Response of giant reed (Arundo donax L.) to nitrogen fertilization and soil water availability in semi-arid Mediterranean environment

The aim of the present work was to evaluate the effect of soil water availability and nitrogen fertilization on yield, water use efficiency and agronomic nitrogen use efficiency of giant reed (Arundo donax L.) over four-year field experiment.After the year of establishment, three levels for each factor were studied in the following three years: I₀ (irrigation only during the year of establishment), I₁ (50% ETm restitution) and I₂ (100% ETm restitution); N₀ (0 kg N ha⁻¹), N₁ (60 kg N ha⁻¹) and N₂ (120 kg N ha⁻¹).Irrigation and nitrogen effects resulted significant for stem height and leaf area index (LAI) before senescence, while no differences were observed for stem density and LAI at harvest.Aboveground biomass dry matter (DM) yield increased following the year of establishment in all irrigation and N fertilization treatments. It was always the highest in I₂N₂ (18.3, 28.8 and 28.9 t DM ha⁻¹ at second, third and fourth year growing season, respectively). The lowest values were observed in I₀N₀ (11.0, 13.4 and 12.9 t DM ha⁻¹, respectively).Water use efficiency (WUE) was significantly higher in the most stressed irrigation treatment (I₀), decreasing in the intermediate (I₁) and further in the highest irrigation treatment (I₂). N fertilization lead to greater values of WUE in all irrigation treatment.The effect of N fertilization on agronomic nitrogen use efficiency (NUE) was significant only at the first and second growing season.Giant reed was able to uptake water at 160–180 cm soil depth when irrigation was applied, while up to 140–160 cm under water stress condition.Giant reed appeared to be particularly suited to semi-arid Mediterranean environments, showing high yields even in absence of agro-input supply.     

Biomass production and N balance of giant reed (Arundo donax L.) under high water and N input in Mediterranean environments

This study aimed to evaluate the productivity of Arundo donax under good water and N availability coming from non-conventional sources, in different Italian environments (Padova and Bologna in the north, Reggio Calabria and Catania in the south) in relation to three harvest periods (autumn; mid-winter; late-winter).In the northern locations A. donax had already reached maximum productivity the year after transplanting, with 85 and 98 t ha⁻¹ of dry matter at Padova and Bologna, respectively. At Reggio Calabria and Catania a further biomass increase was obtained from the second to third year of cultivation, when production was 62 t ha⁻¹ and 51 t ha⁻¹, respectively.The average dry matter production was 74, 66 and 65 t ha⁻¹ with autumn, mid-winter and late-winter harvesting, respectively.Under N input ranging from 225 to 329 kg ha⁻¹ year⁻¹ at the different locations, the apparent N balance (input–output) was negative except in Catania indicating a great potential of A. donax to provide high N uptake, which would be a useful feature in environments under the European Nitrates Directive.     

Effects of water deficit and plant interaction on morphological growth parameters and yield of white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) mixtures

The effects of soil water deficit and interspecific plant interaction were studied on the dry matter (DM) yield of white clover and ryegrass and on the morphogenesis of white clover. Plants were grown either: (1) individually (no interaction); or in a mixture of equal plant numbers with either (2) just shoot interaction, or (3) both shoot+root interaction. Plants were subjected to soil water deficits corresponding to no (0 MPa), moderate (−0.5 MPa) or severe (−1.0 MPa) water deficit. Ryegrass had higher above- and below-ground DM yields than white clover. The above- and below-ground DM yield for ryegrass, and the above-ground DM yield, stolon growth and relative growth rate (RGR), and leaf appearance rate (LAR) for white clover decreased as soil water deficit increased. In shoot+root interaction at no and moderate soil water deficit levels, white clover had the highest proportion of above-ground growth in the leaf form (69%) and had, respectively, 11% and 32% more above-ground DM yield than when grown in just shoot interaction; ryegrass had, respectively, 20% and 25% more above-ground DM yield than ryegrass grown in just shoot interaction. In shoot+root interaction at severe soil water deficit, ryegrass had twice as much above-ground DM yield as white clover (3.50 g per plant versus 1.59 g per plant, respectively) and white clover had 60% less above-ground DM yield than when grown in just shoot interaction. In a soil column of restricted depth (30 cm) at no and moderate soil water deficit levels, remarkable increases in shoot biomass yield were observed for both white clover and ryegrass grown in shoot+root interaction. The increased shoot biomass yield of ryegrass can be attributed to benefits from white clover's N fixing ability, whereas the causes for increased white clover biomass yield need to be studied further. However, at severe soil water deficit, ryegrass had a competitive advantage over white clover when grown in shoot+root interaction. This was due to the larger root system of ryegrass and its ability to control transpirational losses more efficiently, thus prolonging its growth period compared with white clover.     

Genetic analysis of yield and related traits in sunflower (Helianthus annuus L.) in dryland and irrigated environments

The definition of a suitable breeding strategy in drought-prone environments is an important task for sunflower breeders. To achieve this task, reliable information on heritability and gene effects on yield and related traits under these conditions is necessary. Thirty six sunflower hybrids were produced by factorial cross of six male-sterile and six restorer lines. Parents and their hybrids were evaluated in eight environments. Six environments consisted of two adjacent trials in the experimental area, the first under irrigation and the second under dryland conditions, during 1987, 1988 and 1992. The other environments were: one early planting trial in dryland conditions, conducted during 1987, and a winter trial planted in January during 1988. Estimates of female variance (σ_f) were significant for seeds per head, seed weight, head sterile center, days to blooming and oil content. Female × male interactions (σ² _fm) were significant for all characters except harvest index and index of susceptibility to drought. Estimates of narrow sense heritabilities, calculated with information from analyses combined across environments, were 0.65 for yield, 0.80 for seeds per head, 0.84 for seed weight, 0.81 for head diameter, 0.60 for sterile head center, 0.72 for oil content, 0.61 for harvest index, 0.72 for biomass, 0.94 for days to bloom, and 0.42 for drought susceptibility index. Heritability estimates for individual environments showed more variation for yield than for other traits. Estimates for heritability of canopy temperature were high (0.68–0.79). Rainfed yield was positively correlated with yield components and negatively correlated with canopy temperature and susceptibility index. It is concluded that an efficient breeding strategy for sunflower under moderate drought-stressed conditions is the simultaneous selection for seed yield in both rainfed and irrigated environments together with selection for canopy temperature and stem diameter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors affecting root and seed yield in ahipa (Pachyrhizus ahipa (Wedd.) Parodi), a multipurpose legume crop

Ahipa (Pachyrhizus ahipa) is a legume crop, which produces carbohydrate-rich tuberous roots and seeds rich in protein and oil. In the present work, we studied the effect of different agronomic practices and climatic conditions on root and seed yield in order to make a preliminary assessment of the yield potential under different managements for the ahipa crop in south-western Europe. Sowing date affected productivity when delayed, because of growth season shortening. Reproductive pruning greatly increased root yield. Increasing planting density affected root and fruit growth per plant but increased yield to a certain extent. Seed inoculation with effective rhizobia greatly increased root and seed production. Low temperature is a main factor to be considered as it reduced productivity in areas of cool nights. Ahipa has a low environmental impact and low input requirement (fertilizer, pesticides), providing an attractive alternative to traditional sources of carbohydrates for conserving non-renewable resources and maintaining farmer profitability. Competitive yields for the simultaneous production of starch, feed protein and industrial oil may be obtained with low investment using available landraces.     

The stage sensitivity of short‐term heat stress to lodging‐resistant traits and yield determination in canola (Brassica napus L.)

With the expected increase of abiotic stress under global climate change, significant research has been devoted to how abiotic stress will affect crop production. To date, there has been little research on the stage sensitivity of short‐term heat stress to crop lodging and yield determination in canola. This research was conducted in a controlled growth facility and aimed to examine root morphology, pod fertility, seed yield and crop lodging of two contrasting canola genotypes subjected to a short‐term heat stress (27.0/24.3°C, light/dark), imposed respectively at three growth stages, rosette vegetative stage (RVHT), early flowering stage (EFHT) and late flowering stage (LFHT), in comparison with non‐stressed control (CK) (23/17°C). The results demonstrate that heat stress imposed at RVHT and LFHT was less detrimental to seed yield and lodging resistance. However, EFHT showed significant adverse effects on both, which was further confirmed by redundancy analysis (RDA) and structural equation modelling (SEM). Compared with the CK, EFHT resulted in a yield loss of 43%, which was mainly due to poor pod fertility, less number of filled pods (?28%), decreased pollen viability (?38%) and a lower success ratio of filled pods (?29%). The taproot was found to be relatively tolerant to heat stress, but lateral roots were sensitive to heat stress at EFHT and LFHT. Root capacitance could be used as a non‐destructive method for evaluating lateral root morphology. Compared with the CK, EFHT displayed a high risk of stem lodging, as indicated by a 27% lower safety factor. This was mainly attributed to the reduced stem bending strength that was caused by the deterioration of stem mechanical properties under EFHT, as illustrated by SEM. Root lodging resistance was not altered by any stages of short‐term heat stress, as the taproot remained stable.     

Grain nitrogen content of winter bread wheat (Triticum aestivum L.) as related to crop management and to the previous crop

Low-input management for wheat production (less fungicide, low nitrogen rate) could affect grain protein content. The impact of the previous crop could also be a determining factor for wheat quality. A long-term field experiment located near Toulouse (southwestern France), comparing different rotations and management schemes from 1984 to 1993, was used to assess the effect of N availability and diseases on grain nitrogen concentration (GNC) of wheat. GNC ranged from 1.6 to 2.8%, increasing with the input level in 5 years out of 10, as the result of higher nitrogen levels and crop protection with fungicides. Leaf brown rust, high temperatures and water shortage, which affected dry matter accumulation during grain filling, were responsible for high GNC. GNC was generally correlated with N uptake when nitrogen availability was the main limiting factor and to the nitrogen harvest index (NHI) when foliar diseases or drought limited grain production. N uptake in the absence of N fertiliser ranged from 20 to 200 kg ha⁻¹ depending on the previous crop. GNC was closely related to the nitrogen nutrition index (NNI) at anthesis.