MOA 4 WEED

Look at a wheat root under a microscope and you may find it wrapped in threads of fungus. These are arbuscular mycorrhizal fungi (AMF), and they partner with about 80% of land plants. The plant gives the fungus sugar; the fungus reaches far into the soil and brings back nutrients, especially phosphorus.

In this chapter we reviewed what that partnership does for crops. AMF can raise crop growth by up to 30% and phosphorus uptake by 20 to 70% compared with plants that lack them. They also help plants resist disease and cope with heavy metals, which matters most on poor, degraded soils.

There is a catch. Heavy use of chemical fertilizer has reduced how common and how useful these fungi are in farm fields. The chapter also looks at the chemical conversation between roots and fungi, where fungal 'Myc factors' meet strigolactones released by roots, and at pairing AMF with other fungi to restore damaged land.

Most farmers in the Indo-Gangetic Plains feed potassium to their crops as muriate of potash (MOP). Potassium shortage can cut yields by about 20%, so getting it right matters. Polyhalite is a natural mineral that carries potassium together with magnesium, calcium and sulfur.

In the 2021–22 rabi season at ICAR-IARI, New Delhi, we compared polyhalite with bentonite and MOP as potassium sources. Polyhalite came out ahead on several fronts: grain potassium was 30.3% higher than with MOP, roots grew longer (23% higher root length density), and the soil ended the season with more potassium and sulfur in the bank.

The money followed the roots. Agronomic efficiency with polyhalite was 1.83 times that of full-rate MOP, and net returns were 1.35 times higher. For rice–wheat farmers, it is a promising way to fix several nutrient gaps with one product.

A flooded rice field is a world without oxygen. Under the water, soil microbes break down organic matter and release methane, a greenhouse gas far stronger than carbon dioxide over the short term. How much escapes depends on the soil, the way the crop is managed and, above all, the water.

This chapter walks through how methane forms in paddies and why it matters for global warming. Then it turns to solutions: intermittent irrigation instead of constant flooding, rice varieties that emit less, smarter use of organic and inorganic amendments, biochar, and rice–fish farming.

Technology alone is not enough. We also discuss the social, economic and policy factors that decide whether farmers can adopt these practices. It is the same question I later discussed with experts and policymakers at the Mekong Forum 2025 on low-emission rice.

For a long time, a 'healthy' soil meant good nutrient levels and good structure. Today we know that the living part of soil, its microbes, is just as important for growing food, protecting the environment and keeping people healthy.

Intensive farming pushes soils hard, and farms now have to meet many goals at once: yield, income, clean water and lower emissions. In this chapter we argue that no single test or practice can handle that. We need systems approaches that look at the whole farm and landscape.

That means combining models with the knowledge of farmers, local residents and policymakers. The chapter gives examples, from simple field methods to sophisticated assessments, of how to do it.

Conservation agriculture skips the plough to protect the soil. Without tillage to bury them, though, weeds become a bigger challenge. For my M.Sc. at ICAR-IARI, New Delhi, I spent the 2021 and 2022 kharif seasons testing how to control weeds in zero-till maize within a maize–wheat–mungbean rotation.

We compared four ways of preparing the field, including zero-till maize with Sesbania grown alongside and then killed as a 'brown manure'. On top of that, we tested herbicide programs. The Sesbania system alone cut weeds by 28.4% at 60 days after sowing compared with conventional tillage.

The winning combination was zero-till maize with Sesbania brown manure, atrazine plus pendimethalin before emergence, and the newer herbicide tembotrione after emergence. It cut weed dry weight by 81.3% and produced 6.88 t/ha of maize, about the same as a field kept completely weed-free. This paper received the Indian Society of Agronomy Best Paper Award for 2024.

Agriculture uses about 70% of the world's water, and in India drylands make up 68% of the net sown area. Yet irrigation efficiency in the country is only 35 to 40%. Much of the water applied never reaches the crop.

In this review we looked at how precision water management can change that. The idea is simple: give each part of the field the water the crop actually needs, when it needs it. GIS tools bring together maps and timing data to guide those decisions, and variable-rate drip and centre-pivot systems put the plan into action.

Precision irrigation can save up to 25% more water than conventional practice. For dryland farmers, that is the difference between a crop that survives a dry spell and one that does not, and it supports both food security and the Sustainable Development Goals.