Moisture conservation for rainfed wheat production with alternative mulches and conservation tillage in the hills of north-west India

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Abstract

In the hills of north–west India, maize (Zea mays L.)-wheat (Triticum aestivum L.) is the dominant cropping system. However, rainfed wheat suffers from lack of optimum moisture at sowing. Field experiments were conducted for 3 years on a silty clay loam (Typic Hapludalf) to evaluate the effectiveness of mulches and conservation tillage for rainfed wheat in mitigating this problem. The treatments were ten factorial combinations of five mulch-tillage practices and two nitrogen levels (N60 and N120 kg ha−1). Mulch treatments consisted of application of 10 Mg ha−1 (dry weight basis), to previous standing maize, of either wild sage (Lantana camara L.) or eupatorium (Eupatorium adenophorum Sprengel) in combination with either conventional or conservation (minium) tillage prior to wheat sowing. These alternative practices were compared to the conventional farmer practice of soil tillage after harvest of maize with no mulch. The application of these weed mulches to standing maize maintained friable soil structure owing to a five fold higher mean population of earthworms underneath mulch. Mulches resulted in 0.06–0.10 m3 m−3 higher moisture in the seed-zone when wheat was sown compared with the conventional farmer practice of soil tillage after maize harvest. Mulch-conservation tillage treatments favourably moderated the hydro-thermal regime for growing a wheat crop. The mean root mass density under these treatments at wheat flowering was higher by 1.27–1.40 times over the conventional farmer practice during the 3 year study. Conservation tillage holds promise because it does not require elaborate tillage and may ultimately reduce animal draught in the hilly regions. Recycling available organic materials having no fodder value coupled with conservation tillage may help enrich the soil environment in the long-term. The practice also offers gainful use of these obnoxious weeds that cause great menace in grass and forest lands in the region.

Introduction

Himachal Pradesh is one of the hilly states in India. Maize followed by wheat is an important crop rotation in the state up to an altitude of 2500 m above mean sea level. Both crops are grown under rainfed conditions as 82% of the cultivated area of the state lacks irrigation facilities. Average yields are small at about 1.8 and 1.6 Mg ha−1 for maize and wheat, respectively (Anon, 1996). The main climatic and soil related limitations to yields are uneven rainfall, formation of large clods after cultivation leading to poor seed–soil contact for germination and seedling emergence, sub-optimal soil temperature and restricted and imbalanced use of fertilizers (the state average is 25.2 N, 1.0 P and 1.7 K kg ha−1). Farmers in the state follow a subsistence type of agriculture. About 84% of farmers have averaged land holdings of less than 0.68 ha. More than 95% of the farmers cultivate their fields with a animal-drawn plough on terraced land. Small and scattered holdings, poor socio-economic conditions little mechanization, together with the soil and climatic constraints described above prevent farmers who live in the mountains from adopting modern technology as practiced by their counterparts in the adjoining plains. The large area of cultivated land under rainfed conditions remains one of the major constraints to increasing crop yields in this and other states in the Himalayan region. There is a need to evaluate soil moisture conservation techniques that are based on technologies that require little input of external energy and can be easily adopted by the farmers of these mountaineous regions.

In the post-monsoon period of late September or early October farmers plough their fields to conserve moisture. The seed zone moisture rarely remains optimum, resulting in poor germination and consequently poor yields of rainfed wheat. Once the crop germinates it normally does not fail because after December winter rains are sufficient. As the monsoon rains recede in early September the soil profile is wet and conservation and carry-over of this moisture within the seed-zone could help timely sowing of wheat. This might be achieved if the fields could be mulched when the soil profile is wet. However, this is not practiced for want of suitable materials for mulching. Farmers cannot afford crop residues for mulching as these are fed to animals as there is an acute shortage of fodder in the entire Himalayan region.

Acharya and Kapur (1993)reported that sufficient moisture can be conserved for the wheat crop if a mulch of materials like wild sage is applied to standing maize at the recession of monsoon rains. They further observed that when wheat was sown during the years 1987–90, soil structure beneath the mulch was mellow, and soil was easily ploughable. There was a lot of earthworm activity in mulched plots which was absent in control plots.

In addition to wild sage, eupatorium, another widely growing plant, was also evaluated as an alternative to crop residues for soil and moisture conservation. Both wild sage and eupatorium are weeds which are a problem in grass, forest and common lands, and their control is problematic. These materials are succulent, biodegradable and produce prolific growth during the monsoon season. There is no risk of weed seed addition with mulching at the end of August, as seed setting takes place in September for wild sage and in March for eupatorium. The green matter of these materials on dry-weight basis contains about 2% N and 1.5% K but are poor in P (Bhardwaj and Kanwar, 1991).

The objective of the present study was to evaluate the influence of conservation tillage and mulches on the amelioration of the soil hydro-thermal regime, root growth and grain yield of rainfed wheat.

Section snippets

Site and soil information

The study was conducted in the years 1989, 1990 and 1991 at the experimental farm of the Himachal Pradesh Agricultural University, Palampur (longitude 76.3°E, latitude 32.6°N, and elevation 1300 m above mean sea level). The site (Typic Hapludalf-silty clay loam) was low in available N and P, had a steady infiltration rate of 3 mm h−1, pH of 5.7, cation exchange capacity of 12 cmol (P+) kg−1 and an organic carbon content (0–0.15 m) of 8 g kg−1. In the surface (0–0.15 m) layer, clay(<2 μm), silt (2–20 μm),

Soil water content

Depending upon the time that the monsoon rains receded during September, before harvest of maize, mean moisture content for the 0.15 m depth at sowing of wheat over the 3 years of the study ranged between 0.18–0.24 m3 m−3 in the treatments where the standing maize was mulched with wild shrubs (lantana/eupatorium), and 0.10–0.18 m3 m−3 in the conventional farmer practice of tillage after maize harvest (Table 2). The mulching practice was much better at conserving moisture than was the farmer practice

Conclusions

Application of a mulch of wild sage (lantana) and eupatorium to the previous standing maize as monsoon rains receded, in combination with conservation tillage, conserved sufficient moisture in the soil surface until sowing of rainfed wheat, maintained more friable soil structure, provided a favourable soil hydro-thermal regime for greater root growth and early establishment of the crop, and finally, produced higher grain and straw yields of wheat. Since these treatments do not require elaborate

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