Effect of plastic mulching on soil water use and spring wheat yield in arid region of northwest China

Abstract

The field experiments were conducted to study the evapotranspiration (ET), evaporation (E), growth, yield and water use efficiency (WUE) of plastic-mulched spring wheat with hole planting in 1990 and 1991 under full and deficit irrigation at Zhangye Station of Water-saving Agriculture, Gansu Academy of Agricultural Science in northwest China. The experiment was designed to maintain minimum soil water content (MSWC) to different levels: 85%, 70%, 60%, 50%, 40% of field capacity in rooting depth and treatment to be nonirrigation. The treatments were laid out in a randomized complete block with four replications, and a non-mulched replication as control. The study indicated plastic mulched had higher ET than non-mulched due to increase of LAI. Seasonal ET was 269 mm for the plastic-mulch treatments with MSWC 40% and 765 mm with MSWC 85%, increased 19.8% and 2% than non-mulched, respectively. The ET rates of mulch treatments were lower before tillering, and higher after tillering. Plastic mulching could decreased evaporation from soil by 55% in comparison with non-mulched for the treatment of 60% MSWC. The yield was the highest with treatment of MSWC 60% in 1990 and 70% in 1991, and it was significantly higher than treatments of MSWC 40% and nonirrigation. However, there were not significant differences in yield when MSWC were between 50% and 85%. The water use efficiency (WUE) of the plastic-mulched treatment reduced with the increase in MSWC. They were 0.86 kg m⁻³ for the treatment of MSWC 85% in 1990 and 0.89 kg m⁻³ in 1991, significantly lower than MSWC 40–60% and nonirrigation. There were increases of 0.9–30.8% in ET and 4.0–110.3% in yield for all plastic-mulched treatment over non-mulch. The WUE with plastic mulch was 2–61% higher than non-mulch, and the difference increased with the decreasing of MSWC. The net seasonal income, benefit–cost ratio and net profit per mm of water used were bigger compared with non-mulched under less than 60% MSWC, however they became smaller from 60% up to 85%.

Finally, results revealed that spring wheat mulched with plastic maintained higher WUE and net income than non-mulched under low soil water content, which makes it suitable for deficit irrigation in arid circumstance.

Introduction

Water shortage is the major constraint to agricultural production in the arid areas of northwest China where precipitation varies in 40–200 mm. However, the annual potential evaporation is very high and amounts to 1500–3000 mm and water requirement for wheat can exceed 600 mm. Therefore, irrigation is required for crop production in this region. But the total water resources of arid regions of northwest China are scarce, accounting for 4.7% of national resources. Total water resource per 10 000 km² is 532 million m³, which is far lower than the average level for China of 2862 million m³ per 10 000 km² (Liu and Ma, 1998).

Cereals are the major crops in the arid region of northwest China, and more than 80% of water resource is used for cereals. Spring wheat, the most important irrigated crop in that area, has a high seasonal water requirement for maximum yields. In this area, the most common low yield factor is water deficit. A more efficient use of irrigation water under limited precipitation will help sustain agricultural production. Under water limited conditions the largest increase in water use efficiency (WUE) of crops comes by altering the balance between evaporation and transpiration (Cooper et al., 1987). Evaporation (E) from soil surface results in a considerable loss of moisture and has a direct impact on wheat yield. In wheat production, E is usually 30–60% of total ET (Siddique et al., 1990, Amir et al., 1991, Gregory et al., 1992, Yanusa et al., 1993). To increase plant transpiration (T) and decrease soil E is one of the most effective ways to improve WUE, because E from soil is little conducive to crop productivity.

There are many methods to reduce E and improve WUE. One strategy is to reduce E by mulching. The role of various types of soil cover in reducing E has been widely studied: crop residue mulches (Bond and Willis, 1970, Unger, 1976, Jalota and Prihar, 1990, Gicheru, 1994), plastic film (Li et al., 1999), sand mulches (Modaihsh et al., 1985) and rock fragment mulches (Groenevelt et al., 1989, Kemper et al., 1994, van Wesemael et al., 1996). Covering the surface with plant residues can reduce radiation and wind speed at the surface and hence, reduce E. Wang et al. (2001) found that wheat straw mulch reduced E by 50% under winter wheat and this is equivalent to about 80 mm of water in the north China plain. Residue reduces E of soil water primarily by shading the soil surface from the sun, which will delay plant development due to lower soil temperature. Thus, maintaining residue on the soil surface has not always been shown to increase yields. Gravel and sandy mulch was effective in reducing E and runoff, improving infiltration and soil temperature and maintaining soil fertility (Hide, 1954, Adams, 1966, Fairborn, 1973, Poesen and Lavee, 1994, Kemper et al., 1994, van Wesemael et al., 1995, Roundy et al., 1997, Nachtergaele et al., 1998, Li et al., 2000). However, gravel and sandy mulch are labor-intensive to apply and maintain. The benefit is low in gravel and sandy mulch field for wheat. In comparison with other mulching materials, plastic film cannot only reduce E but also improve soil temperature and increasing yield. In addition its cost is lower compared with gravel and sandy, and its operation is simple and so plastic-mulching technique is widely applied.

Plastic-mulching technique was mainly used for thin seeded crops. With the plastic-mulching and hole planting technique invented for wheat and the planting and mulching machine developed in China in 1991, the use of plastic mulching for wheat production is widely extended in China. When the technique was applied in field in 1991, the area was no more than 10 ha, while its area was 40 000 ha in 1996 (Zhang and Guo, 2000). Studies in China have indicated that plastic mulch on wheat can increase yield (Zhang and Yang, 2001), reduce water use and improve WUE (Ma, 1999). The objectives of this study was to determine the effect of water deficit on production of plastic-mulched wheat and compare ET, E, yield, and WUE of plastic-mulched wheat with conventional cultivation.