Influence of cultivars and nitrogen rates on the residual effects of potassium applications to preceding cotton on maize

The long-term residual effects of K application rates and cultivars for preceding cotton (Gossypium hirsutum L.) on subsequent maize (Zea mays L.) and the influence of N rates applied to preceding cotton and to maize on the residual K effects were examined on maize under no-tillage in the United States. Two field experiments were conducted on a no-till Loring silt loam at Jackson, TN during 1995–2008 with N rates (90 and 179 kg ha^?1) × K rates (28, 56, and 84 kg ha^?1) and cotton cultivars (determinate and indeterminate) × K rates (56 and 112 kg ha^?1) as the treatments, respectively, in the preceding cotton seasons. Maize was planted under no-tillage on the preceding cotton experiments without any K application during 2009 through 2011. The residual effects of K rates applied to preceding cotton on soil K levels were significantly influenced by the N rates applied to preceding cotton and to maize when the data were combined from 2008 to 2011. Relative to the standard N management practices of 168 kg N ha^?1 for maize and 90 kg N ha^?1 for preceding cotton, the higher N application rate 269 kg N ha^?1 to maize and 179 kg N ha^?1 to preceding cotton reduced the residual effects of K rates on soil K. However, cultivar for preceding cotton did not affect the residual effects of K fertilizer on soil K fertility, leaf K nutrition, plant growth, or grain yield of subsequent maize on a high K field.     

Recovery of N applied as 15N-manure or 15N-gliricidia biomass by maize,cotton and cowpea

Proper management of N applied in fertilizers is important to optimize crop production and to avoid negative environmental impacts. The best way to study N dynamics in the soil plant system is to use fertilizers labeled with ¹⁵N. Recoveries of nitrogen following fertilization with ¹⁵N-labeled goat (Capra hircus L.) manure and gliricidia (Gliricidia sepium Jacq. Walp) biomass were evaluated in a greenhouse experiment with three successive planting cycles of three crops: maize (Zea mays L.), cotton (Gossypium hirsutum L.), and cowpea (Vigna unguiculata (L.) Walp.). Each 1 kg soil pot received 8 g (equivalent to 20 Mg ha^?1) of either manure (12.3 mg g^?1 of N) or gliricidia (37.8 mg g^?1 of N). Plants were harvested 50 days after germination and real (¹⁵N) and apparent recoveries of the applied N were determined. Biomass and N amounts in the cotton and maize crops in all three cycles were higher with gliricidia application than with manure, except for cotton in the first cycle. The biomass of cowpea was also higher with gliricídia in the first and second cycles but the amount of N was significantly higher only in the second cycle. In the first cycle, the largest recoveries of ¹⁵N were obtained with gliricidia, for all three crops, but in the second and third cycles recoveries were greater with manure, so that the real recoveries of gliricidia and manure were similar (cotton, 35 and 37 %; maize, 27 and 26 %; and cowpea, 41 and 38 % of the applied N, respectively). Estimates of apparent recoveries were different from the real ones and therefore inadequate for cotton and cowpea. The fast release of N from gliricidia prunings and, on the other hand, the strong residual effect of goat manure-N to subsequent cropping cycles should be considered by farmers in their fertilization strategies.     

Assessing internal crop nitrogen use efficiency in high-yielding irrigated cotton

Improving the efficiency of nitrogen (N) fertiliser use is one means of reducing greenhouse gas emissions, particularly in irrigated crops such as cotton (Gossypium hirsutum L.). Internal crop N use efficiency (iNUE) was measured within two N fertiliser rate experiments that covered a wide range of N fertility over six cropping seasons. Crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients other than N limited cotton growth or yield and the crops were irrigated to avoid drought stress. The optimal N fertiliser rates were determined from fitted quadratic functions that related lint yields with N fertiliser rates for each cropping system in each year. When the optimal N fertiliser rate was applied, crop iNUE averaged 12.5 ± 0.2 kg lint/kg crop N uptake. The crop iNUE was then used to determine the degree to which N fertiliser was under or over-applied, with respect to the economic optimum N fertiliser rate. Low iNUE values were associated with excessive N fertiliser application. Crop iNUE was determined in 82 commercial cotton crops in six valleys over the final 4 years of this study. The crop iNUE value was high in 8 fields (10%), optimal in 9 fields (11%) and low in 65 fields (79%). Crop N uptake averaged 247 kg N/ha, yield 2,273 kg lint/ha and crop iNUE 10.1 kg lint/kg crop N uptake for these sites. Averaged over all sites and years, about 49 kg N/ha too much N fertiliser was applied. Apparent N fertiliser recovery by cotton in the N rate experiments ranged from <20% in N-fertile treatments where legume crops had been grown, to more than 60% following winter cereal crops. Information on crop iNUE will enable cotton producers to assess their N fertiliser management and adjust N fertiliser rates for future crops. This study has demonstrated that there is scope to substantially reduce N fertiliser inputs to Australian cotton fields without reducing yields.     

Foliar boron application affects lint and seed yield and improves seed quality of cotton grown on calcareous soils

Cotton (Gossypium hirsutum L.) is one of the most important fiber crops worldwide because of the good fiber quality, high yield, and high adaptability. Cotton has high requirements for B and many times B is applied to correct B deficiency. Despite the fact that B is important for cotton the effect of foliar applications on seed yield and seed quality was not adequately determined and especially when cotton is grown on calcareous soils. A field study was conducted to determine if foliar B application during anthesis increases seed set, lint yield, seed yield, yield components and improves seed quality of cotton grown on calcareous soils. Boron solutions were applied at four rates (0, 400, 800 and 1,200 mg l⁻¹ of B) to field plots exhibiting no vegetative symptoms of B deficiency. Foliar B application increased the number of bolls per plant, the number of bolls per square meter, the mean boll weight, the lint and the seed yield. Cotton yield was increased by an average of 40% over the two locations with B application compared with the control. However, there was no significant difference between the three rates of B. The number of bolls per plant increased by an average of 29% and the number of bolls per square meter increased by an average of 29% with B application in both locations compared with the control treatment. Also foliar application of B improved seed germination by an average of 17% and increased seed vigor determined as accelerated aging (AA) by an average of 25% compared with the control treatment in both locations. The results obtained here suggest that foliar B application can improve the lint and seed yield and seed quality of cotton grown on calcareous soils.     

Phosphorus dynamics and phosphatase activity of soils under corn production with supplemental irrigation in humid coastal plain region,USA

A 3-year (2013–2015) field study was conducted to evaluate the effect of integrated nutrient management (NM) and three irrigation scheduling methods (IS): irrigator pro (IPro); normalized difference vegetative index (NDVI) and soil water potentials (SWP) on phosphorus (P) dynamics and phosphatase activity in four Coastal Plains soil types (ST) at various growth stages (CS: V6, six leaves; V16, sixteen leaves; and R1, silking) of corn (Zea mays L.). Nitrogen fertilizer was applied at two rates: 157 and 224 kg ha^?1 through the irrigation system in three applications. Phosphorus dynamics and phosphatase activity varied significantly (p ≤ 0.0001) with year (Y), CS and ST, but not with NM. Phosphorus uptake of corn had an increase of about 1200% from V6 to R1. Both the Mehlich extractable P and water soluble P showed declining trends from V6 to R1. Concentration of P in pore water differed significantly (p ≤ 0.05) with IS in 2014 and 2015, but not in 2013. The order of the concentrations of P in pore water (averaged across ST) as affected by IS is as follows: 2013 (IPro = NDVI = SWP); 2014 (SWP = IPro < NDVI); and 2015 (IPro < NDVI < SWP). Concentration of phosphatase among the different ST was affected by CS, from V6 to R1 and soil depth, but not with NM. The difference in phosphatase concentration between the upper and lower soil horizons (averaged across Y and ST) was about 67.7 μg g^?1 h^?1. Our results have significant implication on P mobility, availability and management in areas where inputs of P in fertilizers may have had exceeded P output in harvested crops. Our results further suggest that understanding of P inputs and outputs which include P accumulation in soils and plants, as well as P losses is critical to determining the environmental balance and accountability of P in agricultural ecosystem. It is imperative to have a holistic understanding of P dynamics from soil to plant by optimizing P management and improving P-use efficiency.     

Olfaction in the boll weevil,Anthonomus grandis Boh. (Coleoptera: Curculionidae): Electroantennogram studies

Electroantennogram (EAG) techniques were utilized to measure the antennal olfactory responsiveness of adult boll weevils,Anthonomus grandis Boh. (Coleoptera: Curculionidae), to 38 odorants, including both insect and host plant (Gossypium hirsutum L.) volatiles. EAGs of both sexes were indicative of at least two receptor populations: one receptor population primarily responsive to pheromone components and related compounds, the other receptor population primarily responsive to plant odors. Similar responses to male aggregation pheromone components (i.e., compounds I, II, and III + IV) were obtained from both sexes, but females were slightly more sensitive to I. Both sexes were highly responsive to components of the “green leaf volatile complex,” especially the six-carbon saturated and monounsaturated primary alcohols. Heptanal was the most active aldehyde tested. More acceptors responded to oxygenated monoterpenes than to monoterpene hydrocarbons. β-Bisabolol, the major volatile of cotton, was the most active sesquiterpene. In general, males, which are responsible for host selection and pheromone production, were more sensitive to plant odors than were females. In fact, males were as sensitive to β-bisabolol and heptanal as to aggregation pheromone components. Electrophysiological data are discussed with regard to the role of insect and host plant volatiles in host selection and aggregation behavior of the boll weevil.     

Nutrient uptake and export from an Australian cotton field

Soil fertility may decline as a result of nutrient export from high-yielding cotton crops and this may limit the productivity of future crops unless these nutrients are replaced. Uptake of nutrients by cotton (Gossypium hirsutum L.) and nutrient export from the field in seed were measured within two cropping systems experiments from 1999 to 2005 in a flood-irrigated cotton field. Lint yields of the seven crops assessed ranged from 975 to 2725 kg lint/ha. Nutrient uptake was measured at mid to late boll-fill and nutrient removal determined from analysis of delinted seed. Cotton crops accumulated an average of 180 kg N/ha (range 67–403), 27 kg P/ha (range 18–43), 167 kg K/ha (range 88–264), 41 kg S/ha, 160 kg Ca/ha, 36 kg Mg/ha, 7 kg Na/ha, 890 gm Fe/ha, 370 gm Mn/ha, 340 gm B/ha, 130 gm Zn/ha and 51 gm Cu/ha. On average, the seed within harvested seed cotton removed 93 kg N/ha (range 38–189), 18 kg P/ha (range 8–34), 29 kg K/ha (range 13–51), 8 kg S/ha, 4 kg Ca/ha, 12 kg Mg/ha, 0.2 kg Na/ha, 136 g Fe/ha, 12 g Mn/ha, 41 g B/ha, 96 g Zn/ha and 20 g Cu/ha. Nutrients contained in the lint and trash were not included. For crops yielding about 1800 kg/ha, 70% of the Zn and P taken up was removed in the seed, also 52% of N, 38% of Cu, 34% of Mg, 21% of S, 17% of K and Fe, 12% of B and only 3% of Ca, Mn and Na. Predictive equations were developed to allow growers to estimate the removal of nutrients given the lint yield measured from their cotton crops.     

Effect of time and rate of nitrogen application on cotton

Field studies were conducted in nine cotton production areas of Greece, for 15 successive years, to detective the optimum time and rate of N fertilizer application for maximum yields and better fibre characteristics of cotton (Gossypium hirsutum). Two to five rates of N fertilizer (60–180 kg N/ha) were applied: before sowing, when the plants had 3–4 leaves and 20 days later. The yield of cotton increased in most of the cases by N fertilization, but not significantly to both N rates and time of application. Under Greek conditions - limited growing season and low precipitation in spring - the split application of N fertilizers, compared to a single presowing application did not differ, as regards its effect on yield and fibre quality of cotton. Split application of fertilizers, supplementary to that applied at sowing could be of significance, when N plant demands are high and in addition there is a risk for excessive plant growth or for leaching losses. In the case of high N fertilizers rates, the split application must be preferred.     

Impacts of conservation agriculture on soil aggregation and aggregate-associated N under an irrigated agroecosystem of the Indo-Gangetic Plains

We evaluated impacts of conservation agriculture (zero tillage, bed planting and residue retention) on changes in total soil N (TSN) and aggregate-associated N storage in a sandy loam soil of the Indo-Gangetic Plains. Cotton (Gossypium hirsutum) and wheat (Triticum aestivum) crops were grown during the first 3 years (2008–2011) and in the last year, maize (Zea mays) and wheat were cultivated. Results indicate that after 4 years the plots under zero tillage with bed planting (ZT-B) and zero tillage with flat planting (ZT-F) had 15 % higher TSN concentrations than conventional tillage and bed planting plots (CT-B) (0.63 g kg^?1 soil) in the 0–5 cm soil layer. CT-B plots had lower soil bulk density that ZT plots in that layer. Plots under ZT-B (0.57 Mg ha^?1) contained 20 % higher TSN stock in the 0–5 cm soil layer than CT-B plots (0.48 Mg ha^?1). However, tillage had no impact on TSN concentration or stock in the sub-surface (5–15 and 15–30 cm) soil layers. Thus, in the 0–30 cm soil layer, ZT-B plots contained 6 and 5 % higher (P > 0.05) TSN stock compared with CT-B (2.15 Mg N ha^?1) and CT-F (2.19 Mg N ha^?1) plots respectively after 4 years. Plots that received cotton/maize + wheat residue (C/M + W RES) contained 16 % higher TSN concentration than plots with residues removed (N RES; 0.62 g kg^?1 soil) in the surface (0–5 cm) layer. Plots with only cotton/maize residue (C/M RES) or only wheat residue (W RES) retention/incorporation had similar TSN concentrations and stocks in the subsurface layer. Plots under ZT-B also had more macroaggregates (0.25–8 mm) and greater mean weight diameter with lower silt + clay sized particles than CT-B plots in that layer. A greater proportion of large macroaggregates (2–8 mm) in the plots under C/M + W RES compared with N RES were observed. In the 5–15 cm soil layer ZT-B and C/M + W RES treated plots had more macroaggregates and greater mean weight diameter than CT-B and N RES treated plots, respectively. Because of the greater amount of large aggregates, plots under ZT-B and C/M + W RES had 49 and 35 % higher large macroaggregate-associated N stocks than CT-B (38 kg TSN ha^?1) and N RES (40 kg TSN ha^?1) plots, respectively, in the 0–5 cm soil layer, although aggregates had similar TSN concentrations in all plots. Both tillage and residue retention had greater effects on aggregate-associated N stocks in the 5–15 cm layers. In addition to N content within large macroaggregates, small macroaggregate-associated N contents were also positively affected by ZT-B and C/M + W RES. Tillage and residue retention interaction effects were not significant for all parameters. Thus, the adoption of ZT in permanent beds with crop residue addition is a better management option for improvement of soil N (and thus possibly a reduced dose of fertilizer N can be adopted in the long run), as the management practice has the potential to improve soil aggregation with greater accumulation of TSN within macroaggregates, and this trend would likely have additive effects with advancing years of the same management practices in this region.     

Nitrogen loss and rice profits with matrix-based slow-release urea

Paddy fields account for a large proportion of cultivated land, with huge N consumption each year. Reducing N loss via application of low-cost slow-release fertilizers is beneficial for eco-friendly rice production. The current study aimed to investigate the effects of matrix-based urea on soil N availability, rice yield, agronomical efficiency (AE), and rice profits. A 2-year field experiment was conducted during 2015 and 2016 following a randomized block design. It included three treatments, i.e., control test (CK, without urea application), common urea (CU, 150 kg N ha^?1), and matrix-based urea (MU, 150 kg N ha^?1). Besides, three laboratory experiments were conducted to investigate the N leaching, ammonia volatilization, and slow-release mechanism. Results showed that application of MU increased rice yields by > 10%, biomass by > 6%, and AE by > 30% in both seasons. Greater yield, biomass, and AE in MU were largely attributed to higher soil available N, resulted from lower risk of N leaching and ammonia volatilization. Aggregate structure was partly responsible for lower N loss in MU. Greater soil available N in MU increased rice height, leaf area, root area, leaf total chlorophyll, and activity of nitrate reductase and glutamine synthetase in flag leaves, and thus favored rice growth. Compared with CU, MU increased fertilizer cost by about 23 USD ha^?1, but increased rice profits by > 230 USD ha^?1 due to greater yield. Overall, matrix-based urea is suitable for application in field rice production, due to its low risk of N loss and acceptable profitability.     

Cotton growth and yield as influenced by different timing of late-season foliar nitrogen fertilization

Foliar fertilization to meet the nitrogen (N) requirement of the cotton crop during the latter fruiting stages is a production practice that is not well understood. The objective of this study was to investigate the benefits of late-season foliar-N fertilization on growth and yield of cotton in relation to soil-N level and timing based on weeks after first flower (WAFF) and nodes above white flower (NAWF). A 4-year field study was conducted with four foliar-N treatments consisting of a control with no foliar-N, and one, two, or three foliar-N sprays under different soil-N regimes. In 1990, the foliar-N treatments were based on WAFF sprayed during fifth, sixth and seventh WAFF. Foliar-N significantly increased nodes above white flower (NAWF) over the control with no significant differences among the three foliar-N treatments. A negative relationship (r2=0.98) existed between NAWF and days after planting (DAP). Foliar-N also significantly increased plant height, leaf number, leaf area, leaf dry weight, boll number, boll dry weight and yield. The same foliar-N treatments were applied on low and high soil-N regimes in 1991 and 1992, and in 1993 on four different soil-N regimes, 0, 55, 82, and 110 kg N ha-1 at NAWF = 7, 6 and 5. No significant difference was found in NAWF among the four foliar-N treatments within each soil-N level during 1991. Significant differences between the control and the three foliar-N sprays were found for leaf area, boll number, and boll dry weight. In 1992, the NAWF of control plants showed a similar response to the 1990 control plants. In contrast, the foliar-N sprayed plants extended the highest NAWF for an additional week, after which it steadily declined below 5. Foliar-N significantly increased yield in 1990, yield and yield components in 1991 and 1992, and yield in 1993. Neither WAFF nor NAWF appear to be good indicators for timing late-season foliar-N fertilization. The study clearly demonstrated, however, that late-season foliar-N fertilization is beneficial to cotton plants, although the precise timing of such N application is still unclear.     

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha^?1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha^?1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha^?1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha^?1, while leaf N concentration peaked at 90 kg N ha^?1. Further increasing N application to 230 kg ha^?1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha^?1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields.     

Ovipositional response of threeHeliothis species (Lepidoptera: Noctuidae) to allelochemicals from cultivated and wild host plants

The role of plant allelochemicals on the oviposition behavior ofHeliothis virescens (F.),H. subflexa (Guenee), andH. zea (Boddie) was investigated in the laboratory using a “choice” bioassay system. Fresh young leaves of tobacco,Desmodium tortuosum (Swartz) de Candolle, groundcherry (Physalis angulata L.), and cotton (Gossypium hirsutum L.) squares (flower buds) were washed in methylene chloride or methanol, concentrated to 1 g equivalent of washed material, and applied to a cloth oviposition substrate. Each of the extracts—including groundcherry, a nonhost—stimulated oviposition byH. virescens. H. subflexa were stimulated to oviposit by groundcherry extract, its normal host, and extract from cotton squares, a nonhost. None of the extracts stimulated oviposition byH. zea, although all except groundcherry were from reported hosts. The sensitivity of the bioassay was confirmed by givingH. virescens andH. subflexa an opportunity to choose between extracts that showed stimulant qualities when tested independently versus only solvent-treated controls. In these tests, tobacco showed the highest level of stimulant activity forH. virescens; groundcherry exhibited the highest level of stimulation forH. subflexa.     

A short communication on the effect of nitrogen fertilization of willow on yield,combustion emissions and greenhouse gas balance

Nitrogen fertilizer was applied to willow after harvest in 2011, two levels of nitrogen were applied (75; 150 kg N/ha) in addition to a control. The trial was harvested in January 2013, biomass from each treatment was burnt and emissions from combustion were quantified. Nitrogen application increased leaf nitrogen and plant height although there was no difference between the nitrogen treatments. Plant height and maximum stem diameter increased with applied nitrogen at final harvest. Nitrogen fertilization significantly increased yield by 35 % although there was no difference between the two nitrogen treatments. Stem nitrogen content did not differ significantly between treatments and there was no significant difference in NO_x emissions between treatments. A life cycle assessment showed that nitrogen fertilization significantly increased net greenhouse gas benefit by up to 30 % depending on the fuel replaced. The study demonstrated that the application of relatively low levels of nitrogenous fertilizer to willow can significantly improve greenhouse gas mitigation without affecting other aspects of the environment such as air quality.     

Soil N2O and CO2 emissions from cotton in Australia under varying irrigation management

Irrigation is known to stimulate soil microbial carbon and nitrogen turnover and potentially the emissions of nitrous oxide (N₂O) and carbon dioxide (CO₂). We conducted a study to evaluate the effect of three different irrigation intensities on soil N₂O and CO₂ fluxes and to determine if irrigation management can be used to mitigate N₂O emissions from irrigated cotton on black vertisols in South-Eastern Queensland, Australia. Fluxes were measured over the entire 2009/2010 cotton growing season with a fully automated chamber system that measured emissions on a sub-daily basis. Irrigation intensity had a significant effect on CO₂ emission. More frequent irrigation stimulated soil respiration and seasonal CO₂ fluxes ranged from 2.7 to 4.1 Mg-C ha^?1 for the treatments with the lowest and highest irrigation frequency, respectively. N₂O emission happened episodic with highest emissions when heavy rainfall or irrigation coincided with elevated soil mineral N levels and seasonal emissions ranged from 0.80 to 1.07 kg N₂O-N ha^?1 for the different treatments. Emission factors (EF = proportion of N fertilizer emitted as N₂O) over the cotton cropping season, uncorrected for background emissions, ranged from 0.40 to 0.53 % of total N applied for the different treatments. There was no significant effect of the different irrigation treatments on soil N₂O fluxes because highest emission happened in all treatments following heavy rainfall caused by a series of summer thunderstorms which overrode the effect of the irrigation treatment. However, higher irrigation intensity increased the cotton yield and therefore reduced the N₂O intensity (N₂O emission per lint yield) of this cropping system. Our data suggest that there is only limited scope to reduce absolute N₂O emissions by different irrigation intensities in irrigated cotton systems with summer dominated rainfall. However, the significant impact of the irrigation treatments on the N₂O intensity clearly shows that irrigation can easily be used to optimize the N₂O intensity of such a system.     

Spent mushroom compost as a nitrogen source for spring barley

Spent mushroom compost (SMC) contains a range of plant nutrients, including nitrogen (N), a large proportion of which originate from arable crops. Using SMC as an organic fertilizer for crops recycles these nutrients. Effective use of SMC in fertilizer regimes requires knowledge of the nitrogen fertilizer value (NFV) of the SMC, which is the amount of mineral fertilizer N required to give the same N yield, or marketable yield, as an application of SMC. The objectives of these experiments were to evaluate the effect of SMC on spring barley grain yield and quality and to determine its NFV. Experiments were carried out on two soils, light- and medium-textured, over 3 years (2008–2010). The experiments compared the yield response and N uptake of spring barley to fertilizer N with and without SMC. SMC application gave similar or higher grain yield and N uptake compared to fertilizer only treatments at corresponding fertilizer N rates. SMC had no significant (P > 0.05) effect on the economic optimum fertilizer N rate but the maximum yield was significantly (P < 0.05) higher where SMC was applied in two of the six experiments. Effects of SMC on grain quality were small. Results indicated that the NFV, expressed as a proportion of the total N applied in SMC, ranged from 0.05 to 0.29 kg kg^?1 N applied in SMC, with a mean of 0.15 kg kg^?1. It is concluded that SMC can contribute to the nitrogen nutrition of small grain cereal crops in high yield potential environments.     

Growth response,yield and yield components of upland cotton (Gossypium hirsutum L) as affected by rates and time of nitrogen application in the Nigerian savannah

Effects of rate and time of nitrogen fertilization on growth, yield and yield components of upland cotton (Gossypium hirsutum L) were studied in two years (1975–76). Four rates of nitrogen application (0, 26, 52 and 78 kg ha^–1) timed at 3 or 8 weeks after sowing were compared. Seed cotton yield components increased significantly with increased N application at least up to 52 kg N ha^–1, with yield increases between 49% and 73%. Seed cotton yield was influenced by treatments mainly through boll number. Both crop growth rate and fruiting were enhanced by nitrogen fertilization. Applying N at 8 weeks (flowering) favoured yield only slightly over that at 3 weeks (thinning), but improved crop growth and fruiting by about 64% and 24%, respectively. There were significant N rate × time interactions in favour of fertilization at flowering. Applying 52 kg N ha^–1 at 8 weeks seems best for cotton in the Nigerian savannah.     

Mineral nutrition of wheat,chickpea and lentil as affected by mixed cropping and soil moisture

Interspecific complementary and competitive interactions on yield and N, P, K, Fe, Zn and Mn nutrition of mixed wheat/chickpea and wheat/lentil grown in a glasshouse under normal and drought conditions, and intercropping of wheat/chickpea in the field under rainfed conditions were investigated. The results of the experiments confirmed that drought significantly decreased the growth and mineral nutrition of all plant species. Individual plant dry weights of wheat, chickpea and lentil in the glasshouse experiment, and vegetative shoot dry weight of intercropped wheat in the field experiment were significantly increased by the associated plant species as compared with their monoculture. Even though there were increases in vegetative shoot dry weight of wheat, biological and seed yield of intercropped wheat and chickpea were decreased due to the lower row number in intercropping. However, the calculated LER (Land Equivalent Ratio) was found to be higher than 1.0 for biological and seed yields, showing that intercropping of wheat and chickpea has an advantage over monoculture. In many cases, the drought × cropping system interaction on the nutrient concentrations of plant species was not significant. Results of the glasshouse study showed that P nutrition of wheat was improved by chickpea and lentil, which might result from increases in leaf acid phosphatase in mixed cropping. The release of Fe(III)-complexing compounds from the roots was higher in the sole wheat and mixed culture than that of monocultured chickpea and lentil. This improves Fe nutrition of wheat and chickpea, but those improvements were not significant. However, Zn and Mn concentrations of mixed cropped chickpea were also increased. Under the field conditions, shoot concentration of P, K, Fe, Zn and Mn in wheat were increased by intercropping. Furthermore, the concentrations of Zn and Mn in chickpea were increased by intercropping while N, P and K concentrations were decreased. In addition, the concentrations of N, P, K and Fe for wheat seeds and of Zn and Mn for chickpea were improved by intercropping. It is concluded that interspecific interaction was complementary and generally facilitated the mineral nutrition of wheat and chickpea species grown in mixed culture. Besides giving a yield advantage, intercropping of chickpea and wheat also had a positive effect on seed mineral composition.     

Cotton Plant, Gossypium hirsutum L., Defense in Response to Nitrogen Fertilization

Plants respond to insect herbivory by producing dynamic changes in an array of defense-related volatile and nonvolatile secondary metabolites. A scaled response relative to herbivory levels and nutrient availability would be adaptive, particularly under nutrient-limited conditions, in minimizing the costs of expressed defensive pathways and synthesis. In this study, we investigated effects of varying nitrogen (N) fertilization (42, 112, 196, and 280 ppm N) on levels of cotton plant (Gossypium hirsutum) phytohormones [jasmonic acid (JA) and salicylic acid (SA)], terpenoid aldehydes (hemigossypolone, heliocides H₁, H₂, H₃, and H₄), and volatile production in response to beet armyworm (Spodoptera exigua) herbivory. Additional bioassays assessed parasitoid (Cotesia marginiventris) host-searching success in response to cotton plants grown under various N fertilizer regimes. At low N input (42 ppm N), herbivore damage resulted in significant increases in local leaf tissue concentrations of JA and volatiles and in systemic accumulation of terpenoid aldehydes. However, increased N fertilization of cotton plants suppressed S. exigua-induced plant hormones and led to reduced production of various terpenoid aldehydes in damaged mature leaves and undamaged young leaves. While increased N fertilization significantly diminished herbivore-induced leaf volatile concentrations, the parasitism of S. exigua larvae by the parasitoid C. marginiventris in field cages did not differ among N treatments. This suggests that, despite significant N fertilization effects on herbivore-induced plant defenses, at short range, the parasitoids were unable to differentiate between S. exigua larvae feeding on physiologically different cotton plants that share large constitutive volatile pools releasable when damaged by herbivores.     

Effects of cotton leaf surface alkalinity on feeding ofSpodoptera littoralis larvae

The high leaf surface pH in cotton (Gossypium hirsutum) var. Acala SJ2 was bioassayed againstSpodoptera littoralis larvae. Weight gain and leaf consumption of the larvae feeding on leaves devoid of alkalinity, due to daily washing, were recorded. Untreated cotton, with a leaf surface pH of 9.5–10.0 was used as control. The gland exudates contained potassium and magnesium cations, and the gland surface and intergland leaf areas were rich in calcium and phosphorus and low in K or Mg. The role of this plant antibiosis in the insect-host-plant relationship is discussed.Contribution No. 1885-E 1986 series, from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.