Plant biostimulants are diverse substances and microorganisms used to enhance plant growth. The global market for biostimulants is projected to increase 12 % per year and reach over $2,200 million by 2018. Despite the growing use of biostimulants in agriculture, many in the scientific community consider biostimulants to be lacking peer-reviewed scientific evaluation. This article describes the emerging definitions of biostimulants and reviews the literature on five categories of biostimulants: i. microbial inoculants, ii. humic acids, iii. fulvic acids, iv. protein hydrolysates and amino acids, and v. seaweed extracts. The large number of publications cited for each category of biostimulants demonstrates that there is growing scientific evidence supporting the use of biostimulants as agricultural inputs on diverse plant species. The cited literature also reveals some commonalities in plant responses to different biostimulants, such as increased root growth, enhanced nutrient uptake, and stress tolerance.

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Agricultural uses of plant biostimulants

Humic acids: Structural properties and multiple functionalities for novel technological developments

Phosphorus activators contribute to legacy phosphorus availability in agricultural soils: A review

Interaction among plant nutrients can yield antagonistic or synergistic outcomes that influence nutrient use efficiency. To provide insight on this phenomenon, peer-reviewed articles were selected ...

https://www.tandfonline.com/doi/pdf/10.1080/00103624.2017.1407429

Effects of Nutrient Antagonism and Synergism on Yield and Fertilizer Use Efficiency

No-till practices have the potential to increase soil organic C, but little about known about the relative contribution of surface residue and roots to soil organic C accumulation. In a simulated no-till experiment, we studied the fate of (14)C-labeled surface residue and in situ roots during a 1-yr incubation. Soil samples collected during the incubation were chemically dispersed and separated into five particle size and density fractions. The organic C, (14)C, and total N content of each fraction was determined. Alkali traps were used to measure (14)C losses due to respiration. After 360 d, 66% of the (14)C contained in the surface residue on Day 0 had been respired as (14)CO2, 11% remained in residue on the soil surface, and 16% was in the soil. In comparison, 56% of the root-derived (14)C in the soil was evolved as (14)CO2 and 42% remained in the soil. The large (500-2000 micrometer) and small (53-500 micrometer) particulate organic matter (POM) fractions together contained 11 to 16% of the initial root derived (14)C in the soil. In contrast, POM contained only 1 to 3% of the initial surface residue-derived (14)C. These data show clear differences in the partitioning of surface residue- and root-derived C during decomposition and imply that the beneficial effects of no-till on soil organic C accrual are primarily due to the increased retention of root-derived C in the soil.

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Carbon dynamics of surface residue- and root-derived organic matter under simulated no-till. [Erratum: Nov/Dec 2002, v. 66 (6), p. 2040.]

Lignite-Derived Humic Acid Effect on Growth of Wheat Plants in Different Soils

. Application of plant residues as soil amendment may represent a valuable recycling strategy that affects carbon (C) and nitrogen (N) cycling in soil–plant systems. The amount and rate of nutrient release from plant residues depend on their quality characteristics and biochemical composition. A laboratory incubation experiment was conducted for 120 days under controlled conditions (25 °C and 58% water-filled pore space) to quantify initial biochemical composition and N mineralization of leguminous and non-leguminous plant residues, i.e., the roots, shoots and leaves of Glycine max, Trifolium repens, Zea mays, Populus euramericana, Robinia pseudoacacia and Elaeagnus umbellata, incorporated into the soil at the rate of 200 mg residue N kg−1 soil. The diverse plant residues showed a wide variation in total N, C, lignin, polyphenols and C / N ratio with higher polyphenol content in the leaves and higher lignin content in the roots. The shoot of Glycine max and the shoot and root of Trifolium repens displayed continuous mineralization by releasing a maximum of 109.8, 74.8 and 72.5 mg N kg−1 and representing a 55, 37 and 36% recovery of N that had been released from these added resources. The roots of Glycine max and Zea mays and the shoot of Zea mays showed continuous negative values throughout the incubation. After an initial immobilization, leaves of Populus euramericana, Robinia pseudoacacia and Elaeagnus umbellata exhibited net mineralization by releasing a maximum of 31.8, 63.1 and 65.1 mg N kg−1, respectively, and representing a 16, 32 and 33% N recovery, respectively. Nitrogen mineralization from all the treatments was positively correlated with the initial residue N contents (r = 0.89; p l 0.01) and negatively correlated with lignin content (r = −0.84; p ≤ 0.01), C / N ratio (r = −0.69; p ≤ 0.05), lignin / N ratio (r = −0.68; p ≤ 0.05), polyphenol / N ratio (r = −0.73; p ≤ 0.05) and (lignin + polyphenol) : N ratio (r = −0.70; p ≤ 0.05) indicating a significant role of residue chemical composition and quality in regulating N transformations and cycling in soil. The present study indicates that incorporation of plant residues strongly modifies the mineralization–immobilization turnover (MIT) of soil that can be taken into account to develop synchronization between net N mineralization and crop demand in order to maximize N delivery and minimize N losses.

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Impact of the addition of different plant residues on nitrogen mineralization-immobilization turnover and carbon content of a soil incubated under laboratory conditions

Effect of N fertilizer source and timing on yield and N use efficiency of rainfed maize (Zea mays L.) in Kashmir–Pakistan

This research experiment was conducted to examine the effect of Rhizobiuminoculation (RI) and P fertilization (P) on nodulation, growth and yield characteristics of soybean grown in the presence of starter N fertilizer (N). Treatments included: i) 02 levels of RI (RI0, RI1), ii) 02 levels of P (P0, P1 that is, P2O5 @ 90 kg ha-1) iii) 03 levels of N (N0, N1 and N2 that is, N at of 25 and 50 kg N ha-1) iv) 03 replication. Results of the experiment revealed that total number of nodules increased from 73 in the un-inoculated control to 125 and 95 following the application of RI and P representing 70 and 30% increase over control. N supply did not affect the number of nodules; however, combination of RI and P with 25 kg N ha-1 (RI1P1N1) produced the highest number of nodules (152). RI, P, N and their combinations increased shoot and root biomass. Seed yield in the control was 767 kg ha-1 that significantly increased to 1081, 907 and 940 kg ha-1 following the application of RI, P and N demonstrating a 41, 18 and 23% increase over control. The highest seed yield of 1208 kg ha-1 was recorded in the combine treatment of RI1P1N1 indicating 57% increase over control. Relative increase in dry matter yield due to RI, P and N was 63, 46 and 49%. Seed protein content in different treatments ranged between 33 - 40% while oil content ranged between 13 - 18%. Application of RI, P and their combinations increased protein content by 6 - 22% while increase in oil content was 12 - 35%. Concentrations of N and P in plants and their uptake was significantly increased and relative increase in N uptake due to RI, P and K was 77, 21 and 31% , respectively, while the corresponding increase in P uptake was 79, 92 and 56%. It was found that the efficiency of RI and P fertilization increased substantially with the application of 25 kg N ha-1 but the efficiency decreased when N supply increased from 25 kg N ha-1 to 50 kg N ha-1. The results demonstrate the potential benefits of using Rhizobium inoculation and P fertilization with reduced level of N as starter fertilizer in order to achieve plant-growth promotion, increased nodulation and seed yield of soybean.

	 

	Key words: Glycine max L., nodulation, N fertilization, P application, soybean,Rhizobium inoculation, soybean.

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Effect of Rhizobium inoculation and NP fertilization on growth, yield and nodulation of soybean (Glycine max L.) in the sub-humid hilly region of Rawalakot Azad Jammu and Kashmir, Pakistan

Majid Mahmood Tahir

Papers

Lignite-Derived Humic Acid Effect on Growth of Wheat Plants in Different Soils

Impact of the addition of different plant residues on nitrogen mineralization-immobilization turnover and carbon content of a soil incubated under laboratory conditions

Effect of N fertilizer source and timing on yield and N use efficiency of rainfed maize (Zea mays L.) in Kashmir–Pakistan

Effect of Rhizobium inoculation and NP fertilization on growth, yield and nodulation of soybean (Glycine max L.) in the sub-humid hilly region of Rawalakot Azad Jammu and Kashmir, Pakistan

Yield and Nitrogen Use Efficiency of Rainfed Maize Response to Splitting and Nitrogen Rates in Kashmir, Pakistan