A common practice of chlorophyll (chl) determination has been using the chemical analysis that is destructive and time-consuming. A current prospective alternative method such hyperspectral remote sensing offers a non-destructive measurement of chl which provides a result in the rapid and real-time manner. Therefore, the ultimate aims of this study were to propose the chls (chl a, chl b, total chl content (TCC) and relative chl content (RCC)) sufficiency levels via Jenks Natural Breaks (JNB) classification and recommend the best subset of chl-sensitive wavelengths, frond number and classifier for classifying the chls according to the designated sufficiency levels via hyperspectral remote sensing platform. In order to achieve the objectives, an experiment was conducted on mature Tenera palm stands (12 and 15 years old) with N treatments varied from 0 to 2 kg. The Jenks Natural Breaks (JNB) classification was proposed to determine the chl sufficiency levels. Feature selection was carried out to select the chl-sensitive wavelengths while Decision Tree (DT) and Random Forest (RF) classifiers were used to classify the chl sufficiency levels using the selected wavelengths. Results from this study showed that the chl-sensitive wavelengths mostly belong to the red-edge region and importantly, they were frond age-dependent. Generally, the classification accuracy tended to decrease as frond gets older. The RF performed the best in discriminating the chl sufficiency levels with accuracy ranging from 92.79 to 98.77% compared to 56.30-90.48% achieved by DT. In the nutshell, the execution of frond 9 was more ideal than frond 17 for monitoring chl content of mature oil palm via remote sensing and RF portrayed promising insight in assessing chls content of mature oil palm.

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The benefits of washed rice water (WRW) as a plant fertilizer, particularly over a consecutive application period, are not well studied. An experiment was therefore carried out to determine: the continuous effects of applying unfermented (F0) and 3-day fermented (F3) WRW on the: (1) soil chemical properties, soil bacterial count, and the growth and plant nutrient content of a test crop, choy sum (Brassica chinensis var. parachinensis), grown on three contrasting soil textures (sandy clay loam, clay, and silt loam); (2) nutrient leaching losses from these three soils due to the continuous application of WRW; (3) crops’ improvement in water use, if any, in terms of its water productivity (WP) and water use efficiency (WUE); and (4) the relationship between soil bacterial count and plant growth parameters. The effects of F0 and F3 were compared with conventional NPK fertilizer and a control (only tap water; CON). Two factors, treatments and soil types, were used factorially in a randomized complete block design for three consecutive planting cycles. Results showed that NPK and F3 produced a significantly (p < 0.01) higher plant growth in terms of fresh and dry leaf weights and total leaf area by 5 to 61%, compared to that obtained in the other treatments. Furthermore, plants receiving either NPK or F3 had a significantly higher plant nutrient content (P, K, Ca, Mg, and Cu) in the third planting cycle. Clay soil treated with F3, NPK, and F0 had significantly higher NH4+, P, Ca, Mg, Zn, and B, by 19 to 152% relative to the other soils, irrespective of treatments. Soil nutrient leaching losses of P, K, Ca, Mg, Cu, Zn, and B decreased with successive planting cycles for all treatments. However, soils treated with either F3 or F0 experienced higher leaching of NH4+ and NO3−  by 37 to 259% and 13 to 34%, respectively, relative to the NPK and CON. Plants treated with either NPK or F3 also had higher WP by 21 to 42% than the other treatments. For all the treatments, plants’ WUE increased with successive planting cycles; however, there was no significant difference between the treatments. F3 stimulated a significantly higher growth and yield of choy sum due to its nutrient and bacterial contents, and the continuous increase in plant growth with successive planting cycles indicated the carryover effects of the treatments, particularly by F3.

No abstract

Washed rice water (WRW) is often used as liquid plant fertilizer. However, there is no study on nutrient leaching of soils due to frequent WRW application. Therefore, a column study was undertaken to evaluate the rate of nutrient leaching losses, nutrient retention, and recovery of elements in leachates of three different soil textures irrigated with WRW. The treatments were 3 soil textures and 2 water types. The treatments were evaluated for 8 weeks, and the soils and leachates were measured biweekly. Factorial and repeated measurements in a completely randomized design were therefore employed. Higher cumulative leaching of the elements was found in sandy clay loam soil with 666.29, 378.13, 138.51, 50.82, 44.61, and 27.30 mg L-1 of K, P, Mg, Ca, NH4+-N, and NO3--N, respectively. Higher percentages of elements recovery in leachate were found in the sandy clay loam soil with a range of increase by 37.8–283.1% than the other two soil textures. In contrast, after 8 weeks of WRW application, the clay and silt loam soils had a range of increase in nutrient retention by 0.43–1358.5% than the sandy clay loam, with P and NO3--N being the highest and the lowest elements retained, respectively, for all soil textures. This study showed that frequent WRW disposal on sandy textured soils risks higher environmental contamination, mainly due to the soil’s lower water retention and nutrients, leading to nutrient leaching. Therefore, organic amendments should be added to sandy textured soils.