Sustainable Soil Management Options for Integration in Highly Diversified and Intensified Cropping Systems

Excessive use of nitrogen fertilizers for intensified crop production results in high residual nitrogen that accumulates as nitrate nitrogen (NO3-N) in the soil. These residues become a pollutant to water resources and a hazard to human health. Thus, Agustin, Shrestha, Tripathi, Lucas, Pascua Jr., Ladha, Marcos, Culannay, Baga, Bucao, Balasubramanian, Morales and Obien (MMSU) developed a technology that will utilize residual nitrogen and prevent nitrate contamination of surface water resources (through surface runoff) and groundwater (through leaching). The research also established some sustainable soil management options for intensive agriculture or for diversified farming.

NO3-N dynamics was evaluated in rice-based cropping sequence (wet season rice and dry season food or cash crops), with and without catch crops. Catch crops sued were corn, indigo and mungbean. Three N management strategies were investigated, namely: urea tablet deep placement (UT/DP), spad-based N (SB) using a chlorophyll meter, and farmers’ N (FN) management scheme.

Findings

• The technology involved planting nitrogen catch crops (corn, indigo, mungbean, heavy vetch, cereal rye, rye grass, and common sunflower) after the harvest of dry season crops, instead of leaving the land fallow during the short transition period from dry to wet season.
• Results showed that there was serious amount of NO3 leaching in fallow plots than in plots with catch crops. In fallow plots, NO3 declined in the surface soil 45-65 days after planting, but increased in the lower layers, reaching 86 kg NO3/ha at 75-100 cm depth. In plots with catch crops, NO3-N decreased in the surface layer but did not increase in the lower layers, which showed the ability of the catch crops to take up N from the soil beyond 100-cm depth. At 0-25 cm depth, corn reduced NO3-N by 82%, indigo by 73%, and indigo plus mungbean by 66%. However, at 75-100 cm depth, corn reduced NO3-N by 25% only, indigo by 60%, and indigo and mungbean combined by 47%.
• Corn was effective in reducing nitrate at shallower depths due to its larger root density, but not in deeper soil layers because of its shallow rooting system. On the other hand, indigo was effective in reducing NO3 leaching at deeper soils layers (50 cm and even b eyond 100 cm depth) because of its deeper rooting system than corn. These implied that indigo could serve as an effective catch crop after the dry season when there is a higher risk of leaching due to an increase in rainfall during the wet season.
• The evaluation of different nitrogen management schemes revealed that for wet season rice, the urea tablet deep placement could be considered a better management scheme for increasing rice productivity. Urea tablet deep placement gave higher rice yields than that of the prilled urea spad-based management scheme, and the farmers’ scheme.
• In terms of nitrogen use efficiency (NUE), both SB and UT/DP gave comparable performance, which was 2.5 to 4.0 times greater than that of the farmers’ scheme, with NUE of less than 10 kg grain/kg N applied.
• However, the high price of urea tablet posed a constraint on its use. In the spad-based management scheme using prilled urea, though it showed good potential, the price of the chlorophyll meter served as a constraint on its adoption.
  

Source: PCARRD, 1999. Highlights 1998, Los Banos, Laguna.

Organic Farming Information Network
Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD)
©2006