Forage Productivity and Biological Nitrogen Fixation (BNF) in Corn-Soybean Intercropping with Integrated Nutrient in Tropical

Corn productivity in tropical low external input systems is usually limited by low soil fertility because crop uptake leads to a gradual depletion of soil nutrient stocks. Biological nitrogen fixation (BNF) plays an important role in the nitrogen budget of cereal/legume mixed culture. Experiment was carried out to investigate chemical, organic and biofertilizer effect on forage production and acetylene reduction activity (ARA) of corn and soybean roots. Seeds of corn and soybean inoculated with biofertilizer and subsequently applied with biofertilizer produced higher rates of ARA compared to those given NPK and chicken manure (CM) without biofertilizers. Acetylene reduction activity varied between fertilizer treatments. Treatments without fertilizer application, biofertilizer and combination of biofertilizer with NPK or CM treatments gave higher values of ARA compared to sole chemical and sole organic manure fertilizers. Inorganic fertilizer (100% NPK) gave the highest DM yield of forage among single fertilizer treatments and it out yielded the chicken manure (100% CM) treatment. However, when CM was combined with NPK (50% CM + 50% NPK) the DM yield of forage was the same as the 100% NPK. The results indicated that increased nitrogen application had an inhibitory effect on nitrogen fixation. It suggests that increased nitrogen supply with the application of fertilizers inhibited nodule formation in soybean roots, which thus reduced ARA.