Effects of soil compaction in the sub-humid cropping environment in Pakistan on uptake of NPK and grain yield in wheat (Triticum aestivum): II: Alleviation

Alleviation of soil compaction can be achieved through application of appropriate measures which will vary from soil to soil and with the socio-economic factors of the farmers. The effects of alleviation measures applied to artificially compacted soil on yield components, grain yield, dry matter and nutrient uptake by wheat was studied at the Agriculture Research Institute, Mingora, Pakistan, in two separate experiments in 2002–2003 and 2003–2004. The improvement measures included deep ploughing (DP), farmyard manure (FYM) and gypsum (GYP), and comprised a compacted control and four treatments T1 (control), T2 (DP), T3 (DP + FYM), T4 (DP + gypsum) and T5 (DP + FYM + GYP), arranged in completely randomized block design replicated four times. Improvement measures applied to compacted soil significantly decreased soil bulk density and increased total porosity. Bulk density decreased in the range of 12–15% while total porosity showed an increase of 16–23% over the control. Improvement measures significantly increased concentration and uptake of NPK in both years. Higher concentration and uptake was recorded during the second year as compared to the first year, probably as a result of higher seasonal rainfall in the second year. The uptake of NPK by wheat plants increased in the range of 43–51, 25–94 and 11–28%, respectively, over plants in the compacted control. Similarly, improvement treatments increased grains spike⁻¹, thousand grain weight, dry matter accumulation and grain yield in the range of 14–21, 5–14, 3–10 and 21–37% respectively, over the control. This work demonstrates that it is possible to overcome the deleterious effects of compaction induced by wheeled traffic, and improve crop yields and nutrient uptake in intensive cropping systems in rainfed environments in Pakistan and similar environments.     

Estimating maize nutrient uptake requirements

Generic, robust models are needed for estimating crop nutrient uptake requirements. We quantified and modeled grain yield–nutrient uptake relations in maize grown without significant biotic and abiotic stresses. Grain yield and plant nutrient accumulation in above-ground plant dry matter (DM) of commercial maize hybrids were measured at physiological maturity in on-station and on-farm experiments in Nebraska (USA), Indonesia, and Vietnam during 1997–2006. These data were used to model the nutrient requirements for yields up to 20 Mg ha⁻¹ using the QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) approach. The model required estimation of two boundary lines describing the minimum and maximum internal nutrient efficiencies of N, P and K (IE, kg grain per kg nutrient in plant DM), which were estimated at 40 and 83 kg grain kg⁻¹ N, 225 and 726 kg grain kg⁻¹ P and 29 and 125 kg grain kg⁻¹ K, respectively. The model predicted a linear increase in grain yield if nutrients are taken up in balanced amounts of 16.4 kg N, 2.3 kg P and 15.9 kg K per 1000 kg of grain until yield reached about 60–70% of the yield potential. The corresponding IEs were 61 kg grain kg⁻¹ N, 427 kg grain kg⁻¹ P and 63 kg grain kg⁻¹ K. The model predicted a decrease in IEs when yield targets approached the yield potential limit. A spherical model was derived from QUEFTS model outputs and found to be particularly suitable for practical applications such as estimating fertilizer needs. The proposed spherical model offers generality across environments and management practices, allowing users to estimate the optimal N, P and K uptake requirements based on two inputs: estimated yield potential and yield target. Further improvements in modeling the relationship between N uptake and grain yield can be made by taking into account differences in harvest index. Accuracy in the simulation of N uptake using the spherical model was improved from an RMSE of 35 kg N ha⁻¹ to 25 kg N ha⁻¹ when harvest index was accounted for, suggesting that the relationship between N uptake and actual yield is affected by both yield potential and efficiency in biomass partitioning.     

Phosphorus efficiency in long-term (15 years) wheat–maize cropping systems with various soil and climate conditions

Long-term (over 15 years) winter wheat (Triticum aestivum L.)–maize (Zea mays L.) crop rotation experiments were conducted to investigate phosphorus (P) fertilizer utilization efficiency, including the physiological efficiency, recovery efficiency and the mass (the input–output) balance, at five sites across different soil types and climate zones in China. The five treatments used were control, N, NP, NK and NPK, representing various combinations of N, P and K fertilizer applications. Phosphorus fertilization increased average crop yield over 15 years and the increases were greater with wheat (206%) than maize (85%) across all five sites. The wheat yield also significantly increased over time for the NPK treatments at two sites (Xinjiang and Shanxi), but decreased at one site (Hunan). The P content in wheat was less than 3.00 g kg⁻¹ (and 2.10 g kg⁻¹ for maize) for the N and NK treatments with higher values for the Control, NP and NPK treatments. To produce 1 t of grain, crops require 4.2 kg P for wheat and 3.1 kg P for maize. The P physiological use efficiency was 214 kg grain kg⁻¹ P for wheat and 240 kg grain kg⁻¹ P for maize with over 62% of the P from P fertilizer. Applying P fertilizer at 60–80 kg P ha⁻¹ year⁻¹ could maintain 3–4 t ha⁻¹ yields for wheat and 5–6 t ha⁻¹ yields for maize for the five study sites across China. The P recovery efficiency and fertilizer use efficiency averaged 47% and 29%, respectively. For every 100 kg P ha⁻¹ year⁻¹ P surplus (amount of fertilizer applied in excess of crop removal), Olsen-P in soil was increased by 3.4 mg P kg⁻¹. Our study suggests that in order to achieve higher crop yields, the long-term P input–output balance, soil P supplying capacity and yield targets should be considered when making P fertilizer recommendations and developing strategies for intensively managed wheat–maize cropping systems.     

Growth stage impacts tolerance of winter wheat (Triticum aestivum L.) to broadcast flaming

Organic wheat producers are interested in testing propane flaming as part of an integrated weed management program for organic wheat production. Therefore, the objective of this study was to collect baseline information on winter wheat tolerance to broadcast flaming as influenced by its growth stage at the time of flaming and dose of propane. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, Nebraska in 2007–2008 and 2008–2009 utilizing six doses of propane applied at four growth stages including: four leaves-4L, three tillers-3 T, shoot elongation-SE and boot stage-BS. The propane doses were 0, 12, 31, 50, 68 and 87 kg ha⁻¹ and were applied using a custom built flamer driven at a constant speed of around 6 km h⁻¹. Crop response to propane doses was described by log-logistic models based on visual estimates of crop injury, various yield components (spikes m⁻², kernels spike⁻¹ and 1000-kernel weight) and grain yield. Overall response to flaming was influenced by the growth stage of wheat and propane dose. In general, wheat at 3 T was the most tolerant and at BS was the most susceptible stage to broadcast flaming. Flaming negatively affected all yield components of wheat. Reduction of grain yield increased with increase in propane dose at each growth stage. The maximum yield losses of about 21%, 32%, 63% and 74% were obtained with the highest propane dose of 87 kg ha⁻¹ applied at 3 T, SE, 4L and BS growth stages, respectively. Due to unacceptable yield loss, the use of broadcast flaming in winter wheat at the tested growth stages is not recommended.     

A quantitative approach to characterize sink–source relationships during grain filling in contrasting wheat genotypes

We present a simple generic framework to quantify source–sink relationships during grain filling, by using a determinate growth function which has a unique property, namely being able of explicitly describing the time for the end of a growth process. This model framework was applied to analyze these relationships in plants of six wheat (Triticum aestivum L.) genotypes grown in pots in climate-controlled greenhouses under two temperature regimes (day/night: 20/15 and 25/20 °C). The function accurately described the sigmoid pattern of grain growth (sink activity), as its modified form did for the reversed sigmoid shape of flag-leaf area (source capacity), during grain filling. The six genotypes differed significantly in grain number as well as in grain yield, ranging from 54 to 81 grains and from 2.67 to 4.52 g DM per culm, respectively, when grown at 20/15 °C. Biomass and grain yield were significantly reduced by a rise of 5 °C. Grain nitrogen contents raised from 2.1 to 2.6% as a consequence of less carbon accumulation resulting in lower grain weights at the high temperature. On average, a rise of 5 °C in temperature reduced the duration of grain growth by 12 days (>30%), and increased the growth rate from 1.32 to 1.67 mg grain⁻¹ d⁻¹ (20%). Genotypic differences in grain-filling duration were also larger than in rate of grain growth. The genetic variation in the flag-leaf area duration (a proxy for the capacity for intercepting radiation and photosynthesis) was positively associated with sink size. Model analysis showed that whether or not the timing for the cessation of grain filling and for the end of post-anthesis source activity was synchronized depended on temperature. The quantitative approach yielded parameters that characterize genotypic differences of post-anthesis source and sink capacity in responding to environmental variables.     

Using stress tolerance indicator (STI) to select high grain yield iron-deficiency tolerant wheat genotypes in calcareous soils

Despite large variation among crop genotypes in response to Fe fertilization, there is no reliable indicator for identifying Fe-deficiency tolerant wheat genotypes with high grain yield. The aim of this investigation was to compare the grain yield response of 20 spring and 30 winter bread wheat genotypes to Fe fertilization under field conditions and to select high grain yield Fe-deficiency tolerant genotypes using a stress tolerance indicator (STI). Two individual trials, each one consisting two field plot experiments, were conducted during 2006–2007 and 2007–2008 growing seasons. Spring wheat genotypes (Trial l) and winter wheat genotypes (Trial 2) were planted at two different locations. Two Fe rates (0 and 20 kg Fe ha⁻¹ as Fe-EDTA) were applied. Spring and winter wheat genotypes differed significantly (P < 0.01) in the grain yield both with and without added Fe treatments. Application of Fe fertilizer increased grain yield of spring wheat genotypes by an average of 211 and 551 kg ha⁻¹ in Karaj and Isfahan locations, respectively. By Fe application, the mean grain yield of winter wheat genotypes increased 532 and 798 kg ha⁻¹ in Karaj and Isfahan sites, respectively. Iron efficiency (Fe-EF) significantly differed among wheat genotypes and ranged from 65% to 113% for spring wheat and from 69% to 125% for winter wheat genotypes. No significant correlation was found between Fe-EF and grain yield of spring wheat genotypes under Fe deficient conditions. For winter wheat genotypes grown in Mashhad, Fe-efficiency was not significantly correlated with the grain yield produced without added Fe treatment. The STI was significantly (P < 0.01) varied among spring and winter wheat genotypes. The interaction between location and genotype had no significant effect on the STI. According to these results, the STI should be considered as an effective criterion for screening programs, if a high potential grain yield together with more stable response to Fe fertilization in different environments is desired.     

Evaluating sustainable and profitable cropping sequences with cassava and four legume crops: Effects on soil fertility and maize yields in the forest/savannah transitional agro-ecological zone of Ghana

Rotations are important practices for managing soil fertility on smallholder farms. Six cropping sequences (cassava, pigeonpea, mucuna–maize–mucuna, cowpea–maize–cowpea, maize–maize–maize, and speargrass fallow) were evaluated during 2003–2004 in Wenchi district of Ghana for their effects on the profitability of the different rotations and the productivity of subsequent maize. Soil chemical properties were not significantly affected by cropping sequence. On the researcher-managed and farmer-managed plots maize grain yields were significantly influenced by cropping sequence. On the researcher-managed plots maize grain yield ranged from 1.0 t ha⁻¹ after speargrass fallow to 3.0 t ha⁻¹ with cassava cropping when N fertiliser was not applied to maize and from 2.1 t ha⁻¹ with continuous maize to 4.2 t ha⁻¹ with mucuna–maize–mucuna when 60 kg N ha⁻¹ was applied to maize. On the farmer-managed plots where N fertiliser was not applied to maize, maize grain yields ranged from 0.4 t ha⁻¹ on speargrass fallow to 2.2 t ha⁻¹ on plots previously cropped to pigeonpea. High maize grain yields associated with the cropping sequences involving cassava, mucuna and pigeonpea were related to the faster decomposition and N release of the biomass compared with the slower release of N by the poorer quality materials like maize stover and speargrass. Return on investment of the different rotational sequences ranged from −22% with speargrass/maize to 235% with cassava/maize when no N application was made to maize, and from 29% with continuous maize to 196% with cassava/maize when N fertiliser was applied to maize. Cassava/maize rotation was ranked by native farmers as the most preferred rotation whereas migrant farmers ranked cowpea–maize–cowpea–maize as the most preferred rotation. Among natives, male farmers ranked rotation involving cowpea as the next most preferred rotation after cassava/maize. In contrast, female farmers ranked pigeonpea/maize rotation as the second most preferred rotation, due to low labour and external input requirements of pigeonpea compared with cowpea. The choice of a particular rotational sequence is related to access to resources and the needs of the farmer. The study therefore suggests that, in a heterogeneous farming community like Wenchi, technology development should be targeted to suit the needs and resources available to each particular group of farmers.     

Dryland maize yields and water use efficiency in response to tillage/crop stubble and nutrient management practices in China

Rainfed crop production in northern China is constrained by low and variable rainfall. This study explored the effects of tillage/crop residue and nutrient management practices on maize (Zea mays L.) yield, water use efficiency (WUE), and N agronomic use efficiency (NAE) at Shouyang Dryland Farming Experimental Station in northern China during 2003–2008. The experiment was set-up using a split-plot design with 3 tillage/crop residue methods as main treatments: conventional, reduced (till with crop residue incorporated in fall but no-till in spring), and no-till (with crop residue mulching in fall). Sub-treatments were 3 NP fertilizer rates: 105–46, 179–78 and 210–92 kg N and P ha⁻¹. Maize grain yields were greatly influenced by the growing season rainfall and soil water contents at sowing. Mean grain yields over the 6-year period in response to tillage/crop residue treatments were 5604, 5347 and 5185 kg ha⁻¹, under reduced, no-till and conventional tillage, respectively. Grain yields under no-till, were generally higher (+19%) in dry years but lower (−7%) in wet years. Mean WUE was 13.7, 13.6 and 12.6 kg ha⁻¹ mm⁻¹ under reduced, no-till, and conventional tillage, respectively. The no-till treatment had 8–12% more water in the soil profiles than the conventional and reduced tillage treatments at sowing and harvest time. Grain yields, WUE and NAE were highest with the lowest NP fertilizer application rates (at 105 kg N and 46 kg P ha⁻¹) under reduced tillage, while yields and WUE tended to be higher with additional NP fertilizer rates under conventional tillage, however, there was no significant yield increase above the optimum fertilizer rate. In conclusion, maize grain yields, WUE and NAE were highest under reduced tillage at modest NP fertilizer application rates of 105 kg N and 46 kg P ha⁻¹. No-till increased soil water storage by 8–12% and improved WUE compared to conventional tillage, thus showing potentials for drought mitigation and economic use of fertilizers in drought-prone rainfed conditions in northern China.     

Characteristics of canopy structure and contributions of non-leaf organs to yield in winter wheat under different irrigated conditions

Non-leaf green organs of wheat plants may have significant photosynthetic potential and contribute to grain yield when the plants are subjected to stress at late growth stages. Canopy structure, change of green non-leaf organ area (e.g., ear, peduncle, sheath), the proportion of green non-leaf organs area to total green area and the contribution proportion from different organs’ photosynthate to grain yield in winter wheat (Triticum aestivum L.) were studied at Wuqiao Experiment Station of China Agricultural University, Hebei, China, in 2001-2002 and 2002-2003 using two winter wheat cultivars, Shijiazhuang8 (SJZ-8) and Lumai21 (LM-21). Four irrigation treatments used were W0 (no water applied during spring), W1 (750 m³ ha⁻¹ water applied at elongation), W2 (1500 m³ ha⁻¹ applied 50% at elongation and 50% at anthesis) and W4 (3000 m³ ha⁻¹ applied 25% at upstanding, booting, anthesis and grain filling), respectively. Results showed that the area of top three leaf blades decreased and the proportion of green non-leaf organ area to the total green area at anthesis increased with the decreasing of water supply. Root weight increased in the 0-100 cm soil layer and decreased in the 100-200 cm layer when water supply increased, suggesting reducing irrigation enhanced root weight in deep soil layer. The photosynthetic contribution of non-leaf organs above flag leaf node to grain yield increased with decreasing water supply, and was significantly higher than that of the flag leaf blade contribution. Winter wheat grain yield increased, but water use efficiency (WUE) decreased, with increase in water supply. Higher light transmission ratio in the canopy after anthesis was achieved with smaller size and high quality top leaf blades, higher grain-leaf ratio and larger proportion of green non-leaf area, which lead to higher canopy photosynthetic rate and WUE after anthesis. Irrigation of 1500 m³ ha⁻¹ applied in two parts, 750 m³ ha⁻¹ applied at elongation and another 750 m³ ha⁻¹ applied at anthesis, was the best irrigation scheme for efficient water use and for high yield in winter wheat.     

Genotypic variation in linear rate of grain growth and contribution of stem reserves to grain yield in wheat

Grain growth in wheat depends on current photosynthesis and stem water-soluble carbohydrates (WSC). In semiarid regions with terminal drought, grain filling in wheat crops may depend more on stem WSC content than on current assimilates. Reduction in grain yield under drought is attributed to shorter duration of linear grain growth despite increased contribution of stem reserves to grain yield. The amount of stem reserves is measured either by changes in stem dry weight (indirect method) or by stem WSC content (direct method). Genotypic variation in the rate and duration of linear grain growth and in percent contribution of stem reserves to grain yield has not been evaluated in wheat. The objectives of this study were: (i) to quantify the relationship between the direct and indirect measurement of stem reserves during and across the grain-filling period and (ii) to measure the extent of genotypic variation in rate and duration of linear grain growth and in percent contribution of stem reserves to grain yield. Dry weight, WSC content and grain yield of the main stem were measured at 10-day intervals in 11 diverse wheat genotypes under well-watered and droughted-field conditions across 2 years. Drought reduced stem WSC content from 413 to 281 mg and grain yield from 4.6 to 2.5 t ha⁻¹. Stem WSC content and dry weight were positively correlated. Genotypic differences in linear rate of grain growth were significant in well-watered (ranging from 48.9 to 72.4 mg spike⁻¹ day⁻¹) and in droughted-field (ranging from 33.2 to 59.9 mg spike⁻¹ day⁻¹) conditions. Drought, on average, reduced the linear rate and duration of grain growth by 20 and 50%, respectively. Reduction in linear rate ranged from 13 to 43%. The amount of current assimilates and stem reserves contributed to grain yield was reduced, respectively, by 54 and 11% under drought. Genotypic differences in percent contribution of stem reserves to grain yield were significant in well-watered (ranging from 19.1 to 53.6%) and in droughted-field (ranging from 36.6 to 65.4%) conditions. The wheat genotypes responded differently to drought. Main spike grain yield was reduced by 43% under drought due to 26 and 11% reduction in grain weight and number of grains, respectively. Grain yield was correlated with linear grain growth under well-watered (r = 0.96) and droughted (r = 0.83) conditions. The genotypic variation observed indicates that breeding for a higher rate of linear grain growth and greater contribution of stem reserves to grain yield should be possible in wheat to stabilize grain yield in stressful environments.     

Yield formation and tillering dynamics of direct-seeded rice in flooded and nonflooded soils in the Huai River Basin of China

Water shortage in the Huai River Basin prompts farmers to adopt water-saving technologies such as direct-seeded nonflooded or aerobic rice. Different cultivation practices impact on tiller growth and development. Improved insight into tiller dynamics is needed to increase yield in these production systems. We conducted field experiments with four direct-seeded rice varieties under flooded and nonflooded conditions in Mengcheng county, Anhui province, in 2005–2006. The soil water content in the nonflooded treatment varied between saturation and field capacity. Yields in nonflooded soil ranged from 3.6 to 4.7 t ha⁻¹, and did not differ significantly from yields in flooded soil that ranged from 3.6 to 5.1 t ha⁻¹. Variety had a significant effect on biomass, yield, panicle number, spikelet number, grain weight, and grain filling percentage. Panicle number was the main factor limiting yield, resulting from a low tiller emergence frequency and a low fraction of productive tillers in both the flooded and the nonflooded soils. On average, the panicle number was 159–232 m⁻², including 34–167 productive tillers per m² for all the varieties under the two water regimes. The contribution of productive tillers to yield varied between 7% and 47%. There were two peaks of tillers that contributed to yield, one at the low (4th or 5th) and one at the high (10th or 11th) phytomer orders. Frequencies of tiller emergence at most phytomer orders were higher in the flooded soil than in the nonflooded soil. There were no significant differences in frequencies of productive tiller emergence and contributions to yield from tillers between the soil water regimes for three of the four tested varieties. To increase yield in direct-seeded nonflooded rice production systems, both the tiller emergence frequency and the fraction of productive tillers should increase through breeding, improved crop management, or a combination.     

Reducing labour and input costs in soybean production by smallholder farmers in south-western Kenya

We conducted experiments in 2006 and 2007 in south-western Kenya to reduce labour and input cost of soybean production through different planting systems (point-placement was compared to planting in trenches and broadcasting), weeding frequencies (once or twice), and the use of local inputs (at 20 kg P ha⁻¹). Di-ammonium phosphate (DAP) was compared to manure, ashes, combinations of those, 1/2 Tithonia 1/2 DAP (TD) and no input. 1/3rd of the labour was saved when placing seeds in trenches as compared to individual holes without losing significant grain yield. Broadcasting requires 1/9th of the planting time while losing only 15% grain. 5% grain was lost by weeding once instead of twice, while saving 36% of the time. The time saved at planting can be more productively invested in collecting inputs. Plots without input yielded 537 kg ha⁻¹ grain and 642 kg ha⁻¹ biomass in 2006. Inputs increased both grain and biomass yields significantly with 27–51%, without significant difference between local and mineral inputs (with exception of TD). Using local input is thus a reasonable decision for farmers. Farmers concluded that the experiments had led to options for different types of farmers, with different access to resources, to increase their soybean production.     

High-yield irrigated maize in the Western U.S. Corn Belt: II. Irrigation management and crop water productivity

Appropriate benchmarks for water productivity (WP), defined here as the amount of grain yield produced per unit of water supply, are needed to help identify and diagnose inefficiencies in crop production and water management in irrigated systems. Such analysis is lacking for maize in the Western U.S. Corn Belt where irrigated production represents 58% of total maize output. The objective of this paper was to quantify WP and identify opportunities to increase it in irrigated maize systems of central Nebraska. In the present study, a benchmark for maize WP was (i) developed from relationships between simulated yield and seasonal water supply (stored soil water and sowing-to-maturity rainfall plus irrigation) documented in a previous study; (ii) validated against actual data from crops grown with good management over a wide range of environments and water supply regimes (n = 123); and (iii) used to evaluate WP of farmer's fields in central Nebraska using a 3-y database (2005–2007) that included field-specific values for yield and applied irrigation (n = 777). The database was also used to quantify applied irrigation, irrigation water-use efficiency (IWUE; amount of yield produced per unit of applied irrigation), and the impact of agronomic practices on both parameters. Opportunities to improve irrigation management were evaluated using a maize simulation model in combination with actual weather records and detailed data on soil properties and crop management collected from a subset of fields (n = 123). The linear function derived from the relationship between simulated grain yield and seasonal water supply, namely the mean WP function (slope = 19.3 kg ha⁻¹ mm⁻¹; x-intercept = 100 mm), proved to be a robust benchmark for maize WP when compared with actual yield and water supply data. Average farmer's WP in central Nebraska was ∼73% of the WP derived from the slope of the mean WP function. A substantial number of fields (55% of total) had water supply in excess of that required to achieve yield potential (900 mm). Pivot irrigation (instead of surface irrigation) and conservation tillage in fields under soybean–maize rotation had the greatest IWUE and yield. Applied irrigation was 41 and 20% less under pivot and conservation tillage than under surface irrigation and conventional tillage, respectively. Simulation analysis showed that up to 32% of the annual water volume allocated to irrigated maize in the region could be saved with little yield penalty, by switching current surface systems to pivot, improving irrigation schedules to be more synchronous with crop water requirements and, as a fine-tune option, adopting limited irrigation.     

Effect of trifluralin,pronamide, haloxyfop-p methyl,propaquizafop, and isoxaben on weed control and oilseed rape yield in Iran

In order to investigate the effect of trifluralin, pronamide, haloxyfop-p methyl, propaquizafop and isoxaben on weed control and oilseed rape yield, a two year field experiment was conducted at Darab, Iran, during 2004–2005 and 2005–2006 growing seasons. Herbicides reduced weed biomass compared with the weedy check. In 2004–2005, at 16 WAP (weeks after planting), application of trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha and trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha provided best control (80%) of wild mustard (Sinapis arvensis L.), compared to other treatments. At 8 and 16 WAP, wild mustard control decreased to 47 and 42%, respectively, when trifluralin was applied alone at 1400 g a.i./ha. In 2005–2006 at 16 WAP, maximum reduction in wild mustard biomass (82%) was achieved with trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha. In both years, all herbicide treatments controlled fumitory (Fumaria officinalis L.) 64–96%. In 2004–2005, at 16 WAP, wild oat (Avena fatua L.) biomass reduction by trifluralin plus propaquizafop plus isoxaben at 1200 + 200 + 250 g a.i./ha was 95%. In 2005–2006, at 8 and 16 WAP, minimum biomass reduction of wild oat (37–53%) was observed with trifluralin at 1200 and 1400 g a.i./ha. In both years, at 8 and 16 WAP, the most effective herbicide treatments were trifluralin plus propaquizafop plus isoxaben and trifluralin plus haloxyfop-p methyl plus isoxaben regardless of the dose applied and provided maximum reduction in total weed biomass (77–89%) compared to other treatments. Results of both years showed that all herbicide treatments increased oilseed rape grain yield as compared with the weedy check but percentage of oil was not affected by various herbicide treatments. Maximum grain yield was obtained with trifluralin plus haloxyfop-p methyl plus isoxaben at 1200 + 100 + 500 g a.i./ha.     

Assessment of some major yield-limiting factors on maize production in a humid temperate environment

Despite the availability of modern hybrids and better agronomic practices, there existed large gaps between attainable yield of maize (Zea mays L.) grown with recommended practices and producers’ harvest yields in the humid temperate regions of eastern Canada. A field experiment was conducted for 3 years in Ottawa, Canada, to determine the most important management yield-limiting factor(s) on rainfed maize grain production. A package of recommended practices (RP) was composed with the recommended levels of nitrogen (N), phosphorus (P), potassium (K), micronutrients, chemical weed control, and plant population density (PPD). Each factor was modified from the RP, making a total of 11 treatments. Under the low occurrence of diseases or insects, weed infestation was the most important yield-limiting factor, which reduced grain yield by 27–38%. While lack of preplant N application (100 kg ha⁻¹) reduced yield by 10–22%, there was no yield increment with additional sidedressing N (50 kg N ha⁻¹). Grain yield was reduced by 8–13% with low PPD (60,000 plants ha⁻¹) in all years, whereas increasing PPD to 90,000 plants ha⁻¹ did not improve yield, compared with the RP. Withhold P application did not affect yield in all years, but yield was reduced by up to 13% in the absence of K, and by 10% and 12% without Zn or Mn, respectively, in 1 year. Our results indicated that lack of weed control (i.e. herbicide use) was the major yield-limiting factor followed by fertilizer N and PPD. The responses of grain yield to K, Zn, and Mn were site and/or year specific. Our study provided experimental data and an insight understanding of yield gap between genotype's yield potential achievable with recommended practices and yields with producers’ practices.     

Rice responses to soil management in a rice-based cropping system in the semi-arid tropics of southern Lombok,Eastern Indonesia

This paper is the first of a series that investigates whether new cropping systems with permanent raised beds (PRBs) or Flat land could be successfully used to increase farmers’ incomes from rainfed crops in Lombok in Eastern Indonesia. This paper discusses the rice phase of the cropping system. Low grain yields of dry-seeded rice (Oryza sativa) grown on Flat land on Vertisols in the rainfed region of southern Lombok, Eastern Indonesia, are probably mainly due to (a) erratic rainfall (870–1220 mm/yr), with water often limiting at sensitive growth stages, (b) consistently high temperatures (average maximum = 31 °C), and (c) low solar radiation. Farmers are therefore poor, and labour is hard and costly, as all operations are manual. Two replicated field experiments were run at Wakan (annual rainfall = 868 mm) and Kawo (1215 mm) for 3 years (2001/2002 to 2003/2004) on Vertisols in southern Lombok. Dry-seeded rice was grown in 4 treatments with or without manual tillage on (a) PRBs, 1.2 m wide, 200 mm high, separated by furrows 300 mm wide, 200 mm deep, with no rice sown in the well-graded furrows, and (b) well-graded Flat land. Excess surface water was harvested from each treatment and used for irrigation after the vegetative stage of the rice. All operations were manual. There were no differences between treatments in grain yield of rice (mean grain yield = 681 g/m²) which could be partly explained by total number of tillers/hill and mean panicle length, but not number of productive tillers/hill, plant height or weight of 1000 grains. When the data from both treatments on PRBs and from both treatments on Flat land, each year at each site were analysed, there were also no differences in grain yield of rice (g/m²). When rainfall in the wet season up to harvest was over 1000 mm (Year 2; Wakan, Kawo), or plants were water-stressed during crop establishment (Year 1; Wakan) or during grain-fill (Year 3: Kawo), there were significant differences in grain yield (g/1.5 m²) between treatments; generally the grain yield (g/1.5 m²) on PRBs with or without tillage was less than that on Flat land with or without tillage. However, when the data from both treatments on PRBs and from both treatments on Flat land, each year at each site, were analysed, the greater grain yield of dry-seeded rice on Flat land (mean yield 1 092 g/1.5 m²) than that on PRBs (mean 815 g/1.5 m²) was mainly because there were 25% more plants on Flat land. Overall when the data in the 2 outer rows and the 2 inner rows on PRBs were each combined, there was a higher number of productive tillers in the combined outer rows (mean 20.7 tillers/hill) compared with that in the combined inner rows on each PRB (mean 18.2 tillers/hill). However, there were no differences in grain yield between combined rows (mean 142 g/m row). Hence with a gap of 500 mm (the distance between the outer rows of plants on adjacent raised beds), plants did not compensate in grain yield for missing plants in furrows. This suggests that rice (a) also sown in furrows, or (b) sown in 7 rows with narrower row-spacing, or (c) sown in 6 rows with slightly wider row-spacing, and narrower gap between outer rows on adjacent beds, may further increase grain yield (g/1.5 m²) in this system of PRBs. The growth and the grain yield (y in g/m²) of rainfed rice (with rainfall on-site the only source of water for irrigation) depended mainly on the rainfall (x in mm) in the wet season up to harvest (due either to site or year) with y = 1.1x − 308; r² = 0.54; p < 0.005. However, 280 mm (i.e. 32%) of the rainfall was not directly used to produce grain (i.e. when y = 0 g/m²). Manual tillage did not affect growth and grain yield of rice (g/m²; g/1.5 m²), either on PRB or on Flat land.     

Influence of liming and form of nitrogen fertilizer on nutrient uptake,growth, yield,and quality of Virginia (flue-cured) tobacco

Soil acidity is a limiting factor affecting the growth and yield of many crops all over the world. It is recognized that liming is the most common management practice of profitable crop production on acid soils. On the other hand, it is well-known that the form of nitrogen may affect tobacco yield and quality. In this work, the impact of the interaction between three hydrated lime (HL, Ca(OH)₂) rates (0, 1.5 and 3 t HL ha⁻¹) and three nitrogen fertilizer forms (NO₃-N 100%, NH₄-N 100% and NO₃-N 50% plus NH₄-N 50%) on growth, yield and quality characteristics of Virginia (flue-cured) tobacco was investigated in a 4-year (1995–1998) field experiment established in an acid soil (pH_{water 1:1} 5.3) located in Northern Greece. Lime was applied only once in December 1994, while nitrogen fertilizer was applied annually before transplanting. The results showed that the effect of liming on tobacco growth was not dependent on time, weather conditions and form of nitrogen fertilizer. Liming increased soil pH, enhanced the early growth of tobacco (within 30 days after transplanting (DAT)) and finally increased the total gross and trade yield of tobacco proportionally to the amount of HL added. However, the quality index (organoleptic characteristics) of the cured product was improved only at the HL application rate of 3 t HL ha⁻¹. Furthermore, liming significantly increased Ca and P concentrations but decreased K concentration in cured tobacco leaves. Tobacco yield increase was attributed to the increase of P uptake. Liming also increased the ash content of cured leaves, whereas it did not significantly affect nicotine, total nitrogen and reducing sugars. The use of ammonium N in fertilizer delayed the early growth of tobacco, reduced the nicotine concentration and increased the reducing sugars concentration of the cured product. Total-N, P, K and Mg concentrations of cured leaves were not significantly affected by the form of nitrogen fertilizer used. The results suggested that an initial application of hydrated lime at a rate of 3 t HL ha⁻¹ may ameliorate soil acidity and increase the yield and quality characteristics of Virginia tobacco at least over a 4-year period after application, independent of the form of N fertilizer used.     

Physiological characterization of introgression lines derived from an indica rice cultivar, IR64, adapted to drought and water-saving irrigation

Water scarcity threatens sustainable rice production in many irrigated areas around the world. To cope with the scarcity, aerobic rice culture has been proposed as a promising water-saving technology. The objective was to elucidate the physiological attributes behind the performance of rice introgression lines in water-saving culture. We evaluated yield potential and physiological adaptation traits to water deficit of BC₃-derived lines with the genetic background of an elite indica cultivar, IR64, in the field and in pot experiments. One line, YTH183, had 26% higher yield than IR64 under non-stress conditions (895 vs. 712 g m⁻² on average). This was attributed to enlarged sink capacity due to large grain size, which contributed to more efficient use of assimilates and hence a higher harvest index. YTH183 also showed better dehydration avoidance under intermittent soil drying, due to the adaptive response of deep rooting to water deficiency. The grain yield of YTH183 exceeded that of IR64 by 92-102% under moderate water deficit caused by limited irrigation in aerobic rice culture (143 vs. 72 g m⁻²). Two introgressed segments on chromosomes 5 and 6 might, at least in part, confer the higher yield potential and greater dehydration avoidance in YTH183 simultaneously. Advanced backcross breeding combined with molecular genetics and physiological characterization of introgressed segments would be effective for developing new rice cultivars with high yield potential and drought adaptation traits.     

Plant characteristics associated with weed competitiveness of rice under upland and lowland conditions in West Africa

Weeds are a major constraint to rice (Oryza spp.) production in West Africa. Superior weed competitive rice genotypes may reduce weed pressure and improve rice productivity. Two upland and two lowland experiments were conducted in southern Benin to examine genotypic variations in weed-suppressive ability and grain yield under weedy conditions, and to identify plant characteristics that could be used as selection criteria for improved weed competitiveness. A total of 19 genotypes, including Oryza sativa and Oryza glaberrima genotypes and interspecific hybrids developed from crossing O. sativa and O. glaberrima, were grown under weed-free and weedy conditions in an upland with supplemental irrigation and in a flooded lowland. In weedy plots, hand weeding was done once or not at all. Mean relative yield loss across all genotypes due to weed competition ranged from almost 0% to 61%. Large genotypic variations in weed biomass and grain yield under weedy conditions were found. Visual growth vigor at 42 and 63 days after sowing (DAS) under weed-free conditions significantly correlated with weed biomass at maturity in both upland and lowland experiments (R² = 0.26–0.48). Where weed pressure was low to moderate, with mean relative yield loss less than 23%, the multiple regression models using grain yield and plant height at maturity or only grain yield measured under weed-free conditions as independent variables could explain 66–88% of the genotypic variation in grain yield under weedy conditions. At higher weed pressure (mean relative yield loss: 61%), as observed in one of the upland experiments, biomass accumulation of rice at 42 days after sowing was associated with higher grain yield under weedy conditions. Biomass accumulation also significantly correlated with visual growth vigor at the same sampling dates. Therefore, we conclude that grain yield, plant height at maturity and visual growth vigor at 42–63 DAS under weed-free conditions appear to be useful selection criteria for developing superior weed competitive rice genotypes.     

Growing maize in clumps as a strategy for marginal climatic conditions

Under dryland conditions of the Texas High Plains, maize (Zea mays) production is limited by sparse and erratic precipitation that results in severe water stress particularly during grain formation. When plant populations are reduced to 2.0–3.0 plants m⁻² to conserve soil water for use during grain filling, tillers often form during the vegetative growth and negate the expected economic benefit. We hypothesized that growing maize in clumps spaced 1.0 m apart would reduce tiller formation, increase mutual shading among the plants, and conserve soil water for grain filling that would result in higher grain yield. Studies were conducted during 2006 and 2007 at Bushland, TX. with two planting geometries (clump vs. equidistant), two irrigation methods (low-energy precision applicator, LEPA, and low-elevation spray applicator, LESA) at three irrigation levels (dryland, 75 mm and 125 mm in 2006; and dryland, 50 mm and 100 mm in 2007). For dryland plots in 2007, clump plants had only 0.17 tillers (0.66 tillers m⁻²) compared with 1.56 tillers per plant (6.08 tillers m⁻²) for equidistant spacing. Tillers accounted for 10% of the stover for the equidistant plants, but less than 3% of the grain. Clump planting produced significantly greater grain yields (321 g m⁻² vs. 225 g m⁻² and 454 g m⁻² vs. 292 g m⁻² during 2006 and 2007, respectively) and Harvest Indexes (0.54 vs. 0.49 and 0.52 vs. 0.39 during 2006 and 2007, respectively) compared with equidistant plants in dryland conditions. Water use efficiency (WUE) measurements in 2007 indicated that clumps had a lower evapotranspiration (ET) threshold for initiating grain production, but the production function slopes were 2.5 kg m⁻³ for equidistant treatments compared to 2.0 kg m⁻³ for clump treatments. There was no yield difference for method of irrigation on water use efficiency. Our results suggest that growing maize in clumps compared with equidistant spacing reduced the number of tillers, early vegetative growth, and Leaf Area Index (LAI) so that more soil water was available during the grain filling stage. This may be a useful strategy for growing maize with low plant populations in dryland areas where severe water stress is common.