Effect of mulch, irrigation, and soil type on water use and yield of maize

Abstract

Tillage practices that maintain crop residues on the soil surface help reduce evaporation of soil water, which can benefit high water use crops such as maize (Zea mays L.). Management practices, climatic conditions, and soil type may affect how well a crop responds to surface residue. We conducted experiments with short season maize in 1994 and 1995 in Bushland, TX, USA, utilizing a rain shelter facility that has lysimeters containing monolithic cores of the Pullman (fine, mixed, thermic Torrertic Paleustolls), the Ulysses (fine-silty, mixed, mesic Aridic Haplustolls), and the Amarillo (fine-loamy, mixed, thermic Aridic Paleustalfs) soil series. In 1994, the treatments were a flat wheat (Triticum aestivum L.) straw and coconut (Cocus nucifera L.) fiber mulch of 4 Mg ha⁻¹ with infrequent irrigations totaling 25% and 75% of long-term average rainfall for the growing season (200 mm). The 1995 treatments were similar, but used a heavier mulch of 6.7 Mg ha⁻¹ and more frequent irrigations totaling 60% and 100% of long-term average rainfall. The mulch was applied at the 3-leaf growth stage. Mean potential grass reference evapotranspiration for the vegetative and reproductive growth stages in 1994 was 6.6 and 6.3 mm day⁻¹, respectively, and in 1995 it was 6.8 and 7 mm day⁻¹, respectively. The mulched and bare soil surface treatments used similar amounts of water in each year. In 1994, mulch did not affect yield, yield components, or leaf area index (LAI). No significant differences occurred in plant available water (PAW) between mulched and bare soil treatments from emergence through harvest. In 1995, mulch increased grain yield by 17%, aboveground biomass by 19%, and grain water use efficiency (WUE) by 14% compared with bare soil treatments. Mulched treatments also maintained significantly greater PAW compared with bare soil treatments until near anthesis and, after anthesis, LAI was significantly greater in the mulched treatments compared with the bare soil treatments. In 1995, mulch significantly increased grain yield and grain WUE of the maize crop in the Pullman soil, grain yield and biomass WUE of the crop in the Amarillo soil, and had no significant effect on the crop in the Ulysses soil compared with the bare soil treatments. The significant increase in water use efficiency in 1995 was the result of soil water being used for crop growth and yield rather than in evaporation of soil water. The more favorable soil water regime in 1995 compared with 1994 between the mulched and bare soil treatments was possibly due to the higher evaporative demand environment, the increase in mulch mass, and the increased irrigation frequency. This was especially important in soils where textural characteristics affected both rooting and soil water extraction by maize which limited its ability to tolerate water stress.

Introduction

A more efficient use of the region's declining irrigation water and limited precipitation will help sustain agricultural production in the semi-arid central and southern high plains of the USA. Maize (Zea mays L.), a major irrigated crop in that area (Musick et al., 1990), has a high seasonal water requirement for maximum yields (Musick and Dusek, 1980). Due to increased pumping costs and declining water levels in an aquifer used for irrigation, maize producers need to adopt tillage practices that limit evaporative losses and increase crop water use efficiency.

Tillage practices that maintain crop residue on the soil surface have been shown to increase maize yields in numerous studies (e.g., Triplett et al., 1968; Lal, 1974, Lal, 1978, Lal, 1995; Unger, 1986; Wicks et al., 1994). The yield increases were generally credited to increased water contents in the soil due to reduced evaporation. This additional soil water storage can occur during fallow periods prior to planting (Greb et al., 1967) as well as during the growing season (Greb, 1966; Adams et al., 1976). Lal (1974)found that maize grain yields increased by as much as 52% with mulch applied only after planting. However, Unger and Jones (1981)concluded that grain sorghum [Sorghum bicolor (L.) Moench] responded more to the soil water stored during fallow than to additional soil water conserved by mulch applied only during the growing season.

Residue reduces evaporation of soil water primarily by shading the soil surface from the sun. Shading is most effective during the first-stage drying of a wet soil surface (Bond and Willis, 1970; Adams et al., 1976). Evaporation reduction due to crop residue also diminishes with time, especially in periods of drought or infrequent, light rains (Greb, 1966; Lal, 1974). In a laboratory study using soil columns, Unger and Parker (1976)found that evaporation rates were higher for bare soil than for soil with surface residue for about the first 15 days, after which the trend reversed.

The plant canopy can also shade the soil surface, thus substituting for the beneficial effects of residue during latter part of the growing season (Adams et al., 1976; Unger and Jones, 1981). Todd et al. (1991)found that in a dryland maize crop, shading by the canopy accounted for at least three-fourths of the evaporation reduction, while under limited irrigation, residue and canopy contributed equally.

The amount or thickness of residue coupled with atmospheric evaporative potential determine the rate of drying. Greb (1966), Adams et al. (1976), and Unger (1976)reported notable evaporation reduction from wetted soil surfaces covered with about 4 Mg ha⁻¹ of flat wheat (Triticum aestivum) straw. Bond and Willis (1970)found that first stage evaporation rate decreased with either increasing residue rates or decreasing evaporation rates. Unger and Parker (1976)and Steiner (1989)noted that residue thickness (volume) was more critical than mass per unit area for controlling evaporation. On a mass basis, about two times as much sorghum and four times as much cotton (Gossypium hirsutum L.) residues on the surface of the soil were needed to achieve the same evaporation reduction as with wheat straw. Under field conditions, Unger (1978)found that the average precipitation storage in a Pullman clay loam soil covered with 12 Mg ha⁻¹ of wheat residue was over twice that without residue.

Maintaining residue on the soil surface has not always been shown to increase yields. Unger (1986)reported yield reductions with high residue amounts, which was due partially to low N fertility. Wicks et al. (1994)also had yield reductions due to cool, rainy weather. Multi-year studies showed a variable response to residue with each growing season, ranging from 0% up to 70% yield increases. As Wicks et al. (1994)pointed out, yield variations resulted from how long plant development was delayed due to lower soil temperatures, how much water was conserved, how much water stress occurred, the amount and distribution of precipitation, and evaporative demand.

Other variations in response have been credited to the soil type (Triplett et al., 1970; Gajri et al., 1994). Gajri et al. (1994)found that mulching increased maize grain yields from crops in loamy sand for all the 10 years studied, but that mulching decreased yields of maize grown in sandy loam some years and increased yields in other years compared with maize with bare soil surfaces. Triplett et al. (1970)reported that mulching increased yields of maize grown in a silt loam or in a sand, but decreased yields on the fine sandy loam.

In environments where there is limited or poorly distributed precipitation, declining water supplies for irrigation, and relatively high evaporative potential, improved water use efficiency is essential for successful maize farming. The interactive effects of limited irrigation, growing season mulch, and soil characteristics need to be better understood to achieve this objective. The objective of this research was to evaluate the effect of a growing season mulch on the growth, water use, and yield of maize grown in three soil types.