PRECISION AGRICULTURE INITIATIVE FOR TEXAS HIGH PLAINS

2001 ANNUAL COMPREHENSIVE REPORT

Texas Agricultural Experiment Station and Texas Cooperative Extension

Reporting Period:  January 1, 2001 – December 31, 2001

A.     Summary of Progress:

Objective 1—Rhizobium nodule counts per peanut plant were obtained in August at research sites in Gaines and Terry Co.  We noted the inconsistency among plants at each grid point as 3 or 4 plants among 12 at each measurement point may have 1 or less nodules, whereas the other plants would be well nodulated.  This points out that either producer practices or microenvironment may have a large influence nodulation.  Nodulation did correlate with peanut yield at both sites, r = 0.49-0.55, but neither nodulation nor hand-harvested yield correlated with the precision ag. combine yield maps in Gaines Co.  This suggests that relying on the precision ag. combine to evaluate yield at specific points in the field may be inappropriate, rather yield-mapping results are better suited for ‘whole-field’ averages, which is more in keeping with the intent of precision agriculture tools. 

      In general, only low correlations were obtained in Gaines Co. between the degree of nodulation and soil properties.  Most notably, however, is that the degree of nodulation was negatively correlated with pH (r = -0.29), soil Ca (indicative of high pH conditions in a caliche soil, r = -0.31), and soil nitrate (the presence of larger amounts would more likely hinder nodulation of peanuts by Rhizobium, r = -0.25).  Rhizobium is expected to be lower in the condition of higher pH, caliche, and high soil N.  Other factors such as soil K, Mn, salts, etc. were only minimally correlated with peanut plant Rhizobium number if at all. Similar results were obtained in Terry Co.

      In general, overall we believe it is proving difficult to demonstrate Rhizobium nodulation influenced by soil parameters when the scale of soil properties is in the range of 10-20’.  This is in part due to the high variation in nodule number of individual plants.  Thus it appears that the micro-environment is even more important, and further testing will focus on evaluating soil properties in relation to peanut nodulation on a scale of a few feet or even inches.  This does not lend itself to precision ag. technologies, but elucidating any effects will help ascertain if PA technologies are suitable for Rhizobium application and management.

Objective 2—In contrast to the generally negative correlations noted above, low but positive correlations were measured in Gaines Co. between Rhizobium numbers per plant and leaf N (r= 0.25) and spad meter readings (r = 0.40).  The use of the chlorophyll meter as an index of peanut N status (or aerial hyperspectral measures) may prove to be the quick way for farmers to gauge N needs in the plant rather than rely on soil or plant tissue testing.  Because nodulation correlations with leaf N and spad readings were low, little to no correlation was found with any ground-level spectral reflectance measure.  Although the ground level spectral reflectance measures may be useful, the labor intensity required to obtain these readings would not be favorable compared to the possible use of the hyperspectral reflectance techniques other members of the High Plains PA team are using from low-flying aircraft.

Objective 3—Because the correlations are low the ability to pin down economic return to the degree of nodulation are inconclusive.  Other work in terms of Rhizobium rates and yield on small plots have demonstrated that inoculation alone pays in the range of $68 to $187 per acre, but the PA approach to this point raises further questions about how factors such as pH, caliche, soil Ca may be more accurate—or direct—predictors of economic return in a individual field vs. measuring the degree of nodulation.  Rhizobium inoculation is assumed on West Texas peanut fields, but nodulation of the peanut plant is not.  The ongoing project must narrow the focus on soil properties and their influence on nodulation to a shorter scale and attempt to relate how those properties, most likely only if they have a moderate to high degree of variability over a field, can be used to effect site-specific management of Rhizobium or other soil properties for increased economic peanut production in West Texas.

 

B.     Education/technology transfer: Conventional non-PA work on Rhizobium in peanuts has caught the attention of producers in that many have assumed effective nodulation, but it is absent in many cases.  Year 2001 work in Gaines Co. demonstrated at three sites, variable in soil properties and yield potential, that farmers can expect 400 to 1000 lbs./A peanut yield increase when fields are inoculated with Rhizobium.  But also of equal interest is that yield response to Nitrogen is also present in similar magnitude.  We have also observed that poor placement of early season N around the row greatly decreases nodulation.  The PA project enables the collection of a greater degree of chemical and environmental information around the plants.  Peanut Rhizobium and nodulation was discussed in six field tours and four spring or fall crop meetings.  Extension guidelines have been written noting correct handling and common mistakes of handling and applying Rhizobium inoculants to peanuts in West Texas.

C.     Milestones achieved:  More questions have been generated about the relationship of Rhizobium nodulation to peanut yield.  At this point, we believe that soil properties have a greater effect on Rhizobium nodulation than first thought else we would see higher correlation between nodule number and activity in peanut vs. yield.

D.    Publications: (Provide complete references)

E.        Precision agriculture proposals: No new proposals submitted in 2001.

F.      Precision Agriculture meetings attended/papers (posters) presented:  None.

G.     Other developments: