Effect of in-field water harvesting with different mulching practices on crop response
It is well known that in semi-arid areas the growth and yield response of crops depend largely on the amount of rainwater stored in the root zone. Integrating rainwater harvesting and mulching may be an approach to maximize water storage and to minimize water losses through evaporation and runoff. This may improve crop growth and yield. A two year study was conducted to determine the effect of an in-field water harvesting with mulch application in both the basins and runoff strips on growth and yield response of maize (Zea mays L.) and sunflower (Helianthus annus L.).The experiment was conducted at the Glen experimental farm, 25 km north Bloemfontein (28055'l3" latitude and 26°21 '12" longitude) on a heavy clay soil (Bonheim soil form). It consisted of four mulching treatments. Three of the mulching treatments were a combination of rainwater harvesting basin (RWHB) with organic mulch in the basin and organic (00) or stone (OS) mulch on the runoff strip or bare runoff strips (OB). The fourth treatment was the combination of RWHB with stone mulch in the basin and organic mulch on the runoff strips (SO). The organic mulch was a mixture of maize and sunflower stalks at the rate of 8 t.ha-I . The size of the stones in the mulch was approximately 10 to 15 cm in diameter, and they covered 70-80 % of the soil surface.Two adjacent, 24 m x 36 m (288 m²), experimental sites were used to accommodate the four treatments in a completely randomized block design with three replications. Maize, variety Phb 33-V08 and sunflower, variety SNK 74 were planted in a tramline with spacing 1m x 2m on the 7th and 28th of January 2000 and the 5th and 4th of January 2001. respectively. During the two seasons, maize and sunflower were grown in rotation, whereas treatments were maintained in place. The soil water content, rainfall and evaporation demand of the atmosphere were evaluated from the data obtained from ARC-ISCW (Glen). Plant height and stem thickness at maturity were measured to determine whether growth was stimulated or inhibited. Stem growth rates and leaf area indexes were determined during 209°/2001 to evaluate early growth responses of the tested crops. The aerial biomass and grain yield of maize and sunflower were also assessed. The two seasons were different with respect to the amount and distribution of the rainfall. soil water patterns and evaporative demand of the atmosphere. The 1999/2000 growing season was more favourable for crop growth and yield than 2000/2001. Results of soil water measurements showed that the applications of stone or organic mulch on the runoff strips were beneficial to conserve water in the soil profile of the runoff strips irrespective of crop type. Although it is not always significant, organic mulch placement on the runoff strip reduced the amount of water stored in the basins. This effect was not observed when the runoff strips were mulched with stones.' Although not statistically significant, the growth and yield of maize were higher in OS, SO and 00 treatments than in the control (OB). Maximum biomass and grain yield over seasons was obtained in the OS. All plant parameters studied showed that the interaction between mulching and seasons had no significant influence on the growth and yield of maize. Although differences were not always statistically significant, the OS technique seemed to be the best for crop growth and yield. Similar results were obtained for sunflowers, which was regarded as an advantage for farmers enabling them to exercise maize-sunflower rotation without changing mulching practices.