Use of Guar (Cyamopsis tetragonolaba (L.) Taub) for cover crop rotation and green manuring

Final Report for OS06-031

Project Type: On-Farm Research
Funds awarded in 2006: $15,000.00
Projected End Date: 12/31/2007
Region: Southern
State: Texas
Principal Investigator:
Dr. Russell Wallace
Texas A&M University AgriLife Extension
Expand All

Project Information

Abstract:

This research project was initiated in March 2006 to investigate the potential for using guar (Cyamopsis tetragonolaba) as a fresh-pick commodity for retail sales, and as a rotation option and green manure crop in small farm production. Guar is drought tolerant and a legume that can potentially supply organic matter and nitrogen to crop soils. In this test, organic matter measured following crop production and soil incorporation did not show a significant increase. Crop biomass was greatest with guar that was harvested three times and then shredded late and incorporated when compared to all other crop production treatments. Fresh-picked pod weights were highest with southern peas, and based on total production and potential sales revenues, peas would have an increased value of over $5,000/acre. However, guar sales were better than expected, especially to of various ethnic communities who were familiar with its use. Organic matter showed no changes during the crop cycle (one year) and soil nitrogen, while it increased during the growing season, was not substantially higher during post-incorporation sampling. Growth of a fall-planted wheat cover crop showed no significant differences in biomass production when harvested in the spring. No rotational crop data was available for the second year of this trial due to misapplication of herbicides in the trial area which resulted in crop death. As a result, a no-cost extension of this research has been requested. Overall, the results of this study do show the potential for using fresh guar pods as an additional sales item for local growers, and this may potential increase farm revenues. Although no significant increase in organic matter and soil nitrogen was observed during the trial period, guar should be a useful rotation crop in semi-arid areas of the southern high plains.

Introduction

Sustainable practices help to maintain farming systems by optimizing management of natural resources. Crops which have multiple uses are an integral part in sustainable farming. Environmental and economic concerns for introducing new multi-use crops into production on the Texas High Plains include crop monoculture, soil erosion, limited water, and fields low in fertility and organic matter. An associated concern is limited income markets for the farmer.

The main crop grown on the Texas High Plains is cotton with an annual production reaching 3.7 million acres with most grown as cotton following cotton. Lack of rotation contributes to disease and insect buildup. The lack of crop rotation with green manure crops also increases soil erosion, leaves low organic matter, poor tilth, and increased salinity in the soil.

Crops grown in monocultures without rotation are usually fertilized with inorganic nutrients. Anhydrous ammonia is a commonly used nitrogen source on the Texas High Plains; however prices of this fertilizer continue to increase significantly. Because cost of inorganic nitrogen fertilizer continues to rise, alternative sources of fertility need to be researched. While adding nutrients to the soil and plants, inorganic fertilizers do not add organic matter to the soil. Amending soils with green manure crops adds organic matter and nutrients to the soil building an improved environment for crop growth. Organic matter improves soil tilth and helps to maintain nutrients in an exchangeable form for plants while also increasing water holding capacity.

Lubbock County and the surrounding area are in a semi-arid region receiving an average annual rainfall of 18 inches. Sandy soils of the High Plains have low water holding capacity and expanding urban areas across the Southwest continue to increase the demand for more available water. With limited water resources it is critical to plant agricultural crops tolerant to drought and that have low water requirements.

The rising costs of fertilizers and other non-renewable resources and the decline in available water (and increased irrigation costs) are several important reasons for decreased income of farmers. The potential success of using drought-tolerant, low input multi-use crops may stabilize income and other stresses by opening alternative markets. Cover crop rotation and green manure crops not only add organic matter, improve soil tilth, increase water holding capacity, and replace lost fertility, they may also potentially maximize profits during uncertain market cycles.

Project Objectives:

The objective of this research was to examine whether guar is suitable as a summer cover crop rotation or green manure, and whether its pods may be saleable for the fresh market. Field trials were conducted to evaluate different ways of managing guar followed by a rotation to summer squash and to analyze soil quality and yield data when compared to southern peas.

Cooperators

Click linked name(s) to expand
  • Amy Jones
  • Ellen Peffley

Research

Materials and methods:

Guar (var. ‘Matador’) and southern peas (var. “California No. 5”) were used for green manure and as rotation crops. Each crop was inoculated according to standard practices. Treatments including the following: (1) guar shredded and incorporated by disking at first pod drying stage; (2) southern peas shredded and incorporated by disking at first pod drying stage; (3) immature guar pods harvested for marketability and then residual plant material shredded and incorporated into soil; (4) immature southern pea pods harvested for marketability and then residual plant material shredded and incorporated into soil; and (5) a fallow control.

Test plots were located on Sunburst Farms in south Lubbock County as well as at a second location at Texas Tech University (Lubbock). Standard cropping and management practices were followed. Guar and southern peas were incorporated when the first set pod is mature. Soil organic matter and nitrogen content were indicators of the suitability of guar as a rotational crop and green manure. Soils within treatments were sampled for pH, nitrogen and organic matter prior to planting (May), during crop growth (July), and following harvest (September). Plants from one square meter quadrats from each replicated treatment plot were hand cut and collected prior to incorporation to determine crop biomass. During the second season (2007), a follow-up study was conducted by planting summer squash within the individual guar and southern pea treatments, and crop fertility needs and plant growth characteristics (yield and quality) assessed. The trial design in both years was a Completely Randomized Block Design utilizing a 5 x 5 Latin square, and data was analyzed using SAS Statistical Procedures.

Research results and discussion:

Comparison of treatments between guar and southern pea emergence showed that guar generally had higher numbers of plants per 50’ of row, and that there was a significant difference between several treatments. However, variability was not expected (due to the use of a precision planter) and the results may reflect an influence of individual plot soil characteristics rather than any affect of the seed or germination.

Crop dry-weight biomass, measured from 10 randomly-selected plants per treatment showed that the growth of guar (from the harvested plants and incorporated late treatment) was significantly higher compared to both southern pea treatments (regardless of when it was incorporated); or when guar was shredded early at first pod drying. Guar biomass averaged 0.63 lbs/plant when shredded late, and was 0.32 lbs/plant for southern peas shredded late. When shredded early (at first pod drying) guar biomass was 0.13 lbs/plant while peas weighed 0.25 lbs/plant.

Total pod weight, recorded by picking (3 times) green pods from both peas and guar in the late shredded treatments. The cooperator stated that guar crop “seemed to lack a harvest pattern”, and that the southern peas “were a much more easily harvested crop”, and “pods were released from the plant more easily and harvestable pods were more easily identifiable” when compared to guar pods. Additionally, the grower reported that the “pubescence of the Matador variety caused skin irritation”. There was a significant increase in yield with southern peas (5,097 lbs/A) compared to guar (627 lbs/A). Peas sold at Sunburst Market for $1.50/lb while guar pods sold for $4.00/lb. However, revenue based on cost and pounds of pods/acre showed that southern peas averaged $7,646/acre while guar averaged $2,508/acre for a difference of $5,138 (a considerable sum).

Soil NO3 assessed prior to planting and averaged across both locations showed that there was a mean of 18.7 lbs and 18.8 lbs nitrogen available at the 6” and 18” depths, respectively. By mid-season, nitrogen availability in the soil at the 6’ depth was not significantly different between treatments (guar or southern peas), and was also not different from the fallow treatment. When assessed at the 12” depth during mid-season, plots where guar was harvested and shredded late (allowed to grow longer) had significantly higher nitrogen compared to southern peas that were shredded late. There was a 27% increase in nitrogen for the guar treatment. When comparing both guar treatments to both southern pea treatments, guar averaged 33.9 lbs N/A, while peas averaged 26.4 lbs N/A (an increase of 22%). However, soil nitrogen measured post-harvest showed that levels dropped down to pre-planting levels (19.5 lbs N/A) at the 6” depth and even less at 12” depth (17.3 lbs N/A).

Organic matter measured at both locations ranged from 0.3% to 0.8%, but was too variable to show any differences between treatments. It is likely that organic matter in the soil would not change significantly within one year of cropping systems. However, given that overall plant biomass with the late-shredded and incorporated guar treatments was an average 50% higher compared to southern peas, it is possible that guar biomass may favor crop production in the long term.

In the fall, wheat was planted at the Texas Tech Farm site to assess any effects of the treatments on the growth and biomass of a grain cover crop prior to planting yellow squash. Wheat biomass recorded from 0.25 m2 quadrats showed no differences between crop production treatments. However, there was a trend for wheat biomass to be lower in plots that had either guar or southern peas shredded and incorporated early. In fact, the average wheat biomass was 14% higher in plots that had guar or southern peas shredded late (and incorporated), compared to that which was shredded earlier.

Yellow summer squash was planted into the wheat stubble in May of the second year within each crop production treatment, including the fallow plots. Plants emerged well and there were some noticeable differences in growth between treatments. However, before data could be taken, the majority of the plots were over-sprayed with an herbicide that contained a combination of a growth regulator (dicamba) plus a residual (atrazine) which effectively killed the yellow squash. Attempts were made to replant the squash, but seedlings failed to emerge due to the atrazine carryover. As a result, no data could be taken from the plots in 2007. A no-cost extension was applied for in an attempt to repeat the trial (without taking soil samples) in order to determine the effects on a squash crop.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

The intent of this research was to develop a Master’s Thesis and have it published by the grower/student. However, after the first season of the research, for personal reasons the grower/student did not return to school to continue with classes or to write her thesis. A written report for the project was summarized and published with the following notation: Wallace, R.W., E. Peffley and A.T. Jones. 2006. Use of Guar (Cyamopsis tetragonolaba (L.) Taub. For Cover Crop Rotation and Green Manuring. Texas High Plains Vegetable & Weed Control Research Program: Research Summary Reports. pp. 45-46. Texas AgriLife Extension Service. Publication of this booklet is available online at http://lubbock.tamu.edu/horticulture/. This project was discussed informally at several meetings including Texas Tech University Farm Tour (2006) and at the High Plains Vegetable Conference (January 2007). Additionally, the grower/student discussed the use of fresh-picked guar with local customers as part of her project.

Project Outcomes

Project outcomes:

The results of this trial indicate that picking guar for fresh pod sales is feasible for small farmers interested in offering additional commodities for sale at their markets. According to comments by the grower/cooperator, the majority of sales went to ethnic groups that have a past history with edible guar, and who are familiar in how it’s prepared. This research also showed that guar can be an important source of additional income when harvested and sold fresh. Effects on the soil were not so clear, as soil organic matter did not show changes, and there were very few changes in soil nitrogen. However, less irrigation was needed for guar and pea production than would be needed for other vegetables. The test also demonstrated that guar production can be an important part of crop rotation sequences in farming systems. Unfortunately data on crop growth the year following rotation was unavailable due to accidental over-spray of herbicides and no extrapolation of the data was possible.

Economic Analysis

There was a significant increase in yield with southern peas (5,097 lbs/A) compared to guar (627 lbs/A). According to the grower, fresh-picked guar was sold at the farm store for $4.00/lb, while southern peas were sold for $1.50/lb. Revenues based on price and the number of pounds of pods/acre showed that southern peas averaged $7,646/acre while guar averaged $2,508/acre. This accounts for a difference of $5,138. However, prices for guar produced for seed on the High Plains will typically range lower than $400/acre. A study evaluating the time to hand pick guar pods would have help to indicate the costs of labor involved, but this was not part of the scope of this project.

Farmer Adoption

Currently, the use of guar as a crop is mostly limited to fields following hailed-out cotton. Sunburst Markets has grown a limited supply for their customers (mostly of various ethnic groups), and it was the intent of the South Plains Food Bank Farm to plant several varieties in 2008 as part of their Community Supported Agriculture (CSA) program. That program has over 150 participants, and recipes will be shared. However, there is some interest with edible guar, and more studies are needed to evaluate varieties.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.