19602015
  • Authors:
    • Chen, X. P.
    • Cui, Z. L.
    • Zhang, F. S.
    • Ye, Y. L.
    • Zhao, R. F.
    • Meng, Q. F.
    • Yue, S. C.
  • Source: AGRONOMY JOURNAL
  • Volume: 104
  • Issue: 6
  • Year: 2012
  • Summary: Overestimates of N requirements have led to excessive N application and serious environmental pollution in intensively managed agricultural systems. A database comprising 1395 measurements was developed from 2000 to 2011 using 88 on-farm and station experiments conducted in five key winter wheat ( Triticum aestivum L.) domains in northern China. The database was created to evaluate the relationship between aboveground N uptake and grain yield with different N treatments and to quantify N requirements per Mg grain at different grain yield levels. Across all sites, wheat grain yield ranged from 1.6 to 11.8 Mg ha -1. The nitrogen requirement per megagram grain yield (N req.) increased with N supply from 20.8 kg under the treatment without N fertilizer to 25.7 kg under the excess N treatment. For the optimal N fertilizer treatment, the average N req. was 24.3 kg and it declined with increasing grain yield. For the yield ranges between 10.5 Mg ha -1, N req. changed little due to stability in grain N concentrations and HI. In conclusion, the N requirement of a crop was affected by both the amount of N supplied and the grain yield.
  • Authors:
    • Dreccer, M. F.
    • Chenu, K.
    • Zheng, B. Y.
    • Chapman, S. C.
  • Source: GLOBAL CHANGE BIOLOGY
  • Volume: 18
  • Issue: 9
  • Year: 2012
  • Summary: Extreme climate, especially temperature, can severely reduce wheat yield. As global warming has already begun to increase mean temperature and the occurrence of extreme temperatures, it has become urgent to accelerate the 5-20 year process of breeding for new wheat varieties, to adapt to future climate. We analyzed the patterns of frost and heat events across the Australian wheatbelt based on 50 years of historical records (1960-2009) for 2864 weather stations. Flowering dates of three contrasting-maturity wheat varieties were simulated for a wide range of sowing dates in 22 locations for 'current' climate (1960-2009) and eight future scenarios (high and low CO 2 emission, dry and wet precipitation scenarios, in 2030 and 2050). The results highlighted the substantial spatial variability of frost and heat events across the Australian wheatbelt in current and future climates. As both 'last frost' and 'first heat' events would occur earlier in the season, the 'target' sowing and flowering windows (defined as risk less than 10% for frost (35°C) around flowering) would be shifted earlier by up to 2 and 1 month(s), respectively, in 2050. A short-season variety would require a shift in target sowing window 2-fold greater than long- and medium-season varieties by 2050 (8 vs. 4 days on average across locations and scenarios, respectively), but would suffer a lesser decrease in the length of the vegetative period (4 vs. 7 days). Overall, warmer winters would shorten the wheat season by up to 6 weeks, especially during preflowering. This faster crop cycle is associated with a reduced time for resource acquisition, and potential yield loss. As far as favourable rain and modern equipment would allow, early sowing and longer season varieties (i.e. in current climate) would be the best strategies to adapt to future climates.
  • Authors:
    • Passaglia, . M. P.
    • Vargas, L. K.
    • Pinheiro, F. G.
    • Stefanski, T.
    • Beneduzi, A.
    • Ambrosini, A.
  • Source: PLANT AND SOIL
  • Volume: 356
  • Issue: 1-2
  • Year: 2012
  • Summary: This study was aimed at assessing the diversity of putatively diazotrophic rhizobacteria associated with sunflower (Helianthus annuus L.) cropped in the south of Brazil, and to examine key plant growth promotion (PGP) characteristics of the isolates for the purposes of increasing plant productivity. 299 strains were isolated from the roots and rhizosphere of sunflower cultivated in five different areas using N-free media. 16S rDNA PCR-RFLP and 16S rRNA partial sequencing were used for identification and the Shannon index was used to evaluate bacterial diversity. Production of siderophores and indolic compounds (ICs), as well phosphate solubilization activities of each isolate were also evaluated in vitro. On the basis of multiple PGP activities, eight isolates were selected and tested for their N-fixation ability, and their capacity as potential PGPR on sunflower plants was also assessed. All except three Gram-positive strains (phylum Actinobacteria) belonged to the Gram-negative Proteobacteria subgroups [Gamma (167), Beta (78), and Alpha (50)] and the family Flavobacteriaceae (1)]. Shannon indexes ranged from 0.96 to 2.13 between the five sampling sites. Enterobacter and Burkholderia were the predominant genera isolated from roots and rhizosphere, respectively. Producers of siderophores and ICs were widely found amongst the isolates, but only 19.8% of them solubilized phosphate. About 8% of the isolates exhibited all three PGP traits, and these mostly belonged to the genus Burkholderia. Four isolates were able to stimulate the growth of sunflower plants under gnotobiotic conditions. Enterobacter and Burkholderia were the dominant rhizospheric bacterial genera associated with sunflower plants. Inoculation with isolates belonging to the genera Achromobacter, Chryseobacterium, Azospirillum, and Burkholderia had a stimulatory effect on plant growth.
  • Authors:
    • Stelluti, M.
    • Wong, M. T. F.
    • Castrignano, A.
    • De Benedetto, D.
    • Sollitto, D.
  • Source: GEODERMA Volume: 175 Pages:
  • Volume: 175
  • Year: 2012
  • Summary: Geo-electrical sensors are often used as auxiliary variables with sparse direct measurements to estimate soil properties. Using a single sensor is not ideal in some circumstances. For example, sandy, sandy gravelly, sandy salt-affected and clayey soils are poorly identified using an EMI or gamma-ray sensor singularly. The complementary use of these sensors should improve interpretation in landscapes containing these soils. Analysis of multi-sensor data is however problematic. Several methods have been developed to integrate multi-sensor data but there is currently no unequivocally accepted methodology. The objectives of this work were: 1) to define a combined approach of geostatistics and sensor data fusion to integrate field data from electromagnetic induction (EMI) measured with EM38 and EM31, gamma (gamma)-ray and RTK GPS sensors for delineating areas of homogeneous soil; 2) to show the potential of gamma radiometric sensor by estimating a relationship for crop available soil potassium (K) from the gamma-ray signal. The geophysical survey was carried out on an 80-ha cropping field in Corrigin, Western Australia. Seventy-seven soil samples were collected at the nodes of a 100 x 100m-mesh grid and analysed for different properties. The EM38 and EM31 data were strongly correlated with each other and so were gamma-radiometric counts from thorium (Th), uranium (U) and all elements (TC). The multi-sensor data were split into 4 subgroups, based on their similarities: 1) EMI data; 2) gamma-radiometric counts from potassium (emitted from all forms of K including readily plant available, non-exchangeable and structural K); 3) gamma-radiometric counts from Th, U and IC and 4) RTK GPS height. Each group of data was separately analysed using geostatistical techniques. The soil samples and geophysical data were jointly interpolated using multi collocated cokriging. The EMI data showed anisotropy and an anisotropic Linear Model of Coregionalization was fitted before cokriging. The EM31 and EM38 maps looked quite similar. The maps of gamma-U, Th and TC were also similar, suggesting that they reflected the same soil properties, but were somewhat different from the gamma-K maps. High values of EMI coincided with both low radiometric values at the valley bottom, due to moist sandy salinity-prone soil of varying depth to texture contrast, and high gamma-radiometric values at the elevated areas of the field due to emission from finer textured soil. High gamma-radiometric values coincided also with low values of EMI over gravelly sands. Only the use of a multi-sensor platform could discriminate soils that gave similar outputs to one sensor. The first two principal components of the geophysical data were used to partition the field into homogeneous areas. In order to test the utility of geophysical survey for K recommendations, the spatial association between the maps of the estimates of plant available soil K content and gamma-K counts was demonstrated by using different agreement coefficients and a regression model with correlated errors was estimated between the two variables. (C) 2012 Elsevier ay. All rights reserved.
  • Authors:
    • Porter, J. R.
    • Olesen, J. E.
    • Chirinda, N.
  • Source: PLANT AND SOIL
  • Volume: 359
  • Issue: 1-2
  • Year: 2012
  • Summary: In agroecosystems, carbon (C) inputs come from plant roots, retained shoot residues and in some cases from applied manures. Manure and shoot derived C inputs are relatively easy to determine. Conversely, high costs associated with root measurements have caused knowledge on root C input to remain scant. This study aimed at determining macro-root C input and topsoil root related respiration in response to nutrient management and soil fertility building measures. We sampled roots and shoots of cereals and catch crops in inorganic and organic fertilizer-based arable cropping systems in a long-term experiment in 2 years, 2008 and 2010. Sampled shoots and macro-roots of catch crop mixtures and cereals were characterized for dry matter (DM) biomass (C was estimated as 45 % of DM biomass). We also measured topsoil root-related soil respiration throughout the growing season of winter wheat by subtracting soil respiration from soil with and without exclusion of roots. Catch crop roots accounted for more than 40 % of total plant C. For spring barley in 2008 and spring wheat in 2010, root C was higher in the organic than in the inorganic fertilizer-based systems. However, for winter wheat in 2008 and spring barley in 2010, there were similar amounts of root C across systems. The measurements of topsoil root-derived respiration also showed no difference across systems, despite large differences in harvested cereal yields. Cereal biomass shoot-to-root (S/R) ratio was higher (31-131 %) in inorganic than in organic fertilizer-based systems. Our findings show that macro-roots of both cereal crops and catch crops play a relatively larger role in organically managed systems than in mineral fertilizer based systems; and that the use of fixed biomass S/R ratios to estimate root biomass leads to erroneous estimates of root C input.
  • Authors:
    • Abbott, L. K.
    • Murphy, D. V.
    • Solaiman, Z. M.
  • Source: PLANT AND SOIL
  • Volume: 353
  • Issue: 1-2
  • Year: 2012
  • Summary: Background and aims Biochar can be produced from a wide range of organic sources with varying nutrient and metal concentrations. Before making irreversible applications of biochar to soil, a preliminary ecotoxicological assessment is desirable. Methods First, we determined the effect of biochar type and rate on early growth of wheat in a soil-less Petri dish bioassay. Second, we investigated the effect of the same biochars on seed germination and early growth of wheat in ten soils with varying texture using a glasshouse bioassay. Finally, we investigated whether these biochars had similar effects on three plant species when grown in one soil. Results Biochar type and application rate influenced wheat seed germination and seedling growth in a similar manner in both the soil-less Petri dish and soil-based bioassay. Germination and early root growth of mung bean and subterranean clover differed from that of wheat in response to the five biochars. Conclusions We recommend use of the soil-less Petri dish bioassay as a rapid and simple preliminary test to identify potential toxicity of biochars on seed germination and early plant growth prior to biochar application to soil.
  • Authors:
    • Sturrock, C.
    • Korosak, D.
    • Samec, M.
    • Tester, M.
    • Davidson, R.
    • McNeill, A.
    • Roberts, J. A.
    • Black, C. R.
    • Tracy, S. R.
    • Mooney, S. J.
  • Source: PLANT AND SOIL
  • Volume: 353
  • Issue: 1-2
  • Year: 2012
  • Summary: Aims X-ray Micro Computed Tomography (CT) enables interactions between roots and soil to be visualised without disturbance. This study examined responses of root growth in three Triticum aestivum L. (wheat) cultivars to different levels of soil compaction (1.1 and 1.5 g cm(-3)). Methods Seedlings were scanned 2, 5 and 12 days after germination (DAG) and the images were analysed using novel root tracking software, RootViz3D (R), to provide accurate visualisation of root architecture. RootViz3D (R) proved more successful in segmenting roots from the greyscale images than semi-automated segmentation, especially for finer roots, by combining measurements of pixel greyscale values with a probability approach to identify roots. Results Root density was greater in soil compacted at 1.5 g cm(-3) than at 1.1 gcm(-3) (P=0.04). This effect may have resulted from improved contact between roots and surrounding soil. Root diameter was greater in soil at a high bulk density (P=0.006) but overall root length was reduced (P=0.20). Soil porosity increased with time (P<0.001) in the uncompacted treatment. Conclusions RootViz3D (R) root tracking software in X-ray CT studies provided accurate, non-destructive and automated three dimensional quantification of root systems that has many applications for improving understanding on root-soil interactions.
  • Authors:
    • Vrieling, A.
    • Tubiello, F. N.
    • Velde, M. van der
    • Bouraoui, F.
  • Source: Climatic Change
  • Volume: 113
  • Issue: 3-4
  • Year: 2012
  • Summary: Extreme weather conditions can strongly affect agricultural production, with negative impacts that can at times be detected at regional scales. In France, crop yields were greatly influenced by drought and heat stress in 2003 and by extremely wet conditions in 2007. Reported regional maize and wheat yields where historically low in 2003; in 2007 wheat yields were lower and maize yields higher than long-term averages. An analysis with a spatial version (10 x 10 km) of the EPIC crop model was tested with regards to regional crop yield anomalies of wheat and maize resulting from extreme weather events in France in 2003 and 2007, by comparing simulated results against reported regional crops statistics, as well as using remotely sensed soil moisture data. Causal relations between soil moisture and crop yields were specifically analyzed. Remotely sensed (AMSR-E) JJA soil moisture correlated significantly with reported regional crop yield for 2002-2007. The spatial correlation between JJA soil moisture and wheat yield anomalies was positive in dry 2003 and negative in wet 2007. Biweekly soil moisture data correlated positively with wheat yield anomalies from the first half of June until the second half of July in 2003. In 2007, the relation was negative the first half of June until the second half of August. EPIC reproduced observed soil dynamics well, and it reproduced the negative wheat and maize yield anomalies of the 2003 heat wave and drought, as well as the positive maize yield anomalies in wet 2007. However, it did not reproduce the negative wheat yield anomalies due to excessive rains and wetness in 2007. Results indicated that EPIC, in line with other crop models widely used at regional level in climate change studies, is capable of capturing the negative impacts of droughts on crop yields, while it fails to reproduce negative impacts of heavy rain and excessively wet conditions on wheat yield, due to poor representations of critical factors affecting plant growth and management. Given that extreme weather events are expected to increase in frequency and perhaps severity in coming decades, improved model representation of crop damage due to extreme events is warranted in order to better quantify future climate change impacts and inform appropriate adaptation responses.
  • Authors:
    • Zhang, F. S.
    • Yang, X. G.
    • Wang, E. L.
    • Wang, J.
    • Yin, H.
  • Source: CLIMATIC CHANGE
  • Volume: 113
  • Issue: 3-4
  • Year: 2012
  • Summary: In the North China Plain, the grain yield of irrigated wheat-maize cropping system has been steadily increasing in the past decades under a significant warming climate. This paper combined regional and field data with modeling to analyze the changes in the climate in the last 40 years, and to investigate the influence of changes in crop varieties and management options to crop yield. In particular, we examined the impact of a planned adaptation strategy to climate change -"Double-Delay" technology, i.e., delay both the sowing time of wheat and the harvesting time of maize, on both wheat and maize yield. The results show that improved crop varieties and management options not only compensated some negative impact of reduced crop growth period on crop yield due to the increase in temperature, they have contributed significantly to crop yield increase. The increase in temperature before over-wintering stage enabled late sowing of winter wheat and late harvesting of maize, leading to overall 4-6% increase in total grain yield of the wheat-maize system. Increased use of farming machines and minimum tillage technology also shortened the time for field preparation from harvest time of summer maize to sowing time of winter wheat, which facilitated the later harvest of summer maize.
  • Authors:
    • Cao, L.
    • Lobell, D. B.
    • Pongratz, J.
    • Caldeira, K.
  • Source: Nature Climate Change
  • Volume: 2
  • Issue: 2
  • Year: 2012
  • Summary: Crop models predict that recent and future climate change may have adverse effects on crop yields(1,2). Intentional deflection of sunlight away from the Earth could diminish the amount of climate change in a high-CO2 world(3-6). However, it has been suggested that this diminution would come at the cost of threatening the food and water supply for billions of people(7). Here, we carry out high-CO2, geoengineering and control simulations using two climate models to predict the effects on global crop yields. We find that in our models solar-radiation geoengineering in a high-CO2 climate generally causes crop yields to increase, largely because temperature stresses are diminished while the benefits of CO2 fertilization are retained. Nevertheless, possible yield losses on the local scale as well as known and unknown side effects and risks associated with geoengineering indicate that the most certain way to reduce climate risks to global food security is to reduce emissions of greenhouse gases.