Determining Crop and Pan Coefficients for Sugar Beet and Potato Crops under Cool Season Semiarid Climatic Conditions

This study was conducted in a region with semiarid cool climatic conditions during the period from May to October in the years 2003 and 2004, respectively. Actual evapotranspiration (ET_c) of sugar beet and potato crops was calculated according to the water balance approach. Reference evapotranspiration (ET_o) was calculated with FAO Penman–Monteith equation. Evaporation (E_pan) was measured by using class A pan. Seasonal mean ET_c was determined as 492.9 mm for sugar beet and 445.2 mm for potato. Seasonal mean pan coefficient (k_p = ET_o/E_pan) was determined as 0.74, and the seasonal mean crop coefficient (k_c = ET_c/ET_o) was determined as 0.65 for sugar beet 0.60 for potato.     

Winter cover crop: the effects of grass–clover mixture proportion and biomass management on maize and the apparent residual N in the soil

The advantages and disadvantages of varying mixture proportion of crimson clover (Trifolium incarnatum L.) and Italian ryegrass (Lolium multiflorum Lam.), used as winter cover crops, and cover crop biomass management before maize sowing (Zea mays L.) were studied in a series of field experiments in Eastern Slovenia. Pure stands and mixtures of cover crops on the main plots were split into different cover crop biomass management subplots: whole cover crop biomass ploughed down before maize sowing, aboveground cover crop biomass removed before ploughing and sowing, or aboveground cover crop biomass removed before sowing directly into chemically killed residues.Cover crop and cover crop biomass management affected the N content of the whole aboveground and of grain maize yields, and the differences between actual and critical N concentrations in the whole aboveground maize yield. The whole aboveground and grain maize dry matter yields, and the apparent remaining N in the soil after maize harvesting, showed significant interaction responses to cover crop × management, indicating positive and negative effects. Crimson clover in pure stand provided high, and pure Italian ryegrass provided low maize dry matter yields and N content in the yields in all the observed methods of biomass management. However, within individual management, mixtures containing high proportions of crimson clover sustained maize yields and N contents similar to those produced by pure crimson clover. Considering the expected ecological advantages of the mixtures, the results thereby support their use.     

Forage production,quality and water-use-efficiency of four warm-season annual crops at three sowing times in the Loess Plateau region of China

Increasing demand for livestock products is driving development of livestock systems worldwide. That requires improved and new forage production options. The Loess Plateau region in central-northern China is an important area for livestock production, as it supports11% and 19% of the country’s cattle and sheep, respectively (China statistical yearbook 2014). The rain-fed semi-arid environment of the Loess Plateau means that maximizing the water-use-efficiency (WUE) of forage production is vital to guarantee enough fodder supply the livestock demand. A three-year field experiment in north-west Loess Plateau compared forage production, water use and water-use-efficiency as well as crude protein (CP) content of forage maize, Sudan grass, foxtail millet and Japanese millet sown at three sowing dates according to the opening rain during 2011–2013. On average, forage maize produced the highest biomass (12.1 t ha⁻¹) and had the highest WUE (43.4 kg DM ha⁻¹ mm⁻¹). This was followed by Sudan grass (7.8 t ha⁻¹; 26.5 kg DM ha⁻¹ mm⁻¹), Japanese millet (6.7 t ha⁻¹; 26.2 kg DM ha⁻¹ mm⁻¹) and foxtail millet (6.7 t ha⁻¹; 24.6 kg DM ha⁻¹ mm⁻¹). Optimizing sowing date played an important role in maximizing forage production and WUE of all tested forages. Compared to the earliest sowing date, a delay of two weeks reduced forage production by 17% in maize, 35% in foxtail millet, and 16% in Japanese millet. A delay of four to six weeks reduced biomass yield by 58% in maize, 57% in foxtail millet, and 56% in Japanese millet. Late sowing also greatly reduced WUE of forage maize and foxtail millet by 33% and 42%, respectively, when compared to early sowing. The middle sowing date maximized forage production and WUE of Sudan grass in two of the three growing seasons, which was 20% and 38% higher than the early and late sowing, respectively. Late sowing in all forages reduced crop water use by 42–57 mm compared to the early sowing. Among four test crops, CP of Sudan grass (7.9%) and forage maize (7.7%) was higher than foxtail millet (6.8%) and Japanese millet (6.7%). Compared with early sowing, CP_f in late sowing significantly increased in Sudan grass and decreased in Japanese millet, in contrast, no evident sowing date effect was found in forage maize and foxtail millet. This study showed that all four warm-season annual grasses had high forage production potential, forage maize was the most reliable and efficient option. Forage maize and the millets could easily be integrated into existing cropping systems and provide opportunities as both grain and forage-producing crop to provide added flexibility for farmers.     

Determination of the critical nitrogen concentration of white cabbage

A measure of a crop's nitrogen (N) status can be obtained by relating the actual N concentration of the crop to the critical plant nitrogen concentration (PNC_c), the minimum N concentration required for maximum growth. In annual crops, PNC_c declines as plant size increases. Describing this decline is one of the main challenges for the implementation of the PNC_c concept in fertilizer management strategies. From two field experiments with repeated harvests of Dutch white cabbage and with N supply ranging from limitation to excess, the relation between PNC_c and weight per unit ground area of plant dry matter exclusive of roots (W) was estimated as: PNC_c = 5.1W^−0.33% for the linear growth phase (W > 1.5 t ha⁻¹; LAI > 1.4). From a third field experiment, a value of 4.5% N was estimated for PNC_c for the pre-linear growth phase. Also a power function: LAR = 0.011W^−0.33 described the relationship between leaf area ratio and weight. The exponent of the power function determines the rate of the decline. Therefore, having the same value of the exponent: −0.33, LAR and PNC_c declined at the same rates. The proportional decline in LAR and PNC_c corresponded to a constant nitrogen content on a leaf area basis of 4.7 g N m⁻² until onset of head formation.     

Effects of tree windbreak on microclimate and wheat productivity in a Mediterranean environment

The presence of windbreaks is usually considered positive in mitigating the evapotranspiration (ET). For this reason, the windbreak barrier is included among the agro-techniques specific for the dry-farming systems. Objective of the study is to analyze the actual benefits of windbreaks on crop water requirements and yield.The 3-year field study has been carried integrating agronomic and microclimatic approaches. Study concerned durum wheat growing in open field, in a typical Mediterranean environment. A Cupressus arizonica L. windbreak (3 m in height) bordered at North the experimental field.The analysis of the microclimatic observations shows that, when wind blew from the North direction, the windbreak presence influenced the wind speed until the distance 12.7H (H is the windbreak height), and temperature increased in a distance of 4.7H from the barrier.On the basis of the soil water content, continuously measured by TDR technique, evapotranspiration (ET_d) was daily determined and season ET calculated. Windbreaks mitigated ET for a distance of 12.7 times the windbreak height. Out of this area, the ET was 16% higher than the ET measured near the windbreak belt (<4.7H).Yield performances changed accordingly the distance from the windbreak. Within the distance of 18 times the windbreak height, wheat productions were higher than those obtained in the zone not influenced by the windbreaks.Within the protected area, wheat water use efficiency (WUE, calculated as the ratio between yield and seasonal evapotranspiration) attained the maximum value of 1.15; out of the windbreak protection, WUE was 0.70 kg m^?3.Since windbreaks reduce ET, farms of the Mediterranean environments should be re-designed in order to consider the windbreaks as possible issue of sustainability.     

Influence of fertilisation and harvest time on fuel quality of giant reed (Arundo donax L.) in central Italy

The perennial grass giant reed (Arundo donax L.) has been proposed as a promising biomass energy crop in southern Europe. The aim of this study was to investigate the effects of two fertilisation levels (F = 200–80–200 N–P–K kg ha^?1; UF = 0–0–0 N–P–K kg ha^?1) and two harvest times (A: autumn, W: winter) on the biomass quality of giant reed as a solid fuel for combustion. Different aged crops grown in central Italy (latitude 43°40′N, and longitude10°19′E) in the period of 1996–2005 were collected and analysed. Our results confirmed that giant reed biomass is characterized by a high content of ash and silicon. Giant reed showed an increase in ash content from F to UF and from A to W. The production of biomass from fertilised crops harvested in the autumn may thus be a good method for reducing the ash content by about 20%. The results also showed an improvement in biomass combustion quality in 10-year-old crops due to a lower ash content and higher SiO₂/K₂O and CaO/K₂O ratios, which could contribute to a lower slagging tendency. This research should help to improve our knowledge of the chemical composition of giant reed and presents possible agronomic strategies to combine a high biomass yield with good combustion quality.     

High crop barrier reduces gene flow from transgenic to conventional maize in large fields

To test the effectiveness of high crop barriers in reducing gene flow, we conducted experiments in two large fields (around 750 m × 750 m) using yellow transgenic maize and white conventional maize in the growth season of 2013, with Sorghum as a high crop barrier in a shape of 5 m zone. Sorghum barrier affected pollen load at different directions, decreasing pollen number in further locations. It also decreased the cross-pollination incidence between transgenic and non-transgenic maize, with a average rate of 9.35% in the open site and 1.04% in the Sorghum site. But Sorghum barrier had little effect on the maximum distance of pollen flow and cross-pollination, which depends on wind direction and speed. The maximum distance of gene flow from transgenic to conventional maize was 300 m in the open site and 350 m in the Sorghum site. High crop barrier could be proposed as an effective method to reduce the frequency of gene flow from transgenic to conventional crops and to regulate their coexistence.     

Development of critical nitrogen dilution curve in rice based on leaf dry matter

The critical nitrogen (N_c), defined as the minimum N concentration required for maximum growth, is proposed for diagnosis of the in-season N status in crop plants. It has been established for several crops including rice on whole-plant dry matter (DM) basis but has not been determined for canopy leaf basis. This research was undertaken to develop a new N_c dilution curve based on leaf dry matter (L_DM) and to assess its applicability to estimate the level of N nutrition for Japonica rice in east China. Three field experiments were conducted with varied N rates (0–360 kg N ha⁻¹) and three Japonica rice (Oryza sativa L.) hybrids, Lingxiangyou-18 (LXY-18), Wuxiangjing-14 (WXJ-14) and Wuyunjing (WYJ) in Jiangsu province of east China. Five hills from each plot were sampled from active tillering to heading for growth analysis and leaf N determination. The N_c dilution curve on leaf N concentration was described by the equation N_c = 3.76W^−0.218, when L_DM ranged from 0.67 to 4.25 t ha⁻¹. However, for L_DM < 0.67 t ha⁻¹, the constant critical value N_c = 4.09%L_DM was applied. This N_c dilution curve on L_DM basis was slightly higher than the curves on plant DM basis in Japonica rice, yet both lower than the reference curve of high yielding Indica rice in tropics. The N nutrition index (NNI) and accumulated N deficit (N_and) of leaves ranged from 0.65 to 1.06 and 79.62 to −6.39 kg ha⁻¹, respectively, during main growth stages under varied N rates in 2010 and 2011. The results indicate that the present N_c dilution curve and derived NNI and N_and adequately identified the situations of N-limiting and non-N-limiting nutrition in two rice varieties and could be used as reliable indicators of N status during growth of Japonica rice in east China.     

Increased utilization of lengthening growing season and warming temperatures by adjusting sowing dates and cultivar selection for spring maize in Northeast China

Global warming has lengthened the theoretical growing season of spring maize in Northeast China (NEC), and the temperatures during the growing season have increased. In practise, crop producers adjust sowing dates and alternate crop cultivars to take advantage of the lengthening growing season and increasing temperatures. In this study, we used crop data and daily weather data for 1981–2007 at five locations in NEC to quantify the utilization of the lengthening growing season and increasing temperatures by adjusting sowing dates and cultivar selection for spring maize production. If these two positive factors are not fully utilized, then it is important to know the potential impacts of these climatic trends on spring maize grain yields. The results show that in NEC, both the actual and theoretical growing seasons are lengthening, i.e., the sowing dates have been advanced and the maturity dates have been delayed. The actual sowing dates are 1–8 days later and the actual maturity dates are 6–22 days earlier than the theoretical perspective. Advancing sowing dates and changing cultivars led to 0–5 days and 6–26 days extension of the growing season. For the potential thermal time (TT), adjusting the sowing dates decreased the unutilized TT before sowing, while the cultivar selection increased the utilized TT and decreased the unutilized TT after maturity. On average, the unutilized heating resource before sowing is less than that after the maturity date (0.3–1.9% vs. 2.1–7.8%). During 1981–2007, for per day extension of the growing season, the spring maize grain yield increased by 75.2 kg ha⁻¹. The spring maize grain yields have increased by 7.1–57.2% when both early sowing and changing cultivars during 1981–2007. In particular, adjusting the sowing dates increased the grain yield by 1.1–7.3%, which was far less than the increase effect (6.5–43.7%) from switching to late maturing cultivars. Therefore, selecting late maturing cultivars is an important technique to improve maize grain yields in NEC under the global warming context. Nevertheless, if the currently unutilized TT were fully explored, the local spring maize grain yield would have increased by 12.0–38.4%.     

Effect of sustained deficit irrigation on physicochemical properties,bioactive compounds and postharvest life of pomegranate fruit (cv. ‘Mollar de Elche’)

In this study, the influence of sustained deficit irrigation (SDI; 32% of reference evapotranspiration (ET₀)) on physicochemical and sensory quality and bioactive compounds of pomegranates stored for 30, 60 and 90 days in air at 5 °C + 4 days at 15 °C, at each storage period, was studied and compared to a control (100% ET₀). Fruit from SDI had higher peel redness and greater firmness, soluble solids contents, vitamin C (27%), phloretin (98%) and protocatechuic acid (10%) levels, and total antioxidant capacity (TAC) (46%) than the control. Cold storage and shelf-life did not induce significant changes in soluble solids, pH, titratable acidity, and chroma and Hue. SDI fruit had retarded development of chilling injury (CI) symptoms, which appeared after 60 days of storage in comparison to 30 days in the controls. Anthocyanins, catechin, phloretin and protocatechuic, caffeic, p-coumaric and caffeic acids contents had greater increases in SDI fruit than in controls throughout the postharvest life. TAC was significantly (P < 0.05) correlated to anthocyanins, gallic acid and total vitamin C contents. Generally, after long term storage, the fruit grown under SDI showed higher sensory and nutritional quality, more health attributes and a longer shelf-life (up to 90 days at 5 °C + 4 at 15 °C) than fruit irrigated at 100% ET₀.     

Fertilizers,hybrids, and the sustainable intensification of maize systems in the rainfed mid-hills of Nepal

In the rainfed mid-hill region of Nepal, most fields receive 2–3 t ha⁻¹ of organic compost application every year. Despite efficient recovery and use of organics in the mixed crop-animal systems that predominant in the mid-hills, depleted soil fertility is widely understood to be a significant constraint to crop productivity, with most farmers achieving maize grain yields below 2 t ha⁻¹. Increased use of fertilizer may arrest and even reverse long-term soil quality degradation, but few farmers in the mid-hills use them at present and existing recommendations are insufficiently responsive to site, varietal, and management factors that influence the productivity and profitability of increased fertilizer use. Moreover, policy makers and development practitioners often hold the perception that returns to fertilizer use in the mid-hills are too low to merit investment. In this study, on-farm experiments were conducted at 16 sites in the Palpa district, Nepal to assess the responsiveness of a maize hybrid (DKC 9081) and an ‘improved’ open-pollinated maize variety (‘OPV’, Manakamana-3) to four nitrogen (N) rates, i.e., 0, 60, 120 and 180 kg ha⁻¹, with each N rate response evaluated at 30:30 and 60:60 kg ha⁻¹ rates of phosphorus (P₂O₅) and potassium (K₂O), respectively. With sound agronomy and high rates of fertilizer (180:60:60 kg N:P₂O₅:K₂O ha⁻¹), grain yields observed in the field experiments exceeded 8 t ha⁻¹ with hybrids and 6 t ha⁻¹ with OPV. Yield levels were lower for OPV than hybrid at every level of applied N, but both genotypes responded linearly to N with partial factor productivity for N (PFP_N) ranging from 14 to 19 for OPV versus 26–30 for hybrid, with improved N efficiencies obtained when P and K rates were significantly higher. Averaged across phosphorus (P) and potassium (K) levels, a $ 1 incremental investment in fertilizer increased the gross margin (GM) by $ 1.70 ha⁻¹ in OPV and by $ 1.83 ha⁻¹ in the hybrid. For the full response of N, requires higher rate of P₂O₅:K₂O and vice-versa and full response to P₂O₅:K₂O does not occur if N is absent. These results suggest that, i) degraded soils in the mid-hills of Nepal respond favorably to macronutrient fertilizers – even at high rates, ii) balanced fertilization is necessary to optimize returns on investments in N but must be weighed against additional costs, iii) OPVs benefit from investments in fertilizer, albeit at a PFP_N that is 36–47% lower than for hybrids, and, consequently iv) hybrids are an effective mechanism for achieving a higher return on fertilizer investments, even when modest rates are applied. To extend these findings across years and sites in the mid-hills, crop growth simulations using the CERES-maize model (DSSAT) were conducted for 11 districts with historical weather and representative soils data. Average simulated (hybrid) maize yields with high fertilizer rate (180:60:60 kg N:P₂O₅:K₂O ha⁻¹) ranged from 3.9 t ha⁻¹ to 7.5 t ha⁻¹ across districts, indicating a high disparity in attainable yield potential. By using these values to estimate district-specific attainable yield targets, recommended N fertilizer rates vary between 65 and 208 kg N ha⁻¹, highlighting the importance of developing domain-specific recommendations. Simulations also suggest the potential utility of using weather forecasts in tandem with site and planting date information to adjust fertilizer recommendations on a seasonal basis.     

Growth and yield of winter wheat in the first 3 years of a monoculture under varying N fertilization in NW Germany

Different preceding crops interact with almost all husbandry and have a major effect on crop yields. In order to quantify the yield response of winter wheat, a field trial with different preceding crop combinations (oilseed rape (OSR)–OSR–OSR–wheat–wheat–wheat), two sowing dates (mid/end of September, mid/end of October) and 16 mineral nitrogen (N) treatments (80–320 kg N ha⁻¹) during 1993/1994–1998/1999, was carried out at Hohenschulen Experimental Station near Kiel in NW Germany. Single plant biomass, tiller numbers m⁻², biomass m⁻², grain yield and yield components at harvest were investigated. During the growing season, the incidence of root rot (Gaeumannomyces graminis) was observed. Additionally, a bioassay with Lemna minor was used to identify the presence of allelochemicals in the soil after different preceding crops.Averaged over all years and all other treatments, wheat following OSR achieved nearly 9.5 t ha⁻¹, whereas the second wheat crop following wheat yielded about 0.9 t ha⁻¹ and the third wheat crop following 2 years of wheat about 1.9 t ha⁻¹ less compared with wheat after OSR. A delay of the sowing date only marginally decreased grain yield by 0.2 t ha⁻¹. Nitrogen fertilization increased grain yield after all preceding crop combinations, but at different levels. Wheat grown after OSR reached its maximum yield of 9.7 t ha⁻¹ with 210 kg N ha⁻¹. The third wheat crop required a N amount of 270 kg N ha⁻¹ to achieve its yield maximum of 8.0 t ha⁻¹.Yield losses were mainly caused by a lower ear density and a reduced thousand grain weight. About 4 weeks after plant establishment, single wheat plants following OSR accumulated more biomass compared to plants grown after wheat. Plants from the third wheat crop were smallest. This range of the preceding crop combinations was similar at all sampling dates throughout the growing season.Root rot occurred only at a low level and was excluded to cause the yield losses. The Lemna bioassay suggested the presence of allelochemicals, which might have been one reason for the poor single plant development in autumn.An increased N fertilization compensated for the lower number of ears m⁻² and partly reduced the yield losses due to the unfavorable preceding crop combination. However, it was not possible to completely compensate for the detrimental influences of an unfavorable preceding crop on the grain yield of the subsequent wheat crop.     

Determination of optimal sulfur dioxide time and concentration product for postharvest control of gray mold of blueberry fruit

Highbush blueberries (Vaccinum spp.) are a major export fruit crop of Chile which is stored at 0 °C and transported to markets in Asia, Europe, and the USA, using more than 15 d of maritime transportation. Under these conditions, gray mold caused by Botrytis cinerea can produce important economic losses. The effectiveness of sulfur dioxide (SO₂) concentration × time treatments on gray mold control was determined in the laboratory and validated prior to refrigerating the fruit, using pallet scale SO₂ fumigation treatment on the following blueberry cultivars: ‘Brigitta’, ‘Legacy’, ‘Liberty’ and ‘O’Neal’. In inoculated ‘Brigitta’ and ‘Liberty’ blueberries, gray mold prevalence varied from 97.2% to 97.5% in non-treated fruit, and this value was reduced from 7.9% to 6.1% in blueberries that were exposed to a SO₂ concentration × time (Ct) product of 400 (μL L⁻¹) h. The relationship between SO₂ Ct products and gray mold prevalence under laboratory conditions was best explained by exponential models, which had a determination coefficient (R²) that ranged from 0.88 to 0.96. The estimated EC₉₀ values varied between 245 and 400 (μL L⁻¹) h, and the SO₂ Ct between 250 and 350 (μL L⁻¹) h was validated using a pallet scale application treatment to obtain the best control and minimal variation. No visual phytotoxicity symptoms of SO₂ were observed with the Ct that was tested in this study. Therefore, SO₂ fumigation was demonstrated to be an effective and practical technology for reducing the risk of blueberry gray mold decay during storage, and further effort should be given to register the use of this product for blueberries in the main Chilean export markets.     

Optimising crop production and nitrate leaching in China: Measured and simulated effects of straw incorporation and nitrogen fertilisation

The sustainability of growing a maize—winter wheat double crop rotation in the North China Plain (NCP) has been questioned due to its high nitrogen (N) fertiliser use and low N use efficiency. This paper presents field data and evaluation and application of the soil–vegetation–atmosphere transfer model Daisy for estimating crop production and nitrate leaching from silty loam fields in the NCP. The main objectives were to: i) calibrate and validate Daisy for the NCP pedo-climate and field management conditions, and ii) use the calibrated model and the field data in a multi-response analyses to optimise the N fertiliser rate for maize and winter wheat under different field managements including straw incorporation.The model sensitivity analysis indicated that a few measurable crop parameters impact the simulated yield, while most of the studied topsoil parameters affect the simulated nitrate leaching. The model evaluation was overall satisfactory, with root mean squared residuals (RMSR) for simulated aboveground biomass and nitrogen content at harvest, monthly evapotranspiration, annual drainage and nitrate leaching out of the root zone of, respectively, 0.9 Mg ha⁻¹, 20 kg N ha⁻¹, 30 mm, 10 mm and 10 kg N ha⁻¹ for the calibration, and 1.2 Mg ha⁻¹, 26 kg N ha⁻¹, 38 mm, 14 mm and 17 kg N ha⁻¹ for the validation. The values of mean absolute deviation, model efficiency and determination coefficient were also overall satisfactory, except for soil water dynamics, where the model was often found erratic. Re-validation run showed that the calibrated Daisy model was able to simulate long-term dynamics of crop grain yield and topsoil carbon content in a silty loam field in the NCP well, with respective RMSR of 1.7 and 1.6 Mg ha⁻¹. The analyses of the model and the field results showed that quadratic, Mitscherlich and linear-plateau statistical models may estimate different economic optimal N rates, underlining the importance of model choice for response analyses to avoid excess use of N fertiliser. The analyses further showed that an annual fertiliser rate of about 300 kg N ha⁻¹ (100 for maize and 200 for wheat) for the double crop rotation with straw incorporation is the most optimal in balancing crop production and nitrate leaching under the studied conditions, given the soil replenishment with N from straw mineralisation, atmospheric deposition and residual fertiliser.This work provides a sound reference for determining N fertiliser rates that are agro-environmentally optimal for similar and other cropping systems and regions in China and extends the application of the Daisy model to the analyses of complex agro-ecosystems and management practices under semi-arid climate.     

Pod and seed numbers as a function of photothermal quotient during the seed set period of field pea (Pisum sativum) crops

The effects of radiation and temperature during the seed set period (SSP) on pod number per square metre (PN m⁻²) and seed number per square metre (SN m⁻²) and those of temperature during grain filling on unit seed weight (USW, milligram per seed) of field pea (Pisum sativum L.) were examined in experiments involving irrigated crops of three or more cultivars of contrasting maturity sown on two or more dates per year from 1996 to 1998 at Buenos Aires, Argentina. The duration of the seed-setting phase was estimated from records of the progress of flowering on the main stem and an estimate (obtained using an optimisation procedure) of the thermal time from flowering at which the uppermost reproductive node reached the final stage of seed abortion (FSSA). The FSSA at a particular node was assumed to be achieved 200 °C day (T_b=4 °C) after flowering at the same node. The grain-filling phase was assumed to run from the achievement of FSSA at the first reproductive node through to 200 °C day (T_b=0 °C) after the date of achievement of the FSSA by the second flowering node.The treatments (cultivar, sowing date, year) produced important ranges of above-ground biomass (AGB) at maturity (271–782 g m⁻²), seed yield (SY, 119–331 g m⁻²), SN (1062–3698 seeds m⁻²) and USW (67–150 mg seed⁻¹). Seed yield was strongly correlated with SN, and there was full compensation between SN and USW in large-seeded cultivars in the high SN range, but not at lower values of SN or in small-seeded cultivars. Both PN (r=0.83) and SN (r=0.87, P<0.0005) were strongly correlated with the mean daily value of the photothermal quotient (PQ=incident radiation/(mean temperature − base temperature)) for the seed-setting phase. Large- and small-seeded cultivars had PN/PQ and SN/PQ relationships with slopes which did not differ among categories but with significantly different intercepts. When the effects of low temperatures during flowering and early grain growth were allowed for, outliers on the PN/PQ and SN/PQ relationships for unstressed crops fell within the confidence limits of the respective linear regressions. Unit seed weight showed a negative response to mean temperature during the grain-filling phase in large- and small-seeded cultivars. We conclude that the relationships established in these experiments, taken together with previous work by other authors, constitute a robust basis for modelling the yield of unstressed field pea crops.     

Above- and belowground nitrogen uptake of winter catch crops sown after silage maize as affected by sowing date

Regions in north-western Europe characterized by high density of livestock/biogas plants and extensive silage maize production are facing major environmental challenges due to excessive residual soil mineral nitrogen (N) in autumn and hence nitrate leaching. Winter catch crops (CC) have potential to accumulate residual N; however, the N uptake potential after maize harvest in autumn and spring remains unclear. Therefore, a two-year field trial (April 2012–April 2014) was conducted at three sites, to quantify the combined effects of four consecutive CC sowing dates (10 Sep; 20 Sep; 30 Sep and 15 Oct) and two CC species (rye, Secale cereale. L. and Italian ryegrass, Lolium multiflorum Lam.) on DM accumulation and N uptake of CC above- and belowground in autumn and spring, and to derive functional relationships. The results clearly showed that rye was more effective in accumulating biomass and nitrogen than Italian ryegrass. The better performance of rye was related to increased growth intensity of roots and shoot, a different allocation pattern and higher N uptake efficiency. An exponential function of temperature sum (Tsum) produced a reliable prediction of above- and belowground biomass and N. To achieve an agronomically relevant N uptake of 20 kg N ha⁻¹, rye required 278 °Cd Tsum, which corresponds to a sowing date latest in the second decade of September. Under favourable growing conditions, a biomass accumulation of up to 5 Mg DM ha⁻¹, corresponding to 83 kg N ha⁻¹ above- and belowground, seems achievable under the given environmental conditions. In continuous maize grown under the environmental conditions of Northern Germany, however, catch crops will not reach a relevant N uptake on the long-term average.     

Mitigating N2O emissions from cropping systems after conversion from pasture − a modelling approach

Converting pasture to cropping is common in many of the world’s agricultural systems. This conversion results in substantial net mineralisation of soil organic matter that builds up during a phase of pasture. A few studies have shown that this mineralisation leads to increased nitrous oxide (N₂O) emissions compared to long-term pasture or long-term cropping. Understanding of interactions leading to these significant emissions is still scarce but is needed to identify mitigation options for this situation. In this study, the Agricultural Production Systems sIMulator (APSIM) was used to investigate the optimal timing of pasture termination (relative to crop planting) and management of nitrogen (N) in crops after pasture termination to maximise crop yield and limit N₂O emissions. Beforehand, APSIM’s performance in simulating yields and N₂O emissions was tested against data from field experiments conducted in the temperate high-rainfall zone of southern Australia where N₂O emissions were monitored with automatic gas collection chambers during the first year of cropping wheat after terminating long-term pasture on two adjacent sites in two consecutive years. Field experiments and simulation scenarios showed very high N₂O emissions (up to 48 kg N₂O-N ha⁻¹ yr⁻¹) in the first year of wheat after pasture termination, even without N fertiliser application. Measured cumulative N₂O emissions, crop yields and soil mineral N and water content dynamics were simulated well with APSIM. Including a routine into APSIM to account for N₂O transport through the soil profile improved the simulation of daily N₂O emissions considerably, leading to up to 67% of the measured variability in daily N₂O emissions being explained by the model. We predicted that a short fallow between termination of pasture and sowing wheat, instead of a long fallow which is the common practice, reduces N₂O emissions by more than half in the first year of cropping without a noteworthy impact on crop yield. Reducing N fertiliser applications in the first few years after pasture termination by taking available soil mineral N into account, and applying the fertiliser six to twelve weeks after sowing instead of at sowing was predicted to further reduce N₂O emissions. Since the model was calibrated against experimental data during the first year after pasture termination only, experiments determining N₂O emissions in the first two or three years after terminating pasture are needed to confirm our predictions.     

Early assessment of ecological services provided by forage legumes in relay intercropping

In organic agriculture, weeds and nitrogen deficiency are the main factors that limit crop production. The use of relay-intercropped forage legumes may be a way of providing ecological services such as weed control, increasing N availability in the cropping system thanks to N fixation, reducing N leaching and supplying nitrogen to the following crop. However, these ecological services can vary considerably depending on the growing conditions. The aim of this study was to identify early indicators to assess these two ecological services, thereby giving farmers time to adjust the management of both the cover crop and of the following crop.Nine field experiments were conducted over a period of three years. In each experiment, winter wheat was grown as sole crop or intercropped with one of two species of forage legumes; Trifolium repens L. or Trifolium pratense L. Two levels of fertilization were also tested (0 and 100 kg N ha⁻¹). After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Legume and weed biomass, nitrogen content and accumulation were monitored from legume sowing to cover destruction.Our results showed that a minimum threshold of about 2 t ha⁻¹ biomass in the aboveground parts of the cover crop was needed to decrease weed infestation by 90% in early September and to ensure weed control up to December. The increase in nitrogen in the following maize crop was also correlated with the legume biomass in early September. The gain in nitrogen in maize (the following crop) was correlated with legume biomass in early September, with a minimum gain of 60 kg N ha⁻¹ as soon as legume biomass reached more than 2 t ha⁻¹.Legume biomass in early September thus appears to be a good indicator to predict weed control in December as well as the nitrogen released to the following crop. The indicator can be used by farmers as a management tool for both the cover crop and following cash crop. Early estimation of available nitrogen after the destruction of the forage legume can be used to adjust the supply of nitrogen fertilizer to the following crop.     

Germination of fungal conidia after exposure to low concentration ozone atmospheres

The germinability of conidia of Alternaria alternata, Aspergillus flavus, Aspergillus niger, Penicillium digitatum, Penicillium expansum, or Penicillium italicum was determined periodically during exposure for approximately 100 d to a humid atmosphere of air alone or with 150 nL/L ozone at 2 °C. Conidia were exposed on glass coverslips that were removed from chambers at intervals of one week and the germination of 100 conidia of each species was assessed after incubation for 24 h on potato dextrose agar. The period in d when 50% or 95% (ET₅₀ and ET₉₅, respectively) could not germinate and 95% confidence intervals for these estimates were made using Finney's probit analysis. ET₅₀ and ET₉₅ estimates were approximately one month and two to three months, respectively. Some natural mortality of the conidia occurred during these periods, so the entire decline in germinability was not solely due to ozone. The age of the culture from which conidia were collected influenced their susceptibility to ozone. Conidia were harvested from 7, 14, 21, and 28 d old potato dextrose agar cultures of P. digitatum and exposed to 13,000 nL/L ozone at 2 °C. After 48 h of exposure to ozone, none of the conidia from the seven-day old culture germinated, while 30–35% of conidia from 14, 21, or 28 d in age cultures germinated.     

Assessing the impact of increasing carbon dioxide and temperature on crop-weed interactions for tomato and a C3 and C4 weed species

Based on the carboxylation kinetics of the C₃ and C₄ photosynthetic pathway, it is anticipated that C₃ crops may be favored over C₄ weeds as atmospheric CO₂ increases. In the current study, tomato (Lycopersicon esculentum), a C₃ crop species, was grown at ambient (~400 μmol mol⁻¹) and enhanced carbon dioxide (~800 μmol mol⁻¹) with and without two common weeds, lambsquarters (Chenopodium album), a C₃ weed, and redroot pigweed (Amaranthus retroflexus), a C₄ weed, from seedling emergence until mutual shading of crop-weed leaves. Because growth temperature is also likely to change in concert with rising CO₂, the experiment was repeated at day/night temperatures of 21/12 and 26/18 °C. For both day/night temperatures, elevated CO₂ exacerbated weed competition from both the C₃ and C₄ weed species. A model based on relative leaf area following emergence was used to calculate potential crop losses from weeds. This analysis indicated that potential crop losses increased from 33 to 55% and from 32 to 61% at the 21/12 and 26/18 °C day/night temperatures, for ambient and elevated CO₂, respectively. For the current study, reductions in biomass and projected yield of tomato appeared independent of the photosynthetic pathway of the competing weed species. This may be due to inherent variation and overlap in the growth response of C₃ and C₄ species, whether weeds or crops, to increasing CO₂ concentration. Overall, these results suggest that as atmospheric CO₂ and/or temperature increases, other biological interactions, in addition to photosynthetic pathway, deserve additional consideration in predicting competitive outcomes between weeds and crops.