Nitrogen applications modify seed and oil yields and fatty acid composition of winter mustard

Winter mustard (Brassica juncea L.) is not a common crop in the Southeastern United States. With increased interest in biodiesel production, there has been corresponding interest in mustard in this region. The objective of this study was to evaluate the effect of N fertilization (0, 50, 100, 150 kg N ha⁻¹) on productivity, oil content, and oil composition of winter mustard ‘Pacific Gold’ grown at three locations in Mississippi (Stoneville, and two locations at Verona, namely Verona silt loam (Verona-SL) and Verona clay (Verona-C)). Nitrogen did not affect oil content (percent oil). Seed and oil yields (kg ha⁻¹) increased with N application relative to the unfertilized control. At the Verona-C location, the concentration of oleic acid was higher in the 50 kg N ha⁻¹ treatment. At Stoneville, linolenic acid concentration was higher in the 150 kg N ha⁻¹ and lower in the 100 kg/N ha⁻¹ treatment, while it was not different in the other treatments. Overall, the yield of the fatty acids (FA) palmitic, palmitoleic, stearic, oleic, linoleic, linolenic, arachidic, eicosanoic, behenic, erucic, lignoceric, and nervonic acid increased with higher N rates (100 or 150 kg N/h). The highest yield of FA in the two Verona locations were achieved in the 100 kg N ha⁻¹, while greatest yield of FA at Stoneville was achieved in the highest N rate (150 kg N ha⁻¹). Means of mustard oil yields in our study in the higher fertility treatment ranged from 737 to 1094 kg ha⁻¹. This study demonstrated winter mustard production in Mississippi and possibly other areas in the Southeastern United States can be successful and could provide seed and oil yields comparable to yields from other production areas.     

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha⁻¹ in 2002, 310 kg ha⁻¹ in 2003, and 360 kg ha⁻¹ in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha⁻¹ of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.     

Sesame response to nitrogen management under contrasting water availabilities

Sesame is mainly cultivated under traditional, low-input agro-systems. Recent breeding developments promoted the modernization and mechanization of sesame cultivation. However, only a few articles have been published concerning fertilization requirements for both modern and traditional agro-systems. In field trials at two locations,we determined the response of irrigated sesame to nitrogen(N). Three promising sesame lines were tested combining two irrigation levels with four N levels. At a high ...     

Effect of the type of fertilizer and source of irrigation water on N use in a maize crop

An experiment in a maize crop evaluated the influence of several types of commercial nitrogenous fertilizers with different action mechanisms — urea (soluble), Floranid-32 (low water solubility) and Multicote 4 (coated fertilizer) — on maize grain and biomass yields, as well as on plant N use. The fertilizers were applied as a top-dressing of 294 kg N ha⁻¹. All treatments additionally received 64 kg N ha⁻¹ as 8.0 (N):6.5 (P):12.5 (K) compound prior to seedbed preparation. The influence of NO⁻₃ content in the irrigation water was also assessed, using water with either 2.5 or 35 mg l⁻¹ of NO⁻₃. Irrigation plus rainfall totalled 513 mm (1.20 potential ET). Nitrogen lost during the cultivation period was calculated from the N balance of the topsoil.Results obtained under these experimental conditions showed that the type of fertilizer did not alter maize grain and biomass yields. Yields for maize irrigated with the higher NO⁻₃ water were systematically greater than those obtained with irrigation water of low NO⁻₃ content.Nitrogen lost from the topsoil during the cultivation period varied between 240 and 280 kg N ha⁻¹ for all treatments, and was well correlated with NO⁻₃-N leached into the aquifer during the same period.     

Effect of irrigation and nitrogen fertilization on biomass yield and efficiency of energy use in crop production of Miscanthus

The perennial C₄ grass Miscanthus has been proposed as a biomass energy crop in Europe. Effects of crop age, irrigation and nitrogen fertilization on biomass and energy yields and N content of Miscanthus were investigated and the energy costs of production determined. After an establishment period of 1 year, cultivation of Miscanthus resulted in a dry matter production of over 37 t ha⁻¹ year⁻¹ over a period of 4 years. Irrigation and nitrogen level greatly affected Miscanthus biomass yield. In absence of N fertilization, irrigation did not modify biomass yield and the effect of irrigation increased with the increase in N level. The average N response ranged from 37 to 50 kg biomass kg⁻¹ N applied. Because the calorific value of Miscanthus biomass (16.5 MJ kg⁻¹) was not affected by irrigation and N fertilization, energy production depended exclusively on biomass yield. Maximum energy yield was 564 GJ ha⁻¹ year⁻¹. Without N supply and irrigation, energy yield was 291 GJ h⁻¹. Net energy yield, calculated as the difference between energy output and input, but without inclusion of drying costs, was 543 GJ ha⁻¹ with N fertilization and irrigation and 284 GJ ha⁻¹ without; the ratios of energy output to input in crop production were 22 and 47, respectively.     

Effect of nitrogen rates on yield and quality of fennel (Foeniculum vulgare Mill.) accessions

Nitrogen rates and plant genotypes effects yield and quality of medicinal plants therefore, this experiment was conducted in order to determine the effects of nitrogen rates on fennel accessions quality and quantity. The experimental design was a split plot with nitrogen rate (0, 40, 80, 120 and 160 Kg N ha⁻¹) as main and accession (Isfahan, Tehran, Yazd and EU11486) as sub plots and replicated four times. The experiment was conducted at the Isfahan University of Technology Experimental Station, Isfahan, Iran during 2008-2009. Plant height, number of umbel per plant, 1000seed weight, number of seeds per umbel, seed yield, seed essential oil yield, seed and foliage essential oil contents and seed ash, protein and fiber contents were measured. Nitrogen fertilization increased all measured traits, but reduced ash content. On average, the highest seed and foliage essential contents and seed essential yield were produced at 160 kg per N ha⁻¹ and EU11486 was a superior cultivar for these traits. However, there was an interaction between N rate and accession on all traits. Isfahan (11.65 kg ha⁻¹), EU11486 (38.26 kg ha⁻¹), Tehran (15.32 kg ha⁻¹) and Yazd (22.06 kg ha⁻¹) produced the highest seed essential oil yield under application of 160, 80, 160 and 120 kg N ha⁻¹, respectively. Foliage of the accessions contained 0.45-0.91% essential oil and seeds of accessions contained 17.6-18.2% protein and 8.9-9.4% ash suggesting that foliage of fennel also is a good source of essential oil and seeds of fennel are good sources of protein and minerals. The results showed that N fertilization and accession can affect yield and quality of fennel and accessions responded differently to N fertilization rates, thus selection among the accessions and N rates for better fennel production is possible.     

Evapotranspiration,yield, and water-use efficiency responses of Lesquerella fendleri at different growth stages

Lesquerella fendleri (Gray) Wats. is a potential new oilseed crop for the arid southwestern United States. Lesquerella seed oil with similar properties as castor oil is being considered as a domestic replacement for the imported castor oil. Development of new crops with low irrigation needs is of high priority. Because the most critical stage of sensitivity to moisture deficits has not been determined in Lesquerella species, the objectives of this study were: (i) to identify the most critical stage or stages for moisture deficit and, (ii) to determine the effect of moisture deficit on yield, yield components, oil and fatty acid composition. Two-year field studies were conducted at the New Mexico State University, Leyendecker Plant Science Research Center. The experimental design was a randomized complete block. The treatments consisted of (a) T1: Continuous favorable soil moisture [irrigated at 50% soil water depletion (SWD)]. (b) T2: Moisture stress (75% SWD) from establishment to initial flowering with no stress from flowering to final harvest (50% SWD). (c) T3: No stress imposed from establishment to initial flowering (50% SWD) followed by stress to final harvest (75% SWD). (d) T4: Moisture stress (75% SWD) from establishment to final harvest. The amount of water applied ranged from 810 to 729 mm for the first year, and 810 to 625 mm for the second year. Seed weight per plant and number of pods per plant were generally higher when water availability was maintained at or above 50% SWD throughout the growing season. Neither seed number per pod nor seed size was influenced by irrigation treatments. Lesquerella was more sensitive to water availability during flowering and seed development as a greater loss in seed yield occurred when irrigation was delayed to 75% SWD during that stage of development. Seed yield and dry matter production from the 2 year field studies were closely related to the seasonal cumulative evapotranspiration. For each millimeter of evapotranspiration, seed yield increased from 1.8 kg ha⁻¹ mm in 1994–1995 to 1.3 kg ha⁻¹ mm for 1995–1996. The dry matter production increased 13.4 kg ha⁻¹ for each mm increase in seasonal evapotranspiration during 1994–1995. This relationship was a second order polynomial with an R² of 0.86 during 1995–1996. The WUE_gr and WUE_dm were highest under the most favorable water availability conditions for growth and seed development. Delaying irrigation to 75% SWD throughout the crop growth period resulted in the lowest oil content. Lesquerolic acid content was not affected by irrigation during both the growing seasons.     

Safflower yield,chlorophyll content,photosynthesis, and water use efficiency response to nitrogen fertilization under rainfed conditions

Safflower (Carthamus tinctorius L.) is a deep-rooted crop which can tolerate water stress and can be grown in rotation with other crop species. Nitrogen is very important for the growth and yield of safflower, however, the effect of N level on chlorophyll content, assimilation rate, transpiration rate, stomatal conductance, substomatal CO₂ concentration, and water use efficiency (WUE) have not been determined. A 2-year field study was conducted with the objective to determine the effect of N fertilization on yield, yield components, chlorophyll content, photosynthetic characteristics, and WUE of safflower grown under rainfed conditions. Three rates of N were used (0, 100, and 200 kg N ha⁻¹) and two hybrids (CW9048 and CW9050). N fertilization increased seed yield by an average of 19%, the seed weight per plant by 60%, the seed weight per head by 18%, the number of heads per plant by 32%, and the number of seeds per plant by 41% compared with the control. N level also affected chlorophyll content, N concentration at anthesis, protein, and oil yield. N application increased assimilation rate by an average of 51%, stomatal conductance of water vapour by an average of 27%, and WUE by an average of 60% over the 2 years of the study when compared to the control. The present study indicates that N fertilization can affect yield, yield components, photosynthetic efficiency, and physiology of safflower under rainfed conditions.     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: I. Legume biomass production and N fixation

Field experiments were conducted to investigate the performance of temperate legume species in rice-based cropping systems in a warm-temperate environment in Nepal. Over the period 1994–1996, various legume species were grown during the winter season (October–May) in the Kathmandu valley (27° N, 1350 m asl) with the aim of evaluating their biomass production and N fixation. A wide range of legume species including food, feed and green manure crops proved to be very well adapted to the winter growing conditions in this environment. The cultivation of temperate legume crops therefore, constitutes an alternative to traditional cropping practices such as growing wheat or leaving the land fallow. The temperate species appeared to capitalise on generally favourable growing conditions such as long growing season, low pest and disease pressure, high radiant energy receipt and cool night temperatures. However, performance varied greatly between species and years. Total dry matter yields ranged from 2 to 20 t ha⁻¹ obtained with lentil (Lens culinaris Medic) and bitter lupin (Lupinus mutabilis), respectively. Highest seed yields were produced by fababean (Vicia faba) (5 t ha⁻¹) and field pea (Pisum sativum var. arvense) (3 t ha⁻¹) in the first season. Nitrogen yields and quantities of N fixed ranged from 18 to 481 kg ha⁻¹ and from 0 to 463 kg ha⁻¹, respectively. Large amounts of N were fixed by species such as fababean, Persian clover (Trifolium resupinatum) and bitter lupin. Early sowing in autumn was shown to be beneficial for some crops such as fababean, vetch (Vicia benghalensis) and Persian clover. In these cases, it is, therefore, important to reduce the turn-around interval after rice. Further research is required to fully determine the potential of temperate legume species in these environments with particular emphasis given to the identification of the most adapted cultivars and to reduce the need for irrigation of these winter crops.     

Yield response of two potato culivars to supplemental irrigation and N fertilization in New Brunswick

Nitrogen and water are important factors influencing potato production, and crop response to these two factors may vary with cultivars. The yield response of two potato cultivars (Russet Burbank and Shepody) to six rates of N fertilization (0-250 kg N ha^-1) with and without supplemental irrigation was studied at four onfarm sites in each of three years, 1995 to 1997, in the upper St-John River Valley of New Brunswick, Canada. On average, irrigation increased total yield from 31.9t ha^-1 without irrigation to 38.41 ha^-1 with irrigation and marketable yield from 25.61 ha^-1 without irrigation to 30.71 ha^-1 with irrigation. Potato yields were increased by irrigation at nine out of the 12 sites, and the irrigation response was similar for both cultivars. Nitrogen fertilization significantly increased both total and marketable yields at all sites except one. The yield response to N fertilization was greater with irrigation. The N fertilization rate (Nmax) required to reach maximum total and marketable yield, however, was similar with and without irrigation. A large variation in Nmax was observed among sites. With irrigation Nmax varied between 158 and 233 kgN ha^-1 for total yield, and between 151 and 250 kg N ha^-1 for marketable yield. There was no interaction between N fertilization and potato cultivar for both total and marketable yields. The two cultivars had similar total yields (35 t ha^-1). Shepody, however, had a greater marketable yield (28.9 t ha^-1) than Russet Burbank (27.4 t ha^-1). Our results indicate that the response to two of the most significant factors of potato production, irrigation and N fertilization, varies greatly with sites and climatic conditions, and that field specific recommendations are required for the optimum management of N and irrigation.     

Site-specific nutrient management for intensive rice cropping systems in Asia

Irrigated rice (Oryza sativa L.) yield increases in Asia have slowed down in recent years. Further, yield increases are likely to occur in smaller increments through fine-tuning of crop management. On-farm experiments at 179 sites in eight key irrigated rice domains of Asia were conducted from 1997 to 1999 to evaluate a new approach for site-specific nutrient management (SSNM). Large variation in initial soil fertility characteristics and indigenous supply of N, P, and K was observed among the eight intensive rice domains as well as among farms within each domain. Field- and season-specific NPK applications were calculated by accounting for the indigenous nutrient supply, yield targets, and nutrient demand as a function of the interactions between N, P, and K. Nitrogen applications were fine-tuned based on season-specific rules and field-specific monitoring of crop N status. The performance of SSNM was tested for four successive rice crops. Average grain yield in the SSNM increased by 0.36 Mg ha⁻¹ (7%) compared to the current farmers’ fertilizer practice (FFP) measured in the same cropping seasons or 0.54 Mg ha⁻¹ (11%) compared to the baseline FFP yield before intervention. Average nutrient uptake under SSNM increased by about 10% in the same seasons or by 13% (N) and 21% (P, K) compared to the baseline data. Yield increases were associated with a 4% decrease in the average N rate, but larger amounts of fertilizer-K at sites where the previous K use was low. Average N use efficiencies increased by 30–40%, mainly through the use of improved in-season N management schemes. Across all sites and four successive rice crops, profitability increased by US$ 46 ha⁻¹ per crop or 12% of the total average net return. The performance of SSNM did not differ significantly between high-yielding and low-yielding climatic seasons, but improved over time with larger benefits observed in the second year. Average profitability increased from US$ 32 ha⁻¹ pre crop in the first year to US$ 61 ha⁻¹ pre crop in the second year due to improvements in the SSNM approach and re-capitalization of P and K applied in the first year. SSNM required little extra credit for financing, and remained profitable even if rice prices are somewhat lower than current levels. Further, scope for improvement exists at many sites by alleviating other crop management constraints to nutrient use efficiency. Profit increases ranged from US$ 4 to 82 ha⁻¹ per crop among eight rice domains. However, profit decreases occurred in about 25% of all cases, indicating that a certain minimum level of crop care is required for SSNM to be profitable. Yields at sites with labor-saving direct-seeding of larger fields were about 1 Mg ha⁻¹ lower than those achieved at sites with labor-intensive transplanting and good management, raising concern about future trends in rice production. SSNM has potential for improving yields and nutrient efficiency in irrigated rice to close existing yield gaps. The major challenge for SSNM will be to retain the success of the approach while reducing the complexity of the technology as it is disseminated to farmers. The nature of the approach will need to be tailored to specific circumstances in different countries. In some areas, SSNM may be field or farm specific, but in many areas it is likely to be just region and season-specific.     

Agronomy of fibre hemp (Cannabis sativa L.) in Europe

Fibre hemp may yield up to 25 t above ground dry matter per hectare (20 t stem dry matter ha⁻¹) which may contain as much as 12 t ha⁻¹ cellulose, depending on environmental conditions and agronomy. Its performance is affected by the onset of flowering and seed development. Effects of cultivar and management on yield and quality were tested at three contrasting sites in Italy, the Netherlands and the UK in three years, making use of standardised protocols for experimental design and research methodology. Highest yields (up to 22.5 t dry matter ha⁻¹) were obtained in Italy when later cultivars were used. Attainable yields proved slightly lower in the Netherlands and much lower in the UK. The quality of the cellulose was relatively stable over the growing season, but lignification may proceed rapidly some time after flowering. Crop development was very rapid and crops maintained green leaf area for a long time, thus radiation interception was considerable. The radiation use efficiency changed during development. It was lower after flowering (about 1.0 g MJ⁻¹ PAR) than before (about 2.2 g MJ⁻¹ PAR). Growing earlier cultivars to obtain some seed set advanced the reduction in radiation use efficiency. Nitrogen proved to affect yield only slightly. A relatively small amount of fertiliser will be adequate to cover the crop’s needs. Plant density declined during growth in a site-specific manner when it was high initially. Very low plant densities may not show this self-thinning but reduced yield and (especially) quality. Final plant densities were proven to depend more on initial plant stands than expected from literature. This was true at all three contrasting sites and in the different years. Nitrogen and plant density hardly interacted within one site. Results suggest that hemp can yield large quantities of useful cellulose when ecologically adapted cultivars are sown in proper plant densities. The cultivation is environmentally friendly with little harmful accumulation or emission of chemical inputs. More research on ideotyping is required and breeding efforts should be broadened.     

Effectiveness of 1,3-dichloropropene as an alternative to methyl bromide in rotations of tomato (Solanum lycopersicum) and cucumber (Cucumis sativus) in China

Replicated field trials were conducted to determine the effect of 1,3-dichloropropene (1,3-D) as a potential alternative for methyl bromide (MeBr) in tomato–cucumber rotations in two successive cropping seasons in China. Fumigation with MeBr (400 kg ha⁻¹), three 1,3-D doses (180, 120 and 90 l ha⁻¹), an avermectin dose (187.5 g ha⁻¹) and an untreated control were compared. Tomato data revealed that MeBr was generally superior to the treatments involving 1,3-D and avermectin, which in turn were superior to the control, for improving tomato crop yield and inhibiting Meloidogyne incognita, weeds and mortality caused by plant disease. In a successive cucumber crop, all fumigants tested except avermectin, showed significant continual influence in the same plots. In most cases, the highest 1,3-D dose was comparable to MeBr. Overall, in both growth seasons, 1,3-D at the dose of 180 l ha⁻¹ was as effective as MeBr in increasing plant height, yield and in reducing the incidence of soil borne disease, especially in maintaining excellent M. incognita control, but it provided only moderate control of weeds. On the basis of these results, combining 1,3-D with other alternatives to MeBr, is recommended for satisfactory control of soil pests in tomato–cucumber rotations in China.     

Temporal variation in nitrogen concentration of above ground perennial ryegrass applied different nitrogen fertiliser rates

Perennial ryegrass (Lolium perenne L.) was grown for seed in field trials in order to investigate the temporal variation in plant nitrogen (N) concentration during ontogeny. Crops were sown in three successive years and grown with five N fertiliser rates applied in the autumn and in the spring (autumn–spring): 0–0, 0–50, 0–100, 30–120 or 60–140 kg N ha⁻¹. Within each N fertiliser rate, N concentration in the plants increased from the initiation of spring growth and reached a maximum of 4.8% at 450–500 growing degree-days (GDD) after which it decreased to 0.8% at 1150–1200 GDD. This pattern of plant N concentration was consistently low at each N fertiliser rate and between years whereas the variation in plant N concentration within each year was high as a result of the different N fertiliser rates. Nitrogen fertiliser rate up to 150 kg N ha⁻¹ increased the seed yields.During spring growth 89% of the variation in plant N concentration could be explained by a non-linear function of GDD. Maximum variation occurred at 480 GDD, with a 95% confidence interval between 428 GDD and 540 GDD. Plant N concentrations measured at 424 GDD in 1998, 447 GDD in 1997, and 497 GDD in 1996, and the resulting correlation coefficients (r²) between N concentration and seed yield were 0.81, 0.71 and 0.92, respectively.It is concluded that the variation in plant N concentration during ontogeny in perennial ryegrass is related to different N fertiliser rates and that the greatest variation in plant N concentration was in the period from 428 GDD to 540 GDD.     

Influence of applied nitrogen on potato part I: Yield,quality, and Nitrogen uptake

Fertilizer nitrogen (N) may be managed to increase crop production and profitability while reducing nitrate contamination of groundwater. A two-year field investigation was conducted to evaluate the effects of applied N on tuber yield and quality, dry matter production and N uptake of potato (Solanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as ammonium sulfate [(NH₄)₂SO₄] at rates of 0, 56 and 112, kg N ha^?1 in a single application at planting or 112 and 168 kg N ha^?1 in split applications during the growing season. Total tuber yield generally increased with N applications up to 112 kg N ha^?1. Only one of the three experimental sites showed an increase in marketable tuber yield when 112 kg N ha^?1 was split evenly between planting and tuber initiation. Tuber specific gravity was not affected by N rate. Nitrogen rates of 112–168 kg N ha^?1 maximized dry matter production and plant tissue N concentration at onset of maturity and harvest. Tuber N concentration at harvest ranged from 13–17 g kg^?1 at two of the three locations. Values for the third experiment were 10–13 g N kg^?1. Whole crop N uptake at onset of senescence ranged from 45 to 225 kg N ha^?1 across all locations and treatments. An average of 67 percent of this N was found in tubers at harvest. Nitrogen fertilization exceeded N removal in harvested tubers by more than 50 kg N ha^?1 only for the 168 kg N ha^?1 treatment. These results indicate that acceptable tuber yield can be obtained with lower N rates than those currently used by most producers, with the potential for reducing net loss of N from the soil.     

Nitrogen fertilization and row width affect self-thinning and productivity of fibre hemp (Cannabis sativa L.)

In fibre hemp (Cannabis sativa L.) a high plant density is desirable, but inter-plant competition may cause self-thinning, which reduces stem yield and quality. We investigated whether agronomic factors could reduce self-thinning in hemp. The effects of soil nitrogen level (80 and 200 kg ha⁻¹), row width (12.5, 25 and 50 cm), type of sowing implement, and thinning method on self-thinning, growth, yield and quality of hemp were determined in field experiments in 1991 and 1992. Soil nitrogen level affected plant morphology before self-thinning occurred. Due to enhanced competition for light more plants died from self-thinning at 200 than at 80 kg N ha⁻¹. In August, stem yield of living plants was similar at the two nitrogen levels, but 5% of the plants had died at 80 kg N ha⁻¹ and 25% at 200 kg N ha⁻¹. Although dry matter losses resulting from self-thinning were greater at 200 than at 80 kg N ha⁻¹, crop growth rate was greater at 200 than at 80 kg N ha⁻¹. Apparently, the crop growth at 80 kg N ha⁻¹ was affected by a lack of nitrogen. At final harvest in September stem yield of living plants was 10.4 t ha⁻¹ at 80 and 11.3 t ha⁻¹ at 200 kg N ha⁻¹, bark content in the stem was 35.6% at 80 and 34.0% at 200 kg N ha⁻¹. The effect of row width on self-thinning was small relative to that of nitrogen level. More self-thinning took place at 50 cm row width than at 12.5 and 25 cm. During early growth and also in August stem yield was smaller when row width was larger; in September row width did not affect stem yield or quality. Type of sowing implement and thinning method did not affect self-thinning or stem yield.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

Effect of nitrogen supply on the comparative productivity of maize and sorghum in a semi-arid tropical environment III. Grain yield and nitrogen accumulation

Differences in grain yield and grain nitrogen content due to variable N supply in maize and sorghum, grown under irrigation in the semi-arid tropics, were associated with differences in their rates of accumulation and in the extent of mobilization of pre-anthesis dry matter and N. Increases in harvest index, nitrogen harvest index, and grain size during grain-filling were essentially linear, and the rates were constant under variable N supply. Differences in harvest index at maturity at different levels of applied N were small relative to differences in biomass and grain yield, and differences in grain size were small relative to differences in grain number. In effect, variation in harvest index and grain size at maturity was associated with variation in the length of the effective grain-filling period. Nitrogen supply had a greater effect on the effective duration of grain-filling in maize than in sorghum.Maximum grain yields at high levels of N uptake were greater in maize (10.0 t ha⁻¹ at 15.5% moisture) than in sorghum (7.2 t ha⁻¹ at 14% moisture). These differences were related to differences in biomass production, rate of increase in harvest index and the effective duration of grain-filling. The rate of increase in harvest index was greater, but biomass production was less and the duration of grain-filling was shorter, in sorghum than in maize.     

Yield and land-use efficiency of a cassava/cowpea intercropping system grown at different phosphorus rates

Cassava (Manihot esculenta Crantz) is frequently intercropped with cowpea [Vigna unguiculata (L.) Walp subsp. unguiculata] in the tropics. Little is known about the influence of P fertilization practices on the efficiency of land use and yields in cassava/cowpea intercropping systems. Two experiments were conducted on a Typic Dystropept soil with the objective of determining the influence of P application rate on yield and P status of cassava and cowpea grown in sole and intercropping systems, and the influence on land use efficiency. Cassava yields averaged across P rates were reduced 29% from the 28 Mg ha⁻¹ sole crop yield when intercropped with cowpea in 1979–1980. Cowpea yields were reduced by 19–38% from a sole crop yield of 1522 kg ha⁻¹ when intercropped in 1979, and 29–38% from a sole crop yield of 1277 kg ha⁻¹ in 1980. The rate of P application had little influence on cassava yield, except in 1981 when intercropped cassava yields were greater than 40 Mg ha⁻¹. In 1981, increasing the rate of P application from 0 to 44 kg ha⁻¹ resulted in a cassava yield increase from 41 to 47 Mg ha⁻¹. In 1979 and 1980, increasing the rate of P application from 0 to 22 kg ha⁻¹ increased cowpea yield 44 and 92%, respectively, while increasing P rate from 66 to 132 kg ha⁻¹ increased cowpea yield 28 and 18%, respectively. In 1981 and 1982, increasing the rate of P application from 0 to 44 kg ha⁻¹ increased cowpea yield by 1052 kg ha⁻¹. Phosphorus concentration of cassava and cowpea leaf blades increased with increases in rate of P application from 66 to 132 kg ha⁻¹ in 1979 and 1980, and from 0 to 44 kg ha⁻¹ in 1981 and 1982. Intercropping cassava with cowpea resulted in a 30% increase in land-use efficiency when no P was applied, while land-use efficiencies resulting from intercropping were increased by 41–50% with P application rates of 22–132 kg ha⁻¹. Cassava proved to be well-adapted to low-P soils and very competitive even without P application, whereas cowpea required the addition of P for adequate growth and yield. High productivity and a good competitive balance between the two crops were reached with only 22 kg ha⁻¹ of P, showing the great potential of cassava/cowpea intercropping on acid, infertile soils in the tropics.     

Herb and oil composition of dill (Anethum graveolens L.): Effects of crop maturity and plant density

Steam-distilled dill (Anethum graveolens L.) oil yield and composition varies with the relative amount of vegetative and reproductive tissue and the maturity of the plant material distilled. The characteristics of the dill plant at harvest may be manipulated through production practices. A study was conducted in western Montana to determine the effects of crop maturity and plant density on dill plant growth and on oil production and quality. The crop was harvested at intervals from early fruit formation through fruit pigmentation. Oil yield declined with fruit maturity over the sampling period, particularly after the completion of fruit ripening and “seed” shatter. The carvone content of the oil increased and α-phellandrene decreased as the plant progressed from flowering to fruit ripeness. The highest oil yields with maximum carvone levels were obtained when most of the fruits on primary umbels were pigmented but had not become dry and fully mature. The balance between carvone and phellandrene in the oil was a function of the proportion of mature umbel tissue to vegetative and immature umbel tissue. Seeding rates of 2.2–17.9 kg ha⁻¹ resulted in average plant densities of 100–474 plants m⁻². Total biomass production and oil yield were generally unaffected by plant density, but plant population influenced plant architecture and oil composition. Plants grown at low density had a more extensive development of umbellate fruiting structures and a lower proportion of leaf and stem tissue than did plants at high density. Carvone was higher in oil from widely spaced plants, while phellandrene, α-pinene, and dill ether (3,9-epoxy-1-p-menthene) were lower. Harvest date and plant density affected oil composition in a complementary manner. An early harvest or high plant density is preferable if herbaceous oil characteristics are desired, while a late harvest or low plant density is suitable when growing dill for seed or for a high-carvone oil.