- Author: Michelle Leinfelder-Miles
- Author: Dan Putnam
- Author: Rachael Long
A question came to me from a crop consultant. His alfalfa grower asked him how he could increase crude protein (CP) in his alfalfa. The buyer of the alfalfa, for the most part, is happy with the hay. For example, the buyer is happy with the total digestible nutrients (TDN), but he would like to see a little higher CP. The consultant said that the grower is generally on a 28-day cutting cycle and is generally cutting the hay pre-bloom. He wondered if nitrogen (N) fertilizer would help to improve CP.
The best way to improve CP is to: 1) cut early, 2) choose a more dormant variety (but give up yield), and 3) manage the harvest to retain the leaf fraction. Since this grower is already cutting pre-bloom, and since...
Yellow plants equals nitrogen deficits—right? Maybe not!
When we have a very wet winter or spring, alfalfa fields may look yellow with diseased-looking leaves and delayed growth.
As farmers know, yellowing of leaves is a strong indication that nitrogen (N) may be limiting in the crop. Certainly that's true with corn, tomato, or wheat. It may also be the case in alfalfa too – but since alfalfa is a legume, it gets most of its N from biological nitrogen fixation (N2 fixation from bacteria which colonizes the roots, forming nodules), not from the soil. This ability enables alfalfa to grow well even on sandy N-depleted soils. N fertilizers are generally not recommended...
When is nitrogen fertilization of alfalfa beneficial? Almost never!
Nitrogen (N) fertilizer is generally not required for alfalfa production since alfalfa can obtain its own N from N-fixing nodules (Figure 1). Alfalfa fixes most (70-90%) of its N needs from the air through Rhizobium bacteria residing in alfalfa root nodules (Figure 1). Since 78% of our air consists of nitrogen gas, this supply of ‘free fertilizer’ is inexhaustible. A recent unpublished UC Davis-CSU Fresno study showed 90% of N in alfalfa originated from the atmosphere -- but less when soil N levels were high, for example, in manured fields.
Although there have been some reports of yield and forage quality...