The experiment was conducted during the 1986 wet season (May 15 to November 10) in a farmer's field in Kabilang Barrio, Bac al 1, Talavera Nueva Ecija, Philippines. The land with " Maligaya silty clay loam" soil contrained the total N (0.117% dry wt. basis), organic carbon (1.41%) and available K (0.148 me/100 gm) below the critical level (Ponnamperuma, 1985) while available P (Olsen) content (10.0mg/kg) was sufficient for rice production. The experiment was composed of two green manure crops: Azolla (Azolla pinnata var. imbricata) and dhaincha (Sesbania rostrata); while urea was used as the synthetic nitrogen fertilizer (SNF). Following treatments were replicated four times in a Randomized Complete Block Design (RCBD):
T1 Control, i.e. no green manuring and no use of synthetic nitrogen fertilizer in rice crop
T2 30 kg N/ha as urea in rice, top dressed (TD) 25 days after transplanting (DAT)
T3 60 kg N/ha as urea, 1/2 basal and 1/2 as TD at 25 DAT
T4 90 kg N/ha as urea, 2/3 basal and 1/3 as TD at 25 DAT
T5 Azolla (incorporated at 40 days after inoculation) alone
T6 Azolla (incorporated at 40 DAT) + TD of 30 kg N/ha as urea at 25 DAT
T7 Dhaincha (incorporated 40 days after emergence) alone
T8 Dhaincha (incorporated 40 DAE) + TD of 30 kg N/ha as urea at 25 DAT
Initial soil samples were collected from the experimental field after removing the straw of the previous rice crop. Bunds were made around the plots in finally prepared land, water was drained out and dhaincha (Sesbania rostrata) was broadcast seeded in the assigned plots with a seed rate of 50 kg/ha. When dhaincha seedling were found emerged, azolla (Azolla pinnata var, imbricata) inculum was collected from Maligaya Rice Research and Training Center (MRRTC), Munoz, Nueva Ecija and assigned plots were inoculated at an inoculum rate of 2 t/ha (fresh weight basis). Strong bunds were made around the azolla plots for proper water management. Phosphatic fertilizer (solophos) was applied only to the azolla plots at the rate of 10 kg P2O5 per ha in two splits once at inoculation time and another at 20 days after inoculation (DAI) Monocrotophos (Azodrin 02R) at a rate of 4 liters/ha was sprayed at n17 DAI and 30 DAI to control insect ( caseworm-Elophila sp.) in azolla.
After required plant sampling for fresh and dry weight and N analysis, azolla was incorporated into the soil by fool pressing once only at 40 DAI, while dhaincha plants by harrowing with a power tiller. An early maturing (120 days) rice variety IR62 was used. After the incorporation of green manure crops, soil in each plot was well puddled within three days. Twenty-day old seedlings, raised on a wet seed bed with proper fertilizer (urea at 30 kg N/ha at 16 DAS) application, were transplanted in 20 cm x 20 cm spacing. Proper water management was followed. Rice crop was fertilized with urea as per treatments. Before final puddling , P and K fertilizers 60kg P2O5/ha and 40kg K2O/ha respectively were uniformly applied. Rice crop was hand weeded once at 25 DAI. Insect pests were controlled by applying carbofuran (Furadan 3G) at 0.45 kg ai/ha to soil before final puddling and at 25 DAT.
All the additional cost over control plots involved in cultivation green manure crops and rice, according to the treatments were recorded. Returns from each treatment were computed through partial budget analysis (Perrin et al, 1976).
Neighboring farmers and farmers group from different areas around were invited to visit the experimental field during the conduct of experiment to expose than to the experiments and to familiarize them with the green manure crops, especially dhaincha (S. Rostrata). For efficient communication and greater impact of findings of the research, a field day was arranged just before harvest. Responses, comments dhaincha (e.g. S. aculeata , S.sesban and S. rostrata ) were distributed among the attending farmers to initiate their interest and help them multiply their own seed for future use.