Elimination of Irrigation Restriction in Spring Corn(Zea mays) Planting by Relay-Intercropping with Canola(Brassica napus L.)

Water shortage in spring for the cultivation of summer crops is a challenge for farmers in most parts of the country due to the fact that cultivation of these crops coincides with the one or two last irrigations needed for cereals during the critical stage of grain filling. Corn, sugar beet, and other summer crops are cultivated during such periods, and hence water allocation is normally problematic during this period. Relay cropping has been considered as a method to overcome such problems. Furthermore, overseeding of one crop to the stand of another crop in the last stage of development of the second crop (relay intercropping) has been considered as energy-saving and efficient resource use method. The aim of the present work was to investigate the possibility of relay intercropping of corn and canola in order to save water and hence overcome water shortage effects in early spring for summer crops.

In order to evaluate the possibility of relay intercropping of corn and canola, an experiment was conducted 10 kilometers west of Shirvan in two growing seasons of 2012-13 and 2013-14. The experiment was conducted as a randomized complete block design with six treatments and three replications. Treatments included four relay sowing rates of canola and corn (3 rows of canola: 1-row corn, three rows canola: 2-row corn, four rows canola: 2-row corn, six rows canola: 2-row corn), pure stands of canola and corn. Corn seeds were planted between canola rows at the end of the canola growth period to use the latest irrigation of canola for corn germination and emergence. A drip irrigation system was installed, and the amount of water used was measured. All field management operations, including irrigation, fertilizer application, and others, were practiced as the conventional farmers normally conduct. After crop ripening, necessary samples were taken, and finally, LER was calculated for comparison of the treatments.

Analysis Variance of the data showed that the highest 1000-seed weight of canola (3.63 gr) and corn (221.69 gr) were obtained in 4:2 and 3:1 treatments, respectively. This was 3.35 gr for the pure stand of canola and 218.5 gr for the pure stand of corn. Economic and biological yields for both crops of canola and corn were highest in pure stands (2502.5, 9763.5 kg/ha for canola and 6207.6, 15769.2 kg/ha for corn, respectively). The highest seed yield of corn was obtained in 2-row corn and 3-row wheat, but in research, by Adeniyan et al. (2007), the highest seed yield was obtained in pure stand. Harvest index of canola was 26.03 in 3:2 ratio indicating no significant difference with other treatments. The maximum harvest index of corn (40.53%) was observed in the 3:1 ratio. In an experiment by Nassiri Mahallati et al. (2011), the harvest index of corn and wheat was highest in pure stands, but the highest harvest index of canola was found in 4-row canola with wheat cultivation. The highest total LER (1.11) was obtained in 3:1, followed by the 6:2 ratio (1.016). The total water used for the pure stand of canola was 3750 m3/ha, whereas it was 9081 m3/ha for corn. If corn was planted after canola, total water use had been 12831 m3/ha, whereas when they were relay intercropped, water consumption was 10915 m3/ha, saving 1916 m3/ha of water. Zarehaghi et al. (2016) also reported that water consumption in intercropped treatments of corn and bean was less than in pure cultures of these crops.

The highest seed yield of both plants was obtained in pure stand. Between different intercropping ratios of canola and maize, the maximum land equivalent ratio that was more than one (1.11 and 1.016) was observed in 3:1 and 6:2 treatments, respectively. The amount of water saved by relay intercropping of these crops was 1916 m3/ha, which is a considerable amount of water.