THEORY AND PRACTICE IN THE USE OF FERTILIZERS

By PAUL LOPEZ

MAY BE LOWER THAN IN AREAS WHERE CONSUMPTION IS HIGHER LOW EFFICIENCY OF N IS TYPI- CALLY CAUSED BY AN INSUFFICIENCY OF OTHER REQUIRED NUTRIENTS (E G , P, K, AND SECONDARY AND MICRONUTRIENTS, AULAKH AND MALHI, CHAPTER 13, THIS VOLUME), WHICH LIMITS PLANT GROWTH ALONG WITH N IN RICE PRODUCTION, NUES OF 30 PERCENT OR LOWER ARE TYPICAL IN MANY REGIONS, WHEREAS EFFICIENCIES APPROACHING 70 PERCENT ARE NOT UNCOMMON IN AREAS OF INTENSIVE MAIZE PRODUCTION (DOBERMANN AND CASSMAN, CHAPTER 19, THIS VOLUME) EVEN IN THESE HIGH-EFFICIENCY REGIONS, LOSSES OF N OCCUR, EXACERBATING WATER-QUALITY PROBLEMS BOTH LOCALLY AND DOWNSTREAM OF CROP PRODUCTION AREAS AGRICULTURAL NITROGEN CYCLE FERTILIZER SUPPLIES ABOUT 50 PERCENT OF THE TOTAL N REQUIRED FOR GLOBAL FOOD PRODUCTION IN 1996 GLOBAL FERTILIZER N CONSUMPTION TOTALED 83 TG N (SMIL 1999), AND CONSUMP- TION HAS INCREASED LITTLE SINCE THEN, FOR EXAMPLE, 84 1 TG N IN 2002 (FAO 2004) THERE- FORE, SMIL’S ESTIMATES OF THE GLOBAL N FLOWS ARE PROBABLY STILL APPROPRIATE AND ARE USED HERE THE OTHER ANNUAL INPUTS INTO CROP PRODUCTION—BIOLOGICAL N-FIXATION (~33 TG; 25–41 TG), RECYCLING OF N FROM CROP RESIDUES (~16 TG; 12–20 TG) AND ANIMAL MANURES (~18 TG; 12–22 TG) (FIGURE 1 1), ATMOSPHERIC DEPOSITION, AND IRRIGATION WATER (NOT SHOWN IN FIGURE 1 1)—PROVIDE AN ADDITIONAL ~24 TG (21–27 TG) (SMIL 1999) OF THE ~170 TG N ADDED, ABOUT HALF IS REMOVED FROM THE FIELD AS HARVESTED CROP (~85 TG) THE REMAINDER OF THE N IS INCORPORATED INTO SOIL ORGANIC MATTER OR IS LOST TO OTHER PARTS OF THE ENVIRONMENT FOR WHICH GLOBAL ESTIMATES OF INDIVIDUAL LOSS VECTORS ARE HIGHLY UNCER- TAIN LEACHING, RUNOFF, AND EROSION ACCOUNT FOR ~37 TG OF THE ANNUAL N LOSSES; AMMO- NIA VOLATILIZATION FROM SOIL AND VEGETATION CONTRIBUTES ~21 TG YR-1 DENITRIFICATION LOSSES AS GASEOUS DINITROGEN (N2) AMOUNT TO ~14 TG YR-1, AND N2O AND NO FROM NITRIFICA- TION/DENITRIFICATION CONTRIBUTE ANOTHER ~8 TG N TO THE TOTAL LOSS (SMIL 1999; BALASUB- RAMANIAN ET AL , CHAPTER 2; PEOPLES ET AL , CHAPTER 4; GOULDING, CHAPTER 15; BOYER ET AL , CHAPTER 16, THIS VOLUME) VAN DER HOEK (1998) ALSO ESTIMATED THAT MORE THAN THE RELATIVE INEFFICIENCIES OF ANIMAL PROTEIN PRODUCTION EXACERBATE THE INEFFICIENCIES OF N UTILIZATION LARGER N LOSSES FROM GLOBAL FOOD PRODUCTION ARE LIKELY IN THE FUTURE AS THE HUMAN POPULATION AND THE DEMAND FOR ANIMAL PROTEIN INCREASE (GALLOWAY ET AL 2002A) THE INCREASE IN CONSUMPTION OF ANIMAL PRODUCTS WORLDWIDE, EXCEPT FOR REGIONS WITHIN SSA, HAS BEEN ACCOMPANIED BY AN INTENSIFICATION OF ANIMAL PRODUCTS IN SOME REGIONS, PARTICULARLY NORTH AMERICA BECAUSE OF THE CENTRALIZATION OF LIVESTOCK PRODUC- TION IN REGIONS THAT PRODUCE RELATIVELY LITTLE ANIMAL FEED, THE AREAS OF CROP PRODUCTION 1 NITROGEN FERTILIZER: AN ESSENTIAL COMPONENT |