It is known that cropping causes soil carbon loss, which is a critical issue, especially in tropical agriculture. Nitrogen input generally increases net primary production but does not increase soil carbon content because nitrogen input enhances soil organic carbon mineralization by microorgan isms. A farmer conducted a trial in which he applied material with a high carbon:nitrogen (C:N) ratio without additional nitrogen fertilizer, and achieved a higher productivity than that of conventional farms. Based on his results, we conducted a survey to evaluate the effects of high C:N ratio organic material on the productivity, soil profile, microbial activity, and carbon and nitrogen balance of soil. Results demonstrate that high C:N ratio organic material enhanced the formation of the soil A horizon and increased soil carbon and nitrogen content. Approximately, 15 - 20 t·ha -1 ·crop -1 of fresh waste mushroom bed was applied to 15 crops over 4.5 years, and the total input of carbon and nitrogen were 5014 and 129 g·m -2 , respectively. The soil nitrate nitrogen concentration was the same as that of the neighboring forest soil, which was lower than the standard limit for conventional agriculture; however, the average productivity of crops was approximately four times that of the national average. The soil Ap horizon increased in thickness by 7 cm, and aggregates reached a thickness of 29 cm in 4.5 years. The output/input ratios of total soil nitrogen and carbon were approximately 2.68 - 6.00 and 1.30 - 2.35, respectively, indicating that this method will maintain the carbon and nitrogen balance of the system. The observed soil microbial activity was one order of magnitude higher than that of a fallow field. The results indicate that this agricultural method remediates soil degradation, and improves food production.
Soil carbon stocks decline by an average of 42% after land is converted from native forest to crops and by 59% after conversion of pasture to crops [
A farmer in Brazil attempted a new farming method, adding only high C:N organic material, and he successfully obtained high productivity from many crops. The soil structure showed clear development of the soil A horizon. In this study, we evaluated the effect of this new method on the productivity, soil profile, microbial activity, and carbon and nitrogen balance of soil.
This study was carried out on a private farm owned by Mr. Tsutomu Nakamura with his cooperation. The farm is located in the city of Suzano, São Paulo, Brazil, which is located in a hilly area of Ultisols. The field had deteriorated after over 40 years of conventional farming. The application of high C:N ratio organic material was initiated in July 2008, and by 2010 was being used on the entire 2-ha farm. The specific method was as follows: (1) the same crop was planted without a break after harvest, so that a crop was always growing; (2) approximately 15 - 20 t∙ha−1∙crop−1 of fresh waste mushroom bed (C:N ratio, 39; moisture, 61.80%; total carbon (T-C), 19.10%; and total nitrogen (T-N), 0.49%) was added to surface soil to a depth of approximately 10 cm using a rotary tiller; (3) no other materials (nitrogen, phosphorus, or potassium fertilizer, minerals, microelements, growth promoters, pH control chemicals, or agricultural chemicals) were used during the study period; (4) commercially available seedlings and seeds were used; (5) weeds were cut with a brush cutter when they began to compete with crops and were left on the fields; and (6) irrigation of crops was not conducted, except under severe drought conditions, during which irrigation was conducted the day before seeding or planting of seedlings and over the following 2 days. The fresh waste mushroom bed was transported directly from a nearby mushroom farm (Sitio TKM, Suzano) and applied immediately. The NO3-N concentration in the both 0 - 10 cm and 70 - 80 cm of soil were 5.6 mg∙kg−1 soil (determined on Dec 12, 2010). That was the same as that of the topsoil (0 - 10 cm) of the neighboring forest. Despite the low nitrogen concentration, no nitrogen deficiency or pests were observed (
We summed the number of each vegetable harvested from 2010 to 2012 from sales records and multiplied each number by the item’s standard weight. Records of each crop’s area were not available; therefore, the conventional yield of the farm was calculated by weight using the top five items produced on the study field: lettuce (46%), cabbage (23%), napa cabbage (7%), radish (5%), and cauliflower (4%). We converted the weight percentage to an area percentage, then multiplied this by the average yields. The average annual yields per ha for these crops are 21, 32, 32, 29, and 14 t, respectively [
We selected a top point of the study field (SF) for the soil survey, which had no water or soil inflow from the surrounding area. In the soil survey plot, lettuce (12 crops) and cabbage (2 crops) were planted from July 2008, and butter cabbages planted on April 9, 2012 were growing at the time of survey (Nov 19, 2012). We chose a neighboring farmer’s field as the control field (CF). The CF was located in the same topography and was developed at the same time as the Japanese farmers’ colony and implemented almost the same agricultural methods for approximately 40 years. In the CF, cassava was harvested in January 2012, and corn was grown after the addition of waste mushroom bed without fertilizer and harvested in July 2012. The CF was then kept fallow.
Soil profiles were described according to the Handbook of Soil Survey (Japanese Society of Pedology, 1997). We collected wet soil samples from each soil horizon and sieved them to 2 mm. We took two sets of 20-mL samples: one was used for the determination of free adenosine triphosphate (ATP) and the other for the determination of moisture, and carbon and nitrogen content.
We decided to evaluate microbial activity rather than microbial biomass; we therefore measured free ATP, which is a measure of microbial activity. Soil samples selected by soil profiling were analyzed within 30 min. We placed samples in cups, added 50 mL of water, and stirred for 1 min with vibration (Power Masher, Nippi Inc, Tokyo, Japan). We then added 6 mL of the surface water to a sample tube and centrifuged it at 6500 rpm (2200 × g) for 1 min. We then placed 100 μL of the solution using an autopipette into ATP Water Test Devices (Aquasnap AQ100F, Hygiena International, Camarillo, CA, USA). We measured the ATP with a luminometer (SystemSURE Plus, Hygiena International) 20 s after mixing in luciferase. The amount of free ATP was calculated using the weight and soil moisture of a paired sample.
Paired soil samples were air dried. T-N and T-C concentrations of the soil samples were determined with a NC analyzer (SUMI-GRAPH NC 200F, Sumitomo Chemical, Tokyo, Japan) using the dry combustion method. The removal of nitrogen and carbon by harvested products was estimated by the average data for unit area [
The T-C and T-N balance was estimated for lower and upper limits. The lower limit was calculated from the difference between the SF and CF over the entire soil profile; this was used as the lower limit because the CF had already received one input of waste mushroom bed, and the fallow period restores soil fertility [
Thirty-three crop items were sold in the last 2 years, including leafy, fruit, and root vegetables. Lettuce and cabbage accounted for 46% and 23% of the total weight, respectively. The total annual average yield from 2010 to 2012 was 56.5 t∙ha−1, which was higher than the estimated conventional yield (13.0 t∙ha−1).
The structure of the soil showed that aggregates of up to 29 cm formed in soil at the SF (
The above differences between the two fields are related to differences in the soil carbon and nitrogen concentrations. In horizons Ap1 and Ap2, the concentrations of T-C were 76.6 (mg∙g−1 soil) and 54.1 in the SF, and
Soil horizon | Thickness (cm) | Bulk density Mg∙m−3 | Concentration (mg∙g−1 soil) | Amount (g∙m−2) | C/N | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
T-C | T-N | T-C | T-N | |||||||||||||
SF | CF | SF | CF | SF | CF | SF | CF | SF | CF | SF | CF | SF | CF | SF | CF | |
Horizon1 | Ap1 | Ap1 | 15 | 9 | 0.68 | 0.90 | 76.6 | 27.2 | 4.66 | 2.05 | 7812 | 1665 | 475 | 166 | 16.4 | 13.3 |
Horizon2 | Ap2 | Ap2 | 14 | 13 | 0.84 | 0.95 | 54.1 | 27.1 | 3.52 | 1.99 | 6357 | 2962 | 413 | 246 | 15.4 | 13.6 |
Horizon3 | AB | A | 12 | 12 | 0.94 | 0.97 | 21.0 | 22.1 | 1.42 | 1.51 | 2357 | 2480 | 159 | 175 | 14.8 | 14.7 |
Horizon4 | Bw1 | Bw1 | 13 | 16 | 1.03 | 0.99 | 14.3 | 18.6 | 0.83 | 1.13 | 1919 | 3070 | 111 | 179 | 17.3 | 16.5 |
Horizon5 | Bw2 | Bw2 | 26 | 22 | 1.00 | 0.92 | 13.0 | 15.6 | 0.63 | 0.82 | 3354 | 3409 | 162 | 166 | 20.7 | 19.0 |
Horizon6 | Bw3 | Bw3 | 20 | 28 | 0.96 | 0.85 | 12.2 | 15.0 | 0.53 | 0.61 | 2337 | 4029 | 102 | 145 | 23.0 | 24.6 |
Total | ― | ― | 100 | 100 | ― | ― | ― | ― | ― | ― | 24,135 | 17,616 | 1422 | 1077 | ― | ― |
SF-CF | 6520 | 345 |
SF: study field. CF: control field. Bw1: Bw1 horizon of study field. The SF was provided with approximately 15 - 20 t∙ha−1∙crop−1 of waste mushroom bed over 15 applications from Jul 2008 to Nov 2012. The CF was left fallow after corn harvest in July 2012. The differences in soil structure were mainly observed between horizons 1 and 2.
27.2 and 27.1 in the CF, respectively. The concentrations of T-N of horizons Ap1 and Ap2 were 4.66 and 3.52 in the SF, and 2.05 and 1.99 in the CF, respectively. In both fields, concentrations of T-C and T-N in horizon 3 were 21.0 - 22.1 and 1.42 - 1.51, respectively, which are much lower than the concentrations in the upper horizons. The C:N ratios of horizons 1 to 3 were 16.4, 15.4, and 14.8 at the SF and 13.3, 13.6, and 14.7 at the CF, respectively. The soil C:N ratio at the CF increased monotonically from the top to the bottom horizons. However, the C:N ratio at the SF dropped at horizon 3, and the C:N ratio of the remaining horizons were the same as those of corresponding horizons at the CF (
Overall, the bulk densities of soil horizons 3 and below were similar, while the differences in soil structure were mainly observed between horizons 1 and 2.
The microbial activity of soil at the SF was one order of magnitude higher than that of soil at the CF. At the SF,
Horizon | All horizons | Top three horizons | ||||||
---|---|---|---|---|---|---|---|---|
Property | T-C (g∙m−2) | T-N (g∙m−2) | T-C (g∙m−2) | T-N (g∙m−2) | ||||
Base | CF | Bw1 | CF | Bw1 | CF | Bw1 | CF | Bw1 |
Original | 17,616 | 13,137 | 1077 | 761 | 7107 | 4756 | 587 | 275 |
SF Present | 24,135 | 24,135 | 1422 | 1422 | 16,525 | 16,525 | 1047 | 1047 |
Output | 6520 | 10,999 | 345 | 661 | 9418 | 11,769 | 461 | 772 |
In Products | 856 | 856 | 79 | 79 | 856 | 856 | 79 | 79 |
Net output | 7375 | 11,854 | 424 | 740 | 10,274 | 12,625 | 540 | 851 |
Input | 5014 | 5014 | 129 | 129 | 5014 | 5014 | 129 | 129 |
Net output/input | 1.47 | 2.36 | 3.30 | 5.76 | 2.05 | 2.52 | 4.20 | 6.62 |
Output/input | 1.30 | 2.19 | 2.68 | 5.14 | 1.88 | 2.35 | 3.58 | 6.00 |
CF: control field. Bw1: Bw1 horizon of study field. The T-C and T-N balance was estimated for lower limit (CF base) and upper limits (Bw1 base). “SF Present” denotes the present value from the study field. “Output” denotes the difference between the SF present levels and the original levels. “Input” denotes the total amount of waste mushroom bed. The output/input ratio of soil total nitrogen and carbon were estimated to be 2.68 - 6.00 and 1.30 - 2.35, respectively. Results indicate that this agricultural method allows for the maintenance of soil carbon and nitrogen.
ATP was high in the topsoil from horizons 1 to 4 (0.346, 0.125, 0.012, and 0.015 nmol∙g∙soil−1, respectively) and the total thickness of those horizons was 54 cm (
The T-C concentration at the SF was 24,135 g∙C∙m−2, which was 6520 g higher than that at the CF over the entire soil profile (
The productivity of the SF was four times that of the national average; nevertheless, organic farming rarely exceeds conventional farming in yield levels [
The defining characteristic of the soil A horizon is typically the value of the bulk density. The bulk density and C:N ratio of soil horizons 3 and below were similar. Differences in soil structure were mainly observed between
Content | Amount | |||||
---|---|---|---|---|---|---|
(nmol∙g−1 soil) | (mg∙m−2) | |||||
SF | CF | SF/CF | SF | CF | SF/CF | |
Horizon1 | 0.346 | 0.029 | 11.9 | 35.3 | 2.3 | 15.0 |
Horizon2 | 0.125 | 0.052 | 2.4 | 14.7 | 6.4 | 2.3 |
Horizon3 | 0.012 | 0.017 | 0.7 | 1.3 | 2.0 | 0.7 |
Horizon4 | 0.015 | 0.003 | 4.4 | 2.1 | 0.5 | 3.7 |
Horizon5 | 0.002 | 0.002 | 0.8 | 0.5 | 0.5 | 1.0 |
Horizon6 | 0.002 | 0.001 | 2.4 | 0.3 | 0.2 | 1.9 |
Total | 0.502 | 0.104 | 4.8 | 54.2 | 11.9 | 4.6 |
SF: study field. CF: control field. Horizon: refer to
horizons 1 and 2. In general, agricultural activities influence carbon stock to a depth of 0.3 m in the profile in savanna systems [
The rate of formation of the soil A horizon described above is extraordinarily fast. The increase in soil was estimated to range from 9418 to 11,769 g∙C∙m−2 in response to the application of 5014 g C by waste mushroom bed over 4.5 years. The average annual increase was 2093 - 2615 g∙C∙m−2∙year−1. Soil carbon was shown to increase in natural forests by approximately 0.2 - 12.0 g∙C∙m−2∙year−1 globally and by 2.3 - 2.5 g∙C∙m−2∙year−1 in a tropical forest [
The increase in soil nitrogen was estimated to range from 461 to 772 g∙N∙m−2 in response to the application of 129 g N by waste mushroom bed over 4.5 years. Including 79 g N that was removed from the system in the form of harvested material, the soil nitrogen increase was 91 - 160 g∙N∙m−2∙g∙year−1. We topographically surveyed the top point of the field, which had no water or soil inflow from the surrounding area. Therefore, the increase in N is considered to be due to biological nitrogen fixation. This value was one order of magnitude higher than the average increase in soil nitrogen of legume crops (5 - 33 g∙N∙m−2∙year−1) [
With respect to sustainability, the SF required an input of approximately 1000 g T-C m−2∙year−1; however, the high productivity of SF provides considerable carbon to the soil. The current O:I ratio of carbon is greater than 1, meaning that the SF crops are sustainable without external carbon inputs. The current O:I ratio of nitrogen is also greater than 1.
As indicated by the results of this study, productivity increased four-fold, the thickness of the soil A horizon increase by 7 cm, and soil carbon and nitrogen accumulation were 2093 - 2615 and 91 - 160 g∙N∙m−2∙g∙year−1, respectively, over the 4.5-year study period; these are rarely observed phenomena in commercial based tropical agriculture. A similar phenomenon was observed in a method using chopped forest biomass led to carbon accumulation (1160 g∙C∙m−2∙yr−1) over a 1.5-year period following deforestation, but the effect was no longer detectable after 3 years [
1. We conducted a survey on a farm adding only high C:N ratio organic material under practical, commercial based farm management conditions.
2. The application of this material resulted in an increase in productivity, equivalent to approximately four times that of the national average in a 2-ha vegetable field. Irrigation was not needed even when the drought period exceeded 65 days.
3. Soil NO3-N concentration of the study field was 5.6 mg∙kg−1 soil, which was lower than the standard limit for conventional agriculture (20 mg∙kg−1); however, crop growth was vigorous and nitrogen deficiency was not observed.
4. The soil Ap horizon increased in thickness by 7 cm and the aggregates formed a thickness of up to 29 cm over 4.5 years. The amount of water that the soil pores can absorb is approximately 80 mm of rainfall.
5. The O:I ratio of soil T-N and T-C were estimated to be 2.68 - 6.00 and 1.30 - 2.35, respectively. This means that this agricultural method allows for the maintenance of the soil carbon and nitrogen balance.
6. The soil microbial activity was one order of magnitude higher than that in a control field.
7. We found that using only high C:N ratio organic material (without additional nitrogen) drastically enhanced the formation of the soil A horizon and increased the soil carbon and nitrogen content under practical, commercial based farm management conditions.
The authors thank T. Nakamura and M. Nakamura for conducting the field experiment. We thank H. Mine, I. Nakamura, A. Fukushima, K. Toriyama, S. A. Ephraim, and J. S. Caldwell for discussion and their advice. We thank S. Nakamura and M. Yonemura for assisting in soil analysis. The authors would like to thank Edanz (http://www.edanzediting.co.jp/) for the English language review.