Soil property differences among high‐ and average‐yielding soya bean areas in Arkansas,USA

Soya bean [Glycine max (L.) Merr] yields >6719 kg/ha (100 bu/ac) have only recently and infrequently been achieved. Quantifying soil property differences between high‐ and average‐yielding areas can help to further identify non‐plant‐related properties contributing to soya bean yield potential. The objective of this study was to evaluate the effects of region and soil depth on soil property differences between high‐ and average‐yielding areas. In each of the seven regions of the ‘Grow for the Green’ yield contest in Arkansas, prior to or just after harvest in 2014 and 2015, soil samples were collected from the top 20 cm of one contest high‐yield (HY ) area that was in close proximity to an average‐yield (AY ) area. Across all regions and both years, soya bean yields differed (P  <  0.05) between yield areas, averaging 4701 and 5498 kg/ha in AY and HY areas, respectively. Averaged across soil depth and years, numerous soil properties differed (P  <  0.05) between HY and AY areas within at least one of seven regions. Total soil C content was at least 20.2% greater in the HY than in the AY area in three of seven regions. Extractable soil P content was, on average, 19.4 kg/ha greater in HY than in AY areas in three of the seven regions. Results from this study have the potential to help producers better understand soil properties that contribute to or hinder achieving ultra‐high (>6719 kg/ha) soya bean yields.     

Drought Tolerance and Water Use of Cereal Crops: A Focus on Sorghum as a Food Security Crop in Sub‐Saharan Africa

Sub‐Saharan Africa (SSA) faces twin challenges of water stress and food insecurity – challenges that are already pressing and are projected to grow. Sub‐Saharan Africa comprises 43 % arid and semi‐arid area, which is projected to increase due to climate change. Small‐scale, rainfed agriculture is the main livelihood source in arid and semi‐arid areas of SSA. Because rainfed agriculture constitutes more than 95 % of agricultural land use, water scarcity is a major limitation to production. Crop production, specifically staple cereal crop production, will have to adapt to water scarcity and improved water productivity (output per water input) to meet food requirements. We propose inclusion and promotion of drought‐tolerant cereal crops in arid and semi‐arid agro‐ecological zones of SSA where water scarcity is a major limitation to cereal production. Sorghum uniquely fits production in such regions, due to high and stable water‐use efficiency, drought and heat tolerance, high germplasm variability, comparative nutritional value and existing food value chain in SSA. However, sorghum is socio‐economically and geographically underutilized in parts of SSA. Sorghum inclusion and/or promotion in arid and semi‐arid areas of SSA, especially among subsistence farmers, will improve water productivity and food security.     

Movement rules for juvenile steelhead: dynamic linking of movement behaviour to habitat and density

We incorporated explanatory factors including stream habitat type and fish density into individual‐based models with dynamic connections among adjacent habitat units to infer dispersal behaviour of juvenile steelhead Oncorhynchus mykiss in a Great Lakes watershed. We used mark–recapture data and an inverse modelling approach to estimate daily probability of steelhead moving out of a habitat unit, P(move), according to four competing models. The models used included (i) a null model where all fish had equal movement probability; (ii) a habitat‐dependent model where P(move) depended on the habitat type; (iii) a density‐dependent model of P(move); and (iv) a model where P(move) depended on both density and habitat type. The habitat‐dependent model provided the most parsimonious fit to the observed data according to Akaike's information criteria (AICc). In the null model, P(move) averaged 0.70, whereas P(move) averaged 0.75 in pools, 0.68 in riffles and 0.73 in runs in the habitat‐dependent model.     

Time‐lapse monitoring of soil water content using electromagnetic conductivity imaging

The volumetric soil water content (θ) is fundamental to agriculture because its spatiotemporal variation in soil affects the growth of plants. Unfortunately, the universally accepted thermogravimetric method for estimating volumetric soil water content is very labour intensive and time‐consuming for use in field‐scale monitoring. Electromagnetic (EM) induction instruments have proven to be useful in mapping the spatiotemporal variation of θ. However, depth‐specific variation in θ, which is important for irrigation management, has been little explored. The objective of this study was to develop a relationship between θ and estimates of true electrical conductivity (σ) and to use this relationship to develop time‐lapse images of soil θ beneath a centre‐pivot irrigated alfalfa (Medicago sativa L.) crop in San Jacinto, California, USA. We first measured the bulk apparent electrical conductivity (EC_a – mS/m) using a DUALEM‐421 over a period of 12 days after an irrigation event (i.e. days 1, 2, 3, 4, 6, 8 and 12). We used EM4Soil to generate EM conductivity images (EMCIs). We used a physical model to estimate θ from σ, accounting for soil tortuosity and pore water salinity, with a cross‐validation RMSE of 0.04 cm³/cm³. Testing the scenario where no soil information is available, we used a three‐parameter exponential model to relate θ to σ and then to map θ along the transect on different days. The results allowed us to monitor the spatiotemporal variations of θ across the surveyed area, over the 12‐day period. In this regard, we were able to map the soil close to field capacity (0.27 cm³/cm³) and approaching permanent wilting point (0.03 cm³/cm³). The time‐lapse θ monitoring approach, developed using EMCI, has implications for soil and water use and management and will potentially allow farmers and consultants to identify inefficiencies in water application rates and use. It can also be used as a research tool to potentially assist precision irrigation practices and to test the efficacy of different methods of irrigation in terms of water delivery and efficiency in water use in near real time.     

Acquired Thermo‐Tolerance and Trans‐Generational Heat Stress Response at Flowering in Rice

In rice, pre‐exposure to sublethal treatment followed by harsh lethal treatment is known to improve tolerance of different abiotic stresses at the vegetative stage within and across generations. Our major aim was to test the phenomenon of thermo‐tolerance at flowering across (trans)‐generations and within generation using rice cultivars contrasting for heat stress tolerance at flowering. To test trans‐generational response, plants were exposed to higher temperature at flowering stage and seeds obtained from previous generations were exposed to heat stress during flowering, which recorded significantly lower fertility when exposed to the same degree of stress in their subsequent generations. A pre‐acclimation to moderately high acclimating temperatures imposed over three different durations during the vegetative and initial reproductive stage showed positive response in the tolerant N22, particularly under severe heat stress (40 °C). This finding indicates the possibility of acquiring ameliorative thermo‐tolerant mechanisms at anthesis, restricted to tolerant genetic backgrounds to combat subsequent harsh conditions within the same generation. However, trans‐generational memory was ineffective in mitigating spikelet sterility losses in both tolerant and susceptible backgrounds. Rice is extremely sensitive to heat stress during flowering; hence, similar exercise across other crops of interest needs to be carried out before generalizing conclusions.     

Relevance of Osmotic and Frost Protecting Compounds for the Winter Hardiness of Autumn Sown Sugar Beet

The cultivation of autumn sown sugar beet (winter beet) is supposed to result in a marked yield increase compared with spring sown sugar beet. Although the importance of the growth stage reached before winter for the survival of autumn sown sugar beet has already been shown, it is not clear to which extent osmotic and potentially frost protecting compounds may contribute to winter hardiness. The study thus aimed to analyse the acclimatization process of sugar beet to low temperatures and to identify compounds which are important for survival of frost. Field trials with autumn sown sugar beet were conducted at eleven environments in Germany from 2009/10 to 2012/13, which were accompanied by greenhouse experiments with controlled temperature regimes. In the field trials, the survival rates after winter varied from 0 % to 99 %, but only in four environments differences between the five genotypes occurred. During acclimatization, betaine, glutamine, proline and raffinose were markedly accumulated and osmolality was enhanced. In particular betaine, amino acids and osmolality showed a positive correlation to the survival rate and were thus identified as potentially frost protecting substances for sugar beet. In contrast, raffinose and proline seem to act rather as stress indicators as they were negatively related to survival. Possible frost protecting substances were identified which can be used in breeding to improve the winter hardiness of sugar beet.     

Assessing the effectiveness of manure export plus intensive silage cropping for lowering the Olsen‐P status of P‐enriched grassland

A substantial proportion of farmed grassland soils in Northern Ireland (NI) are overly enriched with P and pose a risk to water quality. To address this problem, manure could be exported rather than recycled to P‐enriched land and the latter intensively cropped with grass silage to deplete soil P. To assess the efficacy of such a strategy, a P‐ and K‐enriched grassland site was intensively cropped over a 6‐yr period with fertilizer N alone supplied to support silage growth. By year 6, soil P had declined from index 5 to index 3, and it was estimated that two more years of this management may bring it into the target index 2 range. Soil K, however, declined rapidly from index 4 to index 1 in just 4 yr, with the result that grass production became limited by K deficiency. It was concluded that nonrecycling of manure to P‐enriched grassland under silage management is probably the most effective strategy for lowering soil P status, but care must be taken to prevent K deficiency occurring.     

Summer drought decreases Leymus chinensis productivity through constraining the bud,tiller and shoot production

Extreme drought events can directly decrease productivity in perennial grasslands. However, for rhizomatous perennial grasses it remains unknown how drought events influence the belowground bud bank which determines future productivity. Ninety‐day‐long drought events imposed on Leymus chinensis, a rhizomatous perennial grass, caused a 41% decrease in the aboveground biomass and a 28% decrease in belowground biomass. Aboveground biomass decreased due to decrease in both the parent and the daughter shoot biomass. The decreases in daughter shoot biomass were due to reductions in both the shoot number and each individual shoot weight. Most importantly, drought decreased the bud bank density by 56%. In addition, drought induced a bud allocation change that decreased by 41% the proportion of buds that developed into shoots and a 41% increase in the buds that developed into rhizomes. Above results were supported by our field experiment with watering treatments. Thus, a 90‐day‐long summer drought event decreases not only current productivity but also future productivity, because the drought reduces the absolute bud number. However, plasticity in plant development does partly compensate for this reduction in bud number by increasing bud development into rhizomes, which increases the relative allocation of buds into future shoots, at the cost of a decrease in current shoots.     

Productive and biochemical responses of durum wheat to UV filtration

A UV exclusion experiment was conducted on durum wheat (Triticum durum Desf. var. Claudio) grown in pots. Plants were grown under three different radiative treatments in greenhouses covered with plastic filters: Teflon, transparent to the entire region of natural UV‐visible sunlight (TEF); polyester, transparent above 312 nm (MYL, excluding UVB) and Lee, transparent above 400 nm (LEE, excluding both UVA and UVB). Analyses have been carried out to determine the concentration of photosynthetic pigments in leaves, UV‐absorbing compounds, nitrogen and carbon in leaves, culms and spikes and proteins and gluten in grains. In particular, plants grown under UV exclusion showed a reduction in protein and dry gluten content (consequently without variation in the ratio dry gluten/protein), but at the same time, a significant increase of gluten index, which is a parameter to define the quality of gluten, was observed. The results highlighted the influence played by UV radiation on some biochemical parameters, mainly UV‐absorbing compounds, leaf nitrogen and grain protein characteristics of durum wheat cultivated under Mediterranean conditions. In particular, natural level of UV in the Mediterranean improves the characteristics of durum wheat flour important for pasta production (high dry gluten level), while the UV exclusion could improve characteristics of flour important for bread production (high gluten index).     

Does sand content in spawning substrate result in early larval emergence? Evidence from a lithophilic cyprinid fish

The spawning success of lithophilic salmonids is strongly influenced by the fine sediment content (“fines”) of spawning substrates, yet knowledge on the impacts of fines on the spawning of non‐salmonid lithophiles remains limited, despite their ecological and socio‐economic importance in European rivers. Consequently, the aim here was to use an ex‐situ experiment to investigate the impact of sand content on egg survival and timing of larval emergence of the surface‐spawning cyprinid European barbel Barbus barbus. Thirty incubator boxes within a recirculating system were filled with one of five experimental sediment mixtures (0%–40% sand by mass) that each contained 300 fertilised eggs at a depth of 50 mm. Emerged, free‐swimming larvae were captured and counted daily to assess grain‐size effects on larval survival and emergence. Specifically, total proportion of emerged larvae, cumulative daily proportion of emerged larvae and time required to reach 50% emergence were measured during the study. Whilst the proportion of sand in the sediments did not have a significant impact on egg‐to‐emergence survival (mean survival per treatment 75%–79%), it significantly affected the timing of larval emergence to the water column; early emergence was detected in treatments with elevated sand content (on average, 50% emergence after 12–13 days versus 19 days in the control). Similar to findings from salmonid studies, these results suggest high sand content in spawning gravels can influence timing of larval emergence and potentially cyprinid lithophilic fish survival.