rate with differences in cumulative biomass due to differing crop cycle lengths; cumulative gross primary productivity and ecosystem respiration were higher in the lower elevation field. Contrary to previous studies in Hawaiian sugarcane, we did not see a large decrease in NEP or increase in ecosystem respiration in the 2nd year, which we attributed to suppressed decomposition of dead cane stalks and leaves due to drip irrigation and drought. Biomass RUE also showed little decline in the 2nd year. The results show that Hawaiian sugarcane has a higher productivity than sugarcane grown in other regions of the world and also suggests that a longer (>12 months) growing cycle may be optimal for biomass production.

6. Seasonal variability of NO 3- mobilization during flood events in a Mediterranean catchment: the influence of intensive agricultural irrigation.

• Authors:
  • Sorando, R.
  • Comin, F. A.
  • Darwiche-Criado, N.
  • Sanchez-Perez, J. M.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 200
• Year: 2015
• Summary: The temporal variability, hysteresis loops and various factors involved in the mobilization of nitrates (NO 3-) have been studied for a 3-year period at the Flumen River basin. Multivariate techniques (cluster analysis and pearson correlation matrix) were used to establish the relationship between the water discharge and NO 3- flushing, as well as to identify the agricultural and hydrometeorological parameters that influence its different mobilization trends. The relationship between changes in the NO 3- concentration (Delta C) and the overall dynamic of each hysteresis loop (Delta R) was also analyzed in order to describe the NO 3- trends according to the water discharge. A general dilution pattern of the NO 3- concentration was noted in the Flumen River with respect to the degree of water discharge caused by irrigation return flows. While fertilization increased the NO 3- concentration, the beginning of the irrigation season contributed to its dilution. However, in case of the NO 3- load, the maximum values occurred during high flow periods in the irrigation period, which suggested the influence of the irrigation flow on the NO 3- mass. The NO 3- load increased to 2753 t and 1059 t during the first and second phases of the study period, respectively, with an average specific yield of 1.33 t km -2 y -1. The NO 3- transport in the first phase of the study was 1722 t during the irrigation season and 1031 t during the non-irrigation period. Only 348 t (13%) of NO 3- was exported during the flood events. However, in the course of the second phase of the study, the NO 3- load was 733 t during the irrigation season and 326 t during the non-irrigation period. In this case, 610 t (57%) of nitrate was transported during the floods. These results revealed the clear influence of irrigation return flows on the NO 3- response in Flumen River.

7. Effects of cultivation on chemical and biochemical properties of dryland soils from southern Tunisia.

• Authors:
  • Massaccesi, L.
  • Brecciaroli, G.
  • Agnelli, A.
  • Fornasier, F.
  • Cocco, S.
  • Hannachi, N.
  • Weindorf, D.
  • Corti, G.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 199
• Year: 2015
• Summary: The progressive degradation of cultivated drylands has been mainly ascribed to adoption of intensive soil use, namely repeated soil cultivation with external inputs and disturbances. Consequently, soil managements in equilibrium with environmental and social constrains are required to conserve and improve the soil fertility. We evaluated the impact of soil cultivation and management on chemical and biochemical properties of dryland soils from the Tunisian Jeffara Plain. This study considered three sites (Chenini Nahel, Matmata Nouvelle, and Menzel Habib), with both non-cultivated and cultivated soils. These latter were subjected to different soil management: organic fertilization and irrigation by submersion, chemical fertilization and drip irrigation, no fertilization and sporadic watering. The results showed that the addition of organic matter as compost or manure combined with irrigation may favor pH reduction, with consequently higher enzymatic activity and organic matter storage. The latter occurred because of the encapsulation of organic particles into collars made of re-precipitated gypsum and calcite. In cases where chemical fertilization and drip irrigation were applied, the organic matter stabilization occurred only at the surface; at depth we observed a reduction of organics due to microbially-mediated mineralization processes. When neither organic amendment nor water was supplied, no substantial difference occurred between cultivated and non-cultivated soils. We concluded that, in drylands, agricultural managements providing the use of water and organic amendments is the way to increase soil organic matter storage and improve physical, chemical and biological properties so to enhance the soil fertility.

8. Cotton crop water use and water use efficiency in a changing climate.

• Authors:
  • Johnston, D.
  • Bange, M.
  • Luo, Q. Y.
  • Braunack, M.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 202
• Year: 2015
• Summary: Daily outputs from the CSIRO Conformal Cubic Atmospheric Model, driven by four general circulation models, were used in a stochastic weather generator, LARS-WG, to construct local climate scenarios for key cotton production areas in eastern Australia. These scenarios along with elevated atmospheric carbon dioxide concentration were then linked to a process-oriented cotton model (CSIRO OZCOT) to quantify their potential impacts on cotton lint yield, water use, and water use efficiency (WUE) under irrigated and rain-fed conditions in 2030. For irrigated cotton, we considered four water supply levels (2, 4, 6 and 8 ML/ha) at nine cotton production locations (Emerald, Dalby, St. George, Goondiwindi, Moree, Bourke, Narrabri, Warren and Hillston). For rain-fed cotton, we considered three planting configurations (solid, single skip and double skip) at four locations (Emerald, Dalby, Moree and Narrabri). Simulation results show that (1) season temperatures will increase 1-1.2°C and rainfall will increase 2-16% across locations; (2) for irrigated cotton (assuming full access to water and nitrogen), cotton crop water use will increase 0-4% in more than half of the cases (the combinations of the number of locations and water supply levels); cotton lint yield will increase 0-26% and WUE will increase 0-24% in most of the cases due to counteractive effects of elevated CO 2 and future climate, which are location- and water supply-specific; (3) for rain-fed cotton (assuming full initial soil profile), cotton water use will increase 2-8% at Emerald and Narrabri and decrease by -5 to -2% at Dalby and Moree; cotton lint yield will increase 4-26% in most of the cases and WUE will increase 2-22% in all cases. For irrigated cotton, it was found that water supply level with 2 ML/ha generated the greatest positive effects to future climate scenarios across locations except at Dalby where 4 ML/ha was greatest. For rain-fed cotton, a solid planting configuration had the greatest positive response to future climate scenarios at Emerald, Dalby and Moree while double skip planting generated the maximum benefit in lint yield at Narrabri. This simulation analysis also demonstrated the ability of the OZCOT in capturing the interactive effects of elevated CO 2 and future climate, indicating the usefulness of this tool in this important research area.

9. Organic mulching, irrigation and fertilization affect soil CO2 emission and C storage in tomato crop in the Mediterranean environment

• Authors:
  • Radicetti, E.
  • Brunetti, P.
  • Marinari, S.
  • Mancinelli, R.
  • Campiglia, E.
• Source: Soil and Tillage Research
• Volume: 152
• Year: 2015
• Summary: Carbon stock and CO2 emissions in agricultural systems are highly affected by the management of applied practices in arable farms, such as fertilizer use, irrigation, soil tillage, cover crop management, etc. This study evaluated the effects of various organic mulches, nitrogen fertilization and irrigation levels on soil CO2 emissions, soil carbon sequestration and processing tomato production in the Mediterranean environment. The field experiment was carried out with five main treatments, three cover crops of hairy vetch (HV), lacy phacelia (LF) and white mustard (WM) transplanted in autumn and cut in May to be used as mulches, plus barley straw mulch (BS) and conventional (C) (bare soil). After tomato transplanting, the main plots were split into two nitrogen fertilization treatments (0 and 100kgNha-1) and the sub-plots were then split again into three irrigation levels (irrigation water 100%, 75%, 50% of evapotranspiration). In all treatments, a general effect was observed in the temporal fluctuations of soil CO2 emissions throughout the observation period which were significantly influenced by soil temperature and water content. The temporal fluctuations of the soil CO2 emissions were attributed to climatic conditions and the peaks achieved optimal conditions of soil temperature and water content for soil respiration. A larger amount of TOC was observed in the mulching treatments than in the control after tomato harvesting (on average 1.44% vs 1.33%, respectively and on average 1.43% in HV trastment), probably due to the residual biomass of the cover crops and a greater growth of the tomato. Although the soil carbon output as cumulated CO2 emissions did not show statistically significant differences between the treatments, the soil carbon balance enabled us to estimate the highest net carbon contribution to the soil in HV determined by inputs and input/output ratio. However, except for the BS in 2013, the input/output ratios were ≥1 in all mulch treatments. In the Mediterranean environment, agronomical practices, such as the use of hairy vetch mulch on notilled soil, a slight reduction of irrigation water (-25%) and a rationalized use of N fertilizer potentially could shift the C balance in favor of soil C accumulation.

10. Consideration of total available N supply reduces N fertilizer requirement and potential for nitrate leaching loss in tomato production.

• Authors:
  • Pena-Fleitas, M. T.
  • Thompson, R. B.
  • Gallardo, M.
  • Soto, F.
  • Padilla, F. M.
• Source: AGRICULTURE ECOSYSTEMS & ENVIRONMENT
• Volume: 200
• Year: 2015
• Summary: Effects of increasing total available N (TAN) on agronomic performance, apparent recovery of TAN (AR TAN), NO 3- leaching and soil mineral N accumulation were examined in two tomato crops. Total available N was considered to be the sum of soil mineral N at planting, N mineralized from organic material (soil organic matter and manure), and mineral N fertilizer applied by fertigation. In each crop, four different mineral N fertilizer rates were applied as different N concentrations (N1: 0.6-1.1 mM, N2: 4.4-5.2 mM, N3: 13.4-13.6 mM, N4 20.5-21.7 mM) in nutrient solutions applied in all irrigations every 1-4 days throughout the crop. N3 treatments corresponded to local commercial practice. The first crop was grown in autumn-winter 2010 (AW-2010) and the second in spring 2011 (S-2011). For the two crops, TAN values were 165-215 kg N ha -1 in N1, 287-361 kg N ha -1 in N2, 563-667 kg N ha -1 in N3 and 847-976 kg N ha -1 in N4. In both crops, maximum fruit production was obtained with the N2 treatments. AR TAN decreased exponentially as TAN increased, from values of close to 1.0 for N1 treatments to approximately 0.3 for N4 treatments. The linear relationship between NO 3- leaching and TAN had a shallow slope, with a maximum leaching loss of 36-40 kg N ha -1 in the N4 treatments; NO 3- leaching loss was limited by small drainage volumes associated with good irrigation management. There was an exponential increase in residual soil mineral N with increasing TAN. For N3 treatments, corresponding to common local management practices, residual soil mineral N was 234-262 kg N ha -1, and for N4 treatments was 484-490 kg N ha -1. Therefore, increasing TAN very strongly increased the potential for subsequent N loss. Where TAN was excessive to crop N requirements, limiting NO 3- leaching loss (measured using lysimeters) by good irrigation practices was considered to only delay NO 3- leaching loss. The N3 treatments of 13-14 mM of N that corresponded to local practice were associated with a large potential N loss. Based on TAN, the optimal treatment was N2 of 4-5 mM which was associated with maximum fruit production and a relatively very small potential loss of N. The results demonstrated that by considering (i) TAN rather than just fertilizer N, and (ii) mineral N fertilizer as a supplement to other N sources, that maximum production can be achieved with high AR TAN and with a much reduced risk of N loss to the environment.