The relevance of N fertilization for the amount of total greenhouse gas emissions in sugar beet cultivation

The agricultural sector is highly affected by climate change and it is a source of greenhouse gases. Therefore it is in charge to reduce emissions. For a development of reduction strategies, origins of emissions have to be known. On the example of sugar beet, this study identifies the main sources and gives an overview of the variety of production systems. With data from farm surveys, calculations of greenhouse gas (GHG) emissions in sugar beet cultivation in Germany are presented. Emissions due to the production and use of fertilizers and pesticides, emissions due to tillage as well as field emissions were taken into account. All emissions related to the growing of catch crops during fall before the cultivation of sugar beet were also included. The emissions are related to the yield to express intensity.The median of total GHG emissions of sugar beet cultivation in Germany for the years 2010–2012 amounted to 2626 equivalents of CO₂ (CO₂eq) kg ha⁻¹ year⁻¹ when applying mineral plus organic fertilizer and to 1782 kg ha⁻¹ when only organic fertilizer was applied. The CO₂eq emissions resulting from N fertilization exclusively were 2.5 times higher than those caused by diesel and further production factors. The absence of emissions for the production of organic fertilizers led to 12% less total CO₂eq emissions compared to the use of mineral fertilizer only. But by applying organic fertilizer only, there were more emissions via the use of diesel due to larger volumes transported (126 l diesel ha⁻¹ vs. 116 l ha⁻¹ by applying mineral fertilizer exclusively).As there exists no official agreement about calculating CO₂eq emissions in crop production yet, the authors conclude that there is still need for further research and development with the aim to improve crop cultivation and crop rotations concerning GHG emissions and the therewith related intensity.     

Cassava yield loss in farmer fields was mainly caused by low soil fertility and suboptimal management practices in two provinces of the Democratic Republic of Congo

A better understanding of the factors that contribute to low cassava yields in farmers’ fields is required to guide the formulation of cassava intensification programs. Using a boundary line approach, we analysed the contribution of soil fertility, pest and disease infestation and farmers’ cultivation practices to the cassava yield gap in Kongo Central (KC) and Tshopo (TSH) provinces of the Democratic Republic of Congo. Data were obtained by monitoring 42 and 37 farmer-managed cassava fields during two cropping cycles in KC and one cropping cycle in TSH, respectively. Each field was visited three times over the cassava growing period for the observations. Logistic model was fitted against the observed maximum cassava root yields and used to calculate the achievable yield per field and for individual factor. At field level, the factor that led to the lowest achievable yield (Y_up(i)1) was considered as the dominant yield constraint. Cassava yield loss per field was expressed as the increase in the maximal root yield observed per province (Y_att- attainable yield) compared to Y_up(i)1. Y_att was 21 and 24 t ha⁻¹ in TSH and KC, respectively. With the cassava varieties that farmers are growing in the study areas, pests and diseases played a sparse role in the yield losses. Cassava mosaic was the only visible disease we observed and it was the dominant yield constraint in 3% and 12% of the fields in KC and TSH, respectively. The frequent yield constraints were suboptimal field management and low soil fertility. Cultivation practices and soil parameters led to Y_up(i)1 in 47% and 50% of the fields in KC, and in 47% and 41% of those in TSH, respectively. Individual soil parameters were the yield constraint in few fields, suggesting that large-scale programs in terms of lime application or recommendation of the blanket fertilisers would result in sparse efficacy. In KC, yield losses caused by low soil fertility averaged 6.2 t ha⁻¹ and were higher than those caused by suboptimal field management (5.5 t ha⁻¹); almost nil for cassava mosaic disease (CMD). In TSH, yield losses caused by low soil fertility (4.5 t ha⁻¹) were lower than those caused by suboptimal field management (6.5 t ha⁻¹) and CMD (6.1 t ha⁻¹). Irrespective of the constraint type, yield loss per field was up to 48% and 64% of the Y_att in KC and TSH, respectively. Scenario analysis indicated that the yield losses would remain at about two third of these levels while the dominant constraint was only overcome. We concluded that integrated and site-specific management practices are needed to close the cassava yield gap and maximize the efficacy of cassava intensification programs.     

Explaining rice yields and yield gaps in Central Luzon,Philippines: An application of stochastic frontier analysis and crop modelling

Explaining yield gaps is crucial to understand the main technical constraints faced by farmers to increase land productivity. The objective of this study is to decompose the yield gap into efficiency, resource and technology yield gaps for irrigated lowland rice-based farming systems in Central Luzon, Philippines, and to explain those yield gaps using data related to crop management, biophysical constraints and available technologies.Stochastic frontier analysis was used to quantify and explain the efficiency and resource yield gaps and a crop growth model (ORYZA v3) was used to compute the technology yield gap. We combined these two methodologies into a theoretical framework to explain rice yield gaps in farmers’ fields included in the Central Luzon Loop Survey, an unbalanced panel dataset of about 100 households, collected every four to five years during the period 1966–2012.The mean yield gap estimated for the period 1979–2012 was 3.2 ton ha⁻¹ in the wet season (WS) and 4.8 ton ha⁻¹ in the dry season (DS). An average efficiency yield gap of 1.3 ton ha⁻¹ was estimated and partly explained by untimely application of mineral fertilizers and biotic control factors. The mean resource yield gap was small in both seasons but somewhat larger in the DS (1.3 ton ha⁻¹) than in the WS (1.0 ton ha⁻¹). This can be partly explained by the greater N, P and K use in the highest yielding fields than in lowest yielding fields which was observed in the DS but not in the WS. The technology yield gap was on average less than 1.0 ton ha⁻¹ during the WS prior to 2003 and ca. 1.6 ton ha⁻¹ from 2003 to 2012 while in the DS it has been consistently large with a mean of 2.2 ton ha⁻¹. Varietal shift and sub-optimal application of inputs (e.g. quantity of irrigation water and N) are the most plausible explanations for this yield gap during the WS and DS, respectively.We conclude that the technology yield gap explains nearly half of the difference between potential and actual yields while the efficiency and resource yield gaps explain each a quarter of that difference in the DS. As for the WS, particular attention should be given to the efficiency yield gap which, although decreasing with time, still accounted for nearly 40% of the overall yield gap.     

Yield of bolting winter beet (Beta vulgaris L.) as affected by plant density,genotype and environment

Winter beet roots and shoots might be a favorable substrate for biogas production in Central Europe. However, detailed information about the attainable yield of this crop is lacking. Thus, the impact of plant density, genotype and environmental conditions on total dry matter yield of winter beet crops that bolt after winter was investigated. A significant increase of the dry matter yield (esp. shoot) was expected by harvesting the 1st shoot after flowering in June followed by a final harvest of the whole plant in July. In 2009/10, 2010/11 and 2011/12, three series of field trials with (i) 3 target plant densities (148, 246, 370 thousand plants ha⁻¹) and (ii) 3 different sugar beet genotypes were conducted at Göttingen (Lower Saxony, GER) and Kiel (Schleswig-Holstein, GER); (iii), additional field trials with 5 different sugar beet genotypes cultivated at 2 target plant densities (148, 246 thousand plants ha⁻¹) were conducted in 2011/12, to investigate the relation between maximum taproot diameter and the shoot and taproot yield of bolting winter beet. The total dry matter yield considerably varied between 4 and 23 t ha⁻¹. It was predominantly affected by the environment and to a substantially lower extent by plant density. Increasing plant densities increased the total dry matter yield, resulting in a significantly higher total dry matter yield at plant densities ≥300,000 plants ha⁻¹ compared with lower plant densities. Genotypic differences in total dry matter yield were negligibly small. Pruning in June substantially increased the total dry matter yield in July by ca. 8 t ha⁻¹ only in one out of three environments.Final yield in June (without pruning) and July (pruning in June) was positively related with cumulated temperature and global radiation, but also with taproot dry matter yield before winter. The taproot, shoot (1st, 2nd) and total plant yield were positively correlated with maximum taproot diameter.In conclusion, high dry matter yields close to yields of established energy crops grown over winter were obtained with winter beet roots and shoots only under very favorable conditions (climate, single plant size). High yields can be achieved after good pre-winter development. However, for sufficient frost tolerance the taproot size of plants must be rather small. Hence, the cultivation of bolting winter beet under Central European climate conditions has to face a severe conflict of goals concerning winter survival and yield formation.     

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.     

Analysing the energy balances of sugar beet cultivation in commercial farms in Germany

Energy balances are increasingly used to assess the energy efficiency and productivity of agricultural production. In this study, energy balances for sugar beet cultivation in commercial farms in Germany were calculated. 109 farmers with 285 fields were interviewed about the sugar beet cultivation 2004. The energy input and the energy output were calculated with standardised balance-sheet approaches and energy equivalents. Calculated energy balance parameters were the energy gain (energy output less input), the output–input ratio (energy output versus input) and the energy intensity (energy input versus natural yield measured in Grain Equivalents). A factor analysis was performed to explain the variation of the energy balance parameters between the fields by crucial factors for energetic efficiency and productivity. Fields with similarly valued factors were grouped into common clusters by a cluster analysis and a discriminant analysis. The influence of specific growing conditions and cultivation methods on the energy balances were examined for the clusters.Total energy input (median: 17.3 GJ ha⁻¹), energy output (261.7 GJ ha⁻¹), energy gain (244.6 GJ ha⁻¹), output–input ratio (15.4) and energy intensity (87.4 MJ GE⁻¹) revealed a significant variation. The total energy input was significantly lower and the energy yield was significantly higher than in previous studies. Thus, the energy gain and the output–input ratio have clearly risen compared to earlier studies. Today, sugar beet cultivation is energetically more productive and efficient than the cultivation of many other arable crops in Middle Europe.The intensity of the cultivation measures irrigation, catch crop cultivation, tillage and N fertilisation as well as the management of all cultivation measures and the site were determined as crucial factors for energy efficiency and productivity. The intensity of the different cultivation measures influenced the total energy input significantly, but no influence on the energy output was determined. In contrast, the cultivation management (quality and adaptation of cultivation measures) was mainly responsible for the energy output. Whereas the cultivation management mostly explained the energy gain, the factor cultivation management and the factors representing cultivation intensity together were responsible for the output–input ratio.Cluster and discriminant analysis resulted in the formation of 13 clusters. For clusters with an above-average energy gain and output–input ratio, the intensity and in particular the management of cultivation measures were essential for optimising the energy balance.     

Performance and application of the APSIM Nwheat model in the Netherlands

APSIM Nwheat is a crop system simulation model, consisting of modules that incorporate aspects of soil water, nitrogen (N), crop residues, and crop growth and development. The model was applied to simulate above- and below-ground growth, grain yield, water and N uptake, and soil water and soil N of wheat crops in the Netherlands. Model outputs were compared with detailed measurements of field experiments from three locations with two different soil types. The experiments covered two seasons and a range of N-fertiliser applications. The overall APSIM Nwheat model simulations of soil mineral N, N uptake, shoot growth, phenology, kernels m⁻², specific grain weight and grain N were acceptable. Grain yields (dry weight) and grain protein concentrations were well simulated with a root mean square deviation (RMSD) of 0.8 t ha⁻¹ and 1.6 protein%, respectively. Additionally, the model simulations were compared with grain yields from a long-term winter wheat experiment with different N applications, two additional N experiments and regional grain yield records. The model reproduced the general effects of N treatments on yields. Simulations showed a good consistency with the higher yields of the long-term experiment, but overpredicted the lower yields. Simulations and earlier regional yields differed, but they showed uniformity for the last decade.In a simulation experiment, the APSIM Nwheat model was used with historical weather data to study the relationship between rate and timing of N fertiliser and grain yield, grain protein and soil residual N. A median grain yield of 4.5 t ha⁻¹ was achieved without applying fertiliser, utilising mineral soil N from previous seasons, from mineralisation and N deposition. Application of N fertiliser in February to increase soil mineral N to 140 kg N ha⁻¹ improved the median yield to 7.8 t ha⁻¹ but had little effect on grain protein concentration with a range of 8–10%. Nitrogen applications at tillering and the beginning of stem elongation further increased grain yield and in particular grain protein, but did not affect soil residual N, except in a year with low rainfall during stem elongation. A late N application at flag leaf stage increased grain protein content by several per cent. This increase had only a small effect on grain yield and did not increase soil residual N with up to 40 kg N ha⁻¹ applied, except when N uptake was limited by low rainfall in the period after the flag leaf stage. The economic and environmental optima in winter wheat were identified with up to 140 kg N ha⁻¹ in February, 90 kg N ha⁻¹ between tillering and beginning of stem elongation and 40 kg N ha⁻¹ at flag leaf stage resulting in a median of 8.5 t ha⁻¹ grain yield, 14.0% grain protein and 13 kg N ha⁻¹ soil residual N after the harvest. The maximum simulated yield with maximum N input from two locations in the Netherlands was 9.9 t ha⁻¹.     

Evaluation of long-term conservation agriculture and crop intensification in rice-wheat rotation of Indo-Gangetic Plains of South Asia: Carbon dynamics and productivity

In the context of deteriorating soil health, stagnation of yield in rice-wheat cropping system (RWCS) across Indo- Gangetic plains (IGP) and environmental pollution, a long term field experiment was conducted during 2009–2016 taking four crop scenarios with conservation agriculture (CA), crop intensification and diversified cropping as intervening technology aiming to evaluate the sustainability of the systems. Scenario 1 (S1) represented conventional farmers’ practice of growing rice and wheat with summer fallow. In scenario 2 (S2) and scenario 3 (S3), legume crop was taken along with rice and wheat with partial CA and full CA, respectively. Conventional RWCS was replaced with rice-potato + maize- cowpea cropping system with partial CA in scenario 4 (S4). The S3 scenario registered highest total organic carbon (TOC) stock of 47.71 Mg C ha⁻¹ and resulted in significant increase of 14.57% over S1 (Farmer’s practice) in 0–30 cm soil depth after 7 years of field trial. The S4 scenario having intensified cropping systems recorded lowest TOC of 39.33 Mg C ha⁻¹ and resulted in significant depletion of 17.56% in C stock with respect to S3 in 0–30 cm soil depth. The TOC enrichment was higher in S2, S3 and S4 scenario in the surface soil (0–10 cm) compared to S1. At lower depth (20–30 cm), the TOC enrichment was significantly higher in S2 (12.82 Mg C ha⁻¹) and S3 (13.10 Mg C ha⁻¹ soil) over S1 scenario. The S2 and S3 scenario recorded highest increased allocation of TOC (3.55 and 6.13 Mg C ha⁻¹) to passive pool over S1. The S2 (15.72 t ha⁻¹), S3 (16.08 t ha⁻¹) and S4 (16.39 t ha⁻¹) scenarios recorded significantly higher system rice equivalent yield over S1 (10.30 t ha⁻¹). Among the scenarios, S3 scenario had greater amount of total soil organic carbon, passive pool of carbon and higher system rice equivalent yield, thus, is considered the best cropping management practice to maintain soil health and food security in the middle IGP.     

Managing Tephrosia mulch and fertilizer to enhance coffee productivity on smallholder farms in the Eastern African Highlands

In Maraba, Southwest Rwanda, coffee productivity is constrained by poor soil fertility and lack of organic mulch. We investigated the potential to produce mulch by growing Tephrosia vogelii either intercropped with smallholder coffee or in arable fields outside the coffee, and the effect of the mulch on coffee yields over two years. Two accessions of T. vogelii (ex. Gisagara, Rwanda and ex. Kisumu, Kenya) were grown for six months both within and outside smallholder coffee fields in the first year. Experimental blocks were replicated across eight smallholder farms, only a single replicate per farm due to the small farm sizes. The accession from Rwanda (T. vogelii ex. Gisagara) grew more vigorously in all experiments. Soils within the coffee fields were more fertile those outside the coffee fields, presumably due to farmers’ long-term management with mulch. Tephrosia grew less well in the fields outside coffee, producing only 0.6–0.7 Mg ha⁻¹ of biomass and adding (in kg ha⁻¹) 19 N, 1 P and 6 K in the mulch. By contrast, Tephrosia intercropped with coffee, produced 1.4–1.9 Mg ha⁻¹ of biomass and added (in kg ha⁻¹) 42–57 N, 3 P and 13–16 K in the mulch. Coffee yields were increased significantly by 400–500 kg ha⁻¹ only in the treatments where Tephrosia was intercropped with coffee. Soil analysis and a missing-nutrient pot experiment showed that the poor growth of Tephrosia in the fields outside coffee was due to soil acidity (aluminium toxicity) combined with deficiencies of P, K and Ca.In the second year, the treatments in fields outside coffee were discontinued, and in the coffee intercrops, two Tephrosia accessions were grown in treatments with and without NPK fertilizer. Tephrosia grew well and produced between 2.5 and 3.8 Mg ha⁻¹ biomass for the two accessions when interplanted within coffee fields, adding 103–150 kg N ha⁻¹, 5–9 kg P ha⁻¹ and 24–38 kg K ha⁻¹. Tephrosia mulch increased yields of coffee by 400 kg ha⁻¹. Combined use of NPK + Tephrosia mulch increased Tephrosia biomass production and in turn yielded an additional 300–700 kg ha⁻¹ of coffee. Over the two years, this was equivalent to a 23–36% increase in coffee yield using Tephrosia intercropping alone and a further 25–42% increase in coffee yield when NPK fertilizer was also added. Agronomic efficiency (AE) of nutrients added were 30% greater when the Tephrosia mulch was grown in situ and the two cultivars of Tephrosia did not differ in AE. The AE of Tephrosia mulch was 87% that of NPK fertilizer, reflecting the rapid mineralization of Tephrosia mulch. There was a synergistic effect of Tephrosia mulch on the efficiency with which NPK fertilizer was used by coffee. The increase in coffee yields was positively related to the amount of nutrients added in the Tephrosia biomass. Tephrosia intercropping required 30 man-days ha⁻¹ less than current farmer management due to reduced labour required for weeding, and benefit–cost ratios ranged between 3.4 and 5.5. The Tephrosia-coffee intercropping system offers great potential for agroecological intensification for smallholder farmers in the East African highlands.     

Comparative assessment of maize,finger millet and sorghum for household food security in the face of increasing climatic risk

Questions as to which crop to grow, where, when and with what management, will be increasingly challenging for farmers in the face of a changing climate. The objective of this study was to evaluate emergence, yield and financial benefits of maize, finger millet and sorghum, planted at different dates and managed with variable soil nutrient inputs in order to develop adaptation options for stabilizing food production and income for smallholder households in the face of climate change and variability. Field experiments with maize, finger millet and sorghum were conducted in farmers’ fields in Makoni and Hwedza districts in eastern Zimbabwe for three seasons: 2009/10, 2010/11 and 2011/12. Three fertilization rates: high (90 kg N ha⁻¹, 26 kg P ha⁻¹, 7 t ha⁻¹ manure), low (35 kg N ha⁻¹, 14 kg P ha⁻¹, 3 t ha⁻¹ manure) and a control (zero fertilization); and three planting dates: early, normal and late, were compared. Crop emergence for the unfertilized finger millet and sorghum was <15% compared with >70% for the fertilized treatments. In contrast, the emergence for maize (a medium-maturity hybrid cultivar, SC635), was >80% regardless of the amount of fertilizer applied. Maize yield was greater than that of finger millet and sorghum, also in the season (2010/11) which had poor rainfall distribution. Maize yielded 5.4 t ha⁻¹ compared with 3.1 t ha⁻¹ for finger millet and 3.3 t ha⁻¹ for sorghum for the early plantings in the 2009/10 rainfall season in Makoni, a site with relatively fertile soils. In the poorer 2010/11 season, early planted maize yielded 2.4 t ha⁻¹, against 1.6 t ha⁻¹ for finger millet and 0.4 t ha⁻¹ for sorghum in Makoni. Similar yield trends were observed on the nutrient-depleted soils in Hwedza, although yields were less than those observed in Makoni. All crops yielded significantly more with increasing rates of fertilization when planting was done early or in what farmers considered the ‘normal window’. Crops planted early or during the normal planting window gave comparable yields that were greater than yields of late-planted crops. Water productivity for each crop planted early or during the normal window increased with increase in the amount of fertilizer applied, but differed between crop type. Maize had the highest water productivity (8.0 kg dry matter mm⁻¹ ha⁻¹) followed by sorghum (4.9 kg mm⁻¹ ha⁻¹) and then finger millet (4.6 kg mm⁻¹ ha⁻¹) when a high fertilizer rate was applied to the early-planted crop. Marginal rates of return for maize production were greater for the high fertilization rate (>50%) than for the low rate (<50%). However, the financial returns for finger millet were more attractive for the low fertilization rate (>100%) than for the high rate (<100%). Although maize yield was greater compared with finger millet, the latter had a higher content of calcium and can be stored for up to five years. The superiority of maize, in terms of yields, over finger millet and sorghum, suggests that the recommendation to substitute maize with small grains may not be a robust option for adaptation to increased temperatures and more frequent droughts likely to be experienced in Zimbabwe and other parts of southern Africa.     

White lupine as a beneficial crop in Southern Europe. II. Nitrogen recovery in a legume–oat rotation and a continuous oat–oat

One experiment lasting for two years was carried out at Pegões (central Portugal) to estimate the impact of mature white lupine residue (Lupinus albus L.) on yield of fodder oat (Avena sativa L. cv. Sta. Eulalia) as the next crop in rotation, comparing with the continuous cultivation of cereal, under two tillage practices (conventional tillage and no-till) and fertilized with five mineral nitrogen (N) rates, with three replicates. Oat as a first crop in the rotation provided more N to the agro-ecosystem (63 kg N ha⁻¹) than did lupine (30–59 kg N ha⁻¹). This was at a cost of 100 kg of mineral N ha⁻¹, whereas lupine was grown without addition of N. A positive response of oat as a second crop was obtained per kg of lupine-N added to the system when compared with the continuous oat–oat. The cereal also responded positively to mineral N in the legume amended soil in contrast with the oat–oat sequence where no response was observed, partly due to the fast mineralization rate of lupine residue and a greater soil N immobilization in the continuous oat system. Each kg N ha⁻¹ added to the soil through the application of 73 kg DM ha⁻¹ mature lupine residue (above- and belowground material) increased by 72 kg DM ha⁻¹ the oat biomass produced as the second crop in rotation when 150 kg mineral N ha⁻¹ were split in the season, independent of tillage practice. Mature legume residue conserved in the no-tilled soil depressed the yield of succeeding cereal but less than the continuous oat–oat for both tillage practices, where the application of mineral N did not improve the crop response.     

Factors affecting variation in farm yields of irrigated lowland rice in southern-central Benin

For increasing rice production in West Africa, both expansion of rice harvested area and raising rice yield are required. Development of small-scale irrigation schemes is given high priority in national rice development plans. For realizing potential of the newly developed schemes, it is essential to understand yield level, farmers’ crop management practices and production constraints. A series of field surveys were conducted in six small-scale irrigation schemes in Zou department, Benin during the dry season in 2010–2011 to assess variation in rice yields and identify factors affecting the variation. The schemes were established between 1969 and 2009. Rice yields ranged from 1.3 to 7.8 t ha⁻¹ with an average yield of 4.8 t ha⁻¹. The average yield was only 2.9 t ha⁻¹ for newer irrigation schemes developed in 2002 and 2009. Multiple regression analysis using farmers’ crop management practices as well as abiotic and biotic stresses as independent variables revealed that 75% of the variation in yields could be explained by five agronomic factors (fallow residue management, ploughing method, water stress, rat damage and N application rate) and two edaphic factors (sloped surfaces and sand content in the soil). Removing fallow residue from the fields for land preparation reduced yields. Yields were lower in plots ploughed by hand than by machine. Sloped surface, water stress and rat damage reduced yields. Yield increase due to N application ranged from 0.8 to 1.6 t ha⁻¹. Higher sand content was associated with lowered yields. The low yields in new irrigation schemes caused by sub-optimal crop management practices suggest that farmer-to-farmer learning and extension of good agricultural principles and practices can increase yields. Organizational capacity is also important to ensure the use of common resources such as irrigation water and tractors for land preparation.     

Understanding effects of multiple farm management practices on barley performance

Because of the complexity of farming systems, the combined effects of farm management practices on nitrogen availability, nitrogen uptake by the crop and crop performance are not well understood. To evaluate the effects of the temporal and spatial variability of management practices, we used data from seventeen farms and projections to latent structures analysis (PLS) to examine the contribution of 11 farm characteristics and 18 field management practices on barley performance during the period 2009–2012. Farm types were mixed (crop-livestock) and arable and were categorized as old organic, young organic or conventional farms. The barley performance indicators included nitrogen concentrations in biomass (in grain and whole biomass) and dry matter at two growing stages. Fourteen out of 29 farm characteristics and field management practices analysed best explained the variation of the barley performance indicators, at the level of 56%, while model cross-validation revealed a goodness of prediction of 31%. Greater crop diversification on farm, e.g., a high proportion of rotational leys and pasture, which was mostly observed among old organic farms, positively affected grain nitrogen concentration. The highest average grain nitrogen concentration was found in old organic farms (2.3% vs. 1.7 and 1.4% for conventional and young organic farms, respectively). The total nitrogen translocated in grain was highest among conventional farms (80 kg ha⁻¹ vs. 33 and 39 kg ha⁻¹ for young and old organic farms, respectively). The use of mineral fertilizers and pesticides increased biomass leading to significant differences in average grain yield which became more than double for conventional farms (477 ± 24 g m⁻²) compared to organic farms (223 ± 37 and 196 ± 32 g m⁻² for young and old organic farms, respectively). In addition to the importance of weed control, management of crop residues and the organic fertilizer application methods in the current and three previous years, were identified as important factors affecting the barley performance indicators that need closer investigation. With the PLS approach, we were able to highlight the management practices most relevant to barley performance in different farm types. The use of mineral fertilizers and pesticides on conventional farms was related to high cereal crop biomass. Organic management practices in old organic farms increased barley N concentration but there is a need for improved management practices to increase biomass production and grain yield. Weed control, inclusion of more leys in rotation and organic fertilizer application techniques are some of the examples of management practices to be improved for higher N concentrations and biomass yields on organic farms.     

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.     

Effects of ozone on sugar beet grown in open-top chambers

Sugar beet (Beta vulgaris cv. Patriot) plants were grown on field plots and in open-top chambers (OTCs) in two successive years. In the OTC treatments, plants were exposed to charcoal filtered air, unfiltered air or unfiltered air enriched with additional ozone (O₃). Ozone exposure continued for almost 5 months and the 8-h average concentration was raised from 34 to 39 nL L⁻¹ in the ambient air chambers to 62 nL L⁻¹ in the ozone enriched chambers. In both years, the AOT40 exposure index in the ozone enriched chambers exceeded 30 μL L⁻¹ h during the 5-month exposure period compared to 6.5 and 2.9 μL L⁻¹ h in ambient air in 2003 and 2004, respectively. Visible symptoms in the form of small white necrotic flecks appeared in both seasons in the ozone enriched chambers. When the data for both years were analysed statistically, a significant reduction of root yield of 6% and a slight reduction of sugar content were detected. These changes resulted in an overall reduced sugar yield ha⁻¹ of about 9%. Although the sensitivity of sugar beet to ozone is highly variety-dependent, in general this biennial crop appears less sensitive than annual crops such as wheat and potato. Ozone has limited effects on quality parameters in sugar beet, although an increase in α-amino-N content was observed, in agreement with the increased nitrogen content resulting from ozone exposure of wheat and potato.Enclosure within the OTCs increased aboveground biomass but decreased root yield (fresh biomass) and sugar content. These effects were most likely caused by a reduction of radiation by the chamber walls and annulus. The increased temperature in the chambers reduced yield quality by increasing mineral content.     

Exploring options to combine high yields with high nitrogen use efficiencies in irrigated rice in China

In Jiangsu province, Southeast China, high irrigated rice yields (6–8000 kg ha⁻¹) are supported by high nitrogen (N) fertilizer inputs (260–300 kg N ha⁻¹) and low fertilizer N use efficiencies (recoveries of 30–35%). Improvement of fertilizer N use efficiency can increase farmers’ profitability and reduce negative environmental externalities. This paper combines field experimentation with simulation modeling to explore N fertilizer management strategies to realize high yields, while increasing N use efficiency. The rice growth model ORYZA2000 was parameterized and evaluated using data from field experiments carried out in Nanjing, China. ORYZA2000 satisfactorily simulated yield, crop biomass and crop N dynamics, and the model was applied to explore options for different N-fertilizer management regimes, at low and high levels of indigenous soil N supply, using 43 years of historical weather data.On average, yields of around 10–11,000 kg ha⁻¹ were realized (simulated and in field experiments) with fertilizer N rates of around 200 kg ha⁻¹. Higher fertilizer doses did not result in substantially higher yields, except under very favorable weather conditions when yields exceeding 13,000 kg ha⁻¹ were calculated. At fertilizer rates of 150–200 kg ha⁻¹, and at the tested indigenous soil N supplies of 0.6–0.9 kg ha⁻¹ day⁻¹, high fertilizer N recovery (53–56%), partial N productivity (50–70 kg kg⁻¹) and agronomic N use efficiency (20–30 kg kg⁻¹) were obtained with application in three equal splits at transplanting, panicle initiation and booting. Increasing the number of splits to six did not further increase yield or improve any of the N use efficiency parameters.     

Propensity for seed-mediated gene flow from potato crops and potential consequences for the coexistence of GM and non-GM potato systems

Potato is a critical crop to European growers, both economically and agronomically as a break crop in the standard cereal rotation. As studies investigating the agronomic performance and environmental impact of disease resistant, GM potatoes come to an end across several sites in Europe, past discussions on achieving the effective coexistence of GM and equivalent non-GM crops have too often focussed on the purported risk of excessive pollen-mediated gene flow. Dependent on the crop in question, the impact of seed loss pre- and/or post-harvest presents a greater challenge to securing efficient coexistence practises. To examine this issue for potato, a total of 51 fields that had been commercially cultivated with potatoes were surveyed in two separate cohorts for post-harvest tuber loss and/or volunteer emergence. Across 17 fields studied, the average post-harvest tuber loss was recorded at 141,758 ± 911 tubers ha⁻¹, with volunteer establishment in the following crop ranging from 400 ± 59 ha⁻¹ to 55,698 ± 47 ha⁻¹. In parallel, by surveying a separate cohort of 34 commercial fields an average of 30,789 ± 2658 volunteer ha⁻¹ was recorded in the subsequent cereal crop, with a repeat survey made after an additional year indicating an 87.2% reduction in this mean number of volunteers across the 34 fields (P < 0.001). Of the additional variables studied only location (P < 0.001), herbicide application (P = 0.037) and potato variety used (P = 0.045) significantly influenced volunteer proliferation. Volunteer fecundity was confirmed with upto 3 tubers produced per 1st generation volunteer, with tuber yield from the 2nd generation volunteers reduced significantly (P < 0.001). Assessments of the tuber lots from these 2nd generation volunteers confirmed their ability to sprout post-dormancy, therefore, indicating the potential for 3rd generation volunteers to emerge. Combined, the datasets confirm the potential for significant seed-mediated gene flow from commercial potato systems; indicating that the regulated 0.9% coexistence threshold would in all probability be compromised if GM potatoes were grown in rotations of 1:4 years or less, in the absence of a comprehensive tuber loss and/or volunteer management system.     

The effect of organic and conventional management on the yield and quality of wheat grown in a long-term field trial

The performance of winter wheat was evaluated under organic (ORG) and conventional (CON) management systems in the Nafferton Factorial Systems Comparison (NFSC) long-term field trial. The present study separates out the crop protection and fertility management components of organic and conventional production systems using two levels each of crop protection (CP) and fertility management (FM). The experimental design provided the four combinations of crop protection and fertility (CON-CP CON-FM, CON-CP ORG-FM, ORG-CP CON-FM and ORG-CP ORG-FM) to evaluate their effects on yield, quality (protein content and hectolitre weight) and disease levels during the period 2004–2008. The conventional management system (CON-CP CON-FM) out-yielded the organic management system (ORG-CP ORG-FM) in all years by an average of 3.1 t ha⁻¹, i.e. 7.9 t ha⁻¹ vs. 4.8 t ha⁻¹. Fertility management was the key factor identified limiting both yield and grain protein content in the ORG management system. The CON-FM produced on average a 3% higher protein content than ORG-FM in all years (12.5% vs. 9.7%). However the ORG-CP system produced higher protein levels than CON-CP although it was only in 2008 that this was statistically significant. In contrast to protein content it was ORG-FM which produced a higher hectolitre weight than the CON-FM system (71.6 kg hl⁻¹ vs. 71.0 kg hl⁻¹). The clear and significant differences in yield and protein content between the ORG-FM and CON-FM systems suggest a limited supply of available N in the organic fertility management system which is also supported by the significant interaction effect of the preceding crop on protein content. The pRDA showed that although fertilisation had the greatest effect on yield, quality and disease there was also a considerable effect of crop protection and the environment.     

Light grazing of crop residues by sheep in a Mediterranean-type environment has little impact on following no-tillage crops

Crop residue is often grazed by sheep after harvest, over the dry summer period from December to March in Mediterranean environments. However, soil cover provided by crop residues is a key component of conservation agriculture for maintaining favourable soil structure and high yields.A series of 31 site × year experiments was conducted to assess the effect of summer stubble grazing on residue levels and following crop yields. Relatively light grazing, with stocking rates below 10 dry sheep equivalent (DSE) and between 90 and 471 DSE days ha⁻¹, had no significant effect on the amount of residue, soil properties, soil water, weeds or yield in the following crop. The main effect of grazing was to knock down and scatter the standing crop residues. However, longer term grazing at relatively high intensity (956 DSE days ha⁻¹) on heavy soil, over both summer and winter, as in a pasture phase, did significantly reduce residue levels, infiltration and yield (by 59%). The effect of summer grazing on soil mineral N was small and inconsistent, with increased mineral N, by about 3–7 kg N ha⁻¹, following grazing at two of the 13 sites. By contrast, higher mineral N, by 2–15 kg N ha⁻¹, was measured in the un-grazed plots at three of the 13 sites. This was due to increased growth of legume pastures in the absence of grazing.More research is needed to confirm the yield effects when cropping after an annual pasture/fallow that is grazed over summer and winter, particularly on different soil types.     

White clover living mulch reduces the need for phosphorus fertilizer application to corn

White clover living mulch (LM) increases the uptake of phosphorus (P) and the yield of the main crop by promoting the colonization of arbuscular mycorrhiza (AM). However, the extent to which the P fertilizer application rate can be reduced by using LM is not yet known. This study aimed to address this question. Two field experiments were conducted from 2008 to 2009 (Experiment 1) and from 2009 to 2010 (Experiment 2) at the fields where the available P of soil fluctuated near the lower limit of the optimum P level (43.6 mg kg⁻¹: Truog method). Experiment 1 had a randomized block design, and Experiment 2 had a split-plot design with a factorial arrangement of two cropping systems (LM and no LM) with three P application treatments (0 kg ha⁻¹, 43.6 kg ha⁻¹, and 87.3 kg ha⁻¹). LM increased P concentrations in the early stages of growth and the yield of corn. This can be attributed to the increased AM colonization rate in the early stages of growth. The yield and total digestible nutrient yield of corn in LM with no P application was comparable to the maximum yield in no LM with or without P application. Therefore, LM could make unnecessary P fertilization in soils where P fertilization is required for silage corn.