Low Yield Potential Research Articles

Effects of HPS and LED lighting on cucumber leaf photosynthesis, light quality penetration and temperature in the canopy, plant morphology and yield

In Nordic countries during the winter months supplemental lighting is essential for year-round cucumber production. In this research the effects of full HPS (top and interlights) illumination is compared to hybrid (HPS top, LED interlights) and full LED (top and interlights). The results showed that fruit yield was highest in the HPS-LED treatment whereas the electrical use efficiency (kg yield J-1) increased when HPS was replaced with LED. In LED-LED the light use efficiency (g fruit FW mol-1 PAR) was highest but resulted in a fewer number of fruits in mid-winter particularly and the lowest yield potential. The lower temperature and lower light level due to LED-LED lighting lead to reduced photosynthesis capacity, flower initiation rate and water use efficiency whereas increased stem elongation and leaf expansion compared to other treatments. Differences in light quality of LED and HPS are also discussed in terms of cucumber yield formation.

Impact of Climate Change Adaptation Strategies on Winter Wheat and Cropping System Performance across Precipitation Gradients in the Inland Pacific Northwest, USA

Ecological instability and low resource use efficiencies are concerns for the long-term productivity of conventional cereal monoculture systems, particularly those threatened by projected climate change. Crop intensification, diversification, reduced tillage, and variable N management are among strategies proposed to mitigate and adapt to climate shifts in the inland Pacific Northwest (iPNW). Our objectives were to assess these strategies across iPNW agroecological zones and time for their impacts on 1) winter wheat (Triticum aestivum L.) productivity, 2) crop sequence productivity and 3) N fertilizer use efficiency. Region-wide analysis indicated that WW yields increased with increasing annual precipitation, prior to maximizing at 520 mm yr-1 and subsequently declining when annual precipitation was not adjusted for available soil water holding capacity. While fallow periods were effective at mitigating low nitrogen (N) fertilization efficiencies under low precipitation, efficiencies declined as annual precipitation exceeded 500 mm yr-1. Variability in the response of WW yields to annual precipitation and N fertilization among locations and within sites supports precision N management implementation across the region. In years receiving less than 350 mm precipitation yr-1, WW yields declined when preceded by crops rather than summer fallow. Nevertheless, WW yields were greater when preceded by pulses and oilseeds rather than wheat across a range of yield potentials, and when under conservation tillage practices at low yield potentials. Despite the yield penalty associated with eliminating fallow prior to WW, cropping system level productivity was not affected by intensification, diversification, or conservation tillage. However, increased fertilizer N inputs, lower fertilizer N use efficiencies, and more yield variance may offset and limit the economic feasibility of intensified and diversified cropping systems.

Pineapple (Ananas comusus) Plant Material as Supplement for Maize Residue-based Oyster Mushroom Substrate and Reduction of Cadmium Soil Contamination

Pineapple (Ananas comusus) production generates hard currency and, as a labor-intensive industry, it creates jobs. The profitability of pineapple farming in South Africa faces several challenges, including low yield potential and cadmium (Cd) contamination of soils, which damaged the reputation of the industry. To increase the income of pineapple farmers, research was conducted to evaluate the utilization of pineapple crop residue for oyster mushroom (Pleurotus ostreatus) production and to establish the Cd levels in the mushrooms produced on Cd-contaminated pineapple crop residue. Treatments were maize residue (M), pineapple residue (P), and a mixture of maize and pineapple residues [at 1:1 ratio (on a dry weight basis), M + P]. Biological efficiencies of 90%, 77.6%, and 29% were recorded for the M + P, P, and M treatments, respectively. The P and M + P substrates significantly increased mushroom yield. Mushroom protein contents were 23.3%, 18.86%, and 18.81% (on a dry weight basis) in the M + P, P, and M treatments, respectively. Mushrooms in the P substrate had the highest Cd level (3.3 mg/kg). In the M + P substrate, Cd reduced to a safe level (0.15 mg/kg). This indicates that mushrooms have biosorption capacity, and could be used to solve the problem of Cd pollution and increase the income of pineapple production.

Competitiveness of Winter Rice Varieties against Weed under Dry Direct Seeded Conditions

Aerobic rice or dry direct seeded rice is highly vulnerable to weeds because of lack of “head start” over weeds and standing water layer to suppress weeds. The risks of chemical control and the huge cost involvement in mechanical control demand an eco-friendly and cost-effective integrated weed management. Weed competitive rice cultivar may be considered as a viable tool for integrated weed management. In these circumstances, an experiment was designed to evaluate weed competitiveness of some selected winter rice varieties under aerobic soil conditions. The study was conducted during dry season (February to June) 2016 at the Agronomy Field Laboratory and Weed Management Laboratory, Bangladesh Agricultural University, Mymensingh. Fourteen rice varieties namely, BRRI dhan28, BRRI dhan29, BRRI dhan47, BRRI dhan50, BRRI dhan55, BRRI dhan58, BRRI dhan59, BRRI dhan67, Binadhan-5, Binadhan-6, Binadhan-8, Binadhan-10, BRRI hybrid dhan3 and Agrodhan-14 were grown under weedy and weed-free conditions. Plots with no rice were also maintained to observe the natural growth of weed in absence of rice. The experiment was conducted with split-plot design with three replications. Weeding regime was allocated in main plot and rice variety was allocated in sub-plot. Results showed that rice varieties varied widely in their yield performances and weed competitiveness. Among rice varieties, BRRI dhan59 allowed the minimum weed growth (19.2 g m-2) while Binadhan-5 allowed the maximum weed growth (62.8 g m-2). Grain yield ranged from 1.85 t ha-1 (BRRI dhan55) to 3.92 t ha-1 (Binadhan-5) under weed-free condition and between 0.41 t ha-1 (BRRI dhan55) and 2.06 t ha-1 (BRRI dhan59) under weedy condition. Weed inflicted relative yield loss ranged from 43.4% to 82.1% among the varieties. BRRI dhan59 allowed the least yield penalty (43.4%) while Binadhan-5 had the maximum yield penalty (82.1%) due to weed competition. Although Binadhan-5 is the most productive variety (3.92 t ha-1) for aerobic culture but its weed inflicted relative yield loss is higher (82.1%) than many other varieties with low yield potential. On the other hand, BRRI dhan59 appeared as the most weed competitive variety (only 43.4% relative yield loss) with productivity of 3.84 t ha-1. Therefore, weed competitive variety should be considered as a vital tool while designing integrated weed management system for aerobic rice.

A Mixed Application of Geographically Weighted Regression and Unsupervised Classification for Analyzing Latex Yield Variability in Yunnan, China.

This paper introduces a mixed method approach for analyzing the determinants of natural latex yields and the associated spatial variations and identifying the most suitable regions for producing latex. Geographically Weighted Regressions (GWR) and Iterative Self-Organizing Data Analysis Technique (ISODATA) are jointly applied to the georeferenced data points collected from the rubber plantations in Xishuangbanna (in Yunnan province, south China) and other remotely-sensed spatial data. According to the GWR models, Age of rubber tree, Percent of clay in soil, Elevation, Solar radiation, Population, Distance from road, Distance from stream, Precipitation, and Mean temperature turn out statistically significant, indicating that these are the major determinants shaping latex yields at the prefecture level. However, the signs and magnitudes of the parameter estimates at the aggregate level are different from those at the lower spatial level, and the differences are due to diverse reasons. The ISODATA classifies the landscape into three categories: high, medium, and low potential yields. The map reveals that Mengla County has the majority of land with high potential yield, while Jinghong City and Menghai County show lower potential yield. In short, the mixed method can offer a means of providing greater insights in the prediction of agricultural production.

Mapping marginal croplands suitable for cellulosic feedstock crops in the Great Plains, United States

AbstractGrowing cellulosic feedstock crops (e.g., switchgrass) for biofuel is more environmentally sustainable than corn‐based ethanol. Specifically, this practice can reduce soil erosion and water quality impairment from pesticides and fertilizer, improve ecosystem services and sustainability (e.g., serve as carbon sinks), and minimize impacts on global food supplies. The main goal of this study was to identify high‐risk marginal croplands that are potentially suitable for growing cellulosic feedstock crops (e.g., switchgrass) in the US Great Plains (GP). Satellite‐derived growing season Normalized Difference Vegetation Index, a switchgrass biomass productivity map obtained from a previous study, US Geological Survey (USGS) irrigation and crop masks, and US Department of Agriculture (USDA) crop indemnity maps for the GP were used in this study. Our hypothesis was that croplands with relatively low crop yield but high productivity potential for switchgrass may be suitable for converting to switchgrass. Areas with relatively low crop indemnity (crop indemnity <$2 157 068) were excluded from the suitable areas based on low probability of crop failures. Results show that approximately 650 000 ha of marginal croplands in the GP are potentially suitable for switchgrass development. The total estimated switchgrass biomass productivity gain from these suitable areas is about 5.9 million metric tons. Switchgrass can be cultivated in either lowland or upland regions in the GP depending on the local soil and environmental conditions. This study improves our understanding of ecosystem services and the sustainability of cropland systems in the GP. Results from this study provide useful information to land managers for making informed decisions regarding switchgrass development in the GP.

Remote sensing of land use/cover changes and its effect on wind erosion potential in southern Iran.

Wind erosion is a complex process influenced by different factors. Most of these factors are stable over time, but land use/cover and land management practices are changing gradually. Therefore, this research investigates the impact of changing land use/cover and land management on wind erosion potential in southern Iran. We used remote sensing data (Landsat ETM+ and Landsat 8 imagery of 2004 and 2013) for land use/cover mapping and employed the Iran Research Institute of Forest and Rangeland (IRIFR) method to estimate changes in wind erosion potential. For an optimal mapping, the performance of different classification algorithms and input layers was tested. The amount of changes in wind erosion and land use/cover were quantified using cross-tabulation between the two years. To discriminate land use/cover related to wind erosion, the best results were obtained by combining the original spectral bands with synthetic bands and using Maximum Likelihood classification algorithm (Kappa Coefficient of 0.8 and 0.9 for Landsat ETM+ and Landsat 8, respectively). The IRIFR modelling results indicate that the wind erosion potential has increased over the last decade. The areas with a very high sediment yield potential have increased, whereas the areas with a low, medium, and high sediment yield potential decreased. The area with a very low sediment yield potential have remained constant. When comparing the change in erosion potential with land use/cover change, it is evident that soil erosion potential has increased mostly in accordance with the increase of the area of agricultural practices. The conversion of rangeland to agricultural land was a major land-use change which lead to more agricultural practices and associated soil loss. Moreover, results indicate an increase in sandification in the study area which is also a clear evidence of increasing in soil erosion.

Long Term Sugarcane Crop Residue Retention Offers Limited Potential to Reduce Nitrogen Fertilizer Rates in Australian Wet Tropical Environments.

The warming of world climate systems is driving interest in the mitigation of greenhouse gas (GHG) emissions. In the agricultural sector, practices that mitigate GHG emissions include those that (1) reduce emissions [e.g., those that reduce nitrous oxide (N2O) emissions by avoiding excess nitrogen (N) fertilizer application], and (2) increase soil organic carbon (SOC) stocks (e.g., by retaining instead of burning crop residues). Sugarcane is a globally important crop that can have substantial inputs of N fertilizer and which produces large amounts of crop residues (‘trash’). Management of N fertilizer and trash affects soil carbon and nitrogen cycling, and hence GHG emissions. Trash has historically been burned at harvest, but increasingly is being retained on the soil surface as a ‘trash blanket’ in many countries. The potential for trash retention to alter N fertilizer requirements and sequester SOC was investigated in this study. The APSIM model was calibrated with data from field and laboratory studies of trash decomposition in the wet tropics of northern Australia. APSIM was then validated against four independent data sets, before simulating location × soil × fertilizer × trash management scenarios. Soil carbon increased in trash blanketed soils relative to SOC in soils with burnt trash. However, further increases in SOC for the study region may be limited because the SOC in trash blanketed soils could be approaching equilibrium; future GHG mitigation efforts in this region should therefore focus on N fertilizer management. Simulated N fertilizer rates were able to be reduced from conventional rates regardless of trash management, because of low yield potential in the wet tropics. For crops subjected to continuous trash blanketing, there was substantial immobilization of N in decomposing trash so conventional N fertilizer rates were required for up to 24 years after trash blanketing commenced. After this period, there was potential to reduce N fertilizer rates for crops when trash was retained (≤20 kg N ha–1 per plant or ratoon crop) while maintaining ≥95% of maximum yields. While these savings in N fertilizer use were modest at the field scale, they were potentially important when aggregated at the regional level.

Best management practices of tillage and nitrogen fertilization in Mediterranean rainfed conditions: Combining field and modelling approaches

Abstract In this work, appropriate management practices for crop production under the variable climate conditions of the Mediterranean region, in particular rainfall, were tested with the use of a modelling system applied to long-term (i.e. 18 years) field data. The calibration of the CropSyst model was performed using data collected from 1996 to 1999 at three different Mediterranean locations (i.e., HYP-Guissona, MYP-Agramunt and LYP-Candasnos, i.e. high, medium and low yield potential, respectively) within a degree of yield potential. The model simulated reasonably well barley growth and yield to different tillage and N fertilization strategies. Simulations of barley performance over 50 years with generated weather data showed that yields were often greater and never smaller under no-tillage compared to conventional tillage with a mean increase of 36%, 63% and 18% for HYP-Guissona, MYP-Agramunt and LYP-Candasnos. In MYP-Agramunt, the long-term data showed a 40% increase in grain yields when using no-tillage compared to conventional tillage, as an average of 18 years. The model also predicted that greater N applications in no-tillage were appropriate to take advantage of additional water supply. Taking into account the limited amount of soil water available, overall N fertilizer applications could be reduced to about half of the traditional rate applied by the farmers without yield loss. The 50-yr simulation, confirmed by the long-term experimental data, identified no-tillage as the most appropriate tillage practice for the rainfed Mediterranean areas. Also, N fertilization must be reduced significantly when tillage is used or when increasing aridity. Our work demonstrates the usefulness of the combination of long-term field experimentation and modelling as a tool to identify the best agricultural management practices. It also highlights the importance of posterior analysis with long-term observed field data to determine the performance of simulation results.

Heterogeneity in Rice Tillers Yield Associated with Tillers Formation and Nitrogen Fertilizer

Rice (Oryza sativa L.) farmers generally overcome low seeding rates with additional nitrogen (N) fertilization to develop more productive tillers. However, not every tiller provides high productivity; instead, a sufficient N source leads to the production of tillers with low yield potential. The objectives of this study were (i) to quantify the heterogeneity within tillers regarding yield formation at different N levels and (ii) to examine the differences in tiller growth period, grain yield, and carbon (C) and N concentrations at different N levels. In 2013 to 2014, field experiments consisted of a randomized complete block design with three N fertilizer rates. Gini coefficient was adopted to analyze the heterogeneities of various tillers regarding grain yield. Results showed that tiller heterogeneity was enhanced with increasing N levels. Under the same N rate condition, the grain yield of productive tillers decreased with the later‐emerging tillers. The early‐emerging tillers possessed the characteristics of long growth period, strong intercepted photosynthetic active radiation, and high C/N ratio in straw. The N‐induced enhancement in rice population mainly occurred due to the increase in grain yield of early‐emerging tillers. However, this upward trend would emerge peak value after sufficient N supply. Therefore, analyzing the limiting factors for low production of late‐emerging tillers may provide a novel perspective on further improving the rice population yield.Core Ideas Heterogeneity in rice tillers yield is increased with increasing N rates. Short growth period is not the key limiting factor to late‐emerging tillers. Early‐emerging tillers pre‐empt the uppermost light source and shade the late‐emerging tillers. Early‐emerging tillers possess higher C/N ratio in straw than late‐emerging tillers. Late‐emerging tillers have higher yield potential under sufficient N supply.

Using the CSM–CERES–Maize model to assess the gap between actual and potential yields of grain maize

SUMMARYMaize in Canada is grown mainly in the south-eastern part of the country. No comprehensive studies on Canadian maize yield levels have been done so far to analyse the barriers of obtaining optimal yields associated with cultivar, environmental stress and agronomic management practices. The objective of the current study was to use a modelling approach to analyse the gaps between actual and potential (determined by cultivar, solar radiation and temperature without any other stresses) maize yields in Eastern Canada. The CSM–CERES–Maize model in DSSAT v4·6 was calibrated and evaluated with measured data of seven cultivars under different nitrogen (N) rates across four sites. The model was then used to simulate grain yield levels defined as: yield potential (YP), water-limited (YW, rainfed), and water- and N-limited yields with N rates 80 kg/ha (YW, N-80N) and 160 kg/ha (YW, N-160N). The options were assessed to further increase grain yield by analysing the yield gaps related to water and N deficiencies. The CSM–CERES–Maize model simulated the grain yields in the experiments well with normalized root-mean-squared errors <0·20. The model was able to capture yield variations associated with varying N rates, cultivar, soil type and inter-annual climate variability. The seven calibrated cultivars used in the experiments were divided into three grades according to their simulated YP: low, medium and high. The simulation results for the 30-year period from 1981 to 2010 showed that the average YPwas 15 000 kg/ha for cultivars with high yield potential. The YPis generally about 6000 kg/ha greater than the actual yield (YA) at each experimental site in Eastern Canada. Two-thirds of this gap between YPand YAis probably associated with water stress, as a gap of approximately 4000 kg/ha between the YWand the YPwas simulated. This gap may be reduced through crop management, such as introducing irrigation to improve the distribution of available water during the growing season. The simulated yields indicated a gap of about 3000 and 1000 kg/ha between YWand YW,N-80N for cultivars with high YPand low YP, respectively. The gap between YWand YW,N-160N decreased to <2000 kg/ha for high Ypcultivars with little difference for the low Ypcultivars. The different yield gaps among cultivars suggest that cultivars with high YPrequire high N rates but cultivars with low YPmay need only low N rates.

Role of lutoid membrane transport and protein synthesis in the regeneration mechanism of latex in different Hevea clones

Natural rubber (cis-1,4 polyisoprene) is synthesised in the milky cytoplasm, the latex, of specialized cells called laticifers in the bark tissues of the rubber tree (Hevea brasiliensis). Regeneration mechanism of latex after each tapping (controlled wounding of the bark) was studied in relation to lutoid membrane enzymes and protein synthesis in twelve rubber clones with varying yield potentials during the peak rubber yielding season. High activity of membrane enzymes and better availability of biochemical energy [ATP] were observed in clones viz; RRII 105, RRIM 600, PB 260, RRII 422 and RRII 430. The highest protein biosynthetic capacity was noticed in clone PB 260 and RRIM 600. However, high ATP content, increased invertase activity and protein biosynthesis were observed in the medium yielding clone GT1 compared to clones with low rubber yield potential. Very low sugar content and increased invertase activity in the latex of clone PB 260 indicated intense latex metabolism with high protein turnover that implies fast recouping of the cellular metabolites lost during latex harvesting. Clone PB 217 was characterized by very high sucrose and low ATP concentration and ATPase activity in latex indicating slow metabolism and hence be suitable for inducing latex metabolism using ethylene stimulant. Low rubber yielding clones such as RRII 33 and RRII 38 were consistently recorded a high sucrose content but very low activity of membrane enzymes, reduced ATP concentration and low protein biosynthesis in latex. Among the recently released modern clones (RRII 400 series), latex regeneration capacity was higher in RRII 422 and RRII 430. The significance of lutoid membrane transport and protein synthesis is discussed in relation to general latex metabolism of these rubber clones. The outcome of this study would be helpful to design suitable latex harvesting systems and yield stimulation methods for optimizing latex production in each clone based on metabolic profiling.

English

Soil physical and structural degradation may influence crop productivity over time in long-term no-tillage system areas. A field study was conducted at two sites, Palmeira das Missoes and Nao-Me-Toque, in southern Brazil to quantify soil physical/hydraulic and structural changes in zones with different yield potentials. The sites have been managed under no-tillage system without soil disturbance for more than 10 years. Soils were classified as Oxisols (Hapludox). Each site was divided into three zones with low, medium and high yield potentials based on overlapping of yield maps obtained from harvesters with precision agriculture tools. Within each yielding zone soil samples were collected to determine bulk density, porosity and aggregate stability. In addition, water infiltration rate and initial time for starting surface runoff were measured using a sprinkler infiltrometer (Cornell Sprinkler infiltrometer). Our findings showed that soils under low-yielding zones presented higher bulk density, lower macro-aggregate stability and water infiltration rate as well as shorter time for starting surface runoff compared to high-yielding zones. Therefore, these results suggest that soil physical and structural degradations have induced crop yield losses under long-term no-tillage areas. Macro-aggregate stability (>4.76 mm) and water infiltration rate were efficient parameters for distinguishing yielding zones in Oxisols managed under long-term no-tillage system in southern Brazil. Key words: Soil compaction, Cornell Sprinkler Infiltrometer, soil aggregation, water infiltration.

Effects of water stress on total biomass, tuber yield, harvest index and water use efficiency in Jerusalem artichoke

The objectives of this study were to determine the effects of drought on tuber yield, total biomass, harvest index, water use efficiency of tuber yield (WUEt) and water use efficiency of biomass (WUEb), and to evaluate the differential responses of Jerusalem artichoke (JA) varieties under drought stress. The 3×5 factorial combinations of three water regimes (Field capacity (FC), 50% available soil water (50%AW) and 25%AW), and five JA varieties (JA 60, JA 125, JA 5, JA 89 and HEL 65) were arranged in a pot experiment in a randomized complete block design with four replications for two years. Data were recorded for tuber dry weight, total biomass, harvest index, WUEt and WUEb at harvest. Drought reduced tuber dry weight, total biomass, harvest index, WUEt and WUEb, and reductions were more severe under the severe drought stress of 25%AW. Varieties were significantly different for all traits under drought and well-watered conditions. The JA varieties were classified into three groups. The first category was comprised of the JA 5 variety with high tuber yield potential and low drought tolerance, the second category consisted of JA 60 and JA 125 varieties with low tuber yield potential and high drought tolerance, and the third group included JA 89 and HEL 65 varieties with low tuber yield potential and low drought tolerance. The multiple regression analysis showed that tuber yield, total biomass and harvest index at 50%AW and 25%AW depended largely on the reductions of tuber yield, total biomass and harvest index under drought. Therefore, the results of this study recommend that the selection of JA genotypes with low reduction in yield under drought stress could be a criterion in drought resistance breeding programs for development of JA varieties with high tuber yield under drought stress. JA with drought tolerance in this study means high tuber yield under drought conditions. JA 5 had high yield and WUEt across water regimes and could be used as parental source for drought tolerance breeding programs in further research.

MUSHKBUDJI-Aromatic Land Race of Kashmir

More than 100 landraces have been documented from Kashmir valley, however, majority of them stand replaced from farmer’s field by the high yielding varieties, and have been confined to some specific pockets of the valley. The preference for high yielding varieties has led to genetic erosion and loss of these valuable landraces which once were cultivated for several traits like taste, aroma, other unique quality features and medicinal use. The reasons attributed to loss of heritage rice’s of Kashmir include their low yield potential and susceptibility to biotic and abiotic stresses particularly to paddy blast.

Early testing of S1 lines of maize

Eighty S1 maize (Zea mays L.) lines derived from halfsibfamilies with good yield potential (greater than landraces in theregion) were evaluated, with the purpose of selecting outstandinglines. Native populations are a source of germplasm for genetic improvementthrough selection and hybridization. Analysis of varianceshowed highly significant differences between the lines S1 in thevariables days to anthesis (FM), silking date (FF), plant height (Apl),ear height (Amz), leaves above ear (NHEmz), ear length (Lmz), rownumber (Nhil), kernels per row (Ghil), total kernels per ear (TGmz)and grain yield (Rend). All variables showed high variability, anexpected result given the origin of the evaluated genotypes. Meancomparisons showed seven statistical groups for FF, with an intervalof 77-87 days and 14 statistical groups for FM, with an interval of70-86 days. For the variable AMz a variation of 91.4 to 154.6 cm wasobserved. In LESP, the length range was 29.4 to 50.6 cm. For thevariable Rend, the genotype seven yielded of 14.65 t/ha, which wasstatistically superior to genotype 81, the control check, with 12.38 t/ha. Early testing identified inbred lines with good agronomic characteristicsand high yield potential. It is considered as an appropriatemethod in a corn breeding program for eliminating lines with lowyield potential at an early stage of development of inbred lines.

Effects of long-term full straw return on yield and potassium response in wheat-maize rotation

The effect of long-term straw return on crop yield, soil potassium (K) content, soil organic matter, and crop response to K from both straw and chemical K fertilizer (K2SO4) were investigated in a fixed site field experiment for winter wheat-summer maize rotation in 6 years for 12 seasons. The field experiment was located in northern part of North China Plain with a sandy soil in relatively low yield potential. Two factors, straw return and chemical K fertilizer, were studied with two levels in each factor. Field split design was employed, with two straw treatments, full straw return of previous crop (St) and no straw return, in main plots, and two chemical K fertilizer treatments, 0 and 60 kg K2O ha−1, as sub-plots. The results showed that straw return significantly increased yields of winter wheat and summer maize by 16.5 and 13.2% in average, respectively, and the positive effect of straw return to crop yield showed more effective in lower yield season. Straw return significantly increased K absorption by the crops, with significant increase in straw part. In treatment with straw return, the K content in crop straw increased by 15.9 and 21.8% in wheat and maize, respectively, compared with no straw return treatment. But, straw return had little effect on K content in grain of the crops. Straw return had significant influences on total K uptake by wheat and maize plants, with an increase of 32.7 and 30.9%, respectively. There was a significant correlation between crop yield and K uptake by the plant. To produce 100 kg grain, the wheat and maize plants absorbed 3.26 and 2.24 kg K2O, respectively. The contents of soil available K and soil organic matter were significantly affected by the straw return with an increase of 6.07 and 23.0%, respectively, compared to no straw return treatment. K2SO4 application in rate of 60 kg K2O ha−1 showed no significant effect on wheat and maize yield, K content in crop straw, total K uptake by the crops, soil available K content, and soil organic matter. The apparent K utilization rate (percentage of applied K absorbed by the crop in the season) showed difference for wheat and maize with different K sources. In wheat season, the K utilization rate from K2SO4 was higher than that from straw, while in maize season, the K utilization rate from straw was higher than that from chemical fertilizer. In the whole wheat-maize rotation system, the K absorption efficiency by the two crops from straw was higher than that from K2SO4.

Yield gap analysis in major wheat growing areas of Khorasan province, Iran, through crop modelling

To increase wheat productivity from current levels, the yield gap, the difference between actual and potential yield, should be analyzed. A crop model was calibrated for three winter wheat cultivars and validated for a major wheat growing area to evaluate yield gaps in Khorasan province in northeastern Iran. The validated model was used to simulate long-term yield for 14 locations under three management conditions (potential, water-limited, nitrogen-limited). The results showed that the average simulated potential yield of 7.8Mgha−1 has not yet been realized by farmers and there is a large gap between the actual and potential production levels (about 5.2Mgha−1). The simulation showed considerable difference between cultivars for yield gap. When averaged over locations and seasons, the total yield gap obtained for Chamran wheat was 4.4Mgha−1, for Sionz was 6Mgha−1, and for Gascozhen was 6.1Mgha−1. Across locations, the proportion of yield gap from water-limitation was 1.7% to 19.5% and for nitrogen- limitation was 40% to 47%. The gap caused by other limiting and reducing factors was 33–57%. The highest yield gap was observed in Ghaen for Gascozhen (7.6Mgha−1) and the lowest was observed in Sarakhs for Chamran (3.1Mgha−1). The results of the study suggest that the average farm yield of about 2.6Mgha−1 in irrigated fields in Khorasan province is not limited by low genetic yield potential. This indicates that farmers should emphasize more on management factors such as water availability, timing of nitrogen application, and selection of cultivars adapted for each environment to reduce yield gap.

Selection and Semi-Dwarf Allele Mutants Segregation Pattern as the Result of Gamma Ray Irradiation of West Sumatera Black Rice

Black rice is a local rice originating from East Pasaman which has a low yield potential, long panicles, too high of longevity and plant height and soeasily fall. To reduce plant height has been irradiated rice seedsas much as 200 grams of black rice with a dose of 200 Gy of gamma rays. This study aimed to obtain information about the frequency of mutant semi-dwarf/dwarf and segregation patterns in mutant alleles black rice as the genetic improvement of West Sumatra local rice through mutation induction. From the selection of the M2 generation gained 31 candidates dwarf/semi dwarf mutant frequency of 0.062%. also obtained information that the segregation of alleles that make up the character ofthe semi dwarf/dwarf rodon rice mutant semi dwarf/dwarf trunked together with the distribution pattern of segregation according to Mendel's Law. On the character of the semi-dwarf/dwarf stem is influenced by one or two groups of alleles, where one of the alleles controlling the properties of semi-dwarf/dwarf stem, while the other controls the high stemproperties. Alleles from each group are in a locus that its chromosomes separate.It is evident that the semi-dwarf/dwarf on the mutant is occured due to one or more alleles is dominant on the high stem properties controlling alleles group toward the recessive.

GIS-based multi-criteria analysis for Arabica coffee expansion in Rwanda.

The Government of Rwanda is implementing policies to increase the area of Arabica coffee production. Information on the suitable areas for sustainably growing Arabica coffee is still scarce. This study aimed to analyze suitable areas for Arabica coffee production. We analyzed the spatial distribution of actual and potential production zones for Arabica coffee, their productivity levels and predicted potential yields. We used a geographic information system (GIS) for a weighted overlay analysis to assess the major production zones of Arabica coffee and their qualitative productivity indices. Actual coffee yields were measured in the field and were used to assess potential productivity zones and yields using ordinary kriging with ArcGIS software. The production of coffee covers about 32 000 ha, or 2.3% of all cultivated land in the country. The major zones of production are the Kivu Lake Borders, Central Plateau, Eastern Plateau, and Mayaga agro-ecological zones, where coffee is mainly cultivated on moderate slopes. In the highlands, coffee is grown on steep slopes that can exceed 55%. About 21% percent of the country has a moderate yield potential, ranging between 1.0 and 1.6 t coffee ha−1, and 70% has a low yield potential (<1.0 t coffee ha−1). Only 9% of the country has a high yield potential of 1.6–2.4 t coffee ha−1. Those areas are found near Lake Kivu where the dominant soil Orders are Inceptisols and Ultisols. Moderate yield potential is found in the Birunga (volcano), Congo-Nile watershed Divide, Impala and Imbo zones. Low-yield regions (<1 t ha−1) occur in the eastern semi-dry lowlands, Central Plateau, Eastern Plateau, Buberuka Highlands, and Mayaga zones. The weighted overlay analysis and ordinary kriging indicated a large spatial variability of potential productivity indices. Increasing the area and productivity of coffee in Rwanda thus has considerable potential.