Effect of Acid Aluminous Soil on Photosynthetic Parameters of Potato (Solanum tuberosum L.)

Potato is grown worldwide, in some cases in very acid soils. Aluminum (Al) is a major limiting factor for crop productivity in acid soils. Al toxicity was studied mainly on plant roots, while less attention was given to its effects on leaves. Al tolerance observed in solution cultures has rarely been correlated with Al tolerance in acid soils. Al tolerance was assessed in 12 potato cultivars grown in nutrient solutions containing 0, 25, and 50 μmol Al L^?1 by its relative root elongation (RRE). The effect of acid soil with high level of exchangeable Al on leaf mineral content, chlorophyll content, net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, water use efficiency (WUE), and light use efficiency (LUE) was studied on cultivars, with the greatest differences in RRE (cv. Tresor, 63.1 and 42.5% and cv. Canberra, 23.3 and 19.2%, for the 25 and 50 μmol Al L^?1 treatments, respectively), grown for 49 days after planting (DAP) in acid and limed soil. Growth in acid soil significantly reduced concentrations of nitrogen (?18.51%) and magnesium (?27.17%) in the leaves in cv. Canberra and concentrations of potassium and copper in both cultivars. Canberra grown in acid soil showed a significant decrease in chlorophyll content and photosynthetic rate, from 28 to 49 DAP, and in transpiration rate and LUE when averaged across all measurements, while cv. Tresor was not affected. Physiological disorders observed on leaves of plants grown in acid soil can be correlated with the differences in Al tolerance observed in nutrient solutions.     

Effect of soil salinity on the wheat and bean root respiration rate at low matric suctions

Water logging and salinity often occur together because rising water table brings salt to the surface. We studied the effects of a range of low soil matric suctions (or nearly paddy condition) (2–33 kPa) and salinity (EC = 0.7–8 dS m^?1 for bean and 2–20 dS m^?1 for wheat) on the root respiration (Rr) in two sandy loam and clay loam soils at greenhouse condition. Results showed that the aeration porosity mainly controls Rr especially at 2 kPa matric suction. As matric suction increases, soil aeration rises and consequently the Rr reaches maximum values (7.9 μmol m^?3 s^?1 for bean and wheat) at 6 and 10 kPa suctions in clay loam and sandy loam soils, respectively. Using a mechanistic soil respiration model reveals that these matric suctions, h, are corresponded to the aeration porosities of 0.18 m³ m^?3 in sandy loam and 0.16 m³ m^?3 in clay loam soils. Bean and wheat Rr remains nearly constant at higher suctions (h > 10 kPa) in sandy loam and decreases slightly in clay loam soil. Gas diffusivity and the root surface area may explain the variation of the Rr between the sandy loam and the clay loam soils. Results showed that the salinity (EC = 6–8 dS m^?1 for bean and EC = 16–20 dS m^?1 for wheat) amplifies the effect of aeration stress at 2 kPa matric suction in both soils. We also observed a strong correlation between root surface area, Rs, and the Rr for all experiments. We concluded that the aeration deficit is not only major factor determining differential plant respiration under adverse stress conditions, and the salinity has a pronounced impact on differences in crop physiological responses.     

Response of the leaf photosynthetic rate to available nitrogen in erect panicle-type rice (Oryza sativa L.) cultivar,Shennong265

Increasing the yield of rice per unit area is important because of the demand from the growing human population in Asia. A group of varieties called erect panicle-type rice (EP) achieves very high yields under conditions of high nitrogen availability. Little is known, however, regarding the leaf photosynthetic capacity of EP, which may be one of the physiological causes of high yield. We analyzed the factors contributing to leaf photosynthetic rate (P_n) and leaf mesophyll anatomy of Nipponbare, Takanari, and Shennong265 (a EP type rice cultivar) varieties subjected to different nitrogen treatments. In the field experiment, P_n of Shennong265 was 33.8 μmol m^?2 s^?1 in the high-N treatment, and was higher than that of the other two cultivars because of its high leaf nitrogen content (LNC) and a large number of mesophyll cells between the small vascular bundles per unit length. In Takanari, the relatively high value of P_n (31.5 μmol m^?2 s^?1) was caused by the high stomatal conductance (g_s; .72 mol m^?2 s^?1) in the high-N treatment. In the pot experiment, the ratio of P_n/C_i to LNC, which may reflect mesophyll conductance (g_m), was 20–30% higher in Nipponbare than in Takanari or Shennong265 in the high N availability treatment. The photosynthetic performance of Shennong265 might be improved by introducing the greater ratio of P_n/C_i to LNC found in Nipponbare and greater stomatal conductance found in Takanari.     

Variations in structural,biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)

C₄ plants show higher photosynthetic capacity and productivity than C₃ plants owing to a CO₂-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C₄ plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C₄ dicots. Net photosynthetic rate (P_N) ranged from 19.7 to 40.5 μmol m^?2 s^?1. P_N was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. P_N was also positively correlated with the activity of the C₃ enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C₄ enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with P_N. These data suggest that some of the biochemical and physiological traits are involved in interspecific P_N variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol^?1 N s^?1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol^?1. When these data were compared with previously published data of C₄ grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.     

Effects of poultry manure on soil solution electrical conductivity and early growth of Monochoria vaginalis

We investigated the effect of poultry manure (PM) on the occurrence and early growth of Monochoria vaginalis in relation to soil solution electrical conductivity (SSEC). PM was applied at rates corresponding to 0 g of nitrogen (N) m^?2 (PM-0), 1 g N m^?2 (PM-1), 3 g N m^?2 (PM-3), and 5 g N m^?2 (PM-5). At 7 d post-seeding, the soil solution was sampled to measure EC, and also the emergence and growth of M. vaginalis were evaluated. The emergence rate of M. vaginalis decreased with increasing application rate of PM and SSEC. SSEC was significantly negatively correlated with the emergence rate of M. vaginalis seedlings. The average leaf number and length of M. vaginalis did not differ between PM-0, PM-1, and PM-3, but were significantly lower in PM-5. In summary, PM would allow to better control the emergence and early growth of M. vaginalis.     

Effects of soil types and fertilizers on growth,yield, and quality of edible Amaranthus tricolor lines in Okinawa,Japan

Soil types and fertilizer regimes were evaluated on growth, yield, and quality of Amaranthus tricolor lines, IB (India Bengal), TW (Taiwan), BB (Bangladesh B), and BC (Bangladesh C) in developing management practices in Okinawa. Growth and yield of all amaranth lines were higher in gray soil (pH 8.4) than in dark red soil (pH 6.6) and red soil (pH 5.4). The combined NPK fertilizer resulted in highest growth parameters and yield of amaranths in all soils. Nitrogen fertilizer alone did not affect growth parameters and yield of amaranths in dark red and red soils. Growth parameters and yield increased similarly with the 30, 40, and 50 g m^?2 of NPK fertilizer in BB line, and with the 20, 30, 40, and 50 g m^?2 in BC line. Agronomic efficiency of NPK fertilizer at 50 g m^?2 was not prominent on the amaranths, compared to the fertilizer at 40 g m^?2. Amaranth lines had higher Na in dark red and red soils, while K and Mg in gray soil, Ca in gray and red soils, and Fe in dark red soil. The NPK fertilizer resulted in higher Na, Ca, Mg, and P in BB line in glasshouse. These minerals in BB line were not clearly affected, but in BC line were lower with NPK fertilizer at 20–50 g m^?2 in field. These studies indicate that gray soil is best for amaranth cultivation and combined NPK fertilizer at 20–40 g m^?2 is effective in gray soil in Okinawa for higher yield and minerals of amaranth.     

Chemical fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) in selected paddy soils of Iran

The content and fractionation of seven heavy metals (Cd, Cu, Fe, Mn, Ni, Pb, and Zn) were determined in 28 surface soil samples (0–20 cm) of agricultural topsoil from Isfahan Province in central Iran. The order of abundance of metals in the soils was Fe (1240.4 mg kg^?1) > Mn (95.7 mg kg^?1) > Pb (51.6 mg kg^?1) > Zn (23.8 mg kg^?1) > Ni (13.4 mg kg^?1) > Cu (7.0 mg kg^?1) > Cd (2.8 mg kg^?1). Iron, Mn, Ni, Pb, and Zn existed in paddy soils mainly in Fe-Mn oxides (53.6 %, 65.2 %, 40.4 %, 40.8 %, 53.3 %, respectively), whereas Cu and Cd occurred essentially as residual mineral phase (41.4 %) and carbonate (36.1 %), respectively. The mobile and bioavailable fractions of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in paddy soils averaged 48.8, 20.8, 0.79, 29.2, 28.5, 41.1, and 24.8 %, respectively, which suggests that the mobility and bioavailability of the seven metals probably decline in the following order: Cd > Pb > Mn ≥ Ni > Zn > Cu ? Fe, suggesting greater contribution of anthropogenic Cd. As Cd in soil is easily accumulated by plants through the root system, the concentration of Cd in these paddy soils could be a concern to human health.     

Impact of water management on yield and water productivity with system of rice intensification (SRI) and conventional transplanting system in rice

The system of rice intensification (SRI) reportedly enhances yield with less water requirement. This claim was investigated to determine the effects of alternative cultivation methods and water regimes on crop growth and physiological performance. Treatment combinations compared SRI with the conventional transplanting system (CTS) using standard practices, evaluating both along a continuum from continuous flooding to water applications at 1, 3, 5, or 7 days after disappearance of ponded water (DAD), subjecting plants to differing degrees of water stress while reducing total water expenditure. SRI methods gave significant changes in plants’ phenotype in terms of root growth and tillering, with improved xylem exudation and photosynthetic rates during the grain-filling stage compared to CTS. This resulted in significant increases in panicle length, more grains and more filled grains panicle^?1, greater 1,000-grain weight, and higher grain yield under SRI management. Overall, averaged across the five water regimes evaluated, SRI practice produced 49 % higher grain yield with 14 % less water than under CTS; under SRI, water productivity increased by 73 %, from 3.3 to 5.7 kg ha-mm^?1. The highest CTS grain yield and water productivity were with the 1-DAD treatment (4.35 t ha^?1 and 3.73 kg ha-mm^?1); SRI grain yield and water productivity were the greatest at 3-DAD (6.35 t ha^?1 and 6.47 kg ha-mm^?1).     

Phyto-purification of livestock-derived organic waste by forage rice under subtropical climate

Soil and water pollution caused by organic waste is a concern for livestock-breeding areas. Nitrogen balance in a paddy-field water-purifying system in which cattle feces were applied was studied for 4 years to assess the suitability of the system for a subtropical area, Japan. Three successive harvestings using ratoon of forage rice following one rice transplanting were conducted with chemical fertilizer and high and low rates of cattle-feces application. Nitrogen load was 81.3–495.0 kg N ha^?1 year^?1, while nitrogen uptake was highly dependent on the yield of the first harvesting. Annual variation of forage rice yields was large, ranging from 15.5 to 26.8 Mg ha^?1 owing to fluctuation in the yield at second and later harvestings. On average, nitrogen was lost by leaching at a rate of 2.3–3.4 kg N ha^?1 year^?1. The nitrogen content in soil at a depth of 0–5 cm increased up to 12.2 kg N ha^?1 over the 4-year period compared with that before the field experiment. However, continuous application of cattle feces could slightly increase the nitrogen content in soil at a depth greater than 35 cm. Our results showed the ability of flooded forage rice to remove nitrogen at up to 320.1 kg ha^?1 year^?1 for a field to which cattle feces were applied. Further investigation is needed to produce a high and stable yield at second harvesting each year, to prevent the accumulation of soil nitrogen, and to assess gaseous nitrogen loss.     

Soil property predictors of soybean yield using yield contest sites

State yield contests offer a unique opportunity to examine the high end of crop productivity. Yield-contest-entered and average-yielding areas on the same or a similar soil can provide large yield and soil property variations to better examine the relationships among various near-surface soil properties and soybean (Glycine max L. [Merr.]) yield. The objective of this study was to evaluate the relationships among a suite of near-surface soil properties and soybean yield across average- and high-yield areas using state yield-contest sites. Multiple regression analyses were conducted to evaluate best-fit relationships among various soil physical, chemical, and biological properties and yield separately for average- and high-yielding areas and for data combined across yield areas. Soybean yield variation was most explained for the high-yield-area dataset (R² = 73%) and less explained for the average-yield-area (R² = 51%) and the combined (R² = 50%) datasets. Extractable soil Ca and S explained the largest proportion of yield variation (37% and 31% of total sum of squares) in the high-yield setting and both were inversely related to yield. A better understanding of the soil environment may be a key component of more frequent attainment of the 6270 kg ha^?1 (100 bu acre^?1) soybean yield mark. Additional soil properties, beyond those evaluated in this study, may need to be included for a more complete understanding of the soil environment that is associated with high-yield soybean production.     

Behavior of carbon dioxide in soils affected by tillage systems

Agricultural management plays an important role in the storage of carbon in soils. The behavior of soil CO₂ in an Andisol in two different tillage systems (no tillage and tillage) was studied. Soil-column incubation experiments were performed for a period of 150 days to conduct this study. Soil CO₂ flux, under no-tillage and tillage treatments, was observed to be 0.557 and 0.616 gCO₂-C m^?2 d^?1, respectively. The cumulative CO₂ flux under tillage treatment was observed to be higher than that under no-tillage treatment, but no distinct difference in the soil carbon stock was observed between both treatments. The soil CO₂ concentration under no-tillage treatment was clearly much higher than that under tillage treatment, except at a depth of 2.5 cm. Tillage decreased soil dry bulk density and enhanced soil air-filled porosity. Soil gas diffusivity, which depends on air-filled porosity, was increased by tillage at a depth of 0–15 cm, which contributed to their lower soil CO₂ concentration. CO₂ flux through the soil profile, calculated from the CO₂ concentration, decreased with depth. Compared to the deep soils, the surface soil (0–5 cm) showed greater variation in CO₂ flux. The CO₂ production at depths of 0–10 cm accounted for 62.2 and 51.7 % of the whole CO₂ production of the 0–30-cm soil profile for no-tillage and tillage treatments. CO₂ production was higher for soil under no tillage at depths of 0–10 cm, but contrary results were observed for soil at depths of 10–30 cm.     

Crop response to biochar under differing irrigation levels in the southeastern USA

Application of biochar to soils is hypothesized to increase crop yield. Crop productivity impacts of biochar application in southeastern cropping systems consisting of peanut (Arachis hypogaea L.), corn (Zea mays L.), and cotton (Gossypium hirsutum L.) produced under varying rates of irrigation have not been addressed. This research incorporated biochar at two different rates into a long-term irrigation and cropping systems study to compare yield and quality response of peanut, corn, and cotton. Biochar was incorporated into soil once at the beginning of the 4-year project at rates of 22.4 and 44.8 Mg ha^?1. Peanut, corn, and cotton were produced under three sprinkler irrigation levels (100%, 66%, and 33%), shallow surface drip irrigation (100%), and a nonirrigated control. Crop input management followed best management practices. Sprinkler irrigation was scheduled by Irrigator Pro for Peanuts, Corn, and Cotton at the 100% level and the 66% and 33% levels were applied at the same time as the 100% level. Significant year, irrigation, and year × irrigation effects for corn, cotton, and peanut yield resulted (p < 0.001). No differences resulted for biochar in corn (p = 0.930) or cotton (p = 0.678). Peanut yield showed a significant response to biochar comparing the 44.8 Mg ha^?1 rate to the untreated control in nonirrigated production at the p = 0.05 level and in the 33% irrigated treatment at the p = 0.10 level. No negative effects resulted from biochar opening opportunities for biochar application in southeastern U.S. cropping systems for purposes related to carbon sequestration without compromising productivity of producers and related agricultural sectors.     

Variations in physiological,biochemical, and structural traits of photosynthesis and resource use efficiency in maize and teosintes (NADP-ME-type C4)

C₄ plants show higher photosynthetic capacity and resource use efficiency than C₃ plants. However, the genetic variations of these traits and their regulatory factors in C₄ plants still remain to be resolved. We investigated physiological, biochemical, and structural traits involved in photosynthesis and photosynthetic water and nitrogen use efficiencies (PWUE and PNUE) in 22 maize lines and four teosinte lines from various regions of the world. Net photosynthetic rate (P_N) ranged from 32.1 to 46.5 μmol m^?2 s^?1. P_N was positively correlated with stomatal conductance, transpiration rate, and chlorophyll, nitrogen and soluble protein contents of leaves, but not with specific leaf weight. P_N was positively correlated with the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and the C₄-acid decarboxylases, NADP-malic enzyme and phosphoenolpyruvate carboxykinase, but not with the activity of phosphoenolpyruvate carboxylase. Leaf structural traits (stomatal parameters, leaf thickness, and interveinal distance) were not correlated with P_N. These data suggest that physiological and biochemical traits are involved in the genetic variation of P_N, but structural traits are not directly involved. PWUE is in the lower class of values reported for C₄ plants, whereas PNUE is in the highest class of values reported for C₄ plants. PNUE was negatively correlated with leaf nitrogen content but not significantly correlated with P_N. PWUE was not correlated with δ¹³C values of leaves, indicating difficulty in using δ¹³C values as an indicator of PWUE of maize. In general, teosinte lines showed lower P_N but higher PWUE than maize lines.     

Effect of drip irrigation on soil nutrients changes of saline–sodic soils in the Songnen Plain

A field experiment was carried out to research the changes and spatial distributions of soil nutrients in saline–sodic soil for different number of cultivated years under drip irrigation. The distributions of available potassium (AK), available phosphorus (AP), nitrate nitrogen (NO₃ ^?–N), ammonium nitrogen (NH₄ ⁺–N), as well as the amount of total nitrogen (TN), total phosphorus (TP) and organic carbon (OC) in the 0–40 cm soil layers in saline–sodic soils planted with Leymus chinensis for 1, 2, and 3 years were studied. The results showed that the distance from the emitter had an obvious effect on soil nutrients. Drip irrigation had substantial effects on levels of AK, AP, and NO₃ ^?–N. The contents of AK, AP, and NO₃ ^?–N were very high in the area near the emitter in the horizontal direction. In the vertical direction, levels of all of the available and total soil nutrients decreased with increased soil depth. Levels of AK, AP, NO₃ ^?–N, NH₄ ⁺–N, TN, TP, and OC all increased with continued cultivation of crops on saline–sodic soil using drip irrigation. Compared to the nutrients found in soils from the natural L. chinensis grasslands, the contents of AK and TP were higher in the drip-irrigated soils, although the contents of AP, NO₃ ^?–N, and NH₄ ⁺–N were broadly comparable. Given the rate of improvements in nutrient levels, we forecast that the nutrients in drip-irrigated saline–sodic soils should match those of the natural L. chinensis grasslands after 3–6 years of cultivation.     

Effect of fertilization on crop responses and solute transport for rice crop in a sub-humid and sub-tropical region

In order to increase the efficacy of water and control the losses of fertilizer, it is necessary to assess the influence of level of fertilization on crop responses, movement and balance of water and solutes from fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization on crop responses and fertilizer solute transport in rice crop field in a sub-humid and sub-tropical region. Field experiment was conducted on rice crop (cultivar IR 36) during the years 2003, 2004, and 2005. The experiment included four fertilizer treatments comprising different levels of fertilizer application. The fertilizer treatments during the experiment were: F₁ = control with N:P₂O₅:K₂O as 0:0:0 kg ha^?1; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha^?1; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha^?1 and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha^?1. The results of the investigation revealed that the magnitudes of crop parameters such as grain yield, straw yield, and maximum leaf area index increased with increase in fertilizer application rate. The levels of fertilization had very little effect on water loss via deep percolation and water use by the crop. The levels of fertilization had considerable effect on N leaching loss and uptake of N whereas it had no significant impact on leaching loss of water-soluble phosphorus. This indicated that PO₄-P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. The results also revealed that increase in level of fertilization increased water use efficiency considerably by increased crop yield. From the observed data of nutrient use efficiency, crop yield and environmental pollution, the fertilization rate of N:P₂O₅:K₂O as 80:40:40 kg ha^?1 (F₂) was the most suitable fertilizer treatment for rice crop among studied treatments.     

Potato Response to Phosphorus Fertilization at Two Sites in Nova Scotia,Canada

Identifying phosphorus (P) requirements and P-use efficiency is crucial to a sustainable potato industry in Eastern Canada. In a three-year study (2013–2015) conducted in Nova Scotia, Canada, we assessed the potato (CV Superior) yield response to P fertilization on two different soils in the Annapolis Valley. Soil organic matter ranged from 3.0% to 4.1% and from 2.0% to 2.5% at the Kentville and Sheffield sites, respectively. Initial soil phosphorus was higher at Kentville site, ranging from 81 to 162 mg kg^?1 than at Sheffield site ranging from 75 to 109 mg kg^-1. A randomized complete block design was used with five P rates (0, 17.5, 35, 52, and 79 kg P ha^?1) applied at planting. Tuber yields were assessed at harvest, and P-uptake efficiency characteristics were measured before vine senescence. Total and marketable yields were not impacted by P rates. Marketable yield was 68% and 57% greater for Kentville than for Sheffield in 2013 and 2015, respectively and were significantly affected by P rates × year interactions at a 5.4% probability level. Quadratic functions were used to describe tuber yield responses to P rates (0.61 > R ² < 0.85) and P rates corresponding to the maximum yields were 17.5 kg P ha^?1 in 2013 and 2015 and 35 kg P ha^?1 in 2014 when data from both sites were pooled together. Phosphorus uptake efficiency ranged from 0.47 to 0.54 g DM mg^?1 P offtake at Kentville and from 0.45 to 0.49 g DM mg^?1 P offtake at Sheffield and was 13% and 7% greater at Kentville than at Sheffield in 2013 and 2015, respectively. While further studies are still needed for recalibration, results from this study provide some of the first information regarding potato response to P fertilization in Nova Scotia. Based on current P recommendations in the region for the same soil P levels, our results suggest that current P rates can be reduced without impacting potato yield.     

Photosynthetic response and nitrogen use efficiency of sugarcane under drought stress conditions with different nitrogen application levels

Drought stress which often occurs during early growth stage is one constraint in sugarcane production. In this study, the response of sugarcane to drought and nitrogen application for physiological and agronomical characteristics was investigated. Two water regimes (well-watered and drought stress from 60 to 120 day after transplanting) and four nitrogen levels (0, 4.4, 8.8 and 13.2 g pot^?1 equivalent to 0, 90, 180 and 270 kg ha^?1, respectively) were assigned in a Split-plot design with three replications. The results showed that photosynthetic responses to light intensity and intercellular CO₂ concentrations of sugarcane were different between fertilized and non-fertilized treatments. Photosynthetic rates of 180 and 270 N treatments, normally, were significantly higher than that of 90 N, but not significant at drought conditions. Photosynthetic rates of 0 N treatment were the lowest under both conditions. Higher nitrogen application supported higher photosynthetic rate, stomatal conductance, and chlorophyll content because of higher nitrogen concentration accumulated into the leaf. Drought significantly reduced the potential photosynthetic rate, stomatal conductance, SPAD, leaf area, and biomass production. Higher nitrogen applications with larger root system could support higher photosynthetic activities to accumulate more dry mass. Strong positive coefficient between photosynthetic and biomass nitrogen use efficiency and drought tolerance index may suggest that higher nitrogen use efficiency could help plants have higher ability to tolerate drought stress.     

Alkaline phosphatase activity and its relationship to soil properties in a saline–sodic soil reclaimed by cropping wolfberry (Lycium barbarum L.) with drip irrigation

In order to ascertain the alkaline phosphatase (ALP) activity and its relationship with soil properties in saline–sodic soils during reclamation, a study was conducted in a saline–sodic soil reclaimed by cropping wolfberry (Lycium barbarum L.) with drip irrigation, in Ningxia Plain, Northwest China. The soil EC_e, pH and SAR in 0–30 cm were 12.3 dS m^?1, 9.4 and 44.1 (mmol/L)^0.5, respectively. Soil transects with different planting years were intensively sampled, which had a wide gradient of salinity and sodicity. Ranging from 1.1 to 42.4 μg g^?1 h^?1, soil ALP activities increased with the increasing planting years, and showed a large spatial variability within transect. The higher ALP activities were always found beneath the drip emitters. More soil physicochemical properties became related significantly to the ALP activities as the planting years increased, indicating that the ALP activities could be better predicted by other properties after reclamation. Path analyses showed that the negative direct effects of soil pH on ALP activities became clearly dominant as the planting years increased. The positive effects of organic matter on ALP activities exerted indirectly, mainly through pH, total N, and available P. Soil ALP activities decreased exponentially with pH, which varied from 7.38 to 10.00. Our findings demonstrated that soil pH was the limiting factor for improving soil ALP activities in this saline–sodic soil, and after three planting years, soil biological activities and fertility level increased significantly.     

Analyzing soil-available phosphorus by the Mehlich-3 extraction method to recommend a phosphorus fertilizer application rate for maize production in northern Mozambique

ABSTRACT

The available phosphorus (P) in soil is a major limiting factor for maize productivity in the Nacala corridor, Mozambique. In this study, soils were collected from three representative sites, Ribaue, Nampula, and Nacala, in the area, and each was used for maize pot experiment with five P fertilizer levels. The soil-available P content was determined by the Mehlich-3 method at 30 days after P fertilization. The shoot biomass and P concentration at the tasseling stage increased as the P fertilizer level increased and were significantly expressed as a function of soil-available P. Based on the function, the available P that attains 90% of the maximum shoot biomass was estimated as 79 mg P₂O₅ kg^?1. Consequently, the results in this study suggest a recommendation of 32–74 kg P₂O₅ ha^?1 fertilizer for maize production in the Nacala corridor although a field evaluation and economical evaluation are necessary.     

Characterization and Evaluation of OsLCT1 and OsNramp5 Mutants Generated Through CRISPR/Cas9-Mediated Mutagenesis for Breeding Low Cd Rice

To explore how rice(Oryza sativa L.) can be safely produced in Cd-polluted soil, OsLCT1 and OsNramp5 mutant lines were generated by CRISPR/Cas9-mediated mutagenesis. One of OsLCT1 mutant(lct1×1) and two of OsNramp5 mutants(nramp5×7 and nramp5×9) were evaluated for grain Cd accumulation and agronomic performances. In paddy field soil containing approximately 0.9 mg/kg Cd, lct1×1 grains contained approximately 40%(0.17 mg/kg) of the Cd concentration of the wild type parental line, less than the China National Food Safety Standard(0.20 mg/kg). Both OsNramp5 mutants showed low grain Cd accumulation(< 0.06 mg/kg) in the paddy(approximately 0.9 mg/kg Cd) or in pots in soil spiked with 2 mg/kg Cd. However, only nramp5×7 showed normal growth and yield, whereas the growth of nramp5×9 was severely impaired. The study showed that lct1×1 could be used to produce rice grains safe for human consumption in lightly contaminated paddy soils and nramp5×7 used in soils contaminated by much higher levels of Cd.