Dairy manure was composted with cotton gin byproduct (CGB) at a ratio of three parts dairy manure to two parts CGB using standard composting procedures. At six months the matured compost was sent to an analytical laboratory for standard analysis. Prior to compost application on bermudagrass, the grass leaves were analyzed for nutrient content. In August 2011 the grass was cut and bales were counted and weighed. Later in August 2011 the compost was applied at three different rates. The bermudagrass was sampled again six weeks later for nutrient content. Bales once again were weighed and counted.
Unfortunate limiting impacts of the 2011-2012 drought and a resulting drop in the well’s static level created an unavoidable limiting factor which prevented a fully successful outcome.
Due to water limitations, overall grass production decreased 16% in the composted fields compared to pre-compost production. Nitrogen content of the compost alone was insufficient to grow the bermudagrass; however, the compost did appear to positively impact zinc, iron, manganese and possibly copper within bermudagrass tissue.
Over the period of the study, another impact of the drought became apparent. Whereas the cost of CGB in early 2011 was $17/ton, by the beginning of 2012 the cost had increased to $64/ton, since the CGB was now being avidly bought by the dairies to feed dry cows in place of other more expensive feeds.
The increased cost of CGB made its use in composting economically impractical. Despite this, CGB might yet provide a useful carbon and nutrient source for compounding in the future. It cannot adequately supply nitrogen, however.
My farm is located in the Chihuahua Desert, about 15 miles across the Franklin Mountains from large dairy and cotton producers in the lower Rio Grande Valley of Dona Ana County, New Mexico. Because the major soil deficiency I encounter is the lack of organic material, I proposed to transport dairy manure and CGB to my farm, compost it to maturity and apply it at three different rates to my bermudagrass pastures. I would use identical and uniform nitrogen and water applications, varying only the rates of compost. Compost nutrient content and baseline bermudagrass tissue content would be determined and baseline weights and bale number measured before compost application. The same values would be repeated after compost application. The goals were to determine if this compost improved bermudagrass production and was economically feasible.
1. Determine if compost from dairy manure and CGB can provide adequate nitrogen for bermudagrass production
2. Determine if the compost can provide sufficient other nutrients for bermudagrass production
3. Compare the production and nutrient content of bermudagrass before and after compost application at three different rates.
Dairy manure was composted with CGB at a ratio of three parts manure to two parts CGB. Piles were monitored for temperature and moisture and brought to maturation at six months. Compost samples were sent for analysis, including organic-N, inorganic-N, phosporous, potassium, sulfur, calcium, magnesium, sodium, zinc, iron, manganese, copper, soluble salts, pH and dry matter content (Table 1). Prior to application of compost to a bermudagrass hay field, the leaves were sampled for nutrient content. Bermudagrass was mowed August 19, 2011. The bales of grass were weighed and counted from each of four passes where the compost would be applied. The compost was applied in late August 2011 at three rates (8.2, 17.4 and 24.7 T/ac). Plots were identically fertilized with urea (92 lb N/ac.) and irrigated. Severe drought occurred, and a concomitant drop of the water table caused the well to run dry, thus limiting potential grass growth and optimal results of this project.
Prior to composting, the grass averaged 12 bales (+/- 4) per pass, weighing 52 (+/- 2) lb/bale. Total average grass collected from treated areas averaged 631 (+/- 248) lb/ac. Grass yield was 16% less (530 lb/pass) across all treatment in 2012. This was likely the result of the ongoing drought and failure of the irrigating well. This illustrates the Law of the Minimum where water became the most limiting factor of crop production in 2012 and would have masked any benefits from the application of compost. Compost application did not change N conc. six weeks after application. It did seem to affect Zn, Fe, Mg and Cu conc. six weeks after application, especially at the high compost application rate. The Fe conc. in the composted CGB was over 6000 ppm. This may have implications towards mineral supplements depending on livestock and feeding rates.
Educational & Outreach Activities
Although the project originally proposed a field day, no opportunity arose for such a day. Given the drought, escalated price of CGB and scarcity of farming in the 15 miles around my farm, I concluded that such a field day would be poorly attended.
The decreased overall productivity of bermudagrass (down 16% from 2011), and the somewhat marginally increased nutrient improvements, suggested to me that factsheets and posters would be of little interest.
The project contributed to two major accomplishments:
1. Improved metric skills for assessing productivity and quality
Through many communications with the Technical Advisory, Dr. Robert Flynn, NMSU Ag Extension Service, my workers and I acquired skills in qualitatively assessing crop productivity. We learned a systematic approach to compare pre- and post-application results.
We dealt with the interference created by unexpected variables (the 2011-12 drought) which factored into, but did not, defeat the study’s design and ultimate outcome.
We also gained great skills in composting, building upon the framework we had initially acquired through an earlier Western SARE-funded project.
2. Improved soil and crop quality
Although overall bermudagrass production decreased 16% because of severe water restrictions created by the drought, we have objective evidence that future years’ productivity may be enhanced because of residual nutrients supplied by the compost. The soil also gained valuable organic material from the heavy composting of 2011.
It remains to be seen if CGB compost is economically feasible. Although in 2011 it appeared to be so, by 2012, it did not because of the dramatically higher cost of CGB. That may change over time. I certainly would be keeping my eyes open for another chance to buy CGB at a low price to use as a carbon source for composting.
The soil salts delivered through composting remain low, and it would be possible to re-compost the same fields in the future. Since the bermudagras pastures are used in the winter for sheep grazing, composted CGB without dairy manure (and its inevitable salt-related problems) might be even more applicable.
The study’s results were powerfully, but not fatally, affected by the drought of 2011-12. The benefits of rainfall on cation nutrient root absorption from highly alkaline soils probably prevented fully beneficial effects of the compost. More seriously, the exceptional/extreme drought conditions lowered the static water level in the well used to irrigate the bermudagrass, reducing production by 16% from the baseline. Another unexpected result of the drought was the inflated cost of CGB, since it was now avidly sought by the dairies as a foodstuff for cows. While unfortunate, these drought-related effects suggest that in non-drought years CGB compost might provide a useful non-nitrogen nutrient and soil organic material source for desert farming in the Chihuahua Desert.