Notes from Your Extension Agent

By: Ayman Mostafa and Shawna Loper
Alfalfa: I received some questions about the values for forage quality parameters. Some forage quality parameters such as ADF (acid detergent fiber), NDF (neutral detergent fiber), and protein, are measured. ADF refers to cell wall portions in the silage that are made up of cellulose and lignin and NDF refers to the total cell wall (ADF + hemicellulose). Low values of ADF and NDF are desirable because ADF and NDF are inversely related to digestibility of silage and dry matter intake (the amount of silage the animal can consume). Total digestible nutrients (TDN) is the sum of digestible nutrients in the forage which includes crude protein, fat, sugars, starch, and digestible fiber. TDN can be measured directly, but is most often calculated from a mathematical formula using ADF (acid detergent fiber) as the sole measured value. Although TDN and ADF are related to each other, the relationship varies by region and is subject to different formulas and interpretation by the individual nutritionist. Another important parameter is Relative feed value (RFV) is a calculated index of forage quality that is very useful in comparing different types of forages. RFV provides an indication of digestibility of a forage as does total digestible nutrients (TDN), but also includes intake potential. RFV is calculated from both ADF and NDF, whereas TDN is calculated from ADF only.
Most early planted wheat and barley appear to be at the 1st node stage. This is the point where the plant develops maximum number of florets and, therefore, maximum yield potential. Good nutrient and water supply are important for determining yield potential at this stage. Wheat and barley use about 2 acre-feet of water in Arizona, but 3 to 3.5 ft is often required with surface flood irrigation due inefficiencies in the irrigation system. Water stress at any stage can reduce yields of small grains. Small grains are most susceptible to water stress during jointing, intermediate in susceptibility during tillering, and least susceptible during grain fill. Extreme water stress can reduce potential number of seeds per head.
Late planted wheat appears to be at the 3 to 5 leaf stage to tiller production stage. At this stage, early weed control and good nitrogen management is important. It is time to scout for aphids, stink bugs and other insects.

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