Effects of Croping System and Fertilizer on Sweet Corn and Vegetable Soybean Intercrop

Corn (Zea mays L.) and soybean are two important crops world wide, due to their diversified use. The Malaysian climate is suitable for the production of these two crops but the country imports large quantity of corn and soybean grains per annum to satisfy the country’s demand. These two crops are grown in association in other parts of the world for the sake of yield advantage or risk minimization. However, the available literatures indicate that increased corn yield and declined soybean yield, as well as reduced yield of both corn and soybean under intercropping systems, or no change on yield. Shading, higher nutrient and water uptake by corn was attributed as the major factor causing yield decline of soybean in intercrop. Shading, higher nutrient and water uptake by corn was attributed as the major factor causing yield decline of soybean in intercrop. However, insufficient efforts have been made to study the compatibility of these two crops and effect of fertilizers on soybean and corn intercrop under Malaysian conditions Hence, this research has been carried out in 2004/2005 to determine the effect of cropping systems and fertilizer levels on growth, yield, root morphology, light interception, nutrient uptake and utilization efficiency of sweet corn and vegetable soybean as well as their effect on soil fertility, and protein content of soybean grain. Sweet corn and vegetable soybean were grown in rhizoboxes. Treatments were five cropping systems and three fertilizer levels in factorial combinations. Intercropped vegetable soybean without root separation (Cs3) and with geotextile root separation (Cs5) resulted in 11.2% higher harvest index (HI) than mono-crop vegetable soybean (Cs2). Cs3 had 16.1% higher grain yield and 20.7% more Mg accumulation in the grain than mono-crop vegetable soybean. Intercropped vegetable soybean without root separation and with geotextile root separation enhanced N, K and Ca utilization efficiency of vegetable soybean compared to mono-crop vegetable soybean. Absence of root separation (Cs3) and geotextile root separation (Cs5) did not have significant influence on yield of sweet corn. Mono-crop sweet corn and intercropped sweet corn with plastic sheet root separation had higher total root length compared to intercropped sweet corn without root separation and with geotextile root separation. Intercropped sweet corn with plastic sheet root separation at the highest fertilizer level (Cs4F3) had higher N, K, Ca and Mg utilization efficiency than mono-crop sweet corn. Increasing fertilizer levels enhanced growth and yield of both crops; although increasing fertilizer level more than the recommended rate reduced the total root length and root surface area of vegetable soybean. Increasing fertilizer level from 50% recommended rate (F1) to 100% recommended rate (F2) improved stem (24%), pod (35%), seed (44%) and total dry weight (27%) per plant of vegetable soybean. When the fertilizer level was increased further from 100% (F2) to 150% (F3), stem (17%), pod (19%), seed (17%) and total dry weight (18%) per plant was also enhanced. Similarly, increasing fertilizer level from F1 to F2 enhanced cob fresh weigh (76%) as well as shelled cobs (90%) and total dry weight (95.5%) per plant of sweet corn. Further increase of fertilizer levels from F2 to F3, enhanced cob fresh weight (63%), total dry matter (59%), and seed dry weight (143%) and shelled cob dry weight (57%). There was a positive correlation between growth and yield; yield and nutrient uptake of sweet corn and vegetable soybean, and this indicates better crop response to fertilizer applications. Plastic sheet and geotextile root separation significantly enhanced available soil P after harvest of the crops. In vegetable soybean grown soils, increasing fertilizer level from the lowest level to the medium (F2) improved soil P by 29.1%, further increase of fertilizer level from F2 to F3 (highest level) enhanced soil P by 23.2 %; the exchangeable soil K was enhanced from the medium to highest fertilizer level by 30%. In sweet corn grown soil, available P and exchangeable soil K increased from the lowest to the medium fertilizer level by 96% and 19% respectively, and no further increase was recorded. Hence, intercropped vegetable soybean is a better option than mono-crop vegetable soybean, and better nutrient use is main factor for improved soybean yield in Cs3. The current recommended fertilizer rate is not enough and 150% of the recommended rate seems to be the best choice in this work.

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