T. Scott

Grassland biodiversity bounces back from long-term nitrogen addition

The negative effect of increasing atmospheric nitrogen (N) pollution on grassland biodiversity is now incontrovertible. However, the recent introduction of cleaner technologies in the UK has led to reductions in the emissions of nitrogen oxides, with concomitant decreases in N deposition. The degree to which grassland biodiversity can be expected to ‘bounce back’ in response to these improvements in air quality is uncertain, with a suggestion that long-term chronic N addition may lead to an alternative low biodiversity state. Here we present evidence from the 160-year-old Park Grass Experiment at Rothamsted Research, UK, that shows a positive response of biodiversity to reducing N addition from either atmospheric pollution or fertilizers. The proportion of legumes, species richness and diversity increased across the experiment between 1991 and 2012 as both wet and dry N deposition declined. Plots that stopped receiving inorganic N fertilizer in 1989 recovered much of the diversity that had been lost, especially if limed. There was no evidence that chronic N addition has resulted in an alternative low biodiversity state on the Park Grass plots, except where there has been extreme acidification, although it is likely that the recovery of plant communities has been facilitated by the twice-yearly mowing and removal of biomass. This may also explain why a comparable response of plant communities to reduced N inputs has yet to be observed in the wider landscape.

Effects of sowing date and planting density on the structure and yield of autumn-sown, florally-determinate white lupins ( Lupinus albus) in the United Kingdom

The effects of varying the sowing date (early September-late October) and plant density (14-70 seeds/m 2 ) on the establishment, overwinter survival, structure and yield of an autumn-sown, florally- determinate line (CH304/70) of the white lupin (Lupinus albus) were examined in three contrasting growing seasons between 1991 and 1994. Crops established well when sown in early September and were sufficiently cold-hardy to survive prolonged and extremely severe early winter frosts, but crops sown in late October either lost many plants or were destroyed completely. There was a strong interaction between sowing date and autumn weather on crop structure and yield. Late sowing and cold autumn weather restricted the number of mainstem leaves and first-order lateral branches on the plant, and decreased plant height and yield potential. Despite considerable differences between years in the weather during the summer and autumn, all crops were harvested in early September. Grain yields ranged from 0.3 to 4.5 t/ha depending on season, sowing date and plant density. Yields were strongly correlated with the number of pod-bearing axes and pods per m 2 and, although actual yields differed depending on growing conditions, the same number of pod-bearing axes (100/m 2 ) was required in each year to achieve maximum yield. The effects of sowing date and autumn weather on plant structure were well predicted by a simple developmental model that related vernalization and leaf development to post-sowing temperature.

The causes of over-winter plant losses of autumn-sown white lupins (Lupinus albus) in different regions of the UK over three seasons.

A series of experiments were carried out at 14 sites in the major arable areas of the UK, in the years 1993–94, 1994–95 and 1995–96 to determine the causes and extent of over-winter plant losses of two autumn-sown cultivars of white lupin ( Lupinus albus L.). Over the three seasons frost was the major cause of plant losses. Two mechanisms (one known and one not previously reported in the UK) of frost tolerance under field conditions were identified: (i) lignification of the root parenchyma early in the life of the seedling, and (ii) a large vernalization requirement of the main-stem apex, which delays stem elongation in older plants. A model was developed that could be used to predict the susceptibility of these lupin cultivars to the first severe frost of the winter using accumulated thermal time (above a base temperature of 3 °C). The effect of sowing at the beginning or end of a sowing window, calculated to optimize plant architecture the following summer, therefore varied with the weather during the autumn/winter period. A combination of cool autumn weather and late sowing (outside of the sowing window) resulted in plant losses due to a lack of lignification of the root parenchyma. In unusually warm autumn conditions (1994–95 and 1995–96) plants sown at the beginning of the sowing window were well developed before the first frosts occurred, with consequent stem elongation and plant losses. Although losses due to pests were not severe ( c . 3 to 5 plants/m 2 ), plants were attacked during the autumn by grey field slugs ( Deroceras reticulatum Muller), bean seed flies ( Delia platura Meigen), and probably thrips ( Thrips angusticeps Uzel, Noctuidae), although this has not been confirmed. The fungal pathogens Fusarium spp. and Botrytis cinerea Pers. caused losses in conjunction with frost damage.

Seed and pod development of autumn-sown, determinate white lupins (Lupinus albus) in relation to the assimilation and distribution of dry matter and nitrogen in crops grown at different densities

Pod and seed growth were studied in two experiments in which the plants source-sink relationships were modified by (a) manually pruning an autumn-sown, indeterminate white lupin variety, Lunoble, to a determinate form, and (b) by growing a determinate variety, Lucyane, at densities ranging from 7 to 35 plants/m 2 . The pruning experiments indicated that the faster pod growth rate of determinate genotypes was not an inherent genetic trait but an indirect physiological consequence of the plants changed architecture. In the density experiment, crop dry matter (DM) and nitrogen (N) were maximum at the end of pod extension in late July and similar across the plant density range at c. 12 t DM and 320 kg N/ha. Therefore, the amount of dry matter per plant decreased proportionately with the increase in plant number. The DM and N contents of the pod walls were also maximum at the end of pod extension, but seeds contained only a third of their final DM and a quarter of their final N. Protein accumulation during the final stages of seed growth, therefore, depended on the remobilization of nitrogen from other plant organs, primarily the leaves and pod walls. Nitrogen withdrawn from the leaves accounted for 44% of the gain in the pods, and N withdrawn from pod walls for 50-60% of the gain in the seed. Seed number/m 2 was the major yield component. Seeds and pods mainly aborted during early development, but seed number per pod was also decreased by some seed abortion after full pod extension, especially in first-order pods of plants grown at high density. The number of late-aborted seeds was negatively correlated with the amount of N remobilized from the pod wall. In determinate lupins, which have highly synchronous flowering and pod development, the large and sudden remobilization of nitrogen from leaves and pod walls for seed growth and protein accumulation triggered crop senescence

Field-based nutritional response evaluation of the intolerant white lupin (Lupinus albus) cultivar Lucyanne to a lime-amended soil

Two field experiments examined the nutritional responses of the white lupin (Lupinus albus L.) agronomic cultivar Lucyanne to lime-amended soil. In the first, plots and boundaries of a pre-existing lime-rate experiment were sampled in 1993. The maximum shoot dry matter production occurred between soil pH 4.9 and 7.2. Whole-shoot Al concentrations increased below soil pH 4.9, and plants died at pH 4.4. Although dry matter production declined in soil above pH 7.2, no chlorosis or plant death was seen. Only the whole-shoot soluble Ca concentration changed from neutral to alkaline pH soil: it was greatest when grown in the alkaline-pH soil. In the second experiment, plants were grown in neutral pH or limed soil in 2000. Shoots were divided into specific tissue types and analysed for Fe III and Fe II, as well as soluble and insoluble Ca fractions. When sampled in April after overwintering, the higher Ca concentration in the limed compared with neutral-pH soil-grown plants was due mainly to insoluble Ca. No plants were chlorotic and no differences between the treatments in the concentrations of either form of Fe were found. In June no plants were chlorotic, however the concentrations of both total and soluble Ca fractions were greater in the limed than the neutral-pH soil-grown plants, and there was more stem Fe III and less leaf Fe II in these plants. The present study shows that the cultivar Lucyanne is not a reliable crop plant above pH 7.2, and the loss of shoot dry matter can be attributed to nutritional responses at a sub-chlorotic level of stress.

The electronic Rothamsted Archive (e-RA), an online resource for data from the Rothamsted long-term experiments

The electronic Rothamsted Archive, e-RA (www.era.rothamsted.ac.uk) provides a permanent managed database to both securely store and disseminate data from Rothamsted Research’s long-term field experiments (since 1843) and meteorological stations (since 1853). Both historical and contemporary data are made available via this online database which provides the scientific community with access to a unique continuous record of agricultural experiments and weather measured since the mid-19th century. Qualitative information, such as treatment and management practices, plans and soil information, accompanies the data and are made available on the e-RA website. e-RA was released externally to the wider scientific community in 2013 and this paper describes its development, content, curation and the access process for data users. Case studies illustrate the diverse applications of the data, including its original intended purposes and recent unforeseen applications. Usage monitoring demonstrates the data are of increasing interest. Future developments, including adopting FAIR data principles, are proposed as the resource is increasingly recognised as a unique archive of data relevant to sustainable agriculture, agroecology and the environment.