Tillage, cover crops, and nitrogen fertilization effects on soil nitrogen and cotton and sorghum yields

Sustainable soil and crop management practices that reduce soil erosion and nitrogen (N) leaching, conserve soil organic matter, and optimize cotton and sorghum yields still remain a challenge. We examined the influence of three tillage practices (no-till, strip till and chisel till), four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secaele cereale L.)], vetch/rye biculture and winter weeds or no cover crop}, and three N fertilization rates (0, 60–65 and 120–130 kg N ha⁻¹) on soil inorganic N content at the 0–30 cm depth and yields and N uptake of cotton (Gossypium hirsutum L.) and sorghum [Sorghum bicolor (L.) Moench]. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic, Plinthic Paleudults) from 1999 to 2002 in Georgia, USA. Nitrogen supplied by cover crops was greater with vetch and vetch/rye biculture than with rye and weeds. Soil inorganic N at the 0–10 and 10–30 cm depths increased with increasing N rate and were greater with vetch than with rye and weeds in April 2000 and 2002. Inorganic N at 0–10 cm was also greater with vetch than with rye in no-till, greater with vetch/rye than with rye and weeds in strip till, and greater with vetch than with rye and weeds in chisel till. In 2000, cotton lint yield and N uptake were greater in no-till with rye or 60 kg N ha⁻¹ than in other treatments, but biomass (stems + leaves) yield and N uptake were greater with vetch and vetch/rye than with rye or weeds, and greater with 60 and 120 than with 0 kg N ha⁻¹. In 2001, sorghum grain yield, biomass yield, and N uptake were greater in strip till and chisel till than in no-till, and greater in vetch and vetch/rye with or without N than in rye and weeds with 0 or 65 kg N ha⁻¹. In 2002, cotton lint yield and N uptake were greater in chisel till, rye and weeds with 0 or 60 kg N ha⁻¹ than in other treatments, but biomass N uptake was greater in vetch/rye with 60 kg N ha⁻¹ than in rye and weeds with 0 or 60 kg N ha⁻¹. Increased N supplied by hairy vetch or 120–130 kg N ha⁻¹ increased soil N availability, sorghum grain yield, cotton and sorghum biomass yields, and N uptake but decreased cotton lint yield and lint N uptake compared with rye, weeds or 0 kg N ha⁻¹. Cotton and sorghum yields and N uptake can be optimized and potentials for soil erosion and N leaching can be reduced by using conservation tillage, such as no-till or strip till, with vetch/rye biculture cover crop and 60–65 kg N ha⁻¹. The results can be applied in regions where cover crops can be grown in the winter to reduce soil erosion and N leaching and where tillage intensity and N fertilization rates can be minimized to reduce the costs of energy requirement for tillage and N fertilization while optimizing crop production.     

Delaying senescence of wheat with fungicides has interacting effects with cultivar on grain sulphur concentration but not with sulphur yield or nitrogen:sulphur ratios

Winter wheat was grown in three field experiments, each repeated over two or three seasons, to investigate effects of extending flag leaf life by fungicide application on the concentration, kg ha⁻¹ and mg grain⁻¹ of nitrogen (N) and sulphur (S) as well as N:S ratio and sodium dodecyl sulphate (SDS) sedimentation volume. The experiments involved up to six cultivars and different application rates, timings and frequencies of azoxystrobin and epoxiconazole. For every day the duration to 37% green flag leaf area (m) was extended, N yield was increased by 2.58 kg ha⁻¹, N per grain by 0.00957 mg, S yield by 0.186 kg ha⁻¹ and S per grain by 0.000718 mg. The N:S ratio decreased by 0.0135 per day. There was no evidence that these responses varied with cultivar. In contrast, the relationship between flag leaf life and N or S concentration interacted with cultivar. The N and S concentrations of Shamrock, the cultivar that suffered most from brown rust (Puccinia recondita), increased with the extension of flag leaf life whereas the concentrations of N and S in Malacca, a cultivar more susceptible to Septoria tritici, decreased as flag leaf senescence was delayed. This was because the relationships between m and N and S yields were much better conserved over cultivars than those between m and thousand grain weight (TGW) and grain yield ha⁻¹.     

Beet vinasse applied to wheat under dryland conditions affects soil properties and yield

The effect of six doses of beet vinasse (0, 3, 6, 10, 20 and 40 t ha⁻¹, respectively) on wheat (Triticum aestivum cv. Cajeme) yield in dryland conditions (Guadalquivir Valley, Andalusia, Spain) for 3 years on a Typic Xerofluvent was studied. The results showed that at low doses, beet vinasse is of agricultural interest due mainly to its organic matter concentration. The application of this byproduct to the soil increased soil microbial biomass and mineralization of its organic matter increased NO₃⁻–N concentrations in soil. This caused an increase in grain yield in the three seasons. When the vinasse was applied with high doses, NO₃⁻–N concentrations in soil, soil microbial biomass, soil structure, bulk density, electric conductivity, nutrient uptake, crop yield and grain quality were negatively affected. We assume that the high amounts of monovalent cations, particularly Na⁺, and of fulvic acids, which had been transported into the soil by the vinasse, destabilized the soil structure. This may have led to anaerobic soil conditions being presumably responsible for restricted N mineralization or even for denitrification. This explains the lower N supply to the crops reflected by the low N concentrations in the leaves of treatments A4 and A5.     

Potassium cycling in a corn-brachiaria cropping system

Growing corn mixed with forage crops can be an alternative for pasture and mulch production during relatively dry winters in tropical areas, making no-till feasible in some regions. However, little is known about nutrient dynamics in this cropping system. The objective of the present work was to evaluate K dynamics in a production system in which corn was either grown as a sole crop or mixed with Brachiaria brizantha. In the second year of the experiment, nitrogen rates ranging from 0 to 200 kg ha⁻¹ were applied to the system. Dry matter yields and potassium contents in the soil, as well as residues and plants were determined at corn planting and harvest. Potassium balance in the system was calculated. Corn grain yield in mixed crop responded up to 200 kg ha⁻¹ N. The introduction of brachiaria in the system resulted in higher amounts of straw on the soil surface and higher K recycling. Soil exchangeable K balance showed an excess K for both N rates only in the mixed system; however, when non-exchangeable K was also included in calculations, excess K was found in both mixed and sole corn systems. Large amounts of non-exchangeable K were taken up in the system involving brachiaria, which showed a considerable capacity in recycling K, increasing its contents in the surface soil layer.     

Management alternatives for improved durum wheat production under supplemental irrigation in Syria

In the Mediterranean zone, efforts to optimize combinations of supplemental irrigation (SI), improved varieties, nitrogen (N) and sowing dates aim to improve and stabilize cereal yields and maintain quality, especially for durum wheat. Thus, a 4 year field study (1992/1993 to 1995/1996) on a deep clay soil in northern Syria assessed the impact of SI (rain-fed, 1/3, 2/3 and full SI) combined with variable N application rates (0, 50, 100, 150 kg ha⁻¹) and sowing date (early, normal, late) for four improved durum wheat varieties adapted to rain-fed and irrigated conditions. As rainfall and evapotranspiration varied over the 4 years, the amount of SI water required also varied. Yields varied with the season, and the main factors, except variety, were significant. Delaying sowing from November to January reduced yields and response to both SI and N. With irrigation, crop responses were generally significant up to 100 N ha⁻¹, whereas the optimum response for rain-fed conditions occurred with 50 kg N ha⁻¹. Limited SI (1/3) significantly increased yields, but almost maximum yields were obtained by 2/3 of full SI. Water- and N-use efficiencies were greatly increased by SI, with little variation among varieties. However, irrigation and delayed sowing decreased grain protein levels, which were partially compensated for by added N. A similar effect was observed for kernel vitreousness. Models developed from the response data can facilitate the potential transfer of these findings. Thus, in most growing seasons, minimum irrigation during the winter growing season, combined with appropriate fertilization, can enhance wheat output and yet maintain grain quality.     

Spatial and temporal distribution of the root system and root nutrient content of an established Miscanthus crop

Although a high biomass yield is obtained from established Miscanthus crops, previous studies have shown that fertilizer requirements are relatively low. As little information on the role of the Miscanthus roots in nutrient acquisition is available, a study was conducted to gather data on the Miscanthus root system and root nutrient content. Therefore in 1992, the root distribution pattern of an established Miscanthus crop was measured in field trials using the trench profile and the auger methods. Also, in 1994/1995, seasonal changes in root length density (RLD) and root nutrient content were monitored three times during the vegetation period.

The trench profile method showed that roots were present to the maximum depth measured of 250 cm. The top soil (0–30 cm) contained 28% of root biomass, while nearly half of the total roots were present in soil layers deeper than 90 cm. Using the auger method, we found that RLD values in the topsoil decreased with increasing distance from the centre of the plants. Below 30 cm, RLD decreased markedly, and differences in root length in the soil between plants were less pronounced. The total root dry weight down to 180 cm tended to increase from May 1994 (10.6 t ha⁻¹) to November 1994 (13.9 t ha⁻¹) and then decreased again until March 1995 (11.5 t ha⁻¹). Nutrient concentrations in the roots decreased with increasing depth. The concentrations of N (0.7–1.4%) and K (0.6–1.2%) were clearly higher than those of P (0.06–0.17%). The mean values for N, P and K contents of the roots of all three sampling dates in 1994/1995 were 109.2 kg N ha⁻¹, 10.6 kg P ha⁻¹ and 92.5 kg K ha⁻¹.

Although our results showed that RLD values for Miscanthus in the topsoil are lower than for annual crops, the greater rooting depth and the higher RLD of Miscanthus in the subsoil mean that nutrient uptake from the subsoil is potentially greater. This enables Miscanthus crops to overcome periods of low nutrient (and water) availability especially during periods of rapid above-ground biomass growth.     

Monitoring nitrogen forms in soil/plant systems under different fertilizer managements. A preliminary investigation

A field experiment was carried out on maize (Zea mays, L.) to study the effects of different fertilizer management on nitrogen status in soil and plant response. Three different fertilizers, mineral (MN), mineral plus buffalo manure (MN + BM) and organo-mineral with peat (OMP), were added at the usual (140, 61 and 116 kg ha⁻¹) and the reduced (70, 31 and 58 kg ha⁻¹) rates of N, P and K. respectively. Soil samples were analyzed for N by both the Kjeldahl method and the electro-ultrafiltration technique (EUF). The soil Kjeldahl-N concentrations were scarcely affected by the different fertilizer treatments, while the EUF-N concentrations were closely correlated with the amounts of N added. The EUF also discriminated between the NO₃-N and the sum of the ammonium and the easily extractable organic N forms (EUF-N_org + NH₄). The largest proportions of EUF-Norg + NH₄ were found in the untreated plots and in the plots treated with buffalo manure. The different fertilizer treatments significantly affected grain yield, which ranged from a minimum of 6.3 t ha⁻¹ from the untreated plots, to a maximum of 11.9 t ha⁻¹ from those supplied with 140 kg N, 61 kg P and 116 kg K ha⁻¹ by OMP fertilizer. The highest agronomic efficiency index for N was exhibited in the OMP treatment at the reduced rate. The grain yield was closely correlated with the total extractable EUF-N, but different relationships were found between the rate of N added, the level of EUF-NO,-N in soil and grain yield for the different fertilizer treatments.     

Nitrogen mineralization in sandy loam soils under an intensive double-cropping forage system with dairy-cattle slurry applications

Nitrogen (N) mineralization and soil mineral N contents were measured at 2-week intervals over a 2-year period (June 1994–May 1996) on two different sites in the North West region of Portugal. The experiment was established in fields, which had for many years been under a double-cropping forage system with maize from May to September and a winter crop (mixture of cereals and Italian ryegrass) during the rest of the year. In addition to N fertilizers, dairy-cattle slurry was applied regularly at the sowing of each crop. On this intensive forage system, quantification of N released from slurry, crop residues and soil organic matter becomes important when better N use efficiency and reduced environmental impact from agricultural practices are required. Net N mineralization rates of the 0–10 cm soil layer fluctuated considerably between consecutive incubation periods and ranged from −0.88 to 1.87 mg N kg⁻¹ day⁻¹ with annual average rates of between 0.41 and 0.65 mg N kg⁻¹ day⁻¹. The total N mineralized in the 10 cm depth soil layer reached values between 122 and 224 kg N ha⁻¹ year⁻¹, showing that mineralization was a very important N source for the crops. The amounts of N released during the cold season (November–February) were equivalent to 27–48% of the yearly total. Regression analysis indicated that seasonal variation in N mineralization was only poorly explained by soil moisture and temperature. The changing balance during the year between soil moisture and temperature will contribute to the relatively constant N mineralization rates. Soil mineral N contents during the maize crop were high and exceeded the nutrient requirements for the optimum yield of this crop. Under the climatic conditions of the region and due to the poor development of the winter crop plants at the time, the mineral N left in the soil after the maize crop and released by mineralization during the cold season is particularly vulnerable to nitrate leaching losses.     

NPK farm-gate nutrient balances in dairy farms from Northwest Portugal

Farm-gate nutrient balances (N, P and K) were analysed in three groups of dairy farms from NW Portugal – medium, intensive and very intensive farms – during 3 consecutive years, 2003, 2004 and 2005. Results showed that the N surplus per hectare with values between 200 and 850 kg N ha⁻¹ was positively correlated with the milk production per ha and the stocking rate of the farm, whereas the P and K surpluses showed fewer variations between groups. In all farms the main inputs were the mineral fertilizers and the feed concentrates whereas milk was the main output. Farmers involved in the study were advised in terms of nutrient management and significant decreases in the nutrient surpluses were observed during the 3 years study, mainly due to a decrease of the inputs, namely fertilizers. We conclude that advisory campaigns among farmers are efficient to reduce the nutrient surpluses. The N losses via NH₃ emissions at farm scale were also estimated accordingly to IPCC emission factors and it appeared that such losses were significant and had to be considered together with the nutrient surpluses when strategies to enhance nutrient management are defined. On average, higher N surplus per hectare were observed in the studied dairy farms from NW Portugal relatively to other European regions, but NW Portugal present lower N surplus per production unit (kg milk) as well as higher N efficiency. Nevertheless, a target limit of 450 kg N ha⁻¹ for N surplus should be easily reached as a first step by most of the farms of NW Portugal by improving nutrient management at farm scale. However, more efforts will be necessary to reduce NPK surplus and NH₃ emissions to the mean values in a per hectare basis found in other European dairy regions with less intensive systems.     

Effect of preceding crop combination and N fertilization on yield of six oil-seed rape cultivars (Brassica napus L.)

Information about the effect of the cropping history on the seed yield of oil-seed rape is extremely scarce. In 1992/93 and 1994/95, the effects of different preceding crop combinations (winter barley and winter wheat as preceding crops, oil-seed rape and wheat as pre-preceding crops) on the yield of six double low oil-seed rape cultivars were examined in a field trial at Hohenschulen Experimental Farm, north-west Germany. In addition, eight nitrogen treatments (different amounts and distribution patterns) were tested for their potential to reduce negative effects of the preceding crops. Following the cropping sequence of oil-seed rape then wheat, oil-seed rape yielded only 3.12 t ha⁻¹; after oil-seed rape then barley, the yield was 3.43 t ha⁻¹ compared with 3.77 t ha⁻¹ following wheat then barley and 3.71 t ha⁻¹ following wheat then wheat. The number of seeds per m² showed a similar pattern, whereas the thousand-seed weight partly compensated for the reduced seed number. It was highest if oil-seed rape was grown 2 years previously. The cultivars differed significantly in their yield potential. Express (3.79 t ha⁻¹) yielded 0.6 t ha⁻¹ more than Falcon (3.18 t ha⁻¹). Increasing amounts of fertilizer-N (80–200 kg N ha⁻¹) increased the seed yield from 3.21 t ha⁻¹ to 3.84 t ha⁻¹. Changes in the distribution pattern within one fertilizer amount had no effect on seed yield. In addition, no interactions between preceding crop combination and the different cultivars or N treatments occurred. It is concluded that crop management cannot totally eliminate the negative effects of an unfavourable cropping history on the seed yield of oil-seed rape.     

Yield and quality components of silage maize in killed and live cover crop sods

In sloping areas with high precipitation, planting maize into live winter cover crop sods may help to alleviate the environmental problems associated with clean-tillage production systems of maize. The present study evaluates the performance of silage maize (Zea mays L.) under several cultivation methods: CC (conventional cropping system, i.e., maize was sown into the bare, autumn-ploughed soil); LGS/CK (maize was planted into a living Italian ryegrass (Lolium multiflorum Lam.) sod which was subsequently herbicidally killed); and LGS/MR (similar to LGS/CK, but the ryegrass was mechanically regulated). The research was conducted in the midlands of Switzerland on a fertile sandy loam under humid conditions during three cropping seasons. With 110 kg N ha⁻¹ (fertilizer nitrogen plus mineral nitrogen of the soil at maize planting), the CC system was much more productive than were the LGS/CK and LGS/MR systems in terms of dry matter and nitrogen yields of maize. Increasing the nitrogen supply to 250 kg N ha⁻¹ considerably reduced the yield advantage of CC over the LGS/CK and LGS/MR systems, indicating that nitrogen was the most limiting factor for maize yield in the mulch seeding systems. With 250 kg N ha⁻¹, the LGS/CK and LGS/MR systems produced greater total yields of digestible organic matter (maize plus ryegrass) than did the CC system, whereas the total nitrogen yield was similar for all cropping systems. The whole-shoot concentrations of nitrogen were highest under CC, irrespective of the level of nitrogen supply. With 110 kg N ha⁻¹, concentrations of phosphorus and magnesium were clearly higher for the mulch seeding systems. There were only minor differences among the cropping methods in the concentrations of potassium and calcium in the whole shoot. When 250 kg N ha⁻¹ were applied, there were no significant variations among the cropping systems in the concentrations of minerals. Changes in the botanical composition of the cover crop sod and in the time and method of cover crop control may help to reduce the competition for nitrogen between maize and the living mulch.     

Wheat productivity in the Mediterranean Ebro Valley: Analyzing the gap between attainable and potential yield with a simulation model

Water deficit is an important constraint for wheat yield generation under Mediterranean environments. However, nitrogen (N) availability could limit yield in a more important way than poor water conditions. The aim of the work was to analyze, using the Ceres-Wheat crop simulation model, to what degree N fertilization constitutes a tool for reducing the gap between attainable and potential yield. Firstly, the model was calibrated and validated under a wide range of N and water conditions for the region of the Ebro Valley (NE Spain). Anthesis and maturity date were adequately predicted by the model. Predictions of yield tended to be quite accurate in general, though under severe water deficits precision was lower. We then assessed the gap between attainable and potential yield considering different N availabilities at sowing taking into account a weather database of 17 years for the location of Agramunt (NE Spain), representative of cereal growing conditions of the Mediterranean Catalonia. Potential yield ranged between 3.5 and 8.1 Mg ha⁻¹. Variations in potential yield were explained by the duration of the period from sowing to anthesis and by the level of incident radiation during the period immediately previous to anthesis. Average attainable yield was 1.8 Mg ha⁻¹ for N availability of 50 kg_N ha⁻¹; but increased to 2.8 Mg ha⁻¹ for higher N availabilities (100–250 kg_N ha⁻¹). In the 25% of the worst years there was no effect of N availability on attainable yield. Increasing N availability beyond 100 kg_N ha⁻¹ generated a gain in yield only in 6% of the years. Variations between years in attainable yields were mainly explained by rainfall during the period from sowing to anthesis, whereas differences in attainable yield between N treatments increased with increases in rainfall. The gap between potential yield and attainable yield was higher in years with higher potential yield. On the other hand, the higher the attainable yield, the lower the gap. Thus, the proportion of the yield gap ascribed to N availability varied depending on the conditions of the growing season. In the high-yielding potential years, the main restriction for growth was water shortage, and fertilizing only slightly reduced the gap. Conversely, in rainy years characterized by low potential yields and mild water stresses, N management may constitute a simple tool for effectively reducing yield gap under rain-fed conditions.     

Long-term fate of nitrogen uptake in catch crops

The long-term effects of undersowing a ryegrass catch crop in cereals was analysed with the FASSET simulation model. The model was tested on a 28-year field experiment with ryegrass catch crops in spring barley. The experiment included treatments with nitrogen (N) fertiliser rates, catch crop use and timing of tillage. The modelled effects of these treatments generally agreed with observations on crop production, soil carbon, soil nitrogen and nitrate leaching. Both the observations and the simulations predicted a yield increase of 7 kg N ha⁻¹ and an increase in nitrate leaching of 13 kg N ha⁻¹ due to a prehistory of 24 years with continuous use of catch crops compared to a prehistory without catch crops.

A range of scenarios was constructed to evaluate the fate of the reduced nitrate leaching on crop N uptake, N leaching, gaseous emissions and change in soil organic N, and how this fate interacts with soils and climate and management. These scenarios showed that 22–30% of the reduced nitrate leaching was subsequently leached during the following decades after termination of catch crop use. Between 35 and 40% of the reduced nitrate leaching was harvested in cereals. The exact distribution depended primarily on the soil texture. The scenarios showed that effects of catch crops should be evaluated on the long-term rather than consider short-term effects only.     

Biomass yield and energy balance of giant reed (Arundo donax L.) cropped in central Italy as related to different management practices

In order to evaluate the possibility of reducing energy input in giant reed (Arundo donax L.) as a perennial biomass crop, a field experiment was carried out from 1996 to 2001 in central Italy. Crop yield response to fertilisation (200–80–200 kg ha⁻¹ N–P–K), harvest time (autumn and winter) and plant density (20,000 and 40,000 plants per ha) was evaluated. The energy balance was assessed considering the energy costs of production inputs and the energy output obtained by the transformation of the final product. The crop yield increased by +50% from the establishment period to the 2nd year of growth when it achieved the highest dry matter yield. The mature crop displayed on average annual production rates of 3 kg dry matter m⁻², with maximum values obtained in fertilised plot and during winter harvest time.

Fertilisation mainly enhanced dry matter yield in the initial period (+0.7 kg dry matter m⁻² as years 1–6 mean value). The biomass water content was affected by harvest time, decreasing by about 10% from autumn to winter. With regard to plant density, higher dry matter yields were achieved with 20,000 plants per ha (+0.3 kg dry matter m⁻² as years 1–6 mean value).

The total energy input decreased from fertilised (18 GJ ha⁻¹) to not fertilised crops (4 GJ ha⁻¹). The higher energetic input was represented by fertilisation which involved 14 GJ ha⁻¹ (fertilisers plus their distribution) of total energy costs. This value represents 78% of total energy inputs for fertilised crops.

Giant reed biomass calorific mean value (i.e., the calorific value obtained from combustion of biomass sample in an adiabatic system) was about 17 MJ kg⁻¹ dry matter and it was not affected by fertilisation, or by plant density or harvest time. Fertilisation enhanced crop biomass yield from 23 to 27 dry tonnes per ha (years 1–6 mean value). This 15% increase was possible with an energy consumption of 70% of the overall energy cost. Maximum energy yield output was 496 GJ ha⁻¹, obtained with 20,000 plants per ha and fertilisation. From the establishment period to 2nd–6th year of growth the energy production efficiency (as ratio between energy output and energy input per ha) and the net energy yield (as difference between energy output and energy input per ha) increased due to the low crop dry biomass yield and the high energy costs for crop planting. The energy production efficiency and net energy yield were also affected by fertilisation and plant density. In the mature crop the energy efficiency was highest without fertilisation both with 20,000 (131 GJ ha⁻¹) and 40,000 plants per ha (119 GJ ha⁻¹).     

Reducing atrazine leaching by integrating reduced herbicide use with mechanical weeding in corn (Zea mays)

Concern about the effects of pesticides on the environment and the desire to reduce purchased inputs are stimuli to reduce herbicide use. Field research was conducted for three growing seasons to compare the chemical contamination and effectiveness of three weed management practices. Weed control treatments included application of a herbicide mixture of 1.5 kg ai ha⁻¹ of atrazine plus 0.9 kg ai ha⁻¹ of pyridate, this mixture being broadcast alone or band-applied in combination with mechanical weeding, and mechanical weeding alone. The results show that it is possible to decrease the amount of atrazine residue in soil with the band-applied treatment. Such a method is very attractive because crop yields were not decreased, at least in the short run. However, we do not yet know the long-term efficiency of this method regarding groundwater quality, weed population dynamic and crop yield. Further work is therefore needed to assess the long-term impact of this weeding method.     

Yield and water-use efficiency of water- and nitrogen-stressed wheat crops increase with degree of co-limitation

Availability of water and nitrogen are key constraints to primary productivity in arid and semiarid ecosystems. Theoretically, plant growth is maximised when all resources are equally limiting. This paper tested the hypothesis that for a given amount of available water, the gap between actual and attainable yield of dryland crops in semiarid southern Australia is inversely proportional to the degree of nitrogen and water co-limitation.

Field and simulation experiments were combined in an analysis involving three steps. Step 1 assessed the capacity of a crop simulation model to estimate yield and its responses to water and nitrogen inputs in the semiarid Mallee region. Step 2 derived a boundary function relating grain yield and water availability using simulations with long-term weather records. Step 3 explored the link between degree of co-limitation and deviations between actual yield and the boundary function. Degree of co-limitation (C_WN) was calculated as a function of model-derived nitrogen (NSI) and water stress indices (WSI), i.e. C_WN = 1 − |NSI − WSI|. Stress indices range from zero (no stress) to 1 (maximum stress), and C_WN tends to 1 when both resources impose constraints of similar magnitude to crop growth.

The field experiment combining locations, seasons and management practices generated a range of grain yield from 0.6 to 3.8 t ha⁻¹. Water availability, i.e. seasonal rainfall plus change in soil water content from sowing to harvest, ranged from 127 to 370 mm. Nitrogen fertiliser varied from nil to 36 kg N ha⁻¹ and inorganic nitrogen in the soil profile at sowing ranged from 29 to 497 kg ha⁻¹. For these ranges of conditions, the relationship between simulated and measured yield was statistically undistinguishable from the y = x function.

A factorial modelling experiment combining sites, seasons, initial soil water content and dose of nitrogen fertiliser was used to derive a boundary function which provided an objective and independent upper limit for the field data. Actual yield was below the boundary function in most cases. The difference between actual and attainable yield was inversely proportional to C_WN. This study thus supported the hypothesis that yield and water-use efficiency of water- and nitrogen-stressed crops increase with increasing degree of co-limitation.     

Prediction of grain protein in spring malting barley grown in northern Europe

The ability to predict grain protein concentration at harvest (CP) in Swedish malting barley (Hordeum distichum) from observations of soil conditions, sowing day, fertilisation rate, remote sensing at early stem elongation and the temperature sum during grain filling, was tested for two cultivars; Astoria (Secobra, France) and Wikingett (Svalöf-Weibulls, Sweden) in 16 fertilisation trials in southern Sweden, encompassing 3 years (2001–2003). Fertilisation was applied either as a single dose at sowing, or as both a starting application and an application at early stem elongation. The highest total application rate was 160 kg N ha⁻¹ y⁻¹. The soil was analysed for phosphorus, potassium, magnesium and calcium in the layer 0–0.3 m, and mineral N down to 0.6 m. Canopy reflectance observations at BBCH 32 was used to calculate a vegetation index (TCARI(32)) to reflect the canopy (leaf and straw) chlorophyll concentration. Harvested grain CP correlated only marginally with the observed soil variables. It was, however, for a specific cultivar, possible to make a prediction of grain CP based on day of sowing and TCARI(32) with . Part of the sowing day effect might be due to thermal stress during grain filling, as the risk for high temperatures during this phase was higher when sowing was late. This might also explain why the introduction of accumulated temperature during grain filling, into a model already including sowing day and TCARI(32) as independent variables, did not improve the predictability of grain CP.     

Simulating winter wheat yields under temperate conditions: exploring different management scenarios

This paper describes a methodology for analysing management strategies to find best agronomic practices using a crop simulation model (CERES-Wheat). The study area is the estate of Imperial College at Wye, in the Stour Catchment, Kent, UK, an area highly suited to winter wheat production. The model is validated using historic crop performance data. Yield responses to differing sowing rates (range 200–450 seeds m⁻²), sowing dates and rates of nitrogen application (between 100 and 220 kg ha⁻¹) with soil types of medium to heavy texture were simulated under water-limited conditions using historical daily weather data. In model validation, observed yields ranged between 6.9 and 7.4 t ha⁻¹, while simulated ranges were between 6.9 and 7.8 ha⁻¹. The RSMD of the difference was small (0.24 t ha⁻¹) and non-significant. Optimum management practices (in terms of planting date, seed density and nitrogen application) were thereby defined. Also, simulations of potential yield (i.e. yield with no water and nutrient stress) were run for comparison. Results of this study reveal that the calibrated and validated CERES-Wheat model can be successfully used for the prediction of wheat growth and yield under conditions appropriate to Western Europe.     

The effect of lupins as compared with peas and oats on the yield of the subsequent winter barley crop

New high yielding early maturing cultivars of lupins have been introduced in north-west Europe as grain protein crops in crop rotations. This paper reports on a comparative study of lupins with peas and oats, and of their effect on yield of subsequent winter barley crops. These crops were given five levels of N under irrigated and non-irrigated conditions on sand and loam. Under rain fed conditions the grain yield of pea, oat and lupin varied between 24–36, 34–53 and 18–37 hkg DM ha⁻¹, respectively. Supplemental irrigation raised grain yield of oat to 50–60 hkg DM ha⁻¹, while grain yield in pea was not affected and grain yield in lupin in most cases decreased due to gray mould attack and excessive vegetative growth in the indeterminate lupin variety. Under rain fed conditions, the grain nitrogen content of pea, oat and lupin varied between 137–172, 61–80 and 189–226 kg N ha⁻¹, respectively, and was significantly higher in lupin as compared with pea. On sandy soil, similar low-root densities were found for pea, oat and lupin below 30 cm depth. On sand, at final harvest the residual soil-N of lupin and pea, as measured in a subsequent winter barley crop not supplied with N fertilizer, was 15 and 8–10 kg N ha⁻¹ higher than in winter barley following oat, respectively. The nature of the probably more N-root residues of lupin is discussed. On loam, the residual N of lupin and pea was similar, 18–27 kg N ha⁻¹. On sand, under rain fed conditions preceding lupin and pea as compared with oat, increased the barley grain yield at zero N-application 77 and 49%, respectively; the effect of lupin was significantly higher than that of pea until the highest N-level 120 kg N-application ha⁻¹. On loam under rain fed conditions preceding lupin and pea increased the barley grain yield at zero N-application by 36 and 62%, respectively, as compared with oat; at N-application>60 kg N ha⁻¹ the grain yield was similar after all three crops. For both soil types the same level of effect was found under irrigated conditions. Conclusions: Supplemental irrigation might result in lower grain yield in lupin due to gray mould attack and excessive growth if indeterminate lupin varieties are used. Grain nitrogen yield of lupin is significantly higher than that of pea. On sand, the effect of lupin on the subsequent winter barley grain yield is significantly higher than that of pea, probably due to greater N-root nitrogen residues. On loam, lupin and pea have similar effects on the subsequent winter barley crop.     

N2 fixation and N supply in organic pea (Pisum sativum L.) cropping systems as affected by weeds and peaweevil (Sitona lineatus L.)

Grain legumes, especially peas, could play a key role in organic cropping systems. They could provide nitrogen (N) to the system via N₂ fixation and produce grain rich in protein while improving soil N for the succeeding crop. Thus, maximising N₂ fixation and optimising grain N production together with N contribution to soil is a challenging issue for organic pea crops. However, pest, disease and weed infestation are less easy to control in organic systems than in conventional systems. Therefore, the effects of weed infestation and pea weevil (Sitona lineatus L.) attacks on N nutrition and N₂ fixation of organic pea crops were examined by on-farm monitoring over two years. The magnitude of the net contribution of the crops to the soil N balance in relation to their productivity was also assessed. In many situations, weed infestation together with pea weevil damage severely limited the nitrogen nutrition and grain yield. Percentage of N derived from fixation (%Ndfa) increased with weed biomass because weeds appeared more competitive than peas for soil N. But %Ndfa decreased with pea weevil leaf damage score. The interaction between these two biotic factors affected N yields and the net contribution of the crops to soil N. This latter ranged from −133 kg N ha⁻¹ to 69 kg N ha⁻¹ depending on %Ndfa and nitrogen harvest index (NHI). Optimising both grain N and net balance would require a reduction in root nodule damage by weevil larvae in order to maximise %Ndfa and a reduction in the NHI through the choice of cultivar and/or suitable crop management.