Hay yield and nitrogen harvest in smooth bromegrass mixtures with alfalfa and red clover in relation to nitrogen application

An experiment was conducted in order to investigate hay yield and nitrogen harvest in binary smooth bromegrass (Bromus inermis Leyss cv. Tohum Islah) mixtures with alfalfa (Medicago sativa L. cv. Kayseri) and red clover (Trifolium pratense L. cv. Tohum Islah) in Erzurum, Turkey for 5 years between 1991 and 1995. The Hay yield, nitrogen harvest, protein concentration and land equivalent ratio (LER) in the mixtures with alternating rows of 1:1, 2:1 and 1:2 of smooth bromegrass with alfalfa and red clover were compared to those in pure legume stands without any N-fertilizer application or pure smooth bromegrass stands that received 0, 50, 100 and 150 kg ha⁻¹ N. The mixtures had no N fertilization apart from 40 kg N ha⁻¹ in the establishment year. The dry matter production in all the mixtures receiving no N fertilizer application was higher than in pure legume stands. Pure grass stands were sustained only with the application of 150 kg ha⁻¹ N. The highest hay yields were obtained from the mixtures of smooth bromegrass (Sb) with red clover (Rc) (2Rc 1Sb) (14.65 t ha⁻¹) and with alfalfa (A) (1A 1 Sb) (14.49 t ha⁻¹). Although N application increased Sb yields in pure stands, the highest yields obtained with N fertilization were still lower than the yields in the mixtures without N application. The superiority of the mixtures was also reflected by their large N harvests (e.g. 355.9 kg N ha⁻¹ in 2Rc 1Sb plots) compared to pure Rc (317.8 kg N ha⁻¹), pure A (294.3 kg N ha⁻¹) and pure Sb stands that received 150 kg N ha⁻¹. The nitrogen harvest increased in pure Sb plots as the N doses applied increased. Furthermore, the protein concentration of the hay from the mixtures (158.2–165.7 mg g⁻¹) was equal to that of the pure A stands (165.7 mg g⁻¹) and higher than that of pure Sb stands (122.9 mg g⁻¹ at 150 kg N ha⁻¹ application) although the hay from pure Rc plots had the highest protein concentration (179.3 mg g⁻¹). The LER values were also higher in the mixtures (e.g. 1.28 in 1A 1Sb and 1.28 in 2Rc 1Sb plots) compared with the pure stands. The mixture plots also had a more balanced temporal distribution of hay. The grass component was more productive in early spring, whereas the legume fractions grew better in the summer. In conclusion, for a sustainable production of high-quality hay and greater N harvests without using N fertilizers, binary mixtures of Sb with A in alternating rows (1A 1Sb) were recommended for long-purpose stands and in alternation with double red clover rows (2Rc 1Sb) for short purpose stands under similar conditions. N application could be eliminated in the grass–legume mixtures without any yield depression.     

Agronomic evaluation of unacidulated and partially acidulated Minjingu and Chilembwe phosphate rocks for clover production in Ethiopia

Most soils in sub-Saharan Africa are P deficient, but the high cost of water-soluble P fertilizers limits the use of P fertilizers by resource-poor farmers. A low-cost alternative is to apply phosphate rocks. We evaluated the effectiveness of unacidulated (PR), 25% partially acidulated (PAPR25), and 50% partially acidulated (PAPR50) Minjingu and Chilembwe phosphate rocks relative to triple superphosphate (TSP) on Trifolium quartinianum grown on a Vertisol in the Ethiopian highlands. The fertilizers were applied once at 0–80 kg P ha⁻¹ and their effects were followed in four consecutive clover crops. In the Minjingu phosphate rock experiment, clover DM yields without applied P were below 1 t DM ha⁻¹ in all except the first of four consecutive crops. With P application, herbage yields reached as high as 14 t ha⁻¹. Significant (P<0.05) effects of P on clover DM and P uptake were observed at least up to crop 3. Over all the four crops, PR was 114%, PAPR25 was 113% and PAPR50 was 107% as effective as TSP in increasing clover herbage yields. The corresponding relative responses in P uptake were: 128, 121 and 112% for PR, PAPR25 and PAPR50, respectively. The substitution rates in herbage yields were: 130% for PR, 128% for PAPR25 and 114% for PAPR50 while those for P uptake were 164% for PR, 146% for PAPR25 and 125% for PAPR50. In the Chilembwe phosphate rock experiment, clover DM yields without applied P were below 1.3 t DM ha⁻¹ in the five years of the study. With P application, herbage yields reached as high as 7 t ha⁻¹. Significant effects of P on clover DM and P uptake were observed only in the first two crops. Over all the five crops, PR was 27%, PAPR25 was 57% and PAPR50 was 73% as effective as TSP in increasing clover herbage yields. The corresponding relative responses in P uptake were 18, 49 and 59% for PR, PAPR25 and PAPR50, respectively. The substitution rates in herbage yields were 7% for PR, 32% for PAPR25 and 53% for PAPR50 while those for P uptake were 3% for PR, 24% for PAPR25 and 35% for PAPR50. It was concluded that raw Minjingu phosphate rock is highly effective on clover in these Vertisols and partial acidulation is not necessary, but raw Chilembwe phosphate rock is ineffective and 50% partial acidulation is recommended.     

Effect of spring fertilization on ecosystem services of organic wheat and clover relay intercrops

Nitrogen (N) deficiency and weed infestation are main factors limiting yield and yield stability in organic wheat. Organic fertilizers may be used to improve crop performance but off-farm input costs tend to limit profitability. Instead, forage legumes may be inserted into the crop rotation to improve the N balance and to control weed infestation. In opposition to simultaneous cropping, relay intercropping of legumes in organic winter wheat limits resource competition for the legume cover crop, without decreasing the performance of the associated wheat.The aim of this study is to evaluate the effect of spring organic fertilization on the performance of intercropped legumes and wheat, and on services provided by the legume cover.Two species of forage legumes (Trifolium pratense L. and Trifolium repens L.) were undersown in winter wheat (Triticum aestivum L. cv Lona) in five organic fields during two consecutive crop seasons. Organic fertilizer was composed of feather meal and applied on wheat at legume sowing. The cover crop was maintained after the wheat harvest and destroyed just before sowing maize.Spring organic nitrogen fertilization increased wheat biomass (+35%), nitrogen (+49%), grain yield (+40%) and protein content (+7%) whatever the intercropping treatment. At wheat harvest, red clover biomass was significantly higher than white clover one (1.4 vs. 0.7 t ha⁻¹). Nitrogen fertilization decreased forage legume above-ground biomass at wheat harvest, at approximately 0.5 t ha⁻¹ whatever the specie. No significant difference in forage legume biomass production was observed at cover killing. Nitrogen accumulation in legume above-ground tissues was significantly higher for white clover than for red clover. Both red and white clover species significantly decreased weed infestation at this date. Nitrogen fertilization significantly increased weed biomass whatever the intercropping treatment and decreased nitrogen accumulation in both clover species (−12%).We demonstrated that nitrogen fertilization increased yield of wheat intercropped with forage legume while the performance of legumes was decreased. Legume growth was modified by spring fertilization whatever the species.     

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

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

Mechanical control of clover improves nitrogen supply and growth of wheat in winter wheat/white clover intercropping

The major objective for clover in a winter wheat/white clover intercropping system is to supply nitrogen (N) for the wheat. A field experiment was repeated in 2 years on a loamy sand in Denmark to investigate the possibilities for increasing N supply to the winter wheat by cutting and mulching the clover between the wheat rows. The clover was cut with a weed brusher on three different dates in each year.Intercropped wheat with unbrushed clover had a lower grain yield than wheat as a sole crop. Brushing increased wheat N uptake and wheat grain yields. Intercropping with two or three brushing dates gave higher wheat yields than wheat as the sole crop. The largest increases in grain N uptake, 21–25 kg N ha⁻¹, were obtained for the brushings around wheat flag leaf emergence. The highest yield increases with a single brushing, 0.98–1.11 Mg DM ha⁻¹, were obtained when brushing was performed during the stem elongation phase. The largest grain yields for treatments with two brushings were obtained with a first brushing at start of stem elongation and a second around flag leaf emergence. The first brushing probably provided N to increase the wheat leaf area index and thus the light interception, while the second brushing provided N to sustain the leaf area during grain filling and reduced clover biomass and therefore competition for water. Intercropping wheat and clover increased grain N concentrations by 0.11–0.39%-point compared with wheat as a sole crop. Intercropping may thus offer possibilities for improving the bread-making quality of organically grown wheat.     

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.     

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.     

Appropriate seeding rate for einkorn,emmer, and spelt grown under rainfed condition in southern Italy

Einkorn (Triticum monococcum L.), emmer (Triticum dicoccum Schübler) and spelt (T. spelta L.) are still cultivated in Italy. These three hulled wheat species are more commonly known as “Farro”. Little is known about agronomic practices that optimise the grain yield of these species.This study has been carried out to establish the appropriate seeding rate for einkorn, emmer and spelt which is grown in southern Italy (Apulia region), a typical Mediterranean environment, where durum wheat is principally cultivated. Two years of experimental field trials were conducted with three seeding rates (100, 150 and 200 viable seeds per square meter).Emmer had the highest hulled grain yield (3.54 t ha⁻¹) followed by spelt (2.80 t ha⁻¹) and einkorn (1.42 t ha⁻¹). Emmer also had a higher kernel weight and was heading earlier than the other species. The bad performance of einkorn can be accountable to the excessive time to reach heading and the natural inclination of plants to lodge, factors that reduce the ability of plant to complete grain ripening, resulting in light and shrivelled kernels. The lower grain yield of spelt in comparison to emmer may be due to later heading.Emmer and spelt performed the best when they were sown at 200 seeds m⁻² (3.85 and 3.09 t ha⁻¹, respectively). In contrast, einkorn showed the highest grain yield (1.69 t ha⁻¹) at the lowest seeding rate (100 seeds m⁻²). Further, additional experimentation is required to confirm this.These results indicate that emmer is the most appropriate hulled wheat species for cropping under southern Italy’s growing conditions, and provide further information about the use of these species in the marginal area preservation or when the cultivation of economically profitable crops is precludes by water deficiency and soil poorness.     

Old tall durum wheat cultivars are suited for dual-purpose utilization

The lateness, tallness and high vigour of old tall durum wheat cultivars could be advantageous for dual-purpose use and their high propensity for lodging should be reduced by grazing. A 3-year field trial was performed in Sardinia, Italy, in a typical Mediterranean environment. Crops of the durum wheat cultivar Senatore Cappelli were sown in October, and grazing was simulated by clipping half of the plots at the terminal spikelet stage of development. The forage biomass derived from clipping varied greatly between seasons (from 0.8 to 3.3 t ha⁻¹ dry matter) in response to the notable inter-seasonal variability in weather conditions. Cultivar Senatore Cappelli showed good recovery following clipping, with the ability to attain almost complete radiation interception well before anthesis. The high number of leaves that emerged after clipping might have contributed to this good recovery. Nevertheless, clipping reduced the dry matter produced by anthesis (16 t ha⁻¹ in clipped compared to 21 t ha⁻¹ in unclipped crops) as well as the final dry matter (DM_MAT) (19 t ha⁻¹ in clipped compared to 23 t ha⁻¹ in unclipped crops), although these differences disappeared when the clipped biomass was included. The lower lodging observed at anthesis in the clipped (21%) compared with unclipped crops (63%) likely reduced the difference between treatments. The lower DM_MAT of clipped treatments was reflected in a lower grain yield (GY) (3.4 t ha⁻¹ vs 4.2 t ha⁻¹ in the unclipped treatment). Clipping did not affect the amount of nitrogen present in the biomass, nitrogen uptake efficiency or radiation use efficiency. GY reduction after clipping was mediated by the reduction in spikes m⁻² and kernels m⁻² (KNO). Spike fertility was not affected by clipping, because the same amount of radiation was available for each spike (about 1 MJ). The period with reduced ground cover after clipping was reflected in an increased evaporation and reduced transpiration, which did not alter the total water used and increased the transpiration efficiency in terms of DM_MAT.Old tall durum wheat cultivars manifested good suitability for dual-purpose use in environments with low attainable yields because their low grain yield potential contributed to reducing the negative effects of clipping on GY. Their high straw yield and kernel protein percentage represented an advantage with respect to semi-dwarf cultivars.     

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 cover-cropping managements on productivity and N-utilization efficiency of kenaf (Hibiscus cannabinus L.), under different nitrogen fertilization rates and soil types

Biomass productivity, nitrogen recovery fraction and nitrogen utilization efficiency (NUE) of kenaf (Hibiscus cannabinus L.) cultivar Tainung 2 were tested, under three Lens culinaries treatments (incorporated, harvested before the sowing of the energy crop and mono-cropping) and four nitrogen dressings (0, 50, 100 and 150 kg ha⁻¹), in two field experiments carried out on a fertile, clayey to loamy soil, and on a sandy soil of moderate fertility, in central Greece, over the period 2007–2009. The obtained results showed a positive response in L. culinaries cover cropping on kenaf total yield, on both experimental sites. Total dry biomass fluctuated from 16.07 to 21.46 t ha⁻¹ for incorporated plots and from 13.63 to 16.55 t ha⁻¹ for control treatments (relied only on applications of N-fertilization) for sandy soil, and from 14.98 to 19.28 t ha⁻¹ in case of legume incorporation and from 12.34 to 16.69 t ha⁻¹ for control plots, for clayey soil, respectively. The evaluated NUE was 76 kg kg⁻¹, for sandy soil, and 72 kg kg⁻¹, for clay soil. The recovery fraction escalated from 41% in control plots to 70% in plots with previous L. culinaries cultivation for sandy soil, while for clayey soil an increase of 20% was recorded, indicating a prominent effect of legume cover-cropping management.     

Organic and mineral fertilization management improvements to a double-annual cropping system under humid Mediterranean conditions

The efficient use by crops of nitrogen from manures is an agronomic and environmental issue, mainly in double-annual forage cropping systems linked to livestock production. A six-year trial was conducted for a biennial rotation of four forage crops: oat-sorghum (first year) and ryegrass-maize (second year) in a humid Mediterranean area. Ten fertilization treatments were introduced: a control (without N); two minerals equivalent to 250 kg N ha⁻¹ year⁻¹ applied at sowing or as sidedressing; dairy cattle manure at a rate of 170, 250 and 500 kg N ha⁻¹ year⁻¹ and four treatments where the two lowest manure rates were supplemented with 80 or 160 kg mineral N ha⁻¹ year⁻¹. They were distributed according to a randomized block design with three blocks. The highest N mineral soil content was found in the summer of the third rotation, in plots where no manure was applied. The yearly incorporation of manure reduced, in successive cropping seasons, the amount of additional mineral N needed as sidedressing to achieve the highest yields. Besides, in the last two years, there was no need for mineral N application for the manure rate of 250 kg N ha⁻¹ year⁻¹. This amount always covered the oat-sorghum N uptake. In the ryegrass-maize sequence uptakes were as high as 336 kg N ha⁻¹ year⁻¹. In the medium term, the intermediate manure rate (250 kg N ha⁻¹ year⁻¹) optimizes nutrient recycling within the farming system, and it should be considered in the analysis of thresholds for N of organic origin to be applied to systems with high N demand.     

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.     

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.     

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.     

Evaluation of nitrogen management in maize cultivation grows on soil amended with sewage sludge and urea

This paper analyses the data of a 3 years’ research on the agronomical use of sewage sludge, from a urban waste water plan, to grow maize (Zea mays L.). The experiment was conducted in order to test possible combinations of sewage sludge and urea as source of nitrogen for maize. The experiment comprised a randomized block design composed of a control and 8 treatments with four replicates. Three urea rates (0; 100 kg N ha⁻¹ and 200 kg N ha⁻¹) were assigned combined with three sewage sludge rates (0; 5 t ha⁻¹ and 10 t ha⁻¹), exceeding the limits permitted by the law, and the unfertilized control. Maize was sown and harvested for 2 years (April–September 2006 and 2007) and wheat (Triticum vulgare L.) was sown in October 2007 and harvested in May 2008 without adding any fertilizer or sewage sludge, in order to evaluate the residual effects of the organic fertilizer.The batch that gave the highest grain production was the one that received 10 t ha⁻¹ DM of sewage sludge and 100 kg N ha⁻¹ from urea, reaching values of 16.17 ± 0.97 t ha⁻¹ DM in the first year and 17.52 ± 0.68 t ha⁻¹ DM in the second one, while the effect of the organic fertilization was still available where wheat was grown. ANR values showed a significant increase between the first and the second year: the average value for the treatment 3 (exclusive use of sludge in maximum dose) has shown an increase from 24.3% in 2006 to 63.4% in 2007, highlighting the effect of the sewage sludge. Yields and nitrogen uptake during and after the experiment and the nitrate losses by leachates have been evaluated: linear correlations were statistically significant, with an improvement in the second year of the trial, between yields and the nitrogen applied (R² = 0.757) and yields and the nitrogen removal rate (R² = 0.843).     

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.     

Winter cereal yields as affected by animal manure and green manure in organic arable farming

The effect of nitrogen (N) supply through animal and green manures on grain yield of winter wheat and winter rye was investigated from 1997 to 2004 in an organic farming crop rotation experiment in Denmark on three different soil types varying from coarse sand to sandy loam. Two experimental factors were included in the experiment in a factorial design: (1) catch crop (with and without), and (2) manure (with and without). The four-course crop rotation was spring barley undersown with grass/clover – grass/clover – winter wheat or wheat rye – pulse crop. All cuttings of the grass–clover were left on the soil as mulch. Animal manure was applied as slurry to the cereal crops in the rotation in rates corresponding to 40% of the N demand of the cereal crops.Application of 50 kg NH₄–N ha^?1 in manure increased average wheat grain yield by 0.4–0.9 Mg DM ha^?1, whereas the use of catch crops did not significantly affect yield. The use of catch crops interacts with other management factors, including row spacing and weed control, and this may have contributed to the negligible effects of catch crops. There was considerable variation in the amount of N (100–600 kg N ha^?1 year^?1) accumulated in the mulched grass–clover cuttings prior to ploughing and sowing of the winter wheat. This was reflected in grain yield and grain N uptake. Manure application to the cereals in the rotation reduced N accumulation in grass–clover at two of the locations, and this was estimated to have reduced grain yields by 0.1–0.2 Mg DM ha^?1 depending on site. Model estimations showed that the average yield reduction from weeds varied from 0.1 to 0.2 Mg DM ha^?1. The weed infestation was larger in the manure treatments, and this was estimated to have reduced the yield benefit of manure application by up to 0.1 Mg DM ha^?1. Adjusting for these model-estimated side-effects resulted in wheat grain yields gains from manure application of 0.7–1.1 Mg DM ha^?1.The apparent recovery efficiency of N in grains (N use efficiency, NUE) from NH₄–N in applied manure varied from 23% to 44%. The NUE in the winter cereals of N accumulated in grass–clover cuttings varied from 14% to 39% with the lowest value on the coarse sandy soil, most likely due to high rates of N leaching at this location. Both NUE and grain yield benefit in the winter cereals declined with increasing amounts of N accumulated in the grass–clover cuttings. The model-estimated benefit of increasing N input in grass–clover from 100 to 500 kg N ha^?1 varied from 0.8 to 2.0 Mg DM ha^?1 between locations. This is a considerably smaller yield increase than obtained for manure application, and it suggests that the productivity in this system may be improved by removing the cuttings and applying the material to the cereals in the rotation, possibly after digestion in a biogas reactor.Cereal grain protein content was increased more by the N in the grass–clover than from manure application, probably due to different timing of N availability. Green-manure crops or manures with a relatively wide C:N ratio may therefore be critical for ensuring sufficiently high protein contents in high yielding winter wheat for bread making.     

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.     

Water relations and use-efficiency,plant survival and productivity of nine alfalfa (Medicago sativa L.) cultivars in dryland Mediterranean conditions

The potential for alfalfa to be a valuable rainfed pasture option that can be used to increase livestock and crop production in central-south Chile is demonstrated for the first time. The persistence, productivity and water use efficiency of alfalfa (Medicago sativa) cultivars was evaluated at four sites in dryland Mediterranean environments of Chile between 2012 and 2015. Nine alfalfa cultivars were evaluated for plant persistence, winter growth, forage yield, shoot water potential (Ψ), stomatal conductance (gs), and carbon (δ¹³C) and oxygen (δ¹⁸O) compositions. The percentage of plant survival after four years varied between 69 and 97% of the established plants. Alfalfa forage yield was >9 t ha⁻¹yr⁻¹ at Yungay (Andes foothills) in year two, and at Cauquenes (interior dryland site) in years three and four. The highest forage yield was obtained in cultivars SARDI Ten and Aquarius and the lowest in WL326HQ. In 2015, the forage yield during late spring and early summer (November 2015–January 2016) ranged from 3170 to 3570 kg ha⁻¹ (average of the nine cultivars), which represented between 29% and 38% of the total production. The response of gs to Ψ was different among cultivars but all cultivars exhibited a strong decline when Ψ was <−1.0 MP. Shoot water potential evaluated in October–November was negatively correlated with δ¹³C and δ¹⁸O in shoot biomass. The apparent water use efficiency (kg DM/ha/mm of rainfall) across the nine cultivars was highest in Cauquenes in the three years evaluated (>16 kg mm⁻¹). It is concluded that alfalfa is a high yielding forage that can extend the growing season into early summer and autumn in dryland Mediterranean environments.