Predicting Crop Yields with the Agricultural Reference Index for Drought

A generic agricultural drought index, called Agricultural Reference Index for Drought (ARID), was designed recently to quantify water stress for use in predicting crop yield loss from drought. This study evaluated ARID in terms of its ability to predict crop yields. Daily historical weather data and yields of cotton, maize, peanut and soybean were obtained for several locations and years in the south‐eastern USA. Daily values of ARID were computed for each location and converted to monthly average values. Using regression analyses of crop yields vs. monthly ARID values during the crop growing season, ARID‐yield relationships were developed for each crop. The ability of ARID to predict yield loss from drought was evaluated using the root mean square error (RMSE), the Willmott index and the modelling efficiency (ME). The ARID‐based yield models predicted relative yields with the RMSE values of 0.144, 0.087, 0.089 and 0.142 (kg ha^?1 yield per kg ha^?1 potential yield); the Willmott index values of 0.70, 0.92, 0.86 and 0.79; and the ME values of 0.33, 0.73, 0.60 and 0.49 for cotton, maize, peanut and soybean, respectively. These values indicated that the ARID‐based yield models can predict the yield loss from drought for these crops with reasonable accuracy.     

Drip Irrigation Frequency: The Effects and Their Interaction with Nitrogen Fertilization on Sandy Soil Water Distribution, Maize Yield and Water Use Efficiency Under Egyptian Conditions

Irrigation frequency is one of the most important factors in drip irrigation scheduling that affects the soil water regime, the water and fertilization use efficiency and the crop yield, although the same quantity of water is applied. Therefore, field experiments were conducted for 2 years in the summer season of 2005 and 2006 on sandy soils to investigate the effects of irrigation frequency and their interaction with nitrogen fertilization on water distribution, grain yield, yield components and water use efficiency (WUE) of two white grain maize hybrids (Zea mays L.). The experiment was conducted by using a randomized complete block split‐split plot design, with four irrigation frequencies (once every 2, 3, 4 and 5 days), two nitrogen levels (190 and 380 kg N ha^?1), and two maize hybrids (three‐way cross 310 and single cross 10) as the main‐plot, split‐plot, and split‐split plot treatments respectively. The results indicate that drip irrigation frequency did affect soil water content and retained soil water, depending on soil depth. Grain yield with the application of 190 kg N ha^?1 was not statistically different from that at 380 kg N ha^?1 at the irrigation frequency once every 5 days. However, the application of 190 kg N ha^?1 resulted in a significant yield reduction of 25 %, 18 % and 9 % in 2005 and 20 %, 13 % and 6 % in 2006 compared with 380 kg N ha^?1 at the irrigation frequencies once every 2, 3 and 4 days respectively. The response function between yield components and irrigation frequency treatments was quadratic in both growing seasons except for 100‐grain weight, where the function was linear. WUE increased with increasing irrigation frequency and nitrogen levels, and reached the maximum values at once every 2 and 3 days and at 380 kg N ha^?1. In order to improve the WUE and grain yield for drip‐irrigated maize in sandy soils, it is recommended that irrigation frequency should be once every 2 or 3 days at the investigated nitrogen levels of 380 kg N ha^?1 regardless of maize varieties. However, further optimization with a reduced nitrogen application rate should be aimed at and will have to be investigated.     

Impact of Water Stress on Maize Grown Off-Season in a Subtropical Environment

During the last decade, the production of off‐season maize has increased in several regions of Brazil. Growing maize during this season, with sowing from January through April, imposes several climatic risks that can impact crop yield. This is mainly caused by the high variability of precipitation and the probability of frost during the reproduction phases. High production risks are also partially due to the use of cultivars that are not adapted to the local environmental conditions. The goal of this study was to evaluate crop growth and development and associated yield, yield components and water use efficiency (WUE) for maize hybrids with different maturity ratings grown off‐season in a subtropical environment under both rainfed and irrigated conditions. Three experiments were conducted in 2001 and 2002 in Piracicaba, state of São Paulo, Brazil with four hybrids of different maturity duration, AG9010 (very short season), DAS CO32 and Exceler (short season) and DKB 333B (normal season). Leaf area index (LAI), plant height and dry matter were measured approximately every 18 days. Under rainfed conditions, the soil water content in the deeper layers was reduced, suggesting that the extension of the roots into these layers was a response to soil water limitations. On average, WUE varied from 1.45 kg m⁻³ under rainfed conditions to 1.69 kg m⁻³ under irrigated conditions during 2001. The average yield varied from 4209 kg ha⁻¹ for the hybrids grown under rainfed conditions to 5594 kg ha⁻¹ under irrigated conditions during 2001. Yield reductions under rainfed conditions were affected by the genotype. For the hybrid DKB 333B with a normal maturity, yield was reduced by 25.6 % while the short maturity hybrid Exceler was the least impacted by soil water limitations with a yield reduction of only 8.4 %. To decrease the risk of yield loss, the application of supplemental irrigation should be considered by local farmers, provided that this practice is not restricted by either economic considerations or the availability of sufficient water resources.     

Deficit Irrigation of Soya Bean [Glycine max (L.) Merr.] in a Sub-humid Climate

An experiment was conducted to investigate the influence of different levels of water deficit on yield and crop water requirement of soya beans in a sub‐humid environment (Southern Marmara region, Bursa, Turkey) in 2005 and 2006. One full‐irrigated treatment (T₁), one non‐irrigated treatment (T₅) and three different deficit irrigation (T₂ = 25 % water deficit, T₃ = 50 % water deficit, T₄ = 75 % water deficit) treatments were applied to ‘Nova’ soya bean planted on a clay soil. Non‐irrigated and all deficit irrigation treatments significantly reduced biomass and seed yield and yield components. The full‐irrigated (T₁) treatment had the highest yield (3760 kg ha^?1), while the non‐irrigated (T₅) treatment had the lowest yield (2069 kg ha^?1), a 45.0 % seed yield reduction. T₂, T₃ and T₄ deficit irrigation treatments produced 11.7–27.4 % less seed yield than the T₁ treatment. Harvest index showed less and irregular variation among irrigation treatments. Both leaf area per plant and leaf area index were significantly reduced at all growth stages as amount of irrigation water was decreased. Evapotranspiration increased with increased amounts of irrigation water supplied. Our results indicate that higher amounts of irrigation resulted in higher seed yield, whereas water use efficiency and irrigation water use efficiency values decreased when irrigation amount increased.     

利用RZWQM-ERES模拟华北平原农田土壤水分动态及其对作物产量的影响

农业系统模型是农业生产多元目标优化管理的重要工具,但由于系统模型过程复杂,参数众多,校正和验证工作一直是模型研究的重点和难点。本文对RZWQM (Root Zone Water Quality Model)与CERES (Crop Environment Resource Synthesis)的结合模型RZWQM-CERES模拟土壤水分及作物产量进行了参数优化和验证,结果表明,RZWQM-CERES在禹城站和栾城站模拟不同灌溉处理土壤贮水量与测定值呈相似的变化趋势,均方根差(RMSE)分别为2.38~2.70 cm及3.49~3.73 cm;作物产量模拟结果与实测值对土壤水分的响应趋势一致(R² = 0.83^***,n = 22),其中在禹城站模拟小麦和玉米产量的RMSE分别为550 kg hm^-2和580 kg hm^-2,栾城站模拟小麦产量的RMSE为670 kg hm^-2。以上结果表明RZWQM-CERES可作为华北平原模拟和分析土壤水分对作物产量影响的有效工具。本文初步建立了一套适合华北平原作物生产的模型参数,为利用RZWQM-CERES建立农田水分优化调控策略奠定了基础,并探讨了模型评价过程中应注意的问题。     

利用RZWQM-ERES模拟华北平原农田土壤水分动态及其对作物产量的影响

农业系统模型是农业生产多元目标优化管理的重要工具,但由于系统模型过程复杂,参数众多,校正和验证工作一直是模型研究的重点和难点。本文对RZWQM (Root Zone Water Quality Model)与CERES (Crop Environment Resource Synthesis)的结合模型RZWQM-CERES模拟土壤水分及作物产量进行了参数优化和验证,结果表明,RZWQM-CERES在禹城站和栾城站模拟不同灌溉处理土壤贮水量与测定值呈相似的变化趋势,均方根差(RMSE)分别为2.38~2.70 cm及3.49~3.73 cm;作物产量模拟结果与实测值对土壤水分的响应趋势一致(R² = 0.83^***,n = 22),其中在禹城站模拟小麦和玉米产量的RMSE分别为550 kg hm^-2和580 kg hm^-2,栾城站模拟小麦产量的RMSE为670 kg hm^-2。以上结果表明RZWQM-CERES可作为华北平原模拟和分析土壤水分对作物产量影响的有效工具。本文初步建立了一套适合华北平原作物生产的模型参数,为利用RZWQM-CERES建立农田水分优化调控策略奠定了基础,并探讨了模型评价过程中应注意的问题。     

Optimierung der Produktion von Wintergetreide zur Bioethanolherstellung durch unterschiedlich intensive Anbauverfahren

The investigations were based on biennial field trials carried out at two locations comprising the factors location/previous crop, winter cereal genotype (rye cv. ‘Farino’,triticale cv. ‘Modus’, wheat cv. ‘Batis’) and production intensity level. One agronomical focus was to replace the mineral N‐supply due to its energetic relevance, by either the residues of legumes, or stillage, a processing residue containing organic N. The measurement included the crop yield ha^?1, the bioethanol exploitation dt^?1 and the bioethanol yield ha^?1. The last was closely correlated to the grain yield and thus dominated by intensity level. Highest bioethanol yields with an average peak at 4022 l ha^?1, always occurred at the highest intensity level. Bioethanol exploitation however, was mainly determined by the genotype. The cultivars showed significant exploitation and yield differences. An adequate bioethanol exploitation was observed with the wheat cv. Batis in contrast to diminished grain and bioethanol yields. Considering bioethanol exploitation and bioethanol yield, the triticale cv. Modus was the outstanding genotype. Despite high grain yields, the bioethanol yields of the rye cv. Farino stayed mean, because of a genotypic lowered bioethanol exploitation. Comparing the approaches of mineral nitrogen substitution, legume N was successful, whereas stillage fertilizing, according to the examined conditions, resulted in ample decreased grain and bioethanol yields ha^?1.     

Uncertainty assessment of soya bean yield gaps using DSSAT‐CSM‐CROPGRO‐Soybean calibrated by cultivar maturity groups

Soya bean yield gap can be caused by different factors resulting in uncertainties when the objective is to use such information for farm decision‐making and reference yield determination. Thus, this study aimed to quantify the soya bean yield gap for four sites, located in Southern and Midwestern Brazil, as well as the uncertainties of that related to cultivars, sowing dates, soil types and reference yields. The crop simulation model DSSAT‐CSM‐CROPGRO‐Soybean was calibrated for cultivars with similar maturity groups, based on the data obtained from the best farmers at the county level. The yield gap by water deficit (YG_WD) was obtained through the difference between potential and attainable yields, and that one caused by sub‐optimum crop management (YG_CM) by subtracting actual yield of each county, obtained from official statistics between 1989/90 and 2014/15 growing seasons, from the estimated attainable yield. The yield was simulated using four sowing dates, three soil types and two soya bean maturity groups by county. The reference yield uncertainty was quantified using yield reference from crop model and regional winners of the soya bean yield context, conducted by CESB (Brazilian Soybean Strategic Committee), for the growing seasons from 2013/14 to 2015/16. The crop model showed a good agreement between measured and simulated crop development and growth using calibration by maturity group, with low root mean square error (347 kg/ha). Southern sites had a mean YG_WD of 1,047 kg/ha, while in the Midwest, it was lower than 100 kg/ha. The YG_CM was 1,067, 528, 984 and 848 kg/ha, respectively, for Castro, PR, Mamborê, PR, Montividiu, GO and Primavera do Leste, MT, representing the opportunity for yield gain when having the best farmers as reference. The maturity groups, sowing dates and soil types showed to be an important source of uncertainty for yield gap determination, being recommended to investigate the farms in detail for an appropriate quantification. The reference yield showed expressive uncertainties, with some farmers presenting conditions to increase their soya bean yields by more than 3,000 kg/ha, when considering as reference the yields obtained by the winners’ farmers. These results show that uncertainties must be reduced when assessing farm yield gaps, in order to ensure that expected rate of soya bean yield growth could be reached by adopting the same technologies from CESB winners and best farmers in the county as a reference.     

Drought Tolerance and Water‐Use Efficiency of Biogas Crops: A Comparison of Cup Plant,Maize and Lucerne‐Grass

The cup plant (Silphium perfoliatum L.) is discussed as an alternative energy crop for biogas production in Germany due to its ecological benefits over continuously grown maize. Moreover, a certain drought tolerance is assumed because of its intensive root growth and the dew water collection by the leaf cups, formed by fused leaf pairs. Therefore, the aim of this study was to estimate evapotranspiration (ET ), water‐use efficiency (WUE ) and the relevance of the leaf cups for the cup plant's water balance in a 2‐year field experiment. Parallel investigations were conducted for the two reference crops maize (high WUE ) and lucerne‐grass (deep and intensive rooting) under rainfed and irrigated conditions. Root system performance was assessed by measuring water depletion at various soil depths. Transpiration‐use efficiency (TUE ) was estimated using a model approach. Averaged over the 2 years, drought‐related above‐ground dry matter reduction was higher for the cup plant (33 %) than for the maize (18 %) and lucerne‐grass (14 %). The WUE of the cup plant (33 kg ha^?1 mm^?1) was significantly lower than for maize (50 kg ha^?1 mm^?1). The cup plant had a lower water uptake capacity than lucerne‐grass. Cup plant dry matter yields as high as those of maize will only be attainable at sites that are well supplied with water, be it through a large soil water reserve, groundwater connection, high rainfall or supplemental irrigation.     

Impact of Nitrogen and Plant Growth Promoting Rhizobacteria on yield and yield components of sunflower in a glasshouse environment

The effects of Nitrogen (N) and Plant Growth Promoting Rhizobacteria (PGPR) on growth and development of sunflower (Helianthus annuus L. var. Hysun-33) grown in the greenhouse under a natural environment were studied. The N-use efficiency of a sunflower crop grown under three N rates (N₁ = 0 kg ha^?1, N₂ = 120 kg ha^?1, and N₃ = 240 kg ha^?1) and three PGPR levels (R₁ = 0 kg ha^?1, R₂ = 30 kg ha^?1, and R₃ = 60 kg ha^?1) were investigated. The maximum amount of N resulted in higher total dry matter production per plant and the effect was prominent from 34 days after sowing (DAS). Seed yields differed significantly among different sunflower crops especially at limiting N supply, with significant shifts according to the N level. N uptake was an important parameter for yield at all N rates. The 240 kg N ha^?1 treatments provided the maximum yield, while the oil contents in these treatments of higher yield showed a lower oil content (%). Harvest index was also significantly correlated to yield across N rates; however, its importance depended much on environmental conditions as well. It can be inferred from the study that sunflower crop is well-supplied with respect to growth, development, yield and yield components, to enhance N efficiency and depends very much on the N supply. All the parameters gave maximum results with the increment of N while PGPR regimes had no prominent impact on the sunflower crop, the target environment, and the target yield level grown under a specified controlled glasshouse environment.     

Effects of Time and Rate of Nitrogen and Phosphorus Application on the Growth and the Seed and Oil Yields of Canola (Brassica napus L.)

A field study was conducted to investigate the influence of variable rates of application of N and P fertilizers in splits at various times on the growth and the seed and oil yields of canola (Brassica napus L.) during 1995–97. Rates of fertilizer application were 0 and 0 (F0), 60 and 0 (F1), 0 and 30 (F2), 60 and 30 (F3), 90 and 60 (F4) and 120 and 90 (F5) kg N ha^?1 and kg P₂O₅ ha^?1. All the P was applied at sowing while N was applied in splits, i.e. all at sowing, half at sowing and half with first irrigation, or half at sowing and half at flowering. The responses of growth, seed yield and components of yield were consistent in both years. Increasing the rate of fertilizer application from F4 (90/60 kg N/P₂O₅ ha^?1) to F5 (120/90 kg N/P₂O₅ ha^?1) increased the leaf area index (LAI) relative to the control and to lower rates of fertilizer application. For both crops, application of 90/60 kg N/P₂O₅ ha^?1 significantly enhanced total dry matter (TDM) and seed yield. Seed yield increased mainly due to a greater number of pods per plant and seeds per seed‐pod. The time of fertilizer application did not significantly affect seed yield or components of yield in either season. Oil yield generally followed seed yield, increasing with increasing rate of fertilizer application up to 90/60 kg N/P₂O₅ ha^?1. The maximum oil contents were obtained from the control. The results show that seed and oil yields of canola were maximized at the F4 (90/60 kg N/P₂O₅ ha^?1) rate of application under the agro‐ecological conditions of Faisalabad, Pakistan.     

Response of Mung Bean (Vigna radiata (L.) R. Wilczek) to an Increasing Natural Temperature Gradient under Different Crop Management Systems

Increasing temperatures pose a significant threat to crop production in the tropics. A field experiment was conducted with mung bean at three locations in Sri Lanka representing an increasing temperature gradient (24.4–30.1 °C) during two consecutive seasons to (i) determine the response of mung bean to increasing temperature and (ii) test a selected set of crop management practices aimed at decreasing essential inputs such as water, synthetic pesticides and inorganic nitrogen fertilizer. The control treatment (T₁) consisted of standard crop management including irrigation, chemical crop protection and inorganic fertilizer application. Adaptation system 1 (T₂) included mulching with rice straw at 8 t ha^?1 with 30 % less irrigation and crop protection and nutrient management as in T₁. Adaptation system 2 (T₃) included crop protection using a pretested integrated pest management package with water and nutrient management as in T₂. In adaptation system 3 (T₄), 25 % of the crop's nitrogen requirement was given as organic manure (compost) at 0.8 t ha^?1 while 75 % was given as inorganic fertilizer with water management and crop protection as in T₃. Durations of both pre‐ and post‐flowering phases were reduced with increasing temperature. In the warmer (25.4–30.1 °C) yala season, seed yield (Y) of T₁ decreased with increasing temperature at 366 kg ha^?1 °C^?1. However, in maha season, Y did not show a significant relationship across the narrower temperature gradient from 24.4 to 25.8 °C. Pooling the data from both seasons showed a second‐order polynomial response with an optimum temperature of 26.5 °C. In addition to shortened durations, reduced crop growth rates and reduced pod numbers per plant were responsible for yield reductions at higher temperatures. In yala, yields of all adaptation systems at all locations were on par with yields of the respective controls. Furthermore, yala yields of T₂ and T₃ were less sensitive than T₁ to increasing temperatures (265 and 288 kg ha^?1 °C^?1). In maha, T₃ and T₄ had greater yields than the control at the relatively cooler site while having lower yields than the control at the warmer site. Maha yields of T₂ were on par with the control at both temperature regimes. While demonstrating the significant temperature sensitivity of mung bean yields, results of the present work showed that components of the tested adaptation systems could be promoted among smallholder farmers in Asia, especially in view of their long‐term environmental benefits and contributions to sustainable agriculture in a warmer and drier future climate.     

Nutrient Management Effects on Light Interception, Photosynthesis, Growth, Dry-matter Production and Yield of Indian Mustard (Brassica juncea)

A field experiment was conducted on sandy loam acidic soil to study the effect of nutrient managements on light interception, photosynthesis, growth, biomass production and yield of Indian mustard [Brassica juncea (L.) Czern & Coss.]. Plant height, number of branches per plant, number of siliqua per plant, number of seeds per siliquae, 1000‐seed weight, seed and oil yield of Indian mustard improved at 100 % recommended rates of NPK (N‐P‐K at 80‐17.2‐33.2 kg ha^?1) + 10 t ha^?1 farmyard manure (FYM) (T₃) compared with 100 % NPK rate (T₂). It was also at par with 100 % NPK + 10 kg ha^?1 borax + 20 kg ha^?1 ZnSO₄ (T₆) and 50 % NPK + 10 t ha^?1 FYM +10 kg ha^?1 borax + 20 kg ha^?1 ZnSO₄ (T₁₀). The rate of photosynthesis increased due to appropriate nutrient management treatments (T₃, T₆ or T₁₀) with concomitant increase in photosynthetically active radiation, internal CO₂ concentration and rate of transpiration and decrease in stomatal resistance. Consequent upon the higher rate of photosynthesis, dry‐matter accumulation increased. The crop receiving nutrient treatment T₃ or T₆ maintained higher light interception ratio (LIR), leaf area index (LAI), biomass production, crop growth rate (CGR) and net assimilation rate (NAR) that resulted in greater rate of photosynthesis, harvest index and seed yield. Similarly, T₁₀ was equally efficient in registering greater LIR, LAI, CGR, NAR and seed yield of mustard. The average seed yields were 1692, 1683 and 1668 kg ha^?1 in T₃, T₆ and T₁₀, respectively, and these three treatments were significantly superior to T₂ (1332 kg ha^?1), control (723 kg ha^?1) and other treatments. Significantly greater seed oil contents of 41.30, 40.60 and 41.07 % were recorded in T₃, T₆ and T₁₀, respectively. Thus, significant improvement due to appropriate combination of NPK, FYM, borax and ZnSO₄ was observed for uptake of nutrients.     

Is the Companion Crop Harmless to Alfalfa Establishment in the Highlands of East Anatolia?

This study documented the effects of barley companion crop seeding rate and cutting stage on alfalfa establishment in a highland area. Alfalfa was established with barley at seeding rates of 0, 60, 120 and 180 kg ha^?1 and cut at the milk‐dough and ripe grain stages. In most cases, hay yield and composition of herbage were affected by companion crop seeding rate and cutting stage. Total hay yield increased from 3294 to 5131 kg ha^?1 when the companion crop seeding rate was increased from 0 to 180 kg ha^?1 at the milk‐dough stage. Legume and weed growth was suppressed by the companion crop during establishment, but using a barley companion crop decreased alfalfa plant losses in the seeding year. Few residual effects of barley were seen on hay yield in the subsequent year, but residual effects of companion crop treatments on weed suppression continued in all clippings of the second year. The results suggest that alfalfa should be sown with a barley companion crop in highland areas with adequate moisture. The seeding rate for barley is about the same as that for barley grown alone, and the companion crop could be harvested for hay or grain in the establishment year.     

Effect of Irrigation on Winter-Sown Chickpea in a Mediterranean Environment*

In the dry Mediterranean environments of the West Asia and North Africa region, irrigation is frequently used to supplement rainfall to increase crop productivity and yield stability. Chickpea (Cicer arietinum L.), an important pulse crop of the region, often suffers from drought and can benefit from such a practice. To investigate the response of chickpea to irrigation, experiments were conducted in the field at Tel Hadya, Syria, from 1985 to 1988 using 24 improved chickpea genotypes sown in winter. Irrigation scheduling was done using the daily water balance computed from rainfall and pan evaporation data. Yearly rainfall was 316, 358, and 504 mm and supplemental irrigation amount was 130, 120, and 80 mm in 1985–86, 1986–87, and 1987–88, respectively. Irrigation increased seed yield by 916 kg ha^?1 (44.0%) over the 3-year period. Irrigation requirement for chickpea coincided with flowering and seed development period. The top 10 highest-yielding genotypes under irrigated conditions were ILC 464, ILC 1272, ILC 237, ILC 613, ILC 95, ILC 4291, ILC 142, ILC 147, ILC 295, and ILC 3256. Their mean seed yields ranged from 3877 to 3208 kg ha^?1. Among these four genotypes, ILC 464, ILC 1272, ILC 3256, and ILC 4291 with mean seed yields of 3877, 3726, 3208, and 3266 kg ha^?1, respectively, were with predictable response to favourable conditions. Aboveground biomass contributed 49% of the total increase in seed yield from irrigation followed by plant height (26%) and early maturity (16%). These results indicate that it may be possible to breed chickpea for improved response to irrigation, and irrigation can enhance the yields of winter-sown chickpea grown in the lowland Mediterranean drylands.     

Nitrogen and Phosphorus Effects on Faba Bean Yield and Some Yield Components

The faba bean is among the major grain legumes cultivated in Ethiopia and is used extensively as a break crop in the highlands. Although a blanket application of DAP (diammonium phosphate) at the rate of 100 kg · ha^?1 has been practised in faba bean production in the country, this was not based on research results. In addition, little information is available on the response of the crop to N and P fertilizers under diverse environmental conditions. Hence, field experiments were carried out at three locations in 1991, seven locations during 1992 and 1993 and at one location in both 1993 and 1995 to determine faba bean response to N and P fertilization. Five levels of N (0, 9, 18, 27 and 36 kg N · ha^?1 as urea) in factorial combinations with four levels of P (0, 23, 46 and 69 kg P₂O₅ · ha^?1 as TSP [triple super phosphate]) were studied in a randomized complete block design with four replications in the first year. In the remaining years four levels of N (0, 18, 27 and 36 kg N · ha^?1 as urea) in factorial combinations with four levels of P (0, 23, 46 and 92 kg P₂O₅ · ha^?1 as TSP) were used in a randomized complete block design with three and four replications at one and seven locations, respectively. Results indicated that a positive linear response of faba bean seed yield was noted at all locations (except Debre Zeit and Burkitu) to P fertilization, while a significant quadratic response was also found at Holetta. In addition, plant height, above ground biomass and number of pods per plant were positively influenced by P application while the effect of N on these was mostly nonsignificant. Faba bean seed yield response to N was noted at only two out of eight locations; in most cases, nonsignificant and inconsistent seed yield responses to N fertilization were obtained. There was nonsignificant N × P rate interaction. In conclusion, we do not recommend supplemental N application to faba bean at six out of eight locations but we recommend the application of P fertilizer to faba bean at almost all locations (with the exception of Debre Zeit) and for other soils deficient in available P. Further work is recommended on the determination of critical levels for soil-available P, below which P fertilization should be practised for optimum faba bean seed yield.     

Crop and Weed Growth in a Sequence of Spring Barley and Winter Wheat Crops Established Together from a Spring Sowing (Relay Cropping)

A relay cropping system of cereals, whereby winter wheat (Triticum aestivum L.) was undersown in two‐row spring barley (Hordeum distichum L.), was established in a field trial in central Sweden in 1999 and continued until 2000. The purpose of the study was to examine crop and weed responses to different plant densities of the undersown winter crop. Winter wheat was sown at four seed rates (187, 94, 47 and 0 kg ha^?1) immediately after the sowing of barley. Barley was harvested in the first autumn after sowing and winter wheat in the second autumn. The grain yield of barley was not affected by the seed rate of wheat, and averaged 4580 kg ha^?1. Winter wheat did not vernalize during the first growing season but remained at the vegetative stage. The grain yield of wheat was 1990 kg ha^?1 for the lowest and 5610 kg ha^?1 for the highest seed rate of wheat. Whilst the undersowing process itself stimulated weed emergence in this experiment, increasing the undersowing seed rate reduced the population of perennial weeds by 40–70 %. In the second growing season, the total biomass of weeds was 66 % higher at the highest seed rate compared with the lowest seed rate.     

Mulching Improves Water Productivity,Yield and Quality of Fine Rice under Water‐saving Rice Production Systems

Water‐saving rice production systems are inevitable in the wake of severe water shortage in rice‐growing regions of the world. Mulches can improve water productivity, yield and quality of rice through increase in water retention. Studies were conducted for two consecutive years to assess the potential role of mulches (plastic and straw) in improving the performance of water‐saving rice production systems in comparison with no mulch used and conventionally irrigated transplanted rice. Water‐saving rice production systems in this study comprise aerobic rice and transplanted rice with intermittent irrigation. These systems saved water (18–27 %) with improved water productivity more than the conventional system. However, these systems caused a yield penalty of 22–37 %; nevertheless, these yield losses were compensated with the application of mulches under water‐saving rice production systems. Both plastic and straw mulches were helpful in improving moisture retention and water productivity (0.18–0.25 kg grain m^?3 water) relative to non‐mulch treatments (0.19–0.29 kg grain m^?3 water). Mulch application was also helpful in reducing the number of non‐productive tillers and sterile spikelets, and improving the productive tillers, kernel number and size, and kernel quality. Plastic mulch was more effective than straw mulch in improving water retention, water productivity and reducing spikelet sterility. In conclusion, the mulching improved the soil moisture retention, and thus enhanced the rice water productivity, spikelet fertility, paddy yield and quality of rice. This signifies the importance of mulching in water‐saving rice production systems.     

Potassium Management for Brown Midrib Sorghum × Sudangrass as Replacement for Corn Silage in the North-eastern USA

In recent years, there has been a growing interest in brown midrib (BMR) sorghum (Sorghum bicolor (L.) Moench.) × sudangrass (Sorghum sudanense Piper) hybrids (SxS) as a replacement for silage corn (Zea mays L.) in the north‐eastern USA. Recent studies suggest it is suitable for both rotational grazing and as a hay crop and could compete with corn harvested for silage in years when wet spring conditions prevent the timely planting of corn. However, little is known about its suitability as forage for non‐lactating cows that require low potassium (K) forages to prevent health problems. Our objective was to evaluate the impact of K fertilizer management (0, 112 or 224 kg K₂O ha^?1 cut^?1) under optimum N management (112–168 kg N ha^?1 cut^?1) on yield, quality and K concentrations of BMR SxS over a 2‐year period. Field trials were established on a fine loamy, mixed, active, mesic Aeric Fragiaquepts with medium K‐supplying capacity and characteristic of a large region in New York. Potassium application did not affect dry matter yields in either of the 2 years. Averaged over 2 years, neutral detergent fibre (NDF) significantly increased with K addition with similar but non‐significant trends observed in each of the years individually. The digestibility of NDF was unaffected by K application. Crude protein (CP) concentrations showed a significant decrease with K application in 2002 and similar trends were observed in 2003, although differences were not significant at P ≤ 0.05. The changes in NDF and CP did not significantly impact forage quality expressed as milk production per megagram of silage. Potassium application increased forage K concentration up to 13 mg K kg^?1 dry matter (in the first cut in 2003). Forage Ca and Mg concentrations decreased with K addition except for the first cut in 2002 where differences between 112 and 224 kg K₂O ha^?1 treatments were not significant. Without K addition in the 2‐year period, K concentrations in the forage decreased from 23 g kg^?1 for the first cutting in 2002 to 15 g kg^?1 for the second cut in 2003. Low K forage was obtained for all second‐cut forage unless 224 kg K₂O ha^?1 cut^?1 had been added. First‐cut forage was suitable only when no additional K had been applied. These results suggest low K BMR SxS forage can be harvested from initially high K soils without loss in dry matter yield as long as no additional K is added.     

Effects of Reduced Tillage and Fertilization Practices on Soil Characteristics, Plant Water Status, Growth and Yield of Upland Cotton

Three different tillage practices, conventional (mouldboard ploughing at 22–25 cm plus one rotary hoeing at 5–6 cm, CT), minimum (one rotary hoeing at 12–15 cm, MT), and no‐tillage (direct drilling in soil covered by vetch residues, NT), combined with three fertilization treatments, inorganic (50 kg N ha^?1 as ammonium sulphate), cattle manuring (30 t ha^?1), and control (no‐fertilizer), were applied on a cotton crop (Gossypium hirsutum L. cv. Acala SJ‐2) grown on a clay loam soil in the field of the Agricultural University of Athens. Soil (gravimetric water content, bulk density, and penetration resistance in the top 40 cm) and plant parameters (root growth, leaf water potential, leaf area growth and seedcotton yield) were recorded throughout the cultivation period in all treatments. No‐tillage was associated with significantly higher values of soil water throughout the observation period caused by the vetch mulch. Bulk density and penetration resistance were initially higher in the no‐tilled plots, but they became significantly lower after 2–3 months from sowing. These beneficial effects on soil properties favoured root growth, expressed as root surface density, in the NT‐plots at the top soil layer. Similar, although less spectacular, effects were observed in the manured plots. Plant water status, expressed in terms of the water potential index, was significantly and consistently best in the NT‐ and worst in the CT‐plots throughout crop growth. In addition, NT favoured a better foliage growth and resulted in significantly higher yields than the other tillage practices. In general, NT, and in second instance, MT considerably improved plant water status, and hence foliage growth and yield in comparison with CT by maintaining higher levels of soil water and improving root growth. Manuring positively interacted with the reduced tillage practices for most soil and plant parameters.