Pattern of soil moisture depletion in alley cropping ... - Springer Link

Agroforestry Systems 26: 89-99, 1994. 9 1994 Kluwer Academic Publishers. Printed in the Netherlands.

Pattern of soil moisture depletion in alley cropping under semiarid conditions in Zambia R W, C H I R W A ~, R K. R. N A I R 2 and E N K E D I - K I Z Z A 3 ~Forestry Research Institute of Malawi, P.O. Box 270, Zomba, Malawi; ~School of Forest Resources and Conservation, IFAS, University of Florida, Gainesville, FL 32611, USA; 3 Department of Soil and Water Science, IFAS, University of Florida, Gainesville, FL 32611, USA

Key words: alley cropping, flemingia, leucaena, semiarid, soil moisture, Zambia Abstract. The pattern of soil moisture changes was studied during a cropping season in an alley cropping experiment of maize with Leucaena leucocephala and Flemingia macrophylla at the SADC/ICRAF Agroforestry Research Station in a semiarid region near Lusaka, Zambia (28~ " East and 15~ South). Soil moisture potential was monitored at regular intervals using tensiometers installed at 15, 30 and 45 cm depths in fertilized and unfertilized alleys within the double hedgerow, and the first, second and third rows of maize in the alleys. Soil moisture moved mostly towards the top horizon during very dry conditions. Alleys that had received a combination of fertilizer and hedgerow prunings depleted more moisture than those that had only hedgerow prunings. There were no differences in moisture utilization pattern between leucaena and flemingia hedgerows. The hedgerows depleted the same amount of moisture as the maize plants. However, during dry conditions, there was a higher soil moisture content under the hedgerows than in maize rows, indicating that there was no apparent competition for moisture between the hedgerows and the maize plants.

Introduction

It is well k n o w n that availability o f adequate quantities o f soil moisture is an essential r e q u i r e m e n t for successful plant growth. Soil water potentials in the range o f - 1 0 to 1000 K P a are k n o w n to be essential for processes that facilitate nutrient availability, including nutrient transport to roots by diffusion and mass flow [Frank, 1972; Kozlowski, 1972; Kramer, 1969]. Soil moisture limitation and declining soil fertility are two serious constraints to agricultural production in semiarid tropics. In the unimodal rainfall plateau o f southern A f r i c a where the c r o p p i n g (rainy) season lasts only for a short p e r i o d o f 3 - 4 months, inadequate soil-fertility, rather than moisture stress, is c o n s i d e r e d to be the m o s t serious p r o b l e m during the c r o p p i n g season. B e c a u s e chemical fertilizers are either unavailable and/or are unaffordable to most o f the smallholder farmers o f the region, alley cropping is being tried as a crop production technology as an approach to mitigating the soil-fertility constraint [ A k e a m p o n g et al., submitted; Chirwa et al., 1994]. However, research results on alley cropping under semiarid conditions elsewhere have shown that competition for moisture between the hedgerow species and the alley-cropped food crops could be a major factor causing yield depres-

90 sion of crops near the hedgerows [Ong et al., 1991; Singh et al., 1989]. Such information is lacking from the southern African upland plateau region. Therefore, this study was conducted to monitor soil moisture patterns in a maize + leucaena/flemingia alley cropping system in the semiarid region of Zambia.

Materials and methods

Study site The study was conducted at Chalimbana Agricultural Research Station in Lusaka, Zambia, 20~ " East and 15~ " South, with a mean annual rainfall of 800-1000 mm and mean minimum and maximum temperatures of 9.4 and 22 ~ respectively. The rainfall is greater than evapotranspiration only in the months of December, January, and February. The soils are derived from the quartz muscovite schist and the surface soils are slightly acidic while subsoils are neutral to alkaline [Kamara and Mateke, 1989; Yager et al., 1967]. The soils have been classed as plinthic lixisols (Food and Agriculture Organization) which is the same as fine loamy, mixed isohy-perthermic plinthic kandiustalf under U.S. Department of Agriculture Classification [Chirwa et al., 1994].

Study plots The experiment consisted of alley cropping with Leucaena leucocephala (leucaena) and Flemingia macrophylla (flemingia) as the hedgerow species and hybrid maize (Zea mays) variety MM603 in the alleys. Factorial combinations of two hedgerows species and two fertilizer rates (no fertilizer and 150 kg ha-1 of urea) formed the main plots of a split-plot experiment, and maize rows within each plot were the sub-plots. Each treatment unit consisted of two double hedgerows with six rows of maize between them and three maize rows on both sides of the hedgerows (Fig. 1). Maize was planted at within- and between-row spacings of 25 and 75 cm. The fertilized treatments had basal application of diammonium phosphate at the rate of 200 kg/ha, and two applications of urea at the rate of 75 kg/ha each at planting and five weeks after planting maize.

Soil moisture Soil moisture potential was determined using tensiometers installed to 15, 30 and 45 cm depths within each of the double hedgerows, and in the first, second and third maize rows from the hedgerows (Fig. 1). A pressure transducer, also known as a tensimeter, was used according to the procedure described by Marthaler et al. [1983]. The reading on the pressure transducer in millibars

91 N

Double Hedgerow (H) J

--Maize Row (R1, R2, Pa)

10.0m

- -

D

Tenslometer Location (15, 30, 45 cm)

T I

RI 30

I

I i