Table 2. Mean values of fertilizer application in kgN/ha and ton/year, crop yield in ton/ha, N uptake per area in kgN/ha, N content in crops in kgN/ton, total N uptake by crops in ton/year and net N input in ton/year (NNI; N fertilizer application minus N uptake) for cotton and wheat fields in the Uzbek part of the Amu Darya river basin (UADRB) for the periods 1960–1980 and 1981–2000.

Period	N fertilizer application rate in UADRB [kgN/ha]	Total N fertilizer application in UADRB [ton/year]	Crop yield in UADRB [ton/ha]	N uptake per ha cultivated area in UADRB [kgN/ha]	N content in crops in UADRB [kgN/ton]	Total N uptake by crops in UADRB [ton/year]	Net N input in UADRB [ton/year]
1960–1980	160	194,000	3.4	144	42.3	171,500	22,500
1981–2000	197	283,000	3.7	137	37.0	199,000	84,000