Monitoring forage production for farmers' decision making

GRIGERA, G.; OESTERHELD, M.; PACIN, F.

AGRICULTURAL SYSTEMS

Año: 2007 vol. 94 p. 637 - 648

0308-521X

Objective management of grazing livestock production systems needs monitoring of forage production at the managerial unit level.Our objectives were to develop a system that routinely estimates forage above-ground net primary production (ANPP) at the spatial andtemporal resolution required by farmers in the Pampas of Argentina, and to facilitate adoption of the system by end users as a managerialsupport tool. Our approach was based on the radiation use efficiency (RUE) logic, which proposes that ANPP is determined by theamount of photosynthetically active radiation absorbed by the canopy (APAR), and the efficiency with which that energy is transformedin above-ground dry matter (radiation use efficiency, RUE). APAR is the product of incoming photosynthetically active radiation (PAR)and the fraction absorbed by the canopy (fPAR). We estimated fPAR as a non-linear function of MODIS normalized difference vegetationindex (NDVI). RUE was empirically estimated for the two principal forage resources of the region, yielding the following relations:ANPP = 0.6 · APAR + 12, (R2 = 0.86; p < 0.001; n = 18) for the upland sown pastures, and ANPP = 0.27 · APAR + 26,(R2 = 0.74; p < 0.001; n = 18) for the lowland naturalized pastures, with ANPP in g/m2/60 days and APAR in MJ/m2/60 days. The modelswere able to predict independent ANPP values with acceptable accuracy. Computational procedures were automated and run in aRelational Data Base Manager System that stored and managed all the information. The system is currently monitoring 212,794 hain 83 farms and provides monthly ANPP values for the previous month and a history of the last 6 years. The data so generated showANPP differences between the two major forage resources, considerable variability of a given month’s ANPP among years and paddocks,and contrasting among-farm differences in the efficiency of conversion of ANPP and forage supplements into beef production.The system was well accepted by end users who utilize it mainly for making near real time decisions according to last month ANPP,and explaining results of previous production cycles by incorporating ANPP as an explicative variable. However, there were differencesamong farmers in the degree of utilization, apparently related to the advisor’s attitude toward this new technology. Our results indicatethat (1) forage production of large extensions can be monthly monitored at the paddock level by a small laboratory with capabilities ingeographic information systems, and (2) advisors and farmers apply this information to their managerial decisions.