tration studies also examined total soil N (Bauer and

Pre‐plant soil NO−3–N tests and petiole NO−3–N analysis are bases for Upland cotton (Gossypium hirsutum L.) N management in the western USA. Alternative approaches include proximal multispectral reflectance sensing and chlorophyll meter readings. Our objective was to determine if spectral reflectance and chlorophyll meter measurements correlate with cotton leaf N and biomass. Urea ammonium nitrate was applied after emergence and with low energy precision (LEPA) center‐pivot, surface or subsurface drip irrigation water up to peak bloom. Multispectral reflectance readings 0.5 m above the canopy, chlorophyll meter readings, and biomass samplings were taken at early squaring, early bloom, and peak bloom for 3 site‐years in Lubbock, TX and Ropesville, TX. Green vegetative indices (GVI) and green normalized difference vegetative indices (GNDVI) calculated from reflectance data generally correlated better with leaf N and leaf N accumulation than did red vegetative indices (RVI) and red normalized difference vegetative indices (RNDVI). Biomass and lint yield correlated more often with red‐based indices than green‐based indices. Chlorophyll meter readings correlated with leaf N as often as GVI and GNDVI did. Biomass, however was poorly related to chlorophyll meter readings. These results demonstrate the effectiveness of GVI, GNDVI, and chlorophyll meter readings in assessing leaf N, and RVI and RNDVI in assessing cotton biomass. However, we recommend converting vegetative indices or chlorophyll meter readings to sufficiency indices, which are calculated from indices or readings relative to well‐fertilized plots. Sufficiency indices were able to successfully predict little or no need for in‐season N fertilizer in the low‐yielding 2000 crops (sufficiency index > 0.95), and predicted greater need of N fertilizer in the high‐yielding 2001 crop (sufficiency index < 0.95).

Cellulosic bioenergy production provides opportunities to utilize a range of cropping systems that can enhance the multifunctionality of agricultural landscapes. In a 9-ha field experiment located on fertile land in Boone County, IA, USA, we directly compared a corn-soybean rotation harvested for grain, continuous corn harvested for grain and stover, continuous corn harvested for grain and stover with a rye cover crop, newly reconstructed prairie harvested for biomass and fertilized with nitrogen, and unfertilized newly reconstructed prairie harvested for biomass. Comparisons were made using four performance indicators: harvestable yield, net energy balance (NEB), root production, and nutrient balances. We found trade-offs among systems in terms of the measured performance indicators. Continuous corn systems were the highest yielding, averaging 13 Mg ha À1 of harvested biomass (grain plus stover), whereas fertilized and unfertilized prairies produced the least harvested biomass at 8.8 and 6.5 Mg ha À1, respectively. Mean NEBs were highest in continuous corn systems at 45.1 GJ ha À1 , intermediate in the corn-soybean rotation at 28.6 GJ ha À1, and lowest in fertilized and unfertilized prairies at 11.4 and 10.5 GJ ha À1 , respectively. Concomitant with the high yields of the continuous corn systemswere the large nutrient requirements of these systems compared to the prairie systems. Continuous corn with rye required three times more nitrogen inputs than fertilized prairie. Root production, on the other hand, was on average seven times greater in the prairie systems than the annual crop systems. On highly fertile soils, cornbased cropping systems are likely to play an important role in maintaining the high productivity of agricultural landscapes, but alternative cropping systems, such as prairies used for bioenergy production, can produce substantial yield, require minimal externally derived inputs, and can be incorporated into the landscape at strategic locations to maximize the production of other ecosystem services.