Effects of short-term nitrogen and phosphorus addition on leaf stoichiometry of a dominant alpine grass

The effects of increasing nitrogen (N) and phosphorus (P) deposition on the nutrient stoichiometry of soil and plant are gaining improving recognition. However, whether and how the responses of N cycle coupled with P of the soil–plant system to external N and P deposition in alpine grassland is still unclear. A short-term external N and P addition experiment was conducted in an alpine grazing grassland in the KunLun Mountain to explore the effects of short-term N and P addition on the nutrient stoichiometry in soil and plant. Different rates of N addition (ranging from 0.5 g N m−2 yr−1 to 24 g N m−2 yr−1) and P addition (ranging from 0.05 g N m−2 yr−1 to 3.2 g P m−2 yr−1) were supplied, and the soil available N, P, leaf N and P stoichiometry of Seriphidium rhodanthum which dominant in the alpine ecosystem were measured. Results showed that N addition increased soil inorganic N, leaf C, leaf N, and leaf N:P ratio but decreased soil available P and leaf C:P. Furthermore, P addition increased soil available P, leaf P, soil inorganic N, leaf N, and leaf C and reduced leaf C:N, C:P, and N:P ratios. Leaf N:P was positively related to N addition gradient. Leaf C:P and leaf N:P were significantly negatively related to P addition gradient. Although external N and P addition changed the value of leaf N:P, the ratio was always lower than 16 in all treatments. The influences of P addition on soil and plant mainly caused the increase in soil available P concentration. In addition, the N and P cycles in the soil–plant system were tightly coupled in P addition but decoupled in N addition condition. The nutrient stoichiometry of soil and leaf responded differently to continuous N and P addition gradients. These data suggested that the alpine grazing grassland was limited by P rather than N due to long-term N deposition and uniform fertilization. Moreover, increasing P addition alleviated P limitation. Therefore, the imbalanced N and P input could change the strategy of nutrient use of the grass and then change the rates of nutrient cycling in the alpine grassland ecosystem in the future.

Available Phosphorus in Soils Amended with Organic N-Enriched Composts during Periods of Incubation

Inorganic nitrogen (N) fertilizers, microbial inoculum and biologically-active substances are used to fortify composts which characteristically contain low amounts of N. The potentials of organic wastes from agriculture for N enrichment of composts were indicated by significant increase in soil N while there can be fortuitous improvement in the available phosphorus (P) contents on which information about the extent is lacking. In this study, composts: cow dung + sawdust (CDSD) and poultry droppings + sawdust (PDSD) were enriched with meals from bone (BN), blood (BM), hoof (HF) and horn (HN); and neem leaf (NM) and tithonia leaf (TM) to attain 150, 300, 450 and 600 g kg-1 N and the available P was monitored at four-week intervals during 16 weeks of incubation in soil. Available P increased with all N sources and enrichment rates slightly at week 4 but highly from week 8 and for each source, the enrichment to 600 g kg-1 N gave the highest values. The composts enriched to 450 and 600 g kg-1 N gave 15-20 and 20-29 mg kg-1 available P in week 12 and 16 respectively. CDSDBM and PDSDHF enriched to 600 g kg-1 N at week 4 and 8 respectively can be used for short-season crops while PDSDBM and PDSDNM enriched to 600 g kg-1 N in week 12 and 16 respectively would be suitable for long-season crops. The PDSDNM enriched to 600 g kg-1 N gave the highest available P (29.0 mg kg-1) and was followed by PDSDBN and PDSDHF at the same enrichment level, with 28.0 mg kg-1 each. Although the PMSDNM enriched to 600 g kg-1N had the highest available P in week 16, the enriched composts with values exceeding 20 mg kg-1 also have potentials for the cultivation of long-season vegetables.

Utilization of indigenous phosphate-solubilizing bacteria to optimize the use of coal fly ash for increasing available-P in an Ultisol

Coal fly ash (CFA) is a coal-burning by-product containing macro and micronutrients, and it is the potential material for improving available P in Ultisols. Phosphate-solubilizing bacteria (PSB) play a role in phosphorus solubilization. This study aimed at elucidating the potential use of phosphate-solubilizing bacteria to optimize the use of coal fly ash for increasing soil available P. This study was conducted in two stages, namely isolation of indigenous PSB from an Ultisol and application of the PSB and CFA to improve soil available P. Five indigenous PSB isolated from the soil had the ability to dissolve phosphate. Isolate B5 could dissolve 9.89 ppm P and had a 99.57% closeness to Pseudomonas stutzeri. The application of 20 and 40 t CFA ha-1 increased the soil pH by 4.2% and 7.2%, respectively. Increasing the dose of CFA decreased the content of available P by 50.6%. However, the combination of PSB and 20 t CFA ha-1 increased soil available P, plant growth, plant dry biomass, and P-uptake by plant.

Could biochar amendment be a tool to improve soil availability and plant uptake of phosphorus? A meta-analysis of published experiments

As one of the most important nutrients for plant growth, phosphorus was often poorly available in soil. While biochar addition induced improvement of soil structure, nutrient and water retention as well as microbial activity had been well known, and the effect of biochar soil amendment (BSA) on soil phosphorus availability and plant P uptake had been not yet quantitatively assessed. In a review study, data were retrieved from 354 peer-reviewed research articles on soil available P content and P uptake under BSA published by February 2019. Then a database was established of 516 data pairs from 86 studies with and without BSA in agricultural soils. Subsequently, the effect size of biochar application was quantified relative to no application and assessed in terms of biochar conditions, soil conditions, as well as experiment conditions. In grand mean, there was a significant and great effect of BSA on soil available P and plant P uptake by 65% and 55%, respectively. The effects were generally significant under manure biochar, biochar pyrolyzed under 300 °C, soil pH <5 and fine-textured soil, and soils that are very low in available P. Being significantly correlated to soil P availability (R2=0.29), plant P uptake was mostly enhanced with vegetable crops of high biomass yield. Overall, biochar amendment at a dosage up to 10 t ha−1 could be a tool to enhance soil availability and plant uptake of phosphorus, particularly in acid, heavy textured P-poor soils.

Different sources of phosphorus fertilizers and soil amendments affected the phosphorus and cadmium content in soil, roots and seeds of maize (Zea mays L.)

Phosphorus (P) fertilizers contain cadmium (Cd) as a contaminant at levels varying from trace amounts to high levels and therefore, can be a major source of Cd to agricultural systems. This study was designed to assess the impact on application of Eppawala rock phosphate (ERP) and triple super phosphate (TSP) as P fertilizers and different soil amendments on P and Cd uptake in maize (Zea mays L.). The field trial was carried out at Field Crop Research and Development Institute at Mahailluppallama, Sri Lanka. A randomized complete block design was employed with three replicates as ERP and TSP separately applied with arbuscular mycorrhizal fungi (AMF) and three types of amendments (biochar, compost and dolomite) and the control without adding P fertilizers. Phosphorus content and Cd content of soil, maize roots and seeds were quantified. Results revealed that available soil Cd and total accumulated root and seed Cd amounts were significantly higher in TSP added treatments with and without amendments compared with ERP added soil. Considering soil available P, root and seed P, there was no significant difference observed in different treatments of TSP and ERP added treatments. A similar phenomenon was also observed in growth and yield parameters with both fertilizers added and with the added amendments. There was no colonization of AMF in maize roots in TSP applied soil while 25-60% of colonization was recorded with ERP. Synthetic fertilizer (TSP) must have inhibited the AMF colonization and thereby increasing the Cd content in maize seeds. AMF colonization increased with comparatively low soil available P in ERP added treatments. The results revealed that TSP could be effectively substituted by ERP as a source of P for maize soils. The addition of AMF, compost and biochar further increased the effect.

Using a One-Dimensional Convolutional Neural Network on Visible and Near-Infrared Spectroscopy to Improve Soil Phosphorus Prediction in Madagascar

As a proximal soil sensing technique, laboratory visible and near-infrared (Vis-NIR) spectroscopy is a promising tool for the quantitative estimation of soil properties. However, there remain challenges for predicting soil phosphorus (P) content and availability, which requires a reliable model applicable for different land-use systems to upscale. Recently, a one-dimensional convolutional neural network (1D-CNN) corresponding to the spectral information of soil was developed to considerably improve the accuracy of soil property predictions. The present study investigated the predictive ability of a 1D-CNN model to estimate soil available P (oxalate-extractable P; Pox) content in soils by comparing it with partial least squares (PLS) and random forest (RF) regressions using soil samples (n = 318) collected from natural (forest and non-forest) and cultivated (upland and flooded rice fields) systems in Madagascar. Overall, the 1D-CNN model showed the best predictive accuracy (R2 = 0.878) with a highly accurate prediction ability (ratio of performance to the interquartile range = 2.492). Compared to the PLS model, the RF and 1D-CNN models indicated 4.37% and 23.77% relative improvement in root mean squared error values, respectively. Based on a sensitivity analysis, the important wavebands for predicting soil Pox were associated with iron (Fe) oxide, organic matter (OM), and water absorption, which were previously known wavelength regions for estimating P in soil. These results suggest that 1D-CNN corresponding spectral signatures can be expected to significantly improve the predictive ability for estimating soil available P (Pox) from Vis-NIR spectral data. Rapid and accurate estimation of available P content in soils using our results can be expected to contribute to effective fertilizer management in agriculture and the sustainable management of ecosystems. However, the 1D-CNN model will require a large dataset to extend its applicability to other regions of Madagascar. Thus, further updates should be tested in future studies using larger datasets from a wide range of ecosystems in the tropics.

Effect of Soil Available Phosphorus Levels on Chickpea (Cicer arietinum L.) - Rhizobia Symbiotic Association

Background: Growing chickpea (Cicer arietinum) plants is affected by several environmental constraints as osmotic stress and nutrients deficiency particularly phosphorus (P). For other legume species, it was confirmed that P deficiency affects negatively their rhizobial symbiosis. The purpose of this study was to assess the effect of soil available P level on chickpea-rhizobia symbiosis under field conditions at Oualidia region of Morocco. Methods: Ten farmers’ fields with different soil available P levels were considered to carry out this study based on samples of 10 plants per plot. Result: The results showed that the plants from soil 7, with the lowest pH and the highest available P level (23.52ppm), presented high shoot dry weight (38.3 g/plant). Meanwhile the soil 5 with the lowest available P content showed low plant growth. The shoot P content was positively linked to soil P level but nodule biomass showed an irregular variation with soil available P level. Furthermore, it was confirmed that adequate plant P nutrition results in high chickpea yield and it was the case for plants from soil 7 presenting a mean yield of 62 seeds per plant). Finally, strong correlation was noted between yield and phosphorus concentration in soil (r=0.94).

PENGARUH DOSIS PUPUK MIKORIZA VESICULAR ARBUSKULAR TERHADAP SIFAT KIMIA TANAH PADA TANAMAN KEDELAI (Glycine max (L) Merr)

This study aims at determining the influence of vesicular-arbuscular mycorrhiza dosage on soil chemical properties of soybean and its optimum dosage that can increase the soil available-P on crops of soybean. This research was conducted in Lokoboko village, Ndona Subdistrict of Ende regency. This study used Randomized Block Design and a single-pattern factor consists of five treatments and four replications namely M0 : 0 gr pot-1 or without mycorrhiza, M5: 5 gr pot-1 mycorrhiza, M10: 10 gr pot-1 mycorrhiza, M15: 15 gr pot-1 mycorrhiza and M20: 20 gr pot-1 mycorrhiza. The variables of this study are plant–absorption P (mg tan-1), soil–available P (mg kg-1), soil-organic C (%) and pH of soil. The results showed that the use of vesicular-arbuscular mycorrhiza fertilizer for crops of soybean could increase soil-available P in 56,26%, plant-absorption P in 65%, pH of the soil in 6,06% and soil-organic C in 62,68 %. The use of vesicular-arbuscular mycorrhiza fertilizer on the dosage of 20 g has the better effectivity in increasing soil-available P in the soybean plant.

KANDUNGAN FOSFOR DAN KADMIUM PADA TANAH DAN BERAS SERTA RISIKO KADMIUM BAGI KESEHATAN PENDUDUK DI KELURAHAN TARUS

This research was conducted in Tarus Village, Kupang regency, in May until June 2013, to find out the amount of phosphorus and cadmium content in the soil of rice, and to compare the Cd with a threshold concentration of Standard National Indonesia 7387:2009, as well as to predict the magnitude of the risk to the health. This research is descriptive experimental design with 12 samples of soil and rice. Levels of soil–available P is analyzed using the methods of Olsen, whereas, the levels of Cd from the soil and rice are analyzed in the laboratory with the method of analysis of heavy metals in soils and plants, set by Hall of geochemical soil, the Ministry of agriculture. The results of the analysis of land-available Pranging from low – high, but it is not the only deciding factor the amount of Cd in soil and rice. Laboratory analysis results towards rice Cd, shows there are six samples that undetectable levels of Cd, six other samples detected and then described the risk once compared with the standard quality raw and analysis of health risks. The results of the analysis of the levels of Cd shows all rice samples were still below standard quality raw i.e. 0,4 mg kg-1. Risk analysis indicates that there are two samples of rice produced from the paddy fields are not safe for consumption for the duration of 30 years. While the four other samples were a risk for the duration of the 60 years.