Environmental performances of giant reed (Arundo donax L.) cultivated in fertile and marginal lands: A case study in the Mediterranean

Perennial rhizomatous grasses (PRGs) tend to have a high yield combined with a low environmental impact. Cultivation in marginal or poorly cultivated land is recommended in order not to compromise food security and to overcome land use controversies. However, the environmental impacts of using different types of soil are still unclear. We thus assessed the environmental impact of two giant reed (GR) systems cultivated in a fertile soil (FS) and in a marginal soil (MS) through a cradle-to-plant gate LCA. We analyzed energy balance, GHG emissions (including LUC, not including iLUC), and the main impacts on air, water and soil quality. In both systems the annualized soil carbon sequestration was more than twofold the total GHG emitted, equal to −6464 kg CO₂eq ha⁻¹ in FS and −5757 kg CO₂eq ha⁻¹ in MS. Overall, soil characteristics affected not only GR yield level, but also its environmental impact, which seems to be higher in the MS system both on a hectare and tonne basis. The production of GR biomass in marginal soil could thus lead to higher environmental impacts and a more extensive land requirement.     

The new nitrification inhibitor 3,4-dimethylpyrazole succinic (DMPSA) as an alternative to DMPP for reducing N2O emissions from wheat crops under humid Mediterranean conditions

Nowadays agricultural practices are based in the use of N fertilizers which can lead to environmental N losses. These losses can occur as nitrous oxide (N₂O) emissions as result of the microbial processes of nitrification and denitrification. N₂O together with carbon dioxide (CO₂) and methane (CH₄) are the strongest greenhouse gases (GHG) associated with agricultural soils. Nitrification inhibitors (NI) have been developed with the aim of decreasing fertilizer-induced N losses and increasing N efficiency. One of the most popular NI is the 3,4-dimethylpyrazol phosphate (DMPP) which have proven to be an advisable strategy to mitigate GHG emissions while maintaining crops yield. A new NI, 3,4-dimethylpyrazole succinic (DMPSA), has been developed. The objective of this study was to compare the impact of the new nitrification inhibitor DMPSA on greenhouse gases emissions, wheat yield and grain protein with respect to DMPP. For this purpose a field-experiment was carried out for two years. Fertilizer dose, with and without NIs, was 180 kg N ha⁻¹ applied as ammonium sulphate (AS) split in two applications of 60 kg N ha⁻¹ and 120 kg N ha⁻¹, respectively. A single application of 180 kg N ha⁻¹ of AS with NIs was also made. An unfertilized treatment was also included. The new nitrification inhibitor DMPSA reduces N₂O emissions up to levels of the unfertilized control treatment maintaining the yield and its components. The DMPSA shows the same behavior as DMPP in relation to N₂O fluxes, as well as wheat yield and quality. In spite of applying a double dose of N at stem elongation than at tillering, N₂O losses from that period are lower than at tillering as a consequence of the influence of soil water content and temperature reducing the N₂O/N₂ ratio by denitrification. NI efficiency in reducing N₂O losses is determined by the magnitude of the losses from the AS treatment.     

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.     

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.     

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.     

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.     

Effects of irrigation and nitrogen fertilization on the greenhouse gas emissions of a cropping system on a sandy soil in northeast Germany

Irrigation induces processes that may either decrease or increase greenhouse gas emissions from cropping systems. To estimate the net effect of irrigation on the greenhouse gas emissions, it is necessary to consider changes in the crop yields, the content of soil organic carbon and nitrous oxide emissions, as well as in emissions from the use and production of machinery and auxiliary materials. In this study the net greenhouse gas emissions of a cropping system on a sandy soil in northeast Germany were calculated based on a long-term field experiment coupled with two-year N₂O flux measurements on selected plots. The cropping system comprised a rotation of potato, winter wheat, winter oil seed rape, winter rye and cocksfoot each under three nitrogen (N) fertilization intensities with and without irrigation. Total greenhouse gas emissions ranged from 452 to 3503 kg CO_2-eq ha⁻¹ and 0.09 to 1.81 kg CO_2-eq kg⁻¹ yield. Application of an adequate amount of N fertilizer led to a decrease in greenhouse gas emissions compared to zero N fertilization whereas excessive N fertilization did not result in a further decrease. Under N fertilization there were no significant differences between irrigation and non-irrigation. Increases in greenhouse gas emissions from the operation, production and maintenance of irrigation equipment were mainly offset by increases in crop yield and soil organic carbon contents. Thus, on a sandy soil under climatic conditions of north-east Germany it is possible to produce higher yields under irrigation without an increase in the yield-related greenhouse gas emissions.     

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.     

Efficiency in sugar beet cultivation related to field history

The concept of sustainable intensification in crop production has become more and more important over the last years. Calls for an efficient production demand an increase in yield without extending the agricultural area or increasing the amount of agricultural inputs. Thus, our study aimed to identify which variables influence the efficiency in crop cultivation in Central Europe and how we can explain the variances between fields. The data base for the present study was a survey among sugar beet farmers in all parts of Germany in the years 2010–2014. In order to structure the fields, variables representing environment, management and farm characteristics were extracted. The performed analysis according to components (principal component analysis) did not result in a nationwide structure of the data. Thus, fields were grouped according to similar preconditions such as regions and crop rotations. Sugar yield ranged from 12.5 t ha⁻¹ in 2010 to 15.4 t ha⁻¹ in 2014 on nationwide average. The median value for N fertilization over all fields and years was 137.4 kg ha⁻¹, the median treatment index (TI) reached 3.7, the median field evaluation index (Ackerzahl) was 70 and the median field size 8 ha. We found that over 50% of the variance among the data was explained by environment, management and farm characteristics. The comparison of fields on a regional basis was more sensible than on a nationwide basis as the variance of farms and fields was too broad for a useful clustering. It was concluded that the adaption of the farmer’s management to regional specific conditions is an opportunity to reduce yield gaps and to increase efficiency in terms of a sustainable intensification in sugar beet production.     

Alternative strategies for nitrogen fertilization of overwinter processing spinach (Spinacia oleracea L.) in Southern Italy

To identify the best practice for nitrogen (N) fertilization of overwinter processing spinach, two field experiments were carried out in the Foggia plain (Southern Italy), one of the most vocated area for leafy vegetables production. The field trials were aimed to define and suggest the proper fertilizer dose, typology and the right time of application. Experiment 1 evaluated four N fertilizer doses (0, 150, 225, 300 kg ha⁻¹) in a two-year field trial. Experiment 2 was aimed to assess the effect of the split distribution of prilled urea fertilizer in comparison with the application of nitrification inhibitor (DMPP) containing urea fertilizer, broadcasted at sowing.Spinach yield, yield quality (nitrate – NO₃⁻ – and carotenoids content), N-use efficiency and risk of soil nitrate (NO₃⁻-N) leaching were evaluated. The processing spinach yielded 37.8 and 3.6 t ha⁻¹ of fresh and dry yield, respectively (average of the two experiments). Fresh and dry yield among the fertilizing treatments were similar. Also the β-carotene and the lutein content of spinach leaves (19.5 and 38.1 mg kg⁻¹, respectively) were not affected by the N fertilizer dose. Conversely, the N dose strongly influenced the NO₃⁻ content of the leafy vegetable tissues (1286 mg kg⁻¹ on average, 58% lower than the limits imposed by the EC regulation). As expected, the different rainfall pattern influenced both the leaf NO₃⁻ content and the risk of soil NO₃⁻-N leaching. The results achieved demonstrated that, in order to get a favorable trade-off, among yield, yield quality, N-use efficiency and environmental impact, the processing spinach growers of the Foggia plain area should be encouraged to apply 225 kg N ha⁻¹ as maximum fertilization rate. Also, the split urea fertilizer application appeared as the more effective strategy for N fertilization of overwinter spinach in comparison with the use of the nitrification inhibitor containing urea fertilizer, being the last strategy not able to adequately match the N crop demand.     

Maize yield and water balance is affected by nitrogen application in a film-mulching ridge–furrow system in a semiarid region of China

Poor soil and drought stress are common in semiarid areas of China, but maize has a high demand for nitrogen (N) and water. Maize production using the technique of double ridges and furrows mulched with plastic film are being rapidly adopted due to significant increases in yield and water use efficiency (WUE) in these areas. This paper studied N use and water balance of maize crops under double ridges and furrows mulched with plastic-film systems in a semiarid environment over four growing seasons from 2007 to 2010. To improve precipitation storage in the non-growing season, the whole-year plastic-film mulching technique was used. There were six treatments which had 0, 70, 140, 280, 420 or 560 kg N ha⁻¹ applied in every year for maize. In April 2011, spring wheat was planted in flat plots without fertilizer or mulch following four years of maize cultivation. After four years, all treatments not only maintained soil water balance in the 0–200 cm soil layer but soil water content also increased in the 0–160 cm soil layer compared to values before maize sowing in April 2007. However, under similar precipitation and only one season of spring wheat, soil water content in the 0–160 cm soil layer sharply decreased in all treatments compared to values before sowing in April 2011. Over the four years of maize cultivation, average yield in all treatments ranged from 4071 to 6676 kg ha⁻¹ and WUE ranged from 18.2 to 28.2 kg ha⁻¹ mm⁻¹. In 2011, the yield of spring wheat in all treatments ranged from 763 to 1260 kg ha⁻¹ and WUE from 3.5 to 6.5 kg ha⁻¹ mm⁻¹. The potential maximum grain yield for maize was 6784 kg ha⁻¹ with 360 kg N ha⁻¹ applied for four years, but considerable NO₃N accumulated in the soil profile. A lesser application (110 kg N ha⁻¹) to this tillage system yielded in 82% of the maximum, increased nitrogen use efficiency and mitigated the risk of nitrogen loss from the system. This study suggests that double ridge–furrow and whole-year plastic-film mulching could sustain high grain yields in maize with approximately 110 kg N ha⁻¹ and maintain soil water balance when annual precipitation is >273 mm in this semiarid environment.     

Effect of irrigation and nitrogen fertilization on the production of biogas from maize and sorghum in a water limited environment

The expansion of biogas production from anaerobic digestion in the Po Valley (Northern Italy) has stimulated the cultivation of dedicated biomass crops, and maize in particular. A mid-term experiment was carried out from 2006 to 2010 on a silt loamy soil in Northern Italy to compare water use and energy efficiency of maize and sorghum cultivation under rain fed and well-watered treatments and at two rates of nitrogen fertilization. The present work hypothesis were: (i) biomass sorghum, for its efficient use of water and nitrogen, could be a valuable alternative to maize for biogas production; (ii) reduction of irrigation level and (iii) application of low nitrogen fertilizer rate increase the efficiency of bioenergy production. Water treatments, a rain fed control (I0) and two irrigation levels (I1 and I2; only one in 2006 and 2009), were compared in a split–split plot design with four replicates. Two fertilizer rates were also tested: low (N1, 60 kg ha⁻¹ of nitrogen; 0 kg ha⁻¹ of nitrogen in 2010) and high (N2, 120 kg ha⁻¹ of nitrogen; 100 kg ha⁻¹ of nitrogen in 2010). Across treatments, sorghum produced more aboveground biomass than maize, respectively 21.6 Mg ha⁻¹ and 16.8 Mg ha⁻¹ (p < 0.01). In both species, biomass yield was lower in I0 than in I1 and I2 (p < 0.01), while I1 and I2 did differ significantly. Nitrogen level never affected biomass yield. Water use efficiency was generally higher in sorghum (52 kg ha⁻¹ mm⁻¹) than in maize (38 kg ha⁻¹ mm⁻¹); the significant interaction between crop and irrigation revealed that water use efficiency did not differ across water levels in sorghum, whereas it significantly increased from I0 and I1 to I2 in maize (p < 0.01). The potential methane production was similar in maize and sorghum, while it was significantly lower in I0 (16505 MJ ha⁻¹) than in I1 and I2 (21700 MJ ha⁻¹). The only significant effect of nitrogen fertilization was found in the calculation of energy efficiency (ratio of energy output and input) that was higher in N1 than in N2 (p < 0.01). These results support the hypothesis that (i) sorghum should be cultivated rather than maize to increase energy efficiency, (ii) irrigation level should replace up to 36% of ETr and (iii) nitrogen fertilizer rate should be minimized to maximize the efficiency in biomass production for anaerobic digestion in the Po Valley.     

The effects of dairy cattle manure and mineral N fertilizer on irrigated maize and soil N and organic C

This work was aimed at providing a sustainable approach in the use of manure in irrigated maize crop under Mediterranean climatic conditions. To this end, the effect of continuous annual applications of dairy cattle manure, combined or not with mineral N fertilizer, on the following parameters was studied: grain yield, grain and plant N concentration, N uptake by plant, N use efficiency, and soil N and organic carbon. The experiment was conducted in a furrow-irrigated sandy soil under dry Mediterranean conditions during seven years. Three different rates of cattle manure (CM): 0, 30 and 60 Mg ha⁻¹, were applied each year before sowing. These CM rates were combined with four mineral N rates (0, 100, 200 and 300 kg N ha⁻¹) applied at sidedress.On average, the highest grain yields during the 7 years were obtained with the combination of CM at 30 Mg ha⁻¹ and mineral fertilizer and with CM at 60 Mg ha⁻¹ without mineral fertilizer. With CM at 30 Mg ha⁻¹, mineral fertilizer increased yields during most of the growing seasons, meanwhile with CM at 60 Mg ha⁻¹, there was not any significant effect of the joint application of mineral fertilizer on yields. Overall, best results were obtained exceeding maximum rates according to present legislation. The mean apparent nitrogen recovery (ANR) fraction during the 7 seasons was 29% for N exclusively applied as CM. Overall, increased N rates applied as CM resulted in decreased ANRs. However, ANR with CM at 30 and 60 Mg ha⁻¹ increased during the first two seasons. This increased ANR ascribed to mineralization of residual organic N applied in previous seasons explained the increasing yields observed in the treatments along the study.The application of CM during 7 years increased the soil organic carbon in the first 30 cm by 5.7 and 9.9 Mg ha⁻¹ with CM at 30 and 60 Mg ha⁻¹, respectively, when compared to the initial stock. Thus, manure-based fertilization could be an alternative to mineral fertilizer in order to achieve high maize yields while improving soil quality under dry Mediterranean conditions.     

Steps toward alternative farming system in rice

An experiment was conducted on rice, in old alluvial soil zone, with bio-fertilizer and different doses of organic manure and chemical fertilizer to develop an alternative farming system which is productive, profitable, enhances soil health and conserves the natural resources over a long term. The experiment was conducted for four consecutive years (2007–2010) and it has been observed that 40% N and 25% P chemical fertilizer can safely be supplemented by low-cost, natural resource based bio-fertilizer (Azotobacter sp. and PSB) at 12 kg ha⁻¹ and organic manure (FYM) at 10.00 t ha⁻¹ to achieve long-term sustainability in rice cultivation that is more productive and profitable.     

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.     

Energy balance of winter oilseed rape (Brassica napus L.) cropping as related to nitrogen supply and preceding crop

Data from a field experiment (1995–2000) conducted on a fertile sandy loess in the Hercynian dry region of central Germany were used to determine the energy efficiency of winter oilseed rape (Brassica napus L.) as affected by previous crop and nitrogen (N) fertilization. Depending on the previous crop, winter oilseed rate was cultivated in two different crop rotations: (1) winter barley (Hordeum vulgare L.)–winter oilseed rape–winter wheat (Triticum aestivum L.), and (2) pea (Pisum sativum L.)–winter oilseed rape–winter wheat. Fertilizer was applied to winter oilseed rape as either calcium ammonium nitrate (CAN) or cattle manure slurry. The N rates applied to winter oilseed rape corresponded to 0, 80, 160 and 240 kg N ha⁻¹ a⁻¹.Results revealed that different N management strategies influenced the energy balance of winter oilseed rape. Averaged across years, the input of energy to winter oilseed rape was highly variable ranging from 7.42 to 16.1 GJ ha⁻¹. Lowest energy input occurred when unfertilized winter oilseed rape followed winter barley, while the highest value was obtained when winter oilseed rape received 240 kg N ha⁻¹ organic fertilization and followed winter barley. The lowest energy output (174 GJ ha⁻¹), energy from seed and straw of winter oilseed rape, was observed when winter oilseed rape receiving 80 kg N ha⁻¹ as organic fertilizer followed winter barley. The energy output increased to 262 GJ ha⁻¹ for winter oilseed rape receiving 240 kg N ha⁻¹ as mineral fertilizer followed pea. The energy efficiency was determined using the parameters energy gain (net energy output), energy intensity (energy input per unit grain equivalent GE; term GE is used to express the contribution that crops make to the nutrition of monogastric beings), and output/input ratio. The most favourable N rate for maximizing energy gain (250 GJ ha⁻¹) was 240 kg N ha⁻¹, while that needed for minimum energy intensity (91.3 MJ GE⁻¹) was 80 kg N ha⁻¹ and for maximum output/input ratio (29.8) was 0 kg N ha⁻¹.     

Conservation Agriculture practices reduce the global warming potential of rainfed low N input semi-arid agriculture

Conservation tillage and crop rotations improve soil quality. However, the impact of these practices on greenhouse gas (GHG) emissions and crop yields is not well defined, particularly in dry climates. A rainfed 2-year field-experiment was conducted to evaluate the effect of three long-term (17–18 years) tillage systems (Conventional Tillage (CT), Minimum Tillage (MT) and No Tillage (NT)) and two cropping systems (rotational wheat (Triticum aestivum L.) preceded by fallow, and wheat in monoculture), on nitrous oxide (N₂O) and methane (CH₄) emissions, during two field campaigns. Soil mineral N, water-filled pore space, dissolved organic carbon (C) and grain yield were measured and yield-scaled N₂O emissions, N surplus and Global Warming Potentials (GWP) were calculated. No tillage only decreased cumulative N₂O losses (compared to MT/CT) during campaign 1 (the driest campaign with least fertilizer N input), while tillage did not affect CH₄ oxidation. The GWP demonstrated that the enhancement of C stocks under NT caused this tillage management to decrease overall CO₂ equivalent emissions. Monoculture increased N₂O fluxes during campaign 2 (normal year and conventional N input) and decreased CH₄ uptake, as opposed to rotational wheat. Conversely, wheat in monoculture tended to increase soil organic C stocks and therefore resulted in a lower GWP, but differences were not statistically significant. Grain yields were strongly influenced by climatic variability. The NT and CT treatments yielded most during the dry and the normal campaign, and the yield-scaled N₂O emissions followed the same tendency. Minimum tillage was not an adequate tillage management considering the GWP and the yield-scaled N₂O emissions (which were 39% lower in NT with respect to MT). Regarding the crop effect, wheat in rotation resulted in a 32% increase in grain yield and 31% mitigation of yield-scaled N₂O emissions. Low cumulative N₂O fluxes (<250 g N₂O-N ha⁻¹ campaign⁻¹) highlighted the relevance of soil organic C and CO₂ emissions from inputs and operations in rainfed semi-arid cropping systems. This study suggests that NT and crop rotation can be recommended as good agricultural practices in order to establish an optimal balance between GHGs fluxes, GWP, yield-scaled N₂O emissions and N surpluses.     

Pig slurry fertilization in a double-annual cropping forage system under sub-humid Mediterranean conditions

In areas of Southern Europe with very intensive pig production, most of the pig slurry (PS) is applied as fertilizer. However, in the European Union, no more than 170 kg N ha⁻¹ year⁻¹ can be applied in nitrate vulnerable zones (NVZs) from livestock manures. In this context, a six-year trial was conducted for a maize-triticale double-annual forage cropping rotation under rainfed conditions. Four different N rates were applied (0, 170, 250 and 330 kg N ha⁻¹ year⁻¹), to evaluate their effect on crop yield, N uptake, unrecovered N and soil nitrate content. The corresponding PS rates were defined as zero (PS 0), low (PSL) medium (PSM) and high (PSH). The annual average dry matter (DM) yields (maize + triticale) for the PS fertilization treatments PS0, PSL, PSM and PSH were 12.6, 17.7, 20.2 and 22.0 Mg DM ha⁻¹, respectively. Maize DM yield was influenced mainly by weather conditions, and triticale DM yield was clearly influenced by initial soil NO₃⁻-N and PS fertilization rates. Unrecovered N was affected by PS fertilization rate and initial soil NO₃⁻-N content. A residual effect of the PS when applied to maize had an important effect on soil NO₃⁻-N and subsequent triticale DM yield. Moreover, total annual average unrecovered N, considering the sum of both crops (maize + triticale), were 91, 144, and 222 kg N ha⁻¹ in PSL, PSM and PSH, respectively. In order to avoid part of this unrecovered N, mainly by lixiviation of nitrates, PS fertilization in triticale should be applied as side dressing at tillering. The application of N, in the form of PS, at rates higher than the legally permitted maximum of 170 kg N ha⁻¹ year⁻¹, may result in better yields. However, high rates of PS fertilization may originate in significantly lower N use efficiency and a higher potential environmental impact in double-cropping systems, practiced in rainfed sub-humid Mediterranean conditions.     

Strategies to optimize nitrogen efficiency when fertilizing with pig slurries in dryland agricultural systems

In dryland agricultural systems, pig slurry (PS) is usually applied to cereal crops only at sowing, and slurries accumulate for the rest of the year in pits. In this context, a four-year experiment was established in order to evaluate the feasibility of PS applications at the barley or wheat tillering stage. The main treatments were PS either applied at sowing (25 Mg ha⁻¹) or not, but they alternated after a two-year period. Both were annually combined with eight side-dressing treatments at cereal tillering: mineral N as NH₄NO₃ (M; 60 or 120 kg N ha⁻¹ yr⁻¹), PS from fattening pigs (PSf; 17, 30, 54 Mg ha⁻¹ yr⁻¹), PS from sows (PSs; 25, 45, 81 Mg ha⁻¹ yr⁻¹) and a treatment without N. The combined fertilization treatments were 18 plus a control (no N applied). In the context of crop rotation, the biennial alternation of PS applied at sowing allowed the control of soil nitrate increments, while PS side-dressing improved N recovery compared with a unique application at sowing. The highest yields (>3.6 Mg ha⁻¹ yr⁻¹) were obtained with an annual average (4-yr) N rate close to 173 kg N ha⁻¹ (±40 kg N ha⁻¹). The best overall strategies corresponded to PSs side-dressings of 50–90 kg N ha⁻¹. These PSs rates also recorded the highest values on the five calculated N-efficiency indexes, which were higher than or similar to results from M side-dressings or those recorded in the literature. These similarities (M vs. PSs) were also shown by the reduction of unaccounted-for N inside the overall N balance. Thus, split PS application during the crop cycle is a sound fertilization option in dryland systems.     

Effect of free air carbon dioxide enrichment combined with two nitrogen levels on growth,yield and yield quality of sugar beet: Evidence for a sink limitation of beet growth under elevated CO2

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate the growth of C₃ crops. However, little information exists about the effect of elevated [CO₂] on biomass production of sugar beet, and data from field experiments are lacking. In this study, sugar beet was grown within a crop rotation over two rotation cycles (2001, 2004) at present and elevated [CO₂] (375 μl l^?1 and 550 μl l^?1) in a free air CO₂ enrichment (FACE) system and at two levels of nitrogen supply [high (N2), and 50% of high (N1)], in Braunschweig, Germany. The objective of the present study was to determine the CO₂ effect on seasonal changes of leaf growth and on final biomass and sugar yield. Shading treatment was included to test whether sugar beet growth is sink limited under elevated [CO₂]. CO₂ elevation did not affect leaf number but increased individual leaf size in early summer resulting in a faster row closure under both N levels. In late summer CO₂ enrichment increased the fraction of senescent leaves under high but not low N supply, which contributed to a negative CO₂ effect on leaf area index and canopy chlorophyll content under high N at final harvest. Petioles contained up to 40% water-soluble carbohydrates, which were hardly affected by CO₂ but increased by N supply. More N increased biomass production by 21% and 12% in 2001 and 2004, respectively, while beet and sugar yield was not influenced. Concentration of α-amino N in the beet fresh weight was increased under low N and decreased under high N by CO₂ enrichment. The CO₂ response of total biomass, beet yield and white sugar yield was unaffected by N supply. Averaged over both N levels elevated [CO₂] increased total biomass by 7% and 12% in 2001 and 2004, respectively, and white sugar yield by 12% and 13%. The shading treatment in 2004 prevented the decrease in leaf area index under elevated [CO₂] and high N in September. Moreover, the CO₂ effect on total biomass (24%) and white sugar yield (28%) was doubled as compared to the unshaded conditions. It is concluded that the growth of the storage root of sugar beet is not source but sink limited under elevated [CO₂], which minimizes the potential CO₂ effect on photosynthesis and beet yield.