Eco-friendly ways to reduce crop damage, yield loss

Milkha Singh Aulakh and Kabal Singh Gill

Wheat is the main rabi crop in Punjab, Haryana and UP. During the past few years, climatic adversities have caused substantial crop damage and yield loss. The yield of 19 quintals per acre has been a long-time average in Punjab. In 2021-22, abrupt warming during March (grain-filling stage) reduced the yield to around 17.6 quintals. In 2022-23, untimely rain, hailstorms and high-velocity winds caused lodging and flattening of the crop near maturity, resulting in a reduction in yield by up to 30 per cent. Lodging affects photosynthesis, nutrient movement from roots, flowering, pollination, grain formation and filling, thereby reducing the grain size and yield. The prolonged wetness and high humidity damage grains and causes a loss of lustre.

With wheat being seeded in October-November, farmers should be aware of crop management factors that affect lodging and grain yield so that they can take precautions. According to research at Punjab Agricultural University (PAU) and other institutions, crop varieties having a short plant height, thicker internodes, stiffer tillers and smaller above-ground biomass are lodging-resistant compared to tall cultivars.

Sowing time and seed rate: Lodging during the milky stage results in relatively more yield loss than at the advanced crop stage. Thus, the sowing time affects the extent of lodging and yield loss. A seed rate (45-50 kg per acre) higher than the recommended one (35-40 kg) also leads to more weak tillers that are prone to lodging.

Use of fertilisers: Balanced use of essential fertiliser nutrients such as nitrogen (N), phosphorus (P) and potassium (K) is very important for a healthy crop. Research has shown that excessive fertiliser N leads to luxurious vegetative growth and weaker tillers, which result in lower resistance to lodging. Adequate use of fertiliser P promotes an extensive and strong root system, and potassium enhances the thickness of tillers and lustre of grains, which may reduce lodging and yield loss.

Irrigation frequency: Plants extend their roots deeper into the soil in search of water and utilise nutrients available in deeper soil. Frequent heavier irrigations than required keep the surface soil moist for longer periods, resulting in the development of plant roots mainly in shallow soil. Allow sufficient intervals between irrigations so that the surface soil becomes dry for some days, facilitating the plants to grow their roots into deeper soil. An extensive deeper root system provides resistance to lodging.

Soil texture: Growth and depth of plant roots are affected by the soil structure and texture (sandy versus clayey soil). Soil puddling prior to transplanting rice seedlings breaks the soil structure and creates a hardpan below the surface soil, especially in clayey soils. A hardpan hinders the penetration and growth of roots of the succeeding wheat crop into deeper soil.

Crop residue management and sowing techniques: After combine harvesting of paddy, its residue (parali) is burnt or managed in situ in soil. To avoid burning of parali, several systems are being developed and promoted. Such techniques have a direct and indirect impact on vegetative and root growth, leading to variations in resistance of the succeeding wheat crop to lodging and yield loss.

Drill seeding after irrigation: After harvesting paddy, the parali is incorporated into the soil using disc harrow, followed by pre-seeding irrigation (Rauni). Then, at an adequate moisture, soil is tilled, followed by drilling of wheat seed and fertiliser. Irrigation is applied 3-4 weeks later. The plants develop a deeper root system in the soil. However, this method requires 3-4 weeks and suits early-harvested paddy. But it delays seeding after late-harvested paddy that generally reduces wheat yield. Also, several rounds of disc cultivations, tilling and drilling involve considerable costs.

Seeding with Super Seeder: About a week prior to paddy harvesting, the field is irrigated. After harvesting paddy, wheat is seeded in the soil having adequate moisture using the Super Seeder. It combines cutting, distribution and incorporation of parali plus drilling fertiliser and seed into the soil. Damage due to pests, diseases, weeds, etc. is minimised. The purchase price or rental of a Super Seeder is high and sometimes weeds are an issue.

Surface seeding: After harvesting paddy and even distribution of parali, the wheat seed and fertiliser are broadcast on dry or moist soil surface. It is followed by shredding and spreading of standing stubble using a straw shredder/spreader, creating mulch on the soil surface. Thereafter, the field is irrigated. Mulching reduces evaporation and keeps the surface soil moist for longer periods that likely promote shallow root growth. It is the least costly and a quick seeding operation, and it minimises weed growth (thus reducing the use of weedicides).

Crop damage and grain yield: Following rain accompanied by hailstorms and high-velocity winds in March-April 2023, the lodging and flattening of wheat in surface-seeded fields was less intensive than in drill-seeded fields. However, according to farmers in Amritsar and Tarn Taran districts, vertically standing wheat plants in surface-seeded fields seemed to have been shaken near the plant base in the surface soil, hampering grain-filling and resulting in shrivelled grains and low yields.

Studies have shown that a cooler environment with surface-placed crop residue delayed germination and relatively poor crop growth during the initial period caused relatively slower immobilisation-mineralisation of fertiliser N and release of nutrients, reducing the wheat yield by 8-24%. Conversely, immobilisation of fertiliser N was rapid with incorporated crop residue, and its remineralisation initiated after 5-6 weeks. In the USA and Canada, a lower crop yield in no-till fields compared to tilled ones was observed in the initial few years, followed by improved soil conditions (organic matter, porosity, infiltration, water retention capability, etc.) and a better crop yield in later years. Thus, the yield loss in surface-seeded fields may be compensated by improved soil conditions and better yield in subsequent crops. Increased fertiliser rates in the initial years may help optimise yield in a surface-seeding system.

From the lodging perspective, it is suggested that farmers should choose a suitable crop variety and avoid (i) a high seeding rate in soil with adequate moisture and timely sowing; (ii) excessive fertiliser N; and (iii) heavy and more frequent irrigations than required. Apply recommended fertiliser N in 2-3 phases rather than most of it at seeding.

Aulakh is former VC, Banda University of Agriculture & Technology, UP; Gill is former Research Scientist (ICRISAT, University of Zambia, Agriculture & Agri-Food Canada)

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