Understanding Soil Phosphorus Changes with Rock-Enhanced Compost and Fertilizers

Jenn Hoskins
6th June, 2025

Understanding Soil Phosphorus Changes with Rock-Enhanced Compost and Fertilizers

Brown Mustard (Brassica juncea)

Photo adapted from: Dmitriy Bochkov / CC BY (Source)

Key Findings

  • At the ICAR farm in Rajasthan, using enriched compost with chemical fertilizers nearly doubled soil phosphorus levels and boosted mustard yields
  • The enriched compost also improved soil microbial activity and enzyme function, reducing the need for full-dose chemical fertilizers while promoting sustainable growth
Understanding how plants absorb and utilize phosphorus (P) is crucial when aiming to improve crop yields sustainably, especially for important oilseed crops like mustard. Excessive use of chemical fertilizers can lead to environmental degradation, while low fertilizer inputs may reduce yields. A recent field study conducted at the ICAR Directorate of Rapeseed‐Mustard Research[1] explored different strategies to manage phosphorus more effectively. The study focused on determining how various treatments affect the availability of P in the soil and, as a result, influence the growth and yield of mustard (Brassica juncea L.). In this study, researchers set up a field experiment with five different soil treatments. These treatments were as follows: • T1: a control with no fertilizer, • T2: 100% of the recommended dose of chemical fertilizers (RDF), • T3: enriched compost applied at 6 tonnes per hectare, • T4: a combination of 100% RDF and enriched compost at 6 tonnes per hectare, • T5: a mix of 50% RDF plus enriched compost at 6 tonnes per hectare. The enriched compost used in this research was developed to improve phosphorus availability in the soil in a controlled manner. The study measured several forms of soil phosphorus, including saloid-P, aluminum-bound P (Al-P), iron-bound P (Fe-P), and calcium-bound P (Ca-P). These forms of phosphorus differ based on how the element is bound within the soil and how available it is for plant uptake. A further focus was placed on soil microbial activity by looking at markers like alkaline phosphatase activity (the enzyme that helps release phosphorus from organic compounds), microbial biomass phosphorus (MBP), microbial biomass carbon (MBC), and dehydrogenase activity (DHA, which is linked to general microbial activity in the soil). Results from the experiment indicated notable improvements when using enriched compost in combination with chemical fertilizers. The treatment combining 100% RDF with enriched compost (T4) was particularly effective. This approach showed significant increases in all measured forms of soil phosphorus compared to using either enriched compost or chemical fertilizers separately. Interestingly, a similar level of improvement was seen with the treatment that used 50% RDF combined with enriched compost (T5). This finding suggests that it might be possible to reduce chemical fertilizer use without sacrificing soil P availability and, ultimately, crop yield. Improved soil enzyme activities supported these findings. Specifically, alkaline phosphatase activity increased by 15.5% and 8% when chemical fertilizers were combined with enriched compost compared to the exclusive use of either chemical fertilizers or enriched compost. Enriched compost also boosted the amount of soil microbial biomass phosphorus by 55%, microbial biomass carbon by 34%, and dehydrogenase activity by 45%. These increases imply that the enriched compost not only makes more phosphorus available but also enhances the overall microbial health of the soil. Healthy soil microbes are essential because they help break down organic matter and recycle nutrients, making them more accessible for plant uptake. The combined treatment led to a significant increase in mustard grain yield. The yield observed with the integrated approach reached 2.93 megagrams per hectare (Mg/ha). For context, the mustard grain yield was 16.7% higher in the 100% RDF treatment compared to the control. However, the real improvement was seen when enriched compost was added to the chemical fertilizers, reinforcing the idea that a balanced use of organic amendments with chemical fertilizers can lead to better nutrient availability and soil health. These findings add to a broader understanding of compost use in nutrient management. For example, an earlier study[2] experimented with composting rice straw along with low-grade rock phosphate and other materials. That study showed that while conventional compost provided an initial burst of nutrient release, enriched compost – which included a bioinoculant to boost microbial activity – outperformed ordinary compost at later growth stages in terms of nutrient uptake, yield, and improvement of soil nutrient status. In the present mustard study, the enriched compost similarly contributed to sustained nutrient availability throughout the crop cycle. Both studies underscore the importance of combining organic matter with targeted microbial inputs to improve the efficiency of nutrient management in soils. The recent work highlights that synchronized use of enriched compost and chemical fertilizers is a promising strategy for improving phosphorus dynamics in soil–plant systems. By enhancing both the immediate availability of phosphorus and promoting beneficial microbial activity, this integrated approach supports the growth and development of mustard crops while offering a pathway to reduce the dependence on expensive chemical fertilizers. This balanced strategy not only leads to improved yields but also contributes to the long-term sustainability of soil fertility, especially in areas where soil degradation is a concern. In summary, the study suggests that adopting a combined approach using 100% recommended chemical fertilizers along with enriched compost, or even halving the chemical input when using enriched compost, can achieve robust mustard yields while improving soil nutrient profiles and microbial health. This research supports a broader shift towards agricultural practices that optimize nutrient management, drawing on lessons from previous studies and offering practical insights for farmers and researchers alike.

AgricultureEnvironment

References

Main Study

1) Changes in soil phosphorus dynamics amended with rock phosphate-enriched compost and chemical fertilizers

Published 3rd June, 2025

https://doi.org/10.1371/journal.pone.0324716

Related Studies

2) Kinetics of phosphorus and potassium release from rock phosphate and waste mica enriched compost and their effect on yield and nutrient uptake by wheat (Triticum aestivum).

Journal: Bioresource technology, Issue: Vol 99, Issue 9, Jun 2008


Related Articles

An unhandled error has occurred. Reload 🗙