1. To Mulch Or Not To Mulch:

2. COMPARING BROCCOLI PRODUCTIVITY IN MULCHED AND UNMULCHED AREAS IN NAZARE PAULISTA

3. Zena Lee Park Center for Environmental Research and Conservation, Columbia University, New York, New York, 10027 U.S.A ZLP1@COLUMBIA.EDU

4. INTRODUCTION Mulch acts as the skin of the soil, a protective layer covering the surface of the soil. Often the mulching technique can eliminate fertilizing, thereby economizing the workload of the gardener. Mulch takes away the sunlight weeds need The existence of mulch lessens water evaporation and adds essential microorganisms and nutrients to the soil. Areas that are mulched sustain balanced and healthy soil. The use of mulch is an important strategy to minimize the risks of soil degradation. Since mulching avoids excess watering, it avoids the passage of nutrients into subsoil. The Natural Resources Conservation Service-United States Department of Agriculture claims mulch does the following: protects the soil from erosion, reduces compaction from the impact of heavy rains, conserves moisture, reduces the need for frequent waterings, maintains a more even soil temperature, prevents weed growth, keeps fruit and vegetables clean. Mulching a garden mimics the natural setting of a forest. Since, in nature, there will always be some kind of organic litter or some type of protection on the ground. For example, leaves fall and then cover the soil, thereby cooling and shielding the soil and root system from rain that might cause soil erosion or hardening. In an unmulched area, sun exposure often kills many of the microorganisms that make the soil healthy. The main objective of this study was to determine if there were any differences between mulched and unmulched areas of broccoli, indicating possible differences in productivity. If so, then whether or not there was any correlation between type of treatment and factors that show broccoli productivity. The question was: Does the existence of mulch increase the productivity of an organic garden? The null hypothesis (H o ) was: The existence of mulch does not effect the productivity of an organic garden. The alternative hypotheses were: The existence of mulch increases the level of productivity in an organic garden (H a ). The existence of mulch decreases productivity (H b ).

5. METHODS Description of Study Area The studied area was an organic garden, privately operated by the Center of Light community, in the Atlantic Rainforest of Nazare Paulista, Sao Paulo State, Brazil. On June 16, 2001, all data was collected. The observed eight broccoli plants were found at the following location, according to the GPS unit used (Trimble GeoExplorer3): 23  11’56.907” S, 46  21’234.408”W, at an altitude of 798.3m. The mulched and the unmulched gardens lay evenly, side by side, in a combined rectangular area of 880cm x 300cm. The mulched garden included African Red Grass (Melinis minutiflora) that lay on top of the soil. Summary of Procedures In order to compare broccoli (Brassica oleracea) productivity in mulched versus unmulched treated areas, the following characteristics were calculated and measured: plant height, plant width, number of stalks on each plant, leaf areas, number of leaves on each plant, and soil temperature taken at the base of each plant. There was only one crop of the same species that had been divided equally between mulched and unmulched treatments, located in the same area, and planted at the same time. This crop of broccoli was three months old at the time of the study. Eight individual broccoli plants were chosen for observation within this half mulched, half unmulched area of broccoli. Four rows were chosen randomly, each row had two broccoli plants—one in the mulched area and one in the unmulched.

6. RESULTS Significant differences were found in two out of the six variables looked at: number of broccoli stalks and the leaf sizes (Table 1). According to the statistical test used (t-test), the two variables gave calculated t values that were greater than the critical t values. This indicated that the null hypothesis should be rejected. The average number of broccoli stalks for the mulched area was much greater than the average number of broccoli stalks for the unmulched area (Figure 1, Table 2). The average leaf size found on each broccoli plant in the mulched area was higher than the average leaf size found on each broccoli plant in the unmulched area (Figure 2, Table 3). As for the other variables, leaf abundance (Figure 3, Table 4), plant height (Figure 4, Table 5), plant width (Figure 5, Table 6), and soil temperature (Figure 6, Table 7), t-tests showed no significant differences.

7. Table 1 Statistical Analysis: t-test

8. Figure 1

9. Plant RowMulchedUnmulched A154 B291 C94 D2110 Mean18.54.75 Variance7314.25 Standard Deviance 8.5440043.77491722 Table 2 Number of Broccoli Stalks

10. Figure 2

11. Leaf Size Results* Table 3 *The three larges leaf areas were taken from each area.

12. Figure 3

13. Plant RowMulchedUnmulched A5523 B5819 C2945 D4651 Mean4734.5 Variance170251.6667 Standard Deviance13.038415.8640 Number of Leaves Results Table 4

14. Figure 4

15. Plant RowMulchedUnmulched A90cm50cm B72cm44cm C67cm52cm D48cm63cm Mean69.25cm52.25cm Variance298.25062.917 Standard Deviance17.2707.932 Broccoli Plant Height Table 5

16. Figure 5

17. Plant RowMulchedUnmulched A58.0cm40.0cm B55.0cm40.0cm C70.0cm63.0cm D59.0cm44.0cm Mean60.5cm46.75cm Variance43.0120.916667 Standard Deviance6.55743910.9962115 Broccoli Plant Width Results Table 6

18. Figure 6

19. Plant RowMulchedUnmulched A18.0C18.4C B 18.5C C18.6C19.0C D18.4C19.0C Mean18.35C18.725C Variance.063333.1025 Standard Deviation.2516611.32015621 Soil Temperature Results Table 7

20. CONCLUSIONS The original hypothesis was that the existence of mulch increases productivity—in this case, of broccoli. Of the six variables tested, two of them rejected the null hypothesis, recognizing a significant difference between the mulched and unmulched areas. The two variables that supported the hypothesis were the number of broccoli stalks and leaf sizes found. But it is important to remember that even with the two variables—number of broccoli stalks and average size of the leaves—that rejected the null hypothesis, there was still a five percent chance that the results were inconclusive. There were several possible reasons (sources of error) that the four other variables did not support my hypothesis: the smallness of the sample sizes used, soil quality was not one of the variables, characteristics of the broccoli stalks found on the plants were not considered, more than one crop in an organic garden that has been divided equally into mulched and unmulched sections, the type of mulch used, amount of mulch, the type of mulch used is dependent on the type of crop, and the time of day and the number of times the temperatures were taken. Studying the soil and the effects of mulch can help gardeners all over the world maximize their productivity. The process of mulching protects the soil from weather, efficiently uses the water and heat, protects the plants and soil from harmful insects, and organic mulching enriches the soil. Such advantages provide a better, healthier growing environment for a vegetable or fruit. Researchers and gardeners should be aware that the way to have a productive garden is to have healthy soil. Since mulch is a protective covering that improves the quality and the condition of the soil, it can only be beneficial for the crop and increase productivity.