Innovation with Lagoon Sediments for Soil Conservation and Sustainable Intensification in the Ecuadorian Andes ^†

Abstract

Agricultural production outlines the constant antagonism between the quest to achieve the highest yields and the need to preserve the physical/chemical properties of soils. The constantly increasing global demand for food prompts producers to apply more agrochemicals in order to increase their production, generating soil degradation, which is a costly and complex issue to solve. Based on this context, we targeted a variety of objectives such as (a) to evaluate the effectiveness of lagoon sediments in soil recovery; (b) to analyze the effect of sediment on the yield of the coriander crop; and (c) to determine soil reclamation costs. The experiment was developed in the province of Imbabura, located in northern Ecuador. For this, we occupied a surface area per plot of 3 m² and used a completely randomized block experimental design. Four doses of sediment were applied, being mixed with soil. The benefits of the use of lagoon sediments are evidenced in the nutritional quality of the soil after its application, determined by the physical and chemical analysis that reveals an increase of 3.9 ppm of the initial N, even after vegetative consumption. Similarly, the best electric conductivity (E.C) was 0.85 mS/cm, which promoted a higher crop yield compared to the control treatment, becoming an innovative alternative for soil recovery. This activity allowed reconciliation of the intensive agriculture with soil conservation.

1. Introduction

The inadequate management of the soil as a direct consequence of anthropic use results in its deterioration, based on the responsibility of agriculture, forestry and livestock [1]. Due to the use of agrochemicals, the excessive use of agricultural machinery, the empirical application of synthetic fertilizers, and above all, the agronomic ignorance of the crops, cause constant physical, chemical and microbiological degradation in the soil. In Ecuador, it constitutes the greatest environmental problem, since 48% of the surface of the national territory presents soil erosion [2]. The cause of this reality is that several crops, including coriander, due to its constant, rapid and high consumption of nutrients from the soil, is considered a deterioration of the soil, making it ideal for current research [3].

Therefore, the use of lacustrine material from the Colta lagoon in the province of Chimborazo is proposed as an alternative organic fertilizer, which does not act negatively on the rhizosphere and allows agro-environmentally clean agriculture to be sustained. Through the agro-industrial processes to which the sediment is subjected, heavy metals and pathogens are eliminated, allowing their application in deteriorated soils. This enables the improvement of nutritional quality and soil structure, and the promotion of sustainable agriculture [4].

2. Materials and Methods

The present research was conducted in the La Victoria sector of the city of Ibarra, in northern Ecuador, at 2100 m above sea level, in a sandy loam type soil and a predominantly semi-deciduous forest, within a shrub ecosystem in the north of the valleys (Figure 1).

The condition of the soil was determined through the initial physical–chemical analysis of the soil, in order to determine macro and micro nutrients, organic matter, electrical conductivity and soil pH. The samples were taken in a diagonal pattern in relation to the study area [5]. The study factor of the research is the compost (fertilizer), based on dredged sediments from the Colta lagoon, which were applied in five different treatments (

Table 1. Percentage of treatments applied during the current study.

Code	Compost (%)	Characteristics
T1	100	100% of the compost and 0% of the soil
T2	75	75% of the compost and 25% of the soil
T3	50	50% of the compost and 50% of the soil
T4	25	25% of the compost and 75% of the soil
T5	0	0% of the compost and 100% of the soil (core)

).

The most adequate dosage of compost in the crops promotes the ideal development of the crop. Therefore, based on the recommendation to apply 50% of fertilizer to crops suggested by [6], this amount is considered, along with the alternative of administering doses with 25% less than the starting point, as well as doses with 75% and 100% fertilizer.

The research is based on the statistical model of completely random block design (CRBD), consisting of 15 experimental units distributed in four treatments with a control, and three repetitions of each treatment. Each experimental unit presented an area of 3.00 m² with 3 m in length and 1 m in width.

Evaluation of Phenological Variables

Days to germination and days to harvest: This variable was determined based on the visualization of emerging plants, from their sowing, until the moment when 90% of germinated plants are observed in each experimental unit [7]. On the other hand, the days to harvest were established based on the recommended phenological characteristics, such as leaves with intense green coloration and an average height of 0.44 m [8,9,10].

Stem height: In order to determine this variable, a vernier and a tape measure were required, which allows the measurement from the root neck to the end of the main stem. Hereby, data collection was conducted from day 20 of the crop every 10 days, until 70 days. The choice of plants to be registered was chosen by means of the elimination criterion by edge effect [8].

Crop yield: This variable was determined by means of an analytical balance in which the mass of each experimental unit was recorded, to later determine the number of bundles for each unit, and finally extrapolate them to a production per hectare [9].

Soil evaluation: In order to determine the quality and state of the soil, the pre-sowing physical–chemical analyses were compared with the post-harvest soil analyses. This allowed observation of the effects of the fertilizer at the beginning and at the end of the investigation [11].

Economic analysis: Based on the International Corn and Wheat Center (CIMMYT) [12], the economic analysis was performed, considering the cost of inputs [3], in order to determine the cost of soil recovery with each treatment.

3. Results and Discussion

3.1. Days to Germination and Days to Harvest

The percentage of compost present in treatment T4 (25% compost and 75% soil), and treatment T1 (100% compost and 0% soil), allowed the seeds to germinate in 11 days (on average) (

Table 2. Average days of germination and Tukey test at 5%.

Code	Compost (%)	Average (Days)	Range
T4	25	11	A
T1	100	11	A
T5	0	13	AB
T2	75	13	AB
T3	50	15	B

). This reaffirmed that the use of sediments promotes a prompt emergence thanks to the structural improvement of the soil required in this stage [6,13]. Similarly, the sediment as compost allowed the harvest time to improve (57 days avg.) with the T3 treatment (50% compost and 50% soil), due to the nutritional value provided by the compost [8,10] (

Table 3. Average days to harvest and 5% Tukey test.

Code	Compost (%)	Average (Days)	Range
T3	50	57	A
T4	25	62	AB
T2	75	71	B
T5	0	73	BC
T1	100	76	C

).

3.2. Stem Height

The results obtained by the T3 treatments (50% compost and 50% soil) reflect the highest height obtained at 70 days, with 51.47 cm (avg.), exceeding its average height [9,10] (

Table 4. Average stem height and Tukey’s test at 5%.

Code	Compost (%)	Height						Range
		Day 20 (cm)	Day 30 (cm)	Day 40 (cm)	Day 50 (cm)	Day 60 (cm)	Day 70 (cm)
T3	50	7.70	8.66	19.12	32.51	46.79	51.47	A
T4	25	9.05	10.06	16.95	28.81	43.21	47.53	AB
T2	75	7.09	7.85	15.24	25.90	38.86	42.75	AB
T5	0	6.70	7.40	13.92	23.67	35.50	39.05	B
T1	100	7.00	7.70	14.06	23.90	33.99	37.39	B

). This is in agreement that the addition of 50% sediment-based compost promotes growth, thanks to the provision of nutrients for the plant in the development stage [6,11].

3.3. Yield

In

Table 5. Average yield and Tukey test at 5%.

Code	Compost (%)	Average Yield (g Plant−1)	Range
T3	50	156.94	A
T4	25	145.12	AB
T2	75	130.28	B
T1	100	113.73	BC
T5	0	96.25	C

, it was observed that the T3 treatment (50% of compost and 50% of soil), was characterized as the best, since it reached 156.94 g per plant (avg.), which, when extrapolating towards a production in 1 ha with 200,000 plants, the average and adjusted yield are of about 31,388 kg ha⁻¹ and 23,541 kg ha⁻¹, respectively. This allows 79,800 bundles of 295 g each to be obtained in a production equivalent to 1 ha. Coinciding with the sediment-based compost, due to its nutritional load [14] and structural improvement in the soil, it concedes the best development of the plants [15], increasing their yield [16,17].

3.4. Soil Evaluation

Treatment T1 (100% compost and 0% soil) presented the best results, as it demonstrated less nutritional wear after harvest. Treatments T2 (75% compost and 25% soil), T3 (50% compost and 50% soil) and T4 (25% compost and 75% soil), similarly presented good results, with wear balanced nutritional at the end of the study (

Table 6. Physical–chemical analysis of the soil prior to sowing.

Code	N	P	K	Ca	Mg	S	Fe	B	Zn	Cu	Mn	E.C. 1 mS cm−1	pH	M.O. (%)
	(mg kg−1)		(meq 100 mL−1)			(mg kg−1)
T1	57.92	28.2	1.64	60.58	7.83	132.67	155.28	0.35	2.86	13.57	31.51	1.61	7.42	7.43
T2	70.15	32.3	1.21	49.19	6.95	119.22	105.51	0.25	3.7	8.62	26.32	1	7.45	5.98
T3	23.41	32.24	1.09	46.68	7.19	79.8	103.08	0.31	3.68	7.06	15.56	1.15	7.48	5.54
T4	14.71	46.97	0.87	41.76	5.97	40.13	135.82	0.33	12.6	10.23	41.41	0.92	7.34	3.19
T5	48.06	43.28	0.66	41.23	5.25	19.16	121.79	0.85	3.86	11.83	27.04	0.44	7.22	2.53

¹ Electric conductivity (E.C.) = Ability of the soil to conduct electrical current and take advantage of salts through this conduction [20].

and

Table 7. Post-harvest soil physical–chemical analysis.

Code	N	P	K	Ca	Mg	S	Fe	B	Zn	Cu	Mn	E.C. mS cm−1	pH	M.O. (%)
	(mg kg−1)		(meq 100 mL−1)			(mg kg−1)
T1	37.3	35.27	0.83	17.3	6.1	42.65	163.51	0.25	2.61	7.93	38.0	0.75	7.43	6.97
T2	34.7	42.03	0.83	15.9	5.66	22.03	117.07	0.34	5.45	9.67	35.3	0.71	7.39	5.07
T3	27.3	47.81	0.8	12.9	5.81	12.79	155.58	0.26	6.97	10.7	29.2	0.85	7.32	3.83
T4	41	58.1	0.72	11.4	5.05	27.48	173.8	0.25	5.31	7.53	39	0.74	7.3	3.77
T5	26	35.43	0.59	8.43	3.81	9.71	166.18	0.41	4.92	7.85	31.7	0.38	7.17	2.05

). Nutritional stability and positive structural modification were verified [15], stabilizing the sandy loam soil to loamy soil [18], allowing greater retention of moisture and oxygenation of the soil [11,19], balancing the EC at 0.85 mS cm⁻¹ [20], and also at the end of the study.

3.5. Economic Analysis

The benefit/cost ratio has an index greater than one (B C⁻¹ > 1), in each of the results. On the other hand, treatment T4 (25% compost and 75% soil) presented higher profitability, with a value of $3.38, which reflects that for each monetary unit that is invested, the investment is recovered and a profit of $2.38 is realized (

Table 8. Economic analysis of the research.

	Code
	T1	T2	T3	T4	T5
Average yield (kg ha−1)	22,746	26,056	31,388	29,024	23,890
Adjusted yield (kg ha−1)	17,059.5	19,542	23,541	21,768	14,437.5
Price ($ stranded of 295 g−1)	0.25	0.25	0.25	0.25	0.25
Gross profit from the field (S ha−1)	14,457.2	16,561	19,950	18,447.46	12,235.1
Compost cost ($/ha/ciclo)	6388.67	4791.89	3192.00	1596.78	0
Production cost ($ ha−1)	3866.63	3866.63	3866.63	3866.63	3866.63
Net profit ($ ha−1)	4201.90	7902.50	12,891.37	12,984.05	8368.54
Benefit/Cost (B C−1)	1.41	1.91	2.83	3.38	3.16

). However, the T3 treatment at the end of the study adheres to the main objective of the research, improving the characteristics of the soil and production. Therefore, it would be considered the best treatment at the end of the study.