- Nuts: pecans
- Soil Management: organic matter, nutrient mineralization, soil quality/health
Soil organic material (SOM) is very low (0.7-1.4%) in my Chihuahua Desert farm. For this reason, I sought an effective and efficient carbon source to compost with dairy manure from the nearby Mesilla Valley, New Mexico. The Valley is rich in dairies, pecans, chili and cotton. Pecan shells (C:N 143, measured 2008) appeared to be a reasonable carbon source, which might gradually be broken down, slowly releasing its carbon content and forming a slowly decomposing compost. Following pilot studies in 2008, I composted manure:pecan shells (v:v 9:1) for nine months, creating an approximate C:N 30:1 compost. The compost was applied along with control amendments in four groups: untreated, shells alone, manure alone and compost. Seventy nonbearing pistachio trees (cultivar Kerman grafted onto UCB-1 rootstock) were in each group. Each group received identical irrigation, fertilization and pesticide application.
Nine months after application to the trees, we analyzed soil nutrients. Soil results included: (1) modestly increased SOM and CEC, (2) reduced pH in both the manure and compost groups, (3) reduced sodium content in the compost group compared to the manure group, (4) increased iron and manganese content in the shell group (perhaps because of binding by shell lignin and polyphenols), and (5) shells alone or composted had reduced total nitrates compared to untreated or manure alone. This may have resulted from nitrogen (N) immobilization by the composting pecan shell carbon. After 11 months, we analyzed leaf nutrients and observed differences in tree growth. Leaf N content was highest in the compost group, followed by manure, shell and untreated groups. No changes of tree growth or leaf health were observed at 11 months.
We conclude that, at 9-11 months, mulched or composted pecan shells may lead to N immobilization. Increased SOM and CEC and reductions in soil pH and sodium may result from pecan shell composting. As has been previously reported, we demonstrated that pecan shells may bind iron and manganese. Potential deleterious effects of N immobilization may be corrected by nitrogen application during compost production or application, by reducing the C:N ratio or by using other carbon sources. Alternative carbon sources for composting locally available in the Mesilla Valley (e.g. cotton gin by-product) were discussed and will be proposed in my pending Western SARE grant re-application.
1. Improve low SOM content in the soil of desert farms, such as my own.
2. Gain experience and local producer recognition in large scale agricultural composting.
3. Conduct a systematic process to find an effective and efficient carbon source in the nearby Mesilla Valley, NM for future composting.
4. Measure the effects of manure:pecan shell composting on pistachio tree growth and nutrition.
5. Modify compost composition in future studies and Western SARE grant proposals.