Superabsorbent polymers influence soil physical properties and increase potato tuber yield in a dry-farming region

Purpose

Superabsorbent polymers, new water-saving materials and soil conditioners, are used widely in dry-farming agriculture. However, little is known about their effects on the soil physical properties under dry-farming conditions. To elucidate the effects of two SAPs (Wote and microbe) at different doses on the soil bulk density, water status, potato growth, yield, and economic benefit in a dry-farming region, we conducted a 2-year fixed field position experiment in the semiarid drought-prone area of Ningxia, China.

Materials and methods

The two SAPs were diluted 1:10 (product:soil) and applied at different rates before planting, i.e., Wote SAP 30 kg ha^?1, Wote SAP 60 kg ha^?1, Wote SAP 90 kg ha^?1, microbe SAP 30 kg ha^?1, microbe SAP 60 kg ha^?1, and microbe SAP 90 kg ha^?1. The treatment without SAP was used as the control.

Results and discussion

The tilth soil bulk density decreased under different SAP doses compared with the control, and the soil total porosity improved greatly, where the Wote SAP treatments had the greatest effects. The soil bulk density (0–60 cm) under Wote SAP 90 kg ha^?1 was significantly decreased by 6.4% compared with the control. The Wote SAP treatments had the greatest effects on water conservation during the critical potato growth stage, where the soil water storage (0–100 cm) was significantly higher than the control. The Wote SAP treatments promoted potato growth in the later period, where the plant height and stem diameter were higher than the control. Higher yield and commodity rate improvements were achieved by the application of Wote and microbe SAP compared with the control, where the optimum dose was 60–90 kg ha^?1 for Wote SAP. The application of Wote SAP 90 kg ha^?1 significantly increased crop water use efficiency compared with no SAP, and the commodity rate was highest with Wote SAP 60 kg ha^?1. The mean potato yield, commodity rate, and net income increased significantly using Wote SAP at 60 and 90 kg ha^?1, i.e., by 38.2 and 50.5%, 18.5 and 14.1%, and 28.5 and 35.0%, respectively, compared with no SAP.

Conclusions

The application of SAPs can decrease soil bulk density and significantly improve soil porosity and soil water conservation capacity, thereby promoting potato growth. The application of Wote SAP 60–90 kg ha^?1 significantly increased potato yield and net income in a dry-farming region of Ningxia, China.

     

生物炭和高吸水树脂可改善养殖垫料基质理化性状

【目的】 秸秆常用于养殖业发酵床垫料,用出圈后垫料为主要原料制备的无土栽培基质往往存在保水、透气性差、电导率高等缺陷,限制了其推广应用。本文探讨添加不同比例的生物炭及高吸水树脂 (SAP) 改善该基质的性能,为促进秸秆资源化利用、提高作物产量提供依据。 【方法】 以空心菜 (Ipomoea aquatica Forsk) 为试材进行了盆栽试验。供试基质组成为发酵床垫料堆肥 + 蛭石 + 珍珠岩 + 泥炭 (体积比3∶2∶3∶2),其总氮、磷、钾及速效氮、磷、钾养分含量分别为24.2、8.62、10.1、1.94、0.83和3.72 g/kg。在该基质中添加小麦秸秆制成的生物炭 (600℃) 2%、4%、6%、8%、10%、12%、14%和16%,以不加生物炭基质为对照,上述基质再裂分为加0.8 g/L SAP和不加SAP两种处理,共18个处理。测定了基质的理化性状,并原位测定了生长过程中基质水分空间分布情况,调查了空心菜的出苗率、生长、养分吸收及产量。 【结果】 随生物炭添加比例的增加,基质总孔隙度、持水量、pH和电导率显著提高。添加SAP后,基质pH和电导率随生物炭添加比例升高的趋势减缓,导致高比例生物炭 (10%～16%) 与SAP联合添加的基质pH和电导率显著低于生物炭单独添加处理 (P < 0.05)。添加SAP后,不同生物炭添加比例下基质的持水量、总孔隙度和通气孔隙度分别增加了13.4%～35.7%、5.8%～10.7%和8.9%～17.9%,且盆钵内水分分布更为均匀,改善了因基质保水性差而造成的水分沉积于盆地的状况。随生物炭添加比例的增加,空心菜出苗率、各项生长指标、根部各项指标和空心菜对氮、磷、钾养分的吸收均表现出先升高后降低的趋势,在10%添加比例下达到最高值,且SAP与生物炭联合添加处理明显高于生物炭单独添加处理。 【结论】 基质中添加10%的秸秆生物炭可有效改善基质的理化性能并提高空心菜产量,与0.8 g/L的SAP配施不仅增强了生物炭的正面效应,同时抑制了高生物炭添加带来的基质pH和电导率的过度升高,二者配施可有效改善基质性能及空心菜的生长状况。      

Improvement of wheat (Triticum aestivum) drought tolerance by seed priming with silicon

Silicon has the potential to improve drought tolerance in crops. Seeds primed with silicon were used in the present study to explore its potential benefit to withstand water stress. Seeds of two wheat varieties, NARC-2009 and Chakwal-50, were sown in pots after priming with distilled water and different concentrations (0.5%, 1.0% and 1.5%) of silicon sources (silicic acid, sodium silicate and silica gel) at PMAS, Arid Agriculture University, Rawalpindi. Maximum silicon uptake at three-leaf stage (0.028 µg g^?1 dry weight (DW)), anthesis (0.072 µg g^?1 DW) and maturity (0.103 µg g^?1 DW) was recorded for silica gel. Silicon uptake increased significantly in response to increase in Si concentration from 0.5% to 1.5%. Leaf membrane stability index, epicuticular wax, relative water content and proline remained maximum – 78.90%, 2.6 mg g^?1 DW, 83.88% and 54.90 µg g^?1 – for silica gel treatments compared with others. Silica gel with 1.5% silicon concentration resulted in maximum spike length (14.3 cm), biological yield (7.63 g pot^?1), hundred-grain weight (3.97 g pot^?1) and grain yield (2.46 g pot^?1). Based on the study outcomes, it is concluded that silica gel might be a good priming option with 1.5% silicon concentration to establish plant under drought stress.     

Wheat Straw Biochar Increases Potassium Concentration,Root Density,and Yield of Faba Bean in a Sandy Loam Soil

ABSTRACT

A greenhouse experiment was conducted to study the effect of different irrigation levels (100%, 75%, and 50% of water requirement) and wheat straw biochar levels (0%, 1.25%, 2.5%, 3.75%, and 5% w/w) on faba bean yield, water productivity, root length density, and different ions concentration in soil solution, using a factorial arrangement in complete randomized design with three replications. Results showed that application of high level of biochar (5% w/w) destroyed the plants before they reached maturity. The maximum yield was obtained in 1.25% w/w biochar under full irrigation, while the maximum water productivity was obtained in 2.5% w/w biochar and 50% of water requirement. Further, the root length density in soil top layer (0–8 cm) was significantly more than those in 8–16 cm, due to holding more water content in top layer and no drainage from the pots. Sodium, potassium, calcium and magnesium ions’ concentrations in soil solution were significantly increased by increasing biochar levels; however, the rate of increase in potassium was higher than other ions due to high potassium concentration in biochar in comparison with the soil. In conclusion, application of biochar in the level of 1.25% w/w is suggested as a suitable agent to decrease water consumption and improving the crop performance.     

Improving Strategic Growth Stage-based Drought Tolerance in Quinoa by Rhizobacterial Inoculation

ABSTRACT

Climate change is imposing high temperature resulting in prolonged drought episodes and shrinking of fresh water resources across the globe. In this scenario, even drought tolerant crops like quinoa are also losing significant yield. However, this study was planned to investigate the impact of drought on quinoa at critical growth stages and bacterial inoculation to improve drought tolerance. Drought was imposed by maintaining 25% pot water holding capacity (PWC) at multiple leaf, flowering, and seed filling stage (DSFS), while 80% PWC was considered as control. Three strains of plant growth promoting rhizobacteria (PGPR) named as: Bacillus licheniformis, Pseudomonas fluorescens, and Azospirillum brasilense were inoculated with quinoa seeds before sowing with respect to drought treatments. PGPR inoculation mitigated the drastic effects of drought by improving crop growth, net assimilation rate, water use efficiency, leaf chlorophyll, and phenolic contents, all of these ultimately contributed to improvement in grain yield and its contributing attributes. Moreover, PGPR markedly improves the grain quality attributes including protein, phosphorus, and potassium contents. Principal component analysis linked the different scales of study and demonstrated the potential of physio-biochemical traits to explain the quinoa yield variations under drought condition with response to PGPR inoculation. Among different PGPR, A. brasilense was found most effective both under normal and drought conditions. Overall, DSFS has more detrimental effects among critical growth stages of quinoa and A. brasilense can be used as a shotgun tactic to ameliorate drought stress in quinoa.     

Phosphorus Forms and Availability Assessed by 31P‐NMR in Successively Cropped Soil

Abstract

Soils under no‐tillage gradually increase in organic matter and phosphorus (P) content from the top layer. Because of lack of knowledge about the organic phosphorus fraction contribution to plant nutrition, this research was conducted to estimate the availability of phosphorus fractions to plants. Soil samples of a very clayey Rhodic Hapludox that received 0, 156 and 312 kg P ha^?1 were submitted to 15 successive crops in pots without replacing P extracted by plants. ³¹P nuclear magnetic resonance analysis was performed to detect P fractions before cultivation and after the sixth, ninth and fifteenth crops. Inorganic phosphorus was the unique P fraction acting as P source to plants in soils with previous P addition. Contribution of organic P was observed only when inorganic P content was extremely low, with plants showing severe P stress. Contribution of organic P was not enough to supply the required P for normal plant growth.     

Silicon-induced changes in growth,ionic composition,water relations,chlorophyll contents and membrane permeability in two salt-stressed wheat genotypes

We investigated the effect of exogenously applied silicon (Si) on the growth and physiological attributes of wheat grown under sodium chloride salinity stress in two independent experiments. In the first experiment, two wheat genotypes SARC-3 (salt tolerant) and Auqab 2000 (salt sensitive) were grown in nutrient solution containing 0 and 100 mM sodium chloride supplemented with 2 mM Si or not. Salinity stress substantially reduced shoot and root dry matter in both genotypes; nonetheless, reduction in shoot dry weight was (2.6-fold) lower in SARC-3 than in Auqab 2000 (5-fold). Application of Si increased shoot and root dry weight and plant water contents in both normal and saline conditions. Shoot Na⁺ and Na⁺:K⁺ ratio also decreased with Si application under stress conditions. In the second experiment, both genotypes were grown in normal nutrient solution with and without 2 mM Si. After 12 days, seedlings were transferred to 1-l plastic pots and 150 mM sodium chloride salinity stress was imposed for 10 days to all pots. Shoot growth, chlorophyll content and membrane permeability were improved by Si application. Improved growth of salt-stressed wheat by Si application was mainly attributed to improved plant water contents in shoots, chlorophyll content, decreased Na⁺ and increased K⁺ concentrations in shoots as well as maintained membrane permeability.     

Biochar Application and Drought Stress Effects on Physiological Characteristics of Silybum marianum

Soil amending with biochar has been viewed as a sustainable way to improve soil moisture holding capacity. The potential of biochar application to improve water status of crops under drought stress has not been extensively evaluated. In this study, we evaluated the impact of biochar application (0%, 1%, and 2% w/w soil) on some important physiological traits of milk thistle (Silybum marianum L. Gaertn) under moderate and severe drought stress conditions in a controlled environment. Although, the application of biochar at the higher rate slightly improved soil moisture holding capacity, the magnitude of its effect was not sufficient to influence plant performance under drought stress. To get the positive effects of biochar application on milk thistle performance under drought stress, application with higher rates is probably necessary.     

Effects of a super-absorbent polymer derived from poly-γ-glutamic acid on water infiltration,field water capacity,soil evaporation,and soil water-stable aggregates

ABSTRACT

The poly-γ-glutamic acid super-absorbent polymer (γ-PGA SAP) is an environmentally friendly material. Five different γ-PGA SAPs contents based on weight, including 0% (CK), 0.05% (T1), 0.10% (T2), 0.15% (T3), and 0.20% (T4), were added to the soil in this study. The results showed that cumulative infiltration decreased by 32.4% (T1), 39.2% (T2), 51.0% (T3), and 52.0% (T4) at 90 min and the field capacity was increased by 18.7% (T1), 26.0% (T2), 37.8% (T3), and 58.3% (T4) compared with the CK. The cumulative evaporation of the different treatments with γ-PGA SAPs was 17.1% (T1), 23.5% (T2), 24.4% (T3), and 25.3% (T4) higher than that of the CK at the end of the evaporation experiment. The evaporation experiment lasted 96 h (CK), 132 h (T1), 144 h (T2), 180 h (T3), and 312 h (T4) to progress from field capacity to a soil water content of 10%. Adding γ-PGA SAPs to the soil significantly increase the water-stable aggregate content below 0.25 mm when the γ-PGA SAP addition exceeded 0.10%. So reasonable utilization of γ-PGA SAP can improve water use efficiency and improve soil structure in semi-arid areas.     

Characteristics of synthetic soil aggregates produced by mixing acidic “Kunigami Mahji” soil with coal fly ash and their utilization as a medium for crop growth

Abstract

This study was carried out to examine the characteristics and potential utilization of synthetic soil aggregates (SSA) produced by mixing acidic “Kunigami Mahji” soil in Okinawa, Japan, with waste materials, such as coal fly ash, used paper and starch, as media for crop growth. A series of different SSA were produced by incorporating various percentages (i.e. 0, 20, 40, 60, 80 and 100%) of coal fly ash into the “Kunigami Mahji” soil with used paper and starch. The particle density and bulk density of the original “Kunigami Mahji” soil were 2.67 and 1.23 g cm^?3, respectively. The increased percentages of added coal fly ash, used paper and starch significantly decreased the particle and bulk densities of SSA compared with the original “Kunigami Mahji” soil because of the low particle and bulk densities of the coal fly ash (2.10 and 0.96 g cm^?3, respectively). The SSA particle density varied between 2.39 and 2.14 g cm^?3, and bulk density varied between 0.72 and 0.81 g cm^?3, depending on the additional percentages of coal ash from 20–100%. Maximum water-holding capacity and saturated hydraulic conductivity were increased with the formation of SSA with coal fly ash, used paper and starch binder compared with the original “Kunigami Mahji” soil. The saturated hydraulic conductivity values of the SSA increased because of their low bulk density compared with the original soil. The addition of coal fly ash, used paper and starch to the acidic (pH = 4.62) “Kunigami Mahji” soil to form SSA increased the pH (6.70–9.96), electrical conductivity, exchangeable cation concentration and cation exchange capacity. The addition of coal fly ash up to 60% increased the aggregate strength. The growth and yield of komatsuna and soybean crops with SSA as a crop growth medium was assessed. Both crops showed the highest growth and yield when grown with SSA containing 20% of coal fly ash. Synthetic soil aggregates containing more than 20% of coal fly ash reduced plant growth and yield. Therefore, SSA produced from “Kunigami Mahji” soil with 20% of coal fly ash, used paper and starch can be successfully used as a medium for crop growth.     

Effect of water stress and nickel application on yield components and agronomic characteristics of canola grown on two calcareous soils

A greenhouse experiment (5 × 2 × 2 factorial arranged in randomized-complete-design with three replicates) was conducted to assess the combined effects of nickel (Ni) and drought stress on growth and yield parameters of canola (Brassica napus L. var. Talaye) grown on two calcareous soils of loamy and sandy clay textures. Treatments consisted of five Ni levels (0, 0.05, 0.1, 0.5 and 1 mg Ni kg^?1 soil) and two levels of water status 100% and 60% field capacity (FC and 0.6FC, respectively). Growth parameters and yield components of plants decreased at drought-stress conditions. Almost all of the studied growth/yield parameters of canola grown on loamy soil were significantly more than those of the sandy clay soil, probably due to the increased capability of loamy soil for supplying the plant water/nutrient requirements. Nickel could positively affect some of the mean growth and yield parameters (e.g., grain yield) over both of the water status conditions. Nevertheless, some of the traits not only increased by Ni fertilization but also decreased compared to that of the control. The positive responses of canola was observed with higher amounts of applied Ni in the sandy clay soil than in loamy soil, e.g., the maximum grain yields of canola grown on loamy and sandy clay soils were obtained with applications of 0.5 and 1 mg Ni kg^?1, respectively. Generally, results demonstrated that Ni could not mitigate the negative effects of drought stress on canola growth or yield components.     

Drought response of dry-seeded rice to water stress timing and N-fertilizer rates and sources

Abstract

Dry seeding has been identified as an option for increasing cropping intensity and productivity in rainfed ricelands. Managing drought and nutrients are important for increasing yield, but the interactive effects of drought and nutrients on dry-seeded rice (Oryza sativa L.) growth have not been systematically investigated. Two experiments were carried out in 1994 and 1995 to analyze the effects of N fertilizer rate and the use of controlled-release fertilizers (CRFs) on the growth and yield of dry-seeded rice grown on a silty clay loam (Typic Tropaquept) subjected to water stress at different crop stages. In both years, in the main plots, rice was subjected to water stress at four different stages of development. The subplots were designed to compare the effect of the application of prilled urea and CRFs Osmocote (1994) and Polyon 12 (1995). Four N rates (0, 60, 120 and 180 kg ha^?1) were imposed on rice in the sub-subplots (1994 only). The N fertilizer source did not affect any of the measured parameters. Irrespective of the N the fertilizer rates, grain yield and total dry matter accumulation of rice plants stressed at the flowering stage (WS_FL, 1994) and panicle initiation stage (WS_PI, 1995) were significantly lower than those of well-watered plants and plants stressed at the vegetative stage. Water stress during the grain-filling stage reduced the grain yield in 1995 when the stress was severe. Application of N fertilizer increased the yield compared with zero N in all water treatments, except for the WS_FL plants whose yield did not change. The WS_FL treatment also significantly reduced agronomic N-use efficiency.     

Effect of N rate and split application on bahiagrass production

Abstract

Vegetative and reproductive growth were studied in five tomato (Lycopersicon esculentum Mill) cultivars under saline conditions imposed at the five‐leaf stage by addition of 50 mM NaCl to half strength Hoagland nutrient solution. The plants were raised in pots filled with washed quartz sand kept in a greenhouse. Stem height and number of leaves in tomato plants were significantly reduced when irrigated with saline regimes in contrast with control plants that received only the Hoagland solution. The highest number of flowers were obtained in the cultivar Pearson and the least in cultivar Strain B. Fruit set and yield were little affected by varietal differences and were not related to vegetative growth. Fruit weight was suppressed with NaCl stress, but improvement in weight was achieved when potassium (K) and calcium (Ca) were added to the saline water. The most detrimental effect of NaCl stress was the reduction of biomass yield in tomatoes. However, the relative dry weights of Pearson and Monte Carlo were increased to 60% and 54%, respectively, when NaCl was supplemented with Ca. Large varietal differences in biomass occurred among the NaCl‐treated and control plants. Tomato fruit quality (TSS) was improved by salinization.     

Yield,Petiole Nitrate,and Node Development Responses of Cotton to Early Season Nitrogen Fertilization

Abstract

Nitrogen (N) fertilization continues to be of primary importance in the economically successful production of cotton (Gossypium hirsutum L.). Profit margins of producers might be expanded by increasing the uptake efficiency of applied N. Recently, N fertilization of crops grown in the Mississippi River Delta has been suspected to impact water quality in the Gulf of Mexico. Improving efficiency of N uptake could alleviate some environmental concerns by increasing the retention of N at the site of application. The objective of this study was to determine the impact of replacing preplant N applications with postemergent N applications on the growth and yield characteristics of cotton. Delayed applications of the recommended rate of N fertilizer (112 kg N ha^?1) were tested for four years under irrigated and dry land production conditions. The N rate was applied either preplant, after crop emergence, or at first square. Further, 112 kg N ha^?1 was split applied evenly at preplant + first square, and after emergence + first square. The five 112 kg ha^?1 N treatments were compared to an unfertilized control. Yield tended to be maximized with N treatments that included a first square application. Yields were usually lowest in the unfertilized control and the 112 kg N ha^?1 preplant treatments. Not surprisingly, both yield and plant growth was influenced more by irrigation than N fertilization. Years when drought conditions caused water stress and limited plant growth, dry land cotton had only limited response to the N fertilization treatments. Irrigated cotton responded to N treatments all years with increased growth and yield. Optimizing agronomic considerations, the best N fertilization timing was an after emergence + first square split application.

     

Nutrient Uptake,Water Relations,and Yield Performance lf Different Wheat Cultivars (Triticum aestivum L.) under Salinity Stress

A pot experiment was conducted in the wire house of Department of Crop Physiology, University of Agriculture, Faisalabad to evaluate the effect of salinity stress on water relations, nutrient uptake and yield of six local spring wheat cultivars. The seeds were sown in plastic pots (25 × 15 cm) and experiment was laid out in a randomized complete block design in factorial arrangement with three repeats. De-ionized water was used as control treatment while salinity stress was imposed by irrigating plants with sodium chloride (NaCl) solution of 10 mM at tillering, stem elongation, anthesis, and grain development stages. Results of the study demonstrated that salinity stress decreased water potential by 32%, osmotic potential by 12%, and relative water contents by 20% as compared to control treatment. The nitrogen (N) uptake was decreased by 36% under salinity stress, while phosphorous (P) and potassium (K) uptake were decreased by 56% and 42%, respectively. The yield of wheat plants was also significantly reduced under salinity stress. It reduced grain yield by 25% and grain weight by 7%. The response of different cultivars was also different to salinity stress as cultivars ‘Lasani-08’ and ‘FSD-08’ were found to be more tolerant as compared to other cultivars.     

Potential for the alleviation of arsenic toxicity in paddy rice using amorphous iron-(hydr)oxide amendments

Abstract

A pot culture experiment was conducted to investigate the effects of amorphous iron-(hydr)oxide (Am-FeOH) amendments on arsenic (As) availability and its uptake by rice (Oryza sativa L. cv. BR28) irrigated with As-contaminated water. A rhizobag system was established using 3.5 L plastic pots, each containing one central compartment for plant growth, a middle compartment and an outside compartment. Three levels of laboratory-synthesized Am-FeOH (0, 0.1 and 0.5% w/w) were used to amend samples of the As-free sandy loam paddy soil placed into each compartment of the rhizobag system. The soils were submerged with a solution containing 5 mg L^?1 As(V). Two-week-old rice seedlings were planted in the central compartments and cultured for 9 weeks under greenhouse conditions. The addition of 0.1% Am-FeOH to the soil irrigated with As-contaminated water improved plant growth, reduced the As concentration in the plants and enhanced Fe-plaque formation on the root surfaces. Analysis of soil solution samples collected during the experiment revealed higher pH levels and lower redox potentials in the soils amended with Am-FeOH at the onset of soil submergence, but later the soil solution collected from the 0.1% Am-FeOH treatment was slightly acidic and more oxidized than the solution from the 0% treatment. This indicated active functioning of the roots in the soil treated with 0.1% Am-FeOH. The concentrations of As(III) in the soil solution collected from the central compartment were significantly reduced by the Am-FeOH amendments, whereas in the soil treated with 0% Fe, As(III) accumulated in the rhizosphere, particularly during the late-cultivation period. The improvement in plant growth and reduction in As uptake by plants growing in the Am-FeOH treated soil could be attributed to the reduction of available As in the soil solution, mainly as a result of the binding of As to the Fe-plaque on the root surfaces.     

Combined effect of deficit irrigation and foliar-applied salicylic acid on physiological responses,yield, and water-use efficiency of onion plants in saline calcareous soil

Field-applied salicylic acid (SA) could provide a potential protection against drought stress in onion large-scale production. Two-season field experiments were consecutively conducted in 2013/2014 and 2014/2015 to study the effect of 1 and 2 mM SA on growth, yield, plant water relations, chlorophyll a fluorescence, osmoprotectants, and water-use efficiency (WUE) in onion plants under four levels of irrigation (I₁₂₀ = 120%, I₁₀₀ = 100%, I₈₀ = 80%, and I₆₀ = 60% of crop evapotranspiration). Foliar application of SA enhanced drought stress tolerance in onion plants by improving photosynthetic efficiency and plant water status as evaluated by membrane stability index and relative water content. These results were positively reflected by improving plant growth, productivity, and WUE under drought stress conditions. Therefore, SA application may, in future, find application as a potential growth regulator for improving plant growth and yield under deficit irrigation by 20–40%.     

Early Development and Nutrition of Cover Crop Species as Affected by Soil Compaction

Abstract

A good cover crop should have a vigorous early development and a high potential for nutrient uptake that can be made available to the next crop. In tropical areas with relatively dry winters drought tolerance is also very important. An experiment was conducted to evaluate the early development and nutrition of six species used as cover crops as affected by sub‐superficial compaction of the soil. The plants (oats, pigeon pea, pearl millet, black mucuna, grain sorghum, and blue lupin) were grown in pots filled with soil subjected to different subsurface compaction levels (bulk densities of 1.12, 1.16, and 1.60 mg m^?3) for 39 days. The pots had an internal diameter of 10 cm and were 33.5 cm deep. Grasses were more sensitive to soil compaction than leguminous plants during the initial development. Irrespective of compaction rates, pearl millet and grain sorghum were more efficient in recycling nutrients. These two species proved to be more appropriate as cover crops in tropical regions with dry winters, especially if planted shortly before spring.     

Modulation in growth,development, and yield of Camelina sativa by nitrogen application under water stress conditions

Camelina sativa has rejuvenated as a successful oilseed crop in the recent years. It is a low-input-requiring crop with an unusual fatty acid composition. A pot experiment was conducted in rain-out shelter to investigate the effect of different nitrogen levels (N₀ = 0, N₁ = 50, N₂ = 100, and N₃ = 150 kg ha^?1) on the growth and yield of two C. sativa genotypes (Australian and Canadian) under normal [100% field capacity (FC)] and water stressed (60% FC) conditions. The experiment was laid out in a completely randomized design with factorial arrangement having three replicates in the Department of Crop Physiology, University of Agriculture, Faisalabad. The results indicated that nitrogen doses and water stress levels significantly affected the growth and yield of C. sativa. Maximum values for growth indices like leaf area index (LAI), crop growth rate (CGR), leaf area duration (LAD), net assimilation rate (NAR), and yield attributes were observed under N₂ treatment (100 kg ha^?1) followed by the treatment in which nitrogen was applied at the rate of 50 kg ha^?1. However, growth and yield components significantly reduced under water stress conditions (60% FC). Of both the genotypes, Australian Camelina performed better as compared to Canadian Camelina under both non-stress and drought stress conditions.     

Effects of hydrogel incorporation in peat‐lite on tomato growth and water relations

Abstract

The effects of subirrigation and cylical (surface) irrigation on shoot growth and water stress of tomato grown in peat‐lite amended with 0, 4, 8, 12, and 16 kg Hydrogel/m were examined. While shoot growth showed a quadratic response to increasing Hydrogel rate with maximal growth occurring at the manufacturer's recommended rate (8 kg/m³), growth was greater with cyclical irrigation than with subirrigation. Subirrigation generally resulted in greater plant water stress than cyclical irrigation, but with ≤ 8 kg Hydrogel/m³ this differential irrigation effect diminished temporally. Initially, each kg Hydrogel/m³ increased peat‐lite water content by 9 percent but after 31 days, this value had increased to 27 percent and 16 percent with subirrigation and cyclical irrigation, respectively. The continued hydration resulted in a bulk volume increase sufficiently large with subirrigation to cause the Hydrogel‐amended peat‐lite to overflow the pots.