Modelling shifts in agroclimate and crop cultivar response under climate change

This paper aims: (i) to identify at national scale areas where crop yield formation is currently most prone to climate‐induced stresses, (ii) to evaluate how the severity of these stresses is likely to develop in time and space, and (iii) to appraise and quantify the performance of two strategies for adapting crop cultivation to a wide range of (uncertain) climate change projections. To this end we made use of extensive climate, crop, and soil data, and of two modelling tools: N‐AgriCLIM and the WOFOST crop simulation model. N‐AgriCLIM was developed for the automatic generation of indicators describing basic agroclimatic conditions and was applied over the whole of Finland. WOFOST was used to simulate detailed crop responses at four representative locations. N‐AgriCLIM calculations have been performed nationally for 3829 grid boxes at a 10 × 10 km resolution and for 32 climate scenarios. Ranges of projected shifts in indicator values for heat, drought and other crop‐relevant stresses across the scenarios vary widely – so do the spatial patterns of change. Overall, under reference climate the most risk‐prone areas for spring cereals are found in south‐west Finland, shifting to south‐east Finland towards the end of this century. Conditions for grass are likely to improve. WOFOST simulation results suggest that CO₂ fertilization and adjusted sowing combined can lead to small yield increases of current barley cultivars under most climate scenarios on favourable soils, but not under extreme climate scenarios and poor soils. This information can be valuable for appraising alternative adaptation strategies. It facilitates the identification of regions in which climatic changes might be rapid or otherwise notable for crop production, requiring a more detailed evaluation of adaptation measures. The results also suggest that utilizing the diversity of cultivar responses seems beneficial given the high uncertainty in climate change projections.     

Creation of a non-mycorrhizal control for a bioassay of AM effectiveness

γ -irradiation of soil by 10 and 3 kGy, and the use of a myc⁻ mutant. The methods were examined on clay and loam. Two management histories were included with both soils to study the ability of the methods to differentiate AM effectiveness. For each soil type, two pot experiments were conducted in field soil, one to investigate the effects of the methods on soil nutrient status, and the other to study the effects on mycorrhization and plant response. The test plants, flax (Linum usitatissimum) and pea (Pisum sativum) myc⁺ and myc⁻ mutants, were grown in 1-l pots for 4 weeks in a growth chamber. To test the ability of the bioassay to reflect differences in AM effectiveness in the field, the mutants and benomyl were also studied in the field from which the loam for the pot experiments was obtained. The bioassay accurately represented the situation in the field and the use of benomyl appeared to be the most appropriate method currently available. The advantages were the ability to use a test plant responsive to AM, the use of less elevated nutrient concentrations than with irradiation, and thus the possibility to use untreated soil as the mycorrhizal treatment. The pea mutants proved unresponsive to AM, and reinoculation to irradiated soil resulted in only half the colonization rate in untreated soil. Benomyl may, however, lead to an underestimation of AM effectiveness because the control is not totally non-mycorrhizal. Its use also carries with it health and environmental risks. Received: 9 February 1999 / Accepted: 27 September 1999     

Arbuscular mycorrhizal fungal diversity and species dominance in a temperate soil with long-term conventional and low-input cropping systems

The aim of this work was to study the effect of long-term contrasting cropping systems on the indigenous arbuscular mycorrhizal fungal (AMF) spore populations in the soil of a field experiment located in western Finland. Conventional and low-input cropping systems were compared, each with two nutrient management regimes. The conventional cropping system with a non-leguminous 6-year crop rotation (barley–barley–rye–oat–potato–oat) was fertilized at either full (rotation A) or half (rotation B) the recommended rate. In the low-input cropping system, plant residues were returned to the plots either as such (rotation C) or composted (rotation D). In the rotation of this system, 1 year with barley was replaced by clover, and oat was cultivated mixed with pea. Thus, the 6-year rotation was barley–red clover–rye–oat + pea–potato–oat + pea. Each rotation was replicated three times, starting the 6-year rotation in three different years, these being designated point 1, point 2, and point 3, respectively. In the low-input system, biotite and rock phosphate were used to compensate for K and P in the harvested yield, while animal manure was applied at the start only. After 13 years, rotation points 1 and 3 were studied. Barley was the standing crop in all plots of rotation point 1, while oat and oat + pea were grown in rotations C and D, respectively. AMF spores were studied by direct extraction and by trapping, sampled on 15 June and 15 August. In addition, a special assay was designed for isolation of fast colonizing, dominating AMF. The cropping system did not significantly affect AMF spore densities, although the low-input cropping system with composted plant residues had the highest density with 44 spores on average and the conventional system with full fertilization 24 spores per 100 cm³ soil in the autumn samples. Species richness was low in the experimental area. Five Glomus spp., one Acaulospora, and one Scutellospora were identified at the species level. In addition to these, three unidentified Glomus spp. were found. Species richness was not affected by cropping system, rotation point, or their interactions. The Shannon–Wiener index of AMF spore distributions was significantly higher in the fully fertilized than in the half-fertilized conventional plots. Glomus claroideum was the most commonly identified single species in the experimental area. It occurred in all the cropping systems and their various rotation points, representing about 30% of the total number of identified spores. In August, G. claroideum accounted for as much as 45–55% of the total numbers of spores identified in the conventional system with halved fertilization. In contrast, Glomus mosseae occurred more commonly in June (26%) than in August (9%). A bioassay using roots as inoculum for isolation and culture of dominating AMF was successfully developed and yielded only G. claroideum. This indicates a high probability of being able to more generally identify, isolate, and culture fast colonizing generalist AMF for use as inoculants in agriculture and horticulture.     

Promotion of AM utilization through reduced P fertilization 2. Field studies

The hypothesis of this study was that cumulative P fertilization decreases the contribution of arbuscular mycorrhiza (AM) to crop growth and nutrient uptake in Northern European field conditions. The modes of action of P fertilization were evaluated through effects on mycorrhization, crop dependence on AM, and AM fungal (AMF) community. Field studies were carried out within long-term experiments on soils with low and intermediate initial content of extractable P, where no P fertilization and 45 kg ha^–1 a^–1 P were applied for 20 years. AM effectiveness in terms of growth and nutrient uptake of flax, red clover and barley, percentage root length colonized by AMF, P response of flax, and spore densities and species composition of the AMF communities, were assessed. In the soil with low initial P supply, cumulative P fertilization decreased AM contribution to crop growth and nutrient uptake. The higher AM effectiveness in soil with no added P compensated the cumulative P fertilization (soil P_H2O 2.5 v. 9.5 mg kg^–1) for flax, but not completely for clover. In contrast, barley obtained no benefit from AM at harvest and only a slight benefit from cumulated P. In the soil with intermediate initial P supply, AM reduced growth of flax and barley, especially with no added P, and no response to AM was obtained on clover due to retarded mycorrhization. Cumulative P fertilization reduced yield losses of flax by AM (P_H2O 18.8 v. 5.4 mg kg^–1), because fertilization inhibited mycorrhization. In both soils, root colonization and spore density were decreased by cumulative P fertilization, but no changes in AMF species composition were observed.     

Phosphate transport by hyphae of field communities of arbuscular mycorrhizal fungi at two levels of P fertilization

This study was conducted to elucidate the effect of P fertilisation on the function of field communities of arbuscular mycorrhizal fungi (AMF) measured as P transport to flax. Two methods were applied to soil from a long-term field experiment with NaHCO₃-extractable soil P levels of 24 and 50 mg kg^-1in an experiment under controlled conditions: i) Measurement of plant growth and P uptake in the presence or absence of the fungicide benomyl and ii) measurement of hyphal P transport from a root-free compartment labelled with ³²P. Benomyl successfully prevented mycorrhizal function. The absolute contribution of AMF to plant P uptake was of the same magnitude with or without P fertilisation at 27 days after sowing. Therefore, even though plants grown at the higher soil P level had greater P uptake, the relative contribution of AMF to P uptake was greater at the lower P level than at the higher P level (77 and 49% of total P uptake, respectively). The AMF in P-fertilized soil transported less P³² from the root-free compartment to the plant after 23 days than the AMF in unfertilized soil, but this difference disappeared in plants harvested after 27 and 32 days. The production of hyphae was largely similar in both fertilization treatments, indicating that the capacity for P uptake and transport by hyphae of the two AMF communities was similar. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ethiopian agriculture has greater potential for carbon sequestration than previously estimated

More than half of the cultivation‐induced carbon loss from agricultural soils could be restored through improved management. To incentivise carbon sequestration, the potential of improved practices needs to be verified. To date, there is sparse empirical evidence of carbon sequestration through improved practices in East‐Africa. Here, we show that agroforestry and restrained grazing had a greater stock of soil carbon than their bordering pair‐matched controls, but the difference was less obvious with terracing. The controls were treeless cultivated fields for agroforestry, on slopes not terraced for terracing, and permanent pasture for restrained grazing, representing traditionally managed agricultural practices dominant in the case regions. The gain by the improved management depended on the carbon stocks in the control plots. Agroforestry for 6–20 years led to 11.4 Mg ha^?1 and restrained grazing for 6–17 years to 9.6 Mg ha^?1 greater median soil carbon stock compared with the traditional management. The empirical estimates are higher than previous process‐model‐based estimates and indicate that Ethiopian agriculture has greater potential to sequester carbon in soil than previously estimated.     

Plant-available P supply is not the main factor determining the benefit from arbuscular mycorrhiza to crop P nutrition and growth in contrasting cropping systems

Field studies have indicated that plant-available P supply is the main determinant of the performance of arbuscular mycorrhiza (AM) of crops. Direct evidence is, however, weak. Our aim was to test the hypothesis that plant-available P is the main factor determining the benefit from AM to plant P uptake and growth in contrasting cropping systems. We compared a conventional system with full and half fertilisation rates and a low-input system with and without composting of residues. After 15?years, plant P response functions, with and without AM, were determined in a bioassay. At equal plant availability of P, the benefits from AM were similar to those at the P status in the field: The benefits were greater in the low-input system than in the conventional system, irrespective of the fertilisation rate but clearest with composting. This shows that differences between the systems in the benefit from AM to a particular crop genotype are not mainly due to differences in plant-available P. The results suggest also that differences in P pools, in growth-limiting factors such as N supply and in phytotoxicity to AMF hyphae play roles in determining the benefit. It is not likely that differences in AMF communities are important.     

Promotion of utilization of arbuscular mycorrhiza through reduced P fertilization 1. Bioassays in a growth chamber

The study investigated the possibilities of promoting utilization of arbuscular mycorrhiza (AM) in crop P nutrition in Northern European conditions by decreasing P fertilization. The effect of two contrasting long-term P fertilization regimes on fungal (AMF) infectivity, on contribution of AM to crop growth and nutrient uptake, and on P and N responses was investigated in bioassays in a growth chamber with the original field soil. A control with suppressed AM was successfully created by benomyl application. Functional properties of the field AMF communities were compared after back- and cross-inoculation to the irradiated field soils. The two long-term field experiments that were utilized represented clay and loam soils and P levels from low to high. The results show that annual dressings of soluble inorganic P fertilizers, even in moderate amounts, decrease the infectivity and effectiveness of AMF communities of Northern European field soils. The functional properties of the communities also seem to adapt to the different P regimes. Moderate P fertilization generally decreases the total AM benefit to crops and can lead to growth depression by AM. At the lower end of the P supply of Nordic field soils, however, AM may at least transiently impose a net cost to crops with a high P demand such as flax or with a low dependency on AM such as barley. The impact of the P history on AM was not related to plant P nutrition only. Mycorrhization can be immediately improved by omitting P application. This revised version was published online in June 2006 with corrections to the Cover Date.     

Creation of a non-mycorrhizal control for a bioassay of AM effectiveness

and application times 2 weeks before sowing, at sowing and 1 week after sowing were investigated. Various Finnish field soils with their indigenous AMF communities were used. The main test plant species was oil-seed flax (Linum usitatissimum). In a comparison of sampling time, barley (Hordeum vulgare) was also used and phytotoxicity was studied additionally on red clover (Trifolium pratense), barley and pea (Pisum sativum) mutants. Sampling in the spring after the thaw resulted in the highest infectivity and AM response and the clearest differences between soils with varying AM potential. No evidence of temporal variation in benomyl effectiveness on mycorrhiza was found. The dose of benomyl sufficient to create a control with suppressed mycorrhization was 20 mg per kg soil at target moisture incorporated in the soil. Plant growth reduction in irradiated soil was observed with benomyl application 1 week after sowing only with flax and red clover. The most effective application time for benomyl was immediately before sowing.