Long‐term effects of animal manure and mineral fertilizers on phosphorus availability and silage maize growth

A better appraisal of the plant availability of soil phosphorus (P) added with animal manure is crucial to alleviate environmental impacts from over‐application of P. This study compares the availability of P to maize in the Askov long‐term experiments using unmanured plots and plots receiving corresponding rates of nitrogen (N), P and potassium (K) in mineral fertilizers or manure. Total‐P and water extractable P (Pw) in soil, and plant height, dry weight, P concentration and P uptake were determined in early August. Final yields were determined in late October. Soil Pw was similar for plots receiving corresponding rates of P in mineral fertilizer or manure form. With a strong relationship between Pw, and maize growth and final yields, Pw was a reliable indicator of P availability to maize. Plant dry weight, P concentration and P uptake in early August were 23%, 8% and 31% higher, respectively, for maize grown on soil receiving manure compared with mineral fertilizer, while final maize yield in late October was 13% higher. Plant height and dry weight determined in early August suggested that maize development at this growth stage defined final maize yield. We conclude that the availability of P was similar after long‐term application of corresponding rates of P in animal manure and mineral fertilizers, and that animal manure improves the growth of maize compared to mineral fertilizers. This is ascribed to micronutrients and residual N effects from previous additions of manure.     

不同施肥对城郊菜地土壤质量、叶菜镉及养分含量的影响

通过田间试验研究不同施肥处理对广州市郊菜地土壤质量、叶菜可食部分Cd含量和养分含量的影响。结果表明:与75kg N/hm2处理相比,150kg N/hm2处理没有显著提高叶菜产量,且后者叶菜地上部分Cd含量较前者有不同程度提高。N用量为75kg/hm2时,硝酸铵+磷酸二氢钙+硫酸钾配施处理的芥菜和小白菜产量较高,矿质养分含量较高,Cd含量较低,且土壤肥力和质量得到维持。因此,在试验条件下,以硝酸铵+磷酸二氢钙+硫酸钾配施处理且N,P2O5,K2O用量分别为75,21.75,67.5kg/hm2时有利于改善叶菜品质和安全;而精制有机肥可能提高土壤和叶菜可食部分Cd含量的风险。     

Influence of thigmic stress or chlormequat chloride on tomato morphology and elemental uptake

Root dry weight and leaf number were not affected by thigmic stress or chlormequat chloride. Shoot dry weight, shoot:root dry weight ratio, shoot height, leaf area, and root surface area were decreased by both thigmic stress and chlormequat chloride. However, root length was decreased and root radius increased only by chlormequat chloride. Total element uptake was decreased by both thigmic stress and chlormequat chloride. In the shoot and root, N was not affected, P was increased in the shoots, K decreased in the shoots but increased in the roots, and Mg decreased in the roots as a result of thigmic stress and chlormequat chloride. Whereas, Ca was decreased in the roots and Mg increased in the shoots by chlormequat chloride. The uptake of N, P, Ca, or Mg was not affected by thigmic stress or chlormequat chloride, however, K uptake per root surface area decreased. Thigmic stress decreased K in both the upper and lower stem but did not affect leaf concentration of K. However, chlormequat chloride decreased K in both the stem and leaves. Thigmic stress because of the role of K in cell elongation. Chemical name used: (2‐chloroethyl)trimethyl‐ammonium chloride (chlormequat chloride).     

Nitrogen fertilizer applications to maize after alfalfa: grain yield,kernel composition,and plant mineral nutrients

Nitrogen (N) is often applied to first year maize (Zea mays L.) after alfalfa (Medicago sativa L.) at rates greater than needed to attain maximum yields. This study explored other potential benefits of excess N fertilizer applications to maize after alfalfa. Effects of N fertilizer (no N fertilizer, 73, or 135 kg N ha^?1) to maize after alfalfa on stalk dry weight, stalk mineral concentrations [N, phosphorus (P), and potassium (K)], grain yield, and kernel components (protein, oil, starch, P, and K) were investigated. Fertilizer N increased stalk N concentration but not stalk dry weight. Grain yields and yields of protein, oil, starch, P, and K kernel components, expressed on a kg ha^?1 basis, were also unaffected by N fertilizer treatments. Thus, there appears to be no advantage, in terms of yield or kernel components, in applying N fertilizer to maize after alfalfa under the environments experienced during this two year field experiment.     

Phosphorus bioavailability of sewage sludge‐based recycled fertilizers in an organically managed field experiment

Recycled phosphorus (P) fertilizers from sewage sludge can contribute to the ongoing effort of closing the P cycle. Five recycled P fertilizers (Struvite SSL, Struvite AirPrex®, P‐RoC®, Pyrolysis coal, and Na‐SSA) were tested for their P availability in a two‐year field experiment with maize. The experiment was conducted on an organic certified research station at soil pH 6.5. Other P fertilizer treatments included: phosphate rock (PR), compost, and an unfertilized control. In addition, the rhizobacteria strain Bacillus sp. Proradix (Proradix®) was applied to test its ability to increase P bioavailability. Each year, shoot DM and P offtake of maize was measured and P use efficiency of the tested fertilizers was calculated. No significant differences in shoot DM were found among fertilized treatments and the unfertilized control in both years of experiment. Fertilization with recycled fertilizers increased P offtake by between 0% (Na‐SSA) and 27.5% (Struvite SSL) compared to the unfertilized control. Rhizobacteria application led to an increase in P offtake of maize from 25.9 to 38.7 kg P ha^?1 when combined with PR fertilization in the year of fertilizer application, while no significant effect was found for the recycled fertilizers. Some of the tested recycled fertilizers from urban waste water can be considered as effective fertilizers for their use in organic agriculture.     

Biochar properties and soil type drive the uptake of macro‐ and micronutrients in maize (Zea mays L.)

The use of biochar in agriculture is a promising management tool to mitigate soil degradation and anthropogenic climate change. However, biochar effects on soil nutrient bioavailability are complex and several concurrent processes affecting nutrient bioavailability can occur in biochar‐amended soils. In a short‐term pot experiment, the concentration of N, P, K, S, Ca, Mg, Cu, Zn, Mn, B, Fe, and Na in the shoots of maize grown in three different soil types [sandy soil (S1), sandy loam (S2), and sandy clay loam (S3)] was investigated. The soils were either unamended or amended with two different biochars [wheat straw biochar (SBC) or pine wood biochar (WBC)] at two P fertilizer regimes (–/+ P). We used three‐way ANOVA and Principal Component Analyses (PCA) of transformed ionomic data to identify the effects of biochar, soil, and P fertilizer on the shoot nutrient concentrations. Three distinct effects of biochar on the shoot ionome were detected: (1) both biochars added excess K to all three soils causing an antagonistic effect on the uptake of Ca and Mg in maize shoots. (2) Mn uptake was affected by biochar with varying effects depending on the combined effect of biochar and soil properties. (3) WBC increased maize uptake of B, despite the fact that WBC increased soil pH and added additional calcite to the soil, which would be expected to reduce B bioavailability. The results of this study highlight the fact that the bioavailability of several macro and micronutrients is affected by biochar application to soil and that these effects depend on the combined effect of biochar and soils with different properties.     

Response of maize (Zea mays) to the application of foliar fertilizers in the Sudan and Guinea savanna zone of Nigeria

Soil fertility problems resulting in low maize yields in smallholder farms are common in the West African moist savanna. The effectiveness of commercial foliar fertilizers in improving maize growth and yield was evaluated in three savanna agro‐ecological zones of Nigeria in two steps. In step one, eight commercial foliar fertilizers were assessed in a greenhouse study with two soil types using maize (Zea mays L. cv. 2004 TZE‐Y POPDT STR C4). The treatments included a control and a reference that received the optimum concentrations of nutrients. In step 2, three promising products from the greenhouse study (Turbotop, Agroleaf General, and Agroleaf high‐P) were evaluated under field conditions to validate the efficacy of products to enhance crop growth and yield. The foliar products were applied at the rate of 5 kg ha^?1. The treatments also included three rates of P application (0, 30, and 60 kg P ha^?1) as triple super phosphate (TSP) with or without foliar fertilizers. In the greenhouse study, differences in maize shoot dry matter yield and N and P concentrations, attributable to the spraying of the commercial foliar fertilizers, were observed for both soils. Spraying Turbotop, Agroleaf General, and Agroleaf high‐P gave the highest shoot dry biomass and N and P uptake compared to other products. Under field conditions, foliar spraying of Agroleaf high‐P significantly increased the shoot dry biomass of maize compared with the 0 P treatment in all locations. The grain yield of maize ranged from 1 to 4 t ha^?1 with significant differences across sites. Products with high concentrations of P and N in their formulation improved maize yield suggesting that appropriate management of P and N resources is a prerequisite for a sustainable maize intensification in the savanna agro‐ecologies.     

Phosphorus bioavailability of sewage sludge‐based recycled fertilizers

Six phosphorus (P) fertilizers recycled from sewage sludge [Struvite SSL, Struvite AirPrex®, P‐RoC®, Mephrec®, Pyrolysis coal and Ash (Mg‐SSA)] were tested for their plant availability in potted soil of pH 7.2 under greenhouse conditions. The crop sequence simulated a rotation of red clover (Trifolium pratense L.), maize (Zea maize L.), and ryegrass (Lolium perenne L.). Other P fertilizer treatments included: Phosphate Rock (PR), Calcium dihydrogen phosphate [Ca(H₂PO₄)₂], and an unfertilized control. Additionally, soil was regularly inoculated with two strains of plant growth‐promoting rhizobacteria (PGPR; Pseudomonas sp. Proradix, and Bacillus amyloliquefaciens) to test their ability to increase P availability to plants. Sequential P fractionation was conducted to link the amount of readily available P in fertilizers to plant P acquisition. Shoot P content and dry matter of maize decreased in the following order: Struvite SSL ≥ Ca(H₂PO₄)₂ > P‐RoC® ≥ Struvite AirPrex® ≥ Mephrec® > Pyrolysis coal ≥ Mg‐SSA ≥ PR ≥ unfertilized. Rhizobacteria did not affect shoot biomass or P content. The results show that red clover might have mobilized substantial amounts of P. Sequential P fractionation was not suitable to predict the efficacy of the fertilizers. Generally, the sewage sludge‐based fertilizers tested proved to be suitable alternative P sources relevant to organic farming systems. However, the efficacy of recycled fertilizers is strongly dependent on their specific production conditions.     

Is the salt tolerance of maize related to sodium exclusion? I. Preliminary screening of seven cultivars

Maize (Zea mays L.) plants in the early stage of development were treated with 80 mM sodium chloride (NaCl) with or without supplemental calcium (Ca²⁺) (8.75 mM) for a seven day period. The effects of salinity on dry matter production and shoot and root concentrations of sodium (Na⁺), Ca²⁺, and potassium (K⁺) were measured for seven Pioneer maize cultivars. Salinity significantly reduced total dry weight, leaf area, and shoot and root dry weight below control levels. For all seven cultivars, Na⁺concentrations were reduced and leaf area was significantly increased by supplementing salinized nutrient solutions with 8.75 mM calcium chloride (CaCl₂). The two cultivars with the lowest shoot and root Na⁺ concentrations under NaCl‐salinity showed the greatest increases in total, shoot and root dry weights with the addition of supplemental Ca. Shoot fresh weight/dry weight ratios for all cultivars were decreased significantly by both salinity treatments, but supplemental Ca²⁺ increased the ratio relative to salinity treatments without supplemental Ca. Root fresh weight/dry weight ratios were decreased only by salinity treatments with supplemental Ca. With NaCl‐salinity, cultivars which had lower shoot and root Na⁺ concentrations were found to be more salt sensitive and had significantly lower amounts of dry matter production than those cultivars which had higher shoot and root Na⁺ concentrations. It was concluded that Na⁺ exclusion from the shoot was not correlated with and was an unreliable indicator of salt tolerance for maize.     

Effect of long‐term fertilization and manuring on potassium release properties in a Typic Ustochrept

A long‐term fertilizer experiment, over 27 years, studied the effect of mineral fertilizers and organic manures on potassium (K) balances and K release properties in maize‐wheat‐cowpea (fodder) cropping system on a Typic Ustochrept. The treatments consisted of control, 100% nitrogen (100% N), 100% nitrogen and phosphorus (100% NP), 50% nitrogen, phosphorus, and potassium (50% NPK), 100% nitrogen, phosphorus, and potassium (100% NPK), 150% nitrogen, phosphorus, and potassium (150% NPK), and 100% NPK+farmyard manure (100% NPK+FYM). Nutrients N, P, and K in 100% NPK treatment were applied at N: 120 kg ha^—1, P: 26 kg ha^—1, and K: 33 kg ha^—1 each to maize and wheat crops and N: 20 kg ha^—1, P: 17 kg ha^—1, and K: 17 kg ha^—1 to cowpea (fodder). In all the fertilizer and manure treatments removal of K in the crop exceeded K additions and the total soil K balance was negative. The neutral 1 N ammonium acetate‐extractable K in the surface soil (0—15 cm) ranged from 0.19 to 0.39 cmol kg^—1 in various treatments after 27 crop cycles. The highest and lowest values were obtained in 100% NPK+FYM and 100% NP treatments, respectively. Non‐exchangeable K was also depleted more in the treatments without K fertilization (control, 100% N, and 100% NP). Parabolic diffusion equation could describe the reaction rates in CaCl₂ solutions. Release rate constants (b) of non‐exchangeable K for different depth of soil profile showed the variations among the treatments indicating that long‐term cropping with different rates of fertilizers and manures influenced the rate of K release from non‐exchangeable fraction of soil. The b values were lowest in 100% NP and highest in 100% NPK+FYM treatment in the surface soil. In the sub‐surface soil layers (15—30 and 30—45 cm) also the higher release rates were obtained in the treatments supplied with K than without K fertilization indicating that the sub‐soils were also stressed for K in these treatments.     

Pelletized sewage sludge as a fertilizer for containerized plants: Plant growth and nitrogen leaching losses

To evaluate the effectiveness of sewage sludge pellet fertilizers (SPFs) for growing containerized greenhouse crops and their potential for nitrogen (N) leaching, three experiments were conducted where SPFs were compared to conventional water‐soluble fertilizer (WSF) and controlled‐release fertilizer (CRF). In different experiments ‘First Lady’ marigold (Tagetes erecta L.) and ‘Selenia’ New Guinea Impatiens (Impatiens sp. hybrids) (NGI) were grown in 0.5‐liter pots of soilless growth medium and plants were fertilized with 20N‐ 4.3P‐16.6K WSF, 14N‐6.2P‐11.6K CPF, or two types of SPF, 3N‐1.0P‐0.1K or 5N‐1.3P‐0.1K. CRF and SPFs were incorporated in the growth medium at planting. In each experiment, treatments received the same amount of N and volume of irrigation water. Leachate was analyzed for ammonium‐nitrogen (NH₄‐N) and nitrate‐nitrogen (NO₃‐N) at regular intervals and shoot dry weight was measured at the end of each experiment. SPFs alone as the sole source of N resulted in less N leaching compared to WSF or CRF alone but did not provide adequate N for marigold as shoot dry weight was reduced compared to WSF and CRF and foliar N deficiency symptoms developed. However, SPFs alone caused no such effects on NGI and shoot dry weight was equal to WSF and CRF with less N leaching. Growth of marigold increased and N deficiency symptoms were prevented by combining SPFs with a dilute solution of WSF, but the same treatment did not affect NGI. Combining SPFs and WSF in this manner for marigold resulted in less N leaching than SPFs alone, however with NGI more N leaching occurred, but not to the level of WSF and CRF. Results suggest that SPFs can provide adequate N for slow‐growing plants with low N uptake rates like NGI, but for fast‐growing plants with high N uptake rates, SPFs must be combined with more soluble fertilizers.     

Salinity effects on growth analysis and nutrient composition in four grain legumes‐rhizobium symbiosis

The effect of salinity on growth response, nitrogen (N) fixation and tissue mineral content was investigated for four legumes: faba bean (Vicia faba L), pea (Pisum sativum L), soybean (Glycine max L), and common bean (Phaseolus vulgaris L). Plants were grown in a vermiculite culture system supplied with a N‐free nutrient solution with the addition of 0, 50, and 100 mM NaCl. Plants were harvested at the beginning of the flowering period and the dry weights of shoots and roots and acetylene reduction activity (ARA) were evaluated at the same time plant tissues were analysed for N, potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents.

The depressive effect of saline stress on ARA of nodules was directely related to the salt induced decline in dry weight and N content in shoots. Growth inhibition by NaCl treatments was greater for the pea than for other legumes, whereas the soybean was the most salt‐tolerant Saline stress also affected the N content in shoots and roots. In general the N content accumulated in the shoot and Na in the roots of the four legumes tested, while K accumulated both organs. The acquisition of other macronutrients differed according to the legume species. The legumes most sensitive were P. sativum and V. faba which accumulated Ca in shoot and Mg both in the shoot and the roots. On the contrary, in G. max and P. vulgaris, the two most salt tolerant legumes, accumulated Mg in the roots and Ca in both vegetative organs. Our results suggest a relationship between the salt‐tolerant range in legumes and the macronutrient accumulation in vegetative organs.     

Aluminum toxicity in maize: Biomass production and nutrient uptake and translocation

The effect of increasing aluminum (Al) concentrations on root nutrient contents along with the concurrent translocation to the shoot of C₄ plants prompted this study. Two‐week‐old maize (Zea mays cv XL‐72.3) plants were therefore submitted for 20 days to Al concentrations ranging from 0 to 3.00 mM in a medium with low ionic strength were used as a test system. Aluminum concentrations in root tissues showed a 3‐fold increase between 0 and 3.00 mM Al treatment, and was not detected in the shoot. Root plasma membrane‐H⁺ ATPase activity decreased after the 0.33 mg L^‐1 Al treatment, while membrane permeability increased up to 1.00 mM Al treatment. Root and shoot biomass decreased after the 0.33 mM Al treatment. All elements in the roots, except potassium (K), manganese (Mn), and zinc (Zn) were highest for plants treated with 0.33 mM Al. Potassium increased continuously between 0 and 3.00 mM Al treatments, and iron (Fe) decreased above 0.33 mM. Only a slight decrease in nitrogen (N) was observed. All the measured nutrients in shoots, except N, Mn, and Fe decreased above 0.33 mM, but calcium (Ca) and magnesium (Mg) had little variation as Al varied. Data indicated that maximum net uptake for mineral nutrients, except Mn, occurred up to 0.33 mM Al. Translocation of phosphorus (P), K, Mn, and Zn decreased above 0.33 mM Al, N, and Ca decreased when any Al was added, and no clear trend was observed for Mg and Fe. Between the 0 and the 3.00 mM Al treatments, electrolytic conductance did not increased significantly indicating that the observed inhibitions of translocation from roots to shoots were not directly related to increasing membrane degradation.     

Growth and macronutrient contents of faba bean plants: Effects of salinity and nitrate nutrition

The effects of the interaction between sodium chloride, nitrate, and concentrations on growth and internal ion content of faba bean (Vicia faba L.) plants were studied, to understand the relationship between the above parameters and salt tolerance. Increased salinity substantially reduced the dry weight of roots and shoots and increased the root/shoot biomass ratio. Additional nitrate‐N considerably moderated the salinity effects on these parameters. The promotive effects of nitrate‐N were more pronounced on shoot dry weight. These results suggest that an exogenous supply of nitrate‐N would improve the vegetative growth of V. faba plants by moderating the suppresive effects of salinity. The evolution of the root and shoot content in potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), and nitrogen (N) was monitored during vegetative growth. A high correspondence between total N and Ca content was found. The acquisition of Ca and K in response to salt and nitrate was similar in shoots and roots, whereas Mg uptake showed notable differences in the two organs. In salt‐affected plants, the roots were found to be high in accumulated Na while the shoots exhibited the lowest Na concentration. Potassium accumulation was higher in the shoots. In this way, there was an antagonistic effect between Na and K uptake. Analyses of the nutrient contents in plant organs have provided a data base on salt‐tolerance mechanisms of V. faba plants.     

Long‐term fertilization impacts on corn yields and soil organic matter on a clay‐loam soil in Northeast China

A long‐term fertilization experiment with monoculture corn (Zea mays L.) was established in 1980 on a clay‐loam soil (Black Soil in Chinese Soil Classification and Typic Halpudoll in USDA Soil Taxonomy) at Gongzhuling, Jilin Province, China. The experiment aimed to study the sustainability of grain‐corn production on this soil type with eight different nitrogen (N)‐, phosphorus (P)‐, and potassium (K)–mineral fertilizer combinations and three levels (0, 30, and 60 Mg ha^–1 y^–1) of farmyard manure (FYM). On average, FYM additions produced higher grain yields (7.78 and 8.03 Mg ha^–1) compared to the FYM0 (no farmyard application) treatments (5.67 Mg ha^–1). The application of N fertilizer (solely or in various combinations with P and K) in the FYM0 treatment resulted in substantial grain‐yield increases compared to the FYM0 control treatment (3.56 Mg ha^–1). However, the use of NP or NK did not yield in any significant additional effect on the corn yield compared to the use of N alone. The treatments involving P, K, and PK fertilizers resulted in an average 24% increase in yield over the FYM0 control. Over all FYM treatments, the effect of fertilization on corn yield was NPK > NP = NK = N > PK = P > K = control. Farmyard‐manure additions for 25 y increased soil organic‐matter (SOM) content by 3.8 g kg^–1 (13.6%) in the FYM1 treatments and by 7.8 g kg^–1 (27.8%) in the FYM2 treatments, compared to a 3.2 g kg^–1 decrease (11.4%) in the FYM0 treatments. Overall, the results suggest that mineral fertilizers can maintain high yields, but a combination of mineral fertilizers plus farmyard manure are needed to enhance soil organic‐matter levels in this soil type.     

锌与磷肥不同混合方式对玉米产量及磷、锌利用的影响

  【目的】  研究锌与磷肥以不同混合方式施用对玉米干物质量、籽粒产量及磷、锌利用率的影响,以期为锌与磷肥科学配伍及新型含锌磷肥的研制提供理论依据。  【方法】  将七水硫酸锌(Zn)按0.5%和5%(W/W)的添加量与磷肥(P)分别进行物理混合(P+Zn)和反应混合(PZn),制备含锌磷肥试验产品:P+Zn0.5、P+Zn5、PZn0.5和PZn5。采用玉米土柱栽培试验,设置8个处理,包括分别施用以上4种含锌磷肥(P+Zn0.5、P+Zn5、PZn0.5和PZn5)、普通磷肥(P)和硫酸锌(Zn0.5、Zn5),以不施肥为对照(CK)。所有肥料均作为基肥一次性施入土柱 0—30 cm 土层。玉米成熟后,收获、考种,测定玉米植株不同部位(茎秆、叶片、苞叶、穗轴、籽粒)干物质量、磷和锌含量,以及采集 0—30、30—60、60—90 cm 土层土壤速效磷和有效锌含量。  【结果】  1)与普通磷肥相比,锌与磷肥混合处理玉米地上部干物质量和籽粒产量分别平均提高了15.18%、7.70%,反应混合(PZn)效果优于物理混合(P+Zn),PZn主要通过增加穗粒数实现增产,锌肥低添加量PZn0.5增产效果显著优于高添加量PZn5。2)与普通磷肥相比,PZn0.5处理玉米地上部和籽粒磷吸收量分别提高了8.40% 和 16.67%,磷肥表观利用率提高了5.03个百分点,磷肥农学效率和偏生产力分别提高了41.91%和11.64%;与PZn5相比,PZn0.5的磷肥表观利用率提高4.78个百分点,磷肥农学效率和偏生产力分别提高了14.57%和3.58% (P<0.05)。3)与普通磷肥相比,施用PZn肥玉米籽粒锌累积量平均提高了21.90% (P<0.05);与P+Zn肥相比,施用PZn肥玉米地上部锌累积量平均提高了25.70%,锌肥利用率平均提高了7.83个百分点(P< 0.05)。  【结论】  锌与磷肥混合后施用能够增加玉米干物质量和籽粒产量,其中反应混合方式在提高玉米对磷、锌的吸收量和磷、锌肥利用率以及提高土壤速效磷、有效锌含量等方面的效果优于物理混合,且以硫酸锌0.5%添加量与磷肥反应混合效果最佳。     

Compost and phosphorus amendments for stimulating microorganisms and growth of ryegrass in a Ferralsol and a Luvisol

A greenhouse pot experiment was carried out to investigate the effects of different P‐fertilizer application forms (triple superphosphate [TSP], compost + TSP, TSP‐enriched compost) on the growth of ryegrass and the soil microbial biomass. The fertilizers were applied at equivalent doses for all nutrients to a neutral Luvisol in comparison with an acidic Ferralsol. Fertilizer application led to significantly increased contents of microbial biomass C, N, and P. Furthermore, yields of shoot C and root C, and concentrations of P, Ca, Mg, K, Fe, and Mn in shoots and roots were significantly increased. These increases always followed the order TSP < compost + TSP < TSP‐enriched compost. Sole TSP application led only to maximum concentrations of N and S. In the Ferralsol, TSP had only minimal positive effect on the P concentration of the grass shoots. The positive effect of TSP‐enriched compost, i.e., incubating TSP together with compost for 24 h, did not differ between the neutral Luvisol and the acidic Ferralsol, i.e., the effect is independent of the soil type. Consequently, soluble inorganic P fertilizer should generally be mixed into an organic fertilizer before application to soil.     

Ability of various water‐insoluble fertilizers to supply available phosphorus in hydroponics to plant species with diverse phosphorus‐acquisition efficiency: Involvement of organic acid accumulation in plant tissues and root exudates

Previous studies describe the suitability of a new type of phosphorus (P) fertilizer, called “rhizosphere‐controlled fertilizer” (RCF), to supply available P to plants while reducing soil phosphorus fixation. In order to explore the involvement of organic acid root exudation in P uptake from RCF, we investigated the relationship between shoot and root P concentrations, and the concentration of the main polycarboxylic organic acids in roots, shoots, and plant exudates. Plant species with different P‐acquisition efficiency (low: maize; medium: chickpea; high: lupin) were grown in hydroponics with three different P fertilizers: The water‐insoluble P fraction of RCF (RCF); Phospal, a slow‐release source of phosphate composed of calcium and aluminum phosphates (PH); monopotassiumphosphate (KP), and a control treatment without P (P–). RCF was as efficient as KP in supplying P to plants in the case of chickpea and lupin, and slightly less efficient than KP in maize. However, P from PH was not available for maize and less available compared to KP and RCF in chickpea and lupin. This variation reflects the different efficiencies in P acquisition for the three plant species. Except in the case of maize, plants receiving KP presented the lowest concentration of organic acids in roots and exudates, while those plants suffering severe P deficiency (P– and PH) showed the highest organic acid concentration. However, RCF had a high concentration of organic acids in roots and exudates, as well as a high P concentration in the shoot indicating that P uptake from RCF is enhanced due to root release and action of specific organic acids.     

Comparative effect of human urine and ammonium nitrate application on maize (Zea mays L.) grown under various salt (NaCl) concentrations

The present study investigates the effect of urine and ammonium nitrate on maize (Zea mays L.) vegetative growth, leaf nutrient concentration, soil electrical conductivity, and exchangeable‐cations contents under various concentrations of NaCl in a soil substrate. The experiment was arranged in a completely randomized block design with eight replications under greenhouse conditions. The experimental soil substrate was made from a 1 : 1 : 1 volume‐ratio mixture of compost, quartz sand, and silty‐loam soil. Salinity was induced by adding 0, 15, and 30 mL of 1 M NaCl solution per kg of substrate to achieve an electrical conductivity (EC) of 1.3 (S0), 4.6 (S1), and 7.6 (S2) dS m^–1. Nitrogen sources were urine and ammonium nitrate applied at 180 and 360 mg N (kg soil substrate)^–1. Basal P and K were added as mono potassium phosphate in amounts equivalent to 39 mg P and 47 mg K (kg substrate)^–1, respectively. In the S0 treatment, a 3‐fold increase in EC was measured after urine application compared to an insignificant change in ammonium nitrate–fertilized substrates 62 d after sowing. Under saline conditions, application of 360 mg N (kg soil)^–1 as urine significantly decreased soil pH and maize shoot dry weight. At the highest salt and N dose (S2, N360) 50% of urine‐fertilized plants died. Regardless of salinity there was no significant difference between the two fertilizers for investigated growth factors when N was supplied at 180 mg (kg soil)^–1. Leaf N and Ca contents were higher after urine application than in ammonium nitrate–fertilized plants. At an application rate of 180 mg N (kg soil)^–1, urine was a suitable fertilizer for maize under saline conditions. Higher urine‐N dosages and/or soil salinity exceeding 7.6 dS m^–1 may have a deleterious effect on maize growth.     

The role of non‐crystalline Fe in the increase of SOC after long‐term organic manure application to the red soil of southern China

Because of the important role of soil organic carbon (SOC) in nutrient cycling and global climate changes, there has been an interest in understanding how different fertilizer practices affect the SOC preservation and promotion. The results from this study showed that long‐term application of manure (21 years) could increase significantly the content of SOC, total nitrogen (N) and soil pH in the red soil of southern China. The chemical structure of SOC was characterized by using solid‐state cross‐polarization magic angle spinning (CPMAS) ¹³C nuclear magnetic resonance (NMR) spectroscopy, and the aromatic C, ratio of alkyl C : O‐alkyl C, aromaticity and hydrophobicity of mineral fertilizers N, P and K plus organic manure (NPKM) and organic manure (M) treatments were less than those of mineral fertilizer nitrogen (N) and mineral fertilizers N, P and K (NPK) treatments. Both poorly crystalline (Fe_o) and organically complexed (Fe_p) iron contents were influenced significantly (P < 0.05) by different fertilizers, and it was observed that NPKM and M treatments increased the non‐crystalline Fe (Fe_o‐Fe_p) content. There was a significant (P < 0.01) positive correlation between soil organic C and non‐crystalline Fe in both the surface (0–20 cm) and subsurface (20–40 cm) soils. The results suggested that non‐crystalline Fe played an important role in the increase of SOC by long‐term application of organic manure (NPKM and M) in the red soil of southern China.