Abstract
The Brazilian guava processing industry generates 5.5 M Mg guava waste year−1 that could be recycled sustainably in guava agro-ecosystems as slow-release fertilizer. Our objectives were to elaborate nutrient budgets and to diagnose soil, foliar, and fruit nutrient balances in guava orchards fertilized with guava waste. We hypothesized that (1) guava waste are balanced fertilizer sources that can sustain crop yield and soil nutrient stocks, and (2) guava agroecosystems remain productive within narrow ranges of nutrient balances. A 6-year experiment was conducted in 8-year old guava orchard applying 0–9–18–27–36 Mg ha−1 guava waste (dry mass basis) and the locally recommended mineral fertilization. Nutrient budgets were compiled as balance sheets. Foliar and fruit nutrient balances were computed as isometric log ratios to avoid data redundancy or resonance due to nutrient interactions and the closure to measurement unit. The N, P, and several other nutrients were applied in excess of crop removal while K was in deficit whatever the guava waste treatment. The foliar diagnostic accuracy reached 93% using isometric log ratios and knn classification, generating reliable foliar nutrient and concentration ranges at high yield level. The plant mined the soil K reserves without any significant effect on fruit yield and foliar nutrient balances involving K. High guava productivity can be reached at lower soil test K and P values than thought before. Parsimonious dosage of fresh guava waste should be supplemented with mineral K fertilizers to recycle guava waste sustainably in guava agroecosystems. Brazilian growers can benefit from this research by lowering soil test P and K threshold values to avoid over-fertilization and using fresh guava waste supplemented with mineral fertilizers, especially K. Because yield was negatively correlated with fruit acidity and Brix index, balanced plant nutrition and fertilization diagnosis will have to consider not only fruit yield targets but also fruit quality to meet requirements for guava processing.
Highlights
Guava (Psidium guajava) is a tropical tree grown on Brazilian Oxisols and Ultisols and reaching high productivity 3 years after establishment (Hernandes et al, 2012)
Nutrient budgets except the K were positive across guava waste treatments (Figure 1)
Nutrient use efficiency was increasingly lower for treatments exceeding 9 Mg dry guava waste ha−1
Summary
Guava (Psidium guajava) is a tropical tree grown on Brazilian Oxisols and Ultisols and reaching high productivity 3 years after establishment (Hernandes et al, 2012). Brazil is the world leader in red guava production with 16,000 ha producing 342,000 Mg of fresh fruits annually (IBGE, 2012). The state of São Paulo accounts for 36% of total Brazilian guava production and 55% of the industrially processed production. “Paluma” is the main red guava cultivar (Natale et al, 2009). The typical guava orchard in São Paulo state is 5.6 ha in size. Crop performance for processing is measured in terms of yield, sugar content (“Brix” index) and acidity. Fruit sweetness and acidity may be more influenced by annual climate variations than crop management (Le Bourvellec et al, 2015). Mineral fertilization is required to sustain guava yield and quality (Natale et al, 1995, 1996, 2001)
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